fib Model-Code 2010 Approach for Concrete-to-Concrete Interfaces

Presently, it is widely accepted that three different load transfer mechanisms contribute for the shear strength of the interface between concrete layers cast at different times: i) cohesion; ii) friction; and

iii) dowel action. Since both cohesion (c) and friction (µ) coefficients are directly related with the roughness of the interface surface, it is important to characterize this parameter and to correlate it with the shear strength of the interface.

In all concrete design codes the surface roughness of the interface is qualitatively assessed. The new fib Model-Code (2010) [1] is the first one to quantify this parameter. However, it makes use of one of the simplest roughness parameters to classify the surface roughness and it links this to the four predefined categories (very smooth, smooth, rough and very rough) adopted in most design codes. According to these categories, both coefficients of cohesion (c) and friction (µ) assume different values in the design expression.

Aiming to support the new fib Model-Code (2010) [1] approach, but also with the goal of finding the roughness parameter that best correlates with both coefficients of cohesion and friction, an experimental study was carried out. First, composite concrete specimens were produced having their interfaces prepared with different techniques in order to increase the surface roughness. Next, the 2D-LRA method (2D Laser Roughness Analyser) [2] developed by the authors was used to obtain roughness profiles for each surface. Then, roughness parameters were computed. And last, they were correlated with the bond strength in shear assessed with slant shear tests.