Hydration of Cement Pastes Containing Accelerator at Various Temperatures: Application to High Early Strength Pavement Patching

Accelerators are used to accelerate cement hydration, thereby reducing setting time and increasing early age strength gain. Accelerators are typically developed for use at low temperatures; however, they may be used in other applications such as high early strength concrete mixtures for pavement patching, which requires short closure time. In this study, the effects of a commercial accelerator on the hydration of cement pastes made with Type I ordinary portland cement are investigated at four temperatures. At lower temperatures (10°C and 23°C), the accelerator decreases the time to reach the silicate peak and sulfate depletion peak time and increases the peak heights. At higher temperatures (37.5°C and 50°C), the silicate and sulfate depletion peak times or heights do not change appreciably. At high temperatures, the pastes are very likely undersulfated, as indicated from calorimetry data with added sulfate. The accelerator does not significantly increase the cumulative heat release at 72 hours in any of the pastes. The results from pastes in the laboratory are used to interpret flexural strength results obtained from field concrete. Flexural strength results indicate that accelerated concretes cured at high temperatures have lower strength as compared to concretes cured under standard curing temperatures. The addition of sulfate increases the flexural strength of accelerated concrete cured at higher temperatures. From these results, it is evident that the accelerator is not effective at higher temperatures and that the addition of accelerator may negatively impact hydration and strength gain at higher temperatures. The addition of sulfate alleviates some of the negative impact of accelerator at higher temperatures.