Abstract

The effect of sodium chloride solution, freeze–thaw cycling and externally applied load on the performance of concrete was experimentally investigated. The results show that the concrete specimens subjected to freeze–thaw cycling scaled more severely in chloride salt solution than those in water, and weight losses of the specimens tested in chloride salt solution were twice as much as those tested in water. However, dynamic modulus of elasticity of the concrete specimens decreased more slowly in chloride salt solution than in water due to the decline in the freezing point of the chloride salt solution compared with water. It is also shown that the performance deterioration in the concrete subjected to multidamaging processes was significantly accelerated. The larger the stress ratios, the fewer freeze–thaw cycles the concrete could bear. When steel fiber is incorporated, performance degradation in the steel fiber-reinforced concrete exposed to the multidamaging processes could be considerably retarded.

Abstract

In this paper, the two sets of concretes under attack of erosion solution of sulfate and chloride salt were investigated. The one set is the plain concrete without fly ash addition. The other set is the concrete with 20% and 30% of fly ash addition, respectively. The corrosion solution includes three types: 3.5%NaCl, 5% Na₂SO₄, and a composite solution of 3.5%NaCl and 5% Na₂SO₄. In addition, two corrosion regimes were employed in this study: naturally immersion (stored in corrosion solution for long duration), drying-immersion cycles. The damage process of the two sets of concretes was systematically investigated under the above three types of corrosion solutions and two corrosion regimes. The interaction between sulfate and chloride salt was also quantitatively determined. The experimental results shown that a presence of sulfate in the composite solution increased the resistance to chloride ingress into concretes at early exposure period, but the opposition was observed at latter exposure period. For the damage of concretes, a presence of chloride in the composite solution reduces the damage of concrete caused by sulfate. Addition of fly ash may significantly improve the resistance to chloride ingress into concretes and the resistance to sulfate erosion when a suitable amount of fly ash addition and low water-to-binder (W/B) was employed. Studies of the different corrosion regimes indicate that concretes stored in corrosion solution for about 850 d, the changes in relatively dynamic modulus of elastically (RDME) could be described by three stages: linearly increasing period, steady period, and declining period. Whereas for drying-immersion cycles, an accelerated trend could be found. The changes in RDME included an accelerated decreased stage, linearly increased stage, and then a slowly decreased stage, finally accelerating failure stage. In order to elucidate the above experimental results in a microscopic scale, the mechanism was also investigated by the modern microanalysis techniques.

为了配制抗盐冻混凝土，自行配制了AS型抗盐冻外加剂，并参照CDF混凝土抗盐冻试验方法，研究涂刷该外加剂的三种混凝土的抗盐冻性能。结果表明：涂刷AS型抗盐冻外加剂后，三种水灰比（0.40、0.36和0.32）的混凝土经56次盐冻后剥蚀量是未涂刷该外加剂混凝土的0.09%~0.07%，约降低了99%；动弹性模量损失率降低了 79%~86%。SEM表明，AS型抗盐冻外加剂能够有效减少NaCl在混凝土内部结晶及微裂缝出现。与减小水灰比、掺加引气外加剂和掺合料相比，AS型抗盐冻外加剂显著提高了混凝土的抗盐冻性能。

The timedependent reliability problem of the concrete structure in northern sea regions of China was discussed. The degradation behaviors of the mechanical properties such as Young’s modulus, compressive strength and tensile strength of the concrete structure after the freezethaw cycles were revealed through a great deal of inlab freezethaw tests. The mechanical parameter degradation of the concrete pier with the freezethaw cycle number were obtained, and the strengthtime degradation laws were abtained. A timedependent reliability calculation method of the concrete structure in the freezethaw environment was proposed. The lower concrete structure of the pier of Cangkou searoute of Tsingdao Bay bridge were analyzed numerically by the finite element reliability theory and the proposed method, and the reliability index variation with time was obtained, providing a reference for the engineering maintenance decision making of the pier.

分析了北方海域混凝土结构时变可靠度产生的原因，通过大量室内冻融试验研究，得出了混凝土结构在冻融作用下的弹性模量、抗拉、抗压等力学性能指标的损伤规律。建立了混凝土墩力学参数随冻融次数的衰减规律，继而转化为强度随时间的衰减规律。推导了混凝土结构在冻融环境下的时变可靠度的计算方法，并应用可靠度理论对海湾桥沧口段航道桥墩柱下部结构进行了数值分析，得出可靠度随时间的变化规律，为维护决策提供依据。