UCLA

This study investigates experimentally and numerically the addition of microencapsulated phase change materials (PCMs) into concrete pavements at early ages to limit (i) temperature rise caused by cement-water hydration, (ii) cooldown rate, and (iii) the associated risk of thermal cracking. First, the effect of water-reducing admixture (WRA) on the heat generation rate from cement hydration was quantified using isothermal calorimetry. Second, large cubic PCM-mortar composite specimens representative of a common pavement geometry were prepared and placed in an environmental test chamber simulating realistic diurnal conditions. The results showed that the presence of PCM can reduce considerably the temperature rise and cooldown rate across the cementitious composite section within the first 24 hours following placement provided the PCM melting temperature is selected carefully. This was in spite of the fact that the lower thermal conductivity of PCM-composites inhibited heat dissipation. A transient 1D thermal model of pavement section was developed to simulate the temperature evolution and the rate of change in temperature within PCM-mortar composite sections. Good agreement was found between model predictions and experimental measurements. In addition, a parametric study was carried out to assess the effects of the PCM melting characteristics (temperature, temperature window, latent heat) on local temperature in PCM-mortar composites. The constitutive relationships and the numerical model developed as part of this study can be used to inform the design of concrete pavements containing PCMs for early-age crack resistance.