NIST Technical Note 1906 

Minimizing Paste Content in Concrete 

Using Limestone Powders –

Demonstration Mixtures 

Dale P. Bentz 

Scott Z. Jones 

Didier Lootens 

This publication is available free of charge from:

http://dx.doi.org/10.6028/NIST.TN.1906

NIST Technical Note 1906 

Minimizing Paste Content in Concrete 

Using Limestone Powders –

Demonstration Mixtures 

Dale P. Bentz 

Scott Z. Jones

Materials and Structural Systems Division 

Engineering Laboratory

Didier Lootens 

Sika Technology AG - Central Research

This publication is available free of charge from:

http://dx.doi.org/10.6028/NIST.TN.1906

January 2016

U.S. Department of Commerce 

Penny Pritzker, Secretary

National Institute of Standards and Technology

Willie May, Under Secretary of Commerce for Standards and Technology and Director
Certain commercial entities, equipment, or materials may be identified in this 

document in order to describe an experimental procedure or concept adequately. 

Such identification is not intended to imply recommendation or endorsement by the 

National Institute of Standards and Technology, nor is it intended to imply that the 

entities, materials, or equipment are necessarily the best available for the purpose.

National Institute of Standards and Technology Technical Note 1906

Natl. Inst. Stand. Technol. Tech. Note 1906, 38 pages (January 2016) 

CODEN: NTNOEF 

This publication is available free of charge from: 

http://dx.doi.org/10.6028/NIST.TN.1906
iii

Abstract 

In recent years, there has been great interest in reducing the cement content of concrete, 

due to the high energy and carbon dioxide footprints of cement production. There are numerous 

(waste) materials that can be substituted for cement in the concrete mixture proportions, including 

fly ash, slag, silica fume, metakaolin, waste glass, etc. However, a more abundant material 

substitute would be limestone powder, created from the same limestone that is currently heavily 

employed in cement production as the primary source of calcium oxide. This technical note 

presents an approach to replacing not only cement powder, but effectively cement paste consisting 

of the cement and water, with appropriately sized limestone powder(s). Such an approach 

effectively extends the conventional utilization of centimeter-sized coarse aggregates (rocks) and 

millimeter-sized fine aggregates (sand) that occupy between 65 % and 75 % of the volume of a 

concrete structure to include micro-aggregates ranging between about 1 μm and 100 μm in size. 

Here, to demonstrate the feasibility of this approach, demonstration mixtures of pastes, mortars, 

and concretes are each formulated with limestone powder replacement for a significant portion of 

their cement paste component, achieving cement reductions of up to 28 % in concrete, for example. 

For these mixture modifications, the water-to-cement mass ratio (w/c) is maintained at or above 

0.4 to provide sufficient water to react with all of the cement, so that none of this most costly 

component of cement-based materials goes to waste. Meanwhile, the water-to-solids ratio (w/s) is 

reduced to a value in the range of 0.22 to 0.40 in order to maximize the limestone powder 

replacement level, while still providing sufficient flow and rheology, by using reasonable dosages 

of high range water reducing admixtures. The fresh, early age, and long term performance 

properties of these high volume limestone powder (HVLP) mixtures are contrasted with a w/c=0.4 

ordinary portland cement (OPC) paste or mortar, or a w/c=0.5 OPC concrete reference, 

respectively. In general, the properties and performance of these more sustainable mixtures are 

similar or even superior to those of the corresponding reference mixture, suggesting that these new 

paradigm HVLP concretes could be readily substituted for existing conventional OPC mixtures. 

The reduced shrinkage (autogenous and drying) of the mortars with limestone powder 

replacement, due to their reduced paste content, is highlighted because of its likelihood to reduce 

concrete cracking. However, beyond measurements of electrical resistivity, this study has not 

specifically focused on durability issues and additional research on this topic is recommended as 

these new mixtures are reduced to (field) practice. 

Keywords: Concrete; high range water reducing admixture; high volume limestone powder; 

mortar; paste content; sustainability. 
iv
v

Table of Contents 

Abstract ........................................................................................................................................................ iii

List of Tables ................................................................................................................................................ vi

List of Figures.............................................................................................................................................. vii

Introduction .................................................................................................................................................. 1

Materials and Methods ................................................................................................................................. 3

Materials ................................................................................................................................................... 3

Paste Studies ............................................................................................................................................. 3

Mortar Studies .......................................................................................................................................... 4

Concrete Mixtures .................................................................................................................................... 6

Results ........................................................................................................................................................... 9

Paste Studies ............................................................................................................................................. 9

PSDs and Limestone Blends .................................................................................................................. 9

Binary Blend Optimization ..................................................................................................................11

Mortars ...................................................................................................................................................15

Fresh Properties ..................................................................................................................................15

Calorimetry .........................................................................................................................................17

Compressive Strength .........................................................................................................................18

Autogenous and Drying Shrinkage ......................................................................................................20

Concretes ................................................................................................................................................22

Fresh Properties ..................................................................................................................................22

Setting Times .......................................................................................................................................23

Early-Age Properties ...........................................................................................................................23

Compressive Strength and Drying Shrinkage ......................................................................................27

Relating Strength to Measurements of UPV, Heat Release, and Electrical Resistance ......................27

Summary .....................................................................................................................................................33

Acknowledgements .....................................................................................................................................34

References ..................................................................................................................................................35
vi 

List of Tables 

Table 1. Mortar mixture proportions............................................................................................................. 5

Table 2. Concrete mixture proportions (kg/m3 or L/m3 for HRWRA) ......................................................... 7

Table 3. Properties of mortars investigated in the present study ................................................................16

Table 4. Fresh concrete properties (see Materials and Methods for typical uncertainties).........................23

Table 5. Measured compressive strengths and drying shrinkage for the three concrete mixtures..............28

Table 6. Capillary porosity estimations for the paste components of the three concrete mixtures.............32
vii 

List of Figures 

Figure 1. Two-dimensional slice from a three-dimensional model of spherical cement particles in water. 

Cement particles are grey and shades of blue indicate distances of water from the nearest cement particle 

surface, with lighter blues indicating a greater distance [2].......................................................................... 1

Figure 2. Measured particle size distributions for the cement and the six limestone powders. Each shown 

result is the average of six individual measurements and the error bars (one standard deviation) would fall 

within the size of the shown symbols. .......................................................................................................... 4

Figure 3. Cumulative particle size distributions for limestone powder, cement, sand, and coarse aggregate 

used in the three concrete mixtures............................................................................................................... 7

Figure 4. Cumulative PSD for original cement in comparison to “ideal” gradation [18] for optimum 

packing fraction. The measured result is the average of six individual measurements and the error bars 

(one standard deviation) would fall within the size of the shown symbols. ...............................................10

Figure 5. Computed PSDs for the cement-limestone blends. Numbers in parentheses indicates the 

measured packing fraction for the produced cement paste using each powder. .........................................10

Figure 6. Heat flow (left) and cumulative heat release (right) for the cement-limestone blend pastes. The 

25:50:25 mixtures all employed the 16 μm limestone as the coarse limestone component. Numbers in 

parentheses in legends indicate measured packing fraction for each mixture. ...........................................11

Figure 7. Computed particle size distributions for ternary blends of fine limestone:cement:coarse 

limestone with the indicated volumetric proportions. Numbers in parentheses in legend indicate measured 

packing fraction for each mixture. ..............................................................................................................12

Figure 8. Measured packing fraction and ITC characteristics for pastes prepared with the ternary blends of 

fine limestone:cement:coarse limestone. Each mixture contains a 50:50 volumetric mixture of cement and 

limestone powder with the fine:coarse limestone proportions being 10:90, 30:70, 50:50, 70:30, and 90:10, 

as indicated by the fine limestone value on the lower x-axis......................................................................12

Figure 9. Heat flow (left) and cumulative heat release (right) for the cement-limestone blend pastes in 

phase two of the paste study. Ratios in legend indicate fine limestone:cement: coarse limestone 

proportions on a volume basis. ...................................................................................................................13

Figure 10. Shear stress vs. shear rate for parallel (serrated) plate rheological measurements for the ternary 

blend cement pastes. Typical relative error for viscosity is about 7 % [21]. ..............................................13

Figure 11. Color-coded SEM/X-ray image of the 5:50:45 fine limestone:cement:coarse limestone powder 

blend. Image shown is approximately 439 μm by 586 μm with the following color assignments: cyan –

C3S, orange – C2S, grey – C3A, red – C4AF, magenta – periclase, yellow – calcium sulfate, blue – calcite, 

and tan – dolomite.......................................................................................................................................14

Figure 12. Heat flow normalized per mass of cement (left) and per volume of initial water in the specimen 

(right) vs. time for the six mortars. .............................................................................................................17

Figure 13. Cumulative heat release vs. time for the six mortar specimens.................................................18

Figure 14. Semi-adiabatic temperature vs. time for mortars investigated in the present study. .................18

Figure 15. Compressive strength vs. cumulative heat release for the six mortars measured at 1 d and 7 d. 

Coefficients of variation for strength measurements are given in Table 3. Dotted line indicates a best fit 

relationship determined for a variety of mortars in a previous study [19]..................................................19

Figure 16. Autogenous deformation measured for the six mortars during the course of 28 d. Error bars 

indicate standard deviation for either two or three replicate specimens. ....................................................20

Figure 17. Cumulative particle size distributions for the three concrete mixtures......................................22
viii 

Figure 18. Measured setting times for mortars sieved from the three concrete mixtures, via both Vicat 

needle and penetrometer. Lower and upper dotted lines indicate resistances corresponding to initial and 

final setting times, respectively, via the penetrometer (ASTM C403), while the dashed line indicates 

initial setting criteria for the Vicat needle (ASTM C191). .........................................................................24

Figure 19. Measured electrical resistance (fresh concrete) for the three concrete mixtures. Inset plot shows 

measured (expressed) pore solution resistance for the limestone 2 concrete mixture. ...............................24

Figure 20. Measured ITC heat flow (sieved mortar) for the three concrete mixtures.................................25

Figure 21. Chemical (ICP) analysis for pore solutions expressed from the limestone 2 concrete mixture. 

