隧道初支混凝土抗冲刷溶蚀技术评价及作用机理

Evaluation and Mechanism of Leaching Resistance Technology of Primary Support Concrete for Tunnel

隧道初支混凝土被钙溶蚀破坏将导致孔隙率增加、强度下降,进而缩短其服役寿命。根据溶蚀计算模型,可以从减少可溶性钙含量、降低孔隙率和降低混凝土基体的水分传输速率等方面来提升混凝土的抗溶蚀性能。采用硬化气泡、X射线衍射、扫描电子显微镜、能谱分析、ICP等方法测试分析分别掺加矿物掺和料(AD)、密实材料(纳米二氧化硅,DM)和疏水材料(有机羧酸酯聚合物,HM)混凝土溶蚀前后的孔隙结构、水化产物、微观形貌和钙离子溶出量等指标。结果表明:矿物掺和料AD可以从降低可溶物Ca(OH)_(2)的含量、细化混凝土孔隙等方面提升混凝土的抗溶蚀性能,溶蚀14 d时混凝土钙离子溶出量较纯水泥组降低10%,但混凝土早期强度偏低,不利于隧道初支混凝土施工;密实材料DM同样具有降低可溶物Ca(OH)_(2)的含量、细化混凝土孔隙等优势,且其早期强度较高,溶蚀14 d时钙离子溶出量较纯水泥组降低22%;疏水材料HM可以从细化混凝土孔隙、降低水分传输速率等方面提升混凝土的抗溶蚀性能,溶蚀14 d时钙离子溶出量较纯水泥组降低30%,且对混凝土强度无不利影响。因此,混凝土的抗溶蚀提升效果顺序为:疏水材料HM>密实材料DM>矿物掺和料AD。

Primary support concrete of tunnel is deteriorated by calcium leaching,which will increase porosity,decrease strength,and shorten its service life.According to a model of calcium leaching,reducing content of soluble calcium,porosity,and water transport rate of concrete was an effective method to improve its leaching resistance.Pore structure,hydration products,and microscopic morphology of primary support concrete incorporated with mineral admixtures(AD),densifying material(nano silica,DM)and hydrophobic material(organic carboxylate polymer,HM)before and after leaching test,were measured and analyzed by using hardened bubbles,X-ray diffraction,scanning electron microscopy,energy spectrum analysis,ICP and other methods.The results showed that mineral admixtures AD reduced the content of soluble Ca(OH)_(2) and refined the pores of concrete to improve the leaching resistance of primary support concrete.The leaching of calcium ions in primary support concrete is 10%lower than that of pure cement after 14 days of leaching.However,due to its secondary hydration effect,the early strength of concrete decreased,which was unfavorable to the tunnel’s primary concrete.The densifying material DM reduced content of Ca(OH)_(2) and refined pore structure of the primary support concrete,which improved the corrosion resistance of concrete and its early strength.Therefore,the amount of calcium ion leaching for the concrete added with DM at 14 days is 22%lower than that for the pure cement concrete.Hydrophobic material HM improved the anti-leaching performance of concrete from the aspects of refining concrete pores and reducing water transmission rate.The amount of calcium ion leaching for the concrete added with HM at 14 days is 30%lower than that for pure cement concrete,and it has no adverse effect on the strength of concrete.On the whole,the leaching resistance technology was listed in a descending order:hydrophobic material HM>densifying material DM>mineral admixture AD.