Effect of magnesium sulfate on properties of low calcium fly ash based-geopolymer- treated hemp shiv bio-concrete

Abstract

Sulfate attack is one of the major threats to concrete structures. In this study, strength degradation, by magnesium sulfate (MgSO4) reaction, of low-calcium fly ash geopolymer-hemp shiv concrete was carefully investigated. The hemp shiv was pretreated with AlCl3-KOH to prevent water absorption. Air and water curing were also performed to elucidate the effects of air and water degradation that might have co-contributed to the degradation of the geopolymer concretes. After the MgSO4 treatment, the strength reductions of the geopolymer-hemp shiv concretes were 1.5–2.5 MPa in flexural mode and 0.2–0.6 MPa in compressive mode while the strength reduction of the geopolymer matrix was around 2 MPa in both strength modes. The results suggested the ability to prevent sulfate attack of the AlCl3-KOH pre-treatment and thus degradation was primarily from the geopolymer matrix. However, the TGA and XRD analyses did not observe relevant phase changes or significant occurrences of the strength detrimental phase such as brucite (Mg(OH)2) in the matrix bulk after the MgSO4 treatment, suggesting that the degradation was not according to these factors. Besides, similar degradation was observed in the water-cured samples. Strength degradation was suggested to be due to the migration of sodium ions from the geopolymer gel structure in the aqueous-curing system causing structural disintegration.