ASTM Advances Sustainable Non-Hydraulic Cements

Concrete pavers produced at New Jersey plant with cements that harden when cured with carbon dioxide.

ASTM C01 Committee on Cement recently approved the first standards addressing non-hydraulic cements and specifically, cements that require carbonation curing. With almost several years in the making, ASTM C1905, Specification for Cements that Require Carbonation Curing and ASTM C1910, Standard Test Methods for Cements that Require Carbonation Curing set the requirements for specifying these unique cements. Approval emerged from Committee C01, which in 2016 broadened its scope to include authority over new standards for cements that do not require water to harden, aka non-hydraulic cements.

C1905 and C1910 are under the jurisdiction of ASTM C01.14 Subcommittee on Non-hydraulic Cements, chaired by this article’s author. Subcommittee members rendered considerable assistance in developing and refining these two standards. Additional assistance came from Solidia Technologies and Braun Intertec, who collaboratively developed straightforward carbon dioxide curing equipment and procedures in C1910. The test method used for measuring the permanent capture of CO2 is ASTM C1872 Test Method for Thermogravimetric Analysis of Hydraulic Cement. This test method also can assess the mineralization of CO2 gas into solid carbonates in non-hydraulic cements.

Compared to the 150-plus years of hydraulic cements supported by many ASTM standards, non-hydraulic cements are a recent development. Some non-hydraulic cements harden by permanently capturing or ‘mineralizing’ CO2 during their hardening or curing process. ASTM C1905 enables trade for this new group of cements for use in the manufacture of (non-steel reinforced) concrete products. 

Commercial acceptance of non-hydraulic cement was demonstrated several years ago when a New Jersey producer sold over 1.5 million square feet of concrete pavers cured with CO2. The advantages of the new cement include a cure time of less than 24 hours, no primary efflorescence, and brighter colors due to a lighter cement. The technology has direct applications to the manufacture of concrete masonry units, roof tiles, and other concrete products.

The next step for implementing these new standards is to reference ASTM C1905 in ASTM C936 for concrete pavers and ASTM C1782 on concrete paving slabs. These changes will be introduced over the coming months in ASTM C15.03 Subcommittee on Concrete Masonry and Related Products.

The next step for implementing these new standards is to reference ASTM C1905 in ASTM C936 for concrete pavers and ASTM C1782 on concrete paving slabs. These changes will be introduced over the coming months in ASTM C15.03 Subcommittee on Concrete Masonry and Related Products.

Carbonated materials are not limited to cement meeting ASTM C1905. Supplementary cementitious materials (SCMs) can be carbonated and the precursor materials for making ASTM C1905 cements can also be processed to have pozzolanic properties. Any replacement of portland cement clinker by SCMs results in reduced CO2 emissions and a lower global warming potential. Cement manufacturers may be interested in SCMs carbonated at the cement plant with waste CO2. With additional processing, these SCMs can be blended with portland-limestone cement to further reduce CO2 impacts, or as supplied as a standalone SCM for ready mixed concrete producers. 

Carbonated SCMs have been shown to increase concrete performance exhibiting better strength, durability, and resistance to expansive aggregates compared to using diminishing supplies of conventional SCMs such as fly ash. ASTM Subcommittee C09.24 on SCMs is balloting a performance standard for SCMs that do not necessarily comply with ASTM standards for fly ash, slag, silica fume or ground glass. This emerging standard will advance innovative SCMs while ensuring performance when evaluated according to ASTM C1709, Standard Guide for Evaluation of Alternative Supplementary Cementitious Materials (ASCM) for Use in Concrete. 

At this writing, an ISO-compliant product category rule (PCR) for cements that require carbonation curing is moving forward via ISO program operator Smart EPD with anticipated completion in mid-2024. PCRs establish requirements and guidelines for developing environmental product declarations (EPDs) that characterize environmental impacts for products. In the meantime, as with most ASTM test methods, there will be additional work in improving testing and conducting an inter-laboratory study to add to the single laboratory precision and bias statement currently in C1910. 

In summary, these two new ASTM standards represent a significant step forward by ASTM International in advancing the sustainability of cement and concrete by opening new markets for non-hydraulic cements while offering enhanced cement and concrete performance.

Larry Sutter, Ph.D., P.E., has over 40 years’ experience in materials characterization, engineering and research, with the past 25 years focusing on cement and concrete. He has led numerous concrete research studies and is widely published in the areas of reuse of industrial byproducts such as fly ash and slag cement, and concrete durability. His Michigan-based consultancy, Sutter Engineering, also provides targeted training for engineers, architects, and laborers on concrete-making materials, with an emphasis on new and alternative materials, and how to integrate them into construction practices.