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The increasing global demand for natural resources and the extensive production of construction and demolition waste (CDW) raise concerns for both the economic and environmental consequences that they can induce. Several efforts are being made with the aim to promote sustainable practices in the construction industry. In this context, one of the most relevant options refers to reusing CDW in new construction: specifically, the use of recycled concrete aggregate (RCA) is attracting a growing interest. Unfortunately, although the behavior of recycled aggregate concrete (RAC) has been widely investigated in the last few years, there are still knowledge gaps to fill on various aspects of the RAC performance, such as its durability in extreme conditions. The present study deals with the freeze-thaw performance of normal- (C35) and high-strength (C60) RAC produced with RCAs derived from different sources. Specifically, ten concrete mixtures were subjected to a different number of freeze-thaw cycles (namely, 0, 150 and 300), with the aim of analyzing the degradation of key physical and mechanical properties, such density, compressive strength, elastic modulus and tensile strength. Based on the obtained experimental results, a novel degradation law for freeze-thaw cycles is proposed: it unveils a relationship between open porosity of concrete, which is directly correlated to the peculiar properties of RCAs, and the corresponding damage level determined on RAC specimens.

Although Recycled Concrete Aggregates, RCAs, derived from concrete waste, represent a potential sustainable solution for the structural concrete production, their heterogeneous composition is a feature that still prevents their large-scale use in the construction industry all around the world. In order to find a possible existing relationship between the source of residues and the resulting RCAs characteristics, a pilot scale case study was carried out, in which approximately 20 tons of concrete waste, derived from different origins, were processed to obtain granulometric fractions from coarse aggregates to powders. The RCAs fractions obtained using a controlled processing procedure were then thoroughly characterized to establish quality control parameters that could lead to a classification of different types of recycled aggregate generated. The results show that the source of concrete waste strongly influences the amount of each aggregate fraction produced during processing and aggregate properties were dependent on the waste origin. Despite this, the presented analysis demonstrated, that by evaluating a fundamental parameter such as the Attached Paste/Mortar within the RCAs, a generalized quality-control classification can be proposed for the industrial upscaling of RCAs characterization. It is believed that such a classification could promote the integral and rational re-use of these secondary raw materials in different cement based products of the construction sector.

Recently, concerns have been rising about the impact of increasing the depletion of natural resources and the relevant generation of construction and demolition waste, on the environment and economy. Therefore, several efforts have been made to promote sustainable efficiency in the construction industry and the use of recycled aggregates derived from concrete debris for new concrete mixtures (leading to so-called recycled aggregate concrete, RAC) is one of the most promising solutions. Unfortunately, there are still gaps in knowledge regarding the durability performances of RAC. In this study, we investigate durability of structural RAC subjected to wet-dry cycles. We analyze the results of an experimental campaign aimed at evaluating the degradation process induced by wetting and drying cycles on the key physical and mechanical properties of normal- and high-strength concrete, produced with coarse recycled concrete aggregates (RCAs) of different sizes and origins. On the basis of the results we propose a degradation law for wetting and drying cycles, which explicitly makes a possible correlation between the initial concrete porosity, directly related to the specific properties of the RCAs and the resulting level of damage obtained in RAC samples.

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