Enhancement of the properties of silicate activated ultrafine-slag based geopolymer mortar using retarder

Abstract

Application of high-volume slag based geopolymer mortar is often confined to usage in controlled environments due to its limited flexibility in controlling the setting time. The main aim of the study is to regulate the fast setting of Ultrafine blast furnace slag (UBFS)-based geopolymer mortar (GM) by utilizing mineral admixture. UBFS, partially replaced by Flyash (FA), are investigated by both sodium hydroxide (SH), and a combined solution of sodium hydroxide and sodium silicate (SHSS) of different alkali content and the fresh properties are modified by incorporating Borate, a Type B retarder. The microstructure of the GM is studied by conducting X-ray diffraction (XRD) and Field emission scanning electron microscope (FESEM) tests. Test results indicate that GM containing a high volume of UBFS exhibits prompt setting with a significant mechanical strength when activated by SHSS solution. High molar concentration (M) of SH within 12 M largely enhances the strength of GM, and a good correlation between flexural strength and compressive strength is obtained for SS/SH of 1.5. Application of Borate successfully controls the setting, which also assists in retaining the fluidity of GM. The optimal retarder dose of 4% produces a densely packed microstructure, resulting in improved mechanical properties. The test results show that an ideal GM mix has a strong potential to achieve an acceptable fresh property with improved mechanical strength.