CRMCA Guest Blog by Joe Diedrich – Technical Services Manager – CEMEX
Considering all of the improvements in terms of environmental impact, energy conservation, and also health and safety performance, the US cement industry has an impressive track record. Owners, designers, and engineers are striving to satisfy the call for more environmentally friendly products and structures and are taking voluntary steps to make this happen. The role of portland, blended, and performance cements will be discussed to give the reader a better understanding of how their use and application will make their projects more environmentally sustainable.
The Portland Cement Association (PCA) annually presents numerous awards to companies and individual cement plants. These include energy star, sustainable leadership, environmental, and safety awards. Cement manufacturers have been recognized for the use of supplemental fuels such as used tires, waste oils, rice hulls, pet coke, waste solvents, wood chips carpet fibers and even sewage sludge. The use of these materials may even replace primary fuel sources and have a direct impact on emissions during the manufacturing process. Recognition is also given for the use of recycled materials such as cement kiln dust (ckd), foundry sand, mill scale and slag, lime sludge, and fly ash. The use of recycled products may also apply towards LEED credits on buildings and structures. The PCA and its member companies continue to strive to implement changes which will have a positive influence on our environment.
Portland cement as we know it today (ASTM C150 and AASHTO M85) has recently changed allowing the addition of up to 5% limestone and some inorganic processing additions. These additions have allowed cement manufacturers to decrease the amount of CO2 created per ton of finish cement manufactured. The performance of these cements manufactured using limestone and/or inorganic processing additions often have the same or better performance characteristics than the control cement. ASTM C150 and AASHTO M85 cover cement Types I and IA, II and IIA, III and IIIA, IV, and V. Both ASTM and AASHTO are prescriptive specifications requiring cement manufacturers to meet specific compositional requirements.
Blended cement specifications are found in ASTM C595 and AASHTO M240. These cements contain the typical Portland cement types mentioned above with the addition of a supplemental cementitious material such as limestone, slag cement, or pozzolan. The most recent addition to C595 and M240 is Type IL cement. Type IL cement allows from 5 to 15 percent limestone added to a Portland cement. The specification also designates Types IS(X), IP(X), and IT (X)(X), the (X) designates the percentage of limestone, slag or pozzolan added to the cement. These specifications also give requirements as air entrained (A) portland cement products. The benefit of using these products is that it allows the producer and end user to use supplement cementitious systems with a healthier impact on the environment. For blended cements, the percentage of slag or pozzolan added equates directly into CO2 reduction for each finished ton of blended cement sold. The CO2 reduction using blended cements often is much greater than using C150 or M85 cement.
ASTM also recognizes strictly performance based cements as specified in ASTM C1157. At the present time, AASHTO does not have an equivalent specification to C1157. ASTM C1157 was designed to meet the needs of the specifiers and end users. Unlike C150 and C595 specifications which are prescriptive, C1157 is performance based and addresses specific needs such as high early strengths (HE) or high sulfate resistance (HS). ASTM C1157 covers 6 types of cement. General Use (GU) is used in general construction. High Early (HE) is used when early or high strengths are required. Moderate Sulfate (MS) is used when moderate sulfate resistance is required. High Sulfate (HS) is used when high sulfate resistance is required. Moderate Heat of Hydration (MH) is used for minimizing the heat of hydration. Low Heat of Hydration (LH) is used when an even greater reduction in the heat of hydration is necessary. ASTM C1157 also allows for an additional option, Option R, which is specified when low reactivity with alkali-reactive aggregates is required. The benefits of using or specifying C1157 cements are numerous. The user and designer can select cements meeting the specific properties in the job requirements. It is then the responsibility of the cement manufacturer to furnish the product and the backup data meeting these specific requirements. Because there are no restrictions on the composition of the cement or constituents used, the potential reduction in CO2 per ton of finished cement can be dramatic.
Comparison of ASTM C150 Portland Cements and C1157 Performance Specification for Hydraulic Cement
|Purpose of Type:||ASTM C150/AASHTO M85||ASTM C1157|
|General Concrete Construction||I||GU|
|High Early Strength||III||HE|
|Moderate Sulfate Resistance||II||MS|
|High Sulfate Resistance||V||HS|
|Low Heat of Hydration||IV||LH|
|Moderate Heat of Hydration||II||MH|
Acceptance of Cement Types by Governing Specifications
|Application||ASTM C150||ASTM C595||ASTM C1157|
|ASTM C55 Concrete Brick||Yes||Yes||Yes|
|ASTM C90 Concrete Block||Yes||Yes||Yes|
|ASTM C94 Ready Mixed Concrete Specification||Yes||Yes||Yes|
|ACI 301 Structural Concrete Specification||Yes||Yes||Yes|
|ACI 318 Building Code||Yes||Yes||Yes|
|Uniform Building Code||Yes||Yes||Yes|
The role of portland, blended, and performance cements can usher in change as we look to the future regarding environmental wants and needs. The cement industry is striving to reduce CO2 emissions per ton of finished cement produced. Until users, specifiers, designers, and owners learn what cement based products are available, people will continue to only use what they know – ASTM C150 and AASHTO M85.
Education is just one key to success when using blended or performance cements. If you would like to learn more, you can ask your local ready mix producer or cement supplier about availability of these products, or visit the following websites: