The use of lithium salts and supplementary cementing materials to control reactivity of recycled concrete aggregate

This thesis covered the second phase of a study that focused on the reactivity of recycled concrete aggregate (RCA) produced from concrete affected by alkali-silica reaction (ASR). The first phase investigated the reactivity of ASR-affected RCA and the use of Supplementary Cementing Materials (SCM) as a preventive measure. The second phase was carried out to study the efficacy of lithium nitrate, when used individually and in combination with SCM, in suppressing the reactivity of RCA. The use of different dosages of lithium nitrate combined with SCMs reduced expansion due to ASR. However, the expansion results showed that increasing the dosage of lithium beyond a certain level does not help in suppressing the expansion. The high reacitivity of the tested RCA was attiributable to its relatively high alkalis and calcium hydroxide contents that fuel further ASR. The alkalis consumed or contributed from RCA were evaluated through leaching the aggregate particles in distilled water and alkaline solutions at different molarities with and without lithium nitrate. Alkalis consumption was found to decrease when lithium was presented in the leaching solutions. Examining RCA samples under scanning electron microscope (SEM) showed that the crushing process of the RCA exposes fresh surfaces of the reactive virgin aggregate and creates cracks within the particles that provide an easy path of alkalis to reactive sites within the RCA. Examination of the composition of ASR gel showed that exposing the RCA to lithium solution decreased the calcium content and Ca/Si of the gel. This could add to the suggested mechanisms by which the lithium mitigates ASR.