Portland Limestone Cement

FHWA Publication No.: FHWA-HRT-23-104

FHWA Contact:

Michelle Cooper 

(ORCID: 0000-0001-8112-693X), HRDI-10, 

202–493–3691, michelle.cooper@dot.gov

Robert Spragg 

(ORCID: 0000-0001-9205-1486), HICP-40, 

202–366–0120, robert.spragg@dot.gov

INTRODUCTION

Portland limestone cement (PLC) is a binary blended cement manufactured 

according to ASTM International (ASTM) C595(1)

 or American Association 

of State Highway and Transportation Officials (AASHTO) M 240.(2)

 PLC 

contains 5- to 15-percent blended or interground limestone and is alternatively 

identified with the term “IL,” which indicates portland cement-limestone 

blended cement in ASTM C595 and AASHTO M 240.(1,2)

 PLC is engineered to 

provide 28-d performance equivalent to that of ordinary portland cement (OPC) 

(ASTM C150(3)

 or AASHTO M 85(4)) for 1:1 replacement while reducing 

global-warming potential (GWP) 8.3 percent on average, thanks to its 

lower clinker content.(5)

 Cement suppliers are typically producing PLC with 

10- to 12-percent limestone powder because such a blend results in a more 

optimal, 1:1 performance.

Though PLC has now become widely available throughout the United 

States, several agencies and contractors have reported challenges with its 

implementation due to limited field experience using the material in the United 

States.(6)

 This TechNote is designed to help State highway agencies (SHAs) 

and contractors become more acquainted with technical and background 

information regarding PLC and to promote its successful application nationwide. 

The document provides information regarding the history, specifications, 

sustainability, manufacture, engineering principles, and performance of PLC. 

In addition, the document presents successful case studies and best practices for 

implementing PLC.

History of PLC in the United States 

ASTM C150 began allowing the use of up to 5-percent interground 

limestone in OPC types I–V in 2004.(3)

 Before then, in North American 

specifications, limestone had not been permitted as an addition to cement. 

AASHTO M 85 was harmonized with ASTM C150 in 2007, when the 

5 percent allowable limestone content for OPC was balloted and accepted.(4)

PLC was introduced in the United States in 2005 through ASTM C1157 as a 

performance cement.(7)

 While cements with high ground limestone contents 

have been successfully used in Europe for 15–20 yr, North American PLC 

differs in that it was designed to have mechanical properties similar to 

those of OPC at 28 d, and the concrete producers often add supplementary 

cementitious materials (SCMs) to PLC.(8)

 Beginning in 2012, ASTM C595 

and AASHTO M 240 standard specifications for blended hydraulic cements 

started allowing up to 15-percent blended or interground limestone to be 

used in binary blended cements, and the specifications defined the product 

as IL or PLC.(1,2)

 While PLC has been allowed in many States since 2012, 

TECHNOTE

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and Technology

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Research Center 

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2

only producers in Utah and Colorado were using PLC in 

significant quantities.

Thanks to continuous research and education initiatives 

such as the Transportation Research Board (TRB) 

workshop in 2012, successful implementation cases, 

and increasing concerns regarding the sustainability 

of the cement and concrete industries, the use of PLC 

has been steadily increasing in the United States since 

its introduction.(9)

 A survey sponsored by the Portland 

Cement Association reported that around 890,000 metric 

tons of PLC were produced in the United States in 

2016.(10)

 A U.S. Geological Survey mineral industry 

survey reported that 24 million metric tons of blended 

cements were imported into or manufactured in the 

United States from January to November 2022, the vast 

majority of which was expected to be PLC.(11)

 PLCs are 

progressively replacing Type I and Type I/II cements in 

most plants, making OPC Types I and I/II more difficult 

to find in some regions. 

REVIEW OF ASTM C595 AND AASHTO 

M 240 HIGHLIGHTS

ASTM C595 and AASHTO M 240 specifications 

prescribe a list of performance and constituent 

requirements for blended hydraulic cements that use 

slag, pozzolan, limestone, or some combination of 

them.(1,2)

 The two standards use a naming convention 

in which “PLC” is designated as “Type IL(xx),” 

where “xx” designates the percentage of limestone 

in the blend. For example, Type IL(10) designates a 

binary blended cement with 10-percent limestone. 

Additional suffixes can be added ahead of the cement 

name based on special properties, such as “(MH)” for 

“moderate heat of hydration” or “(HS)” for “high sulfate 

resistance.” The next sections describe the chemical and 

physical requirements for PLC that ASTM C595 and 

AASHTO M 240 specify.(1,2) Table 1 provides a summary

of these requirements.

