Composite concrete consists of two elements cast at different times which are the concrete base and concrete topping. To achieve composite action, interface shear strength must be sufficient to resist the sliding motion between the two concrete surfaces in contact. The interface shear strength is mainly depended on concrete cohesion, friction and dowel action. A total of 36 “push-off” tests were performed to study the interface shear strength and to assess the influence of surface texture and steel reinforcement crossing the interface. Three different concrete base surfaces are prepared which include smooth or “left as-cast”, roughened by wire-brushing in the transverse direction and steel reinforcement projecting from the concrete base. Eurocode 2 provides design equations for determining the interface shear strength with different surface textures and also the one where projecting steel reinforcement crosses the interface. The experimental results show that the transverse roughened surface produced the highest interface shear strength of 1.89 N/mm2 (sn = 0 N/mm2), 4.69 N/mm2 (sn = 0.5 N/mm2), 5.97 N/mm2 (sn = 1.0 N/mm2) and 6.42 N/mm2 (sn = 1.5 N/mm2) compared with the other surface textures. This proves that the increase in the degree of roughness contributes to higher concrete cohesion and friction coefficient. However, for the surface with projecting steel reinforcement, the failure is not sudden as experienced by the surface without one. This is due to the contribution of the clamping stress from the dowel action of the steel reinforcements. Meanwhile, for specimens without any projecting steel reinforcements, the interface shear strength depended solely on friction and concrete cohesion of the surface textures. The interface shear strength of surface with and without the projecting steel reinforcement can be predicted using the Mohr-Coulomb failure envelope. This paper also proposed design expressions for concrete-to-concrete bond on surfaces provided with and without projecting steel reinforcement that can be adopted in Eurocode 2.
展开▼
机译：复合混凝土由在不同时间浇筑的两个元素组成，分别是混凝土基础和混凝土浇筑面。为了实现复合作用，界面剪切强度必须足以抵抗两个接触的混凝土表面之间的滑动。界面剪切强度主要取决于混凝土的内聚力，摩擦力和销的作用。总共进行了36次“下推”测试，以研究界面的剪切强度，并评估表面纹理和跨界面的钢筋的影响。准备了三种不同的混凝土基础表面，包括光滑的或“左铸件”，通过在横向方向上的钢丝刷进行粗糙化处理以及从混凝土基础上突出的钢筋加固。欧洲规范2提供了用于确定具有不同表面纹理的界面抗剪强度的设计方程，还提供了突出的钢筋穿过界面的设计方程。实验结果表明，横向粗糙化表面产生的最高界面剪切强度为1.89 N / mm2（sn = 0 N / mm2），4.69 N / mm2（sn = 0.5 N / mm2），5.97 N / mm2（sn = 1.0 N / mm2）和6.42 N / mm2（sn = 1.5 N / mm2），与其他表面纹理相比。这证明粗糙度的增加有助于提高混凝土的内聚力和摩擦系数。但是，对于带有突出钢筋的表面，这种破坏不会像没有表面的情况那样突然发生。这是由于钢筋的销钉作用引起的夹紧应力的作用。同时，对于没有任何突出钢筋的标本，界面剪切强度仅取决于表面纹理的摩擦和混凝土内聚力。可以使用Mohr-Coulomb破坏包络线预测带有或不带有突出钢筋的表面的界面抗剪强度。本文还提出了带有或不带有突出钢筋的表面上混凝土与混凝土粘结的设计表达式，可以在欧洲规范2中采用。
展开▼
