Blended Cements

Limestone content of a PLC is chosen by the manufacturer as part of the optimization process. In addition, PLCs are typically ground more finely than PC, which helps with early-age strength development. Manufacturers often also optimize other characteristics of the cement, including clinker chemistry and sulfate form and content. Control of all of these variables provides for equivalent behavior or even slight benefits when limestone is used in amounts up to 15%.

PLCs perform similarly to portland cement in concrete, but represent on average an 8.2% reduction in associated CO2 emissions compared to PC, according to industry-wide average environmental product declarations. PLCs are the easiest change that designers and specifiers can implement to bring down the carbon footprint of their concrete. It requires no different mixing, handling, delivery, or placing equipment. It simply requires an allowance in the specification to use an ASTM C595 Type IL cement instead of an ASTM C150 Type I or Type II cement. PLCs are a readily available and proven technique to reduce the carbon footprint of concrete.

Portland-limestone cements, or Type IL, are general-purpose cements suitable for all uses where the special properties of other cement types are not required. Blended cement uses in concrete include pavements, floors, reinforced concrete buildings, bridges, tanks, reservoirs, pipe, masonry units, and precast concrete products. General purpose cements are also used in cement-specific applications including roller-compacted concrete (RCC), soil-cement, and other geotechnical applications.

For special applications, specifiers can request special properties for Type IL cement by appending modifiers to the cement designation as follows:

• MS – for moderate sulfate resistance
• HS – for high sulfate resistance
• HE – for high early strength, with specific minimum compressive strength requirements for 1 day and 3 days
• A – for air-entraining cement, with maximum and minimum air content limits

Visit the Types of Cement page to learn more.

• Similar performance in concrete
  • PLC is generally designed to replace portland cement at the same cement content to result in comparable concrete performance. The production of PLC includes controlling cement fineness, particle size distribution, and sulfate content to provide similar performance when compared to portland cement made from the same clinker.
• Up to 10% lower CO2
  • By specifying PLC, you can typically achieve a reduction of up to 10% of the CO2 footprint for concrete. For the
    best understanding of your CO2 savings with PLC, ask your cement provider.
• Widespread adoption
  • The cement industry has made great strides toward the acceptance of PLC, allowing the U.S. to transition to environmentally friendlier concrete. Both the availability and acceptance of PLCs have increased over the past decade in the U.S. ACI 318, Building Code Requirements for Concrete Construction, includes PLCs and other blended cements. Along with code recognition, PLCs are similarly included in ACI 301, Specification for Structural Concrete and ASTM C94, Specification for Ready Mixed Concrete. In addition, PLCs are in recognized by the International Code Council, the Federal Aviation Administration, and the American Institute of Architects Master Specification.
• Widely available
  • Many states have been placing PLC concrete pavements for more than a decade—with positive results. For buildings, pavements, bridges, and other applications, PLC concrete is a natural fit for structural members of any type or size, and it’s also great for exterior finishes and hardscaping. As of February 2024, U.S. State Departments of Transportation have accepted the use of portland-limestone cements in all 50 states.

The most common pozzolan to date has been fly ash, which is captured from the exhaust stack of a coal-burning electricity generating plant. The fine material is collected and shipped to cement or concrete producers for use in blended cement or ready mixed concrete. When some of the material can’t be used at the time it’s collected, it is shipped to storage impoundments. Coal ash can include both fly ash and bottom ash, along with harvested coal ash. Bottom ash is not material captured from the smokestack but located at the bottom of the stack. As the electric industry faces pressures to reduce its environmental impacts, the availability of fly ash may decline. In recognition of this, ASTM C618, Standard Specification for Coal Ash and Raw or Calcined Natural Pozzolan for Use in Concrete replaced the term “fly ash” in 2023 with the broader term “coal ash” to recognize harvested coal ash for use in cement or concrete, as well as other forms of coal combustion products with acceptable properties.

Another pozzolan that can be used in a Type IP blended cement is silica fume, meeting ASTM C1240, Standard Specification for Silica Fume Used in Cementitious Mixtures, from the production of silicon and ferrosilicon alloys. Silica fume is ultrafine, so it is typically used in amounts between 5% and 10% by mass of total cementitious materials because it can make concrete mixtures sticky and more difficult to finish.

