Experimental study on the interface between low cement recycled aggregates concrete and ultra-high durability concrete

Abstract

Increasing the durability of concrete structures and reducing the environmental consequences associated with their production is essential to contribute to the sustainability of this industry. Bearing this concern in mind, a concept was developed that consists of considering an eco-friendly concrete only in the core of the structural members, combining a concrete with reduced cement dosage (LCC) with a recycled aggregate concrete (RAC) from construction and demolition waste and, in the outer layer, an ultra-high-durability concrete (UHDC) to significantly improve their durability. The structural behavior and durability of these composite reinforced concrete members are greatly dependent on their connection. Thus, the main objective of the present study is to evaluate the shear strength at the interface between the considered UHDC and two concrete mixtures, one to be used as reference (CC) and the other with low cement dosage and with recycled aggregates (LCRAC). To achieve that goal, an experimental program was carried out based on the slant shear test, where the type of concrete, the roughness of the substrate, and the way how the UHDC is applied are the main variables. The results were compared with the predictions of the main codes, Eurocode 2 and fib Model Code 2010. The used technique to place the UHDC proved to have a major influence on the shear strength at the interface, reaching differences around 60%. It was also concluded that the strength and the porosity of the binder matrix, the waviness profile of the indented interface, and the characteristics of the aggregates have a great influence on the shear strength at the interface.