What’s Old Is New Again: A Vision and Path Forward for Calcined Clay Use in the USA

Abstract

Calcined materials have a long history of use in concrete structures, with some now over 80 years old. Beginning in the 1950s, by-product supplementary cementitious materials (SCMs) began to replace natural pozzolans because of cost, availability, performance, and benefits of reuse. Specifications, mix designs, and performance data collected were built around an assumed continuous supply of these recycled SCMs. SCM availability, quality, and cost, especially for fly ash, is now in question. This has brought significant interest in alternative SCMs to provide durability in concrete structures. Calcined clay now appears to be a viable option going forward for concrete mixtures in the United States, especially when combined with ground limestone. This paper discusses the history of SCM use in the USA, potential for calcined clay use in concrete in the USA, barriers to use, and a path forward to overcome those barriers with only minimal changes in concrete specification, production, and placement methods. This paper will also discuss options to apply these and other potential strategies to other markets to speed adoption of concrete calcined clay use.