Table 1. Chemical and physical requirements for PLC from ASTM C595 and AASHTO M 240.(1,2)

REQUIREMENTS ASTM 

STANDARD

AASHTO 

STANDARD PROPERTY SPECIFIED LIMIT FOR PLC

Chemical C114(15) T 105(16)

Sulfur reported as sulfate (SO3), maximum, percent 3

LOI, maximum, percent 10

Physical

C191(17) T 131(18) Time of initial set, 

Vicat test

Set minutes, not less than 45

Set hours, not more than 7

C185(19) T 137(20) Air content of mortar, volume percent, max 12

C109/

C109M(21)

T 106 M/

T 106(22)

Compressive 

strength, 

minimum, 

megapascals (psi)

3 d 13.0 (1,890)

7 d 20.0 (2,900)

28 d 25.0 (3,620)
3

Chemical Requirements

Limestone used in the manufacture of PLC or a 

ternary blended cement is required to have a calcium 

carbonate content of at least 70 percent by mass, which 

is determined by multiplying the calcium oxide content 

of the limestone by a factor of 1.785,(1)

 which is the 

ratio between the calcium carbonate and calcium oxide 

molar mass. A 3-percent maximum sulfate (SO3 when 

expressed as sulfur trioxide) content is specified for 

PLCs and for ternary blends in which the limestone 

content is larger than or equal to slag or pozzolan.(1) For 

these cements, no maximum chemical limit is imposed 

on magnesium oxide, sulfide (S2-), or insoluble residue 

content. The sulfate limit was set mainly to maximize 

the potential reactivity of the calcite in the system.(12)

However, when pozzolans with high alumina content 

(e.g., slag, metakaolin, or high alumina fly ash) are 

included in the blended cement, the performance may 

be improved by having SO3 concentrations higher than 

3 percent.(13)

 Because of that potential improvement, 

ASTM C595(1)

 and AASHTO M 240(2) allow for SO3

contents higher than 3 percent, provided ASTM C1038/

C1038M is used to demonstrate that the cement with 

the increased SO3 content will not develop expansion 

exceeding 0.020 percent at 14 d.(14)

 This sulfate 

optimization may assist with optimizing strength or 

setting time. For PLC and ternary cements, the maximum 

loss on ignition (LOI) is specified as 10 percent to 

control the cement limestone content and potential 

moisture contaminations.(15,16)

While not specifically mentioned in ASTM C595, due 

to the wide range of limestone contents allowed in 

PLC, Bogue equations cannot be applied to calculate 

the main cement phases (i.e., alite, belite, tricalcium 

aluminate, and ferrite).(1)

 The cement phases of PLC 

can be quantified reliably only by means of x-ray 

diffraction analysis.

Physical Requirements

ASTM C595(1) and AASHTO M 240(2) define physical 

limits for PLCs with respect to minimum and maximum 

time of initial setting by Vicat test (ASTM C191(17)

and AASHTO T 131(18)

), maximum air content 

(ASTM C185(19)

 and AASHTO T 137(20)), and minimum 

compressive strength at 3, 7, and 28 d (ASTM C109/

C109M(21)

 and AASHTO T 106M/T 106(22)). Blended 

cements that incorporate accelerating or retarding 

elements such as admixtures are not required to meet the 

time of setting requirements listed in table 1. Blended 

cements with special properties (e.g., MH or HS) have 

separate physical requirements. Testing time, sampling 

methods, and specimen-handling requirements are all 

described within ASTM C595 and AASHTO M 240.(1,2)

WHY SWITCH FROM OPC TO PLC?

Cement production was responsible for 0.86 percent of 

U.S. carbon dioxide (CO2) emissions in 2020.(23)

 Those 

emissions originate mainly from three major processes: 

• The use of fuels to raise the cement kiln temperature 

to around 1,500 °C. 

• The decomposition of calcium carbonate (calcination) 

in the cement kiln during the transformation of raw 

materials to clinker. 

• The transportation of materials (raw materials to the 

cement kiln and the finished product to the users).

With the overarching goal of becoming carbon neutral 

industries by 2050, the cement and concrete industries 

have been exploring different strategies to progressively 

reduce their carbon emissions.(24)

 For example, almost 

all cement plants now implement a dry-kiln process 

instead of using the previous, wet-kiln process.(25)

 This 

change in the manufacturing process reduces the amount 

of fuel needed to heat and dry the raw materials during 

the clinkering process by predrying them using waste 

heat from the cement kiln.(26)

 Another strategy that 

has become more widely adopted involves the use of 

alternative, low-emission fuels (such as natural gas) or 

waste fuels instead of the more traditional, coal-based 

fuels.(27)

 By implementing these and other more 

energy-efficient strategies, cement producers have 

progressively reduced the carbon footprint related to 

cement production.(28,29)

In parallel to the cement industry, the concrete industry 

has been investigating options to further reduce 

its carbon emissions. Two of the most promising 

implementation-ready strategies being explored are the 

production of durable concrete with reduced cement 

content and reduced clinker content.(30)

 Reducing 

the cement content can be achieved by, for example, 

minimizing the paste content in concrete by optimizing 

aggregate gradations or increasing the use of SCMs. 

