Use of a Lithium-Bearing Admixture To Suppress Expansion in Concrete Due to Alkali-Silica Reaction

Abstract

The findings of a laboratory study on the effects of a lithium-based admixture on alkali-silica reaction are presented. The admixture essentially represents an intermediate stage in the lithium extraction process of the ore spodumene. Spodumene ore is normally crushed and fired in a kiln to “untie” the lithium prior to its extraction. The material at this stage is known as decrepitated spodumene (DS). DS is basically an amorphous alumino-silicate that contains significant quantities of “available” lithium. As such, DS has the potential to act both as a pozzolanic mineral admixture as well as a chemical suppressant of alkali-silica reactivity. Laboratory testing included pore solution studies of pastes and mortars containing DS and expansion studies of mortar bars containing Pyrex glass (ASTM C311) and concrete prisms containing reactive aggregates from three different sources in North America. The results show that significant quantities of lithium are released by the DS into the pore solution of pastes and mortars over time. After 1 year, the Li+ concentration of pastes with 15 to 20 percent DS (mass replacement of high-alkali cement) was approaching 0.3 moles/liter. The efficacy of DS in controlling expansion in concrete containing reactive aggregates was found to depend on the nature of the reactive aggregate. Higher quantities of DS were required with more reactive aggregate. This is thought to be due to the rapid expansion observed for concretes containing such aggregates. The expansion occurs before significant lithium is released from the DS, and thus higher levels of DS are required. It is possible that the efficiency of DS with such aggregates may be improved by increasing the fineness or modifying the manufacturing process.