Thermal Compatibility of Concrete and Composite Reinforcements

Abstract

Experiments on commercially-produced composite reinforcements have shown that the transverse coefficients of thermal expansion (CTE) of these rebar are 3–5 times higher than the CTE of concrete. In this paper, thermoelastic solutions of plain and spirally wrapped composite rebar, embedded in concrete and subject to a uniform temperature increase, are presented. Comparisons are made between bars with no spiral wrapping and those produced with a spiral wrap of unidirectional rovings. Results show that the spiral wrapping, included primarily to improve the bond between the concrete and the composite rebar, also aids in the reduction of overall thermal expansion of the rebar. Thermoelastic solutions of unidirectional composite rods and concrete predict that the tensile stresses in the concrete surrounding the rebar will exceed the tensile strength of the concrete for relatively small temperature increases. The extent of this cracking cannot be determined from the analytical predictions. To predict the extent of the cracking, nonlinear thermoelastic simulations, completed using the COSMOS-M finite-element code, are used to determine the extent of concrete cracking. Results show that cracking decreases with a decreasing rebar diameter and increasing confining pressure of the concrete.