Production of geopolymer concrete using natural pozzolan: A parametric study

Abstract

An experimental investigation was undertaken to study the mechanical properties of geopolymer concrete (GPC), produced with Jordanian natural pozzolan (JNP) as base material and commercially available alkaline solution made of sodium silicate (NS) and sodium hydroxide (NH). GPC mixtures with limestone aggregates were proportioned considering various ratios of NSNH-to-JNP, and NS-to-NH, and concentrations of NH then tested for fresh and hardened properties using the technology currently used for conventional concrete. The compressive strength was determined over time for specimens that were either cured in laboratory air or dry cured in an oven for 24 or 48h at three different curing temperatures (40, 80, and 120°C) after 24h of casting. Scanning Electron Microscopy (SEM) images were also taken for samples representing various GPC specimens and dry curing temperatures. The parameters considered in proportioning various GPC mixtures had significantly impacted strength; confirming the behavior observed in literature; with optimal mixtures achieving matured compressive strengths in excess of 30MPa. Dry curing of GPC in an oven at 40°C and 80°C for less than 48h imparted significant increase in compressive strength at 25% and 32% of that obtained at normal curing in laboratory air, respectively. Extending dry curing period at the present temperatures beyond the first day after casting has resulted in a limited increase in compressive strength at 28days. The present GPC mixtures demonstrated high early strength development exceeding 70% of ultimate strength at three days of dry curing. SEM pictures confirmed the behaviors noticed for compressive strength for GPC mixtures, prepared at various proportions or heat cured at various temperatures.