Full-scale sustainable structural concrete containing high proportions of by-products and waste

The construction industry in general is, through minor low-cost processing methods, converting several of its by-products into viable materials; furthermore, some siderurgic sector by-products are likewise of use. In this context, large-scale batches (mix volumes over 0.5 m3) of good quality structural concrete are proposed, in which two kinds of binder and two kinds of aggregate (steel slag and recycled concrete) are used to perform four concrete mixtures, containing more than 80 % in mass of good-quality recycled materials. A batch of tests, both in the fresh and in the hardened state, are performed, covering on-site placement and long-term properties, to guarantee the suitability and the quality of the mixtures as structural concretes. Most of the results were encouraging, mainly depending on the aggregate and the binder types that were used. The fresh-state workability of all the test mixtures was good. All the results in terms of hardened properties, strength (42 MPa in type I cement mixtures, and 32–38 MPa in type III cement mixtures), stiffness, long-term shrinkage, and microstructural state (porosity, permeability) were acceptable, their quality depending on the type of each component. The good results of the mixtures based on the slag-based binder deserve attention. Some weak points found were the slightly higher specific weight of the slag aggregate mixes (amounting to more than 2.7 Mg/m3), plastic shrinkage rates (in some cases greater than 1.2–1.5 thousand), and loss of resistance against chlorine penetration in recycled concrete mixes. However, drawbacks of that sort are no obstacle to their use in most structural applications.