Durability and Microstructural Properties of Alkali-Activated Mortar: Influence of Constituent Parameters

This study investigates the influence of constituent parameters on workability, compressive strength, microstructure, and durability properties of alkali-activated mortar (AAM) made with ground granulated blast furnace slag (GGBS). The variable parameters considered for AAM mixes were liquid-to-binder (Lq/Bi) ratio and sand-to-binder (Fa/Bi) ratio. The durability of AAM mixes was studied by exposing the specimens to conjoint chloride-sulfate salt solution and acidic solution for a duration of 120 days and compared with specimens cured under ambient condition. The ionic concentration of Na+, Ca2+, and K+ ions was evaluated in a pore solution of AAM mixes. The evolution of microstructure of AAM were analyzed by performing X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), and Fourier transform infrared analyses. The results of seven days compressive strength indicated increase in strength with the Lq/Bi ratio. However, at 28 and 148 days of ambient curing, strength was reduced with an increase in the Lq/Bi ratio. At 148 days, the strength of AAM mixes increased with the Fa/Bi ratio. The strength loss (%) was higher in AAM specimens exposed to the acidic solution than those specimens exposed to the salt solution. The XRD analysis of AAM mixes exposed to the salt solution showed a decrease in CSH gel peak intensity with increase in the Lq/Bi ratio, whereas the opposite variation was found in peak intensity of the CSH gel with increase in the Lq/Bi ratio in AAM mixes exposed to the acidic solution. The FESEM micrographs indicated the presence of gypsum in AAM mixes exposed to the salt solution. The influence of variations in Lq/Bi and Fa/Bi ratios on durability performance and microstructural characteristics of AAM mixes cured under ambient condition and subjected to the salt solution were different than that in the case of exposure to the acidic solution.