Shear Load Capacity of Concrete Members with Recycled Aggregates within the Scope of Application of BK-E

The concept of circular construction counteracts the increasing scarcity of raw materials by reusing components or demolition material as new building materials. One approach to circular construction is the use of crushed concrete as recycled aggregate in new concrete. With the introduction of DIN 1045-2:2023, up to 45 % by volume of the coarse natural aggregate may be replaced by recycled aggregate of Type 1 (≥ 90 % concrete demolition) or up to 35 % by volume of Type 2 (≥ 70% concrete demolition) in concrete class BK-E. The use of fine recycled aggregate of Type 1 may also be used up to 20 % by volume of the exchangeable coarse aggregate fraction, provided that the requirements for material composition are met. The strength class in BK-E is currently limited to C30/37, although reliable concrete production with recycled aggregate also appears realistic in higher strength classes.

In a current joint research project of the Institute of Structural Concrete at RWTH Aachen University and the Department of Materials in Civil Engineering at RPTU Kaiserslautern-Landau, theoretical and experimental investigations are carried out with the aim of extend the application limits in BK-E. From a design perspective, investigating the shear strength of members with recycled aggregates is relevant (fig.), as the next generation of Eurocode 2 proposes a reduction of up to 20 % in the calculated shear strength of members without shear reinforcement, depending on the substitution rate. Existing and future design rules are to be reviewed and refined through systematic experimental investigations and the evaluation of databases.