Influence of accelerating admixtures on high early strength cement performance using heat curing method

Recently, early-strength concrete has been applied widely in high-rise buildings and rigid pavement maintenance due to its advantages in time and cost reduction, and its construction efficiency. Admixtures including setting accelerators and hardening accelerators, are usually used to achieve high early-strength concrete. However, the mechanism of those admixtures at the early age of cement hydration was not clearly examined. Hence, this research investigated the influence of setting accelerators, hardening accelerators and their combinations on the hydration of cement paste using the heat curing method for the application to rigid pavement maintenance, and precast concrete. By evaluating the differences between the setting time, early compressive strength, exothermic curves, XRD patterns, and Fe-SEM images of the cement paste with and without adding Potassium bromide (KBr), Calcium formate (Ca(HCOO)₂), and their combination, the results indicated that the addition of setting accelerators such as Ca(HCOO)₂ had a significant effect on the setting behavior of cement paste instead of the compressive strength enhancement. Therefore, the addition of Ca(HCOO)₂ also had a low effect on the mechanical strength of the paste when increasing the curing temperature. In contrast, the addition of hardening accelerators such as KBr had a greater accelerating impact on the mechanical strength of the cement paste when increasing the curing temperature. Combining a setting accelerator and a hardening accelerator could greatly improve cement paste early-age compressive strength for both normal and heat curing. Based on the XRD analysis, and the Fe-SEM results, numerous hydration products were formed in early-age cement hydration by the addition of 2.0 % KBr with 3.0 % Ca(HCOO)₂, especially in 8 h of 50 °C curing temperature. Hence, this combination significantly enhanced the early mechanical strength of the cement pastes.