Drying shrinkage stresses in concrete patch repair systems

This paper proposes an approach to prediction of the build-up of stresses due to drying shrinkage in concrete patch repair systems. The technique suggested consists of a twofold sequential approach, requiring the solution of the moisture diffusion equation followed by execution of an appropriate stress analysis program. Solution of the non-linear moisture diffusion problem is obtained conveniently through a finite element formulation, which outputs the variation of moisture content in time and space. Inasmuch as drying shrinkage occurs by virtue of loss of moisture, a phenomenological relationship between moisture loss and free shrinkage strain is established and used to convert the finite element output of moisture loss to the free shrinkage strain. Time- and space-dependent values of free shrinkage strain are then fed as input to an appropriate stress analysis program, conceptually similar to a thermal stress analysis program, with the resulting output yielding the sMss build-up in the patch repair system due to drying shrinkage. The influence of repair layer variables including the diffusivity K_c, ultimate free shrinkage strain ε_sh and modulus of elasticity E_r on the build-up of drying shrinkage stress is highlighted.