季冻区路面混凝土界面区劣化行为及与强度相关性

Deterioration Behavior of Interfacial Transition Zone and Its Correlation with Strength of a Concrete Pavement in Seasonal Frost Region

为了揭示季冻区路面混凝土界面区在自然环境与车辆荷载耦合作用下的劣化机理,以及界面区劣化对路面耐久性的影响,通过室内设计普通交通环境和超载条件下的荷载-冻融-干湿循环三场耦合试验模拟路面水泥混凝土实际工作环境,并与普通交通条件下的疲劳荷载单因素试验及荷载-冻融双场耦合试验进行对比,以探求季冻区路面混凝土界面区劣化的主要影响因素;采用扫描电镜观测和X射线能谱分析分别测定在混凝土处于不同耦合作用阶段的界面区细观结构、钙硅比变化;采用静态弯拉强度试验测定三场耦合下各阶段的混凝土力学性能,并采用多元回归分析方法揭示路面混凝土界面区劣化行为与混凝土强度的相关性。结果表明:季冻区路面混凝土运营时,车辆荷载主要引起混凝土界面区沿原生微裂缝的局部损坏;冻融循环伴随干湿交替的环境作用促使裂缝在各方向蔓延形成大片缺陷,且该界面区劣化行为是物理-化学过程。主要表现为,路面混凝土的抗弯拉强度呈下降趋势;界面区大量裂缝交叉贯通,密实度显著降低,氢氧化钙结晶析出;超载情况下,疲劳寿命急剧缩短,且界面区内部微裂纹的宽度显著增大。混凝土疲劳破坏时,界面区临界损伤阈值为:界面区宽度为70μm;密实度为50.96%~54.25%;微裂缝最大长度在24.48~26.04μm之间;微裂缝最大宽度在11.73~15.72μm之间。可利用多元线性回归方程描述混凝土强度与界面区结构缺陷之间的定量关系,各结构参数对强度影响程度从大到小依次为:密实度、裂纹宽度、裂纹长度。

To obtain the deterioration behavior of the interfacial transition zone(ITZ)and its effect on the durability of concrete pavement suffering from a combination of an environment attack and mechanical fatigue load(in a seasonal frost region),coupled loading condition of fatigue load(normal traffic and overload),freeze-thaw cycles(FTC)and dry-wet cycles(DWC)was conducted to simulate this interactive effect on concrete during service.The single fatigue load condition and the coupled loading condition of fatigue load and FTC were designed under normal traffic to discover the critical factor that influences the deterioration behavior of ITZ.Studies on the microstructure and Ca/Si ratio of the ITZ at different loading stages have been conducted by means of scanning electron microscopy(SEM)and energy dispersive X-ray analysis(EDXA).The mechanical properties of pavement concrete under coupled condition of load,FTC,and DWC were measured through a static flexural tensile strength test.Furthermore,the correlation between strength and ITZ deterioration were studied using multiple regression analysis.The results demonstrate that during concrete pavement service in seasonal frost region,the mechanical load leads to localized damage around the principle intrinsic cracks while the environment attack of FTC and DWC contribute to crack propagation in all directions to form large defects,during which the ITZ deterioration is observed to be a physico-chemical process.As the flexural tensile strength of concrete keeps decreasing,many cracks intersect and breakthrough in ITZ,the density C decreases,and calcium hydroxide crystallizes;during overload,the fatigue life of concrete is much shorter and the micro-cracks in ITZ widens.When concrete ruptures,the ITZ width is 70μm,density C is 50.96%-54.25%,maximum length and width of micro-cracks are 24.48-26.04μm and 11.73-15.72μm,respectively.The multiple linear regression equation could be used to quantitatively analyze the relationship between the strength of concrete and ITZ structural defects.Their extents of effect on strength are density C>crack width>crack length.