Early strength and durability of metakaolin-based geopolymer concrete

Approaches to improve the early strength of geopolymer mortar were studied in order to apply it to a fast-tack concrete pavement repair. The effects of modifying the molar ratio of silicon dioxide/sodium oxide (SiO2/Na2O) of the alkaline solution in a conventional geopolymer mixture and the addition of calcium aluminate cement and slag were studied. The early strength measured in the experiments was at curing times of 8 and 24 h, which are typically construction controlling times for pavement repair. It was found that a molar ratio of silicon dioxide/sodium oxide of 1.0 gave the shortest curing time and the highest early strength after 24 h. Adding calcium aluminate cement was found to reduce the curing time, but decrease the early strength. Slag substitution helped workability, but reduced the early strength at 8 and 24 h. Durability was also tested for the purpose of finding an economical pavement repair solution. A freeze-thaw durability experiment of the suggested metakaolin-based geopolymer concrete was conducted. It was found that a mix with a silicon dioxide/sodium oxide molar ratio of 1.0 produced higher durability than a mix with a silicon dioxide/sodium oxide molar ratio of 1.4. The geopolymer concrete mix with slag showed less weight loss than the other mixes.