我国西北地区土壤及地下水中含有浓度较高的Cl-、SO42-和Mg2+,侵蚀性离子会渗入到隧道中衬砌混凝土,严重威胁着混凝土结构的服役寿命。本文采用正交试验探究了水胶比、硅灰掺量、粉煤灰掺量对衬砌混凝土性能的影响。为了更好地模拟实际环境,分别配制了5种不同类型的含Cl-、SO42-和Mg2+复合盐溶液,并选取正交试验中的最优因素组合开展了56天侵蚀后其抗压强度以及表层氯离子浓度的变化规律的研究,采用扫描电子显微镜(SEM)和X射线衍射(XRD)对侵蚀过程进行了微观分析。结果表明:水胶比、粉煤灰掺量、硅灰掺量为0.33、30%、8%时,衬砌混凝土力学性能及抗氯离子侵蚀性能最佳;当混凝土在Cl-和SO42- 共同作用下,水化产物钙矾石膨胀破坏其内部结构,导致抗压强度下降,Cl-侵入速率加快;而Cl-和Mg2+共同作用下,Mg2+的侵入会破坏混凝土内部的碱性环境,也会造成抗压强度的降低,但其生成物Mg(OH)2会阻碍Cl-侵入材料内部;当Cl-、SO42-和Mg2+共同作用下,Mg2+和SO42-可分别在不同程度上抑制Cl-的侵蚀速率,同时SO42-和Mg2+存在相互抑制的复合作用,使得有效降低混凝土的抗压强度损失。
The soil and groundwater in the northwest region of China contain high concentrations of Cl-, SO42- and Mg2+, and the aggressive ions will penetrate into the tunnel lining concrete, seriously threatening the service life of the concrete structure. In this paper, orthogonal tests were used to investigate the effects of water-cement ratio, silica fume mixing amount and fly ash mixing amount on the performance of lining concrete. In order to better simulate the actual environment, five different types of composite salt solutions containing Cl-, SO42- and Mg2+ were prepared, and the optimal combination of factors in the orthogonal test was selected to carry out a study on the change rule of the compressive strength and the chloride concentration in the surface layer after 56 days of erosion, and the micro-analysis of the erosion process was carried out by using Scanning Electron Microscope (SEM) and X-ray diffraction (XRD). The results show that the mechanical properties and anti-chlorine ion erosion performance of lined concrete are best when the water-cement ratio, fly ash dosage, and silica fume dosage are 0.33, 30%, and 8%; when the concrete is under the joint action of Cl- and SO42-, the expansion of the hydration product calcite destroys its internal structure, which results in the decrease of the compressive strength and the acceleration of the rate of Cl- invasion; and under the joint action of Cl- and Mg2+, the Mg2+ invasion will destroy the alkaline environment inside the concrete, which will also cause the reduction of compressive strength, but its product Mg(OH)2 will hinder the invasion of Cl- into the interior of the material. When Cl-, SO42- and Mg2+ act together, Mg2+ and SO42- can inhibit the erosion rate of Cl- to different degrees, respectively, while SO42- and Mg2+ exist in a compound effect of mutual inhibition, which makes it possible to effectively reduce the loss of compressive strength of concrete.
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