Rheological, fresh, and mechanical properties of mechanochemically activated geopolymer grout: A comparative study with conventionally activated geopolymer grout

Abstract

In this research, a mechanochemically activated geopolymer (MG) grout is adopted to activate slag, fly ash, sodium hydroxide, and sodium silicate by dry grinding in a ball mill for 2 h, after which water is the only additive required to initiate the geopolymerization reaction. A conventionally activated geopolymer (CG) grout was also evaluated for comparison purposes. Twenty-four different slag and fly ash mixtures have been prepared at different slag/fly ash ratios (0S100F, 50S50F, 75S25F, and 100S0F) at three different molarities of sodium hydroxide (1.25, 2.5, and 3.75) to assess the behavior of both MG grout and CG grout. A series of tests were examined, such as rheological characteristics, setting time, bleeding, unconfined compressive strength (UCS), ultrasonic pulse velocity (UPV), and scanning electron microscopy (SEM). The experimental results showed that the mechanochemical activation technique reduced the rheological characteristics and fresh properties (setting time and bleeding) of geopolymer grout compared to the conventional activation process. Considering mechanical properties, both UCS and UPV of MG grout were higher than that of CG grout. Furthermore, slag content and sodium hydroxide concentration significantly affected the rheological, fresh, and mechanical properties of all geopolymer grouts regardless of the activation method. Both the rheological characteristics and mechanical properties were increased considerably with the increase in molar concentration and slag content. Whereas the bleeding capacity and setting time dramatically reduced with the increase of molar concentration and slag content.