Sustainability Improvements in the Concrete Industry

The use of recycled aggregates concrete (RAC) with coarse recycled concrete aggregates (CRCA) has been widely studied in literature. A number of works investigated both mechanical and durability-related properties of these concretes; however, fresh properties of RAC have not been extensively analyzed yet. Limited studies were focused on the influence of some recycled aggregate properties on slump, which is the most frequently used measure to evaluate workability. Since this measure is a single-value and it is often operator-sensitive, a more quantitative estimate can be derived in terms of fundamental physical quantities, such as plastic viscosity and yield stress. The higher heterogeneity in terms of experimental slump measure occurs indeed when recycled aggregate concrete is tested. In this chapter, a review of the existing experimental methods for the evaluation of fresh concrete workability is given. Additionally, the behavior of fresh concrete is explored, aiming to understand which physical phenomena govern the macroscopic rheological behavior, under some specific conditions, e.g. in terms of mix composition, casting conditions, etc. Some experimental results about fresh recycled concretes workability and rheology, collected from literature, are also discussed.

The aim of this section is to comprehensively investigate the possibility of substituting natural aggregates with Black/Oxidizing Electric Arc Furnace (EAF) slag, at high replacement ratios, to produce structural concrete. The properties of the slag are described in detail, in terms of chemical composition, mineralogy, microstructure and physical characteristics. A review of the main physical and mechanical properties of concrete containing EAF slag is reported, analyzing the effect of the substitution on compressive and tensile strength and on elastic modulus, both for producing ordinary strength and high strength concretes. Durability-related properties in aggressive environments are also discussed, paying attention on freezing/thawing, drying/wetting conditions, and chlorides-contaminated exposure. Results showed that high substitution ratios of coarse natural aggregates are possible without decreasing mechanical properties of concrete, and on the contrary, slag use enhances concrete strength. Conversely, replacement of fine natural aggregates with fine slag seems feasible at lower substitution ratios only. Presence of calcium and magnesium oxides in the slag does not seem to represent a limit for the durability of concrete, due to their stabilization in crystalline lattice.

A significant number of green concrete have been recently designed to meet the growing request of reducing construction industry impacts, saving raw materials and preventing industrial by-products’ discard. Between these, recycled aggregates coming from construction and demolition waste (CDW) and Black/Oxidizing Electric Arc Furnace (EAF) slag have been founded to be suitable for structural concrete applications, when used as replacement of natural coarse aggregates. However it is necessary to solve the arising question about how those recycled materials effectively improve the sustainability of concrete industry. A quantitative estimate of the environmental impacts’ related to the production of those concretes can be performed using several environmental indicators. In this section a review of the available environmental tools, useful to assess concrete impacts, is reported. Particularly Life Cycle Analysis (LCA) and abiotic depletion indicator can be satisfactorily applied to quantify the emission reduction due to the use of recycled aggregates instead of natural gravel in structural concrete. The procedure described in this section can be applied to determine the impacts of other recycled aggregates concretes, practically estimating the environmental footprint of the material.

An experimental database about the properties of electric arc furnace slag is gathered. Data have been collected in literature from more than 40 research works, where the slag has been used in many applications, e.g. in mortar, concrete and for applications in bituminous mixtures. Physical properties, chemical composition, leaching and expansion potential are here included. The properties of the products have been also collected, including mix proportions and performances. The database represents an important-state-of-the-art about the use of EAF slag in civil engineering applications, with a particular attention paid to the uses in structural concrete.