Effects of Lime-Based Expansion Material and Freeze-Thaw Cycles on Air-Void Blockage in Concrete

Air voids in concrete are sometimes observed to be blocked by white precipitates. In this study, the authors conducted freeze-thaw tests on concrete mixed with lime-based expansion material and then performed microscopic observations using scanning electron microscopy, elemental analysis using energy-dispersive X-ray spectroscopy. The size distributions of air voids in the concrete during the curing period (28 days after placement) and before, during, and after the tests were also measured in order to investigate the effects of the expansion material on air-void blockage as well as the underlying processes. During the curing period, no air-void blockage was observed. However, as the concrete aged, precipitates formed on the inner surfaces of the air voids. During the freeze-thaw tests, the number of air voids with diameters of ≤0.15 mm decreased, and the air-void spacing factor increased as the relative dynamic modulus of elasticity decreased. It was found that freeze-thaw cycles caused calcium-based precipitates to form inside the air voids of concrete mixed-with lime-based expansion material, and that the air voids became blocked.