Properties and sustainability evaluation of green
concrete utilizing waste and recycled materials

廃棄物やリサイクル材料を活用したグリーンコンクリートの物性および持続可能性評価

Michael Henry & Yoshitaka Kato
International Center for Urban Safety Engineering
Institute of Industrial Science, The University of Tokyo

ICUS Report No. 51
March 2011

International Center for Urban Safety Engineering (ICUS)
Institute of Industrial Science, The University of Tokyo

TABLE OF CONTENTS
Abstracti

Acknowledgementiii

Chapter 1: Introduction
1.1 Background1

1.2 Report overview

2

Chapter 2: Sustainability and usage of waste and recycled materials in concrete
2.1 Introduction
3
2.2 Environmental impact of concrete

4

2.3 Strategies for sustainable practice6

2.3.1 Resource conservation

7

2.3.2 Concrete durability

10

2.3.3 Holistic approach11

2.4 Examples of sustainable concretes

12

2.5 Conclusion

14

References

14

Chapter 3: Environmental impact and sustainability evaluation methods
3.1 Introduction
3.2 Evaluating sustainability

17
17

3.2.1 Sustainability indicators

17

3.2.2 United Nations sustainability indicators

18

3.2.3 Visualization of sustainability indicators

19

3.2.4 Sustainable evaluation systems in the construction industry

20

3.2.5 Life cycle assessment

21

3.3 Evaluating concrete sustainability

22

3.3.1 Current methods and systems

22

3.3.2 Environmental performance indicator23

3.3.3 Evaluation using analytic hierarchy process

23

3.4 Conclusion

24

References

24

Chapter 4: Effect of recycled aggregates and fly ash on concrete properties
4.1 Introduction
4.2 Effect of recycled aggregate quality

25
26

4.2.1 Overview

26

4.2.2 Experimental program

26

4.2.2.1 Materials

26

4.2.2.2 Mix proportions and fresh properties26

4.2.2.3 Specimens and curing27

4.2.2.4 Testing and results statistics

27

4.2.3 Variation of compressive strength results

27

4.2.3.1 Effect of water-cement ratio

27

4.2.3.2 Effect of aggregate type

28

4.2.3.3 Effect of combining aggregate types

29

4.2.4 Strength estimation index factor

29

4.2.4.1 Mix proportion-strength relationship29

4.2.4.2 Aggregate property-strength relationship30

4.2.4.3 Index factor for strength estimation30

4.2.4.4 Index factor for past research results

30

4.2.5 Summary
4.3 Effect of reduced cement content and aggregate type31
32

4.3.1 Overview

32

4.3.2 Experimental program

33

4.3.2.1 Materials

33

4.3.2.2 Mix proportions and fresh properties

33

4.3.2.3 Specimens and curing33

4.3.2.4 Mechanical performance testing34

4.3.2.5 Environmental performance assessment

34

4.3.3 Mechanical performance results

34

4.3.3.1 Compressive strength34

4.3.3.2 Flexural strength36

4.3.3.3 Air permeability

36

4.3.4 Environmental performance results

37

4.3.4.1 CO2 footprint

37

4.3.4.2 Volume raw materials

37

4.3.4.3 Comparison of CO2 vs. raw materials volume37

4.3.5 Mechanical vs. environmental

38

4.3.5.1 Compressive strength vs. CO2 footprint38

4.3.5.2 Compressive strength vs. volume raw materials

39

4.3.5.3 EPI vs. other environmental performance39

4.3.6 Summary
4.4 Effect of mix proportions, binder type, and aggregate volume

40
41

4.4.1 Overview

41

4.4.2 Experimental program

41

4.4.2.1 Materials

41

4.4.2.2 Mix proportions and fresh properties

41

4.4.2.3 Specimens and curing42

4.4.2.4 Testing42

4.4.2.5 Environmental impact assessment

42

4.4.3 Results and discussion

43

4.4.3.1 Compressive strength43

4.4.3.2 Young’s modulus

44

4.4.3.3 Air permeability

45

4.4.3.4 Drying shrinkage

46

4.4.3.5 Environmental impact

47

4.4.4 Balancing durability and environmental impact

48

4.4.4.1 Performance trade-off

48

4.4.4.2 AHP calculation results and discussion

49

4.4.5 Summary

50

4.5 Conclusion

51

References

51

Chapter 5: Combining recycled rubber with waste materials in concrete
5.1 Introduction
5.2 Experimental program

53
53

5.2.1 Materials

53

5.2.2 Mix proportions and fresh properties

54

5.2.3 Specimens and curing

55

5.2.4 Testing and environmental assessment

55

5.3 Results

55

5.3.1 Compressive strength55

5.3.2 Young’s modulus

57

5.3.3 Compressive failure mode

57

5.3.4 Air permeability

58

5.3.5 Environmental impact

59

5.3.6 Relationship between mechanical and environmental

59

5.3.7 Mechanical-environmental efficiency

60

5.4 Discussion

61

5.5 Conclusion

62

References

63

Chapter 6: Utilizing recycled fibers in fly ash mortar and concrete
6.1 Introduction
6.2 Experimental program

65
65

6.2.1 Materials

65

6.2.2 Mix proportions and fresh properties

66

6.2.3 Mixing & casting68

6.2.4 Mechanical performance testing68

6.2.5 Environmental performance assessment

68

6.3 Results

68

6.3.1 Effect of sand-binder ratio for mortar

68

6.3.2 Effect of fly ash-binder ratio for mortar and concrete696.3.3 Effect of fiber type for mortar

71

6.3.4 Effect of sand-aggregate ratio and recycled aggregate for concrete71

6.3.5 Environmental impact for mortar and concrete72

6.4 Summary

73

References

74

ABSTRACT
Properties and sustainability evaluation of green concrete
utilizing waste and recycled materials
Michael Henry & Yoshitaka Kato
ICUS Report No. 51
This ICUS report is a summary of several years of research works and experimental investigations
conducted at the Institute of Industrial Science, the University of Tokyo, on the usage of various
waste and recycled materials in “green” concrete towards reducing the environmental impact ofconcrete materials and structures and improving sustainable practices in the concrete industry. These
works and experiments approached the problems related to green concrete from two perspectives: theeffect of utilizing waste and recycled materials in concrete and the properties and performance ofgreen concrete materials; and the development of different metrics and methods for evaluating theenvironmental performance and means for balancing the mechanical and environmental performances.
Chapter 2 is a review of sustainability and environmental issues in the concrete industry, including
environmental impact, strategies for sustainable practice, and examples of sustainable concretes.
Chapter 3 reviews environmental impact and sustainability evaluation methods, focusing particularly
on sustainability indicators. The environmental performance indicator is introduced as a means forweighting mechanical performance by environmental impact, and the application of the analytic
hierarchy process, a multi-criteria framework for making complex decisions, is proposed as an
original means for examining the balance between different concrete properties and environmental
impacts. Both of these were applied during the experimental investigations.
Chapter 4 introduces the results of three experimental phases designed to investigate problems withrecycled aggregate and fly ash, such as the statistical relationship between varied aggregate quality
and reduced performance and the quantitative effect of these materials on the environmental impact aswell as the balance between the mechanical and environmental performance by applying the methods
proposed in Chapter 3. Some key results from these investigations are as follows: Variation of compressive strength for concrete with low-grade recycled aggregates was higher
than for normal aggregates, but still fell below a JSCE-specified limit and thus an overdesign
factor does not need to be considered. Mixing different types of aggregates, however, increased
the variation higher than when using either of the aggregates types alone; particularly whenmixing two types of recycled aggregate, the JSCE-specified limit was exceeded.
 An index factor combining cement-water ratio and aggregate density and absorption properties
was proposed and could be used to estimate the compressive strength of recycled aggregate
concrete with a very high degree of linear correlation.
 CO2 footprint of concrete is primarily affected by binder composition and secondarily by binder
content, whereas the volume of raw material is affected primarily by aggregate type; thus,
evaluating the environmental performance of concrete by CO2 footprint doesn’t show the valueof low-grade recycled aggregate, whereas evaluating by volume of raw materials doesn’t show
the value of fly ash. After calculating the environmental performance indicators, it was seenthat replacing cement with fly ash or reducing the amount of binder reduced the CO2 footprint
more than it reduced strength; in contrast, low-grade recycled aggregates reduced raw material
volume more than they reduced strength.
 When comparing CO2 footprint vs. air permeability and CO2 footprint vs. volume of raw
materials, a single material could be found to have the best balance, but when comparing
volume of raw materials vs. air permeability no single material could be selected as having thebest balance due to the direct relationship between recycled aggregate usage and these twoi ifactors. Applying the analytic hierarchy process with four weighting scenarios showed that, ingeneral, the usage of normal aggregates was preferred in most cases except when giving highimportance to the volume of raw materials. In addition, a water-binder ratio of 45 with 25% fly
ash, 25% blast furnace slag, and 50% cement was the preferred binder composition in mostcases because it met the required strength with a reduced CO2 footprint and better air
permeability coefficient.
Chapter 5 introduces the results from an investigation on the properties and environmental impact ofconcrete combining recycled rubber crumbs with recycled aggregates and fly ash in concrete.
Increasing the amount of rubber crumbs was shown to linearly reduce compressive strength, and the
combination of rubber crumbs with recycled aggregates, with fly ash, and with both recycled
aggregates and fly ash reduced strength in that order. The effect of rubber crumbs on air permeability
depended primarily on binder type and presence of recycled aggregates. The mechanicalenvironmental efficiency was calculated as the environmental performance indicator utilizing volumeof raw materials and compressive strength, and overall the usage of only 100% recycled aggregates
had the highest efficiency. Rubber crumbs were found to be an inefficient means for reducing
environmental impact when using weighted strength as an index.
Chapter 6 summarizes an investigation on fly ash mortar and concrete reinforced with fibers madefrom recycled PET bottles. The PET fiber-reinforced mortars performed similarly in compressive andflexural strength testing as polypropylene fiber-reinforced mortar. For the concrete mixes,
environmental performance indicators were used to normalize the mechanical performance byconsidering the environmental impact, and it was found that these indicators could reverse the trends
shown by the mechanical performance alone, particularly in the case of high volume fly ash concrete.
Overall, these experimental investigations showed that certain combinations of waste and recycledmaterials could achieve similar performance as normal-use concretes currently in practice, and do sowhile reducing environmental impact such as CO2 footprint and volume of raw materials. However,
without the means for evaluating and balancing the environmental impact with the mechanicalperformance, it’s difficult to quantify the value of these green concretes. The value of the approaches
taken in this report can therefore be clearly understood, but it will require institutional changes in theattitudes and systems used for evaluating and selecting concrete materials before green concretes canbecome more widely applied.

ii ii

ACKNOWLEDGEMENTAs this report is a summary of extended research and experimental work in Katoyosh Laboratory in
the International Center for Urban Safety Engineering (ICUS), the authors would first like to express
their appreciation for the hard work of the students who prepared, mixed, cast, and tested the concrete
reported here:

Mr. German Pardo, master student, the University of Tokyo
Mr. Wataru Hirata, undergraduate student, Shibaura Institute of Technology
Mr. Hiromichi Yamashita, undergraduate student, Shibaura Institute of Technology
Mr. Kazuya Hagiwara, undergraduate student, Shibaura Institute of Technology

The authors are also greatly indebted to Mr. Tsugio Nishimura (senior technical support specialist,
Institute of Industrial Science, the University of Tokyo) for giving his time, energy, and expertise insupport of all the students investigating green concrete materials.
Thanks are also due to all the members of Kishi-Kato Laboratory who contributed to these researchworks.

iiiiii

iv iv

Chapter1

Introduction

1.1 BACKGROUND
Concrete is the most widely used construction material on the planet, and the second-most utilized
natural resource after water. It’s a composite material, consisting of a binder (typically Portland
cement), water, fine and coarse aggregates, and chemical admixtures. The hydraulic reaction between
the cement and water causes the concrete to solidify, binding the different phases together andcreating a hardened, rock-like material. Concrete serves as the primary material utilized forconstructing the infrastructure necessary to provide society with basic safety and living requirements.
Globally, the usage of concrete has been increasing as developing countries have begun investing ininfrastructure systems such as highways, bridges, tunnels, and so on. As human populations continue
to grow and urbanize, so too will the demand for infrastructure increase, resulting in increased
utilization of concrete to meet that demand. Growth and urbanization has, however, also been a
primary driver of environmental deterioration, from destruction of ecosystems to increased emissionsof greenhouse gases and other air-born pollutants. Observed changes in the global climate haveincreased awareness of the impacts of human activities on environmental systems, and led to theformation of international committees on how to reduce environmental deterioration and mitigate
future climate changes.
The environment is one aspect considered by sustainable development, along with society and theeconomy. The basic concept of sustainable development is that the effects of development in modern
societies need to consider and protect the ability of future societies to develop. There is a complex
interaction between the three aspects. Although they are sometimes considered as separate entities tobe integrated, a better approach considers them as systems contained within each other – economy
exists within society and society exists within its surrounding environment. Viewed this way, theeffects of changes in the environment can be felt in both of the aspects that exist within it.
Increased awareness of the environment has led the concrete industry to consider its environmental
impact. Concrete’s negative impact comes in several forms, from large-scale emission of greenhousegases to massive consumption of natural resources such as water, sand, and aggregates. Approaches toreducing the industry’s environmental impact include increasing the durability of concrete structures,
utilizing the waste products of other industries as a replacement material, and the recycling of11

ICUS Report No. 51

March 2011

demolition waste back into the construction process. The concrete material itself is an important partof the shift to sustainable practice and reduced environmental impact. Durable materials utilizing
waste and recycled materials could form the foundation of sustainable concrete. However, there isoftentimes a trade-off between the environmental impact and mechanical properties, such as the
reduction in quality and durability when utilizing recycled aggregates or the increase in CO2emissions when reducing water-binder ratio to increase strength. Therefore, it’s important not only toinvestigate the usage of the waste and recycled materials in concrete but to also consider their effects
on the environmental performance and material properties and develop metrics whereby both themechanical and environmental aspects can be considered simultaneously.

1.2 REPORT OVERVIEWThis ICUS report is a summary of several years of research works and experimental investigations
conducted at the Institute of Industrial Science, the University of Tokyo, on the usage of various
waste and recycled materials in “green” concrete towards reducing the environmental impact ofconcrete materials and structures and improving sustainable practices in the concrete industry. These
works and experiments approach the problems related to green concrete from two perspectives: first,
the effect of utilizing waste and recycled materials in concrete and the properties and performance ofgreen concrete materials; and second, the development of different metrics and methods forevaluating the environmental performance and means for balancing the mechanical and environmental
performances.
The contents of this report are broken into five chapters which provide background and the results anddiscussion of each of the experimental investigations. Chapter 2 is a review of sustainability andenvironmental issues in the concrete industry, including the environmental impact, strategies forsustainable practice, and examples of sustainable concretes. Chapter 3 reviews environmental impact
and sustainability evaluation methods, focusing particularly on sustainability indicators, and also
includes means for evaluating sustainability and environmental impact of concrete and an original
approach utilizing the analytic hierarchy process. Chapter 4 covers three related experimental
investigations on the usage of low-grade recycled aggregates and fly ash in concrete, including quality
variation and estimation of recycled aggregate concrete strength and the relationship and balance
between mechanical and environmental performance utilizing methods proposed in Chapter 3.
Chapter 5 introduces the results from an investigation on the properties and environmental impact ofconcrete combining recycled rubber crumbs with recycled aggregates and fly ash in concrete. Finally,
Chapter 6 summarizes an investigation on mortar and concrete reinforced with fibers made fromrecycled PET bottles and combined with fly ash.

22

Properties and sustainability evaluation of green concrete utilizing waste and recycled materials

Chapter2

Sustainability and usage of waste
and recycled materials in concrete

2.1 INTRODUCTION
Concrete is an integral part of infrastructure construction, providing the very foundation upon whichsociety and its quality of life are built. However, concrete also plays a major role in environmental
deterioration. The environmental impact comes from a variety of sources over the entire life cycle,
from material manufacturing to the disposal of waste concrete, and various strategies for reducing this
impact have been proposed which target different aspects of concrete practice. General concepts forsustainable practice in the concrete industry have, therefore, primarily targeted the reduction of theindustry’s negative environmental impact.
In order to meet the challenges of sustainability, the American Concrete Institute (ACI) established a
Board Advisory Committee on Sustainable Development (BACSD) to develop recommendations for
ACI on how to promote sustainable practice. In 2005, the BACSD proposed that the concrete industry
adopt a definition of sustainability containing the following elements (ACI BACSD, 2005):
 Specification, design, and proportioning of concrete must be performed considering durability,
conservation, and minimal environmental impact; Production of ingredients, concrete, and construction practice must be environmentally
responsible
 Concrete industry must remain competitive
In addition to this definition, the BACSD also made several recommendations to ACI for promoting
sustainable practice in the concrete industry, ranging from policy statements to documentation andguidelines for sustainable practice to education for both concrete engineers and non-engineers alike.
Although different professional groups around the world, like ACI, have tried to establish guidelines
for sustainable practice, no over-arching guideline has yet been decided upon – perhaps due to thelarge regional differences between construction cultures around the world. However, there still remain
two unavoidable challenges. The first is to meet the growing demand for infrastructure necessary toprovide an acceptable standard of living as the human population continues to grow and urbanize. The
second challenge is to achieve the first while reducing the environmental impact caused by concrete

33

ICUS Report No. 51

March 2011industry activities. This chapter will review the environmental impact of concrete, and discuss
practices and approaches taken in the concrete industry to meet these challenges and move towards
the ultimate goal of sustainable development.

2.2 ENVIRONMENTAL IMPACT OF CONCRETE
Sakai (2009) estimated that the global consumption of concrete, based on the assumption that all
cement produced world-wide was used in concrete, is roughly 3.2 tons per person, making it thesecond-most used resource after water. Although the utilization of concrete is necessary for producing
the infrastructure to maintain quality-of-life requirements, it also carries with it a high environmental
impact in several forms: CO2 and other GHG emissions, particulate matter and air contamination,
natural resource and energy consumption, waste material generation and contaminants disposal, as
well as other impacts such as noise and vibration from manufacturing and construction.
The CO2 emissions of selected concrete-making materials are given in Figure 2.1. From this figure, it
is clear that cement is the largest source of CO2 emissions in concrete production, and global cement
production is a major contributor to world GHG emissions. In 2000, roughly 1.37 billion metric tonsof CO2 were emitted by the production of cement, representing roughly 6% of the world’s total
emissions at that time.

800

784

766.6

767.4

624
600

458.7

400

3.7

3.1

17.7

26.5

19.6

Recycled aggregate (type I)

Blast furnace slag

Fly ashElectric furnace steel

2.9

Recycled aggregate (type III)

Normal eco-cement

Fly ash cement (typeB)

Blast furnace slag cement(typeB)

Normal portland cement

0

Fine aggregate

200

Coarse aggregate

CO2 emissions (kg-CO2/ton)

1000

Figure 2.1 CO2 emissions for concrete-making materials in Japan (data source JSCE, 2006)
Although cement is the primary contributor of CO2 in concrete, most of the volume in concrete is
occupied by fine and coarse aggregates. However, as seen in Figure 2.1, these materials contributeonly a small amount of CO2 emissions. Emissions related to water, an essential ingredient in concrete
production, are so small that typically they are not considered. Modern reinforced concrete structures
typically utilize steel reinforcement in addition to concrete, which contributes CO2 on the same level
as cement; however, the reinforcement ratio may vary widely depending on the loading conditions,and emissions are much higher for blast-furnace steel than for electric furnace. For Japan, roughly
0.11 tons of CO2 emissions are attributed to reinforcement for every ton of cement (Sakai, 2009).
44

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ICUS Report 51

In addition to the manufacturing emissions, there are also emissions related to the actual mixing of
concrete as well as transportation of concrete from the ready-mix concrete factory to the construction
site. These emissions contribute roughly 25% of the total concrete production emissions, but thisestimation was based on the prevailing conditions in the Japanese industry and global conditions andefficiency vary widely, so the global average may be much higher (Sakai, 2009).
Figure 2.2 shows the input energy needed for producing concrete-making materials. Again, it can beseen that most energy is used in the production of cement. This figure, however, does not include theenergy consumed in the transportation of these materials or in the production of concrete material.

8
6.4
6
4.24

3.4
2.28

3.02

0.07

0.06

0.38

0.58

0.43

Recycled aggregate (type III)

Recycled aggregate (type I)

Blast furnace slag

Fly ashNormal eco-cement

Fly ash cement (typeB)

Blast furnace slag cement(typeB)

Normal portland cement

0

0.05

Fine aggregate

2Electric furnace steel

4

Coarse aggregate

Input energy (GJ/ton)

10

Figure 2.2 Input energy for concrete-making materials in Japan (data source JSCE, 2006)

Cement production not only requires energy but also consumes large quantities of natural resources
such as clay and limestone. Concrete production consumes roughly 10 to 11 billion tons of sand,gravel, and crushed rock per year, in addition to over 1 trillion liters of water (Mehta, 2001). Thiswater consumption does not include water used for washing at ready-mix concrete plants or applied
for concrete curing. The mining of these materials results in deforestation and loss of top soil, and has
a large effect on forest and river ecology.
Worldwide generation of concrete and masonry rubble from construction demolition in 1998 wasestimated at roughly one billion metric tons (Lauritzen, 1998). In Japan, total construction waste wasestimated to be roughly 85 million tons in 2000, of which 41% (35 million tons) was waste concrete(Figure 2.3). However, between 1995 and 2000 the recycling rate of concrete increased from 65% to96%, but the majority of this material was utilized as fill for road construction (MLIT, 2009). While
recycling for usage in road construction is better than disposal to landfills, this could be considered“down-cycling” because it does not help reduce the consumption of virgin aggregates in concrete
construction (Mehta, 2001).

