Pozzolan

Both are what are called pozzolans, reactive materials that help make the concrete stronger.

The U.S. Bureau of Reclamation (Gilliland & Moran 1949; Moran & Gilliand 1950) developed a mortar bar expansion test using Pyrex glass as a “standard reactive aggregate” to evaluate the efficacy of pozzolans for controlling ASR. For example, in the specification for the Davis Dam in Arizona the requirement for the pozzolan, among other properties, was to affect a reduction of at least 75% in the 14-day expansion of mortar bars produced with high-alkali cement plus 20% pozzolan plus Pyrex glass when stored over water at 100°F (38ºC).