Cement can also be manufactured with a lower quantity 

of clinker.(30)

 PLC is an example of a lower clinker 

cement and constitutes an additional tool to further 

reduce the carbon emissions of concrete while still 

ensuring adequate performance.(31)

IMPACT ON EMISSIONS

The main motivator for switching from OPC to PLC is 

to reduce CO2 emissions from the cement and concrete 

industries. Environmental product declarations (EPDs) 

are the most commonly used tools for quantifying the 

sustainability of cement and concrete. Based on the 

industry-average EPDs for OPC and PLC, PLCs reduce 

GWP by 8.3 percent on average.(29,32)

 Using field and 
4

laboratory concrete paving mixture designs to develop 

GWP values for the A1 to A3 lifecycle stages of the 

concretes, PLCs tend to result in GWP reductions of up 

to 10 percent, as shown in figure 1.

(5)

 The amounts of 

limestone powder and cement significantly influence the 

impact of PLC on concrete’s embodied emissions. 

HOW IS PLC MANUFACTURED?

The PLC and OPC manufacturing processes are similar, 

with the primary exception being that a greater portion 

of the clinker is replaced with limestone powder in PLC. 

Typical limestone contents in PLC range from 10 to 

15 percent instead of the typical 2 to 4 percent found 

in OPC. The added limestone is first heated to remove 

inherent water and is later blended or interground with the 

clinker and gypsum. Because the limestone has a lower 

hardness than the clinker, it is typically ground to a finer 

particle size (figure 2). 

Concrete mixtures produced with the resulting PLC 

have been shown in several studies to perform similarly 

to comparable mixtures produced with OPC alone. 

(See references 8, 9, 31, and 34.) To ensure similar 

performance by PLC and to offset dilution of the clinker 

content, PLC is typically ground to a higher fineness than 

regular OPC. The increased fineness of PLC is reflected 

in a higher Blaine fineness (generally 10–30 percent 

higher for PLC than for OPC) or in a finer particle size 

distribution, which is influenced partially by the greater 

quantity of smaller limestone particles.(33)

One important consequence of the increased limestone 

content in PLC is the decrease in the total energy 

consumption and CO2 released during its production when 

compared with OPC.(8)

 Because limestone avoids the 

calcination process and is not heated to the 1,500–2,000 °C 

that the clinker requires, less fuel is used and less CO2

from limestone decomposition is released into the 

atmosphere. Moreover, no additional transportation-related 

costs and CO2 emissions are typically experienced, since 

the same limestone source used in the clinker production 

can be used as partial clinker replacement.

Figure 1. Graph. OPC-concrete and PLC-concrete 

GWPs from the A1–A3 lifecycle stages compared 

with cement content.

Source: FHWA.

Figure 2. Photo. Scanning electron microscopy images of OPC and PLC illustrating ground clinker (gray) 

and ground limestone (yellow).(34)

A. OPC. B. PLC.

© 2013 Barrett. 
5

In addition to reduction in the CO2 produced, less limestone 

is used in the manufacture of the same quantities of PLC 

than OPC, thereby extending the life of the quarry. This 

concept may seem counterintuitive because PLC has an 

increased limestone content. However, because part of the 

limestone is lost during the calcination process—in the 

form of CO2—the total quantity of limestone used in the 

production of PLC is reduced, since less clinker is required. 

That reduced quantity is an additional and often forgotten 

sustainability benefit of PLC.

Due to increased limestone content in the cement, some 

adjustments to the gypsum content may be required 

to ensure the PLC’s proper performance. In particular, 

Campiteli and Florindo report a change in optimum sulfate 

content as a function of the limestone content and the 

cement fineness.(35)

 A change in the sulfate content of PLC 

may affect the way the cement interacts with other SCMs. 