Chapter 2: Sustainability and usage of waste and recycled materials in concrete55

ICUS Report No. 51

March 2011

5

2

Asphalt concrete

8
30

5

Concrete
Wood waste
SludgeMixture waste
Other(million tonnes/year)

35

Figure 2.3 Japan construction waste in 2000 (data source MLIT, 2009)
In addition to GHG emissions, concrete construction also contributes to air pollution and healthconcerns from concrete dust. Water and soil may also be contaminated by operations related to
cement and concrete production, such as mining or transportation, and water quality compromised bywater runoff over impervious concrete surfaces such as roads, where the water picks up pollutants andthen carries it downstream. Surface runoff can also increase soil erosion, and water which cannot
properly drain decreases the safety of vehicles traveling on roadways.
Concrete as a paving and surfacing material also contributes to the urban heat island effect. Lightercolored concrete can reflect radiation, such as light, which reduces the amount of energy absorbed andkeeps the concrete cooler (EPA, 2005). Darker-colored paving materials, such as asphalt, absorb moreheat and raise the temperature in the surrounding area.
Finally, there are other indirect environmental impacts such as the noise and vibration produced when
producing cement, concrete-making materials, concrete itself, or at the construction site; as well as theimpacts over the service life of the structure, such as those related to repair, maintenance, and theultimate demolition and disposal of the structure (JSCE, 2006). These can generally be measured
directly and correlated to different construction activities.

2.3 STRATEGIES FOR SUSTAINABLE PRACTICE
Mehta (1999) proposed one of the first strategies for sustainable practice in the concrete industry withhis foundation for environmentally friendly concrete technology, shown in Figure 2.4. This proposal
consisted of three elements: conserving the raw materials used for producing concrete, improving the
durability of new construction, and shifting to a holistic approach in both technology and education.
For conserving concrete-making materials, he identified recent research works which examined thereplacement of normal aggregates with demolition waste or the usage of recycled water from concrete
plants for mixing water, but the utilization of alternative cementitious materials, particularly fly ash,for reducing the usage of Portland cement consumption was emphasized as the most important target.
Enhancing the durability of concrete construction would conserve natural resources by reducing
consumption, but many problems with new construction, such as poor workmanship and cracking due
to the chemical composition of cements with high early-age strength gain, need to be addressed. For
existing structures, extending the service life through maintenance, repair, and rehabilitation should beconsidered options. Finally, a holistic approach should be taken which considers the concrete industry
as part of society, so that the concrete industry should not only be responsible for providing a

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construction material but also take social and environmental obligations. However, this will require a
shift in philosophy from the current reductionist practices in not only the concrete industry, but also in
the education of concrete engineers and education in general.
Sustainable development of
the concrete industry

Conservationof concretemaking
materials

A holistic
approach toconcretetechnology
research andfield practiceEnhancementof durability ofconcrete
structures

Figure 2.4 Mehta’s foundation for sustainable development in the concrete industry(adapted from Mehta, 1999)

Sakai (2009) reviewed four CO2 reduction scenarios for the concrete industry. Although CO2
reduction is just one aspect of sustainability, most emphasis on sustainability in the concrete industry
focuses on reduction of the environmental impact. Sakai’s four scenarios included: utilization ofcarbon capture and storage (CCS); reducing CO2 emissions and energy usage from cement production
by developing new cement systems; reducing cement content by utilizing alternative cementitious
materials or water-reducing admixtures; and selection of low-impact construction methods. Although
the IPCC recommends implementing carbon capture and storage to the cement industry as a
mitigation technique, the level of technology is still too low to be practically implemented, andfocusing on CCS may distract from the development of other mitigation techniques. Since Japan has
the lowest CO2 emissions for producing cement (Figure 2.5), CO2 and energy reduction could beachieved by transferring Japanese cement production technology to other countries, such as
specialized kiln systems and the usage of industrial waste as raw material and fuel for cement kilns.
Another approach is utilizing admixtures to reduce the unit water content, which then allows for a
reduction of the unit cement content. This approach requires no specialized technology, only carefulconsideration of mix design and access to high-range water reducing admixtures. The final scenario
for reducing CO2 focuses on the concrete structure, rather than the material. New structural forms orconstruction methods can have a large effect on the CO2 emissions, so low-impact options should beselected.
2.3.1 Resource conservation
Conservation of virgin materials for making concrete can be achieved by utilizing replacement
materials such as industrial by-products or recycled waste. The term “industrial ecology” refers to thepractice of recycling waste products from one industry as a substitute for virgin materials in anotherindustry. Not only does this reduce the consumption rate of virgin materials, but it also reduces thevolume of material being sent to landfills. For the concrete industry, there are many opportunities forthis practice to be implemented, and many different replacement materials have already been
investigated for concrete application, as summarized in Figure 2.6.

Chapter 2: Sustainability and usage of waste and recycled materials in concrete77

ICUS Report No. 51

March 2011

0.8

0.73

0.79

0.9

0.92

0.9

0.93
0.81

0.89

0.82

0.85

0.85

Middle East

0.84

Af rica

0.91

S. & L. America

0.99

Rep. of Korea

1.0

SE Asia

1.2

0.6
0.4
0.2

Other E. Europe

Former Soviet Union

India

China

Australia & NZ

Japan

W. Europe

Canada0.0

USA

CO2 emissions (kg-CO2/kg-cement)

One widely-used industrial by-product is fly ash. Fly ash is a pozzolanic material generated by the
combustion of coal and can be used as a replacement for Portland cement due to its cementitious
properties when mixed with lime. The addition of fly ash to concrete improves long-term strength anddurability. In addition, the spherical shape helps improve the workability of fresh concrete and allows
for the reduction of mixing water. Ground-granulated blast furnace slag (GGBS), a by-product of thesteel industry, is more common in Japan and, similar to fly ash, improves durability and long-term
strength. The production of one ton of pig iron produces roughly 300 kilograms of slag, and therecycling of slag which can be utilized in the concrete industry – either in blended cements or as amineral admixture – provides the concrete industry with a way to practice industrial ecology and help
reduce the steel industry’s environmental impact, which in turn has a greater benefit to Japan as awhole by reducing waste generation and raw material consumption.

Figure 2.5 Comparison of CO2 emissions in cement production(data source Humphreys & Mahasenan, 2002)

Virginmaterials

CementReplacement
materials

Concrete

Fly ashGGBS
Silica fumeRice-husk ash
Metakaolin
Eco-cement
Recycled cement

Water

Fine aggr.

Coarse aggr.

Recycled water

Crushed glass
Recycled rubber

Recycled aggr.
Recycled rebar
Recycled glass

Figure 2.6 Selected replacement materials

The demand for concrete is particularly high in developing countries such as China and India. Thesesame countries also produce large amounts of fly ash and blast furnace slag, the majority of which is88

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Chapter 2: Sustainability and usage of waste and recycled materials in concrete

ICUS Report 51

not being utilized in concrete construction (Mehta, 1998). Utilizing these materials instead of cement
could meet increasing demand without increasing production capacity, thus demonstrating theimportance of utilizing by-products in future development. Other supplementary cementing materials
include silica fume, metakaolin, and rice-husk ash. The availability and application of all thesematerials depends highly on regional characteristics, but their use is generally increasing.
In addition to fly ash and blast furnace slag, by-products from other industries also have potential
application in the concrete industry. Some examples include: semimetallic waste from metallurgicalprocesses as aggregate for producing high-density concrete; filter cake from calcium carbide
production as filler in concrete mixes; and anhydrite from flocculant production residue as a partial
cement replacement material in controlled conditions (Jahren, 2002). Limited practical application ofthese materials has already been achieved and demonstrates the new opportunities for the concrete
industry to practice industrial ecology.
Another source of waste is the demolition of old buildings and infrastructure. This waste concrete canbe processed and reused as a replacement for aggregates in new construction, which reduces the needfor virgin materials as well as the volume of material disposed of in waste sites and landfills.
Recycled aggregates, however, typically have greater porosity and water absorption characteristics
due to the cement mortar attached to the surface of the original coarse aggregate, which results inlower durability and strength. Furthermore, low-quality recycled aggregate may contain large amounts
of non-cementitious demolition waste, such as nails, glass, wood, and so forth, as shown in Figure
2.7. The production process of the recycled aggregate plays an important role in assuring the qualityof concrete constructed using these aggregates. Unfortunately, increased processing time for
producing better quality recycled aggregates requires large amounts of energy and CO2.

Figure 2.7 Demolition waste mixed with low-grade recycled aggregates

Some research works have investigated the application of recycled glass as a raw material for concrete.
In particular, lightweight aggregate made from foamed glass has potential for future applications(Jahren, 2002). This type of aggregate has an uneven surface which increases bonding capability but
requires cement paste with a high filler content to meet workability requirements. However, glass may
be considered reactive in some forms when used in concrete, so careful mix design is necessary if thismaterial is to be used. Waste material from other industries can be used as a replacement for the fuelnecessary to produce Portland cement. Eco-cement, while not a waste product itself, is made by using
reactive kiln materials to reduce the energy consumption of the production process, which reduces theCO2 emissions related to energy production.

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In order to reduce the amount of water consumption, mixing water can be reduced by improved
aggregate grading or the utilization of admixtures for retaining workability at lower water content.
Also, the concrete industry could utilize recycled industrial water or non-potable (brackish) water inconcrete mixing or for washing or curing.
2.3.2 Concrete durability
Material conservation can also be achieved by extending the service life of infrastructure. For
concrete, durability is typically associated with cracking, which allows the ingress of corrosive agentsand leads to deterioration of structural performance and appearance. Unfortunately, modern concretes
tend to crack at an early age due to the increased use of high-early-strength cements, which are prone
to cracking, and research has found that the emphasis on fast construction schedules and achievingload-carrying capacity as soon as possible is responsible for the large volume of low-durability
structures constructed in the 1980s and 1990s (Mehta, 2002). Poor workmanship in concrete
construction, such as insufficient vibration, low-quality formwork, incorrect placement of steel
reinforcing, premature removal of formwork, and so forth also result in poor structural durability. A
lack of communication between the structural designer and the contractor, resulting in difficult-toconstruct structural forms or congested steel reinforcement, is another factor.
Cracks are primarily caused by thermal contraction and drying shrinkage in the early stages of
construction or through fatigue loading. These cracks, by themselves, do not reduce the durability ofthe structure unless they form an inter-connected pathway which allows for water or corrosive agent
transport. These cracks may propagate under loading or from exposure to weather until the watertightness of the structure is lost. Deterioration then occurs as a cyclic process whereby deterioration
processes cause further cracking, which then allows for water intrusion and thus more deterioration.
The deterioration of concrete can be broken down into four primary causes: corrosion of steel
reinforcement, frost action, alkali-silica reaction, and sulfate interactions in cement paste. These
causes have several common factors, such as the need for water saturation, presence of microcracks,
and occurrence of defects in the cement paste microstructure. In order to adopt a new approach fordurability design and improvement, Mehta (2009) proposed several key points. First, reducing theamount of cement paste and eliminating inhomogeneities in the cement paste can have a large
influence on the reduction of microcracks. Second, reducing the water-cement ratio (a typical means
for improving durability under the current-popular reductionist approach to durability design) alone is
not sufficient – the actual cement paste content should also be reduced along with the water content.
Finally, sources of defects in the microstructure should be reduced by transforming the weaker phases
into stronger phases through the application of pozzolanic materials, producing a more homogeneous
cement paste.
For new construction, under certain conditions utilizing slag or fly ash may help reduce cracking, thus
improving crack resistance and durability. Other solutions include admixtures for preventing
corrosion, epoxy-coated bars, surface coatings, and cathodic protection. Some materials, such as selfcompacting concrete, were designed to provide durability in response to human factors such as poor
workmanship.
For existing structures, unless high durability is specified and assured at the construction phase,proper maintenance management consisting of inspection and repair is necessary to assure thestructure’s performance over time and prevent deterioration. The goal of maintenance is to keep the
structural performance above the limit of performance, below which the safety of the structure cannot
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be assured. If the structure is constructed with high durability, then the structural performance will
only gradually decrease over time, as shown in Figure 2.8 (left), so the cost for maintenance will
decrease. Specifying high durability at the early age, however, usually results in a higher initial cost.
If the structure does not have high durability, then it becomes necessary to conduct repair works torestore performance to acceptable levels. Conducting minor maintenance before reaching themaintenance or performance limit will increase the number of times maintenance works must be
conducted (Figure 2.8, middle), but may reduce total life cycle costs as the extent of work done forminor maintenance is significantly less than that required for major corrective maintenance. If theperformance of the structure is allowed to deteriorate past the maintenance limit to the performance
limit (Figure 2.8, right), then large-scale, corrective maintenance works must be conducted. Since thecost of these works can be prohibitively expensive, this may increase the life cycle cost immensely.

High durability performance
Maintenance limit
Performance limit

Maintenance limit
Performance limit

InitialMinor
maintenance

Structural performance

Initial

Structural performance

Structural performance

InitialCorrective
maintenance
Maintenance limit
Performance limit

Figure 2.8 Maintenance strategies for deteriorating structures(adapted from Yokota et al., 2008)

In developed countries, such as the USA and Japan, where most of the necessary infrastructure isalready in place, maintenance management of that infrastructure will be necessary in the future inorder to extend service life. If the service life can be extended, this can reduce material consumption
and waste generation by avoiding the demolition of the existing structure and the construction of a
new structure. However, as structures age and the loading requirements increase (due to increasing
traffic from a growing population, for example), there may be a point where it is more economicallyand environmentally feasible to construct a new structure rather than extend the service life of theexisting structure.
2.3.3 Holistic approach
In his paper on sustainable technology, Mehta proposed that the concrete industry’s reductionist
approach is responsible for many unsustainable practices (Mehta, 1999). A holistic approach isnecessary to shift the concrete industry toward sustainable practice.
A holistic approach values the whole as greater than the sum of its individual parts. For the concrete
industry, this approach would suggest that society is the greater whole, with the concrete industry as
just one part. One way to implement a holistic approach would be to place more emphasis on durable,
crack-free construction rather than faster construction speed (Mehta, 2002). Such an approach would
place responsibility on the concrete industry to provide not only a cheap construction material, butalso carry other societal needs. Considering other societal needs could open up new markets for theconcrete industry. Jahren (2002) suggests that the concrete industry should look at the production of
artificial reefs and sea life breeding-ground restoration as two areas where the concrete industry could
create a product which would contribute to the well-being of society by helping to meet the growing
demand for seafood necessary to feed a growing world population.

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Following Mehta’s model, another example of a holistic approach in concrete materials can be shownby using a ternary representation of concrete durability (Collepardi, 2008). This representation, shownin Figure 2.9, demonstrates the interaction between the different factors which cause damage anddeterioration of concrete structures. Damage only occurs if all three elements – interconnected pores,
water, and aggressive agents – are present. In situations where only one or two elements are present,
there is no risk of damage to the concrete structure. The concrete industry’s reductionist approach has
resulted in policies which assume that damage will occur, regardless of whether all three of theelements are present or not. As an example, in the case of alkali-silica reaction, this has led to therejection of materials such as high-alkali cement or reactive aggregates, thus requiring the use of othervirgin materials, even though the usage of these cements or aggregates would not be damaging to thestructure if a proper holistic approach to durability and structural design were taken (Mehta, 1999).
According to Collepardi (2008), such a holistic approach to durability design can be taken with other
deterioration mechanisms, such as sulfate attack or corrosion of reinforcing steel.

Interconnectedporosity (permeability)

DAMAGE
Presence ofwater

Exposure toaggressive
agentsFigure 2.9 Ternary representation of damage in reinforced concrete(adapted from Collepari, 2008)

The difficulty in shifting from reductionist to holistic practice lies with problems in how engineeringand science are taught at the university level (Mehta, 1999). There is a lack of courses on concrete
technology and few students pursue graduate-level study of concrete material. In addition, theproblems faced in the real world often cannot be solved by application of scientific or engineeringknowledge alone, but require an integration of knowledge from many fields such as the social
sciences or humanities. A holistic approach is necessary to bring together these different areas ofknowledge and apply concrete material technology for sustainable practice.

2.4 EXAMPLES OF SUSTAINABLE CONCRETES
Early papers on the topic of sustainability in the concrete industry often mentioned high-volume fly
ash concrete as one of the best options for the concrete industry to institute sustainable materials(Malhotra, 1999; Mehta, 2002). As discussed in Section 2.3.1 on resource conservation, fly ash is aby-product from the coal industry, and can be used as a supplementary or replacement cementitious
material. While the replacement of fly ash is often limited by prescriptive codes, high-volume fly ash
concrete has been developed which replaces up to 60% of Portland cement (Sivasundaram et al., 1989;
Malhotra, 1994). This technology not only provides superior strength and durability performance, but
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also greatly reduces the amount of cement necessary in construction, resulting in concrete mixtureswith significantly lower environmental impact and reducing the amount of waste disposed in landfills.
Enhancing the durability of concrete structures is another strategy for improving sustainable practicein the concrete industry, so materials which improve durability may also be thought of as sustainable
materials. One example of high-durability concrete is self-compacting concrete, a material with highflowability in the fresh state which allows the concrete to fill the formwork around the steel
reinforcement without requiring the use of vibrators (Figure 2.10). This material was developed in
response to observed durability problems caused by poor workmanship and lack of communication
between the structural designers and the contractors. Two solutions were proposed to solve these
problems: the first was to establish a comprehensive design method for durability, and the second was
to develop a material which could provide structural durability even under poor conditions (Okamura,1986). Self-compacting concrete was developed in response to the second solution, and was designed
to have high durability in each material state (fresh, early age, and hardened) (Ozawa, 1990).

Figure 2.10 Concrete with self-compacting behavior (high flowability)
Another approach to durable performance is self-healing concrete, a special type of concrete which
has the capability to autogeneously repair cracks under water supply conditions (Ahn, 2008). The
development of this material derives from the concept of “maintenance-free” construction, which
reduces both direct and indirect costs associated with maintenance works. Maintenance-freeconstruction is part of a shifting trend in construction philosophy, whereby the contractor is
responsible not only for the design-construction aspects, but maintenance as well. Self-healing
concrete ensures water-tightness by closing cracks of a certain width in the presence of water (Figure2.11), thus preventing further intrusion into the concrete and enhancing durability. The application ofthis material is currently limited to structures which are under constant water supply, such as tunnels
or other underground structures.
Pervious (or porous) concrete is a special type of concrete which is composed mostly of aggregatesand cement paste. The lack of fine aggregate results in concrete with high permeability and allows
water to easily pass through. This greatly reduces the amount of water runoff associated with concrete
pavements, and is recommended as an effective means for managing stormwater runoff. Moreefficient land use can also be realized by eliminating other stormwater management devices which areneeded in conjunction with normal concrete pavements.
Although concrete materials which reduce environmental impact are often referred to as “green
concrete,” no material better embodies the meaning of green concrete than concrete materials which
serve as foundations for the growth of plants. Green concrete was developed as a means for
introducing nature in urban spaces, such as on buildings, in parks or as part of infrastructure
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(Yanagibashi & Yonezawa, 1998). This material, which consists of no-fines concrete, a water
retentive material, and a light layer of soil on the surface, not only serves as a structure, such as slope
retention, but also encourages plant growth within the structure itself, improving the structure’s
aesthetic image and allowing for a wider variety of landscaping options. The development ofmaterials such as green concrete not only represents a holistic approach to material development byconsidering needs beyond the concrete industry, but also serves to open new markets and lead to newtechnological challenges.

Figure 2.11 Crack self-healing under water supply (Ahn & Kishi, 2008)

2.5 CONCLUSION
The concrete industry is a fundamental part of the construction industry, as concrete is the world’s
most-utilized construction material and second-most utilized resource after water. Although concrete
contributes positively to the improvement of society through the construction of civil infrastructure, italso carries with it a significant environmental impact in the form of GHG emissions, resource andenergy consumption, and waste generation. Strategies for adopting sustainable practice in the concrete
industry generally focus on reducing these three impacts by utilizing waste and recycled products,
which reduces consumption of raw materials and recycles waste back into the product life cycle, andby enhancing the durability of concrete structures. The concrete industry’s reductionist approach topractice and education has, however, had a negative effect which needs to be overcome by adopting aholistic approach. In such an approach, the concrete industry would consider itself as a part of thegreater society, and serve not only to provide a cheap construction material but also takeresponsibility for other social needs, such as the disposal of waste materials. A holistic approach
would also help durability design by considering the actual exposure conditions of a structure.
Concrete material itself is an important part of the paradigm shift to sustainable practice, and there are
currently several material technologies available or under development which can help the industry
reduce its environmental impact.

REFERENCESACI Board Advisory Committee on Sustainable Development. (2005). White Paper on Sustainable Development. ConcreteInternational, 27 (2), 19-21.