Natural pozzolans meeting either ASTM C618 or ASTM C1945, Standard Specification for Raw or Natural Pozzolan for Use in Concrete, are an emerging category of materials for use in Type IP blended cement. Due to the evolving availability of coal ash, limitations of silica fume dosage, and the regional aspects of where materials are located, natural pozzolans offer much potential. They typically require minimal processing and are broadly available throughout the U.S.

Portland-pozzolan cement, or Type IP, are general-purpose cements suitable for all uses where the special properties of other cement types are not required. Blended cement uses in concrete include pavements, floors, reinforced concrete buildings, bridges, tanks, reservoirs, pipe, masonry units, and precast concrete products. General purpose cements are also used in cement-specific applications including roller-compacted concrete (RCC), soil-cement, and other geotechnical applications.

For special applications, specifiers can request special properties for Type IP cement by appending modifiers to the cement designation as follows:

• MS – for moderate sulfate resistance, as demonstrated by ASTM C1012 testing
• HS – for high sulfate resistance
• HE – for high early strength, with specific minimum compressive strength requirements for 1 day and 3 days
• A – for air-entraining cement, with maximum and minimum air content limits

Visit the Types of Cement page to learn more.

Unlock the Benefits of SCMs

Coal ash and natural pozzolans are the most commonly used SCMs in the U.S., and the benefits of using these SCMs on fresh and hardened concrete properties is well-established. SCMs such as coal ash and natural pozzolans are commonly used in concrete applications to improve workability, lower the heat generated during hydration of portland cement and to control alkali silica reactions (ASR). Widespread adoption of blended cements in practice can simultaneously lower the environmental impacts and maintain or improve the performance of future concrete applications.

Reduce the CO2 Footprint of Concrete

The use of SCMs is an effective way to reduce the CO2 footprint of concrete for the purpose of minimizing greenhouse gas emissions linked to climate change. The growth in use of blended cements is a key lever to the U.S. cement and concrete industry’s formal commitment to achieve carbon neutrality across the entire cement and concrete value chain by the year 2050. For more information on how the cement and concrete industry is becoming more sustainable, visit www.cementprogress.com.

It should be noted that some codes and specifications restrict >70% slag to non-structural applications. A 2014 survey of cement manufacturers indicated Type IS cements produced in the U.S. had a range of slag content between 20% and 40% by mass.

Portland blast-furnace slag cement, or Type IS, are general-purpose cements suitable for all uses where the special properties of other cement types are not required. Blended cement uses in concrete include pavements, floors, reinforced concrete buildings, bridges, tanks, reservoirs, pipe, masonry units, and precast concrete products. General purpose cements are also used in cement-specific applications including roller-compacted concrete (RCC), soil-cement, and other geotechnical applications.

For special applications, specifiers can request special properties for Type IS cement by appending modifiers to the cement designation as follows:

• MS – for moderate sulfate resistance, as demonstrated by ASTM C1012 testing
• HS – for high sulfate resistance
• HE – for high early strength, with specific minimum compressive strength requirements for 1 day and 3 days
• A – for air-entraining cement, with maximum and minimum air content limits

Visit the Types of Cement page to learn more.

Unlock the Benefits of SCMs

Blast furnace slag is one of the most commonly used SCMs in the U.S., and the benefits of using slag on fresh and hardened concrete properties is well-established. SCMs such as blast-furnace slag are commonly used in concrete applications to improve workability, lower the heat generated during hydration of portland cement and to control alkali silica reactions (ASR). Widespread adoption of blended cements in practice can simultaneously lower the environmental impacts and maintain or improve the performance of future concrete applications.

Reduce the CO2 Footprint of Concrete

The use of SCMs is an effective way to reduce the CO2 footprint of concrete for the purpose of minimizing greenhouse gas emissions linked to climate change. The growth in use of blended cements is a key lever to the U.S. cement and concrete industry’s formal commitment to achieve carbon neutrality across the entire cement and concrete value chain by the year 2050. For more information on how the cement and concrete industry is becoming more sustainable, visit www.cementprogress.com.

Ternary blended cements expand the potential combinations of materials and may optimize the overall performance of these cements for a specific application. For example, a rapidly reacting pozzolan like silica fume might be combined with a slower reacting material such as fly ash to enhance both early and longer-term strength development. Few Type IT products are currently available across the U.S., however, as environmental considerations continue to grow, new sources of pozzolans and other ternary blends are already being developed and studied to meet the anticipated need for lower GWP-impact materials.

