Concrete hydration, temperature development, and setting at early-ages.

摘要

Findings from past research efforts have demonstrated that the concrete temperature development during the first 24 to 72 hours has a major impact on long-term pavement performance. The development of excessive portland cement concrete (PCC) temperatures may result in reduced pavement performance. These factors emphasize that concrete temperature control during construction in hot weather conditions is essential to improve the durability of PCC pavements.; The primary objective of this study is to develop mitigation techniques to control the in place temperature development of early-age concrete, as this will improve the performance of PCC pavements constructed under hot weather conditions. Longer lasting PCC pavements will be produced if the assumptions made during design are achieved in the field. This study proposes a method to integrate the design assumptions to the construction process by means of an end-result temperature control specification.; During this study, a general hydration model for cementitious materials and a model to predict the temperature gain in hardening concrete is developed and calibrated. The temperature prediction model was calibrated for field conditions with data collected from seven concrete paving projects. The model accounts for different pavement thicknesses, mixture proportions, cement chemical composition, cement fineness, amount of cement, mineral admixtures, material types, climatic conditions, and different construction scenarios. The temperature prediction model will enable the development of performance based specifications to guard against premature concrete failures. This model will further provide the designer, contractor, and specification developer with the means to evaluate and quantify the effect of most of the various complex interactions that affect the concrete temperature development during early-ages.; A model to predict initial and final setting of hardening concrete is presented, and calibrated, with data collected under laboratory and field conditions. The effects of concrete temperature, different cements, and mineral admixtures on the initial and final times are characterized.; Finally, an innovative temperature control specification is presented, which encourages contractor innovation and focuses on material selection for the particular location and environmental conditions. This approach accounts for the impact of modern paving materials, and will ensure improved concrete performance under hot weather placement conditions.