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Ahn, T.H. (2008). Development of self-healing concrete incorporating geo-materials: a study on its mechanism and behavior
in cracked concrete (Doctoral dissertation, Department of Civil Engineering, The University of Tokyo, 2008).
Ahn, T.H. and Kishi, T. (2008). The effect of geo-materials on the autogeneous healing behavior of cracked concrete. In
Proceedings of 2nd ICCRRR2008, Cape Town.
Collepardi, M. (2008). Damage of concrete by sulfate attack and alkali-silica reaction. In W.L. Jin, T. Ueda, and P.A.M.
Basheer (Eds.), Advances in concrete structural durability, Vol. 1 (pp. 3-9). Hangzhou: Zhejiang University Press.
Environmental Protection Agency. (2005). Cool Pavement Report. USA Environmental Protection Agency. Retrieved 2009
Nov. 17: http://www.epa.gov/heatisland/resources/pdf/CoolPavementReport_Former%20Guide_complete.pdf
Humphreys, K. and Mahasenan, M. (2002). Toward a sustainable cement industry, Substudy 8: Climate change. World
Business Council for Sustainable Development. Retrieved 2009 Nov. 16:
http://www.wbcsdcement.org/pdf/battelle/final_report8.pdf
Japan Society of Civil Engineers. (2006). Recommendation of environmental performance verification for concrete
structures (Draft). Tokyo: JSCE Task Force on Environmental Aspects.
Jahren, P. (2002). Do not forget the other chapters!. Concrete International, 24 (7), 41-44.
Lauritzen, E.K. (2008). The global challenge for recycled aggregate. In Symposium on sustainable construction: the use ofrecycled aggregate (pp. 505-519). London: Thomas Telford.
Malhotra, V.M. (1994). CANMET investigations dealing with high-volume fly ash concrete. In V.M. Malhotra (Ed.),
Advances in Concrete Technology, 2nd Edition (pp. 445-482). Ottawa: CANMET.
Malhotra, V.M. (1999). Making concrete ‘greener’ with fly ash. Concrete International, 21 (11), 61-66.
Mehta, P.K. (1998). Role of pozzolanic and cementitious materials in sustainable development of the concrete industry. In
V.M. Malhotra (Ed.), ACI Special Publication SP-178: Fly ash, silica fume, slag and natural pozzolans in concrete(pp. 1-20). Detroit: American Concrete Institute.
Mehta, P.K. (1999). Concrete technology for sustainable development. Concrete International, 21 (11), 47-53.
Mehta, P.K. (2001). Reducing the environmental impact of concrete. Concrete International, 23 (10), 61-66.
Mehta, P.K. (2002). Greening of the concrete industry for sustainable development. Concrete International, 24 (7), 23-28.
Mehta, P.K. (2009). A new approach to address concrete durability issues. Lecture given at Sustainability in Concrete &Concrete Structures, Special Lecture Series by Internationally Renowned Persons, The University of Tokyo, Tokyo.
Ministry of Land, Infrastructure, and Transportation. (2009). MLIT Annual Report. Tokyo: MLIT.
Okamura, H. (1986). Waiting for innovation in concrete materials. Cement and Concrete, No. 475. (in Japanese)
Ozawa, K. (1990). Development of high performance concrete (Doctoral dissertation, Department of Civil Engineering, The
University of Tokyo, 1990).
Sakai, K. (2009). Towards environmental revolution in concrete technologies. In Proceedings of the 11th Annual
International fib Symposium, Concrete: 21st Century Superhero. London.
Sivasundaram, V., Carette, G.G., and Malhotra, V.M. (1989). Properties of concrete incorporating low quantity of cement
and high volumes of low-calcium fly ash. In V.M. Malhotra (Ed.), ACI Special Publication SP-114: fly ash, silica
fume, and natural pozzolans in concrete (pp. 45-71). Detroit: American Concrete Institute.
Yanagibashi, K. and Yonezawa, T. (1998). Properties and performance of green concrete. In V.M. Malhotra (Ed.), ACI
Special Publication SP-179: Advances in concrete technology (pp. 141-1580. Detroit: American Concrete Institute.
Yokota, H., Iwanami, M., Kato, E., and Yamaji, T. (2008). Life-cycle management of concrete structure in coastal areas. In
H. Yokota, W.L. Jin, T. Shimomura (Eds.), Life Cycle Management of Coastal Concrete Structures 2 (pp. 53-58).
Yokohama: Port and Airport Research Institute.

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3

Environmental impact andsustainability evaluation methods

3.1 INTRODUCTION
Means of evaluating sustainability are necessary in order to determine whether practices are more orless sustainable and to evaluate the state of a system. By evaluating the state of a system, decisions
can be made on how to improve the sustainability of that system or to get feedback on theeffectiveness of a practice. This is popularly achieved by using sustainability indicators, such as those
provided by the United Nations, but there are problems with simplifying the behavior of a complex
system into discrete variables. The construction industry has also developed means for evaluating
sustainable practice, most notably in the form of green building rating and evaluation systems. Thesesystems, however, typically do not have explicit consideration or evaluation of the concrete materials
themselves, although there are a few standards being developed specifically to address the issues of
the concrete industry. This chapter will introduce the general concept behind sustainability andenvironmental impact evaluation, followed by general sustainability evaluation systems andconstruction industry-specific approaches. Finally, standards developed for the concrete industry will
be introduced, followed by the proposal of an evaluation system for concrete materials which utilizes
analytic hierarchy process as a means for balancing different performance characteristics of concreteand for integrating variable socio-economic conditions into the evaluation process.

3.2 EVALUATING SUSTAINABILITY
3.2.1 Sustainability indicators
Sustainability indicators (SI) are typically used to evaluate different aspects of a system, with the total
trend of all the indicators providing some idea of how sustainable the system is. As shown in Figure
3.1, this requires breaking a system down into representative indicators, then evaluating the state ofthose indicators and interpreting the results of the evaluation for future action. However, the key
points are how many indicators to use and which indicators are necessary for properly representing
the system. This simplification is critical and will be discussed later.

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Use

Interpretation

SI 1

SI 2

SI 3

SI 4

SI 5
Collection

SystemFigure 3.1 Concept of sustainability indicators (Bell & Morse, 2008)
SIs can be divided into two types: state SIs and pressure SIs (Bell & Morse, 2008). The UN also
includes a third type, the response indicator. State SIs are used to describe the state of a variable, suchas contaminant level. Pressure SIs, which may also be called control, process, or driving force SIs,
evaluate the processes which affect state SIs, such as how traffic density affects ambient air pollution.
The UN’s response indicator was developed to measure the progress governments were making
towards sustainable development.
SIs are typically established by a top-down approach, where experts decide on a set of SIs based upon
research, theory, and so forth. However, a bottom-up approach may be more appropriate, as thestakeholders may be the best-placed to define sustainability and determine the SIs (Bell & Morse,
2008). In addition, how to interpret the SI is also important – whether the indicator is absolute(sustainable versus not sustainable) or discrete (various levels or grades). Taken over time, a trend in
an SI’s behavior may emerge, so relative change may become more important than the absolutevalues.
The primary criticism of SIs is that they attempt to represent an immensely complex system withquantitative values. These values are selected through a simplification process which is reductionist innature, contrary to the holistic approach typically advocated for sustainability-related issues. Sincedifficulties necessarily arise in the simplification process, transparency in how values were arrived at,
and what assumptions were made, becomes increasingly important. In the end, however, sustainability
is a human vision with human values (Bell & Morse, 2008). Beginning with an established definitionof sustainability, the SIs relevant for reaching that goal should be identified, but the SIs themselves do
not need to be tested for whether they describe sustainability – this would create complications if theSIs were changing while progress was being evaluated.
3.2.2 United Nations sustainability indicators
The UN first established a list of indicators for sustainable development (ISD, which is the same asSI), from the Agenda 21 document at the 1992 Rio Earth Summit. At that time, the UN’s framework
was based around the concept of driving force-state-response (DSR), whereby a force drives ordetermines the state of some variable, which then requires action or a response to deal with thatchange (Bell & Morse, 2008). The original UN indicators were grouped into categories based on the
structure of the Agenda 21 document, such as social, economic, environmental (water, land,
atmosphere, and waste), and institutional aspects of sustainable development.

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The most current approach to SIs by the UN, however, is based around a theme/sub-theme approach,rather than the DSR model. The themes are divided into four different areas: social, environmental,
economic, and institutional, and the themes and sub-themes are given in Table 3.1. Each of the subthemes has indicators related to it, such as “percent of population living below poverty line,” “Giniindex of income equality,” and “unemployment rate” for poverty; “floor area per person” for living
conditions; “emissions of greenhouse gases” for climate change; “abundance of selected key species”
for species; “GDP per capita” and “investment share in GDP” for economic performance;“implementation of ratified global agreements” for international cooperation; and “expenditure on
research and development as a percent of GDP” for science and technology.
Table 3.1 UN sustainable themes and sub-theme framework (United Nations, 2001)
Theme
EquityHealth
Education
Housing
Security
Population
Atmosphere
Land
Oceans, seas, and coasts
Fresh water
Biodiversity
Economic structure
Consumption andproduction patterns
Institutional framework
Institutional capacity

Sub-themes
SOCIAL
Poverty; gender equality
Nutritional status; mortality; sanitation; drinking water; healthcaredelivery
Education level; literacy
Living conditions
Crime
Population change
ENVIRONMENTAL
Climate change; ozone layer depletion; air quality
Agriculture; forests; desertification; urbanization
Coastal zone; fisheries
Water quantity; water quality
Ecosystem; species
ECONOMIC
Economic performance; trade; financial status
Material consumption; energy use; waste generation and management;
transportation
INSTITUTIONAL
Strategic implementation of SD; international cooperation
Information access; communication infrastructure; science andtechnology; disaster preparedness and response

3.2.3 Visualization of sustainability indicators
Another problem with using SIs to describe a complex system – besides the loss of detail throughsimplification – is that the models and theories for modeling these systems are necessarily complex.
However, the policy makers who use these indicators for decision making need simple and clear
presentation instead of complicated scientific models (Ten Brink, 1991). In order to simply andvisually display the results of SI calculations, a visual approach called AMOEBA was proposed by
Ten Brink (1991). In this approach, the quantitative data is translated into a visual representation of
the change in a system over time, and a reference condition or baseline is also included which may
represent the system’s level of sustainability – but the baseline selection is difficult because it’s notalways clear whether the baseline actually represents a sustainable state and the selected condition can

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greatly affect final conclusions. A simple example of what an AMOEBA looks like is shown in
Figure 3.2. With just one AMOEBA, comparisons can be made between different indicators toevaluate which ones are closer or further from the baseline level, but comparing different AMOEBAS– either over time or at different locations – can give an idea of how different conditions change the
distribution of SIs relative to the baseline level. Some criticisms of the AMOEBA approach are that it
doesn’t consider the mechanism leading to the changes observed; that it is still a reductionist approach
which combines a large number of SIs into a single representation; equal weight is given to thedifferent SIs, so a diverse number of perspectives are not considered.
Sustainableindicators

Baselinecondition
Current
condition

Figure 3.2 Example of AMOEBA

3.2.4 Sustainable evaluation systems in the construction industry
The green building movement has been one of the most visible approaches to evaluation ofsustainability and environmental impact in the construction industry. It should be noted that “green
building” – which focuses just on reduced environmental impact – and “sustainable building” – which
considers all three aspects of sustainability – are different terms which get used interchangeably.
As summarized in Table 3.2, many green building assessment tools exist around the world. In 1990,
the United Kingdom’s Building Research Establishment Environmental Assessment Method(BREEAM) was the first such system developed. The United States Green Building Council’s(USGBC) Leadership in Energy and Environmental Design (LEED) system, started in 1998, isperhaps the most well-known system. Both of these systems use a criteria-based system for assigningpoints based upon the evaluation of a wide variety of parameters. In Japan, the Japan Sustainable
Building Council’s Comprehensive Assessment System for Built Environment Efficiency (CASBEE)
is an example of a system which combines a single efficiency index with life cycle assessment. Thesesystems generally focus on energy and resource efficiency, indoor air environment, water resourcesmanagement, and sustainable site selection (Baruah et al., 2008).
Although there has been a strong movement in the commercial construction sector for environmental
certification, the civil construction sector still lacks assessment systems. However, the International
Organization for Standardization (ISO) has developed several standards which are starting to be
applied in the civil engineering field. ISO 14040, Environmental management – life cycle assessment– principles and framework, and its accompanying series provide a general outline for conducting theassessment of environmental impact over the service life of any type of product, and will be discussed
in further detail in the following section. ISO 1568-6, Buildings and constructed assets – service life
planning – Part 6: procedures for considering environmental impacts, focuses on how to assess future

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environmental impacts during the design stage and the comparison of design alternatives. It also
considers the interaction between service life planning and environmental life cycle assessment.
Table 3.2 Green building assessment systems around the world (Baruah et al., 2008)
Country
United Kingdom

USA

CanadaAustralia
Germany
Netherlands
Japan
Korea
Singapore
Hong Kong
China
India
BrazilAssessment system
BRE Environmental Assessment Method (BREEAM)
Environmental Estimator (ENVEST)
USBGC Leadership in Energy and Environmental Design (LEED)NAHB National Green Building Standard
USA-EPA Energy Star for New Homes
DOE Building America
Building Environment and Economical Sustainability (BEES)
Green Building Tool (GB Tool)
Green Globes CEE & EEC
LEED-Canada
BREEAM-Canada
Green Star AGBC
National Building Environment Rating Scheme (NABERS)
German Ministry of Transport, Construction, and Urban Development(DGNB) Sustainable Building Certificate
BREEAM-Netherlands
Eco Quantum
JSBC Comprehensive Assessment System for Building Environmental
Efficiency (CASBEE)
Korea Green Building Label
Building and Construction Authority (BCA) Green MarkHong Kong Building Environment Assessment Method (HK-BEAM)
China Green Building Standard
Green Olympic Building Assessment System (GOBAS)
LEED-India
The Energy and Resources Institute GRIHA
LEED-Brazil
AQUA

3.2.5 Life cycle assessment
Life cycle assessment is a technique for evaluating the environmental impact of a product over its life
cycle. The method was standardized by ISO in the 14040 series, Environmental management – life
cycle assessment – principles and framework. Following the ISO methodology, there are four phases
to an LCA: goal and scope definition, inventory analysis, impact assessment, and interpretation (ISO,2006). The goal and scope definition phase establishes the application and reasons for the LCA,
identifies the target audience, describes the target system and its characteristics, defines the systemboundaries, and reviews the assumptions and limitations involved in the analysis. The inventory
analysis phase develops data regarding the system inputs and outputs utilizing collection andcalculation methodologies. The life cycle impact assessment phase examines the environmental
impact by considering the inventory analysis results in terms of the actual impact on the environment,
and consists of several elements, such as selecting impacts, indicators, and models; classifying
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inventory results; and characterizing the indicator results through calculation to produce categorized
results by indicators. The final phase, interpretation, considers the inventory and impact assessment
results and provides conclusions within the context of the established boundary conditions and goals
set in the goal and scope phase. Reporting and review of the results are also important steps –particularly critical review, which is necessary to ensure transparency and credibility of the results.
The inventory analysis and impact assessment phases are iterative in nature, whereby as results are
obtained, analyzed, and their role in the system understood, they can lead to new data or changes in
the analysis and assessment phases. LCA can be widely applied, but is intended generally for use inmanagement, performance evaluation, labels and declarations, integration into design, development,
or into standards, and for quantifying, monitoring, and reporting of impacts (ISO, 2006).
Consideration of the decision-making process is necessary when considering the potential applicationof LCA.

3.3 EVALUATING CONCRETE SUSTAINABILITY
3.3.1 Current methods and systems
There are very few evaluation standards for directly examining the sustainability of concrete materials,
although ISO currently is working on a standard to specifically address life cycle assessment for theconcrete industry and the Japan Society of Civil Engineers (JSCE) has a draft standard for evaluating
and verifying environmental performance of concrete structures. In many cases, the sustainability
evaluation systems used in the construction industry, such as LEED, BREEAM, CASBEE, and soforth, do not specifically consider or evaluate concrete, but the usage of concrete can help improve thefinal sustainability rating. An example of this will be given below for the LEED rating system.
In the USGBC LEED rating system, usage of concrete materials can earn from 19 to 28 LEED points(NRMCA, 2009). These credits are earned in four credit categories: sustainable sites (brownfieldredevelopment; site development, protect or restore habitat/maximize open space; stormwater design,quantity/quality control; heat island, non-roof/roof), energy and atmosphere (minimum energy
performance; optimize energy performance), materials and resources (building reuse, maintain75%/95% of existing walls, floors and roof; construction waste management, divert 50%/75%;
recycled content, 10%/20%; regional materials, 10%/20%), and innovation and design process(durability; concrete walls and ceiling with no coating; apply for other credits demonstrating
exceptional performance; LEED accredited professional). Some of these credits are earned directly by
concrete materials, such as recycled content or regional materials, whereas other credits are obtained
indirectly by utilizing concrete materials, such as pervious concrete for stormwater design. The
USGBC LEED system does not apply to civil infrastructure.
Although other ISO environmental standards for building have been established, such as ISO 15686-6,
Buildings and construction assets – Service life planning – Part 6: Procedures for considering
environmental impacts and ISO 21930, Sustainability in building construction – Environmental
declaration of building products, members of the concrete industry felt that a separate standard which
addressed the specific needs and practices of the concrete industry needed to be developed (Sakai,2008). This led to the establishment of SC 8, Environmental management for concrete and concrete
structures, a subcommittee of ISO/TC71, Concrete, reinforced concrete, and pre-stressed concrete.
This standard is currently under development, and will consist of several parts, such as the2222

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establishment of boundary conditions and inventory data, environmental design, execution and usage,and end-of-life considerations, among others.
JSCE established the “Recommendation of Environmental Performance Verification for Concrete
Structures (Draft)” to provide general principles for establishing performance requirements,
evaluating environmental impacts, verifying environmental performance, inspecting environmental
performance, and recording for the design, construction, usage, maintenance, dismantling, disposal,
and reusage phases of a concrete structure (JSCE, 2006). The environmental impacts considered in thespecification include greenhouse gases, air contaminants, resources, energy, waste, water and soil
contaminants, noise, and vibration. Life cycle assessment and inventory analysis methodologies areequivalent to those presented in the ISO standards (ISO 14040 series).
3.3.2 Environmental performance indicator
Nielsen (2009) proposed a simple means for evaluating the balance between a single mechanicalperformance and single environmental performance, the environmental performance indicator (EPI).
The EPI is a weighted index which evaluates the mechanical-environmental efficiency by normalizing
a mechanical performance, such as compressive strength, by an environmental performance, such as
CO2 emissions. This approach will be applied during the second experimental phase in Section 4.3
as well as in Chapters 5 and 6.
3.3.3 Evaluation using analytic hierarchy process
One means for considering the balance between different performance indicators is through theapplication of the analytic hierarchy process (AHP), a multi-criteria framework for making complex
decisions (Henry, 2010). The premise of AHP is to model a decision-making problem as a hierarchy
composed of quantifiable elements and their relations and alternatives towards a goal (Saaty, 1999).
The weights of the elements towards the goal is determined by comparing elements against each otherin pairs using qualitative or quantitative judgment values, which are converted to numerical values
that can be used to determine weights for the elements in the hierarchy and allows comparison
between different elements. Weights can be similarly applied to the various alternatives for achieving
the goal, based upon the weights of the elements in the hierarchy and the characteristics of thealternatives, and a decision can be made by analyzing the weights of the different alternatives. Thisevaluation methodology will be demonstrated in the third experimental phase in Section 4.4.
This approach can be used not only for finding the best balance between materials of differing
performances, but can also be applied to convert qualitative values into quantitative data which canthen be used for evaluating concrete sustainability. This is particularly useful considering that, as
proposed by Bell & Morse (2008), sustainability is a human vision with human values, and it varies
depending on who is applying it and under what conditions it is being applied. The concrete industry
is composed of many stakeholders, each of which have their own perspectives and goals, and thus
AHP can be flexibly applied to consider these different perspectives when attempting to select amaterial which best meets a specific group’s definition of sustainability (Henry, 2010). For example,
if the government establishes a goal of reducing CO2 emissions by 20%, then the reduction of CO2
emissions could be given higher weight in the material assessment process than other factors, suchthat a reduction in CO2 could outweigh reduced performance in other aspects.
Furthermore, when assessing the sustainability of concrete materials, it is necessary not only todetermine the relative sustainability between potential material alternatives but to also identify
whether the properties of that material are moving towards overall sustainability. Therefore, it is
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condition, or a reference state, which can provide an indication of overall direction. Setting a baseline
condition for the concrete industry is not easy because, unlike ecological systems, there is no
historical reference point which can be labeled as a “sustainable” state to return to. Rather, thebaseline condition should be set by looking forward and considering the direction the industry should
move towards. As it has already been established that the concrete industry needs to become moresustainable and reduce its environmental impact from its current state, sustainable concrete shouldlook to meet or exceed the performance of the general-use concrete in the areas identified forassessing sustainability. Therefore, when conducting the evaluation of concrete material sustainability,
setting normal-use concrete as a baseline performance can provide a good indicator of the relative
sustainability during the evaluation process. Naturally, this does not address the issue of absolutesustainability, but it does provide a means for moving in a more sustainable direction.

3.4 CONCLUSION
In this chapter, general means for evaluating sustainability and environmental impact were introduced,
along with methods for the construction industry and for concrete in particular. Indicators are avaluable means for tracking and evaluating sustainability and representing the state of a system, but
the complex details of the system may be lost when breaking it down into representative indicators. In
the case of the concrete industry, there are few systems specifically designed to evaluate thesustainability of concrete materials, although green building assessment systems do take into accountthe beneficial performance of concrete. To directly assess the environmental impact and sustainabilityof concrete materials, the usage of environmental performance indicator and the application ofanalytic hierarchy process, respectively, were proposed as useful methods. These methods will beapplied in the following experimental investigations on concrete containing various waste andrecycled materials.

