On average, around 46% of mineral construction and demolition waste is recycled in the EU member states, although there are significant differences between the individual countries. The Waste Framework Directive (2008/98/EC) requires a recycling quota of 70% by 2020.
Over the last decades, extensive research on recycled aggregates was carried out and im-plemented in national and international standards. Up to now, the use of the fine recycled aggregates (fine fraction 0-2 mm) in concrete is not allowed according to EN 206, so that these fractions (up to 50% of the processed recycled aggregates) are in practice used for landfill. The use of these fine fractions as cement constituents is currently insufficiently investigated and requires further research. The basic prerequisite for the utilisation of the fines from concrete recycling plants as cement main constituent will be to characterise the material properties as quickly and compre-hensively as possible and to ensure a constant material flow. An essential part of the research project is therefore the development of a rapid test method, with which the properties of these fines can be estimated by measuring the residual reactivity.
In the research project, both artificial crushed sands and crushed sands from industrial con-crete recycling plants are investigated. The crushed sands are ground to a target fineness and characterized with regard to their content of dangerous substances, e.g. sulfate and chloride. In the next step, the residual reactivity is determined. For this purpose VDZ uses the measurement of the heat of hydration by means of isothermal calorimetry according to ASTM C1897.Besides, mortar prisms are produced in accordance with EN 196-1 and the activity index of the crushed sands is determined at the age of 7 and 28 days. The project partners from Austria and Belgium are developing their own methods to describe a possible residual reactivity. A further mechanical or moderate thermal treatment of the crushed sands to increase the reactivity will be decided in the course of the project. In the following work packages, cements with different crushed sands and crushed sand contents will be produced. Fresh concrete properties, compressive strength and durability of concretes with these cements will be investigated.