ENGINEERING PRINCIPLES BEHIND PLC 

AND PLC CONCRETE

Because of PLC’s reduced clinker content, the total 

number of hydraulic reactive phases of the cement is 

expected to be diluted when compared with OPC. The 

reduction in reactive phases can potentially delay the 

setting time and the rate of strength development. To offset 

the dilution of reactive phases, PLC and PLC concrete 

can be engineered differently from traditional OPC and 

OPC concrete.(8)

 One example of engineering strategies, 

already mentioned in the manufacturing section, requires 

PLC to be ground finer than OPC (figure 2). The increase 

in fineness enhances the rate at which the cement particles 

can react and hydrate when in contact with water.(36)

Moreover, the additional limestone in the PLC can interact 

with the clinker to further enhance the performance 

of the system and offset any clinker dilution effect. 

Figure 3 provides a visual representation of the different 

mechanisms that enable PLC to offset loss in performance 

from the dilution of clinker.(8)

 First, the increased fineness 

of the limestone particle size in PLC provides additional 

nucleation sites (figure 3) where the products of the 

clinker hydration reactions can precipitate, or seed. 

As such, the increase in nucleation sites can accelerate 

cement hydration and partially compensate for the reduced 

clinker content at early ages.(37,38)

 Second, by enhancing 

particle packing through the filler effect (figure 3), the 

space between single particles is reduced and the system 

microstructure densified.(34)

 Third, a portion of the 

limestone can chemically react with alumina-rich phases in 

the system (figure 3) to form carboaluminate and ettringite 

phases, which can further contribute to the microstructural 

development of the concrete by filling the pore space.(39–41)

Although limestone is often considered an inert material 

or a filler, limestone can affect the reaction products 

of OPC and PLC systems. For example, limestone can 

participate in chemical reactions with alumina-rich phases 

in the cement and SCMs by forming carboaluminates, 

which can reduce setting time, decrease porosity, and 

increase compressive strength.(42)

 Because the reactivity 

of the limestone in PLC is tied to the presence of reactive 

alumina phases, it is more significant when alumina-rich 

SCMs such as metakaolin, slag cement, calcined clay, 

or natural pozzolan are used. Moreover, systems with 

PLCs and SCMs have also been shown to promote the 

occurrence of pozzolanic reactions when compared 

Figure 3. Illustration. The nucleation, particle-packing, and chemical effects.

Source: FHWA.
6

with traditional, OPC-SCM systems.(31) This increase 

in pozzolanic reactions can potentially contribute 

to reductions in pore connectivity and thus result in 

improved concrete transport properties (e.g., rapid chloride 

permeability test (RCPT) or resistivity) of concrete.(31)

To showcase the beneficial interaction between limestone 

and alumina-rich SCMs, figure 4 shows the synergistic 

effect of limestone and reactive alumina (Al2O3) on the 

porosity of pastes produced with increasing limestone 

replacement levels.(31)

 For the purposes of this study, 

amorphous alumina was used as a surrogate for 

alumina-rich SCMs. All systems in figure 4 had the same 

water-to-cementitious materials ratio (w/cm), and the 

porosity was derived from thermodynamic simulations.(31)

Figure 4 demonstrates that if no alumina is present, an 

increase in limestone from 0 to 2 percent (2–3 percent is 

a typical limestone content for ASTM C150 OPC) causes 

a decrease in porosity from 38 to 34 percent. At higher 

limestone concentrations (>2 percent), the porosity 

increases due to dilution of the reactive phases in the 

clinker. When reactive alumina is added to the system, 

it can react with limestone to form carboaluminate 

phases. These reactions can contribute significantly to 

reduction of the system porosity, so that a PLC system 

with 15-percent limestone and 5-percent reactive alumina 

(contributed to the system by an SCM) has lower 

porosity than an OPC system (2- to 3-percent limestone) 

with no alumina. 

Figure 4 shows that for systems containing reactive 

alumina in the form of SCMs, PLC concretes can 

be engineered so that their strengths match or even 

surpass those of comparable OPC concretes. Moreover, 

optimizing the alumina content may make it possible to 

obtain adequate performance with limestone contents 

higher than 15 percent.(31)

PERFORMANCE OF PLC CONCRETE

This section discusses the effect of the replacement 

of OPC with PLC on key concrete performance 

characteristics, including fresh, mechanical, volume 

stability, and durability properties. 

Fresh Properties (Workability, Bleeding, 

and Setting Time)

The literature indicates conflicting results regarding 

the effect of limestone inclusion on the workability 

of cementitious materials.(33)

 In general, particle size 

distribution and particle packing are key properties 

of PLC that affect the fresh properties of concrete.(33)

Due to its higher fineness, the limestone is expected to 

decrease the void space between particles by increasing 

the cement particle-packing density, potentially 

decreasing the water demand.(33)

 However, increased 

cement surface area may have an opposite effect 

on the water demand due to adsorption of a larger 

quantity of water on the surface of the finer particles. 