REFERENCES
Baruah, P.J., Sumi, A., and Endo, T. (2008). Green buildings: current status and prospects. In Proceedings of the 7thInternational Symposium on New Technologies for Urban Safety of Mega Cities in Asia (pp. 767-778). Beijing:
Tsinghua University.
Bell, S. and Morse, S. (2008). Sustainability Indicators: Measuring the Immeasurable?. London: Earthscan.
Henry, M. (2010). Formation and evaluation of sustainable concrete based on social perspectives in the Japanese concrete
industry (Ph.D. dissertation, Department of Civil Engineering, The University of Tokyo.)International Organization for Standardization. (2006). ISO 14040 (2006): Environmental management – life cycle
assessment – principles and framework. Geneva: ISO.
Japan Society of Civil Engineers. (2006). Recommendation of environmental performance verification for concrete
structures (Draft). Tokyo: JSCE Task Force on Environmental Aspects.
National Ready Mixed Concrete Association. (2009). Concrete helps achieve LEED certification. Retrieved 2009 Nov. 17:
http://www.greenconcrete.info/GreenBenefits/LEED_Credit.html
Nielsen, C.V. (2009). Towards sustainable concrete structures. Lecture given at Sustainability in Concrete & Concrete
Structures, Special Lecture Series by Internationally Renowned Persons, The University of Tokyo, Tokyo.
Saaty, T.L. (1999). Decision making for leaders: the analytic hierarchy process for decisions in a complex world. Pittsburg:
RWS Publications.
Ten Brink, B. (1991). The AMOEBA approach as a useful tool for establishing sustainable development?. In O. Kuik and H.
Verbruggen (Eds.), In Search of Indicators of Sustainable Development (pp. 71-87). Dordrecht: Kluwer.
United Nations. (2001). CSD Theme Indicator Framework from 2001. United Nations Division for Sustainable Development.
Retrieved 2009 Nov. 18: http://www.un.org/esa/sustdev/natlinfo/indicators/isdms2001/table_4.htm

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Chapter

4

Effect of recycled aggregates andfly ash on concrete properties

4.1 INTRODUCTION
The recycling of construction and demolition waste to conserve natural resources and reduce waste
generation is an important part of sustainable practice in the concrete industry. As discussed earlier in
Section 2.3.1, usage of aggregate recycled from demolition waste in new concrete has been
investigated in many past research works, where it has been shown that as the quality of recycled
aggregate decreases the amount of residual mortar increases and thus the properties of the recycled
aggregate become more varied (Lo et al., 2008). The interfacial transition zone (ITZ) between therecycled aggregate and new cement mortar is generally weaker than in the case of normal aggregates
due to bonding between the new and old mortar layers and the core aggregate, which results in adecrease in concrete properties including workability, strength, and durability (Otsuki et al., 2003;
Poon et al., 2004). The past research works have not, however, examined the statistical relationshipbetween varied aggregate quality and reduced performance. On the other hand, the addition of fly ash
to recycled aggregate concrete has been found to improve concrete properties, particularly durability,
due to improvement of the pore structure and bonding (Corinaldesi et al., 2001; Reiner et al., 2010).
As fly ash is a by-product of the coal industry, this provides an opportunity to practice industrial
ecology by utilizing the waste of other industries as raw material in the concrete production process
and helps limit CO2 emissions by reducing cement content. Unfortunately, there is a lack of researchon the quantitative effect of these waste and recycled materials on the environmental impact as well as
the balance between the mechanical and environmental performance.
The results introduced in this chapter are the summary of three experimental phases designed toinvestigate the problems with recycled aggregate and fly ash concrete mentioned above. The firstphase focused on lower-grade recycled aggregates considering various quality levels, whereas thesecond and third phases attempted to combine environmental impact with mechanical evaluation to
explore the best balance of mix proportions, binder content, aggregate content, and other factors
towards improving the sustainability of concrete at the material level. This was performed bothexperimentally and by utilizing some of the environmental impact and sustainability evaluation
methods introduced in Chapter 3.

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4.2 EFFECT OF RECYCLED AGGREGATE QUALITY
4.2.1 Overview
Although past research works have shown that the usage of recycled aggregates reduces performance,
the effect of recycled aggregate quality and variation – particularly at lower quality levels – on thevariation in concrete properties has not been clarified. This experimental phase therefore focused oninvestigating this effect in the case of compressive strength, looking at how lower quality recycled
aggregates and combinations of normal and recycled aggregates affected the statistical distribution ofcompressive strength. Next, this study examined the relationship between aggregate properties andproposed an index factor which combines both mix proportions and aggregate properties for
estimating the strength of recycled aggregate concrete.
4.2.2 Experimental program
4.2.2.1 Materials
Four different types of coarse aggregates – one normal and three recycled – were used in thisexperimental phase (Figure 4.1). Saturated surface dry (SSD) density and absorption were measured
following JIS A 1109 ten times for each aggregate type and the averages and coefficients of variation
are given in Table 4.1. The relationship between density and absorption for all data points is shownin Figure 4.2. The density of the recycled aggregates is lower and the absorption higher than thenormal aggregates and it can be seen that the variation in density is also larger. The recycled
aggregates were also classified according to JIS A 5002, with R1 meeting “low” grade requirements,
whereas types R2 and R3 were ranked as “below low” grade due to their absorption properties
exceeding the 7% maximum. In addition to coarse aggregates, concrete was prepared using tap water(W), type-I portland cement (C), river sand (S), and air-entraining and super plasticizer admixtures.
4.2.2.2 Mix proportions and fresh properties
Concrete mix proportions and fresh properties are given in Table 4.2. Three different water-cement
ratios (W/C=30, 50, 70) were examined, along with the four different coarse aggregate types. Two
combinations of coarse aggregates (N1-R1, R1-R3), split evenly by volume, were also investigated.

Figure 4.1 Four types of recycled aggregates (from left): normal, R1, R2, and R3
Table 4.1 Properties of coarse aggregates
Type
Normal (N)Recycled 1 (R1)
Recycled 2 (R2)
Recycled 3 (R3)2626

Density (g/cm3)[coeff. var.]2.71 [0.14]
2.45 [0.53]
2.38 [0.59]
2.36 [0.49]

Absorption (%)[coeff. var.]0.78 [9.76]
5.66 [6.32]
7.53 [3.32]
7.91 [4.02]

Grade
Low
< Low
< Low

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Absorption (%)

10
N
R1
R2
R3

8
6
4
2
0
2.3

2.4

2.5

2.6

2.7

2.8

Density (g/cm3)

Figure 4.2 Relationship between density and absorption
Table 4.2 Concrete mix proportions and fresh properties
Series
30-N
30-R1
50-N
50-R1
50-R2
50-R3
50-N-R1
50-R1-R3
70-N
70-R1

W
177
171
177
177
166
176
175
177
179
187

C
589
569
353
354
332
352
350
353
256
267

Mix proportions(kg/m3)
S
N
R1
596
989
609
914
742
1042
785
897
771
787
789
503
453
749
466
857
1001
841
887

R2
932
-

R3
866
448
-

Slump
(mm)

Air content
(%)

14.0
14.0
13.0
13.5
9.5
14.5
13.0
13.5
13.0
13.5

5.8
6.9
5.5
6.5
5.9
5.3
6.6
5.8
5.5
4.8

4.2.2.3 Specimens and curing
Cylinder specimens (10Ø×20cm) were cast for each concrete mix following JSCE-F 552. Aftercasting, molded specimens were covered in plastic wrap and cured in the molds for 24 hours, after
which they were removed from the molds and placed in water curing at 20°C.
4.2.2.4 Testing and results statistics
Compressive strength testing was conducted 28 days after casting according to JIS A 1108. Following
the JSCE “Guideline for Experiment on Materials of Civil Works” (6.3.2C), 30 specimens were tested
per series in order to statistically identify the mean and standard deviation of the compressive strength
results, and the coefficient of variation was calculated as the percentage ratio of the standard deviation
to the mean, which represents the normalized dispersion.
4.2.3 Variation of compressive strength results
4.2.3.1 Effect of water-cement ratio
The effects of water-cement ratio on compressive strength and coefficient of variation for normal andtype-R1 aggregates are shown in Figure 4.3. The effect of recycled aggregate on compressive
strength was found to decrease as water-cement ratio increases; at water-cement ratio of 30, recycled
aggregate has only 76.2% of the strength of normal aggregate concrete, but this percentage increases
to 77.5% and 83.9% for water-cement ratios of 50 and 70, respectively.

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The effect of recycled aggregate on the coefficient of variation of the compressive strength results
also varies depending on the water-cement ratio. The coefficient of variation for normal aggregate
concrete at water-binder ratio 30 is actually higher than that of the recycled aggregate concrete at thesame water-binder ratio. This may be related to the compressive failure behavior of high-strength
concrete, rather than the aggregate type. In addition, the coefficient of variation for the normal
aggregate concrete at water-cement ratio 30 barely falls below 5%. According to the JSCE “Guideline
for Experiment on Materials of Civil Works” (3.10.3B), if the coefficient of variation exceeds 5%then the overdesign factor needs to be increased beyond the base factor of 1.1. It can be seen that thecoefficients of variation for the recycled aggregate concretes, although higher than that of the normal
aggregate concretes at water-cement ratios 50 and 70, still fall below the 5% threshold. Furthermore,
the coefficients of variation for the recycled aggregate concretes remain similar regardless of thewater-cement ratio or strength level.

75

N

60

R1

45
30
15
0
30

50
Water-cement ratio

Coef f . of variation (%)

Comp. strength (MPa)4.2.3.2 Effect of aggregate typeFigure 4.4 shows the compressive strength and coefficient of variation results by varying aggregate
type at water-cement ratio of 50. While the normal aggregate concrete has a 28-day compressive
strength of 41.9 MPa, the strengths of the recycled aggregate concretes are generally similar and fall
between 32.7 MPa (for type-R2) and 28.8 (for type-R3). This result shows that the varying propertiesof the recycled aggregates do not have a large effect on the compressive strength. The coefficient ofvariation results are also similar, with the normal aggregate concrete at 2.9% while the coefficients ofvariation for the recycled aggregates range from 3.9% (for type-R1) to 4.3% (for type-R2). Similar to
the results by water-cement ratio, although the variation is higher for the recycled aggregate concretes
the values still fall below the 5% limit established by JSCE.
6

N

5

R1

4
3
2
1
0
30

70

50
Water-cement ratio

70

50

Coef f . of variation (%)

Comp. strength (MPa)Figure 4.3 Effect of water-cement ratio on compressive strength (left)
and coefficient of variation (right)

40
30
20
10
0
N

R1

R2

R3

N-R1 R1-R3

7
6
5
4
3
2
1
0
N

R1

R2

R3

N-R1 R1-R3

Figure 4.4 Effect of aggregate type on compressive strength (left)
and coefficient of variation (right)

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4.2.3.3 Effect of combining aggregate types
The effects of combining different aggregate types on compressive strength and coefficient ofvariation are also shown in Figure 4.4. The combination N-R1 has strength similar to concrete withjust type-R1 but is 25.3% less than the strength of the normal aggregate concrete. This appears toindicate that the recycled aggregate quality played a limiting factor, even though it was used in equalvolume as the normal aggregate. For the combination R1-R3, the strength is similar to that of theconcrete containing just type-R3 but only slightly less than that of concrete containing just type-R1.
Again, this seems to suggest that the lowest-grade recycled aggregate has a limiting effect.
In contrast, the combination N-R1 has a slightly higher coefficient of variation than either of theconcretes containing only one type of aggregate. The value does, however, fall below 5%. On theother hand, the combination R1-R3 has a much higher coefficient of variation than either of theconcretes with only one type of recycled aggregate, and this value exceeds the 5% limit. Therefore,
although combining aggregate types may not have a detrimental effect on the compressive strength
the coefficient of variation may increase significantly. In the case of the combination of N-R1, thehigher quality of the normal aggregates may have served to help reduce the variation fromcombination, whereas combining two low-quality recycled aggregate types may amplify the variation.
4.2.4 Strength estimation index factor
If the variation of strength when using recycled aggregates falls within acceptable limits, as wasshown for all cases except the combination of different recycled aggregate types, then the estimationof recycled aggregate concrete strength may be achieved simply by understanding how much strength
reduction occurs as a function of the aggregate quality. Aggregate quality can be quantified by thedensity and absorption, as shown in Figure 4.2. However, the estimation of concrete strength also
needs to take into account the mortar mix properties – specifically, the mix proportioning.

Comp. strength (MPa)4.2.4.1 Mix proportion-strength relationshipThe relationship between mix proportions and compressive strength was examined using the cementwater ratio. Figure 4.5 shows the results for all series, and it can be seen that strength linearly
increases with the cement-water ratio. In this case, the strength is represented only by the mix
proportion and doesn’t take into account the aggregate properties; however, a good linear correlation(R2=0.8689) between just the cement-water ratio and compressive strength can be seen.
75
60
45
30
y = 20.662x - 8.7469
R² = 0.8689

15
0
1.0

1.5

2.0
2.5
3.0
Cement-water ratio

3.5

Figure 4.5 Relationship between cement-water ratio and compressive strength

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50

Comp. strength (MPa)Comp. strength (MPa)4.2.4.2 Aggregate property-strength relationshipThe relationship between aggregate properties and compressive strength are shown in Figure 4.6 forweighted density and weighted absorption. The aggregate properties were weighted by multiplying
the properties of the utilized aggregates by their aggregate volume ratio; this is intended to provide
representation for concretes with mixed aggregate types. In addition, for this relationship there is no
consideration of the effect of the mix proportions so only the results from mixes with the same watercement ratio of 50 are shown. The relationship between the weighted density and compressive
strength can be represented with a direct linear relationship, whereas that of the weighted absorption
and compressive strength can be represented with an inverse linear relationship. In both cases, thecorrelation is lower than that of the cement-water ratio/compressive strength case.

40
30
20
y = 29.281x - 40.019
R² = 0.6834

10
0
2.3

2.4
2.5
2.6
2.7
Weighted density (g/cm3)

50
40
30
20
y = -1.4091x + 40.11
R² = 0.6558

10
0

2.8

0

2
4
6
8
Weighted absorption (%)

10

Figure 4.6 Relationship between weighted density (left) or weighted absorption (right)
and compressive strength

4.2.4.3 Index factor for strength estimation
The relationships between the aggregate properties and the compressive strength considered thestrength only in terms of a single aggregate property; however, as was shown in Figure 4.2, thedensity and absorption are also related and so strength estimation should take into account both
simultaneously. However, focusing only on the aggregate properties neglects the contribution of thecement-water ratio. Therefore, the following index factor was proposed by Pardo (2010) to combine
all three variables for estimating the compressive strength of recycled aggregate concrete.
������ � �1 ���� � � � � � �
�
����
100

Where IF: index factor, C/W: cement-water ratio, Dw: weighted density (g/cm3), Dabs: absolute density(g/cm3), Aw: weighted absorption (%). For this calculation, the absolute density is set as that of theaggregate with the highest density (normal aggregate in the case of this investigation).
The relationship between the index factor and compressive strength for all series is shown in Figure
4.7. As the index factor increases the compressive strength also increases linearly with a very highcorrelation (R2=0.9629). Therefore, it can be clearly seen that the index factor provides the best
estimation of recycled aggregate concrete compressive strength by considering both aggregate andmix proportion properties.
4.2.4.4 Index factor for past research results
The applicability of the index factor was examined by applying it to results reported in literature (Dhiret al., 1999; Otsuki et al., 2003; Kou et al., 2008). As summarized in Table 4.3, these cover 18
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Comp. strength (MPa)different cases from three separate investigations. Figure 4.8 shows the relationship between theindex factor and compressive strength for the past research results. For each of the three investigations
a high correlation can be seen; for Dhir et al. and Kou et al., the R2 value exceeds 0.98. This result
strongly demonstrates the applicability of the proposed index factor to research results obtained atother institutions using other methods and materials.
75
60
45
30
y = 22.147x - 6.8003
R² = 0.9629

15
0
1.0

1.5

2.0
2.5
Index f actor

3.0

3.5

Figure 4.7 Relationship between index factor and compressive strength
Table 4.3 Summary of past research results
SourceDhir et al, 1999

Otsuki et al, 2003

Kou et al, 2008

W/C

Dw
(g/cm3)

Aw
(%)

0.29
0.32
0.36
0.40
0.44
0.45
0.40
0.55
0.55
0.55
0.55
0.55
0.59
0.60
0.40
0.45
0.50
0.55

2.60
2.41
2.60
2.43
2.41
2.60
2.44
2.41
2.44
2.47
2.45
2.54
2.36
2.58
2.53
2.53
2.53
2.53

2.50
5.05
2.50
5.90
5.05
2.50
4.50
5.13
4.50
3.58
6.46
2.68
6.71
5.50
3.89
3.89
3.89
3.89

Comp.
strength
(MPa)
71.5
62.5
60.0
40.1
52.0
52.0
44.0
30.0
33.0
32.0
32.0
30.0
39.0
32.5
58.5
52.1
43.4
38.1

4.2.5 Summary
The following conclusions were made based on the results of this experimental investigation:
The effect of recycled aggregate on compressive strength variation was fairly similar regardless ofwater-cement ratio. Although the variation for recycled aggregate concrete was higher than for normal
recycled aggregate concrete, it still fell below the JSCE-specified limit of 5% and thus the overdesign
factor does not need to be increased. At the same water-cement ratio, varying the type of recycled
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aggregate did not greatly affect the compressive strength. Furthermore, the variation of the recycled
aggregate concrete was higher than for normal aggregate concrete but within the JSCE-specified limit.
When combining aggregate types, it was seen that the lowest-grade aggregate limited the strength
level but the variation in strength was greater than when either of the aggregate types was utilized
alone. When combining two different recycled aggregate types, the variation exceeded the JSCEspecified limit.

Comp. strength (MPa)

Otsuki et al, 2003
Kou et al 2008

Dhir et al, 1999

y = 34.268x - 17.383
R² = 0.9888

75
60

y = 16.032x + 19.92
R² = 0.9838

4530

y = 21.999x - 3.2849
R² = 0.9291

15
0
1.0

1.5

2.0
2.5
Index f actor

3.0

3.5

Figure 4.8 Relationship between index factor and compressive strength for past results

Linear relationships between both mix proportion (cement-water ratio) and weighted aggregate(density, absorption) properties and 28-day compressive strength could be seen, with stronger
correlation for the cement-water ratio than for density or absorption. An index factor integrating all
three of the afore-mentioned properties was then proposed, and a very strong linear correlation
between this index factor and the compressive strength of recycled aggregate concrete was shown.
This result demonstrates the usefulness of the index factor as a means for estimating strength byconsidering both mix proportion and aggregate properties. The applicability of the index factor was
examined using results from literature. A very strong correlation could be seen between the index
factor determined from the experimental cases and the compressive strength, thus verifying theapplicability of the proposed index factor to other material and experimental conditions.

4.3 EFFECT OF REDUCED CEMENT CONTENT AND AGGREGATE TYPE
4.3.1 Overview
In the previous phase, focus was only given to the reduction of compressive strength due to varying
recycled aggregate quality. Conversely, this experimental phase was conducted to investigate how
reducing the volume of cement by either reducing absolute binder volume or by replacing cementwith fly ash affected the mechanical behavior and environmental performance. The amount of binder,
binder composition, and aggregate type were all treated as experimental variables, and a control series,
representative of general-use concrete, was also used a reference. The effect of these variables wasinvestigated by examining strength, air permeability, CO2 footprint, and volume of raw materials, andthe relationship between mechanical and environmental performance was considered using theenvironmental performance indicator (Nielsen, 2009) as introduced in Section 3.3.2.

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4.3.2 Experimental program
4.3.2.1 Materials
Concrete was prepared using water (W), type-I portland cement (C), JIS type-II fly ash (FA), riversand (S), normal coarse aggregates (N), low-grade recycled coarse aggregates (RA), and air entraining
and super plasticizer admixtures. The density and fineness were 3.15 g/cm3 and 3300 cm2/g for
cement and 2.19 g/cm3 and 4040 cm2/g for fly ash, and met specifications of JIS A 6201. The specificproperties of the utilized fly ash are also shown in Table 4.4. The recycled aggregate was obtained
from crushed demolition waste and processed and classified as low grade by the recycled aggregate
supplier following JIS A 5023. Wastes mixed with the recycled aggregates such as wood, glass andsuch were removed prior to mixing. Density and absorption were measured according to JIS A 1110
and are given in Table 4.5 along with the properties for sand and normal aggregates. Based upon themeasured results the low-grade recycled aggregates were submerged in water for two days prior to
casting and then surface dried using cloth in order to obtain saturated surface dry conditions.
Table 4.4 Properties of utilized JIS type-II fly ash
Property

SiO2 content
Moisture content
Loss on ignition
Density
Specific surface area (Blaine value)
Flow value ratio
28 days
Activity index
91 days

Unit
%
%
%
g/cm3
cm2/g
%
%
%

Value
62.6
0.11
2.2
2.29
4.087
107
86
98

Table 4.5 Properties of sand and coarse aggregates
Material
Sand
Normal aggregate
Recycled aggregate

SSD density(g/cm2)
2.62
2.72
2.43

Absorption
(%)
2.09
0.50
5.81

Fineness modulus
2.74
6.67
6.73

Maximum size
(mm)
4
20
20

4.3.2.2 Mix proportions and fresh properties
Mix proportions are given in Table 4.6. The term binder is used to represent all cementitious
materials – in this case, fly ash and portland cement. All mixes used a constant water-binder ratio of
30 and sand-aggregate ratio of 39. The effect of binder volume was obtained by varying the amount ofbinder from 550 kg/m3 (normal binder) to 450 kg/m3 (low binder), and at both binder volumes twobinder compositions were used: 100% cement or 50% cement-50% fly ash. Both normal and recycled
aggregates were used for all combinations of binder volume and composition to test the effect ofaggregate type. Fresh properties are also shown in Table 4.6, where slump and air content were
measured according to JIS A 1101 and JIS 1128, respectively.
4.3.2.3 Specimens and curing
Cylinder and beam specimens were cast for each concrete mix following JSCE-F 552. After casting,molded specimens were covered in plastic wrap and cured in the molds for 24 hours (non-fly ash
concrete) or 48 hours (fly ash concrete), after which they were removed from the molds and water
cured up to 56 days.
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Table 4.6 Mix proportions and fresh properties
SeriesControl
NB-NA
NB-RA
LB-NA
LB-RA
NB-NA-FA50
NB-RA-FA50
LB-NA-FA50
LB-RA-FA50

W
171

C
342

165

550

Mix proportions(kg/m3)
FA
S
746
624
-

135

450

687

165

275

275

590

135

225

255

659

NA
1015
1009
1111
955
1067
-

RA
0
905
996
856
957

Slump
(mm)

Air content
(%)

11.0
18.5
12.0
8.5
7.5
10.0
16.0
15.0
16.0

4.0
5.1
5.2
3.5
4.5
3.0
4.5
2.0
4.0

4.3.2.4 Mechanical performance testingThree mechanical properties of the concrete mixes were tested experimentally. Compressive strength
was measured according to JIS A 1108 and tested at 7, 28, and 56 days; flexural strength wasmeasured according to JSCE-G 552 and tested at 28 days only. For all tests, reported values are theaverage of three specimens.
Durability was evaluated by the air permeability coefficient, which was measured at 28 days as
follows. Air permeability specimens were taken from cylinders by cutting a 40 millimeter-thicksection from the center of the cylinder. Specimens were then placed in an oven and dried for one weekat 40°C. After dry conditions were met, the specimens were set into the air permeability machine andthe volume of air flow was measured under steady-state conditions. The air permeability coefficient
was calculated as follows and the reported values are the average of three specimens.
����� ∙ � ∙ � �∙��� � ��� �

