Recycling of Waste Fresh Concrete as Aggregate Granules

A significant part of the fresh concrete is returned to the production plants. In our study, we investigated the influence of recycled waste fresh concrete as aggregate granules on the fresh properties, strength of concrete, and transport properties. In this method, the fresh concrete is recycled with its cement paste or mortar fraction. The recyclable aggregate granules were produced using fresh concrete according to the product instructions. This new recycled aggregate must be distinguished from aggregates produced by backwashing fresh concrete or crushing demolished concrete. The recycled aggregate granules were used in increasing doses (5%, 30%, and 50%) according to the reference concrete recipe, and compared with the properties of the reference concrete. The particle size distribution of the original aggregate and the recycled aggregate granules was determined. The sieve analysis resulted in a coarser aggregate for recycled aggregate granules as for the original natural aggregate. Consistency, workability, density, and air content were measured on fresh concrete mixtures. The compressive strength was tested at the ages of 2, 7, and 28 days, and the chloride ion migration test was performed at the age of 28 days. The apparent porosity, water absorption coefficient, and capillary water absorption were also studied. After evaluating the tests, the following conclusions could be drawn: a 5% dosage of recycled aggregate granule does not significantly affect the properties of the concrete. According to the MSZ 4798:2016 standard and its amendments, 5% by weight of recycled aggregates can be used in concrete without any further requirements. The dosages of 30 or 50% also met our expectations, however, future research is needed to study the long-term behavior of concretes made with these recyclable aggregate granules. The innovative material and method allow the returned fresh concrete to be fully recycled, thus reducing the amount of waste concrete. With these achievements, the concrete industry can also move towards a circular economy.