Rheology and microstructure of alkali-activated slag cements produced with silica fume activator

Abstract

The effects of silica fume and sodium silicate-based activators (SFA and SSA, respectively) with different Ms (SiO2/Na2O) values on the setting behavior, rheological, mechanical, and microstructural properties of alkaliactivated slag cement (AASC) were investigated. Setting time test results showed that the setting time of AASCs activated by SFA prolonged significantly with an increase of Ms value opposite to SSA activation case. From the rheological point of view, SFA-activated mixtures exhibited a slower structural build-up in the early stage and better workability retention than SSA-activated mixtures. In addition, SFA mixtures showed lower drying shrinkage and slightly higher mechanical properties as compared to SSA mixtures. Microstructure analysis revealed that the mixture produced by SFA with Ms value of 1.2 had less micro-cracks and a well-packed microstructure as compared to the mixtures produced by SSA. The overall evaluation of the test results revealed that SFA could be more economical and sustainable alternative to SSA with its lower cost, much lower CO2 emissions, and more favorable engineering properties.