In-field adjustments for bleeding may be necessary 

because finer cements bleed less than coarser cements,

resulting in PLC concretes that generally bleed less than 

comparable OPC concretes.(43)

 The reduction in bleeding 

is associated with the increased surface area of the PLC 

due to finer grinding, which increases the water adsorbed 

on the cement particles’ surfaces.(33)

PLC setting time is thought to be controlled mostly 

by the change in cement fineness and the limestone 

replacement level. The literature shows different results, 

ranging from no influence to significant decrease 

in setting time.(33)

 A series of studies conducted on 

cement pastes reported a decrease in setting time 

of PLCs, which was somewhat proportional to the 

measured cement fineness.(36,44)

 A study by the Indiana 

Department of Transportation (DOT) reported that the 

setting time for PLC concrete mixtures was on average 

10 percent shorter than the setting time of comparable 

OPC concrete mixtures.(34)

 When SCMs are combined 

with PLC, the reductions in the initial and final setting 

times may become more significant.(45,46)

 Differences 

in limestone mineralogical composition, replacement 

levels, and fineness might generate varied outcomes in 

terms of fresh properties.(34,44,47)

Figure 4. Graph. Thermodynamically simulated 

porosity of PLC+Al2O3 systems, showing the 

synergy between limestone and alumina. 

(Adapted from Bharadwaj et al. 2021.(31)

)

Source: FHWA.
7

Mechanical Properties

When PLC is ground to the appropriate fineness, it 

performs comparably to OPC concrete in terms of 

compressive strength, flexural strength, and elastic 

modulus at 28 d.(34)

 As previously discussed, the 

addition of alumina-rich SCM can further promote 

the development of mechanical properties, potentially 

enabling the PLC-SCM concrete to outperform those 

of an equivalent OPC concrete.(40)

Volume Stability

Some SHAs have raised concerns regarding the 

potentially detrimental effect of the increased fineness 

of PLC (i.e., higher surface area) on the shrinkage 

and shrinkage-induced cracking of PLC concrete. The 

shrinkage performance of systems containing limestone 

is largely a function of the size of the limestone 

particles.(48)

 Coarse limestone powders demonstrated 

less shrinkage, while more finely ground powders 

demonstrated similar or slightly more shrinkage.(49)

Drying shrinkage measurements have been generally 

found to be statistically similar in comparisons of 

OPC and PLC.(31,34) One exception, as identified 

by Bharadwaj et al., regarded the use of PLC in 

combination with slag, which exhibited increased total 

shrinkage (7- to 8-percent increase).(31)

 The researchers 

attributed the observed shrinkage increase to enhanced 

slag reactivity induced by the additional limestone. 

Barrett, Sun, and Weiss found an average increase 

in 28-d drying shrinkage of 5 percent when PLC 

concrete specimens were compared with equivalent 

OPC concrete.(34)

Durability

The durability indicators of PLC systems have been 

generally found to be similar to mixtures made with 

OPC.(50)

 Thomas et al. reported similar freeze–thaw 

performance, scaling, and chloride transport for 

PLC systems.(51)

 Barrett, Sun, and Weiss observed 

that transport properties in PLC concrete were 

within +/− 30 percent of comparable OPC concrete 

mixtures.(34)

 Alkali–silica reaction and sulfate testing 

showed that PLC concretes perform similarly to or better 

than OPC concretes.(8)

 The measured porosity, formation 

factor, and apparent chloride diffusion coefficient of 

PLC concretes were found to be comparable to those 

obtained for equivalent OPC concretes.(31)

CASE STUDIES

Various cement suppliers, concrete producers, and 

researchers have performed a multitude of case studies 

to investigate the performance of PLC compared with 

OPC. The studies incorporate plain OPCs and PLCs, 

as well as binary OPC and PLC concrete mixtures with 

the inclusion of SCMs. While this document focuses on 

PLC implementation in the United States, successful 

implementation of cements with high limestone contents 

has occurred worldwide. Therefore, the presented case 

studies discuss the use of PLC for projects in both 

Canada and the United States in order of the amount of 

valuable, new information each case study provides. 

Ready-Mixed-Concrete Plant, 

Quebec, Canada

In 2008, a parking slab in Quebec was developed with 

eight different concrete materials, including plain 

PLC (or IL(12)) and OPC as well as binary PLC and 

OPC with 25-percent, 40 percent, and 50-percent 

SCM replacements. Performance tests included fresh 

air content, slump, hardened air content, air spacing 

factor, strength, RCPT, chloride diffusion coefficient, 

and scaling tests. The study found adequate mechanical 

and durability performance by the PLC mixtures, 

thereby exhibiting performance similar to that by 

the OPC mixtures.(8)

Cement Plant, Alberta, Canada

A cement plant in Alberta provided IL(12) cement 

for a project that developed pavement, retaining 

walls, and slipform curb.(8)

 The project successfully 

incorporated plain PLC and OPC as well as PLC and 

OPC with 15-percent, 25-percent, and 30-percent SCM 

replacements. Testing on the project included fresh air 

content, slump, setting time, strength, RCPT, and scaling 

resistance. The project observed similar performances by 

the PLC and OPC concretes.