Error bars indicate one standard deviation for three replicate measurements at each time. .......................26

Figure 22. Cumulative heat release from ITC measurements on mortars vs. time for the concrete mixtures, 

normalized by either mass of cement (left) or mass of water (right). .........................................................26

Figure 23. Estimated chemical shrinkage vs. time for the three concrete mixtures. Error bars indicate 

standard deviation for six replicate specimens. ..........................................................................................27

Figure 24. Measured drying shrinkage vs. mass loss for the three concrete mixtures. Error bars indicate 

one standard deviation for measurements of four replicate specimens (only two for the limestone 2 

concrete mixture). .......................................................................................................................................28

Figure 25. Cylinder compressive strength vs. measured (left) and normalized (right) UPV for the three 

concrete mixtures at ages of 1 d, 3 d, 7 d, 14 d, and 28 d (data points from left to right). Error bars 

indicate one standard deviation for measurements on three cylinders at each age for each mixture, except 

for the limestone 2 concrete mixture at the ages of 1 d and 3 d where five cylinders were tested and 7 d 

where four cylinders were tested. ...............................................................................................................29

Figure 26. Cylinder compressive strength vs. measured cumulative heat release (from sieved mortar) for 

the three concrete mixtures at ages of 1 d, 3 d, and 7 d (data points from left to right). Dashed and thin 

solid lines indicate previously established relationships for limestone and gravel aggregate concretes, 

respectively [16,19].....................................................................................................................................30

Figure 27. Photographs of specimen (twin) surfaces for OPC (left) and limestone 2 (right) concrete 

mixtures that were broken using a split cylinder test. Tube-shaped hole at top corner of each specimen 

corresponds to location of a plastic tube where a thermocouple was inserted. Dark grey aggregates in each 

case indicate fractured aggregates, as can be verified by matching them on the opposite side of the twin 

specimen. Each cylinder half is nominally 100 mm by 200 mm. ...............................................................31

Figure 28. Comparison of uniaxial (left) resistivity measurements using two different measurement 

devices and uniaxial vs. surface resistivity (right) for the three concrete mixtures at ages of 1 d, 3 d, 7 d, 

14 d, and 28 d (data points from left to right). Error bars indicate one standard deviation for measurements 

performed at each age for each mixture. The dashed line indicates a one-to-one relationship in each plot.

....................................................................................................................................................................31

Figure 29. Measured compressive strength vs. uniaxial (left, measured at 10 kHz)) and surface (right) 

electrical resistivity for the three concrete mixtures at ages of 1 d, 3 d, 7 d, 14 d, and 28 d (data points 

from left to right). Error bars indicate one standard deviation for measurements on three cylinders at each 

age for each mixture, except for the limestone 2 concrete mixture at the ages of 1 d and 3 d where five 

cylinders were tested and 7 d where four cylinders were tested. Fitted line on each plot is for the OPC 

mixture only................................................................................................................................................32
1

Introduction 

Over the years, extensive effort and discussion has been focused on optimal aggregate 

gradations for concrete [1], such as the 0.45 power law and the original Fuller curve (0.5 power 

law). One focus of these efforts is on increasing the volume fraction of (fine and coarse) aggregates 

in concrete from 60 % upwards to about 75 %, recognizing that a reduced paste content generally 

corresponds to reduced shrinkage and improved transport properties, since the aggregates are 

generally non-shrinking and relatively impermeable. Typically, in a 75 % aggregate volume 

fraction concrete, the remaining 25 % is occupied by cement paste and entrained air. For a watercement by mass ratio, w/c=0.4, cement paste (such as exemplified in Figure 1 [2]), the volume 

fraction of the paste occupied by the water is about 56 %. If one had continued to apply the packing 

considerations being implemented at the aggregate level, a much lower water volume fraction 

within the paste (perhaps moving towards 35 % of the paste volume, equivalent to a w/c of about 

0.17) would have been expected. 

Figure 1. Two-dimensional slice from a three-dimensional model of spherical cement particles in 

water. Cement particles are grey and shades of blue indicate distances of water from the nearest 

cement particle surface, with lighter blues indicating a greater distance [2]. 

While it is well known that reducing the water content (and w/c concurrently) will increase 

strengths (e.g., Abram’s law [3]) and reduce transport rates, it is only with the advent of water 

reducers and subsequent development of high-range water reducing admixtures (HRWRA) that 

the production of low w/c (or water-to-cementitious materials, w/cm) concretes have become 
2

commonplace. However, below a w/c of about 0.42 for sealed conditions (0.36 for saturated 

curing), there is insufficient space (or water in the case of sealed curing) for all of the cement to 

hydrate and a portion remains unreacted as a rather expensive filler material [4]. While it has been 

previously suggested to replace this unreacted portion of the cement with a less expensive and 

greener material such as limestone powder [4,5], an alternative and perhaps more appropriate view 

is to consider the replacement of both cement and water (i.e., cement paste) with the limestone 

powder, producing a high volume limestone powder (HVLP) mixture. Such an approach has the 

potential to substantially reduce the carbon and energy footprints of the concrete and can also 

conserve a significant volume of water in drought-stricken regions of the world.

The recent results of Li and Kwan have quantitatively demonstrated the utility of these 

limestone fines concretes [6]. Here, as a further proof of this concept, results from demonstration 

mixtures for pastes, mortars, and concretes will be presented, with an ordinary portland cement 

(OPC) paste/mortar/concrete with a w/c=0.4 (0.5 for concrete) serving as a reference. While the 

limestone powder mixtures presented in this study are similar to some of the current mixtures being 

employed for self-consolidating concrete (SCC) applications (particularly in Europe), it is hoped 

that these results will spur the construction sector to consider such mixtures for a wider variety of 

applications, leading to significant reductions in the consumption of cement and water by the 

concrete industry, without reducing concrete production or sacrificing performance. The use of the 

limestone powder as the filler is particularly attractive in that the limestone particle surfaces serve 

as nucleation and growth sites for the products of cement hydration, accelerating and amplifying 

the early-age hydration reactions [7]. Additionally, the fine limestone particles, while much less 

reactive than cement, do react slightly within the cementitious system to form carboaluminate 

hydration products, including calcium hemicarboaluminate and calcium monocarboaluminate, 

while stabilizing the ettringite that is formed at early ages. Thus, the limestone particles are not 

“inert”, but instead become an integral part and stabilizer of the percolated network of particles 

and hydration products that lead to setting and strength development in cement-based 

systems [7,8].
3

Materials and Methods 

Materials

The portland cement used in the present study was an ASTM C150 Type I/II portland 

cement [9] with a 3.7 % limestone (91.0 % CaCO3) addition. According to the mill test certificate 

reports provided by the manufacturer for various batches employed in this study, it has a Blaine 

fineness of 374 m2/kg to 384 m2/kg and an adjusted potential Bogue composition of 53.5 % to 

58.9 % C3S

1

, 11.6 % to 16.2 % C2S, 6.8 % to 7.4 % C3A, and 9.5 % to 10.3 % C4AF by mass. The 

density of the cement measured using helium pycnometry at NIST was 3164 kg/m3 ± 2 kg/m3. A 

series of limestone (> 95 % CaCO3) powders obtained from a single manufacturer with median 

diameters of 1.6 μm, 2.2 μm, 4 μm, and 16 μm (as measured at NIST, see Figure 2) were employed 

in the initial paste studies. Additionally, two limestone powders with broader particle size 

distributions (PSDs) and median particle sizes of 6.7 μm and 19.2 μm, obtained from two other

manufacturers, were employed in the later mortar and concrete studies. The 6.7 μm limestone 

powder was obtained from a local limestone crushing operation as the dust of fracture passing a 

#100 sieve (150 μm opening). Based on thermogravimetric analysis (TGA), its calcium carbonate 

content was estimated as 98.1 % ± 0.6 % (standard deviation for three replicates), assuming that 

only CaCO3 is present in the dust and ignoring any MgCO3 that may be present.

The measured BET (Brunauer-Emmett-Teller) surface area of the cement using nitrogen 

gas as the sorbent is 1.39 m2/g, while the series of four limestone powders from the same 

manufacturer have surface areas of 9.93 m2/g, 7.06 m2/g, 2.42 m2/g, and 0.83 m2/g, respectively, 

as measured previously at NIST [10]. For the 2.2 μm median diameter powder, three replicate 

measurements indicated a standard deviation of 0.14 m2/g in surface area. The measured surfaces 

areas for the 6.7 μm and 19.2 μm limestone powders were 1.54 m2/g and 0.696 m2/g, respectively, 

indicating a good ranking of limestone powder surface area according to median particle size. The 

density of the initial limestone powders was reported by their manufacturer to be 2710 kg/m3,

while those of the broad distribution 6.7 μm and 19.2 μm limestone powders were measured at 

NIST as 2740 kg/m3 ± 10 kg/m3and 2760 kg/m3 ± 10 kg/m3, respectively. The measured PSDs of 

each of the seven powders (cement and six limestones) as obtained using laser diffraction [11] are 

provided in Figure 2.

Various polycarboxylate-based commercial HRWRA admixtures obtained from three 

different manufacturers were used to provide adequate flow/slump for the pastes, mortars, and 

concretes prepared with the cement/limestone powders blend. The w/c=0.4 control OPC paste and 

mortar specimens were prepared without any chemical admixtures, while the w/c=0.5 OPC 

concrete contained a dosage of 1.08 L/m3of one of the HRWRA.

Paste Studies

Initial studies focused on pastes in order to investigate the best combination of (two) 

limestones to utilize in subsequent mixtures, as well as their proportions. To produce a 

homogeneous and reproducible paste, samples were prepared using a (kitchen) mixer in a two-

 

1

In conventional cement chemistry notation, C=CaO, S=SiO2, A=Al2O3, and F=Fe2O3.
4

Figure 2. Measured particle size distributions for the cement and the six limestone powders. 

Each shown result is the average of six individual measurements and the error bars (one 

standard deviation) would fall within the size of the shown symbols.

stage mixing procedure in which approximately half of the water (with admixture HRWRA A) 

was added to the powder blend and mixed for 30 s on the lowest speed of the mixer. Next, the 

remainder of the liquid was added and mixing continued for another 30 s on the lowest speed. 

