Experimental Characterization and Multi-Factor Modelling to Achieve Desired Flow, Set and Strength of N-A-S-H Geopolymers.

The interaction between compositional ratios, namely, SiO/AlO, NaO/AlO, HO/NaO and the liquid-to-solid ratio, triggers mutual sacrifice between workability, setting time and strength for N-A-S-H geopolymers. The present study characterizes the mechanism underlying the effect of these compositional ratios and, in turn, develops guidelines for mixture design that requires a simultaneous and satisfactory delivery of these engineering properties. The experimental results show that an increase in either the SiO/AlO, NaO/AlO or HO/NaO ratio raises the liquid-to-solid ratio, which in turn improves the workability of fresh mixtures. A continuous increase beyond 2.8 for the SiO/AlO ratio boosts its strength, but also significantly extends its final set. Lowering the NaO/AlO ratio from 1.3 to 0.75 raises the compressive strength significantly, while the shortest final set was seen at the median value, 1.0. A HO/NaO ratio of 910 yields the highest strength and the fastest final set simultaneously, due to the maximized degree of geopolymerization. Moreover, the accompanying sensitivity analysis indicates that the workability depends chiefly upon the HO/NaO ratio, the final setting time on the SiO/AlO ratio and, that the compressive strength relies on both of them. Also, this study proposes an optimal range of 2.83.6 for SiO/AlO, 0.751.0 for NaO/AlO and 910 for HO/NaO to guarantee high strength, together with high flow and within the allowable final setting time. Furthermore, multi-factor predictive models are established with acceptable accuracy for practitioners to regulate oxide compositions in N-A-S-H geopolymers, which will guide future mixture design.