Ternary cement, or Type IT, are general-purpose cements suitable for all uses where the special properties of other cement types are not required. Blended cement uses in concrete include pavements, floors, reinforced concrete buildings, bridges, tanks, reservoirs, pipe, masonry units, and precast concrete products. General purpose cements are also used in cement-specific applications including roller-compacted concrete (RCC), soil-cement, and other geotechnical applications.

For special applications, specifiers can request special properties for Type IT cement by appending modifiers to the cement designation as follows:

• MS – for moderate sulfate resistance, as demonstrated by ASTM C1012 testing
• HS – for high sulfate resistance
• HE – for high early strength, with specific minimum compressive strength requirements for 1 day and 3 days
• A – for air-entraining cement, with maximum and minimum air content limits

Visit the Types of Cement page to learn more.

Unlock the Benefits of SCMs

Ternary cements can contain two SCMs, and the benefits of using SCMs on fresh and hardened concrete properties is well-established. SCMs such as coal ash, slag and natural pozzolans are commonly used in concrete applications to improve workability, lower the heat generated during hydration of portland cement and to control alkali silica reactions (ASR). Widespread adoption of blended cements in practice can simultaneously lower the environmental impacts and maintain or improve the performance of future concrete applications.

Reduce the CO2 Footprint of Concrete

The use of SCMs is an effective way to reduce the CO2 footprint of concrete for the purpose of minimizing greenhouse gas emissions linked to climate change. The growth in use of blended cements is a key lever to the U.S. cement and concrete industry’s formal commitment to achieve carbon neutrality across the entire cement and concrete value chain by the year 2050. For more information on how the cement and concrete industry is becoming more sustainable, visit www.cementprogress.com.

While it’s critically important for the concrete industry to make progress towards its goal of achieving carbon neutrality, the concrete performance is equally critical. Concrete mixtures formulated with blended cement can be designed to perform comparably to those formulated with traditional portland cement. However, additional trial batching and evaluation are necessary when material sources change. There are also additional considerations that should be addressed among all project stakeholders for the best and most efficient possible outcomes. The process used may be different for evaluating a new material or different source, as opposed to monitoring changes of an existing source.

A material change to a concrete mixture must be communicated to all stakeholders that could be impacted. Each party plays a vital role and early, transparent, and frequent communication is the key to success. This requires commitment and collaboration among all stakeholders.

A mill test report, or manufacturer’s certification, verifies that the cement complies with the applicable specification. The information in the mill test report is an average of multiple tests run during a production period, typically about a month. Cement manufacturers are responsible for evaluating the test results to ensure compliance with the appropriate standards and project specifications. These test data include time of setting and compressive strength, Blaine fineness, air content, density, insoluble residue, and sulfate content. Optional data such as heat of hydration, chloride content, and alkali content are provided upon request. Note ASTM C595 does not contain instructions for the use of Bogue equations to calculate cement phases for blended cements because the presence of limestone, gypsum, IPAs, and SCMs make those estimates irrelevant and inaccurate (link to Bogue Fact Sheet IS791.02).

The strength uniformity of the predominant cement from a single source may be determined by following the procedures outlined in ASTM C917, Standard Test Method for Evaluation of Variability of Cement from a Single Source Based on Strength. In addition, ASTM C1451, Standard Practice for Determining Variability of Concrete-Making Materials from a Single Source, can be used to provide uniformity data for characteristic properties of other concrete ingredients.

It is possible to perform additional mortar or concrete tests to evaluate cement performance based on specific applications (i.e., flatwork, tilt-up, foundations, paving, etc.). These test mixtures are intended to give the cement manufacturer and/or concrete producer a general idea of the performance of the mixture and its interaction with different chemical admixtures, placement conditions, etc., which can be communicated to downstream stakeholders. Test results that may be helpful include: strength gain curves (1, 3, 7, 28 days), slump and slump loss, shrinkage, bleed timing and rate, water demand, setting time, early stiffening, admixture dosages, and/or an indication of finishability. (Note: No standardized test method currently exists to measure finishability.) Many of these characteristics are impacted by characteristics of multiple concrete ingredients, so noting differences between test mixtures and specific field mixtures can be important.

Mixture optimization is typically achieved by making changes in mixture proportions such as modifying aggregate gradation, adjusting admixture or cementitious materials content in order to maintain the desired concrete properties. In general practice, this translates to using the right amount of cementitious materials to meet the requirements of the specific application. Using more cement to achieve compressive strength in excess of the project requirements is perhaps the fastest way to unnecessarily drive the carbon footprint of a concrete mixture up.

