Evaluating the Combined Effects of Stress and Exposure on the Deterioration Rate of Concrete

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Concrete is inherently a brittle material, exhibiting low tensile strength and strain capacities. From a structural viewpoint, this is overcome by the addition of reinforcing steel to carry applied tensile loads. However, tensile stresses are still present in the concrete and it tends to crack relatively easily in service. The initiation of cracking leads to accelerated deterioration as deleterious agents penetrate more readily into the cracks. At this point, the rate of deterioration increases exponentially as cracks widen or more cracks form. In addition, the majority of durability-related deterioration processes affecting concrete share a similar basic damaging mechanism; internal expansion resulting in tensile stresses that ultimately lead to cracking. Tensile stresses induced by loading and those resulting from durability-related deterioration processes should be additive, thus accelerating the degradation rate of concrete when acting in concert. However, standard durability tests do not include the effects of stress on deterioration, being instead limited to unloaded specimens. This situation results in a gross overestimation of the deterioration resistance of concrete exposed to deleterious environments. The intent of the proposed research project is to evaluate the effect of combining service loads with deleterious exposure conditions in order to more closely simulate real-world concrete deterioration processes in structures. This type of combined approach is truly unique in the area of standardized durability testing. During exposure, specimens will also be monitored on a regular basis using nondestructive techniques in an attempt to develop better evaluation techniques and criteria for the inspection of real-world structures. The primary focus of the proposed research will be to develop a systematic approach to evaluate and quantify the resultant cracking and its effect on mechanical and transport properties, and ultimately service life.