高海拔强盐沼泽区桥梁桩基损伤现场模拟试验

为了探明高海拔强盐沼泽区公路桥梁桩基受干湿循环和冻融循环的损伤状况, 采用现场模拟试验, 研究了桩身位置、混凝土配合比、混凝土掺合料与外防护措施等对桥梁桩基力学性能的影响, 采用SEM分析、EDS分析和化学成分分析等手段探究了桩基损伤的微观机理。研究结果表明: 桩基混凝土抗侵蚀能力及其内部钢筋锈蚀受桩身位置影响, 对于基准混凝土试件, 龄期为360 d时, 水中、地表、地下0.25与1.25 m的桩基混凝土抗侵蚀系数依次为0.80、0.63、0.75和0.76, 对应位置钢筋面积锈蚀率依次为76%、91%、66%和65%;桩基混凝土抗侵蚀能力受混凝土配合比与掺合料的影响, 整体上掺入矿渣的混凝土抗侵蚀能力最强, 龄期为360 d时, 当砂子、水、碎石、减水剂、水泥、阻锈剂和膨胀剂的含量一致时, 掺入87.25 kg·m-3粉煤灰、21.8 kg·m-3硅灰、87.25 kg·m-3矿渣的混凝土试件的平均抗侵蚀系数分别为0.79、0.89、0.91;钢护筒在短期内能保护桩基混凝土不受到外界侵蚀, 在长期侵蚀下保护期限一般为2~3年; 从90 d龄期到360 d龄期, 桩基混凝土中C元素的质量分数从0增长到9.61%, 生成了越来越多的CaCO₃分子, 再加上钙矾石等晶体的膨胀, 使得桩基混凝土膨胀开裂。 

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.