Moisture-Related Cracking Effects on Hydrating Concrete Pavement

Hydrating concrete pavement is typically subjected to both moisture and temperature-induced stresses that drive cracking mechanisms at early concrete ages. Undesirable cracking resulting from these mechanisms plays a key role in both short- and long-term performance of most concrete pavement systems. Short-term performance is heavily dependent upon curing quality and construction weather while curling and warping behavior can have both short- and long-term consequences. The focus of this report is primarily on the short-term perspective and how moisture profile and curing quality effects are involved in warping behavior and ultimately delamination cracking and spalling distress. Based on this perspective, mathematical models were developed for the calculation of moisture and temperature profiles to help investigate the effect of different combinations of climate, construction, and materials on the development of the moisture and temperature profiles and their subsequent effects on early-aged cracking. These models appear as nonlinear time-dependent partial differential equations and are solved by the finite element method simultaneously that involves both backward and forward calculation. Using measured test data, moisture diffusivity and thermal conductivity were back-calculated to facilitate accurate modeling of moisture and temperature flows in hardening concrete. On the whole, the calculated moisture and temperature profiles using the moisture diffusivity and thermal conductivity models corresponded to the measured data. Spalling typically occurs at random cracks and occasionally at joints subjected to high delamination stresses during and shortly after construction. The incidence of this distress type is strongly correlated to pre-existing horizontal delaminations that occur within 25 mm of the pavement surface and can later grow into a spall due to a variety of causes, The cause of the shallow, horizontal delaminations that occur within the top 25 mm of the pavement surface is primarily from early-age nonlinear shrinkage strains in addition to temperature variations through slab depth. Thus, the factors of the most importance are those related to the effectiveness of the curing medium in minimizing moisture loss during the hydration of the concrete and the bond strength between the aggregate and the paste. By increasing the effectiveness of the curing system, moisture gradients near the surface are substantially reduced and delamination stress minimized.