Temperature Effect on the Thermal Expansion Coefficient of Concrete

The coefficient of thermal expansion (CTE) is typically assumed to be constant in RC bridge design. In fact, under freezing temperatures, the CTE of concrete exhibits hysteretic nonlinear response, which, however, is rarely considered in design and analysis. A review of the literature indicates that the temperature dependence of the CTE of concrete materials can induce significant length changes to the structural components, leading to cracking and delamination, significant internal stresses if restrained, and a gradual deterioration in cold regions that experience repeated frost events. Contrary to contraction under low temperatures, which is expected in isotropic elastic materials, the length change is expansive when the concrete material is saturated or partially saturated, the amount of expansion being a function of the w/c ratio of the paste and the aggregate characteristics. The experimental study presented in this paper aims to investigate and quantify the effect of freezing temperature on the thermal expansion of concrete, considering mixes with different compositions and degrees of saturation. Freezing–thawing cycles to temperatures of −40°C are applied to test specimens of the various concrete materials in order to collect data regarding the resulting thermal strain. The effect of the number of consecutive freezing–thawing cycles on the accumulation of the resulting residual strain is also investigated. The test data illustrate the effect of the w/c ratio on expansion under freezing conditions, provided that the degree of saturation exceeds a critical limit in the range between 80% and 90%. It was also determined that aggregate size affects the thermal behavior of concrete under low temperatures, but the residual length change converges to a limiting value after repeated cycles of thermal loading, therefore, the residual strain increments decrease with the increase in number of freezing and thawing cycles.