Optimum Curing Regimes of Early Strength Concrete Inclusive of Heat Transfer and Hydration Effects

The optimum curing regime (OCR) empirically obtained from a number of small-sized specimens may be overly conservative or inaccurate due to neglecting the effects of exothermic hydration and geometries of full-sized members related to heat transfer. This study presents a theoretical model considering these effects to determine the OCRs of early strength concrete (ESC) in a Pareto set from an extensive design space. To validate the model, experiments were performed to measure the temperature histories and strength development under steam-curing conditions for a full-sized beam segment and match-cured small cylinders made of ESC. Parametric studies showed that energy savings of 7.5%, 20.4%, 42.7%, and 56.3% in steam curing could be achieved with the increase of the maximum steam temperature, sectional area, cooling period in the curing regime, and compressive strength of ESC, respectively. The most significant energy saving, 66.1%, was realized by including the favorable effects of hydration, compared with the results of OCR without hydration for the section considered in this study.

Approximately 28 days or longer are needed in ambient temperatures for flowable fresh normal concrete to reach its hardened strength. The curing period can be shortened significantly by supplying steam for approximately 12 h at elevated temperatures, which accelerates the chemical reactions between cement particles and water (termed hydration) and allows concrete to reach approximately 70% of the target compressive strength in 1 day. Although steam curing may enhance the production efficiency and quality control, it increases the fuel consumption and intensifies the greenhouse effect. In this study, the heat consumption was reduced by the use of early strength concrete and the beneficial effect of increased temperature of ESC through hydration. Using the proposed steam-curing regimes for ESC, significant energy savings of as much as 66.1% were achieved, compared with those attainable through conventional curing regimes that do not include the hydration effect. The proposed curing technology can be applied to any type of concrete to reduce the energy consumption and greenhouse effects in the precast fabrication industry.