Influence of different activators on microstructure and strength of alkali-activated nickel slag cementitious materials

Abstract

Comparisons between three alkali-activators (NaOH, NaOH/Na2CO3, water glass) on the performance of alkali-activated nickel slag cementitious materials (ANC) were made. The properties of ANC, including setting time, mechanical properties, morphology of hydration products and pore structure were investigated by scanning electron microscope (SEM), X-ray diffraction (XRD) and nitrogen adsorption test etc. The average pore size and total pore volume of water glass-activated system (NS6) are the smallest, and then the NaOH/Na2CO3-activated system (NN42), and the average pore size and total pore volume of NaOH-activated system (NH6) are the largest. Interfacial transition zone (ITZ) between aggregate and hardened cement paste (HCP) decreased from large to small is in the order of NS6 > NN42 > NH6. The microcracks of NS6 in HCP is most obvious, and then the NH6, and the microcracks of NN42 in HCP is least obvious. The pore structure and ITZ play dominated role on mechanical properties, and therefore the compressive and flexural strengths of alkali-activated nickel slag mortar are ranked from large to small in the order of NS6 > NN42 > NH6.