Fresh and hardened properties of alkali-activated fly ash/slag binders: effect of fly ash source, surface area, and additives
Yanru Wang, Yubin Cao, Yuwei Ma, Shanshan Xiao, Jie Hu, Hao Wang
Abstract
The variation of the raw materials is critical for the wide application of alkali-activated fly ash/slag (AAFS) in practice. In this study, four fly ashes sourced from different power plants were collected and analyzed. The calcium content in fly ash had insignificant impact on setting time, flowability and compressive strength of AAFS binders when the slag content was 50%. Low calcium content in fly ash promotes the formation of C-(N)A-S-H gel with high Al substitution and improves the compressive strength at later age. It seemed that the grinding process promoted the dissolution of reactive SiO2 in fly ash, resulting in reduced setting and flowability. The replacement of silica fume promotes the formation of Si-rich C-(N)A-S-H gel with reduced gel pore size. The replacement of metakaolin accelerated the initial reaction and increased the compressive strength of binders at early age due to the reduced gel pore size in C-(N)A-S-H gel.