Performance and optimization design of high-strength geopolymer cold-bonded lightweight aggregate: Effect of silica fume

Abstract

Geopolymer cold-bonded aggregate (GCBA) is a new artificial aggregate manufactured by agglomeration of aluminosilicate precursor powder hardened by alkali activation. This paper presents a multi-objective material design procedure for GCBA based on the simplex centroid design method, using metakaolin (MK), fly ash (FA), and silica fume (SF) as the ternary precursor materials. Based on the test data from 10 groups of GCBAs with designed compositions and response surface models established thereby, the optimal composition domain of the precursors was determined and experimentally validated. The effect of the precursor composition, especially the content of SF, on the performance of GCBA was evaluated. Results showed that in the optimal composition domain of the precursor (36–48 wt% of MK, 33–46 wt% of FA, and 15–24 wt% of SF), the developed GCBA achieved the given high-performance targets of bulk crushing strength higher than 21.0 MPa, the loose bulk density less than 1200 kg/m3, and water absorption less than 10%. SF content (Si/Al ratio) has a great influence on the performance of GCBA: a suitable amount of the incorporated SF (Si/Al<1.7) promoted the formation of K-A-S-H gels in GCBA, leading to an increase in strength and density, and a decrease in water absorption; while excessive SF (Si/Al>1.7) induced a self-foaming reaction, resulting in a porous microstructure and reduced strength and density.