Where K: air permeability coefficient (mm/s), P1: loading pressure (MPa), P2: atmospheric pressure(MPa), h: specimen thickness (mm), r: unit volume weight of air (1.205×10-6 MPa), Q: volume of air
flow (mm2/s), and A: sectional area (mm2).
4.3.2.5 Environmental performance assessment
Environmental performance was evaluated using the CO2 footprint and volume of raw materials. The
CO2 footprint was calculated from the mix proportions given in Table 4.6 and the CO2 inventory datafor concrete-making materials given in Section 2.2. The volume of raw materials was calculated by
the percent volume of cement, water, sand, and normal aggregates per cubic meter of concrete. The
environmental performance indicator (EPI) was calculated as the ratio of the mechanical performance(56-day compressive strength) to the environmental impact (CO2 footprint and volume raw materials).
4.3.3 Mechanical performance results
4.3.3.1 Compressive strength
Compressive strength results are shown in Figure 4.9 for 7, 28, and 56 days curing. It can be seenthat non-fly ash concrete mixes all achieved higher strength than the control mix, whereas only the fly
ash mixes with normal aggregates have exceeded the control mix strength by 56 days. Strength3434

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development behavior for normal aggregate concrete without fly ash occurs at a similar rate to thecontrol series, but the recycled aggregate concrete without fly ash does not show any strength gainfrom 28 to 56 days. This result may indicate that the strength of the mortar matrix reached or
exceeded the strength of the recycled aggregates. The fly ash concretes are weaker than the control
series at 7 days, but exhibit greater strength gain up to 28 days due to the delayed reaction speed of fly
ash. From 28 to 56 days, the normal aggregate fly ash concretes continue to develop strength at agreater rate than the control series, but the recycled aggregate fly ash concretes’ strength development
is roughly the same as the control series. The weakness of recycled aggregates may be due to theresidual mortar, which reduces the bond between the aggregate and the new matrix. Failure botharound the aggregate as well as through the aggregate was observed (Figure 4.10).
In all cases, the recycled aggregate series are weaker than their counterpart normal aggregate series,
but the difference is more pronounced for non-fly ash than for fly ash concrete because the strength of
the non-fly ash mortar matrix is higher. Similarly, all the fly ash series are weaker than theircounterpart non-fly ash series, but the difference is greater for normal aggregates. Finally, for normal
aggregate non-fly ash concrete, the low binder specimens are stronger than the normal binder
specimens; this may be due to the greater amount of aggregate, which increases the strength of themix. In contrast, for the normal aggregate fly ash concrete, the normal binder specimens are slightly
stronger than the low binder specimens. For both binder compositions types, there is almost no
difference in strength between normal and low binder for recycled aggregate concrete.
100Compressive strength (MPa)Compressive strength (MPa)

100
80
60
40
Control
NB-RA
LB-RA

20
0
0

7

14

21

28 35 42Age (days)

NB-NA
LB-NA
49

56

63

Control
NB-RA-FA50
LB-RA-FA50

80

NB-NA-FA50
LB-NA-FA50

60
40
20
0
0

7

14

21

28 35 42Age (days)

49

56

63

Figure 4.9 Compressive strength development for non-fly ash (left)
and fly ash (right) concretes
Failure aroundbondAggregate
shear

Figure 4.10 Compressive failure around or through recycled aggregates

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4.3.3.2 Flexural strength
Flexural strength results at 28 days are shown in Figure 4.11. Non-fly ash concretes show greater
flexural strength than the control series, whereas the fly ash concretes show lower flexural strength.
For the non-fly ash series, there is a large difference between normal and recycled aggregate
specimens, but for the fly ash series normal and recycled aggregate concrete have similar flexuralstrength levels. This may be due to the weaker of the fly ash mortar matrix, whereas the non-fly ash
matrix is strong enough that the aggregate shape has some influence on the failure plane. For bothbinder compositions, low binder specimens have higher flexural strength than the normal binder
specimens, but the difference is larger for non-fly ash concrete than it is for fly ash concrete. In thecase of the non-fly ash concrete, the increase in aggregate volume may improve flexural strength dueto the influence of aggregate on the failure plane.

Flexural strength (MPa)

10

NA

8

RA

6
4
2
0
Control

NB

LB

NB-FA50 LB-FA50

Figure 4.11 Flexural strength results at 28 days

4.3.3.3 Air permeability
The air permeability results at 28 days are shown in Figure 4.12. Unlike the compressive and flexuralstrength results, the air permeability of all the test series fell below the control series. The only clear
difference which could be seen was between the normal and recycled aggregate series, as normal
aggregate concrete consistently had much lower air permeability than recycled aggregate concrete.
This result is due to the lower quality of recycled aggregates, which reduces the concrete durability.
The normal aggregate series all showed roughly the same values, except for the low binder fly ash
series, which was slightly higher. For recycled aggregate concrete, again the series all showed roughly
the same values, but in this case the normal binder non-fly ash series was slightly higher.

Air perm. (cm/sec) x10-11

100
NA

RA

10

1
Control

NB

LB

NB-FA50 LB-FA50

Figure 4.12 Air permeability results at 28 days

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4.3.4 Environmental performance results
4.3.4.1 CO2 footprint
The CO2 footprints are shown in Figure 4.13. Since normal and low-grade recycled aggregates haveroughly the same CO2 emissions, there is little difference between the normal and recycled aggregate
series. Reducing the binder content also reduces the CO2 footprint, although the effect is larger for
non-fly ash concretes than for fly ash concretes. The non-fly ash series all have much higher
footprints than the control series, and the fly ash series are all lower. Replacing cement with fly ash
produces the largest reduction in CO2 footprint for both normal and low binder series because fly ash
emissions are a fraction of the cement emissions.

CO2 footprint (kg CO2/m3)

500

NA

400

RA

300
200
100
0
Control

NB

LB

NB-FA50 LB-FA50

Figure 4.13 CO2 footprint

4.3.4.2 Volume raw materials
The volumes of raw material are shown in Figure 4.14. It can be seen that the largest contribution to
reducing raw material comes from recycled aggregates. Reducing the binder content slightly reduces
the volume of raw materials for recycled aggregate series, but slightly increases it for normal
aggregate fly ash concrete. The replacement of cement with fly ash also produces a reduction in raw
volume for both normal and low binder series.

Vol. raw materials (%)

100
80

NA
RA

60
40
20
0
Control

NB

LB

NB-FA50 LB-FA50

Figure 4.14 Volume raw materials

4.3.4.3 Comparison of CO2 vs. raw materials volume
The CO2 footprint and volume of raw materials results are plotted together in Figure 4.15. Reduced
environmental impact is achieved by lower CO2 footprint and lower volume of raw materials, so
results trending leftwards and downwards indicate higher sustainable value. The results are clustered

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in four groups according to aggregate type and binder composition. The least sustainable mixes are
the normal aggregate non-fly ash concrete mixes. Switching from normal to recycled aggregates
reduces the volume of raw materials but doesn’t reduce CO2, whereas replacing cement with fly ash
reduces CO2 but doesn’t greatly reduce raw volume. The most sustainable mixes are those withrecycled aggregates and fly ash. The control mix falls between the normal aggregate non-fly ashgroup and the normal aggregate fly ash group.

Vol. raw amterials (%)

100

Control
NB-NA
NB-RA
LB-NA
LB-RA
NB-NA-FA50
NB-RA-FA50
LB-NA-FA50
LB-RA-FA50

80
60
40
20
0
0

50

Less sustainable

More sustainable

100 150 200 250 300 350 400 450
CO2 footprint (kg CO2/m3)

Figure 4.15 Comparison of CO2 vs raw volume

100

Control
NB-NA
NB-RA
LB-NA
LB-RA
NB-NA-FA50
NB-RA-FA50
LB-NA-FA50
LB-RA-FA50

80
60
40
20
0
0

More sustainable

Less sustainable

50 100 150 200 250 300 350 400 450
CO2 footprint (kg CO2/m3)

56day comp./CO2 (MPa/kg CO2)

56day comp. strength (MPa)4.3.5 Mechanical vs. environmental
4.3.5.1 Compressive strength vs. CO2 footprint
Figure 4.16 shows the 56-day compressive strength results plotted against the CO2 footprint and thecalculated compressive strength-CO2 EPI values. It can be seen that the general trend for strength vs.
CO2 is for increasing strength with increasing CO2 footprint. The slope is greater for normal
aggregates than for recycled aggregates, and the control series follows the trend of the recycled
aggregate series. For non-fly ash concrete, it can be concluded that low binder mixes are superior tonormal binder mixes, as they have higher strength and lower CO2; this is supported by the EPI for lowbinder non-fly ash series, which is much higher than that of the equivalent normal binder series. For
fly ash concrete, the difference is not as clear when looking at the difference in strength against CO2 –low binder normal aggregate has lower CO2 but lower strength when compared to normal binder
normal aggregate. However, the highest EPI is for low binder normal aggregate with fly ash,indicating that CO2 decreases faster than strength.
0.4
0.3

NA
RA

0.2
0.1
0.0
Control

NB

LB

NB-FA50 LB-FA50

Figure 4.16 Compressive strength vs. CO2 footprint (left) and
EPI for compressive strength and CO2 (right)

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Two primary trends can be seen for the compressive strength-CO2 EPI results: normal aggregates arehigher than recycled aggregates and the EPI increases with decreasing cement content. Although therecycled aggregate non-fly ash mixes have a lower EPI than the control series, all other series arehigher. This is due to the reduction in strength without an accompanying reduction in CO2 whenchanging from normal to recycled aggregates, as seen in the top right of the EPI results. In general, it
appears that reducing CO2 has a greater effect on the EPI than increasing strength does.

100

Control
NB-NA
NB-RA
LB-NA
LB-RA
NB-NA-FA50
NB-RA-FA50
LB-NA-FA50
LB-RA-FA50

80
60
40
20
0
0

10

20

More sustainable

Less sustainable

30 40 50 60 70 80
Vol. raw materials (%)

90 10056day comp./vol. raw (MPa/%)

56day comp. strength (MPa)4.3.5.2 Compressive strength vs. volume raw materials
Figure 4.17 shows the 56-day compressive strength results plotted against the volume of raw
materials and the calculated compressive strength-raw volume EPI values. Similar to Figure 4.16, thegeneral trend of increasing strength with increasing volume of raw materials can be seen, but the slope
is greater for non-fly ash concrete than for fly ash concrete. The normal and low-binder series are also
more closely clustered together than for the CO2 footprint. No single series stands out as superior, but
the recycled aggregate non-fly ash concrete does show better overall performance than the normal
aggregate fly ash concrete, with roughly the same strength level but significantly lower volume of raw
materials. All the experimental mixes have roughly the same or better performance than the control
series, with higher strength at the same level of raw materials, higher strength and less raw materials,
or similar strength with fewer raw materials. This is supported by the EPI results, where the control
series is the lowest.
1.5
1.2

NA
RA

0.9
0.6
0.3
0.0
Control

NB

LB

NB-FA50 LB-FA50

Figure 4.17 Compressive strength vs. volume raw materials (left) and
EPI for compressive strength and raw materials (right)
For the EPI results, the primary trend is that the EPI is higher for recycled aggregate concrete than for
normal aggregate concrete. Among the recycled aggregate mixes, normal binder non-fly ash and both
fly ash mixes have similar EPI values, but the low binder non-fly ash concrete value is higher; it isalso the highest value among all series. Normal aggregate fly ash mixes are lower than the non-fly ash
mixes, and the trend is also different, with normal binder specimens higher than low binder; for nonfly ash mixes, the low binder EPI is higher for both normal and recycled aggregates.
4.3.5.3 EPI vs. other environmental performance
Finally, in order to examine all three performances (compressive strength, CO2 footprint, and volumeof raw materials) simultaneously, the EPI were plotted against the environmental performances not
used in the EPI. These results are shown in Figure 4.18. For the compressive strength-raw volume
EPI vs. the CO2 footprint, the results are clustered in two groups according to the binder composition
because binder composition has the largest effect on CO2 footprint, and in these two groups the
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recycled aggregate mixes have higher compressive strength-raw volume EPI values. From theseresults, it can be seen that the low binder recycled aggregate fly ash concrete has the best overall
performance, as its EPI is higher than or similar to all other series except low binder recycled
aggregate non-fly ash concrete, and its CO2 footprint is the lowest of all series.

1.5

Control
NB-NA
NB-RA
LB-NA
LB-RA
NB-NA-FA50
NB-RA-FA50
LB-NA-FA50
LB-RA-FA50

1.2
0.9
0.6
0.3
0.0
0

More sustainable

Less sustainable

50 100 150 200 250 300 350 400 450
CO2 footprint (kg CO2/m3)

56day comp./CO2 (MPa/kg CO2)

56day comp./vol. raw (MPa/%)

For the compressive strength-CO2 EPI vs. the volume of raw materials, the results are again clusteredin two groups but by aggregate type, rather than binder composition, because aggregate type has thelargest effect on volume of raw materials. In both these groups, the fly ash concretes have the highest
compressive strength-CO2 EPI, as well as slightly lower volume of raw materials. Again, it can beseen that the low binder recycled aggregate fly ash concrete offers the best overall performance.
Although its EPI value is lower than those of normal and low binder normal aggregate fly ash series,
the volume of raw materials is not only significantly lower than those two series, but the lowest out of
all series. Furthermore, all series have either higher EPI value, lower volume of raw materials, or both,compared to the control series.
0.4

Control
NB-NA
NB-RA
LB-NA
LB-RA
NB-NA-FA50
NB-RA-FA50
LB-NA-FA50
LB-RA-FA50

0.3
0.2
0.1
0.0
0

10

20

More sustainable

Less sustainable

30 40 50 60 70 80
Vol. raw materials (%)

90 100Figure 4.18 Compressive strength-raw volume EPI vs. CO2 footprint (left) andcompressive strength-CO2 EPI vs. volume raw materials (right)

4.3.6 Summary
In this section, the mechanical and environmental performance of concrete with variable binder
content, composition, and aggregate type were evaluated, and the balance between mechanical andenvironmental performance was also investigated. It was found that all series except recycled
aggregate fly ash mixes gave compressive strength higher than the control series at 28 and 56 days,
but at 28 days only non-fly ash series had higher flexural strength. However, all series had lower air
permeability than the control series. In general, the strength and quality of the recycled aggregates are
believed to be a limiting factor to compressive strength gain. The CO2 footprint is affected primarily
by the binder composition and secondarily by the binder content, whereas the volume of raw materials
is primarily by the aggregate type. All series had higher sustainable value than the control series
except for the normal aggregate non-fly ash concretes, which has the same volume of raw materials
but a larger CO2 footprint.
When comparing the compressive strength with the CO2 footprint and volume of raw materials, it was
found that evaluation only considering CO2 footprint reduced the value of recycled aggregate concrete,
as the strength for these specimens was typically much lower for the same level of CO2. Replacing
cement with fly ash or reducing the amount of binder reduced the CO2 footprint more than it reduced
the strength, so the value of these two approaches could be clearly seen. In contrast, when evaluating
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by the volume of raw materials the influence of recycled aggregates was much higher, as recycled
aggregates reduced raw material volume consumption more than they reduced strength. However, theaddition of fly ash reduced strength without significant reduction of materials. When evaluating
compressive strength against both CO2 footprint and volume of raw materials, low binder recycled
aggregate fly ash concrete could be clearly identified as providing the best overall balance between
the performance parameters. However, the overall strength behavior of this concrete was slightly
lower than that of the control series.

4.4 EFFECT OF MIX PROPORTIONS, BINDER TYPE, AND AGGREGATE VOLUME
4.4.1 Overview
In the previous phase, different combinations of binder volume, binder type, and aggregate type were
investigated considering both mechanical and environmental performances. A control concrete used
to represent “normal-use” concrete was also cast and the performance of the target concretes wascontinually compared to the normal-use concrete. This comparison was conducted because, in order toimprove sustainability in the concrete industry, current concretes in use need to be replaced withmaterials which can meet the same performance requirements with a lower environmental impact.
From the previous phase’s results, two materials (low binder fly ash concrete with and without
recycled aggregates) with 28-day compressive strength similar to the normal-use concrete and withthe lowest environmental impacts were selected as the base conditions for the next investigation. This
experimental plan was conducted in order to understand the effect of mix proportion (water-cement
ratio), binder type (combinations of cement, fly ash, and/or blast furnace slag), and aggregate volume(recycled aggregate replacement ratio) on the durability and environmental impact of the concrete
mixes. Materials with similar strengths to the normal-use concrete were focused on and therefore
durability was selected as the primary mechanical performance. In addition, recycled aggregate usage
in particular has been identified in past research results as having a negative effect on durability(Otsuki et al., 2003), so the latter part of this phase applied the analytic hierarchy process (AHP), as
outlined in Section 3.4, to determine the best balance between durability and environmental impact.
4.4.2 Experimental program
4.4.2.1 Materials
The materials used in this phase were the same as those introduced in Section 4.3.2.1, with theaddition of ground granulated blast furnace slag (BS) as another cementitious replacement material.
The density and fineness of the blast furnace slag are 2.91 g/cm3 and 4440 cm2/g, respectively, andmeet the specifications of JIS A 6206.
4.4.2.2 Mix proportions and fresh properties
Concrete mix proportions and fresh properties are given in Table 4.7. Three different water-binder
ratios (0.3, 0.375, and 0.45), two different binder combinations (C50%-FA50% and C50%-FA25%BS25%), and three different recycled aggregate replacement ratios (0%, 50%, and 100%) wereselected for this experimental investigation. The 50% replacement of cement with mineral admixturesand reduction of mixing water content from the standard 170 kg/m3 to 135 kg/m3 were selected based
upon the results of the previous phase. A control concrete with a water-binder ratio of 50 and no wasteor recycled materials was also prepared to serve as a reference for normal-use concrete.

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Table 4.7 Mix proportions and fresh properties
SeriesControl
WB30-RA0
WB30-RA50
WB30-RA100
WB375-RA0
WB375-RA50
WB375-RA100
WB45-RA0
WB45-RA50
WB45-RA100
WB45-BS-RA0
WB45-BS-RA50
WB45-BS-RA100

W
171

C
342

FA
-

(kg/m3)
BS
-

225

225

-

659

180

180

-

721

150

-

772

75

75

788

S
746

135
150

NA
1015
1067
533
1095
548
1114
557
1125
563
-

RA
478
957
491
982
500
999
506
1011

Slump
(cm)
11.0
15.0
13.5
16.0
6.5
12.0
9.0
7.5
9.5
12.0
7.5
7.5
5.5

Air
(%)
4.0
2.0
6.0
4.0
4.7
5.5
4.5
4.5
3.7
5.6
5.6
3.5
4.0

4.4.2.3 Specimens and curing
Cylinder (10Ø×20 cm) and beam (10×10×40 cm) specimens were cast for each concrete mix. Aftercasting, molded specimens were covered in plastic wrap and cured in the molds for 24 hours, after
which they were removed from the molds and placed in water curing at 20-21°C.
4.4.2.4 TestingCompressive strength was measured according to JIS A 1108 and conducted at 7, 28, and 91 days.
Young’s modulus was measured according to JIS A 1149 at 28 and 91 days using stress values
calculated from the compressive strength load data and strain values obtained from strain gauges
installed on the cylinder under compressive testing. Reported values are the average of three
specimens. The air permeability coefficient, an indicator of durability, was also measured at 28 and 91
days following the procedure outlined in Section 4.3.2.4.
The drying shrinkage test was conducted according to JIS A 1129. Beams were withdrawn from water
curing after 28 days and simply supported (to allow free movement) in an atmospheric environment
at 20-21°C and approximately 50% relative humidity, then two contact gauges spaced approximately
300 millimeters apart were attached to each beam. After this, shrinkage was measured periodicallyand calculated as follows.
ߝൌሺܺ଴ଵ െ ܺ଴ଶ ሻ െ ሺܺ௜ଵ െ ܺ௜ଶ ሻ‫ܮ‬଴

Where ε: shrinkage, X01: initial length of calibration bar (mm), X02: initial length of specimen (mm),Xi1: length of calibration bar at time i (mm), Xi2: length of specimen at time i (mm), and L0: reference
length (mm).
4.4.2.5 Environmental impact assessment
Environmental impact was evaluated using the CO2 footprint and volume of raw materials as outlined
in Section 4.3.2.5.

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4.4.3 Results and discussion
4.4.3.1 Compressive strength
Compressive strength development from 7 to 91 days for all series is shown in Figure 4.19. The
control series has the highest strength level at 7 days but, from 7 to 28 days, the strength development
is higher for the W/B=0.3, W/B=0.375, and W/B=0.45 with blast furnace slag series, regardless ofaggregate type. In the case of the W/B=0.3 and W/B=0.45 with blast furnace slag, the strength level iscomparable to the control by 28 days, but for W/B=0.375 the strength level is still lower than thecontrol even though the strength development is higher. Finally, from 28 to 91 days the strength
development follows a similar rate as the control series. For the W/B=0.45 series, the strength
development is similar to the control from 7 to 91 days, albeit at a much lower level.
70

50
40
30

Control
RA0
RA50
RA100

20
10
0
0
70

Comp. strength (MPa)Comp. strength (MPa)

WB30

60

14

28

42
56
Age (days)

70

84

40
30

Control
RA0
RA50
RA100

20
10
0
14

40
30

Control
RA0
RA50
RA100

20
10
0
70

50

0

50

0

WB45

60

WB375

60

98

Comp. strength (MPa)Comp. strength (MPa)

70

28

42
56
Age (days)

70

84

14

28

42
56
Age (days)

70

84

98

WB45-BS

60
50
40
30

Control
RA0
RA50
RA100

20
10
0

98

0

14

28

42
56
Age (days)

70

84

98

Figure 4.19 Compressive strength development from 7 to 91 days
Figure 4.20 shows the relationship between compressive strength and binder-water ratio for themixes containing 50% fly ash. This relationship is linear for normal concrete (Uomoto, 2007), and it
can be seen that the tendencies for the mixes combining 50% fly ash with 100% normal aggregate, 50%
normal-50% recycled, or 100% recycled aggregate are also linear with a high degree of correlation.

