Effect of steel slag on fresh, hardened and microstructural properties of high-calcium fly ash based geopolymers at standard curing condition

摘要

This study presents an extensive experimental investigation on the effect of steel slag (SS) usage on the fresh, hardened and microstructural properties of high-calcium fly ash (FA) based geopolymer pastes at standard curing condition. SS was used to partially replace FA to form a binary composite raw material system and six experimental groups were designed according to the replacement levels of 0, 10%, 20%, 30%, 40% and 50% (by mass). The fresh properties including setting times, flowability and viscosity, as well as the hardened properties including compressive strength, flexural strength, elasticity modulus and sorptivity of the geopolymer pastes with different SS contents were investigated. In addition, the microstructural properties of 28-day geopolymer pastes were studied by various microscale analysis methods. The results indicated that the incorporation of SS obviously increased the setting times and flowability of fresh geopolymer pastes. SS can replace up to 20% FA without 28-day compressive strength loss. A strong correlation between sorptivity and compressive strength of hardened geopolymer pastes was observed. The strength of hardened geopolymer paste was related to its porosity and capillary pore volume, and the sorptivity was related to the critical and threshold pore diameters of geopolymer matrix. (C) 2019 Elsevier Ltd. All rights reserved.