Effect of Alkali Activator on the Standard Consistency and Setting Times of Fly Ash and GGBS‐Based Sustainable Geopolymer Pastes

Abstract

In this study, an attempt has been made to study the effect of alkali activator on the standard consistency and setting times of low calcium fly ash (FA) and ground granulated blast furnace slag (GGBS)- based sustainable geopolymer pastes. Different proportions of FA and GGBS were blended into mixes of geopolymer paste using sodium hydroxide (SH) and sodium silicate (SS) as alkaline activator solution (AAS). Tests on geopolymer pastes for consistency and initial and final setting times were carried out for three different SH : SS ratios of 1 : 1, 1 : 2, and 1 : 3 for both 2.5 M (molarity) and 5.0 M of SH concentration. While increasing the molarity of SH, both consistency and setting time decreased. For all the blended binder mix, the setting time decreases with an increase in the quantity of SS in the alkali activator solution. An increase in the amount of GGBS content in the geopolymer blended binder mix increases the consistency and decreases the setting time. For both 2.5 M and 5 M blended geopolymer mixes, a decrease in the percentage of GGBS and an increase in the percentage of FA increased the setting time. Microstructural studies such as X-ray fluorescence analysis (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FT-IR) analyses were carried out, and the results are presented. The FT-IR spectra for the blended binder mixes demonstrated the formation of geopolymerization and the presence of the functional groups.

Fresh mechanical and durability properties of alkali-activated fly ash-slag concrete: a review

“…The early-age high strength values of AAC is due to polymerization reaction caused by aluminosilicate with the alkaline liquid, leading to the formation of N-A-S-H bonds. Similar observations were reported in other studies [53,59].…”

“…Slag was added into the alkali activated binders' mixture that reduce setting time with increase in slag content. Similar results were reported in other studies [26,31,35,37,53]. Fang et al [54] investigated setting time on the alkaline liquid to binder ratio of 0.35 and 0.4 with varying slag replacement of 15%, 20%, and 25% respectively, ratio of sodium silicate to sodium hydroxide was 2, and molarity of sodium hydroxide was 10 M. The alkaline activator to binder ratio was increased from 0.35 to 0.4 than initial setting time was increased from 189 to 285 min for 15% slag replacement and 102 to 129 min for 25% slag replacement.…”

“…9). Similar results were reported in other studies [27,31,35,53,58]. The early dissolution of aluminosilicate compounds with increasing molarity of NaOH above 16 M resulted in a decrease of CS.…”

Mechanical Properties and Microstructure of Geopolymer Binder Based on Umeanyar Slatestone Powder

“…The results of the compressive strength test as one of the mechanical properties of the binder are very important as a parameter of a test object. Several studies have been carried out using several precursors activated with alkaline activators [31][32][33][34][35][36]. In addition to compressive strength as a mechanical property of binders, physical properties also need to be considered in the manufacture of geopolymer binders.…”

“…The greater the P/A ratio, the higher the compressive strength value {Formatting Citation}. As for the mechanical property in the form of volume weight, the value increases when the P/A and SS/SH ratios increase [35][36][37]. In addition to mechanical properties in the form of compressive strength and volume weight tests, this study will also discuss the microstructure of geopolymer binders based on Umeanyar slatestone powder.…”