Following a scraping of the mixing bowl, mixing concluded with 60 s of mixing on the 2nd lowest 

speed of the mixer. The total preparation time of a paste was thus on the order of 3 min. 

Pastes were characterized by their fresh temperature, rheology as measured using a parallel 

(serrated) plate rotational rheometer, isothermal calorimetry (ITC), and packing fraction via 

centrifuging of about 50 g of the prepared paste at 800 g for 3 min at 25 °C [12]. For the rheology 

measurements, the plates had a diameter of 35 mm, with a gap of 0.4 mm. A sweep in shear rate 

was performed on each mixture, with the resultant shear stress being recorded. For ITC, the 

average absolute difference between replicate specimens was previously measured to be 

2.4 x 10-5 W/g (cement), for measurements conducted between 1 h and 7 d after mixing [13].

Mortar Studies

Following the paste studies, six mortar mixtures were examined; their mixture proportions 

are provided in Table 1. Each mortar was prepared using a blend of four sands to achieve a 55 % 

sand volume fraction (neglecting air entrapped in the mixture). For the lower water-to-solids mass 

ratio (w/s=0.25) mortars, cement/limestone powder mixtures were prepared both with a 10:90 

blended mixture of the fine (2.2 μm) and coarse (16 μm) limestone powders and with just the 

coarser limestone. For the five mortars using a cement-limestone blend, all of the powder 

components were pre-mixed for 30 min using a three-dimensional laboratory mixer that 

simultaneously rolls and tumbles the (mixing) container. The w/c=0.4 OPC reference mortar was 

prepared without any chemical admixtures and mixed according to the documented ASTM 

Practice C305 procedures for mortars [9]. Meanwhile, a 5 mL/kg powder dosage of the liquid 

HRWRA was used in the w/s=0.25 and w/s=0.28 cement/limestone powder mortars, with an 
5

Table 1. Mortar mixture proportions

w/c=0.4 

control

w/s=0.25 

LS blend

w/s=0.25 

16 μm LS

w/s=0.28 

LS blend

w/s=0.30 

6.7 μm LS

w/s=0.30 

19.2 μm LS

Cement 1250 g 956.3 g 956.3 g 775.7 g 829.9 g 828.7 g

2.2 μm limestone --- 57.0 g --- 66.5 g --- ---

16 μm limestone --- 512.9 g 569.9 g 598.7 g --- ---

6.7 μm limestone --- --- --- --- 575.7 g ---

19.2 μm limestone --- --- --- --- --- 579.1 g

Water 500 g 381.6 g 381.6 g 403.4 g 421.7 g 422.3 g

F95 fine sand 712.5 g 713.2 g 713.2 g 713.3 g 713.3 g 713.3 g

C778 graded sand 541.5 g 542.0 g 542.0 g 542.1 g 542.1 g 542.1 g

C778 20-30 sand 541.5 g 542.0 g 542.0 g 542.1 g 542.1 g 542.1 g

S16 coarse sand 1054.5 g 1055.5 g 1055.5 g 1055.7 g 1055.6 g 1055.6 g

Polycarboxylatebased 

HRWRA 

(mL/kg powder)

--- 5.0 mL/kg

HRWRA B

5.0 mL/kg

HRWRA B

5.0 mL/kg

HRWRA B

3.17 mL/kg

HRWRA D

with 0.8 mL/kg

HRWRA E

3.56 mL/kg

HRWRA C

w/c 0.40 0.40 0.40 0.52 0.51 0.51

Cement reduction --- 23.5 % 23.5 % 37.9 % 33.6 % 33.7 %

Water reduction --- 23.5 % 23.5 % 19.3 % 15.7 % 15.5 %

Cement paste

volume reduction

--- 23.5 % 23.5 % 27.5 % 23.5 % 23.5 %
6

assumed solids content of 50 % for the HRWRA. For the two w/s=0.30 cement/limestone powder 

mortars, different HRWRAs were employed at the dosages indicated in Table 1. For these latter 

five mortars, about 2/3rd of the mixing water was added to the mixing bowl and blended with all 

of the powder for 30 s on low speed, prior to adding the remainder of the mixing water and all of 

the HRWRA dosage. This second water addition was followed by another 30 s of mixing on low 

speed. Next, the sand was added during 30 s of low speed mixing, followed by 1 min of medium 

speed mixing. Following a 1 min rest, the preparation concluded with 1 min of medium speed 

mixing. In an attempt to control the temperature of the prepared mortars, all materials were 

conditioned overnight and mixing was conducted inside an environmental chamber maintained 

at 21 °C ± 1°C, except for the w/s=0.28 mortar that was prepared under laboratory conditions 

(nominally 23 °C ± 2 °C).

The following measurements [9] were conducted on the prepared mortars: unit (cup) 

weight and air content (ASTM C185-08), temperature, flow table (ASTM C1437-13), Vicat needle 

penetration measurements (following ASTM C191-13), ITC (ASTM C1702-15) to 7 d, semiadiabatic calorimetry to 3 d, compressive strength (cubes, per ASTM C109/C109M-13) at 1 d, 7 d, 

28 d, and 91 d, autogenous shrinkage (ASTM C1698-09) to 28 d, and drying shrinkage 

(ASTM C596-09) to 28 d. For the semi-adiabatic calorimetry, replicate specimens have indicated 

a standard deviation of 1.4 °C in the maximum specimen temperature achieved during a 3 d 

test [14].

Concrete Mixtures

In the final stage of the current study, concrete mixtures were prepared with a batch size 

of 60 L in a rotating pan mixer with bottom discharge. Mixture proportions of the three concrete 

mixtures are provided in Table 2. As indicated in the table, the (volume) fractions of the fine and 

coarse aggregates were held constant in all mixtures with a total aggregate volume fraction 

of 70 %. The densities of the fine and coarse aggregates taken from their manufacturers’ 

specifications were 2610 kg/m3and 2810 kg/m3, respectively. The measured absorptions of the 

fine (silica concrete sand) and coarse (dolomitic limestone) aggregates were 1.1 % ± 0.1 % and 

0.40 % ± 0.05 % by dry mass, respectively, and both were added to the concrete in an oven dry 

condition, with the mix water being adjusted (increased) accordingly. The particle size 

distributions of all dry materials used in the concrete mixtures are provided in Figure 3. A single 

HRWRA (HRWRA C) was utilized in all of the concrete mixtures (based on its previously 

observed minimal retardation of cement hydration).

The fresh concrete mixtures were characterized by measurements [15] of fresh concrete 

temperature (ASTM C1064, ± 0.1 °C), unit weight (ASTM C138, ± 10 kg/m3) and calculated air 

content, and slump (ASTM C143, ± 10 mm). Concrete was sieved through a number 8 sieve

(2.38 mm opening) to obtain mortar for ITC (about 7.5 g of mortar in a sealed vial) and setting 

measurements using both a Vicat needle (ASTM C191 protocol) and a mortar penetrometer 

(ASTM C403, ± 3.5 min for initial set and ± 4.4 min for final set). For each mixture, 

twenty 101.6 mm (4”) diameter by 203.2 mm (8”) length cylinders were cast, along with 

four 50.8 mm by 50.8 mm by 286 mm drying shrinkage prisms. Capped cylinders were cured in 

an environmental chamber maintained at 23 °C ± 1 °C (>99 % RH), while the drying prisms were 

cured in the same chamber, but double bagged in plastic. Following demolding after 1 d, cylinders 
7

Figure 3. Cumulative particle size distributions for limestone powder, cement, sand, and coarse 

aggregate used in the three concrete mixtures.

Table 2. Concrete mixture proportions (kg/m3or L/m3for HRWRA)

OPC 6.7 μm limestone - 1 6.7 μm limestone - 2

Cement 343 254.9 248.1

Limestone powder --- 127.3 178.2

Water 171.45 152.9 136.5

Fine aggregate 822 822 822

Coarse aggregate 1082 1082 1082

HRWRA C (L/m3) 1.08 2.5 2.5

w/c 0.50 0.60 0.55

w/s 0.50 0.40 0.32

w/(c+k∙LP)

k=0.25A

0.50 0.533 0.466

Cement reduction --- 25.7 % 27.7 %

Cement paste volume 

reduction

--- 16.5 % 23.2 %

Ak indicates a cementing efficiency factor for the limestone, taken to be 0.25 in this study (e.g., one unit of limestone 

powder is assumed to be equivalent to or able to replace 0.25 units of cement).

were stored in water saturated with lime (calcium hydroxide) at 23 °C ± 1 °C until their age of 

testing, while the drying prisms were immersed for 2 d in the limewater and then exposed to drying 

in an environmental chamber maintained at 23 °C ± 2 °C and 50 % ± 2 % RH. Cylinders were 

broken in triplicate at the ages of 1 d, 3 d, 7 d, 14 d, and 28 d. At each of these testing ages, prior 

to the compression testing, the cylinders to be broken, along with any remaining cylinders, were 

characterized by measurements of their mass, surface electrical resistance (one device), uniaxial 

(bulk) electrical resistance (two separate devices, one employing a square wave with a frequency 

of 40 Hz and the other a sine wave with a frequency of 10 kHz), and surface ultrasonic pulse 

velocity (UPV). Cylinder mass measurements under saturated curing were subsequently used to 

estimate the chemical shrinkage occurring within the paste portion of each concrete mixture. The 

remaining two of the freshly cast cylinders were utilized in making continuous measurements of 
8

electrical resistance using two different commercial devices (one modular with remote data 

acquisition via Bluetooth, but at a single fixed frequency of 10 kHz, the other with frequency 

varying from 10 Hz to 10 kHz). Finally, pore solutions were expressed from small cylindrical 

specimens of the hardened (sieved) mortar at various ages and their conductivity determined using 

one of the electrical resistance devices; for select specimens, the composition of their pore solution

was also analyzed using inductively coupled plasma atomic emission spectroscopy (ICP-AES). 

