Effect of curing conditions on physico-mechanical properties of metakaolin-based geopolymer concrete containing calcium carbide residue

Today, hydraulic concrete remains the most used construction material in spite of the very polluting character of its main binder, namely portland cement. However, alternatives exist, such as geopolymer concretes. Current studies reported that the performances of geopolymer concretes can significantly be affected by the curing conditions, among other parameters. The present study specifically assesses the physico-mechanical properties of geopolymer concrete produced in ambient conditions, i.e., cured at controlled temperature (20 +/- 2 degrees C) and uncontrolled ambient temperatures (30 +/- 5 degrees C) of the laboratory. The metakaolin (mk)-based geopolymer concrete was designed by partial substitution of mk with 10 to 15 wt% ccr (calcium carbide residue), a lime-rich industrial by-product. The concrete was characterized in fresh state and hardened state after curing for 7, 14, and 28 days. The results indicate that the curing temperature has a significant effect on the physico-mechanical properties of geopolymer concretes. Setting times are longer at 20 degrees C (> 2970 min) than at 30 degrees C (< 2500 min) for all mix designs. At 7 days, the compressive strength increased by 77% (6.1 to 10.8 mpa) and 67% (3.1 to 5.2 mpa), respectively, for the concrete containing 0 and 15% ccr cured from 20 to 30 degrees C. At 14 days, the compressive strength increased by 26% (12 to 15.2 mpa) for the concrete containing 15% ccr cured from 20 to 30 degrees C. Although their 7-day strengths are lower compared to the reference concrete, all the samples containing ccr reach better strength from the 14th day regardless of the curing temperature.