45

65

28 daysComp. strength (MPa)Comp. strength (MPa)

50

40
35
30

RA0
RA50
RA100

25
20
2.0

2.3

2.6
2.9
Binder/water

3.2

60

91 days

55
50
45

RA0
RA50
RA100

40
35

3.5

2.0

2.3

2.6
2.9
Binder/water

3.2

3.5

Figure 4.20 Binder-water ratio vs. compressive strength (50% fly ash series only)
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The effect of recycled aggregate replacement ratio at different water-binder ratios is given in Figure
4.21 for both 28-day and 91-day compressive strengths. At 28 days, increasing usage of recycled
aggregates to 50% did not affect the compressive strength of the W/B=0.3 and W/B=0.45 with blast
furnace slag series; however, by 91 days a large difference developed between compressive strengthof concrete with 0% and 50% recycled aggregate replacement. These two water-binder contents
achieved higher strength than the W/B=0.375 and W/B=0.45 series, which have a similar trend forrecycled aggregate usage regardless of curing time. It is possible that the strength development in the
cement mortar exceeded the strength of the interface, thus limiting the strength of concrete utilizing
recycled aggregates. Some researchers have suggested that replacement of normal aggregates withrecycled aggregates in low amounts can be performed without an accompanying reduction in concrete
compressive strength [26]. The results obtained here, however, cannot confirm this possibility as thenumber of replacement ratios investigated is not enough to identify at what point the usage ofrecycled aggregates becomes detrimental. Furthermore, the past results focused on recycled
aggregates of various grades, and such a replacement ratio may not exist for low-grade recycled
aggregates as the development of strength in the cement mortar matrix may exceed the strength of thebond with the recycled aggregate more easily for low-grade than for high-grade.
28 days

RA0

RA50

RA100

60

70
Comp. strength (MPa)Comp. strength (MPa)

70
50
40
30
20
10
0

91 days

RA0

RA50

RA100

60
50
40
30
20
10
0

Control

WB30

WB375

WB45 WB45-BS

Control

WB30

WB375

WB45 WB45-BS

Figure 4.21 Effect of recycled aggregates at different water-binder ratios
on 28-day and 91-day compressive strengths

4.4.3.2 Young’s modulus
Figure 4.22 shows the effect of recycled aggregate on the Young’s modulus at 28 and 91 days.
Increasing recycled aggregate usage clearly reduces the Young’s modulus, with the effect being fairly
consistent at all water-binder ratios and at both 28 and 91 days. The Young’s modulus results for all
series are also lower than the control mix.
The relationship between compressive strength and Young’s modulus is shown in Figure 4.23 forboth 28 and 91 day compressive strengths for specimens with 50% fly ash. In this figure, the Japan
Society of Civil Engineers standard curve, calculated per the following equation, is used as areference (JSCE, 2002).
‫ܧ‬௘ ሺ‫ݐ‬ሻ ൌ ]ሺ‫ݐ‬ሻ ൈ ͶǤ͹ ൈ ͳͲଷ ට݂௖′ ሺ‫ݐ‬ሻ

Where Ee: Young’s modulus (MPa), f’c: compressive strength (MPa), t: days, and Ø(t): 0.73 up to 3days, 1.0 after 5 days. It can be seen that the standard curve overestimates the Young’s modulus ofconcretes using recycled aggregates, particularly when the compressive strength increases. At low
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ICUS Report 51

50

28 days

RA0

RA50

RA100
Young's modulus (103 MPa)

Young's modulus (103 MPa)

compressive strengths, series with 50% recycled aggregates still fall above the curve at 28 and 91
days, whereas at higher strengths the gap between 0%, 50% and 100% recycled aggregates increases.
Concretes with 0% recycled aggregates fall on or above the standard curve at both 28 and 91 days.

40
30
20
10
0
Control

WB30

WB375

50

91 days

RA0

RA50

RA100

40
30
20
10
0

WB45 WB45-BS

Control

WB30

WB375

WB45 WB45-BS

40

RA0
RA100

35

Young's modulus (103 MPa)

Young's modulus (103 MPa)

Figure 4.22 Effect of recycled aggregates at different water-binder ratios
on 28-day and 91-day Young’s modulus
RA50
JSCE

30
25

28 days

20
20

25

30
35
40
45
Comp. strength (MPa)50

4091 days

35
30
25

RA0
RA100

20
35

40

RA50
JSCE

45
50
55
60
Comp. strength (MPa)65

Figure 4.23 Compressive strength vs. Young’s modulus with JSCE standard curve(50% fly ash series only)

4.4.3.3 Air permeability
The results of the air permeability test are given in Figure 4.24 by aggregate replacement ratio andwater-binder ratio at 28 and 91 days. At 28 days, increasing the amount of recycled aggregate
increases the air permeability for all water-binder ratios, and the effect is larger as water-binder ratio
increases. By 91 days, however, the effect of recycled aggregate on air permeability is reduced, mostsignificantly in the case of W/B=0.375 and 0.45, which may be attributed to the continued reaction of
fly ash past 28 days. The air permeability coefficients of W/B=0.45 with 25% fly ash-25% blast
furnace slag are similar to that of W/B=0.3 with 50% fly ash at 28 days, but the concretes with 50%
fly ash see a further reduction in air permeability up to 91 days while there was little change for the 25%
fly ash-25% blast furnace slag concretes, which again indicates the long-term development of pore
structure in the fly ash concrete and suggests that the concrete combining fly ash and blast furnace
slag develops most of its durability during the early curing period. When compared to the control mix,
most of the mixes had lower air permeability at 28 days, a trend which continued to 91 days when
only the two mixes with W/B=0.45 and 100% recycled aggregate had higher air permeability than thecontrol. As found by past research works, the ITZ between the recycled aggregate and the new mortar
matrix is a weak point for the durability of concrete utilizing recycled aggregates due to increased
porosity and weak bonding (Otsuki et al., 2003; Poon et al., 2004). However, the usage of fly ash was
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shown here to reduce the effect of recycled aggregate, perhaps through densification of the ITZ, andhigher durability performance could be achieved, even at higher water-binder ratios.
28 days

RA0

RA50

RA100

Air perm. (10-9 mm/sec)

Air perm. (10-9 mm/sec)

12
10
8
6
4
2
0

12

91 days

RA0

RA50

RA100

10
8
6
4
2
0

Control

WB30

WB375

WB45 WB45-BS

Control

WB30

WB375

WB45 WB45-BS

Figure 4.24 Effect of recycled aggregates at different water-binder ratios
on 28-day and 91-day air permeability coefficientsControl
RA0
RA50
RA100

500
400
300
200
100

WB30

0

Shrinkage strain (10-6 m/m)

0

7

600

14

21 28 35
Age (days)

42

49

400
300
200
100

WB45

0
0

7

14

21 28 35
Age (days)

42

49

600

56

Control
RA0
RA50
RA100

500
400
300
200
100

WB375

0

56

Control
RA0
RA50
RA100

500

Shrinkage strain (10-6 m/m)

600

0Shrinkage strain (10-6 m/m)

Shrinkage strain (10-6 m/m)

4.4.3.4 Drying shrinkage
Drying shrinkage strain results up to 56 days are given in Figure 4.25 for specimens tested after 28
days of water curing. For the W/B=0.3 and W/B=0.45 with blast furnace slag series, shrinkage iscomparable to that of the control series. In case of W/B=0.375 and W/B=0.45, however, early-age
shrinkage is much higher than the control series; only after 28 days does shrinkage slow to a rate
similar to that of the control.

7

600

14

21 28 35
Age (days)

42

49

56

Control
RA0
RA50
RA100

500
400
300
200
100

WB45-BS

0
0

7

14

21 28 35
Age (days)

42

49

56

Figure 4.25 Drying shrinkage strain up to 56 days after 28 days water curing

Figure 4.26 shows the effect of recycled aggregate replacement ratio at different water-binder ratios
on the 56-day drying shrinkage strain. Increasing the amount of recycled aggregates produces only a
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56-day shrinkage (10-6 m/m)slight increase in 56-day shrinkage strain for the water-binder ratios with shrinkage behavior
comparable to the control series (W/B=0.3 and W/B=0.45 with blast furnace slag). It has beenpreviously reported that the usage of recycled aggregates, particularly highly-porous types such as the
low-grade aggregates used in this investigation, may greatly increase shrinkage (Ravindrarajah &Tam, 1985; Meinhold et al., 2001); however, the usage of 50% fly ash appears to reduce the shrinkageof recycled aggregate concrete to levels comparable to that of normal aggregate concrete with 50% fly
ash in this investigation. Overall, the highest 56-day shrinkage was observed for W/B=0.45 with 50%
fly ash and 100% recycled aggregates and the lowest was observed for W/B=0.3 with 50% fly ash and100% normal aggregate and W/B=0.45 with 25% fly ash-25% blast furnace slag and 100% normal
aggregate.
RA0

600

RA50

RA100

500
400
300
200
100
0
Control

WB30

WB375

WB45 WB45-BS

Figure 4.26 Effect of recycled aggregates at different water-binder ratios
on 56-day drying shrinkage strain

4.4.3.5 Environmental impact
The CO2 footprint calculation results are shown in Figure 4.27. The usage of 50% fly ash can beclearly seen to reduce CO2 relative to the control series, even at lower water-binder ratios with higher
binder volume. At W/B=0.3, the CO2 footprint is 32% less than the control series; this value increases
to a 45% and 54% reduction for W/B=0.375 and W/B=0.45, respectively. The combination of fly ash
and blast furnace slag has no effect on the CO2 footprint, nor does increasing the amount of recycled
aggregate, as the emissions for low-grade recycled aggregates are nearly the same as the emissions fornormal aggregates.
RA0

RA50

RA100

250
200
150
100
50
0

RA0

100

Vol. raw materials (%)

CO2 footprint (kg-CO2/m 3)

300

RA50

RA100

80
60
40
20
0

Control

WB30

WB375

WB45 WB45-BS

Control

WB30

WB375

WB45 WB45-BS

Figure 4.27 CO2 footprint (left) and volume of raw materials (right) calculation results

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ICUS Report No. 51

March 2011For volume of raw materials, the calculation results are also shown in Figure 4.27. Replacing 50% of
cement with fly ash provides a 6% to 10% decrease for all series; thereafter, the decrease in raw
material volume is linear depending on the replacement rate of recycled aggregate, with 50% and 100%
aggregate replacement reducing raw material volume roughly 20% and 40%, respectively. Mixes with
100% recycled aggregate have the lowest volume of raw materials at 51% to 53%.
4.4.4 Balancing durability and environmental impact
4.4.4.1 Performance trade-off
In order to improve sustainable practice in the concrete industry, current normal-use concrete should
be replaced with materials which meet or exceed the required performance while reducing
environmental impact. For concrete structures, the 28-day performance of test pieces (particularly the
28-day compressive strength) is the primary requirement; therefore, replacement materials should
achieve similar or better strength at 28 days but enhance durability and reduce environmental impact –in other words, they need to meet the performance requirements while contributing additional value.
As shown in the previous test results, however, there is oftentimes a trade-off between these, so it isnecessary to examine the balance between different additional value characteristics.
Seven mixes provided similar or better compressive strength results than the control at 28 days:
W/B=0.3 and W/B=0.45 with blast furnace slag (all three recycled aggregate ratios) and W/B=0.375(0% recycled aggregate). The relationship between air permeability, CO2 footprint, and volume of raw
materials were examined for these seven materials in Figure 4.28. Drying shrinkage was not included
as an additional parameter as the selected mixes showed comparable drying shrinkage behavior over
the observed period.

80
60
40
20
0

100

Vol. raw materials (%)

100
Air perm. (%control)

Air perm. (%control)

100

80
60
40
20
0

0

20 40 60 80 100
CO2 footprint (%control)

Control
WB375-RA0

80
60
40
20
0

0 20 40 60 80 100
Vol. raw materials (%control)

WB30-RA0
WB45-RA0-BS

WB30-RA50
WB45-RA50-BS

0

20 40 60 80 100
CO2 footprint (%control)

WB30-RA100
WB45-RA100-BS

Figure 4.28 Comparison of mixes meeting strength requirement of control mix

It can be clearly seen that all seven mixes have better durability (represented by lower air permeability)
and lower environmental impact than the control mix, so any single mix would satisfy the target ofenhanced durability and reduced environmental impact. For CO2 footprint vs. air permeability,
W/B=0.45 with 25% fly ash-25% blast furnace slag and 0% recycled aggregates has the best balance.
For volume of raw materials vs. air permeability, it’s difficult to select a single mix due to the direct
relationship between recycled aggregate usage and air permeability. Finally, for CO2 footprint vs.
volume of recycled materials, W/B=0.45 with 25% fly ash-25% blast furnace slag and 100% recycled
aggregates has the lowest environmental impact. The two materials mentioned above (with the bestbalances for two of the comparisons) fall at opposite ends of the spectrum when looking at volume of
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raw materials vs. air permeability. The mix with 0% recycled aggregates has low air permeability butvery high volume of raw materials, whereas the mix with 100% recycled aggregates has higher air
permeability but lower volume of recycled materials. Therefore, it is difficult to determine whichmaterial provides the best balance between durability and environmental impact.
As introduced in Section 3.4, analytic hierarchy process (AHP) can be applied to quantitatively
determine which material provides the best balance. The hierarchy for assessing the materials wasconstructed as given in Figure 4.29. Four different weighting scenarios were applied (Table 4.8):
one applies equal weight to all three criteria, and the other three place high importance on one
criterion over the others. For the equal-weight scenario, each criterion carries 33.3% of the weight.
For the other three scenarios, the target criterion carries 71.4% of the weight while the other two
criteria carry 14.3% of the weight.
Goal

Elements

Sustainable concrete

Air permeability

CO2 footprint

Alternatives

Vol. raw materials

Concrete mixes

Figure 4.29 Analysis hierarchy including assessment criteria and alternative materials
Table 4.8 Weighting scenarios for additional value criteria
Criteria
Air permeability
CO2 footprint
Vol. raw materials
Criteria
Air permeability
CO2 footprint
Vol. raw materials

Equal
Importance
WeightNormal33.3%
Normal33.3%
Normal33.3%
CO2 high importanceImportance
WeightNormal
14.3%
High
71.4%
Normal14.3%

Air perm. high importanceImportance
WeightHigh
71.4%
Normal
14.3%
Normal14.3%
Vol. raw high importanceImportance
WeightNormal
14.3%
Normal
14.3%
High
71.4%

4.4.4.2 AHP calculation results and discussion
From the material properties and criteria weights, the comparative weights of the concrete mixes were
calculated and are summarized in Figure 4.30 for the four weighting scenarios. When placing equal
importance on the three additional value criteria, W/B=0.45 with 25% fly ash-25% blast furnace slag
and 0% recycled aggregate has the best performance balance, which can be attributed to its low airpermeability and CO2 footprint. When placing high importance on air permeability over the othercriteria, the W/B=0.3 with 50% fly ash and 0% recycled aggregate has the highest weight, which isdetermined primarily by its low air permeability. For the CO2 footprint scenario, W/B=0.45 with 25%
fly ash-25% blast furnace slag and 0% recycled aggregate again is the preferred alternative. In thiscase, all the series with W/B=0.45 and 25% fly ash-25% blast furnace slag have the same CO2
footprint; the mix with 0% recycled aggregate gained the highest weight because it had the bestbalance between air permeability and volume of raw materials. Finally, when placing high importanceon volume of raw materials, W/B=0.45 with 25% fly ash-25% blast furnace slag and 100% recycled
Chapter 4: Effect of recycled aggregates and fly ash on concrete properties

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aggregate had the highest weight. Although W/B=0.3 with 50% fly ash and 100% recycled aggregate
had the lowest amount of raw materials, the other mix was preferred for this scenario because it had areduced CO2 content which, even at low importance, balanced out the difference in volume of raw
materials.

Comparative weight

0.20

Control
WB30-RA0

0.16

WB30-RA50

0.12

WB30-RA100

0.08

WB375-RA0

0.04

WB45-RA50-BS

WB45-RA0-BS
WB45-RA100-BS

0.00
Equal

Air perm.
high importanceCO2high importanceVol. rawhigh importance

Figure 4.30 AHP calculation results by scenario
The combination of fly ash and blast furnace slag was the preferred binder composition in three of the
scenarios, including the “equal” scenario in which the importance of all criteria was the same. Thismay be attributed to the higher strength of this mix at a higher water-binder ratio (W/B=0.45) which
reduced CO2 greatly compared to the W/B=0.3 mixes, as it could be seen that reduced CO2 did, insome cases, serve to tip the balance. These results also showed that replacing only 50% of the normal
aggregates with recycled aggregates generally reduced the mechanical performance more than it
improved the environmental impact – thus, none of the mixes with 50% recycled aggregates wereselected as the preferred option, with either the 0% or 100% recycled aggregate mixes being rated
higher. Lastly, 0% recycled aggregates (that is, 100% normal aggregates) was the preferred alternativein the “equal” and “CO2 footprint” scenarios, whereas 100% recycled aggregates was only thepreferred option in the “volume of raw materials” scenario. This demonstrates that the decrease in air
permeability outweighs the additional value of utilizing recycled materials, as this was thecontributing factor when the 0% recycled aggregates mix was selected over the 100% recycled
aggregate mix in both of the scenarios.
4.4.5 Summary
In this phase, mechanical properties and environmental impacts of concrete combining low-grade
recycled aggregates in various amounts with mineral admixtures were measured and reported, and thebalance between durability and environmental aspects was examined utilizing analytic hierarchy
process. Mixes with W/B=0.3 with 50% fly ash or W/B=0.45 with 25% fly ash-25% blast furnace
slag were found to reduce the effect of recycled aggregate, with performance comparable or better
than the control series even when utilizing 100% low-grade recycled aggregates, and the improvement
may possibly attributed to the densification of the ITZ. The effect of recycled aggregates was seen
when examining Young’s modulus, where it was shown that the JSCE standard curve overestimates
the Young’s modulus values for concrete with recycled aggregates, and also for the air permeability
coefficient, where the effect was larger at 28 days than at 91 days. In the case of shrinkage, the effectof recycled aggregate was generally small, with the difference in shrinkage behavior due to the waterbinder ratio. When examining the environmental impact, all mixes were found to have lower CO2
footprint and volume of raw materials than the control series, with recycled aggregates contributing
primarily to the latter and mineral admixture usage and water-binder ratio contributing to the former.
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When examining the balance between durability and environmental impacts, a single material could
be clearly identified as having the best balance when comparing CO2 footprint vs. air permeability andCO2 footprint vs. volume of raw materials; however, no single material could be selected when
examining volume of raw materials vs. air permeability due to the direct relationship between
recycled aggregate usage and these two factors. Applying AHP with four importance weighting
scenarios showed that, in general, the usage of normal aggregates (0% recycled aggregates) was
preferred in most cases – except when high importance was given to volume of raw materials – as theusage of recycled aggregates in either 50% or 100% replacement ratios tended to reduce airpermeability more than increase volume of raw material relative to the other mixes. In addition, theW/B=0.45 with 25% fly ash-25% blast furnace slag binder composition was also preferred in mostcases because it achieved strength similar to the control mix but with a higher water-binder ratio thanthe other mixes, thus reducing CO2 footprint, and similar or better air permeability.
Although the experimental results showed performance comparable to the control mix could beachieved even when utilizing 100% low-grade recycled aggregates, mixes with recycled aggregateswere not selected in the AHP analysis. However, it is important to consider that the mixes comparedin the AHP analysis all had lower environmental impact and air permeability than the control, so any
single mix would satisfy the goal of reducing resource consumption and CO2 emissions andenhancing durability. As there exists any number of combinations of materials and mix proportions
which can meet a given strength level, the utility of AHP for comparing these mixes to identify themix with the best balance of performance is clearly demonstrated by these results.

4.5 CONCLUSION
In this chapter results from various investigations on the usage of recycled aggregate and fly ash inconcrete were introduced. These investigations focused not only on the mechanical performance but
also addressed other issues such as the statistical variation and estimation of strength and therelationship and balance between the mechanical and environmental performances. The usage of thesewaste and recycled materials in concrete reduced both mechanical properties as well as environmental
impact, and thus the utility of the mechanical-environmental efficiency and the analytic hierarchy
process as methods for quantitatively evaluating and balancing these trade-offs could be clearly seen.

REFERENCES
Corinaldesi, V., Titarelli, F., Coppola, L, and Moriconi, G. (2001). Feasibility and performance of recycled aggregate inconcrete containing fly ash for sustainable buildings. In V.M. Malhotra (Ed.), ACI Special Publication SP-202:
Sustainable development of cement and concrete (pp. 161-180). Farmington Hills: American Concrete Institute.
Dhir, R.K., Limbachiya, M.C., and Leelawat, T. (1999). Suitability of recycled concrete aggregate for us in BS 5328
designated mixes. Proc. of ICE: Structures and Buildings, 134 (3), 257-274.
Japan Society of Civil Engineers. (2002). Standard specifications for concrete structures – 2002 “materials andconstruction”. Tokyo: Japan Society of Civil Engineers.
Kou, S.C., Poon, C.S., and Chan, D. (2007). Influence of fly ash as cement replacement on the properties of recycled
aggregate concrete. Journal of Materials in Civil Engineering, 19 (9), 709-717.
Lo, C.Y., Kotrayothar, D., Tam, V.W.Y., and Loo, Y.C. (2008). Comparison of recycled and natural aggregate properties.
3rd Asian Concrete Federation International Conference, 450-454.

