Effects of mixing duration on engineering properties of geopolymer concrete

Despite being investigated for over 50 years, the adaptation and application of geopolymers in construction are still very limited. One major reason behind this slow and often underappreciated acceptance of geopolymer concrete in industries is the lack of reports outlining observations and knowledge gained in field applications. Although geopolymers are well-accepted in the research community owing to their comparable or even better performance as a substitution of cement as a concrete binder, major initiatives still need to be undertaken in studying and reporting field observations of this product. The flash set phenomenon of a proven geopolymer concrete mix on a field trial motivated this investigation to identify the effects of mixing duration on geopolymer concrete performance. As such, this paper describes laboratory investigations undertaken to study the fresh, hardened, and durability properties of geopolymer concrete incorporating 65% fly ash and 35% slag, mixed for durations of 1 min and 10 min. The longer mixing duration significantly improved the workable time, at least five times longer workable time was achieved. It also resulted in relatively better mechanical strength and durability. The importance of proper mixing of geopolymer concrete constituents has been emphasized based on knowledge acquired from a combination of field trials and subsequent laboratory experiments.