Synthesizing alkali-activated binder from locally available sedimentary rock as precursors

Significant research efforts have been made recently to broaden the selection of precursors for alkali-activated binders, especially to utilize the locally available resources. This study presents the experimental investigation of utilizing sedimentary rocks rich in silica and alumina excavated during the construction of Jurong Rock Caverns in Singapore for alkali-activated binders. The precursors were synthesized by calcinating rock powder mixed with alumina and sodium hydroxide. The crystalline structure of the quartz and albite was broken after being subjected to calcination, and disordered, amorphous minerals were formed. The influence of the initial Si/Al and Na/Al molar ratios on the chemical composition and reactivity was investigated. The degree of polymerization decreased with the increase in the alumina and sodium hydroxide content. Higher alumina content also promoted the formation of aluminosilicate crystals during the cooling process, which reduced the reactivity of the precursors. The compressive strength of the alkali-activated binder was found to be dependent on the concentration of the soluble Si and Al released during alkali activation. Overall, the excavated sedimentary rocks could be used as potential precursors in alkali-activated binders.