Effect of curing on the compressive strength development in structural grades of geocement concrete

Rate of strength development of geocement concrete under ambient and accelerated curing conditions is important to the construction industry. This paper reports the results of an experimental investigation into the development of compressive strength with age for Grades 40, 50, 65 and 80 geocement concretes subjected to ambient (20 °C) and accelerated (70 °C for 4 and 24 h) curing conditions. Two types of powder-activated geocement, having fly ash: slag (ground granulated blast furnace) weight ratio, of 7:3 and 4:6, were used to produce four grades of geopolymer concrete mixtures. For comparison, similar grades of ordinary Portland cement concrete were also investigated for their strength development under similar curing conditions. At ambient curing condition, similar to Portland cement concretes, geocement concretes showed gradual strength development with age at a decreasing rate. However, geocement concretes showed 15-20% increase in strength from 28 to 90 days, compared to 3-8% for the Portland cement concretes. Grade 65 geocement concrete recorded 45% and 79% of its 28-day ambient cured strength after 4 and 24 h of heat-curing at 70 °C. Empirical relationships between heat-cured and 28-day ambient-cured strengths for geocement concretes are developed and could be used by precast industry for quality assurance purpose.