湿热地区水性环氧树脂对桥面板混凝土疲劳性能的改善

Improvement of fatigue performance of bridge deck concrete by waterborne epoxy resin in hot and humid regions

为解决湿热地区桥面板混凝土抗弯拉强度和抗疲劳性能不足的问题,对浆体进行水化热测试,分析水性环氧树脂掺量对水泥水化过程的影响规律;在室内模拟湿热地区桥面板混凝土工作环境,设计抗弯拉强度试验和疲劳试验,研究水性环氧树脂掺量对桥面板混凝土抗弯拉强度和疲劳性能的影响,并对其疲劳寿命采用S-N曲线进行拟合,研究应力水平S与疲劳寿命N间的关系;采用扫描电镜(SEM)观测浆体内部结构变化及混凝土界面过渡区微观形貌,从微观角度对水性环氧树脂改性桥面板混凝土疲劳性能进行剖析。试验结果表明:水性环氧树脂能够降低浆体水化放热速率和放热总量,起到延缓水泥水化的作用,有利于避免因水化热过高导致混凝土早期开裂;水性环氧树脂明显提高了桥面板混凝土抗弯拉强度且延长了疲劳寿命,当水性环氧树脂掺量(质量分数,下同)为3%时,改善效果最明显,7 d抗弯拉强度较普通混凝土提高20.4%,同时在0.75应力水平下,疲劳寿命也提高了1.7倍,S-N曲线可较好预估水性环氧树脂改善桥面板混凝土在不同应力水平下的疲劳寿命分布;水性环氧树脂改性桥面板混凝土内部分布着无规则形状的聚合物膜,与水泥石形成致密网状复合结构,增加了桥面板混凝土的黏聚性与保水性、细化了混凝土孔结构并可使混凝土界面过渡区更加紧实致密,有利于改善桥面板混凝土疲劳性能。

In order to solve the problem of insufficient flexural tensile strength and fatigue resistance of bridge deck concrete in hot and humid regions,the slurry was tested for heat of hydration and the influence of waterborne epoxy resin content on the hydration process of cement was analyzed.Then the working environment of bridge deck concrete in hot and humid regions was simulated indoors,flexural tensile strength test and fatigue test were designed,the influence of waterborne epoxy resin content on flexural tensile strength and fatigue performance of bridge deck concrete were studied,and its fatigue life was fitted with S-N curve to study the relationship between stress level S and fatigue life N.Moreover,scanning electron microscope(SEM)was used to observe the changes of internal structure of the slurry and the microscopic morphology of the interfacial transition zone of the bridge deck concrete,and the fatigue performance of the waterborne epoxy resin modified bridge deck concrete was analyzed from a microscopic point of view.The results show that waterborne epoxy resin can reduce the heat release rate and total heat release of slurry hydration,and play a role in delaying cement hydration,which is beneficial to avoid early cracking of concrete due to excessive heat of hydration.The flexural tensile strength and fatigue life of bridge deck concrete are obviously improved by waterborne epoxy resin.When the content(mass fraction,the same below)of waterborne epoxy resin is 3%,the improvement effect is the most obvious.The 7 d flexural tensile strength is 20.4%higher than that of ordinary concrete,and the fatigue life is also increased by 1.7 times under the stress level of 0.75.The S-N curve equation can well predict the fatigue life distribution of the waterborne epoxy resin to improve the bridge deck concrete under different stress levels.Then the waterborne epoxy resin modified bridge deck concrete is distributed with irregularly shaped polymer membranes,which form a dense network composite structure with the cement stone,so that the cohesiveness and water retention of the bridge deck concrete are increased,the concrete pore structure is refined and make the interfacial transition zone of concrete more compact and dense,which is conducive to improve the fatigue performance of bridge deck concrete.