 

 
9

Results 

Paste Studies

PSDs and Limestone Blends

The first question addressed in the paste portion of the current study was which 

combination of available limestones to blend with the cement. Both the cost and the performance 

of the limestone depend on its fineness. The cost of the limestone powder is highly variable, with 

the additional grinding (energy) required to produce the finer powders resulting in increased 

consumer prices. For example, the 1.6 μm limestone might cost 50 % more than the comparable 

16 μm powder. However, the increased surface area provided by the finer powders provides 

additional nucleation sites for cement hydration products, reducing setting times, increasing earlyage strengths, and reducing transport coefficients [7,10,16,17]. Improving the overall packing 

efficiency of the cement/limestone powder mixture could also result in a reduced water demand 

that would further contribute to strength increases.

Based on the PSDs in Figure 2, it was envisioned to broaden the initial cement PSD on 

both its fine and coarse ends by adding a blend of two different limestone powders, with the goal 

of increasing the maximum packing fraction of the powder component of the paste. According to 

Brouwers [18], for a continuous PSD, the maximum packing fraction is obtained when the 

cumulative PSD falls on a straight line when plotted using a logarithmic x-axis. As shown in 

Figure 4, the original cement appears to be far from achieving this optimal (packing) distribution, 

when considering 0.75 μm and 70 μm as the lower and upper endpoints for the target 

continuous PSD. Indeed, centrifuge measurements indicated a packing fraction of only 52.6 % for 

this cement powder, when initially prepared as a w/c=0.4 paste.

Four different blends of limestone(s) and cement were considered in the first series of 

pastes, with a w/c=0.4 ordinary cement paste considered as a reference. For these mixtures, a 50:50 

mixture by mass of cement and limestone was arbitrarily employed, and the water-to-solids mass 

ratio (w/s) was fixed at 0.22 (with HRWRA)2, with the exception of a binary blend of the 4 μm 

limestone powder and cement where the w/s was set at 0.3 and no HRWRA was used. Thus, this 

last mixture directly investigated the capability of limestone powder to enhance rheology and 

permit a water reduction without the use of HRWRA. For all of the ternary powder mixtures, a 

fixed 25:50:25 proportion of fine limestone (FLS):cement:coarse limestone (CLS) was employed. 

With a 50 % mass replacement of cement by limestone powder and a w/s=0.22, a reduction in 

cement content of about 36 % would be achieved. All of the w/s=0.22 pastes were prepared with 

a 7.5 mL/kg powder dosage of the polycarboxylate-based HRWRA A. 

For these mixtures, as shown by the computed cumulative PSDs in Figure 5, the 2.2 μm 

limestone blended with the 16 μm limestone in equal proportions lies closest to the “ideal grading” 

line and also yielded the highest measured packing density (63.5 %), consistent with the theoretical 

 

2 While maintaining w/c=0.4 for a 50:50 mixture of limestone and cement would infer a w/s=0.2, here w/s was adjusted 

upward slightly to 0.22 with the anticipation that the limestone powder will react slightly and contribute to strength 

development [7].
10

Figure 4. Cumulative PSD for original cement in comparison to “ideal” gradation [18] for 

optimum packing fraction. The measured result is the average of six individual measurements 

and the error bars (one standard deviation) would fall within the size of the shown symbols.

Figure 5. Computed PSDs for the cement-limestone blends. Numbers in parentheses indicates 

the measured packing fraction for the produced cement paste using each powder.

derivations of Brouwers [18]. Additionally, as shown in the ITC results in Figure 6 (normalized 

per unit volume of water in each paste mixture), the 1.6 μm and 2.2 μm limestone powders produce 

similar performance in terms of both the timing of the early-age calorimetry peaks and the later 

age cumulative heat release, the latter correlating to strength development [19]. The 25:50:25 blend 

prepared with the 4 μm fine and the 16 μm coarse limestone powders was not able to offset the 

retardation produced by the HRWRA (Figure 6, left), resulting in reduced cumulative heat release 

(strength) at early ages, although by 7 d, it exhibited a similar cumulative heat release value as the 
11

other mixtures. Given its reasonable performance as assessed by calorimetry, anticipated lower 

cost, and slightly higher packing fraction, the 2.2 μm limestone powder was selected for blending 

with the 16 μm limestone in the studies that followed next.

Figure 6. Heat flow (left) and cumulative heat release (right) for the cement-limestone blend 

pastes. The 25:50:25 mixtures all employed the 16 μm limestone as the coarse limestone 

component. Numbers in parentheses in legends indicate measured packing fraction for each 

mixture.

Binary Blend Optimization

Next, various ratios of fine (2.2 μm) to coarse (16 μm) limestone in the blended cement 

were considered. Here, five ratios of the two limestone powders, namely 10:90, 30:70, 50:50, 

70:30, and 90:10 for the fine to coarse ratio were considered in the second paste-based study. In 

this phase of the study, the three powders were blended on a volumetric basis (50 % cement 

and 50 % limestone by volume) to account for the inherent differences in density between the 

cement and limestone. The w/s was maintained at 0.22 (cement reduction of 31 %) resulting in 

w/c=0.41. For these pastes, a second HRWRA (B) that produces less retardation was employed at 

a dosage of 5 mL/kg powder. As shown in Figures 7 and 8, the 50:50 mixture lies closest to the 

theoretical line for maximum packing and also yields the highest measured packing fraction, once 

again consistent with the theoretical derivations of Brouwers [18].

However, while the 50:50 mixture of the fine and coarse limestone powders is optimum 

from a maximum packing fraction point of view, it is the surface area of the limestone “filler” that 

has a much larger influence on performance, as indicated by the performance metrics presented in 

Figures 8-10. As the fine limestone fraction (and thus surface area) in the blend increases, the 

hydration is accelerated (and amplified) as indicated by the time to the first and second calorimetry 

peaks in Figure 8. However, this early age acceleration is accompanied by a reduction in 

cumulative heat release at the ages of 1 d and particularly at 7 d, perhaps due to the rapid initial 

precipitation of hydrates covering up cement clinker particle surfaces and reducing their 

subsequent reaction rates. Since cumulative heat release generally correlates well with 

compressive strength [19,20], the highest strength mixture would likely be the 10:90 mixture of 

fine:coarse limestone. Similarly, in viewing the rheology results in Figure 10, the 10:90 mixture 

produces the lowest stresses at all measured strains, suggesting enhanced flow at a given HRWRA 

dosage or alternately a lower required dosage of HRWRA to achieve a desired flow.
12

Figure 7. Computed particle size distributions for ternary blends of fine limestone:cement:coarse 

limestone with the indicated volumetric proportions. Numbers in parentheses in legend indicate 

measured packing fraction for each mixture.

Figure 8. Measured packing fraction and ITC characteristics for pastes prepared with the 

ternary blends of fine limestone:cement:coarse limestone. Each mixture contains a 50:50 

volumetric mixture of cement and limestone powder with the fine:coarse limestone proportions 

being 10:90, 30:70, 50:50, 70:30, and 90:10, as indicated by the fine limestone value on the 

lower x-axis.

At this point, in light of the above results and discussion, it would be fair to raise the 

question of whether any of the fine limestone is needed in the blended powder, given its generally 

negative impact on rheology and longer term cumulative heat release (and presumably strength). 

Indeed, in OPC concretes with 10 % limestone substituted for the cement on a volume basis 

investigated in a previous study [7], measured performance was similar for the 1.6 μm and 16 μm 

limestone powders, with the exception of setting times, where the finer limestone provided a 

reduced setting time relative to the coarser one. Similar results have been obtained in a recent 
13

Figure 9. Heat flow (left) and cumulative heat release (right) for the cement-limestone blend 

pastes in phase two of the paste study. Ratios in legend indicate fine limestone:cement: coarse 

limestone proportions on a volume basis.

Figure 10. Shear stress vs. shear rate for parallel (serrated) plate rheological measurements for 

the ternary blend cement pastes. Typical relative error for viscosity is about 7 % [21].

Canadian study that compared the performance of limestone powders with median particle 

diameters of 3 μm and 17 μm and found basically equivalent performance [22]. Due to the requisite 

high dosage of HRWRA that is envisioned for the low w/s mixtures being developed in this study, 

it was decided to maintain about a 5 % proportion of the fine limestone (i.e., 10:90 fine:coarse in 

the 50 % limestone, 50 % cement blend) to help offset the anticipated retardation produced by the 

HRWRA. The initial overlap of the w/c=0.4 control and 5:50:45 paste heat flow curves in Figure 9

is consistent with this hypothesis. However, if some delay in the setting times, such as 1 h to 2 h, 

were not an issue for the field application, it is possible that acceptably performing 

cement/limestone powder blends could be engineered using only the 16 μm limestone powder or 

even the 19.2 μm one, for example, likely minimizing both costs and materials storage 
14

requirements. This issue will be explored further in the mortar mixtures to follow where the 

performance of mixtures with a blend of fine and coarse limestone and with only a coarser 

limestone will both be contrasted against the reference w/c=0.4 OPC mortar.

To give an idea of the particle shapes (packing, etc.) for this ternary blend of two limestone 

powders with portland cement, a well-blended mixture of the 5:50:45 proportions was mounted in 

epoxy and imaged using a scanning electron microscope with X-ray imaging capability. Using a 

newly released imaging tool [23], the two-dimensional image set was processed and segmented 

into individual phases as shown in Figure 11. Both the fine and coarse limestone particles are 

clearly visible in Figure 11, with a small portion of them being identified as dolomite (magnesium 

carbonate) as opposed to calcite (calcium carbonate). All three powders have been produced by 

grinding, so that their general shapes are somewhat similar, with the limestone particles tending to 

be perhaps a bit more elongated and angular. The general characteristics of the particles in 

Figure 11 would certainly support the validity of considering their composite blend as representing 

a single continuous PSD of “similar” particles, for comparison to the linear-log maximum packing 

fraction line of Brouwers [18], as was performed in Figures 5 and 7. Thus, it is perhaps not 

surprising that the measured packing fractions were consistent with the theoretical predictions.

