2.3　Specimen Preparation Procedures

For all geopolymer mortar/concrete specimens,the weighted sodium hydroxide,sodium silicate solution and water were firstly mixed to form an alkali activator solution.A large amount of heat was released when sodium hydroxide was dissolved in water,so the alkali activator solution was prepared one day before casting of the specimen,to ensure that the solution was cooled down to ambient temperature.The weighted GGBFS,fly ash,sand and coarse aggregate were added into a mixer and dry-mixed for 2 minutes.After the dry materials were uniformly mixed,the alkali activator solution was added and mixed with the solid fraction for another 2 minutes.The final mixture was then poured into the prepared molds.The mixing process of PC mortar and PC concrete was simpler.Weighted solid fractions were dry-mixed for 2 minutes then water was added and mixed with the solid fractions for another 2 minutes.The curing conditions of the PC and GC mortar/concrete specimens were the same.All the specimens were demolded 24 hours after the casting and cured in an environmental chamber with a constant temperature of(21±1)℃and a related humidity of≥95%for 28 days.(https://www.daowen.com)