Experimental and Optimization Modeling of Room-Cured Alkali-Activated Binder Derived from Discarded Limestone Powder

A novel attempt was made in this study to activate discarded limestone powder (DLSP), mostly comprising crystalline CaCO₃. The key mix design parameters were varied to obtain superior strength and workability. For this purpose, the Taguchi method was used. The influence of each of the factors used in this study was assessed by conducting the analysis of variance (ANOVA). To further augment the compressive strength (CS) of the developed alkali-activated binder (AAB), marginal quantities of ordinary portland cement (OPC) were incorporated. In addition to monitoring strength development, selected mixes of alkali-activated paste (AAP) were prepared and utilized to examine the characteristics of the binder by means of XRD, SEM, and FTIR. Alkali-activated DLSP gained a maximum strength of more than 6 MPa when cured at room temperature conditions. Pirssonite (CaCO₃ · Na₂CO₃ · 2H₂O) phase was the dominant character of the AAB formed. Incorporation of OPC extraordinarily improved the morphology, mineralogy, and CS of AAB using DLSP. There was a more than fivefold increment in the strength when 30% of DLSP was replaced by OPC. Phases including Pirssonite, C-S-H, and C/N-A-S-H were formed during the polymerization of DLSP introducing OPC. It is postulated that DLSP can be utilized in synthesizing a sustainable cementitious binder that would enable mitigation of the carbon footprint associated with OPC manufacturing. The usage of universally available DLSP in the synthesis of cementitious binder could significantly boost mass production and the commercial viability of AAB. Further, such encouraged use of DLSP can also lead to enhanced prospects of upscaling the developed laboratory-scale expertise to the industrial levels.