Water absorption and desorption in concrete

Absorption and desorption are a transport property that affects the durability of concrete [1]. Recent work shows that absorption and desorption can be used to determine the freeze-thaw durability of concrete elements [2]. This work examines various aspects of concrete drying and wetting. First, this work examines the absorption of partially dried concrete. Second, this work assesses desorption-absorption isotherms for concrete mixtures and considers the effect of air content on the water absorption behavior of concrete. Third, the work assesses the drying behavior of concrete. In this study, three tests were used to investigate water transport in concrete: the water absorption test, dynamic vapor desorption test, and drying test. Four series of samples were used: Series 1: water-to-cement ratio = 0.45 AE90 Series 2: water-to-cement ratio = 0.40 AE90 Series 3: water-to-cement ratio = 0.40 AE90 + water reducer Series 4: water-to-cement ratio = 0.35 AE90 + water reducer The American Society for Testing and Materials (ASTM) C1585-13 [3] is a common test method that is used to determine the initial sorption, secondary sorption, and total absorption of partially saturated concrete. In this study, absorption tests were conducted using concrete with different water-to-cement ratios, varying air contents and air void quality, and different sample conditioning at 50 percent and 75 percent relative humidity (RH). Because the use of mass change alone is insufficient to characterize concrete performance, the degree of saturation (DOS) was used to describe the behavior of the samples. Plots of the DOS versus the square root of time also were developed. The results indicate that, as expected, the samples conditioned at 50 percent RH can absorb more water than samples from the same mixture that were conditioned at 75 percent RH. Also, the samples that contained a higher volume of air had a lower DOS after conditioning. This study found that secondary sorption is not related to air content. The dynamic vapor sorption (DVS) test was used to determine the desorption and absorption of a sample 5-mm x 4-mm x 1-mm thick that was saturated in limewater. This test was used to determine how the water vacated and filled the air voids, capillary pores and gel pores. The DVS results show the mass changes of the samples. The results also show that the higher the water-to-cement ratio, the more the water in the sample is absorbed and desorbed. The third test employed in this study was a drying test that followed a SIMCO laboratory test protocol [4]. In this test, 100-mm diameter cylindrical samples were cut to 50 mm in thickness. After the samples were saturated in limewater, they were placed in a 50 percent RH chamber. The mass changes were reported after 30 days [4]. The results show that the higher water-to-cement ratio samples lost more water than the samples with lower water-to-cement ratios