Transient heat transfer analysis of two-lift concrete pavements under various climatic conditions of India

Two-lift concrete pavements are constructed using a wet-on-wet placement method with a strong and thin concrete layer being placed over a thick and weaker concrete layer. The top lift is typically composed of conventional pavement-grade concrete, while recycled or marginal materials are predominantly utilized in the bottom lift concrete. Consequently, unlike conventional single-lift concrete pavements, temperature distribution and resulting temperature differentials across the slab thickness are significantly influenced by the thermophysical properties of both concrete lifts. In the present study, two-dimensional transient heat transfer analysis was performed using a commercial finite element modelling software (Abaqus/Standard) to evaluate the temperature distribution across the slab thickness and to propose the maximum positive temperature differential ( MPTD ) and maximum negative temperature differential ( MNTD ) for two-lift concrete pavements corresponding to four predominant climatic zones of India, namely hot and dry, composite, warm and humid, and cold regions. Simulations were performed for the summer and winter periods of five randomly chosen years from 2011 to 2025 for the selected twenty-seven representative cities. The effect of the thickness of the top and bottom lifts, as well as the thermophysical properties (thermal conductivity, specific heat and density) of the bottom concrete, was studied. 95th percentile MPTD values and 5th percentile MNTD values were proposed for estimating the fatigue damage due to bottom-up and top-down cracking, respectively, in single- and two-lift concrete pavements. In the case of single-lift concrete pavements, the critical MPTD values ranged from 0.98 to 1.46 times the Indian Roads Congress (IRC)-recommended MPTD values, while the corresponding MNTD values ranged from 0.72 to 1.43 times the IRC-recommended MNTD values. Two-lift concrete slabs with higher bottom lift thickness resulted in higher MPTD values due to delayed heat conduction, whereas the slabs with higher top lift thickness reduced the MPTD values due to their increased heat-storing capacity. The study recommended a decreasing rate of 14.6–24.8 °C per meter increase in thickness of top lift for estimating design MPTD values. Regression models were developed for the temperature distribution across the slab thickness for design MPTD and MNTD cases in single- and two-lift concrete pavements. Finally, design MPTD and MNTD values for two-lift concrete pavements were proposed for different climatic zones of India, which can be effectively useful in estimating the fatigue damage associated with bottom-up and top-down cracking, respectively.