Effect of Na2O content, SiO2/Na2O molar ratio, and curing conditions on the compressive strength of FA-based geopolymer

Abstract

Many researches have been performed on performance improvement of geopolymer considering low calcium materials and alkaline solutions. In the binder of geopolymer, OPC (Ordinary Portland Cement) which can cause environmental load such as CO2 emission is not used. The mechanical properties of geopolymer are directly affected by various parameters like binder types, SiO2/Na2O molar ratios, alkali activator concentrations, and curing conditions (temperature and period), but very limited researches have been performed on comprehensive evaluation of the influencing parameters. In the work, compressive strength in FA (Fly Ash)-based geopolymer is evaluated considering four test variables covering Na2O content, SiO2/Na2O molar ratios, curing temperature/period, and pre-curing temperature/period. The results reveal that higher compressive strength can be obtained with higher Na2O content, higher curing temperatures, and longer pre-curing periods at the relatively low temperature (23 degrees C). On the other hand, an extension of curing period at high temperatures leads to strength reduction due to increasing macro-pores over 50 nm. Through the various tests, strength grade contours considering SiO2/Na2O molar ratios, Na2O content, and curing temperatures are obtained, which can be utilized for an effective mix design for FA-based geopolymer. (C) 2017 Elsevier Ltd. All rights reserved.