Cement Plant, Nova Scotia, Canada

A concrete-paving project in Nova Scotia used blended 

cements that included 15-percent ground granulated 

blast furnace slag and two different limestone levels: 

3–4 percent and 12 percent. The blended cements were 

then combined with fly ash at 0 percent, 15 percent, and 

20 percent. After investigating the fresh, mechanical, 

and durability properties of the different materials, 

the project identified lower strength by approximately 

10 percent in the PLC mixtures at later ages.(8)

 However, 

the plant attributed these lower strengths to the measured 

0.02 higher w/cm ratios and 0.8-percent higher air 

contents of the PLC concrete compared with the 

OPC concrete. 

40th Avenue and Havana Street, Denver, CO

A concrete-paving project in the winter of 2007 on 

local roads in Denver used an IL(10) with 20 percent 

class C fly ash.(52)

 The project achieved adequate 

compressive and flexural strength at 7 d, and the 

paving mixture performed similarly to comparable 
8

OPC paving mixtures. At the time of this case study 

report, the pavement had sustained two winters with no 

visible degradation. 

U.S. Highway 287, Lamar, CO

Seven miles of rural highway were paved in Lamar using 

an IL(10) with 20-percent class F fly ash and a total 

cementitious content of 540 lb of cementitious materials 

per cubic yard (lb/yd3

).(52) Despite being placed in hot, dry 

summer conditions, the concrete achieved satisfactory 

flexural strength performance at an age of 28 d.

I–25, Castle Rock, CO

An interstate highway section of dowel-jointed 

plain concrete pavement on I–25 in Castle Rock was 

repaved using an IL(10) with 20-percent class F fly 

ash, 0.42 w/cm ratio, and total cementitious content 

of 517 lb/yd3

.

(52)

 Once again, the concrete obtained 

satisfactory flexural strength performance at 28 d. 

Lost Creek Road, Morgan, UT

A rural pavement with major truck traffic in Morgan was 

paved using IL(10) with 20-percent class F fly ash. The 

concrete pavement obtained satisfactory performance with 

regard to compressive and flexural strength at 28 d.(53)

104th South, Salt Lake City, UT

As part of a pooled fund study with the University of Utah, 

a concrete pavement with IL(10) and 25-percent class F 

fly ash was placed in Salt Lake City. The compressive 

strengths at 28 d achieved satisfactory performance.(53)

Utah State Route (SR)-201, Salt Lake City, UT

The eastbound lanes of Utah SR–201 near Salt Lake City 

were paved with OPC, while the westbound lanes were 

paved with IL(10) with 25-percent class F fly ash.(9,53)

The eastbound lanes achieved a higher internal pavement 

temperature and slightly higher strength than the 

westbound lanes, which Utah DOT reported as a likely 

result of the seasonal temperature variations between 

summer—when the eastbound lanes were paved—and 

autumn, when the westbound lanes were paved. The 

general contractor reported no differences in air stability 

or finishing quality between the OPC and PLC materials. 

I–80 Reconstruction Project, Silver Creek 

Junction to Wanship, UT

The I–80 reconstruction project repaved 7.55 mi using 

OPC with 25-percent class F fly ash in the eastbound 

lanes and PLC with 25-percent class F fly ash in the 

westbound lanes.(9)

 The two concretes performed similarly 

and met all project requirements. After 10 yr in the field, 

both directions of transport remained in good condition.

COSTS

In general, once full market penetration is observed, 

PLCs are anticipated to cost similarly to OPCs.(45)

Although it might seem initially that using lower cost 

limestone to replace clinker could result in cost savings, 

cement producers have highlighted a few factors 

that result in similar pricing between OPC and PLC. 

For example, the need for additional quality control 

operations on the material (limestone powder), the 

increased amounts of handling and blending that need to 

occur, and the increased grinding that is associated with 

the production of PLCs versus that of OPCs all result in 

similar cost evaluations between PLC and OPC. 

