Analysis of Stresses Due to Traffic and Thermal Loads in Two-Lift Bonded Concrete Pavements by Finite Element Method

The current practice in the construction of jointed plain concrete pavements in India is to lay paving quality concrete (PQC) over roller-compacted concrete designated as dry lean concrete (DLC). A 125-mu m plastic sheet is placed as a bond-breaking layer at the interface of the DLC and PQC. By placing the PQC layer directly over fresh lean concrete (LC), the two layers will bond without any extra bond-breaking layers, and there may be a considerable reduction in PQC thickness. Reducing the PQC layer thickness decreases the amount of aggregates used, which helps preserve quality aggregates that are rapidly depleting. Pavements in which the PQC is laid directly over LC can be designated as a two-lift concrete pavement (TLCP). Joints must be provided with deep saw cuts to avoid random cracking. The LC can be made up of recycled concrete or marginal aggregates to obtain a sustainable pavement. However, readymade analytical solutions are not available for the computation of stresses in two-lift bonded concrete layers for pavement design. This article presents a three-dimensional finite element solution for stresses in bonded concrete pavements. Stresses in both layers are presented in order to arrive at an optimum thickness combination so that both layers are safe during the design life. Stress computation is done for the conditions of simultaneous application of temperature gradients and axle loads. The cracking of the LC layer because of high flexural stresses at the bottom is found to be the critical factor in the design of TLCP.