Figure 11. Color-coded SEM/X-ray image of the 5:50:45 fine limestone:cement:coarse limestone 

powder blend. Image shown is approximately 439 μm by 586 μm with the following color 

assignments: cyan – C3S, orange – C2S, grey – C3A, red – C4AF, magenta – periclase, yellow –

calcium sulfate, blue – calcite, and tan – dolomite.
15

Mortars

For several of the mortars, the limestone content of the powder blend was reconsidered and 

reduced slightly to meet specific targets for w/c and w/s. Given specified target values for the massbased w/c and w/s, the volume fraction of the cement in the powder blend can be computed as:

Vcem

f =

1

{1−(

ρcem

ρLS

)[1−

(

w

c

)

(

w

s

)

]}

(1)

where ρcem and ρLS are the densities of the cement and limestone powder, respectively. For two of 

the cement-limestone blend mortars, w/c and w/s were set at 0.4 and 0.25, respectively, resulting 

in a volumetric-based blend of 59 % cement and 41 % limestone powder via equation 1. 

Maintaining w/c=0.4 will allow nearly all of the cement to hydrate even under sealed curing 

conditions, while w/s=0.25 was viewed as the lower end of the acceptable range for producing a 

flowable mortar while staying within the manufacturer-recommended range of HRWRA dosage 

(i.e., about 5 mL/kg of powder). Such a mixture is also consistent with a previously presented

analysis based on Powers’ model for cements with limestone fillers [4]. A mixture with these 

proportions achieves a 23.5 % reduction in cement paste (both cement and water) content for the 

mortar. For the w/s=0.25 mortars, both a 10:90 blend of the 2.2 μm and 16 μm limestone powders 

and just the 16 μm limestone powder by itself were used for cement paste replacement for 

comparison to the w/c=0.4 100 % OPC reference mortar. To investigate possibly more economical 

mixtures, three additional mortars were prepared. First, a mortar with w/s=0.28, w/c=0.52 and a 

50:50 volumetric ratio of limestone to cement powder was investigated, using the 10:90 mixture 

of the 2.2 μm and 16 μm limestones. This mixture provides a 27.5 % reduction in cement paste 

content and a 37.9 % reduction in cement content. Second, two mortars with w/s=0.30, w/c=0.51 

and a 44.5:55.5 volumetric ratio of limestone to cement powder were investigated using either

the 6.7 μm or the 19.2 μm limestone powder, providing about a 33.6 % reduction in cement 

content. These two mixtures, along with the two w/s=0.25 mortars, provide an indication of the 

influence of limestone powder fineness on mortar performance. The measured fresh and hardened 

properties of these six mortars are summarized in Table 3, while Figures 12 through 14 provide 

graphical representations of their isothermal and semi-adiabatic calorimetry data.

Fresh Properties

As can be seen in Table 3, the fresh mortar temperatures of the mixtures with reduced w/s

were a few degrees higher than the w/c=0.4 mortar, likely due to the extra energy imparted to the 

materials during (their more viscous) mixing. Air contents and flows of the w/c=0.4 and the 

w/s=0.25 and 0.30 mortars were generally similar, with a slightly elevated air content of 4.7 % in 

the w/s=0.30 mortar prepared with the 19.2 μm limestone powder and HRWRA C. It was noted 

that the w/s=0.25 mortars prepared with the HRWRA generally did not maintain their flow well 

during the approximately 1 h required to cast the various specimens being evaluated in the present 

study, particularly for the mixture prepared with only the coarse limestone powder. This situation 

was somewhat improved in the w/s=0.30 mortars, due to both their higher water content and to the 

switch to different HRWRAs (C, D, and E). The w/s=0.28 mortar exhibited an extremely low air 

content and an excessive flow, and it is likely that the HRWRA was overdosed in this particular 

mixture, although both cube and autogenous deformation tube specimens were castable (pourable).
16

Table 3. Properties of mortars investigated in the present study

w/c=0.4

control

w/s=0.25 

LS blend

w/s=0.25 

16 μm LS

w/s=0.28 

LS blend

w/s=0.30

6.7 μm LS

w/s=0.30 

19.2 μm LS

Temperature (°C) 22.9 25.4 26.4 25.5 25.2 24.5

Mortar density (kg/m3) 2.26 2.33 2.32 2.35 2.29 2.23

Air content (%) 2.6 2.5 3.0 0.4 2.3 4.7

Flow/spread (%) 118.5 106 109 Overflow 96 110

Initial “set” (h) 2.6 1.2 1.3 1.6 2.3 2.2

1-d strength (MPa) 29.8 (4.2 %)A 43.8 (3.0 %) 39.2 (4.7 %) 32.9 (1.1 %) 29.4 (2.2 %) 26.7 (3.0 %)

7-d strength (MPa) 55.9 (4.4 %) 68.6 (1.5 %) 65.1 (6.8 %) 60.3 (4.1 %) 55.2 (1.9 %) 49.8 (3.0 %)

28-d strength (MPa) 65.3 (0.9 %) 78.9 (1.8 %) 77.5 (6.4 %) 77.5 (2.7 %)B 58.2 (2.9 %) 59.3 (0.3 %)C

91-d strength (MPa) 80.6 (3.5 %) 92.8 (4.3 %) 82.3 (4.0 %) 81.0 (3.3 %) 68.1 (4.2 %) 61.4D

7-d autogenous shrinkage 

(μstrain)

185 157 196 116 99 94

28-d autogenous shrinkage 

(μstrain)

286 203 246 155 160 147

28-d drying 

shrinkage (μstrain)

800 605 560 Not 

Measured

600 620

Ultimate drying shrinkage 

via ASTM C596 (μstrain)

945 685 640 Not 

measured

690 780

ANumbers in parentheses indicate coefficient of variation for three replicate specimens, or two specimens where noted.

BTested at 56 d.

CAverage of only two test specimens.

DOnly one specimen tested.
17

While the early-age calorimetry curves are similar in Figures 12 and 14 (up to 5 h for example), 

the w/s=0.25 and w/s=0.28 mortars did set about an hour earlier than the w/c=0.4 mortar, likely 

due to both their reduced water content [24] and their rapidly stiffening (denser) matrix (loss of 

flow mentioned earlier). This earlier setting could potentially be a problem in field concrete 

mixtures that might have to be addressed by the addition of a retarder, for example.

Calorimetry

Figure 12 shows the heat flow results normalized both per unit mass of cement and per unit 

volume of water (since w/c is variable in the different mortars). Clearly, the addition of any of the 

limestone powders to the mortar is providing an amplification of both the silicate and aluminate 

hydration reactions [7,10,16]. It is probable that the additional surface area provided by the 

limestone powder(s) is also accelerating these reactions, but that effect is likely masked by the 

retardation produced by the substantial dosage of HRWRA required in these mixtures. This 

enhanced hydration should contribute to an increase in early-age compressive strength [19] in these 

mortars, consistent with the measured increases shown in Table 3, particularly when the finer 

limestone powders are employed. This effect can be seen more clearly in Figure 13 that shows the 

cumulative heat release normalized per unit volume of initial (mixing) water vs. age for the six 

mortars; here, it can be observed that the heat release of the two w/s=0.25 mortars exceeds that of 

the w/c=0.4 mortars at ages beyond about 6 h, with the maximum deviation occurring at 

approximately 24 h. In terms of both isothermal and semi-adiabatic calorimetry, for the w/s=0.25 

mixtures, the differences between the limestone powder blend and the coarser limestone powder 

only are minimal, as are the differences for the two w/s=0.3 mortars prepared with different size 

limestone powders.

Figure 12. Heat flow normalized per mass of cement (left) and per volume of initial water in the 

specimen (right) vs. time for the six mortars.

Interestingly, the semi-adiabatic temperature rise curves shown in Figure 14 are fairly 

similar for the six mortars, particularly for the reference and w/s=0.25 mortars. While the w/c=0.4 

reference mortar contains 23.6 % more reactive cement per unit volume of material relative to the 

w/s=0.25 mixtures, it also has an increased heat capacity due to the 23.6 % increase in water, with 

its corresponding relatively high heat capacity of 4.18 J/(g∙K). These two factors, along with any 

amplification of the hydration reactions provided by the limestone powder(s), balance each other 

out, so that the semi-adiabatic temperature response for the ≈375 g mortar specimens investigated 

in the present study are all quite similar. The peak temperatures achieved for the w/s=0.28 and 
18

w/s=0.30 mixtures are about two to four degrees less than that observed for the other three mortars, 

due to their increased water content relative to the w/s=0.25 mortars, for example. For these 

mortars, there is also some indication of enhanced reactivity at the later ages of 36 h to 72 h where 

several shallow fairly broad peaks in temperature are observed in Figure 14.

Figure 13. Cumulative heat release vs. time for the six mortar specimens.

Figure 14. Semi-adiabatic temperature vs. time for mortars investigated in the present study.

Compressive Strength

The compressive strength results in Table 3 indicate that the w/s=0.25 and w/s=0.28 

mortars have higher strengths at all ages than the w/c=0.4 control. Generally, concrete strength is 

related to w/c [3], so it might be expected that the three mortars with equivalent w/c would exhibit 

equivalent strengths (at equivalent degrees of hydration, for example). While a portion of the 
19

measured strength increases is surely due to the amplification of the hydration reactions as 

indicated in Figures 12 and 13, plotting strength vs. heat release (Figure 15) indicates an additional 

contribution to strength, particularly in the two mortars prepared with the 10:90 blend of fine and 

coarse limestone powders. This additional strength may be due to the enhanced particle packing 

provided by the blended limestone powder, as well as the ability of its surfaces to serve as 

nucleation and growth sites for hydration products. In this way, the limestone particles become an 

integrated component of the three-dimensional (percolated) network of particles and hydration 

products that provides setting and strength to the developing microstructure [7]. Specifically, the 

blend of fine and coarse limestone powders outperforms the use of the coarse limestone powder 

by itself in the w/s=0.25 mortars, producing a 5 % to 10 % increase in measured compressive 

strengths at ages of 1 d, 7 d, and 91 d. All of the measured variations for compressive strength 

listed in Table 3 are within the range of variations permitted by ASTM C-109 (8.7 % for three 

cubes and 7.6 % for two cubes) [9].

