Physical properties and mechanical behaviour of concrete made with recycled aggregates and fly ash

Enhancing the environmental sustainability of human activities and industrial processes is a common challenge in various branches of modern research and technology. Being characterised by a huge demand of both energy and raw materials and by a significant contribution to the global emissions of greenhouse gases (GHGs), the construction industry is fully concerned by this challenge. Particularly, since concrete is the most widely used construction material, several solutions are nowadays under investigation to reduce the environmental impact of its production processes. They often consist of partially replacing natural constituents (i.e. aggregates, cement, water, fibres) with recycled ones, in view of the twofold objective of reducing both the demand of raw materials and the amount of waste to be disposed in land-fills. However, the formulation of reliable relationships between the main physical and mechanical properties of concrete produced with the aforementioned recycled constituents is still considered as an open issue. This paper is a contribution to such topic. The results of a wide experimental campaign carried out on concretes made using recycled concrete aggregates (RCAs) and fly-ash (FA) in partial substitution of natural aggregates (NAs) and cement (C) are presented and discussed herein. Particularly, concretes characterised by variable water-binder ratios and produced with different percentages of RCA and variable the content of FA have been tested. Test results have allowed estimating the time evolution of the compressive strength, as well as the tensile strength at 28 days, along with some relevant physical properties, such as permeability and resistance to chloride ion penetration. The feasibility of producing structural concrete made with even significant amounts of the aforementioned recycled constituents and industrial by-products clearly emerges from the experimental results. (C) 2013 Elsevier Ltd. All rights reserved.