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Meinhold, U., Mellmann, G., and Maultzsch, M. (2001). Performance of high-grade concrete with full substitution of
aggregates by recycled aggregate. In V.M. Malhotra (Ed.), ACI Special Publication SP-202: Sustainable
development of cement and concrete (pp. 85-96). Farmington Hills: American Concrete Institute.
Otsuki, N., Miyazoto, S., and Yodsudjai, W. (2003). Influence of recycled aggregate on interfacial transition zone, strength,chloride penetration and carbonation of concrete. Journal of Materials in Civil Engineering, 15 (5), 443-451.
Pardo, G. (2010). Design methodology for green concrete containing high volume of recycled materials (Master thesis,
Department of Civil Engineering, The University of Tokyo)
Poon, C.S., Shui, Z.H., and Lam, L. (2004). Effect of microstructure of ITZ on compressive strength of concrete preparedwith recycled aggregates. Construction and Building Materials, 18, 461-468.
Ravindrarajah, R.S. and Tam, T.C. (1985). Properties of concrete made with crushed concrete as coarse aggregate. Magazineof Concrete Research, 37 (130), 29-38.
Reiner, M., Durham, S.A., and Rens, K.L. (2010). Development and analysis of high-performance green concrete in theurban infrastructure. International Journal of Sustainable Engineering, 3 (3), 198-210.
Uomoto, T. (2007). Material design for structural concrete. Tokyo: Ohmsha Corporation.

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Chapter

5

Combining recycled rubber with
waste materials in concrete

5.1 INTRODUCTION
Application of recycled coarse aggregates and fly ash only reduces the usage of raw coarse aggregatesand cement-making materials; to further reduce resource consumption other waste materials need tobe combined in concrete in order to reduce the usage of natural sand for fine aggregates. The recycled
rate of waste rubber tires in Japan is high – roughly 89% in 2009 – but this materials is generally not
used as raw material in concrete (JATMA, 2009). The usage of recycled rubber crumbs as areplacement for sand, however, has been investigated to some extent, with results showing that, whilerubberized concrete has high energy absorption capacity, it may not be attractive as a structural
material due to significantly reduced strength and adverse effects on fresh and hardened properties(Eldin and Senouci, 1994; Topçu, 1995; Toutanji, 1996). On the other hand, rubberized high-strength
concrete may be applicable when combined with mineral admixtures and extended curing (Wong andTing, 2009).
Considering these research results and setting the reduction of raw materials as a target, this chapter
introduces the results of an investigation on the effect of replacing sand with recycled rubber crumbs
in concrete containing both recycled aggregates and fly ash. High-strength concrete was set as thebase concrete mix, and the effect of each combination of waste material on the hardened properties
and the environmental impact – evaluated as the volume of raw materials – was investigated. As it canbe expected that this combination will reduce mechanical performance, the mechanical-environmental
efficiency was calculated using the environmental performance indicator introduced in Section 3.3.2
and normalizing it against a control material used to represent general-use concrete.

5.2 EXPERIMENTAL PROGRAM
5.2.1 Materials
Concrete was prepared using tap water (W), type-I portland cement (C), JIS type-II fly ash (FA), riversand (S), recycled rubber crumbs (GC), normal coarse aggregates (NA), low-grade recycled coarse

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aggregates (RA), and air-entraining (AE) and super plasticizer (SP) admixtures. The specificproperties of the cement and type-II fly ash are given in Section 4.3.2.1, and the properties anddetails of preparation for the low-grade recycled coarse aggregates are also given in Section 4.3.2.1.
Rubber crumbs with a maximum size of 3 millimeters, as shown in Figure 5.1, were processed fromwaste tires, and no steel wires or other materials were included. The properties of both the rubber
crumbs and sand (fine aggregates) are summarized in Table 5.1.

Figure 5.1 Rubber crumbs (size 1 to 3 mm) from recycled rubber tires
Table 5.1 Properties of rubber crumbs and sandMaterial
Rubber crumbs
Sand

SSD density(g/cm2)1.10
2.62

Absorption
(%)
2.09

Fineness modulus
2.74

Maximum size
(mm)
3
4

5.2.2 Mix proportions and fresh properties
Concrete mix proportions and fresh concrete properties are given in Table 5.2. The water-binder ratio
was set at 0.3, and two recycled aggregate replacement ratios (0% and 100% by volume), two binder
combinations (C100% and C50%-FA50% by mass), and three rubber crumb replacement ratios (0%,25%, and 50% replacement of sand by volume) were selected for this experimental investigation. A
control concrete with a water-binder ratio of 0.5 and no waste or recycled materials was also prepared
to serve as a reference for normal-use concrete.
Table 5.2 Mix proportions and fresh properties
SeriesControl
WB30
WB30-RAWB30-FA50
WB30-RA-FA50
WB30-GC25
WB30-RA-GC25
WB30-FA50-GC25
WB30-RA-FA50-GC25
WB30-GC50
WB30-RA-GC50
WB30-FA50-GC50
WB30-RA-FA50-GC50

5454

W
171

165

C
342

FA
-

(kg/m3)
S
746

550

-

624

-

275

275

590

-

550

-

468

65

275

275

442

62

550

-

312

131

275

275

295

124

GC
-

NA
1015
1009
955
1009
995
1009
955
-

RA
905
856
905
856
905
856

Slump
(cm)
11.0
18.5
12.0
10.0
16.0
10.0
9.5
17.0
13.5
9.5
13.0
11.0
12.5

Air
(%)
4.0
5.1
5.2
3.0
4.5
3.6
5.1
2.7
5.1
5.7
5.0
4.4
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5.2.3 Specimens and curing
Cylinder (10Ø×20cm) specimens were cast for each concrete mix. After casting, molded specimens
were covered in plastic wrap and cured in the molds for 24 hours, after which they were removed
from the molds and placed in water curing at 20-21°C.
5.2.4 Testing and environmental assessment
Compressive strength testing and the measurement of Young’s modulus and the air permeability
coefficient were conducted as explained in Sections 4.3.2.4 and 4.4.2.4 and conducted at 7, 28, and91 days for strength and 28 days only for Young’s modulus and air permeability.
The environmental impact was assessed using the volume of raw materials, which was calculated
from the percent volume of cement, water, sand, and normal aggregates per cubic meter of concrete.
Therefore, if the volume of raw materials in a given mix decreases then this is assumed to represent a
reduction in natural resource consumption and thus a reduced environmental impact. CO2 emissions
and input energy – which may conversely increase for waste and recycled materials due to processing– were not considered in this investigation due to a lack of inventory data on the rubber crumbs.

5.3 RESULTS
5.3.1 Compressive strength
Compressive strength development from 7 to 91 days is shown in Figure 5.2 for concrete mixes with
0%, 25%, and 50% rubber crumb replacement ratios. At 0% rubber crumbs, the strength developmentof concretes with normal aggregate (both 100% cement and 50% cement-50% fly ash) and concretewith recycled aggregate and fly ash follows a similar trend, with the largest difference occurring fromcasting up to 7 days. In the case of concrete with recycled aggregate and no fly ash, very little strength
gain was observed from 28 to 91 days; this may indicate that the bond between the high-strengthmortar and the low-grade recycled aggregate is limiting the strength gain, as the mix with normal
aggregates and 50% fly ash exceeds this mix’s strength by 91 days. The strength development of themix combining recycled aggregates and 50% fly ash is close to the behavior of the control mix up to
91 days.
At 25% replacement of sand with rubber crumbs, the overall strength levels are much lower than for 0%
rubber crumbs and are either comparable to or lower than the control series, and there is less strength
development observed from 28 to 91 days. Furthermore, the difference between normal and recycled
aggregates is smaller, but again little strength gain is observed for the mix with recycled aggregate
and no fly ash from 28 to 91 days. Finally, at 50% rubber crumbs the strength levels of all series aremuch lower than the control series and little to no strength development can be seen after 28 days,
except in the case of the concrete with normal aggregates and 50% fly ash.
The effect of the rubber crumb replacement ratio on the 28-day compressive strength is shown in
Figure 5.3. Increasing the amount of rubber crumbs linearly reduces the compressive strength
regardless of binder composition or coarse aggregate type. The concretes with normal aggregates lose
the greatest percentage of strength (59.1% and 58.6% for 100% cement and 50% cement-50% fly ash,respectively) when increasing the rubber chip replacement ratio from 0% to 50%; in contrast, theconcretes with recycled aggregate lose only 47.8% and 49.8% for normal cement and 50% fly ash,respectively. The effect of recycled aggregates and fly ash is also reduced as the amount of rubber
crumbs increases, but by 50% rubber crumb replacement ratio only the effect of fly ash can be seen.
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Increasing the amount of rubber crumbs to 25% reduces strength below the level of the control mix
for the fly ash concretes, and at 50% rubber crumb replacement ratio all mixes have lower strengththan the control.

Comp. strength (MPa)100

Control80

WB30
WB30-RA60

WB30-FA5040

WB30-RA-FA50

GC0

20
0
0

14

28

42 56 70
Age (days)

84

98

Comp. strength (MPa)100

Control80

WB30
WB30-RA60

WB30-FA5040

WB30-RA-FA50

GC25

20
0
0

14

28

42 56 70
Age (days)

84

98

Comp. strength (MPa)100

Control80

WB30
WB30-RA60

WB30-FA5040

WB30-RA-FA50

GC50

20
0
0

14

28

42 56 70
Age (days)

84

98

Figure 5.2 Compressive strength development from 7 to 91 days for 0% (top), 25% (middle),
and 50% (bottom) rubber crumb replacement ratios
28d comp. strength (MPa)100

Control80

WB30
WB30-RA60

WB30-FA5040

WB30-RA-FA50

20
0
0

10
20
30
40
50
Rubber crumb replacement ratio (%)

Figure 5.3 Effect of rubber crumb replacement ratio on 28-day compressive strength

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5.3.2 Young’s modulus
Figure 5.4 shows the effect of rubber crumb replacement ratio on the 28-day Young’s modulus.
Similar to the 28-day compressive strength, increasing the replacement ratio linearly reduces theYoung’s modulus. Unlike the compressive strength, however, the effect of recycled aggregate and fly
ash remains fairly constant at all replacement ratios. It can also be seen that the Young’s modulus forconcretes with just fly ash and concretes with just recycled aggregate is nearly the same regardless of
the amount of rubber crumbs. The Young’s modulus of the control series is higher than that of the allseries except for the concrete containing no waste materials.

Young's modulus (103 MPa)

The relationship between 28-day compressive strength and Young’s modulus is shown in Figure 5.5.
In this figure, the Japan Society of Civil Engineers (JSCE) standard curve is used as a reference(JSCE, 2002). The standard curve generally overestimates the Young’s modulus for most of theconcrete mixes, with the exceptions being the control mix and the two mixes containing 25% rubber
crumbs without recycled aggregates. Other mixes without recycled aggregates also fall near to thestandard curve, but mixes with recycled aggregates generally fall further below the curve, regardlessof the amount of rubber crumbs.
50

Control40

WB30
WB30-RA30

WB30-FA5020

WB30-RA-FA50

10
0
0

10
20
30
40
50
Rubber crumb replacement ratio (%)

Young's modulus (103 MPa)

Figure 5.4 Effect of rubber crumb replacement ratio on 28-day Young’s modulus
50
40
30
20
10
0
15

25

35 45 55 65 75
Comp. strength (MPa)Control

JSCE

WB30

WB30-RAWB30-GC25

WB30-RA-GC25

WB30-GC50

WB30-RA-GC50

WB30-FA50

WB30-RA-FA50

WB30-FA50-GC25

WB30-RA-FA50-GC25

WB30-FA50-GC50

WB30-RA-FA50-GC50

85

Figure 5.5 Compressive strength vs. Young’s modulus with JSCE standard curve

5.3.3 Compressive failure mode
Differing failure modes under compressive loading could also be observed, as shown in Figure 5.6.
Mixes without rubber crumbs, particularly those with high strength such as the non-fly ash concretes
with normal and recycled aggregates, underwent brittle failure with specimens suddenly exploding
into small pieces at the peak load. On the other hand, usage of 25% rubber crumbs significantly
affected this failure mode, with specimens failing in a much less brittle fashion. The strength of these
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specimens, however, is much lower than that of the high-strength specimens but comparable to thestrength of the normal concrete mix, but Figure 5.7 shows that even at this strength level normal
concrete also undergoes brittle failure under compressive loading, so the effect of rubber crumbs on
failure mode can be clearly seen.

Figure 5.6 Failure mode of specimens under compressive loading: no waste (top left),recycled aggregate (top right), 25% rubber crumbs (bottom left),and recycled aggregate+25% rubber crumbs (bottom right)

Figure 5.7 Failure mode of normal concrete under compressive loading

5.3.4 Air permeability
The air permeability coefficient measurement results are given in Figure 5.8. The effect of rubber
crumbs is markedly different depending on the binder composition. For non-fly ash concrete,increasing the amount of rubber crumbs increases the air permeability consistently, with a smaller

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increase from 25% to 50% than from 0% to 25%. A large difference can also be seen between normal
and recycled aggregates for the non-fly ash concretes, with this difference remaining fairly constantregardless of rubber crumb replacement ratio. For the fly ash concretes, however, increasing theamount of rubber crumbs from 0% to 25% has little effect on the air permeability, but increasing from
25% to 50% produces a large increase. In addition, the type of aggregate does not have as large aneffect in the fly ash concretes as it does in the non-fly ash concretes.

Air perm. (10-9 mm/s)

100

Control
WB30

10

WB30-RAWB30-FA50
WB30-RA-FA50

1

0.1
0

10
20
30
40
50
Rubber crumb replacement ratio (%)

Figure 5.8 Effect of rubber crumb replacement ratio on 28-day air permeability coefficient

5.3.5 Environmental impact
The calculation results for volume of raw materials are shown in Figure 5.9. Increasing the rubber
crumb replacement ratio linearly decreases the volume of raw materials roughly 6% for each 25%
increase in amount of rubber crumbs. Replacement of 50% cement with fly ash reduces the volume of
raw materials roughly 12%, whereas the usage of 100% recycled aggregates reduces the volume of
raw materials roughly 37%. The combination of both fly ash and recycled aggregates can achieveroughly a 47% reduction, with the combination of all three waste and recycled materials reaching amaximum reduction of 52.8% and 58.5% for 25% and 50% rubber crumb replacement ratio,
respectively.

Vol. raw materials (%)

100

Control (100%)

80

WB30
WB30-RA60

WB30-FA5040

WB30-RA-FA50

20
0
0

10
20
30
40
50
Rubber crumb replacement ratio (%)

Figure 5.9 Effect of rubber crumb replacement ratio on volume of raw materials

5.3.6 Relationship between mechanical and environmental
In order to examine the relationship between environmental impact and mechanical performance, thevolume of raw materials and 28-day compressive strength are plotted together in Figure 5.10. As
both these properties varied linearly with the amount of rubber crumbs, the relationship between themis also linear with compressive strength increasing as volume of raw materials increases. The data
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points fall into two main groups depending on the type of aggregate, with recycled aggregate mixes
having the lowest volume of raw materials but lower strength than the normal aggregate mixes. The
results of the mixes combining fly ash and recycled aggregates and the mixes with just recycled
aggregates also follow a linear trend, with the strength and volume of raw materials of the mixes
combining fly ash, recycled aggregates, and 0% and 25% rubber crumbs falling near to the strengthand volume of raw materials of the mixes combining recycled aggregate with 25% and 50% rubber
crumbs. The difference between fly ash and non-fly ash mixes is slightly larger in the case of thenormal aggregate concretes.
28d comp. strength (MPa)100

Control

80
60
40
20
0
0

20
40
60
80
Vol. raw materials (%)

WB30

WB30-RAWB30-GC25

WB30-RA-GC25

WB30-GC50

WB30-RA-GC50

WB30-FA50

WB30-RA-FA50

WB30-FA50-GC25

WB30-RA-FA50-GC25

WB30-FA50-GC50

WB30-RA-FA50-GC50

100

Figure 5.10 Volume of raw materials vs. 28-day compressive strength

5.3.7 Mechanical-environmental efficiency
While Figure 5.10 clearly shows that decreasing the volume of raw materials reduces strength, it isdifficult to determine which mix has the best balance of strength and raw materials – that is, the mostefficient combination of mechanical and environmental performance. To address the problem ofwhich mix has the best mechanical-environmental efficiency, the following equation (based on theconcept of the environmental performance indicator as proposed by Nielsen [2009]) was proposed tocreate a weighted strength index considering both the compressive strength as well as usage of raw
materials.
ᇱ
݂௖ି௪
ൌ

݂௖ᇱ
ሺܸ ΤͳͲͲሻ

Where f’c-w: weighted strength index (MPa), f’c: compressive strength (MPa), and V: volume of raw
materials (%).
The calculation results are shown in Figure 5.11, where the effect of rubber crumb replacement ratioon the weighted strength can be seen. Relative to the normal compressive strength results, theweighted strength of the mixes with only rubber crumbs increased only slightly, as did the mixes
combining fly ash and rubber crumbs. Mixes combining fly ash and recycled aggregates with rubber
crumbs have the second-highest weighted strength. Furthermore, at 0% rubber crumb replacement
ratio the weighted strengths of the mix combining fly ash and recycled aggregates and the mix with nowaste materials are roughly the same; however, increasing the amount of rubber crumbs reduces theweighted strength faster in the case of the concrete with no waste, indicating that combining all threewaste materials together is more efficient than utilizing rubber crumbs on their own. Finally, themixes with recycled aggregates and rubber crumbs have the highest weighted strengths.

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Weighted strength (MPa)100

Control80

WB30
WB30-RA60

WB30-FA5040

WB30-RA-FA50

20
0
0

10
20
30
40
50
Rubber crumb replacement ratio (%)

Figure 5.11 Effect of rubber crumb replacement ratio on weighted strength calculation results
The efficiency of normal-use concrete is represented by the weighted strength of the control mix, so tounderstand the efficiency of the concretes utilizing waste materials relative to this baseline theweighted strengths were normalized by the control mix. The results, given in Figure 5.12, show that
almost all combinations of waste materials are more efficient than the control mix. The only
exceptions to this result are the mixes using 50% rubber crumbs only or with fly ash. Concretes
combining recycled aggregates with fly ash, with no waste materials, and combining 25% rubber
crumbs with recycled aggregates all have comparable efficiency and are second-highest behind theconcrete with only recycled aggregates.

Weighted strength ratio(normalized by control)

2.5

GC0

GC25

GC50

2.0
1.5
1.0
0.5
0.0
WB30

WB30-RAWB30-FA50

WB30-RA-FA50

Figure 5.12 Weighted strength calculation results normalized by control mix

5.4 DISCUSSION
The test results showed that the usage of rubber crumbs clearly reduces the mechanical performance;
however, combining rubber crumbs with other waste materials reduces mechanical performance evenfurther, as the best compressive strength and Young’s modulus (and reasonable air permeability) were
all obtained in the case of high-strength concrete containing only rubber crumbs. The bonding
between rubber and hardened paste has been cited as a weakness in rubberized high-strength concrete(Wong and Ting, 2009), and the results shown here demonstrate that this may also be the case evenwhen using fly ash, as the amount of strength development between 28 and 91 days decreased as theamount of rubber crumbs increased. One exception to this is the combination of fly ash and rubber
crumbs, which generally had a higher strength development in this time period compared to the otherrubberized concrete mixes. The usage of fly ash also showed some benefit regarding air permeability,
as the air permeability coefficient of concrete combining rubber crumbs and fly ash was generally
lower than when fly ash was not used, although there was some unclear behavior when the amount ofrubber crumbs was increased to 50%. The improvement of air permeability without an improvement
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in strength shows that, while fly ash may not necessarily improve the bonding of the cement matrix
with the rubber crumbs, it can contribute to reducing mass transport properties to some extent. In
addition, it was also observed that as the rubber crumb replacement ratio increased the effect ofrecycled aggregate was greatly reduced in the case of compressive strength, but this trend was
different for air permeability, where the behavior varied depending on whether fly ash was included.
In non-fly ash concrete, the effect of recycled aggregate on air permeability remained fairly constanteven when 50% rubber crumbs were included, but for fly ash concrete the effect of recycled aggregate
was almost entirely reduced when rubber crumbs were included. Therefore, fly ash does not serve toimprove the bonding with recycled aggregates (as similar differences in strength between normal andrecycled aggregates were observed for both non-fly ash and fly ash concretes) but it can improve airpermeability when combined both with recycled aggregate and rubber crumbs.
Weighting the compressive strength by the volume of raw materials was conducted as a way toconsider the environmental impact along with the mechanical performance. Considering thiscalculation, most combinations of waste materials may be considered more “efficient” than thecontrol mix, as was shown when the weighted strengths were normalized by the control mix. However,when considering the actual specification of concrete materials, the foremost requirement is that theconcrete meets a certain performance requirement, and the weighted strength does not explicitly
consider this as it is a function of both strength and volume of raw materials. However, thenormalized weighted strength may be useful when comparing mixes with similar strength levels. The
control mix, used to represent a “normal concrete,” had a 28-day strength of 43.5 MPa. Other mixes
with compressive strengths around this level include recycled aggregates and fly ash at 39.7 MPa, 25%
rubber at 47.6 MPa, recycled aggregates and 25% rubber at 42.2 MPa, and fly ash and 25% rubber at
35.4 MPa; the normalized weighted strengths for these four mixes are 1.73, 1.16, 1.71, and 0.99,
respectively. From this comparison, it can be said that at this strength level the combination ofrecycled aggregates and fly ash has the best balance of mechanical and environmental performance
while meeting the strength requirement. Performing a similar exercise with a target strength level ofaround 30 MPa would yield recycled aggregates, fly ash, and 25% rubber (28-day strength: 29.1 MPa)
as the most efficient combination of waste materials. This methodology of weighting mechanical byenvironmental to identify the efficiency of different combinations of waste materials could also be
extended to other properties as well as other mix proportions or wastes.