Before reaching full market penetration, PLCs are 

often produced at the end or beginning of a run of OPC 

production at a cement plant. The increased complexity 

associated with producing two materials (OPCs and 

PLCs) and limited supply of PLC can result in initially 

variable costs of PLCs. For example, if PLCs and OPCs 

need to be produced at the same facility, PLCs require 

additional silo space at a concrete plant or dry storage 

at a bag facility. Outside of the transportation sector, 

however, PLCs are becoming increasingly important 

for their ability to help reach sustainability targets 

and their voluntary certification programs, which are 

causing PLCs to reach full market penetration scenarios. 

However, in markets that remain with limited PLC 

availability, this demand coupled with the challenges of 

producing both OPC and PLC may result in PLCs being 

considered premium materials and therefore may result 

in higher costs. 

IMPLEMENTATION

Many concrete producers have shared that replacing 

OPC with PLC is accomplished without any 

modifications other than changing the type of cement. 

In general, to minimize risks and difficulties during 

the transition period, it may be useful to treat PLC as 

a cement coming from a different source and therefore 

implement typical control practices such as trial batching 

to ensure adequate performance. Some producers have 

noted that slight adjustments in admixture dosage or 

mixture proportions were needed to obtain equivalent 

performance.(6)

 These changes are consistent with what 

may be expected when changing cements or using a 

cement with a different fineness. In an effort to provide 

information regarding the implementation of PLCs, this 

section offers anecdotal observations of challenges and 

best practices shared by those in the industry. 
9

Anecdotal Challenges

As more cement suppliers transition from OPC to PLC, 

some in the construction industry have reported PLC 

implementation challenges.(6)

 While some of the reports 

may be the result of increased scrutiny due to the novelty of 

the material, others may be consequences of slight changes 

in material behavior that were not accounted for ahead of 

construction or during trial batching. No matter the cause, 

this section reports anecdotal implementation challenges 

that those in the industry recently shared and that may be 

considered while obtaining experience with the use of PLC: 

• Differing air contents and slump between PLC 

concretes and comparable OPC concretes, which may 

require admixture dosage adjustments before field 

implementation. This challenge is often experienced 

when changing cement fineness, aggregate particle 

size, or mixing action. In instances in which a 

decreased slump is not corrected before construction, 

contractors may wish to add water to increase concrete 

workability during field operations, which can lead to 

a decrease in strength and durability performance. 

• Differing sulfate content requirements for PLC 

concretes—especially with SCMs, compared 

with OPC-concretes. Similarly to OPC concretes, 

sulfate imbalances may arise in PLC-concrete 

mixtures with SCMs because of differences in PLC 

sulfate content, which may affect setting time and 

strength development.

• Improper blending of limestone powder with clinker, 

resulting in an inhomogeneous product that can cause 

inconsistent performance. Materials should always 

be mixed and ground homogeneously to ensure 

appropriate performance.

• Improper intergrinding of clinker, limestone, and 

gypsum, which can result in an overground or 

underground cement that may negatively affect 

concrete performance.

• Decreases in early age strength or changes in strength 

development at low or high temperatures. 

• Lower bleed rates, which may result in finishing 

operations occurring prematurely. This challenge is 

typical of concretes using finer cements. Contractors 

tend to use visual observations of the water on the 

surface of the concrete based on their experience 

to determine when finishing operations should 

begin. PLC concretes may bleed more slowly, 

which may result in water being trapped under the 

finished surface and may lead to pop-out or scaling 

deterioration on the concrete surface.

Best Practices

To help mitigate the previously described 

implementation challenges, industry members 

recommend possible best practices that include the 

following measures:

• Perform trial batches by using the same materials

that will be used in the field. Performing trial 

batches using the same SCMs and admixtures 

that are planned for use in the field can improve 

understanding of water demands, setting time, and 

strength development.

• Use tools such as maturity or temperature match

curing to monitor concrete strength development for 

projects in which strength development is critical. 

• Consider the effects of temperatures on the reactivity 

of the material. Be prepared to use extra precaution 

with heating blankets or other cold-weather 

concreting techniques when temperatures are low. 

Conversely, hot weather can exacerbate reductions in 

workability. Adjust the mixture accordingly during 

trial batching and field concrete mixing to account 

for job site temperatures.

• Use tools such as calorimetry to investigate the

early-age reaction behavior of the PLC or the PLC 

in combination with the anticipated admixtures and 

SCMs. Calorimetry can provide information on the 

early-age behavior of concrete, including estimations 

of setting time and temperature development. Use 

such information to adjust the concrete mixture 

design during qualifying operations or whenever 

field performance does not meet expectations.

• Use mockups or monitoring technologies to

determine the optimal time between placing and 

finishing. Make contractors aware that the bleed 

rate is lower and that a visual determination 

of when to finish the concrete may result in 

adverse performance.

