The effect of water-to-binder ratio (W/B) on pore structure of one-part alkali activated mortar

Abstract

One-part alkali-activated materials (AAMs) are alternative cementitious materials to respond to the shortcoming of conventional two-part systems. Combining aluminosilicate precursor by-products with ordinary Portland cement (OPC) helps develop a robust performance. It can potentially be used as a patching product for concrete repair materials.Mix design for the one-part AAMs in this report is formulated to ensure its application is according to the structural concrete repair materials Class R4, EN1504-3 specification. In addition, the lower alkalinity alkali activator employed is helpful for economic reasons and less harmful to handle. Furthermore, the addition of powdered admixture enhances the performance of hardened products for retarding effect, provides additional calcium for geopolymer reactions, and offers stable mechanical strength. Finally, an adequate water-to-binder (W/B) ratio has completed the mix design proportion and effectively activated the chemical reaction of the dry mixed ingredients in the geopolymerization process for binding purposes.In this study, the water-to-binder ratio was set in the range of 0.30, 0.35 and 0.40 for all mortar samples at constant mix design formulation and activated by low alkalinity of solid potassium carbonate (K2CO3). At 0.30 W/B ratio, the setting time is delayed to 120 min but shorter than other W/B ratios. Mechanical strength of the mortar increased over time up to 63 N/mm2 at 56 days of curing age, recorded low porosity level of 16%, minimal pore structure area of 17.374 m2/g and documented above 2.0 MPa of pull-off bonding strength that encounters restrained drying shrinkage and expansion impact at 56 days of age under different curing conditions.