5.5 CONCLUSION
The following conclusions were made based on the results of this experimental investigation:
Increasing the amount of rubber crumbs from 0% to 50% linearly reduced the compressive strength
regardless of the aggregate or binder type, and also reduced the rate of strength development from 28
to 91 days. Combination of rubber crumbs with recycled aggregates, with fly ash, and with bothrecycled aggregates and fly ash reduced strength in that order. As the amount of rubber crumbs
increased the effect of recycled aggregates on strength was reduced until only the effect of fly ash
could be seen at 50% rubber crumb replacement ratio. The usage of fly ash did not appear to improvebonding between the rubber crumbs and the cement matrix nor between the recycled aggregates andthe cement matrix.
Increasing the amount of rubber crumbs also linearly reduced the Young’s modulus, and the effect
was the same regardless of aggregate or binder type. The effect of fly ash and recycled aggregate
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could be seen even when increasing the amount of rubber crumbs to 50%. The JSCE standard curve
was found to overestimate the Young’s modulus of nearly all the experimental series.
The usage of 25% rubber crumbs could drastically reduce brittle failure under compression loadingand prevent explosive destruction of the high-strength specimens. This was observed to occur bothwhen the water-binder ratio was held constant as well as between mixes with comparable compressive
strength, and also for both normal and recycled aggregates.
The effect of rubber crumbs on the air permeability coefficient depended primarily on the binder type.
In the case of non-fly ash concretes, air permeability increased steadily as the amount of rubber
crumbs increased, and the effect of recycled aggregates was marked and constant. For fly ash
concretes increasing the rubber crumbs to 25% produced only a small change, but increasing to 50%
drastically increased the air permeability. The effect of recycled aggregates was small regardless of
the rubber crumb replacement ratio, and the effectiveness of fly ash for improving the air permeabilityof both rubber crumb and recycled aggregate concretes could be seen.
The mechanical-environmental efficiency of the mixes was calculated using an index which weighted
the compressive strength by the volume of raw materials in each experimental mix. Overall, the usageof only 100% recycled aggregates had the highest efficiency, followed by the mixes with no wastematerials, combining recycled aggregate with 25% rubber crumbs, and combining recycled aggregateswith fly ash. Rubber crumbs were found to be an inefficient means for reducing environmental impact
when using the weighted strength as an evaluation index. When comparing the weighted strengths ofconcretes at a target strength level, the combination of recycled aggregates and fly ash was mostefficient at the 40 MPa level and the combination of recycled aggregates, fly ash, and 25% rubber
crumbs was most efficient at the 30 MPa level.

REFERENCES
Eldin, N.N. and Senouci, A.B. (1994). Measurement and prediction of the strength of rubberized concrete. Cement andConcrete Composites, 16, 287-298.
Japan Automobile Tyre Manufacturers Association. (2009). Tyre industry of Japan. Tokyo: JATMA. (in Japanese)
Japan Society of Civil Engineers. (2002). Standard specifications for concrete structures – 2002 “materials andconstruction”. Tokyo: JSCE.
Nielsen, C.V. (2009). Towards sustainable concrete structures. Lecture given at Sustainability in Concrete & Concrete
Structures, Special Lecture Series by Internationally Renowned Persons, The University of Tokyo, Tokyo.
Topçu, İ.B. (1995). The properties of rubberized concrete. Cement and Concrete Research, 25 (2), 304-310.
Toutanji, H.A. (1996). The use of rubber tire particles in concrete to replace mineral admixtures. Cement and Concrete
Composites, 18, 135-139.
Wong, S.F. and Ting, S.K. (2009). Use of recycled rubber tires in normal- and high-strength concretes. ACI Materials
Journal, 106 (4), 325-332.

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Chapter

6

Utilizing recycled fibers in
fly ash mortar and concrete

6.1 INTRODUCTION
Durability is an important aspect of improving sustainability in the concrete industry, as extending theservice life of infrastructure can contribute to reducing resource consumption and demolition waste,
and as such a durable concrete which replaces virgin materials with industrial waste or recycled
products could provide an even more sustainable option for construction materials. Fly ash, as
discussed in the previous chapters, is one means for improving some durability parameters while
reducing CO2 emissions. Another means of improving durability is the utilization of fibers, which
may help reduce crack formation and propagation through their crack-bridging properties. This cangreatly contribute to reducing the deterioration of concrete structures due to fatigue or corrosion ofreinforcing steel. The combination of high-volume fly ash and polypropylene fiber has been
investigated in shotcrete applications, where it was found that satisfactory fresh and hardened
properties could be achieved (Malhotra et al., 1994). Fibers made from recycled plastics have also
been successfully applied in concrete (Moriwake et al., 2004). These applications demonstrate thedifferent possibilities which exist for utilizing alternative materials to develop sustainable concrete.
In this chapter, fly ash mortar reinforced with fibers was tested for strength and durability. Various
mix proportions were examined to determine the best combination at the mortar level before
examining the effect of recycled aggregates. The strength characteristics of concrete reinforced withrecycled fibers in both mortar and concrete was also examined and compared to polypropylene fibers.
Finally, the effect of these different mix proportions on the CO2 emissions was also calculated.

6.2 EXPERIMENTAL PROGRAM
6.2.1 Materials
Cement mortar was prepared using tap water (W), normal Portland cement (C), river sand (S), JIS
type-II fly ash (FA), normal (NG) and recycled (RG) coarse aggregates, polypropylene (PP) andrecycled (RF) fibers, and air entraining (AE) and super plasticizer (SP) admixtures.

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The properties of the normal Portland cement are given in Section 4.3.2.1, whereas the fly ash
properties are given in Table 6.1, with fly ash meeting the requirements given by JIS A 6201. The
properties of the sand, normal and low-grade recycled aggregates along with the preparation of therecycled aggregates are all outlined in Table 6.2. The polypropylene fibers are shown in Figure 6.2
along with the recycled fibers, which are manufactured from recycled polyethylene terephthalate(PET), and their properties are summarized in Table 6.3.
Table 6.1 Fly ash properties
Properties
Density
Specific surface area(g/cm3)(cm2/g)JIS A 6201
requirement
1.95<
2500<

Utilized
fly ash2.19
4040

Table 6.2 Properties of sand and coarse aggregates
Material
Sand
Normal aggregate
Recycled aggregate

SSD density(g/cm2)
2.62
2.71
2.43

Absorption
(%)
2.09
0.63
5.81

Fineness modulus
2.74
6.28
6.73

Maximum size
(mm)
4
20
20

Figure 6.1 Polypropylene (left) and recycled PET (right) fibers
Table 6.3 Fiber properties
Fiber type
Polypropylene (PP)
Recycled (RF)Dia. (mm)
0.75
0.70

Length (mm)3230

Density (g/cm3)
0.91
1.35

Strength (MPa)450

6.2.2 Mix proportions and fresh properties
Mortar and concrete mix proportions are given in Table 6.4. The term binder (B) is used to represent
all cementitious materials – in this case, fly ash and Portland cement. All mixes used a constant waterbinder ratio of 30% except the normal concrete mix, which used a water-binder ratio of 50%. To
investigate the effect of sand-binder ratio, mortar with a constant fly ash-binder ratio of 30% was usedwith PP fibers at 2% volume, and three sand-binder ratios of 60%, 80%, and 100% were chosen. For
investigating the effect of fiber type and fly ash-binder ratio, mortar mixtures containing either PP or
recycled fibers at 2% volume were mixed at a constant sand-binder ratio of 80% with three fly ashbinder ratios of 30%, 50%, and 70%. The effect of recycled aggregate was investigated by holding the
fly ash-binder ratio constant at 50% and varying the sand-aggregate ratio between 60% and 80%. The

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effect of varying fly ash with recycled aggregate was also examined by setting the sand-aggregate
ratio at 60% and varying the fly ash-binder ratio between 30%, 50%, and 70%.
The fresh properties of mortar and concrete are summarized in Table 6.5. The slump flow test was
conducted according to JIS A 1150; efflux time (flowability) was measured according to JSCE-F 5121999; and air content was measured according to JIS A 1116. AE and SP were varied as necessary tomaintain satisfactory fresh mortar properties.
Table 6.4 Mix proportions
Series
FA30-SB60-M
FA30-SB80-M
FA30-SB100-M
FA30-PP-M
FA50-PP-M
FA70-PP-M
FA30-RF-M
FA50-RF-M
FA70-RF-M
FA50-sa60-NG
FA50-sa60-RG
FA50-sa80-RG
FA30-sa60-RG
FA70-sa60-RG

W/B
30

30

(%)
S/B FA/B
60
30
80
100
30
50
70
80
30
50
70
50

30

s/a
-

-

60
80

80
30
70

60

W
298
274
254
274
266
259
274
266
259
226
226
253
231
221

C
695
639
593
639
443
259
639
443
259
377
377
422
539
221

(kg/m3)FAS
298 596274 731254 847274 731443 709604 691
274 731443 709604 691377 603377 603422 675
231 616516 589NG

RG(% vol.)
PP
RF

-

-

2.0

-

2.0

-

-

2.0

-

2.0

-

416
-

-

373
156
381
364

Table 6.5 Fresh properties
Series
FA30-SB60-M
FA30-SB80-M
FA30-SB100-M
FA30-PP-M
FA50-PP-M
FA70-PP-M
FA30-RF-M
FA50-RF-M
FA70-RF-M
FA50-sa60-NG
FA50-sa60-RG
FA50-sa80-RG
FA30-sa60-RG
FA70-sa60-RG

Slump flow
(mm)
495
495
585
600
360
650
595
415
660
600
570
615
600
600

Efflux time
(s)
6.5
5.7
5.7
4.7
10.7
4.4
5.5
6.7
4.6
5.3
5.4
4.6
5.3
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Air content
(%)
11.6
12.1
9.1
9.9
11.6
8.6
9.0
10.0
10.0
10.0
10.0

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6.2.3 Mixing & casting
Mixing for specimens investigating the effect of sand-binder ratio was performed in two batches in a
25 liter mixer. Water, cement, and fly ash were mixed first, then sand was added, and finally the fibers
were added gradually. Fiber mortar for investigating the effect of fiber type and fly ash-binder ratio
was mixed in a 75 liter mixer in one batch. First sand, then cement and fly ash were added and mixed,
then water was added. After that, the fibers were gradually added. Mixing for fiber concrete wassimilar to fiber mortar with the addition of coarse aggregate to sand at the beginning of mixing.
Cylinder (10Ø×20cm) and beam (10×10×40cm) specimens were cast for each concrete mix following
JSCE-F 552-1999. Cylinder specimens were cast in two layers and beam specimens in one layer, witha vibrator applied to the outside of the mold after each layer was placed. After casting, molded
specimens were covered in plastic wrap and cured in the molds for 24 hours, after which they were
removed from the molds and moved to water curing. Testing was conducted 28 days after casting.
6.2.4 Mechanical performance testing
Four mechanical properties were tested experimentally. Compressive strength was measured
according to JIS 1108, and flexural strength and flexural toughness were determined according toJSCe-G 552. Air permeability was measured following the procedure outlined in Section 4.3.2.4. Allfour properties were evaluated for mortar, whereas only compressive and flexural strength were
evaluated for concrete. Reported values are the average of three specimens.
6.2.5 Environmental performance assessment
Environmental impact was evaluated using the CO2 as outlined in Section 4.3.2.5. The mechanicalenvironmental efficiency was calculated using compressive and flexural strength along with the CO2
footprint for the concrete mixes.

6.3 RESULTS
6.3.1 Effect of sand-binder ratio for mortar
Compressive strength results are shown in Figure 6.2. It can be seen that increasing the sand-binder
ratio resulted in a marginal decrease in compressive strength; from 60% to 80% the compressive
strength decreased 1.4 MPa, and from 80% to 100% the decrease was 4 MPa. The effect of sandbinder ratio is more pronounced for flexural strength and toughness, as shown in Figure 6.3, whichshows that increasing the sand-binder ratio from 60% to 80% and from 80% to 100% resulted in
flexural strength increases of 1.91 MPa and 0.54 MPa, respectively; flexural toughness increased 1.35
MPa and 0.37 MPa, respectively.
From these results, a sand-binder ratio of 80% is considered optimal, as it produces the best
combination of compressive strength and flexural performance. A sand-binder ratio of 60% hasslightly higher compressive strength but much lower flexural strength and toughness values, whereasa sand-binder ratio of 100% produces the highest flexural performance but with a much lower
compressive strength value.

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Comp. strength (MPa)

60
50
40
30
20
10
0
60

80
Sand/binder (%)

100

Figure 6.2 Compressive strength for variable sand-binder ratio with mortar
10

Flex. toughness (MPa)Flex. strength (MPa)

10
8
6
4
2
0

8
6
4
2
0

60

80
Sand/binder (%)

100

60

80
Sand/binder (%)

100

Figure 6.3 Flexural strength (left) and flexural toughness (right)
for variable sand-binder ratio with mortar

6.3.2 Effect of fly ash-binder ratio for mortar and concreteCompressive strength results are shown in Figure 6.4, where it can be seen that the compressive
strength decreases constantly for increasing fly ash-binder ratio; from 30% to 50% the compressive
strength decreased by 12 MPa and 14.1 MPa for PP and recycled fibers, respectively, and from 50%
to 70% it decreased by 14.4 MPa and 15.1 MPa for PP and recycled fibers, respectively. The effect of
fly ash-binder ratio on flexural performance was different from that on compressive strength at higher
ratio values, as seen in Figure 6.5. An increase in fly ash-binder ratio from 30% to 50% was
accompanied by a 2.73 MPa and 1.41 MPa decrease in flexural strength for PP and recycled fiber
specimens, respectively, and by a 2.01 MPa and 0.98 MPa decrease in flexural toughness for PP andrecycled fiber specimens, respectively. However, increasing the fly ash-binder ratio from 50% to 70%
resulted in a much smaller decrease of 0.33 MPa and a small increase of 0.30 MPa in flexural strengthof PP and recycled fiber specimens, respectively, as well as small decreases of 0.17 MPa and 0.36
MPa in flexural toughness of PP and recycled fiber specimens, respectively.
For the air permeability results in Figure 6.6, the effect of higher fly ash-binder ratio is more
apparent, as the air permeability increased 10.74×10-12 m/s for PP and 6.84×10-12 m/s for recycled
fibers from 50% to 70%. In contrast, the change in air permeability was much lower when increasingfrom 30% to 50% - 0.07×10-12 m/s and 1.15×10-12 m/s decreases for PP and recycled fibers,
respectively.

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From these results, it can be seen that a higher volume of fly ash results in decreased strength anddurability characteristics. However, it is important to note that these tests have been performed after
28 days of curing. While the behavior of plain cement mortar at 28 days can be assumed to bereflective of its overall behavior, fly ash requires a much longer curing period in order to realize its
performance benefits. Since the fly ash reaction is delayed, the amount of cementitious reaction which
has occurred by 28 days will be far less for mortars containing higher volumes of fly ash. This effectcan be clearly seen in the air permeability results, as there is a sharp increase in air permeability whenincreasing the fly ash-binder ratio to 70%.

Comp. strength (MPa)

60
50
40
30
20
Recycled
PP

10
0
30

50
70
Fly ash/binder (%)

Figure 6.4 Compressive strength for variable fly ash-binder ratio with mortar
10

Flex. toughness (MPa)Flex. strength (MPa)

10
8
6
4
Recycled
PP

2
0
30

50
70
Fly ash/binder (%)

8
6
4
Recycled
PP

2
0
30

50
70
Fly ash/binder (%)

Figure 6.5 Flexural strength (left) and flexural toughness (right)
for variable fly ash-binder ratio with mortar

Air perm. (m/s)×10-12

15

Recycled
PP

12
9
6
3
0
30

50
70
Fly ash/binder (%)

Figure 6.6 Air permeability for variable fly ash-binder ratio with mortar

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The fly ash-binder ratio also has a large effect on the mechanical performance of recycled aggregate
concrete, as shown in Figures 6.7. Increasing the fly ash-binder ratio results in a consistent decreasein compressive and flexural strength, although the effect is more pronounced for compressive strength.
This reduction can be explained by the slower reaction speed of fly ash in concrete, which results inslower strength development.
1050

Flex. strength (MPa)Comp. strength (MPa)

60
40
30
20
10
0

8
6
4
2
0

30

30

50
70
Fly ash/binder (%)

50
70
Fly ash/binder (%)

Figure 6.7 Compressive strength (left) and flexural strength (right)
for variable fly ash-binder ratio with concrete with recycled aggregate

6.3.3 Effect of fiber type for mortar
Both PP and recycled fiber results are shown in Figures 6.4 through 6.6. From these figures, and as
discussed above, it can be seen that fiber type does not have a significant effect on any of the strength
properties measured. In the case of durability, it is difficult to interpret the air permeability results at
this time due to the delayed reaction of fly ash, but as air permeability typically evaluates the cement
paste, no significant difference is expected to occur.
6.3.4 Effect of sand-aggregate ratio and recycled aggregate for concreteCompressive and flexural strength results are shown in Figure 6.8 for variable aggregate volume. It
can be seen that increasing the volume of aggregates does not significantly affect the compressive or
flexural strength. At the 15% aggregate volume, replacing the recycled aggregates with normal
aggregates causes a slight increase in both compressive and flexural strength.
10

50
40
30
20
Recycled agg.
Normal agg.

1000Flex. strength (MPa)Comp. strength (MPa)

60

8
6
4
Recycled agg.
Normal agg.

2
0

6.4
15
Aggregate vol.(% conc.)

0

6.4
15
Aggregate vol.(% conc.)

Figure 6.8 Compressive strength (left) and flexural strength (right)
for variable aggregate volume with normal and recycled aggregate

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6.3.5 Environmental impact for mortar and concrete
The CO2 footprints for the mortar and concrete series are shown in Figures 6.9 and 6.10,
respectively. For the mortar, the total CO2 of the mixes decreases significantly when replacing cementwith fly ash, with the FA70-PP/RF-M mixes releasing just less than 40% of the FA30-SB60-M mix.
For the concrete mixes, a similar trend can be seen that the highest CO2 emissions are produced by theconcrete which contains only 30% fly ash replacement, whereas the lowest CO2 emissions areproduced by the concrete with 70% fly ash replacement. There is little difference between normal andrecycled aggregates as the mix proportions are similar and the aggregates themselves have similar
emissions values. Increasing the volume of aggregates produces a slight reduction in emissions. The
value of fly ash replacement for reducing CO2 is therefore clear, as a large savings in emissions can berealized by replacing the largest emitter of GHG with another material with a much smaller impact.
CO2 footprint (kg CO2/m3)

600
500
400
300
200
100
0

CO2 footprint (kg CO2/m3)

Figure 6.9 CO2 footprint for mortar
500
400
300
200
100
0

Figure 6.10 CO2 footprint for concrete

Environmental performance indicators considering the compressive and flexural strength and the CO2
footprint were calculated for the concrete series only and the results are shown in Figure 6.11 forvariable aggregate volume and Figure 6.12 for variable fly ash-binder ratio. For variable aggregate
volume and type, the slightly downward trends displayed by the mechanical behavior became slightly
upward trends when normalized by the environmental impact. This is due to the slight decrease inCO2 emissions as aggregate volume increased. Normal aggregate concrete displayed the highest
normalized environmental performance. For variable fly ash-binder ratio, the environmental
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indicators show that the low emissions of higher volume fly ash concretes can significantly change thetrend showed by the mechanical performance alone, particularly in the case of flexural strength.
0.15
0.12

Flex. MPa/kg CO2

Comp. MPa/kg CO2

0.03
0.02

0.09
0.06

0.01

Recycled agg.
Normal agg.

0.03
0
0

Recycled agg.
Normal agg.

0

6.4
15
Aggregate vol.(% conc.)

0

6.4
15
Aggregate vol.(% conc.)

Figure 6.11 Environmental performance indicators for compressive strength (left)
and flexural strength (right) by variable aggregate volume
0.15
Comp. MPa/kg CO2

0.03
Flex. MPa/kg CO2

0.12

0.02

0.09
0.06

0.01

0.03
0

0
30

50
70
Fly ash/binder (%)

30

50
70
Fly ash/binder (%)

Figure 6.12 Environmental performance indicators for compressive strength (left)
and flexural strength (right) by fly ash-binder ratio

6.4 SUMMARY
The following conclusions were made based on the results of this experimental investigation:
For the mortar series mixes, a sand-binder ratio of 80% provided the best balance between
compressive and flexural behavior. Decreasing the sand-binder ratio produced slightly higher
compressive strength but lower flexural strength, whereas increasing the sand-binder ratio reduced
compressive strength but slightly increased flexural strength. Increasing the fly ash-binder ratio from
30% to 70% resulted in lower strength and durability properties. While the compressive strength
decreased constantly, the flexural strength only slightly decreased when changing from 50% to 70%.
Conversely, air permeability underwent a huge increase when moving from 50% to 70%. The
decreased performance of higher-volume fly ash mortars may be attributed to the slow reaction speedof fly ash, which requires longer curing before full performance can be achieved. There was noobserved significant difference in the performance between polypropylene and recycled fiberreinforced mortars.

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When considering the environmental impact of the mortar mixes, Portland cement is the primarycontributor of CO2 emissions in the mortar mixes. While replacing cement with fly ash at a fly ashbinder ratio up to 70% does not decrease the fraction contribution of cement, it can help reduce total
CO2 emission of the mortar mixture by over 60%. At this time it is difficult to fully determine thecontribution of recycled materials such as recycled fibers to CO2 emissions or other environmental
measurements. However, the usage of such materials has an inherent positive benefit to society, so
appropriate methods for evaluating this benefit need to be developed.
For the concrete mixes, environmental performance indicators were used to normalize the mechanicalperformance by considering the environmental impact of concrete materials. It was found that these
indicators could reverse the trends shown by the mechanical performance alone, particularly in thecase of high volume fly ash concretes, which develop strength more slowly than normal concrete but
have significantly lower CO2 emissions. The concrete with the highest environmental indicator forcompressive strength had a fly ash-binder ratio of 50% and normal aggregates. The advantage ofutilizing recycled aggregates is difficult to see in this case since recycled aggregates have the same
CO2 emissions as normal aggregates, but generally lower performance. The concrete with the highest
environmental indicator for flexural strength had a fly ash-binder ratio of 70% and 100% replacementof normal aggregates with recycled aggregates. This value was driven by the extremely low CO2
emissions achieved by replacing high volume of Portland cement with fly ash.

REFERENCES
Malhotra, V.M., Carette, G.G., and Bilodeau, A. (1994). Mechanical properties and durability of polypropylene fiber
reinforced high-volume fly ash concrete for shotcrete applications. ACI Materials Journal, 91 (5), 478-486.
Moriwake, A., Habuchi, T., Kushida, M. (2004). Short fiber for concrete reinforcement produced from recycled PET bottles.
Cement Concrete, 694, 20-25.

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