• Communicate early and often with cement and

concrete suppliers to identify when the transition 

from OPC to PLC will occur and how the transition 

could affect projects.

• Evaluate production variation (e.g., strength or

air content) prior to transitioning from OPC to 

PLC to provide an understanding of within-plant 

product variations. The use of OPC production 

variation data can help inform evaluation of PLC 

production variation.
10

SUMMARY

PLC provides an option to implement a proven 

technology for obtaining concrete with desired 

performance and reduced environmental impacts. PLC 

(ASTM C595(1)

/AASHTO M 240(2)) is produced using 

the same clinker as that used in OPC (ASTM C150(3)

/

AASHTO M 85(4)

); however, PLC typically replaces 

10–15 percent of the clinker with limestone instead 

of the typical 2- to 4-percent replacement exhibited 

in an OPC.(8)

 The reduced clinker content reduces the 

concrete’s embodied carbon emissions. To achieve 

performance similar to that of OPC, PLC is ground 

more finely during the manufacturing process. The 

increased fineness helps offset the dilution of the clinker 

by accelerating the early-age hydration reactions and 

by providing additional nucleation sites for the clinker 

to react at. Moreover, a fraction of the limestone 

content in PLC is expected to react with aluminate 

phases, further reducing porosity. Differences in cement 

fineness may affect admixture demand; however, after 

slight adjustments to admixture dosages, PLC can be 

used with a seamless transition. Several studies were 

performed to demonstrate that in the United States. (See 

references 8, 9, 52, and 53.) PLC can substitute OPC with 

minimal changes in performance. In general, PLC has 

compressive strength, flexural strength, elastic modulus, 

shrinkage, resistance to chloride ingress, resistance to 

alkali–silica reaction, resistance to scaling, and resistance 

to sulfate attack that are similar to those of its OPC 

counterpart at 28-d ages. Some differences in fresh 

properties might result due to PLC’s increased fineness. 

In particular, PLC concretes may experience minor losses 

in workability and reductions in setting times and may 

exhibit slower bleed rates that require more time between 

placement and finishing. PLC can be used with the same 

equipment and procedures contractors currently use. 

PLCs perform synergistically with SCMs; therefore, the 

SCMs that the industry currently uses in OPC concretes 

can be used for PLC concretes as well. 

As the industry shifts to manufacture more ASTM 

C595(1)

 cements, PLC is becoming more available in 

a wider range of markets. ASTM C150(3)

 OPC may no 

longer be available in certain markets as the transition 

continues. Based on the volume of OPC used in the 

United States in 2021, the replacement of OPC with 

PLC has the potential to reduce CO2 emissions by 

approximately 8 million tons a year, which is the 

equivalent of removing more than 1.7 million cars from 

roadways. In general, PLC can successfully replace OPC 

in concreting applications—with minimal changes to 

current practices and methods. However, this document 

can help ease the transition from OPC to PLC and assist 

in addressing challenges that may arise.

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12

Researchers—This study was conducted by the FHWA Office of Infrastructure Research and Development and Luca 

Montanari of the Turner-Fairbank Highway Research Center Concrete Laboratory and W. Jason Weiss and O. Burkan 

Isgor under contract number 693JJ318F000011.

Authors— Luca Montanari, GENEX Systems, (ORCID: 0000-0002-2886-9096), luca.montanari.ctr@dot.gov

Michelle A. Helsel, FHWA (ORCID: 0000-0001-8112-693X), michelle.cooper@dot.gov

Robert Spragg, FHWA (ORCID: 0000-0001-9205-1486), robert.spragg@dot.gov

O. Burkan Isgor, Oregon State University (ORCID: 0000-0002-0554-3501), burkan.isgor@oregonstate.edu

W. Jason Weiss, Oregon State University (ORCID: 0000-0003-2859-7980), jason.weiss@oregonstate.edu

Distribution—This TechNote is being distributed according to a standard distribution. Direct distribution is being 

made to FHWA division offices and the Resource Center.

Availability—This TechNote may be obtained at https://highways.dot.gov/research.

Key Words—Portland limestone cement, concrete, PLC, sustainability, cement, limestone.

Notice—This document is disseminated under the sponsorship of the U.S. Department of Transportation (USDOT) in 

the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained 

in this document. The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers’ 

names appear in this TechNote only because they are considered essential to the objective of the document.

Quality Assurance Statement—The Federal Highway Administration (FHWA) provides high quality information to 

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reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

OCTOBER 2023 FHWA-HRT-23-104

HRDI-10/10-23(WEB)E

Recommended citation: Federal Highway Administration, 

Portland Limestone Cement (Washington, DC: 2023) 

https://doi.org/10.21949/1521434

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