Interface Shear Strength of Concrete-to-Concrete Bond With and Without Projecting Steel Reinforcement

Abstract

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 (σn = 0 N/mm2), 4.69 N/mm2 (σn = 0.5 N/mm2), 5.97 N/mm2 (σn = 1.0 N/mm2) and 6.42 N/mm2 (σn = 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.

Influence of Steel Fibers on the Interfacial Shear Strength of Ternary Blend Geopolymer Concrete Composite

“…However, the load carrying capacity of monolithic specimens was more than that of the bilithic specimens. Additionally, all the control specimens failed in a brittle manner, and were separated into two L halves without crushing due to the breaking of the cohesion bond of concrete at the interface [29]. In Figure 3b, for the specimens with steel fibers, there is a short linear portion where a decrease in slip was observed at the early stages of loading, i.e., increased stiffness and ductile behavior were experienced at the ultimate stage of loading.…”

“…The effect of surface texture and steel reinforcement at the interface of the interfacial shear strength was studied on three different base surfaces; smooth, roughened, and steel projecting from the base concrete surface. An increase in the roughness degree was proven to contribute to higher friction and cohesion coefficients, producing higher shear strength at the interface [29]. The direct shear strength of ternary blend geopolymer concrete with varying volume fractions of crimped steel fibers, i.e., 0.25, 0.50, 0.75, and 1%, showed that the addition of steel fibers up to 1% delayed crack propagation and improved the shear capacity [30].…”

Shear performance of the interfaces for precast concrete shear wall components by novel preparation method

“…As mentioned above, the cohesion, friction, and dowel action form the shear mechanism of the concrete‐to‐concrete interface. More further research studies have been carried out on the friction and cohesion coefficients, 24 influence of recycled aggregate concrete 25 and lightweight aggregates concrete, 26 projecting steel reinforcement, 27 geometry of interfaces, 28 and so forth. Bond agents are also applied to enhance the bond capacity of the concrete‐to‐concrete interface 8,29 …”

Concrete–Concrete Bond in Mode-I: A study on the Synergistic Effect of Surface Roughness and Fiber Reinforcement

“…In this study, the mean peak height (S pm ) and the average roughness (S a ) parameters were selected [24][25][26]. These parameters have been suggested as reliable roughness parameters [27,28]. S pm was calculated as the average of the maximum peak height (p i ) from each sampling length where sampling length is equal to 1/5 of the total length, while S a was given by the arithmetic mean of the absolute values Z(x,y) within sampling length (l) and sampling width (b).…”