内蒙古盐碱地区冻融循环后钢筋与再生混凝土黏结性能及计算模型研究

Based on the strategy of sustainable development and the requirements of civil engineering construction, it is a general trend to apply the new type of green building materials such as recycled concrete to civil engineering. In the Inner Mongolia saline-alkali area, concrete often suffer from multiple factors together to destroy. In order to promote the application of recycled concrete in the Inner Mongolia saline-alkali area engineering, study on the bond behavior between recycled concrete and reinforced steel after the freeze-thaw cycles in saline-alkali environment has a very important theoretical significance and practical value..In this project we are using the center pull-out tests to test the bond-slip performance between the reinforced steel and the recycled concrete specimens which are 100% recycled coarse aggregate. Exploring the bond-slip mechanism of steel bar and recycled concrete under the different influence factors and establish the bond-slip constitutive relationship between recycled concrete and steel bar after freezing-thawing damage in saline-alkali environment. Bond properties between recycled concrete and steel bar were analyzed by the finite element software named ANSYS, and the results were compared with the experimental results. On this basis, the formulas for calculating the lap length and anchorage length of steel bar in recycled concrete structures are given, which has very important engineering significance for promoting the application of recycled concrete in Inner Mongolia saline-alkali areas.

基于可持续发展战略思想和土木工程建设的需要，将再生混凝土这种新型绿色建筑材料应用到土木工程，已是大势所趋。在内蒙古盐碱地区，混凝土往往遭受多因素共同破坏。为了推进再生混凝土在内蒙古盐碱地区工程中应用，研究盐碱环境下冻融循环作用后钢筋与再生混凝土的黏结性能具有十分重要的理论意义和实用价值。.本项目采用中心拉拔试验对粗骨料取代率为100%的再生混凝土与钢筋黏结-滑移性能展开试验研究。分别探讨单盐和复合盐环境下再生混凝土抗压强度、劈裂抗拉强度随冻融循环次数的变化规律，建立考虑腐蚀环境和冻融循环次数的再生混凝土抗压强度、劈裂抗拉强度计算模型；研究不同影响因素下钢筋与再生混凝土黏结-滑移试验曲线，建立盐碱环境下冻融循环后钢筋与再生混凝土的黏结-滑移本构关系。基于锚固可靠度理论，并考虑工程经验，提出内蒙古地区盐碱环境下不同耐久年限的钢筋与再生混凝土锚固长度计算模型。

本项目首先通过快速冻融法以盐溶液类型、复合盐浓度和混凝土强度等级等为变量，研究了不同冻融循环次数下再生混凝土的破坏形态和抗压强度损失、劈裂抗拉强度损失、相对动弹性模量和质量损失，分析了盐碱-冻融耦合环境下的力学性能变化规律，并建立该环境下的力学性能损伤模型，为后续盐冻损伤后再生混凝土与钢筋黏结性能提供基础数据；其次通过位移计测量钢筋与再生混凝土试件加载端及自由端滑移值、破坏荷载等，并采用钢筋开槽内贴贴应变片的形式测量再生混凝土锚固区段内钢筋应变变化，并探究再生混凝土试件的破坏形态、荷载-滑移破坏曲线及黏结强度。研究结果表明，再生混凝土试件的黏结性较普通混凝土试件要差；钢筋锚固长度越长，其与再生混凝土的极限荷载越大，黏结性能越好，锚固长度在3d-5d之间时，其对黏结性能提高影响很大，而锚固长度在5d-8d之间时，其对黏结性能提高影响变缓，因此给出la / d = 5的钢筋标准埋入长度建议值；并且钢筋直径越大，极限拉拔荷载越大，黏结性能越好，但在相同盐冻循环次数下，钢筋直径最大的试件组由于其相对黏结面积的减少导致的极限黏结强度反而最小。针对盐碱环境下冻融循环后再生混凝土与钢筋的黏结特征点的变化规律，包括峰值滑移、初始黏结强度、极限黏结强度和残余黏结强度，建立该环境下的黏结特征点计算模型，并建立盐冻循环下考虑位置函数的黏结-滑移本构关系；最后对试件进行仿真模拟，发现混凝土的破坏有一定的局部效应，破坏围绕钢筋肋边缘发生，远离钢筋的部分并未发生损伤破坏；同时各组试件的模拟值与试验值吻合较好，所得内蒙古地区复合盐环境下再生混凝土与钢筋粘结滑移本构关系具有较好的适用性。