Effect of sodium hydroxide amount on compressive strength of cementitious matrix with high fly ash amount

Abstract

This paper focuses on investigating effect of sodium hydroxide (NaOH) amount on compressive strength of cementitious matrix with high amounts of fly ash (i.e., 80, 85 and 90% by mass) to find out an optimum NaOH amount towards production of artificial fly ash aggregate as natural aggregate replacement for manufacturing concrete. The NaOH amounts added to the matrix were 0, 2.5, 3.0, 3.5, and 4.0% by mass. A ratio of water-to-binder for all mixture proportions was 0.22. The experimental results showed that NaOH amount significantly affected compressive strength of cementitious matrix with high amounts of fly ash. The NaOH use increased compressive strength by 8.6–40.7% at an early age (i.e., 3 days) of all the matrixes, and the matrix containing 3.5% NaOH reached highest compressive strength. However, at the age of 28 days, the compressive strengths of the control matrix without NaOH and the matrix containing 3.5% NaOH were nearly the same. Consequently, the addition of NaOH helped promoting the compressive strength at the early age of the cementitious matrix containing high volumes of fly ash and the optimum NaOH amount was 3.5% by mass.