Pore structure in concrete exposed to acid deposit

Pore structure has a significant effect on the mechanical response and durability of concrete. To well understand damage evolution of concrete exposed to the acid deposit, the pore characteristics inside the concrete were studied from multi-scale levels. To simulate the acid deposit, acid solutions with pH level of 1.0, 1.5 and 2.5 were deposed by the mixture the sulfate and nitric acid in the laboratory. The pore structures of concrete under various deterioration states were examined by mercury intrusion porosimetry (MIP) test and scanning electron microscopy (SEM). Contents of the chemical elements in the concrete samples were measured by Energy Dispersive Spectra (EDS) analysis. Computed tomography (CT) test was carried out to examine the meso-structure in concrete at the desired exposure ages. The CT digital images were processed and analyzed by Pro-Plus software. According to the probabilistic analysis of the porosity, it is indicated that the porosity in all the concrete specimens under various damage conditions obeys to the normal distribution. A distribution density function of the porosity in concrete specimens was suggested, and it was revealed that the mean and variance values of the porosity decrease linearly with the conditioning age. It was illustrated that the porosity has a slight increase at the initial exposure period, and decreases gradually with the elongation of the conditioning age. The higher acidity of the conditioning environment was, the more obvious changes of the porosity in concrete occurred. The evolutions of pore character are discussed from both the micro- and meso- levels, which can well discover the development mechanism of macro- behavior of concrete exposed to acidic environment.