In terms of matching the compressive strength development of the w/c=0.4 reference 

mortar, the initial w/s=0.25 mortars provided an excess, suggesting that further cement reductions 

could be implemented. Specifically, the current limestone replacement level in the w/s=0.25 

mortars produces strength increases (relative to the reference w/c=0.4 mortar) on the order of 32 % 

to 47 % at 1 d, 16 % to 23 % at 7 d, 19 % to 21 % at 28 d, and 2 % to 15 % at 91 d. To maintain the 

conditions specified by equation (1) while maintaining w/s at 0.25, the required reduction in 

cement would produce a concurrent increase in the w/c ratio of the limestone blended paste above 

its current value of 0.4, similar to the w/c=0.52 that was produced in the w/s=0.28 mortar and the 

w/c=0.51 used in the w/s=0.30 mortars. The w/s=0.28 mortar did produce strengths that were 

basically equivalent or slightly superior to those of the w/c=0.4 reference mortar at all ages, while 

the w/s=0.30 mortar with the 6.7 μm limestone powder produced similar strengths to the reference 

at ages of 1 d and 7 d, before falling behind at the later ages of 28 d and 91 d, ultimately producing 

about 85 % of the reference strength value at 91 d.

Figure 15. Compressive strength vs. cumulative heat release for the six mortars measured at 1 d 

and 7 d. Coefficients of variation for strength measurements are given in Table 3. Dotted line 

indicates a best fit relationship determined for a variety of mortars in a previous study [19].
20

Autogenous and Drying Shrinkage

The shrinkage results of the mortars (Table 3 and Figure 16) are particularly intriguing. 

The autogenous deformation results in Figure 16 indicate less shrinkage for the limestonecontaining mortars, up to nearly 50 % less than that of the w/c=0.4 OPC reference mortar for the 

w/s=0.30 blended limestone mortars, for example. The addition of the limestone particles, reducing 

w/s, should also reduce the interparticle spacing and thus the size of the water-filled capillary 

pores [2]. Normally, this would produce an increase in autogenous shrinkage as the largest of these 

pores begin to empty [25], but in these mortars, this increase is counterbalanced by the significant 

decrease in paste content, as the paste (cement and water) is the major component contributing to 

the shrinkage of the mortar, as opposed to the effectively non-shrinking sand and limestone powder 

particles. It is interesting to note that the autogenous shrinkage of the w/s=0.25 mixture with only 

the coarse limestone powder during the first day is increased relative to that experienced by the 

mortar with the blend of fine and coarse limestones. The increased stiffness (strength) of the latter 

mixture due to the enhanced reactivity of the finer limestone and a more efficient particle packing 

may contribute to this reduction in strain, assuming the internal stresses in the two mortars to be 

approximately equivalent. 

Figure 16. Autogenous deformation measured for the six mortars during the course of 28 d. 

Error bars indicate standard deviation for either two or three replicate specimens.

Another potential contribution to the reduced autogenous shrinkage in the mortars 

containing limestone powder replacements is its stabilization of ettringite, due to the formation of 

carboaluminate phases as opposed to sulfoaluminates [26,27]. At early ages, ettringite forms as 

needles that can contribute to an autogenous expansion that is commonly overwhelmed by the 

greater ongoing autogenous shrinkage (due to chemical shrinkage). When sulfate is depleted from 

the system, these ettringite needles become unstable and dissolve to form sulfoaluminate phases

of a different morphology, removing their restraint and likely introducing additional autogenous 

shrinkage. Thus, when the ettringite is stabilized by the presence of the limestone powder, this 
21

contribution to autogenous shrinkage will be removed. This hypothesis has been recently verified 

in two repair mortars that generate substantial ettringite by replacing 5 % of the repair mortar with 

the 16 μm limestone powder and observing a reduction (of greater than 5 %) in their measured 

autogenous shrinkage [28]. This stabilization of ettringite could also contribute to the increased 

strengths observed in the cement-limestone blended mortars, as the dissolution of ettringite needles 

to form monosulfoaluminate phases would also be expected to weaken (at least temporarily) the 

three-dimensional microstructure.

This improvement in shrinkage performance due to the replacement of cement paste with 

limestone powder also carries over to the drying shrinkage values given in Table 3. Perhaps not 

surprisingly, the observed reductions in drying shrinkage correspond closely to the 23.6 % 

reduction in cement paste content in the w/s=0.25 cement/limestone blended mortars (constant 

w/c=0.4), as once again, it is basically only the paste component that is subject to drying shrinkage. 

The reduced paste (water) content thus leads to a proportional reduction in drying shrinkage (and 

mass loss). Similarly, the shrinkage reduction is slightly less dramatic in the w/s=0.30 mortars due 

to their relatively higher water content (w/c).

These reductions in shrinkage could produce concretes that are more resistant to early-age 

cracking, a problem that has plagued bridge decks and other concrete structures for many 

years [29]. The HVLP mixtures are particularly intriguing in that they can provide increases in 

compressive strengths along with concurrent reductions in shrinkage, as most mixture 

modifications that will increase strength (reduction in w/c or w/s, finer cement, etc.) generally also 

produce increases in shrinkage, particularly autogenous shrinkage [14,24,30,31]. In the HVLP 

mixtures, however, the limestone powder allows for a substantial reduction in paste content and 

stabilization of the ettringite (reducing shrinkage), while accelerating/amplifying cement hydration 

and contributing to the developing solid framework that is responsible for setting and (increased) 

strength. These benefits of HVLP mixtures were investigated further in a set of concrete mixtures 

as discussed in the section that follows.
22

Concretes

The composite cumulative particle size distributions for the dry ingredients (limestone 

powder, cement, sand, and coarse aggregate) for each of the three concrete mixtures are provided 

in Figure 17. While the overall PSD does not follow a linear trend (on the logarithmic x-scale), 

arbitrarily setting a cutoff of 200 μm (0.2 mm) as the delineation between powder and aggregates

produces two data subsets that are each roughly linear. In this regard, the powder components of 

the limestone powder concretes lie closer to the theoretical line [18] than that of the OPC mixture.

Figure 17. Cumulative particle size distributions for the three concrete mixtures.

Fresh Properties

The fresh concrete properties for the three concrete mixtures are summarized in Table 4.

Given the significantly higher slump of the first mixture prepared with the limestone powder, the 

second mixture was prepared with less water and more limestone powder (to increase strength and 

decrease slump, as opposed to with less HRWRA that likely would have only reduced slump) and 

did achieve the desired effect of a slump more similar to that of the OPC control. All three of the 

mixtures have a hardened air content (AC) that is quite representative of typical non-air entrained 

concrete prepared in a laboratory setting. The lower fresh air content of the first limestone concrete 

mixture is unexplained at this time, but it should be noted that the sample for the unit weight 

measurement (air content determination) was obtained directly from the concrete following the 

slump measurement without remixing. For the second mixture with limestone, unit weights were 

obtained on both slump-tested and fresh from the mixer concrete, with both values being provided 

in Table 4. For this third mixture, the slump-tested concrete exhibited a fresh air content of 1.4 % 

vs. 1.8 % for the concrete freshly discharged from the mixer.
23

Table 4. Fresh concrete properties (see Materials and Methods for typical uncertainties)

OPC 6.7 μm limestone – 1 6.7 μm limestone - 2

Temperature (°C) 26.8 25.3 26.1

Slump (cm) 14.6 24.1 17.1

Unit weight (kg/m3) 2390 2450 s=2480 , f=2470 A

Fresh air content (%) 3.1 1.5 s=1.4, f= 1.8

Hardened AC (%) 2.9 3.5 2.5

C403 initial set (h) 4.2 3.9 2.9

C403 final set (h) 5.6 5.5 4.3

As=slump test concrete; f= freshly discharged concrete

Setting Times

The setting time measurements performed on the sieved mortar via Vicat needle 

(ASTM C191) and penetrometer (ASTM C403) are provided in Figure 18 and summarized in 

Table 4. The ASTM C191 test method is strictly only applicable to cement paste, but has been 

applied here to mortar without any modifications. Since they are based on different critical 

resistance levels obtained under different loading conditions, it is not surprising that the initial 

setting times via the Vicat needle precede those determined using the penetrometer by about 1 h

(3 h vs. 4 h). Although their mixture proportions are significantly different, the OPC control and 

the first mixture prepared with the limestone powder exhibit quite similar setting behavior. It 

appears that any retardation produced by the higher dosage of the HRWRA used in the limestone 

mixture is offset by its reduced water content (more solids per unit volume) and any acceleration 

provided by the fine limestone powder surfaces, such that the setting behaviors of the two mixtures 

are nearly identical. This would be beneficial to a contractor in the field, as they would not need 

to adjust their schedule of operations when switching from the OPC to the limestone powder 

concrete mixture. Because of its further reduced water content and some acceleration and 

amplification of its early-age hydration, the second mixture prepared with limestone powder

exhibited about a 1.3 h reduction in setting times relative to the OPC and first limestone mixture. 

If this were to present a problem for field use, a mild dosage of a chemical retarder might be 

required to extend the setting times back towards those measured for the OPC and first limestone

concretes. On the other hand, during the winter construction season, such a mixture might be ideal 

in its current form.

Early-Age Properties

Electrical resistance and ITC heat flow measurements obtained for the three mixtures 

during the first 24 h of curing are compared in Figures 19 and 20, respectively. The ITC was 

conducted at a temperature of 23.00 °C ± 0.01 °C, while the temperature (measured) of the 

concrete in the electrical resistance cylinders ranged between 24 °C and 28 °C (in a controlled 

environment maintained at 24 °C ± 0.5 °C) for all mixtures. In comparing the results from the 

modular and tabletop electrical resistance units in Figure 19, excellent agreement is observed for 

the first limestone mixture, while a systematic difference (of about 15 %) is observed for the other 

two mixtures, perhaps due to some consolidation variations with the stiffer (lower slump) 

concretes. 
24

Figure 18. Measured setting times for mortars sieved from the three concrete mixtures, via both 

Vicat needle and penetrometer. Lower and upper dotted lines indicate resistances corresponding 

to initial and final setting times, respectively, via the penetrometer (ASTM C403), while the 

dashed line indicates initial setting criteria for the Vicat needle (ASTM C191).

