Effect of curing regime on the strength development and microstructure evolution of high strength concrete

Abstract

Autoclaved curing can increase the compressive strength of high strength concrete (HSC) element at early age, but it has a negative impact on the properties of the concrete at long-term service due to the “thermal-damage effect”. This study aims to identify a suitable curing regime for HSC on the premise of ensuring early strength requirements and production efficiency. The influence of six different curing regimes on the strength development of HSC was investigated, and the hydration products of the binder, morphology and pore structure of the concrete were also explored. Results showed that enclosed curing at room temperature in the summer season and hydrothermal curing at 35 °C promoted the early strength development of concrete, and the compressive strength at 1 day exceeded 60 MPa. Continuous strength gain occurred at later age, with a value of 107.9 MPa at 28 day. It was ascribed to the fact that hydration products under these conditions refined the pore structure to produce a denser structure. Hydrothermal curing at 60 °C contributed the strength development at super early age (e.g. 10 hours), but the strength at late age was reduced due to the delayed formation of ettringite and the deterioration of pore structure. Autoclaved curing resulting in the uneven distribution of hydration products and the poor distribution of pore size was not recommended.