Effect of multiple chemical activators on mechanical property of high replacement high calcium fly ash blended system

•Li2CO3, Na2CO3, K2CO3 and Al2(SO4)3 were used to enhance mechanical property of the HRHF blended system.•The different activation mechanisms with multiple activators were revealed in the HRHF blended system.•The combination use of Li2CO3 and Al2(SO4)3 was effective to obtain the superior mechanical property, and the mechanism of which was researched. Although the alkali activation of high calcium fly ash has been well studied, there is limited research has been conducted about the activation with carbonates and aluminum sulfates in the high replacement high calcium fly ash blended system. In this study, the activation effect of four types of chemical activators (Li2CO3, Na2CO3, K2CO3 and Al2(SO4)3) on the mechanical property was researched, and the high replacement of high calcium fly ash was kept as 50%. The activation mechanisms were revealed by the analyses of the non-evaporated water content, the reaction degree of fly ash and the hydration products. It was found that the addition of Li2CO3 was more effective to enhance the compressive strength development and reduce the setting time of the blended mixture due to distinct acceleration of hydration of cement with more formation of C-S-H. Due to the effective promotion of hydration of cement and activation of pozzolanic reaction by the addition of Al2(SO4)3, the combination of 0.6% Li2CO3 and 0.6% Al2(SO4)3 was used to obtain the superior mechanical property, and the mechanism of which was also proposed that the existence of the LiAl2(OH)7·2(H2O) and Li2SO4·H2O might induce the precipitation of amorphous Li-containing C-S-H and that would act as the seeds for the nucleation of C-S-H, so that the compressive strength development would be faster. However, the above hypothesis requires further research to confirm it.