A study on early age properties of hybrid alkali activated mortars cured under ambient condition

Abstract

Fly ash based geopolymer can only be used in precast sections because of the need for heat curing. To expand its application beyond precast members, ambient cured geopolymer is required. In this investigation, an experimental study was performed to assess early age properties of ambient cured hybrid alkali activated mortars where the effect of ordinary Portland cement (OPC) content and molarity of NaOH solution on flowability and compressive strength were evaluated. The hybrid alkali activated mortars were prepared from combination of fly ash and ordinary Portland cement (OPC) at different proportions i.e., 90%:10%, 85%:15%, and 80%:20%, and activated with an alkaline solution. Sodium silicate (Na2SiO3) solution and sodium hydroxide (NaOH) solution were mixed to make alkaline solution. The sodium hydroxide solution was prepared with two different molarity i.e. 8 M and 16 M. The flowability was measured in terms of flow percentage and compressive strength was determined at the age of 1 day, 3 days, and 7 days. The obtained results revealed that flow percentage of hybrid alkali activated mortars declined as the OPC content and the NaOH solution’s molarity increased. On the other hand, compressive strength amplified when OPC content and the molarity of the NaOH solution increased. The compressive strength at the age of 7-day was increased from 19.73 MPa to 22.136 MPa i.e., 12.20 % with a rise in ordinary Portland cement content from 10% to 20% for 8 M NaOH solution. Similarly, for NaOH solution of 16 M, the compressive strength at the age of 7-day was increased by 21.62 % with a rise in OPC content from 10% to 20%. The XRD (X-ray diffraction) analysis revealed that in hybrid alkali activated mortars, there is a coexistence of calcium silicate hydrate (C-S-H) gel and geopolymer gels, resulting in a denser microstructure and higher compressive strength.