Figure 19. Measured electrical resistance (fresh concrete) for the three concrete mixtures. Inset 

plot shows measured (expressed) pore solution resistance for the limestone 2 concrete mixture.

Initially, for the tabletop unit measurements, the electrical resistance of the limestone 

mixtures (w/c=0.6 or 0.55) is slightly higher than that measured for the OPC mixture (w/c=0.50), 

likely due to the cement dilution producing a less concentrated pore solution (with a lower ionic 

conductivity). Following an increase in resistivity with time that begins between 1 h and 2 h, 

starting just before 8 h for the OPC and first limestone mixture and just before 6 h for the second 
25

limestone mixture, the OPC mixture experiences a plateau, while the limestone mixtures actually 

decrease somewhat over the course of 2 h or so, before all mixtures continue their gradual increase. 

This is likely related to both microstructural and pore solution changes induced by the renewed 

hydration of the clinker phases as sulfate is depleted in these mixtures. One example of a 

microstructural alteration that could decrease resistivity would be the dissolution of ettringite 

(needles), which subsequently reprecipitates as other sulfoaluminate and carboaluminate phases. 

As sulfates are depleted from the pore solution, the hydroxide ion concentration (along with the 

solution pH) increases dramatically [32]; this would likely decrease the resistivity (increase the 

conductivity) of the pore solution and concurrently decrease the measured resistance of the 

concrete specimen. In support of this, measured resistances for small volumes (1 mL or so) of pore 

solutions expressed (squeezed) from hardened mortar specimens of the second limestone concrete 

mixture at early ages are shown in the inset of Figure 19. A dramatic decrease in resistance is 

observed during the same time window when the measured concrete specimen resistance is 

decreasing (e.g., 6 h to 9 h time window). Further compositional analysis was conducted on the 

expressed pore solutions for the limestone 2 concrete mixture and the results are provided in 

Figure 21. The depletion of sulfate, along with a concurrent decrease in calcium and increases in 

aluminum and silica are all consistent with the depletion of calcium sulfate (gypsum) and a 

renewed reactivity of the cement clinker (aluminate and silicate) phases during this time period.

Figure 20. Measured ITC heat flow (sieved mortar) for the three concrete mixtures.

The additional carbonate ions present in the system with limestone intensify this effect, as 

evidenced also in the ITC curves in Figure 20, where a substantially greater heat flow is observed 

during this time period in the systems with the additional limestone powder than that found in the 

OPC mixture. This is especially noticeable for the limestone 2 concrete mixture with its higher 

limestone powder (surface area) to cement ratio (see Table 2). The isothermal calorimetry curves 

also support the setting time measurements in that the initial rise following the induction period 

for the various mixtures all occur within the same time frame (1.5 h to 4 h), with that of the 

limestone 2 concrete mixture occurring slightly earlier than those of the other two mixtures. Any 

retardation caused by the additional HRWRA used in the limestone mixtures has been offset by 

the acceleration provided by the nucleation and growth sites offered by the fine limestone particle 
26

surfaces [7,10]. The limestone 2 concrete mixture provides 43 % more limestone surface area per 

unit cement than its limestone 1 counterpart, obviously leading to additional acceleration and 

amplification of the early-age hydration reactions (Figure 20).

Figure 21. Chemical (ICP) analysis for pore solutions expressed from the limestone 2 concrete 

mixture. Error bars indicate one standard deviation for three replicate measurements at each 

time.

The cumulative heat release curves normalized on either a unit mass of cement or a unit 

volume (mass) of water basis are provided in Figure 22. The enhanced reactivity of the cement 

produced by the limestone additions is indicated by the cumulative heat of these mixtures 

exceeding that of the OPC mixture at ages beyond about 12 h for the data normalized per unit mass 

of cement (see also Figure 20). Conversely, when the data are normalized by unit volume of 

(mixing) water in each concrete mixture, the cumulative heat produced in the two mixtures with 

limestone falls below that of the OPC control, once again after about 12 h. As will be shown 

subsequently, the cumulative heat normalized per unit volume of water is a good indicator of 

strength development in these different concrete mixtures [16,19,20].

Figure 22. Cumulative heat release from ITC measurements on mortars vs. time for the concrete 

mixtures, normalized by either mass of cement (left) or mass of water (right).
27

The mass gains of the cylinders during their curing in lime water were used to estimate the 

ongoing chemical shrinkage in their cementitious binder as an alternate indication of reactivity. 

The obtained results are provided in Figure 23, where the initial acceleration provided by the 

limestone powder surfaces is clearly indicated. While the first limestone mixture remains above 

the OPC curve at all ages as it capillary porosity likely remains percolated (see Table 6 below), 

the limestone 2 mixture approaches the OPC values and falls below it at later ages, as the capillary 

porosity in this mixture likely becomes depercolated, limiting the rate at which lime water can be 

imbibed into the cylinders from the curing tank and concurrently reducing their hydration rate.

Figure 23. Estimated chemical shrinkage vs. time for the three concrete mixtures. Error bars 

indicate standard deviation for six replicate specimens.

Compressive Strength and Drying Shrinkage

The measured compressive strengths and drying shrinkages for the three concrete mixtures 

are provided in Table 5. While the first limestone mixture produced compressive strengths that 

were between 10 % (1 d) and 2 % (3 d) lower than those of the OPC concrete reference, the second 

mixture with a further reduced water content significantly surpassed (by 13 % to 20 %) the strength 

developed in the OPC mixture at all ages, even though it contains 27.7 % less cement. The 

measured drying shrinkages are plotted against the measured mass losses for each of the three 

concrete mixtures in Figure 24. While a linear relationship with a high correlation coefficient is 

obtained for each mixture, the drying shrinkage to mass loss relationship is not universal across 

these three mixtures, as the mixtures with limestone powder have a higher mass loss due to their 

higher w/c ratio (more evaporable water per unit cement) but exhibit less shrinkage for a given 

mass loss (consistent with their lower paste content in Table 2).

Relating Strength to Measurements of UPV, Heat Release, and Electrical Resistance

A comparison of the compressive strength measurements with the measured ultrasonic 

pulse velocity (UPV) using a handheld surface unit is provided in Figure 25. For any given mixture, 

the data for the various testing ages exhibits a highly linear relationship (r2 > 0.99), but the slope 
28

Table 5. Measured compressive strengths and drying shrinkage for the three concrete mixtures

OPC 6.7 μm limestone - 1 6.7 μm limestone – 2

1-d strength (MPa) 17.9 (1.5 %)A16.1 (1.3 %) 21.4 (2.7 %)

3-d strength (MPa) 29.0 (1.0 %) 28.3 (2.3 %) 34.2 (1.1 %)

7-d strength (MPa) 34.2 (1.7 %) 32.9 (2.7 %) 38.9 (1.4 %)

14-d strength (MPa) 36.7 (1.6 %) 35.8 (3.3 %) 43.5 (0.2 %)

28-d strength (MPa) 40.5 (2.8 %) 38.2 (1.6 %) 47.4 (1.7 %)

28-d drying shrinkage 

(μstrain)

380 (3.5 %) 400 (3.0 %) 290 (12 %)

Ultimate drying 

shrinkage (μstrain)

470 480 390

ANumber in parentheses indicates coefficient of variation for three replicate specimens for strength and four replicate 

specimens for drying shrinkage, except for strength measurements on the limestone 2 concrete mixture at 1 d and 3 d

where five specimens were tested and 7 d where four specimens were tested and for drying shrinkage on the 

limestone 2 concrete mixture where only two specimens were evaluated.

Figure 24. Measured drying shrinkage vs. mass loss for the three concrete mixtures. Error bars 

indicate one standard deviation for measurements of four replicate specimens (only two for the 

limestone 2 concrete mixture).

and intercept are variable depending on the specific mixture proportions, as has generally been 

observed previously when comparing UPV to compressive strength data [33]. For these concretes 

all prepared using the same aggregates and same volume fractions of fine and coarse aggregates, 

a normalization of the ultrasonic data was attempted based on the measured density and initial 

solids content determined for each of the three mixtures. The first component of the normalization 

was to multiply the UPV by the square root of the measured density of the concrete, since modulus 

is computed as density times UPV squared and strength is generally proportional to the square root 

of modulus (ACI 318, for example). For the solids content, the basic concept being explored is 

that the transmission speed of a sound wave depends on both its speed through the solid phases 

(related to their inherent stiffness/strength) and the volume of solid phases present. Thus, the 

quantity obtained by multiplying (1-air content)*(initial solids volume fraction) was used as the 
29

second normalization factor for each mixture. In this factor, the air content was taken as the value 

estimated from the hardened cylinders after 1 d of sealed curing (assuming no mass loss during 

this curing, see Table 4) and the initial solids volume fraction included all solids present (cement, 

limestone powder, fine and coarse aggregate) with the exclusion of water and the HRWRA in the 

concrete mixture. While dividing the UPV values shown in the plot on the left side of Figure 25

by this normalization factor did bring the various curves closer together, dividing them by this 

normalization factor raised to the second power (squared) produced an almost perfect overlap for 

two of the three data sets. One hypothesis for why this normalization by the solids content raised 

to the second power works so well would be that the sound wave must propagate from one solid 

volume element to another to traverse the concrete specimen. Once the correlation length of the 

underlying microstructure is greatly exceeded, this probability of propagation (as characterized by 

the two-point correlation function) asymptotes to a value of the volume fraction squared [34,35]. 

While this normalization works well for two of the three concretes prepared with the same 

aggregates (and volume fractions), further research is necessary (and planned) to determine its 

universality across a wider range of concrete mixtures, including those prepared with different 

aggregate sources.

Figure 25. Cylinder compressive strength vs. measured (left) and normalized (right) UPV for the 

three concrete mixtures at ages of 1 d, 3 d, 7 d, 14 d, and 28 d (data points from left to right).

Error bars indicate one standard deviation for measurements on three cylinders at each age for 

each mixture, except for the limestone 2 concrete mixture at the ages of 1 d and 3 d where five 

cylinders were tested and 7 d where four cylinders were tested.

