Study of fly ash-slag geopolymer mortar as a rapid strengthening agent for concrete structures

A fly ash-slag geopolymer mortar (GPM) was developed as an efficient bond material for rapidly strengthening concrete structures. To determine the most significant factors affecting fluidity, setting time, and early compressive strength, we studied the following six factors using an orthogonal test: the amount of slag in the binder (SL/B), the mass ratio of sodium silicate to sodium hydroxide (SS/SH), the molarity of NaOH (MN), the mass ratio of alkali solution to binder (A/B), the superplasticizer addition to binder (SP/B), and the mass ratio of fine aggregates to binder (F/B). Different admixtures have been studied to improve the fluidity of the GPM. Bonding tests were conducted to investigate the differences in the bond behavior of the GPM. The results indicate that SL/B and A/B significantly affected the properties of the GPM. Increasing SL/B was beneficial for enhancing the early compressive strength of the GPM and decreasing its fluidity and setting time, whereas A/B exhibited the opposite trend. It is challenging to meet the requirements of high early strength and fluidity of the GPM by only changing the chemical composition, and admixtures should be added. The 1-day GPM without the interfacial agent exhibited a bond strength similar to that of the PCM at 7 days and the existing interfacial agent was not suitable for the early-strength GPM.