Efficiency of Different Superplasticizers and Retarders on Properties of ‘One-Part’ Fly Ash-Slag Blended Geopolymers with Different Activators

Abstract

Currently, there are a very limited number of studies on the effect of admixtures on properties of ‘one-part’ geopolymers. This paper reports the effects of different superplasticizers and retarders on fresh and hardened properties of one-part fly ash-slag blended geopolymers made by different solid activators. Two different grades of sodium silicate, namely anhydrous sodium metasilicate powder (nSiO2/nNa2O = 0.9) and GD Grade sodium silicate powder (nSiO2/nNa2O = 2.0) were used as the solid activators. Five different commercially available superplasticizers, including three modified polycarboxylate-based superplasticizers (denoted as PC1, PC2, and PC3) and two naphthalene-based superplasticizers (denoted as N1 and N2), as well as three different retarders, including sucrose, anhydrous borax and a commercially available retarder, were investigated. Workability, setting time and compressive strength of the mixtures without and with addition of each ‘individual’ admixture were measured. The results showed the effect of admixtures on the properties of the one-part geopolymers significantly depended on the type of solid activator and the type of admixture used. When GD Grade sodium silicate powder was used as the solid activator, all investigated admixtures not only had no positive effect on the workability and setting time, but also significantly reduced the compressive strength of the mixture. However, when anhydrous sodium metasilicate powder was used as the solid activator, the PC1 and sucrose were the best performing superplasticizer and retarder, respectively, causing no reduction in the compressive strength, but significant increase in the workability (up to + 72%) and setting time (up to + 111%), respectively as compared to the mixture with no admixture. In addition, the results also showed that addition of ‘combined’ admixtures (i.e., PC1 in the presence of sucrose) significantly increased the workability (up to + 39%) and setting time (up to + 141%), but slightly reduced the compressive strength (−16%) of the mixture activated by anhydrous sodium metasilicate powder, as compared to the mixture with no admixture.

Performance of Porous Slabs Using Recycled Ash

“…The superplasticizer density was 1.1 kg/L. The chloride content was less than 0.1%, and the alkaline content was less than 3%, which confirms Bong et al [ 52 ].…”

Waste-Based One-Part Alkali Activated Materials

“…According to the authors [ 20 ], 6 wt.% of borax is the suitable amount since it improved the paste fluidity without significantly affect the mechanical properties of the samples. Bong et al [ 21 ], besides testing the effect of additives, studied two activators (as powder): Anhydrous sodium metasilicate and sodium silicate. The authors observed that the workability and setting time of the AMMs mixtures prepared with sodium silicate did not fill the requirements, even when additives were used, and a decrease of the compressive strength was observed.…”

Sucrose retards the reaction of non‐calcium geopolymers: An implication for developing kinetics‐controlling admixtures

“…A study regarding the effects of sucrose on the hydration of C 3 S (i.e., a main hydrous phase in ordinary portland cement) confirmed the adsorption of sucrose at hydrated silicate sites based on NMR characterizations, 35 further suggesting the potential of sucrose to control the reaction kinetic of aluminosilicates. However, to the best of our knowledge, as also discussed above, the effects of sucrose on setting have been investigated only in geopolymer pastes that contain additional calcium or portland cement 22,36‐38 …”

“…However, to the best of our knowledge, as also discussed above, the effects of sucrose on setting have been investigated only in geopolymer pastes that contain additional calcium or portland cement. 22,[36][37][38] Our objective in this study is to examine the effects of sucrose on the reaction kinetics of non-calcium geopolymers, including both metakaolin-based samples and synthetic gels. Metakaolin is a pure and amorphous aluminosilicate precursor material that facilitates any mechanistic understanding of the reaction kinetics of geopolymers.…”