## 1 Introduction
The study presented herein intends to fill some of the existing gaps in the knowledge on the incorporation of RA from CDW in concrete. It should be noted that there is currently a low confidence of the construction sector in the use of concrete with RA from CDW, due to the lack of technical knowledge and low experience in its use, compared to those on conventional concrete. Therefore, the thermal characterization of concrete with RA from CDW made in this study intends to increase the existing knowledge on its possible uses in the construction industry, whether as structural or non-structural concrete. This paper is part of an extensive research in which the evaluation of the mechanical [7], durability [8], rheological [9], microscopic [10] and thermal behaviour of concrete with RA sourced from different CDW (coarse RA from Valnor (Avis, Portugal) and Retria (Porto, Portugal) and fine RA from Vimajas (Algueirao-Mem Martins, Portugal) and Ambilei (Leiria, Portugal)) was carried out. To date, investigations that analyse the thermal behaviour of concrete with RA from CDW are scarce. [PERSON] et al. [11] and [PERSON] et al. [12] indicate that the thermal conductivity of concrete decreases as the percentage of replacement of natural aggregates (NA) with coarse recycled aggregates (CRA) increases. [PERSON] et al. studied the thermal behaviour of concrete made with CRA from CDW and found that the thermal conductivity of the concrete mixes with 100% CRA and 100% NA was of 1.58 and 2.00 W/m.K, respectively. [PERSON] [13] carried out an investigation in which the influence of the simultaneous incorporation, in several percentages, of RA made of concrete and of rubber on the thermal behaviour of concrete was assessed. Three 150 \(\times\) 150 \(\times\) 150 mm specimens were prepared from each mix. The specimens were cured in the laboratory in water at a temperature of 20 \(\pm\) 2 \({}^{\circ}\)C for 28 days. This author found that the use of 10% of concrete RA and 10% rubber RA reduces the thermal conductivity of the recycled aggregate concrete (RAC) by 32% in comparison with that of natural aggregate concrete (NAC). Hence, this author concluded that it is feasible to use this hybrid concrete as a non-structural thermal insulation material. In the case of concrete RA, the decrease in thermal conductivity of the RAC mix is related to the increase in the air content of the cement paste, which is responsible for a lower density [14]. [PERSON] et al. [15] studied the thermal behaviour of RAC with concrete RA and ceramic RA. Two 200 \(\times\) 200 \(\times\) 30 mm specimens were produced for each mix, totalling 18 specimens. The specimens were cured in the standard condition of temperature and relative humidity for 28 days (20 \(\pm\) 2 \({}^{\circ}\)C and 95%, respectively). Regarding the former, the study showed that the thermal conductivity of RAC decreases with the increase of aggregate replacement ratio. The authors also concluded that the use of CRA was the one that most influenced the thermal conductivity of concrete. Through this investigation, it was also observed that the use of 70% ceramic RA caused a decrease of the thermal conductivity of RAC. One of the explanations suggested by the authors for this trend is that the high water absorption of the ceramic RA can cause a greater evaporation of the water present in the cement paste, causing a decrease in the density of the RAC. The analysis of the thermal behaviour of concrete is important, since this property influences the behaviour of concrete in several domains, among which is the onset of cracks with thermal origin, due to the heat of hydration. Cement hydration is an exothermic chemical process, during which significant volumetric variations occur in the concrete, which, if partially or totally restrained, can lead to the appearance of tensile stresses and, consequently, to the onset of cracks. This type of cracks can lead to serious durability problems, due to the increased permeability of concrete to the entrance of external aggressive agents [16].