Influence of hydraulic pressure on pore structure evolution and chloride transport in concrete

Abstract

To study the influence of hydraulic pressure on pore structure evolution and chloride transport behaviour in concrete, the mass transport depth, chloride concentration and pore characteristics of specimens with different water/cement (w/c) ratios were investigated using silver nitrate spraying, potentiometric titration, mercury intrusion porosimetry, nitrogen adsorption tests and confocal laser scanning microscopy. The results showed that the chloride concentration increased with increases in the hydraulic pressure and w/c ratio. With increasing hydraulic pressure, the transport depths of water and chloride ion transport expanded from 5.2 mm to 25.4 mm. An increase in hydraulic pressure changed the pore structure of the concrete, leading to a surge in the specific surface area, greater porosity and larger average pore diameters. Notably, ink-bottle shaped pores emerged prominently and the proportion of fine mesopores and capillary pores markedly increased after the application of hydraulic pressure. A relationship between the chloride diffusion coefficient and hydraulic pressure was developed and a relationship between the modified permeability coefficient and hydraulic pressure was constructed based on the mesoporous contribution to express the hysteresis effect of chloride.