Microstructural Characterization and Analysis of Hybrid Alkaline Mortars: Examining the Factors Influencing Fresh and Mechanical Characteristics

This present study aims to develop hybrid paste/mortar by using hybrid alkaline cement, where various influencing factors such as ordinary portland cement (OPC) content (5% and 15%), molarity variations of NaOH solution (6 M, 9 M, and 12 M), and sodium silicate to sodium hydroxide (SS/SH) ratio (1 and 1.5) were varied and their effect on hydration kinetics and fresh and mechanical properties were substantiated by justifications from microstructure analysis. It was found that rapid exothermic reaction of OPC at lower molarity of NaOH solution accelerates the polymerization process, which leads to sudden loss of plasticity. The measured heat of hydration of hybrid paste was higher at higher OPC content and at higher SS/SH ratio. Greater heat of hydration was obtained during the initial hydration period at lower molarity of NaOH solution; however, opposite variation in cumulative heat with molarity of NaOH solution was observed during later stages of hydration reaction. Further, the higher peak intensity of aluminoslicate gels, higher bound water content, and shifting of the Si─ O─ T band toward lower wavenumber suggested the formation of denser matrix at higher dosages of the aforementioned parameters and thus led to higher strength development. Moreover, the increase in bridging oxygen contribution in O 1 s spectra and lower value of nonbridging oxygen to bridging oxygen ratio substantiate the development of a higher extent of aluminosilicate gels by crosslinking more bridging oxygen in the aluminosilicate network.