Recycled concrete and mixed rubble as aggregates: Influence of variations in composition on the concrete properties and their use as structural material

The recycling of concrete, bricks and masonry rubble as concrete aggregates is an important way to contribute to a sustainable material flow. However, there are still various uncertainties limiting the widespread use of recycled concrete (RC). The fluctuations in the composition of commercial grade recycled aggregates (RAs) and their influence on the properties of fresh and hardened concrete are of particular concern regarding the use of RC. In this project, variations in the composition of RA were studied over a period of several weeks. Concrete mixtures were then produced with these aggregates in order to evaluate the resulting variations in concrete properties. Using two of them, consisting a high content of RA, the principal applicability of RC-mixtures for structural use in comparison to conventional concrete (CC) was shown in web shear and flexural reinforced beams, which were tested to their ultimate shear force resistance. Evaluating experimental and analytical results based on the modified truss methodology, no significant drop for beams made of RA in their shear force resistance was observed. Although the high variability in aggregate composition causes corresponding variations in concrete properties, the results obtained demonstrate that RA is suited for a wide variety of applications in the building industry.