Another approach to predicting concrete compressive strength is based on using its relation 

to cumulative heat release, as shown in Figure 26 (see also Figure 15 for corresponding results for 

mortars). This relation is typically limited to the first 7 d to 14 d of curing, as beyond this point, 

the signal to noise ratio for the measured heat release becomes too small for reliable data 

acquisition. However, out to 7 d, a linear relationship between cumulative heat release (normalized 

per unit mass of initial mixing water) and measured compressive strength is observed that is the 

same for two of the three concrete mixtures examined in the current study. As shown in Figure 26, 

the linear relationship found in this study for the OPC and limestone 1 concretes lies basically 

parallel to and between similar relationships found for two other aggregates (limestone and 

siliceous gravel) in previous studies [16,19], as the level of bond between the aggregates and the 

hydrating cement paste also influences strength, along with the porosity reduction produced by the 

cement hydration [7]. The dolomitic limestone (along with the siliceous sand) employed in the 

current study apparently produces a bond that is intermediate between that found in the limestone
30

Figure 26. Cylinder compressive strength vs. measured cumulative heat release (from sieved 

mortar) for the three concrete mixtures at ages of 1 d, 3 d, and 7 d (data points from left to 

right). Dashed and thin solid lines indicate previously established relationships for limestone

and gravel aggregate concretes, respectively [16,19].

(high bond) and gravel (low bond) concretes. However, with a higher limestone powder content

and still less water (lower w/s), the line for the limestone 2 concrete mixture shifts upward to nearly 

match that of the previous limestone aggregate concrete, likely indicating a superior bonding 

between coarse aggregate and binder. Further support for a superior bond in the limestone 2 

concrete mixture is provided in Figure 27 that contrasts split cylinder specimen (twin) surfaces 

(1 d breaks) for the OPC and limestone 2 concrete mixtures. The dark grey aggregates visible in 

each specimen generally correspond to aggregates that were fractured during the test, as can be 

verified by matching up the two pieces of each broken aggregate, one on each side of the broken 

specimen. There are far more of these broken aggregates present in the limestone 2 concrete 

mixture specimen, once again indicating a superior interfacial bond in this particular concrete.

The resistivity measurements for the three concrete mixtures at various ages are 

summarized in the graphs in Figure 28. At any given age (proceeding from left to right in the 

graph), the values measured for the OPC concrete generally lie between those measured for the 

two limestone concretes. As indicated in Table 6, this is the ordering that would be expected based 

on the estimated capillary porosity (Powers model) present in the three mixtures as a function of 

the degree of hydration of the cement (α) and the assumption that about 20 % capillary porosity in 

the paste is the volume fraction at which depercolation occurs [36,37]. Results obtained using 

either different devices to make uniaxial measurements or surface vs. uniaxial measurements are 

generally within 10 % to 20 % of one another, with the exception of the 28 d measurement of 

uniaxial resistivity of the limestone 2 mixture using device 1 that is abnormally high. Contributing 

factors to this could include the depercolation of the capillary porosity producing self-desiccation 

within these cylinder specimens and the lower measurement frequency (40 Hz) used with this 

device. One potential reason for a slightly greater difference between surface and uniaxial 

measurements (right side of Figure 28) than that found in a previous study [17] is that in the 

previous study, curing was conducted in a fog room, while in the present study, curing was 
31

conducted in limewater where leaching of alkalis and other constituents from the surface of the 

concrete cylinders can impact particularly the measured surface resistivity [38,39]. Much less (if 

any) leaching would be expected under the standard fog room curing used in [17].

Figure 27. Photographs of specimen (twin) surfaces for OPC (left) and limestone 2 (right) 

concrete mixtures that were broken using a split cylinder test. Tube-shaped hole at top corner of 

each specimen corresponds to location of a plastic tube where a thermocouple was inserted.

Dark grey aggregates in each case indicate fractured aggregates, as can be verified by matching 

them on the opposite side of the twin specimen. Each cylinder half is nominally 100 mm by 

200 mm.

Figure 28. Comparison of uniaxial (left) resistivity measurements using two different 

measurement devices and uniaxial vs. surface resistivity (right) for the three concrete mixtures at

ages of 1 d, 3 d, 7 d, 14 d, and 28 d (data points from left to right). Error bars indicate one 

standard deviation for measurements performed at each age for each mixture. The dashed line 

indicates a one-to-one relationship in each plot.

A comparison of concrete cylinder compressive strength plotted vs. the measured uniaxial 

resistivity (via device 2) is provided in Figure 29. For these three concrete mixtures, a single curve 

provides a reasonable representation of the relationship between strength and electrical resistivity, 
32

either uniaxial or surface. However, once again, the strength values for the limestone 2 concrete 

mixture lie slightly above those of the other two concretes, further supporting its enhanced binderaggregate bonding. While both electrical resistivity and compressive strength are largely 

influenced by the volume of capillary porosity within the hydrating cement paste component of 

the concrete, it is surprising that a single curve with some scatter is found to characterize fairly 

well the relationship between them for these concretes with quite different binder compositions. 

This would suggest that despite differences in binder composition, the impact of pore solution 

conductivity on measured electrical resistivity would be minimal; indeed, measurements of pore 

solution resistivity on the three mixtures have indicated values all within ± 20 % of 0.15 Ω∙m, at 

ages of 1 d and beyond. 

Table 6. Capillary porosity estimations for the paste components of the three concrete mixtures 

Concrete Porosity at α=0.85 α for 20 % porosity (depercolation)

OPC 23.4 % 0.926

Limestone 1 26.5 % > 1.0

Limestone 2 21.4 % 0.893

Figure 29. Measured compressive strength vs. uniaxial (left, measured at 10 kHz)) and surface 

(right) electrical resistivity for the three concrete mixtures at ages of 1 d, 3 d, 7 d, 14 d, and 28 d

(data points from left to right). Error bars indicate one standard deviation for measurements on 

three cylinders at each age for each mixture, except for the limestone 2 concrete mixture at the 

ages of 1 d and 3 d where five cylinders were tested and 7 d where four cylinders were tested.

Fitted line on each plot is for the OPC mixture only.
33

Summary 

Studies in paste, mortar, and concrete have all confirmed the high potential for replacing a 

significant fraction of the cement paste in these materials with a fine limestone powder to produce 

more sustainable high volume limestone powder (HVLP) mixtures with equivalent or even 

superior performance. A key paradigm shift present in this approach is the concept of replacing 

cement paste (cement powder and water) with the limestone powder, as opposed to just replacing 

the cement powder. While particle packing can be optimized based on previously derived 

theoretical considerations [18], a fluid mixture generally requires moving away from any 

close-packed configuration, so that optimum packing is not paramount to obtaining acceptable 

performance in these systems.

Results in OPC and HVLP mortars indicated the viability of achieving cement reductions 

between 23 % and 38 %. In the mortar studies, the reduced autogenous and drying shrinkages of 

the HVLP mixtures were highlighted, being mainly due to their reduced paste content. In a series 

of three concretes, two HVLP concretes that provided 25.7 % and 27.7 % reductions in cement, 

respectively, performed similarly to the OPC reference mixture, with the second mixture actually 

offering a compressive strength boost on the order of 10 % to 20 % at ages to 28 d. With similar 

rheology (slump) and setting behaviors, these HVLP mixtures could be substituted for current OPC 

formulations, with minimal adjustments by the contractor and concrete construction crew being 

anticipated.

Although not the focus of the current study, the results for the three concrete mixtures have 

illustrated the strong relationships that exist between cumulative heat release, UPV, or electrical 

resistivity and measured compressive strength, which will be useful for developing noninvasive in 

situ measurements of in-place concrete compressive strength in an ongoing NIST exploratory

research project. In this regard, a new approach to normalizing UPV data based on the solids 

contents of the concrete formulations was presented and partially verified using the data developed 

in this study. While isothermal calorimetry heat release is not easily monitored in the field (and 

certainly not in an in situ manner), UPV and (surface) electrical resistivity measurements can be 

easily adapted to the construction site and standardized for field deployment. One complication in 

using these techniques to predict strength that was highlighted in this study is their general inability 

to capture information concerning the binder-aggregate interfacial bond. In general, the limestone 

2 concrete mixture, with a superior bond, did not follow the trends between these three measures 

and strength that were established for the first two concrete mixtures in this study. Further research 

on quantifying and improving the aggregate-binder bond in sustainable cement-based materials is 

needed and will be pursued by NIST in the future.

While the electrical resistivities measured on the concrete mixtures indicated a similar or 

superior performance for the HVLP mixtures in reference to the OPC mixture, further research 

will be needed to assure the durability of these higher replacement level sustainable concretes. 

Still, one encouraging fact is that concretes with up to 35 % limestone replacement for cement 

have been used for many years in parts of Europe with minimal durability concerns.

 
34

Acknowledgements 

The authors would like to thank BASF, Carmeuse Lime and Stone, Huber Engineered 

Materials, the Lehigh Cement Company, OMYA Inc., U.S. Concrete, Inc., and W.R. Grace & 

Co.-Conn. for providing materials used in the present studies. The assistance of Mr. Max Peltz 

(NIST) in providing the measured particle size distributions, BET surface areas, and densities and 

assisting with the preparation of the mortar mixtures, Dr. Pan Feng (NIST) in obtaining the 

SEM/X-ray composite images of the powder blends, Ms. Lakesha Perry in conducting inductively 

coupled plasma atomic emission spectrometry (ICP-AES) measurements on pore solutions, 

Mr. Paul Rothfeld (NIST) in assisting with preparation of the mortar mixtures, Mr. Michael 

Boisclair (NIST) in performing data entry and analysis, and Mr. José David Betancourth Mendoza 

(UANL, Monterrey, MEXICO) in performing rheology measurements is gratefully acknowledged. 

The efforts of the following individuals (NIST) in assisting with the preparation and evaluation of 

the concrete mixtures is also greatly appreciated: Mr. Michael Boisclair, Mr. Richard Eason, 

Dr. Chiara Ferraris, Ms. Michelle Helsel, Mr. Max Peltz, and Mr. Paul Rothfeld. 
35

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