A low-cost test method to quantify the reactivity of supplementary cementitious materials (SCMs) has been developed by researchers from the University of Miami College of Engineering in collaboration with The Ohio State University, South Dakota School of Mines and Technology, and University of Toronto.
SCMs are low-carbon (calcium) aluminosilicates used to replace a portion of cement in concrete. These materials, which are often industrial byproducts, make concrete more sustainable and durable and are critical to reduce the massive CO2 impact of concrete. SCMs improve concrete durability because of secondary reactions that they undergo in the alkaline conditions of concrete. While the use of SCMs is critical, shortfalls in the supply of conventional SCMs have necessitated the identification and use of novel SCMs
Unfortunately, specifications by the American Society for Testing and Materials (ASTM International) are often unable to differentiate reactive SCMs from inert materials. Thus, it is critical that SCM reactivity tests be developed. Much work on this has been done across the world, including my own research. Building on the work of others, I co-developed a new reactivity test method as a post-doc at Oregon State University. This modified R3 test can quantify SCM reactivity and differentiate various types of SCMs. In this test, two measures of reactivity, heat release and calcium hydroxide consumption, are quantified for SCMs in an alkaline solution.
Since then, our team at the University of Miami has published extensively on this topic, providing an understanding of reaction kinetics and reactivity for various materials. Receiving the prestigious RILEM Gustavo Colonnetti Medal was due, in part, for my work on SCM reactivity. Professor Luis Ruiz Pestana and I also received a National Science Foundation (NSF) award to study dissolution and reactivity of synthetic SCMs. One Ph.D. student who worked on this topic, Dr. Sivakumar Ramanathan, is now a post-doc at Oregon State University, while another Ph.D. student, Ying Wang, is doing research on reactivity and reactivity tests for unconventional fly ashes, as part of a funded National Cooperative Highway Research Program (NCHRP) project.
Despite many advances, there is still a major issue that must be addressed: Reactivity testing equipment now costs up to $100,000. Our research team wanted to see if we could develop a “cheap” SCM reactivity test method that could estimate the heat release and calcium hydroxide consumption.
A recently published study in the journal Materials and Structures shows that a furnace can be used to measure a heat release proxy (bound water) and estimate calcium hydroxide consumption. The furnace protocol was successful based on thermogravimetric analysis results. While further testing is needed, we found that the new test is extremely promising in differentiating various types of SCMs using bound water and calcium hydroxide consumption.
But as the saying goes, there is no such thing as a free lunch. While costs are cut down by ~90%, the data quality and data scatter results are lower than with more expensive tests. But this tradeoff may very well be worth it for some types of applications.
This work was funded by NCHRP 10-104: Recommendations for Revision of AASHTO M 295 Standard Specification to Include Marginal and Unconventional Source Coal Fly Ashes, with Professor Chris Shearer, at South Dakota School of Mines and Technology as principal investigator.
Looking ahead, we will continue our research on SCMs, as their processing and reactivity are critical to reduce concrete CO2 emissions. To advance this field, we are collaborating with various universities, large companies, and start-ups.
