冻融损伤后再生混凝土在复杂应力下与钢筋的粘结性能研究

The interface cracking and internal crack propagation for recycled aggregate concrete （RAC）are different from those of natural aggregate concrete after freezing and thawing cycled (FTC) due to the inferior characteristics of recycled coarse aggregate (RA), such as more complex interface, porosity and cracking. The bond properties of reinforced RAC also will be affected by these characteristics. This proposal systemically study the bond properties between RAC and rebar after FTC according to following four levels by select different grades of RA: the damage mechanism for bond between the interface of RAC and rebar, pull-out test without lateral pressure, pull-out test under multiaxis pressure and beam test under bending shear stresses. The distribution of capillary water, internal crack and interface crack propagation law after FTC will be firstly studied using mercury porosimetry, precision cutting technology and SEM to reveal the bonding damage mechanism. Then, the bond behaviors between RAC and rebar after FTC would be studied implemented according to aforementioned four levels. The effects of FTC, RA, substitution, and anchorage parameters on bond behavior will be analyzed, and the bond strength theories and failure criteria also will be established. Lastly, this proposal accurately obtain the bond stress distribution using distributed optical fiber sensing technique, and establish the bond-slip constitutive relationship. The results derived in this proposal will be important for application of RAC in cold area.

再生粗骨料具有多界面、多孔隙、多裂纹等特点，冻融环境下再生混凝土各界面冻胀开裂和内裂缝扩展与普通混凝土有较大差异，严重影响其与钢筋间的界面粘结行为。项目选取不同品质再生粗骨料，从再生混凝土-钢筋界面粘结损伤机理、简单应力、多轴应力、弯-剪应力四个层面系统研究冻融损伤后再生混凝土与钢筋的粘结性能。结合压贡仪、精密切割技术及SEM观测手段，掌握钢筋再生混凝土试件中毛细水分布及冻融后内裂缝、界面裂缝扩展规律，揭示界面粘结损伤机理。通过系统的粘结试验，研究冻融后再生混凝土在简单应力、多轴应力、弯-剪应力下与钢筋的粘结性能，分析冻融循环次数、再生骨料品质、取代率、锚固参数对两者粘结性能影响，建立冻融后上述应力下再生混凝土-钢筋粘结强度理论、破坏准则；借助分布式光纤传感技术，准确获取冻融后不同应力状态下粘结应力分布、建立粘结-滑移本构关系。研究成果对指导寒冷地区再生混凝土应用具有重要工程和科学意义。

本项目首先通过再生骨料混凝土切片微观结构试验，研究了再生混凝土冻融损伤后微观界面形态、裂缝发展途径，从细微观层次揭示冻融损伤后再生骨料混凝土受力过程中复杂的界面反应对钢筋再生混凝土界面粘结力学行为的影响机理。其次，项目研究了经历不同冻融循环次数后不同再生粗骨料取代率混凝土的基本力学性能（抗压、劈裂抗拉、弹性模量、箍筋约束前后再生混凝土的本构关系等），为后续冻融损伤后再生混凝土-钢筋粘结性能提供基础数据。再次,项目从简单拉拔、单向侧压拉拔、双向侧压拉拔、纯弯曲作用拉拔以及弯曲剪切作用拉拔五个层面开展再生混凝土冻融损伤后与钢筋间的粘结滑移性能。分析了不同锚固参数对冻融损伤后再生混凝土与钢筋粘结性能影响规律，建立了多轴应力状态下再生混凝土与钢筋的粘结强度理论以及不同应力状态下再生混凝土-钢筋粘结滑移本构关系。借助开槽内贴片方法，获取冻融损伤后不同锚固位置处粘结应变，计算相应粘结应力，得到冻融损伤后粘结位置函数的变化规律。研究结果表明相同冻融循环后再生混凝土各相损伤的严重程度由大到小依次是：旧砂浆-旧粗料界面>新砂浆-旧砂浆界面>新砂浆-旧粗骨料界面>新砂浆内部。混凝土的冻融损伤存在一个界限冻融次数n，当冻融次数不超过n时，冻融损伤仅限发展到外围，当冻融次数超过n，切片核心区域也会发生冻融损伤。冻融损伤发生后，长锚试件的粘结应力分布曲线变得更加平缓，而短锚试件的相应曲线变得更加陡峭，长短锚固试件粘结应力分布曲线差异更大。将空间强度分析理论和界限劈裂角理论融入软化套筒理论，建立了修正软化套筒理论模型以计算冻融损伤后不同侧压作用下再生混凝土的峰值粘结强度，将原软化套筒理论的适用范围从劈裂破坏扩展到拔出破坏。最后，基于粘结可靠度原理计算，项目给出冻融损伤后再生混凝土结构中纵向受力钢筋基本锚固长度的建议公式。