An Insight into Moisture-Dependence of Concrete Coefficient of Thermal Expansion in Concrete Pavements

The mechanistic-empirical design of concrete pavements traditionally assumes that concrete coefficient of thermal expansion (CTE) is a constant, however, experimental evidence shows that CTE can increase up to 60% as concrete dries. The research presented in this paper provides insight into the mechanisms that lie behind this phenomenon, by establishing a link between the diurnal variations of concrete internal relative humidity (RH) and the moisture-dependence of concrete CTE. The experimental data come from four concrete pavements, built with different high early strength mixes, that were instrumented with sensors to measure slab deformations and concrete internal temperature and RH. RH measurements in the four concrete mixes indicate that—depending on concrete moisture content—the RH of the air in concrete pores may experience considerable diurnal variations that are mainly driven by changes in temperature. These RH changes take place in opposite direction compared to what typically occurs in the open air. In the concrete pores, the RH of the air increases as temperature increases and decreases as temperature decreases. These temperature-dependent changes in concrete internal RH are indication of temperature-dependent changes in concrete pore water suction which, at the same time, result in changes in drying shrinkage deformation. Since this deformation occurs as temperature changes, it is interpreted as thermal deformation. The consequence is that the CTE of the concrete increases. As shown in this paper, the magnitudes of the temperature-dependent changes in concrete internal RH are sufficient to explain by themselves the increase in CTE that concrete experiences as it dries.