Concrete producers typically perform trial batching to determine if the fresh and hardened properties of a concrete mixture meet the requirements for a specific application. Trial batching is done in advance of production placement using the same materials that will be used in the field to provide the opportunity for adjustments of the mixture components and proportions. The process is often iterative until the optimum proportions are determined. If possible, trial batches should be produced using the exact mixing equipment that will be used for the project. Also consider the effects of placement temperatures on the reactivity of the materials.

As new blended cement products are introduced to the market, relying on existing field test records is not sufficient. Changing the type or amount of any single ingredient in a concrete mixture can affect the fresh and/or hardened properties. SCMs can have varied effects on water demand and air contents. Chemical admixture efficiency must also be evaluated along with the compatibility between cement, SCM, and admixtures. Each aggregate source is different and can influence concrete properties differently as well.
Blended cements with higher proportions of SCMs may not be practical for all construction methods, but designers and concrete producers can make adjustments based on the specific application. For example, SCMs are essential in mass concrete construction to reduce heat of hydration (HOH) but higher SCM contents result in slower strength development. For this situation, the concrete producers may make adjustments for applications where the specification allows later age (for example, 56 days or 90 days) strength for acceptance. Adjustments can also be made for different applications to take advantage of the performance benefits that different SCMs contribute to both the fresh and hardened properties of concrete. SCMs are used to improve workability, control alkali-silica reaction (ASR), improve sulfate resistance, reduce permeability and improve corrosion resistance.

The size of the trial batch is often dependent on the equipment available and on the number and size of test specimens to be made. Relatively small trial mixtures can be made with laboratory precision or larger batches of a quantity similar to normal concrete production can be produced. The larger batches will produce more accurate data. Regardless of batch size, sufficient quantity should be produced to measure all relevant concrete properties (such as workability, density, air content, and strength) to ensure that the mixture performs as desired. Additionally, it may be appropriate to conduct truck trials to validate results obtained during trial batching on selected mixes.

Some examples of the key factors that should be evaluated for trial batched concrete include:

• Compressive strength
• Slump/water demand
• Slump loss
• Bleeding
• Setting time
• Air content
• Strength development

If there are specialty mixture requirements, it may be necessary to run a subset of trial batches to evaluate performance characteristics specified only in certain applications. The specialty performance characteristic may include:

• Sulfate resistance
• Chloride resistance
• Heat of hydration (e.g. mass concrete)
• Shrinkage
• Freeze-thaw resistance

It is critical to communicate any changes to the other project stakeholders by ensuring modified mixture designs are reflected in updated project submittals accompanied by the supporting test data.

The rollout of PLC in recent years has underscored the importance of understanding the impacts of blended cement on fresh concrete properties that are often not specified or confirmed with laboratory testing. Field verification with test sections or mock-ups performed after trial batching is the best method to assess the performance of fresh concrete properties.

Mock-ups are typically constructed by the concrete contractor, in coordination with the concrete producer, which provides the opportunity to demonstrate the anticipated fresh and hardened properties of the concrete mixture. It also allows the contractor to demonstrate that their chosen means and methods are suitable to execute the work using the exact materials, placing/finishing/curing equipment, and procedures in the specific environmental conditions of the project site. This should include expected variations in temperature during placement and any other considerations for repeating the same level of work as the approved mock-up, and the mock-up should be protected from physical damage and retained until final acceptance of structure.

Where feasible, trial batch mixtures can be used to construct the field verification mock-ups to confirm the suitability of the batching, mixing, transporting, and placing systems to be used. The fresh concrete used for a mock-up should be tested for slump, air content, temperature, and density and cast into standard cylinders. A test section or mock-up can also be instrumented to record temperatures and temperature gradients. It can also be cored and tested to provide correlation of strength with standard cylinder test results. The cores can be tested to provide the designer with in-place strength and modulus values for reference during construction. The heat characteristics of the mixture can also be determined using embedded sensors and computer programs, and the data used to determine how thermal control should be applied to the project. Maturity or temperature match curing can also be used to monitor strength development and may have the added benefit of confirming when formwork may be removed.

Field verification should be performed at an acceptable location on the project site. When aesthetics are part of the acceptance criteria, a preconstruction mock-up should be made for each finish to determine the timing and steps involved for special concrete placements and architectural concrete. These mock-ups should serve as the reference to which concrete will be compared for periodic and final acceptance and provide a simulated repair area to demonstrate an acceptable repair procedure with an acceptable color and texture match.