Field simulation test of bridge pile foundation damage in high altitude and strong salt marsh area

In order to explore the damage status of highway bridge pile foundation subjected to dry-wet cycle and freeze-thaw cycle in high altitude and strong salt marsh area, the effects of pile body positions, concrete mix proportions, concrete admixtures and external protective measures on the mechanical properties of bridge pile foundation were studied by the field simulation test. The microscopic mechanism of pile foundation damage was analyzed by the SEM analysis, EDS analysis and chemical composition analysis. Research result shows that the anti-erosion ability and inner steel bar corrosion of pile foundation concrete are affected by the position of pile body. For the benchmark concrete specimens, when the curing age is 360 d, the erosion resistance coefficients of pile foundation concrete in the water, on the ground, and at the depths of 0.25 and 1.25 m are 0.80, 0.63, 0.75, and 0.76, respectively, and the corrosion rates of steel bar area at the corresponding positions are 76%, 91%, 66%, and 65%, respectively. The anti-erosion ability of pile foundation concrete is affected by the concrete mix proportion and concrete admixture, and the anti-erosion ability of the concrete with slag is the strongest on the whole. When the contents of sand, water, gravel, reducer, cement, rust inhibitor, and expansion agent are consistent, the average erosion resistance coefficients of concrete specimens with 87.25 kg·m^-3 fly ash, 21.8 kg·m^-3 silica ash, and 87.25 kg·m ^-3 slag are 0.79, 0.89, and 0.91 at the curing age of 360 d, respectively. The steel casing has a protective effect on the concrete erosion in a short time, but the protection period under long-term erosion is generally 2-3 years. When the curing age changes from 90 d to 360 d, the mass fraction of element C in pile foundation concrete increases from 0 to 9.61%, so that more and more CaCO₃ molecules are produced, together with the expansion of ettringite and other crystals, resulting in the swelling and cracking of pile foundation concrete.