## 4 Conclusions  
This research intended to analyse the thermal behaviour of concrete mixes with recycled aggregates (RA) from four construction and demolition waste (CDW) plants in Portugal.  
With respect to the thermal conductivity test, a value of 2.08 W/m.K was obtained for the reference concrete (RC), made with natural aggregates only. According to Eurocode 2, the thermal conductivity of a standard density concrete, at a temperature of 20 \({}^{\circ}\)C, has a value between 1.33 and 1.95 W/m.K. Hence, it was concluded that the value obtained in the present study for the RC mix is similar to the maximum limit suggested by the Eurocode 2.  
In this investigation, the thermal conductivity coefficients of the concrete mixes with RA from CDW were also evaluated, and it was concluded that the use of RA causes a decrease of the thermal conductivity coefficients of the concrete mixes. This decrease was quite significant (between 17% and 42%) when all the NA were replaced with fine or coarse RA. As in the analysis performed regarding the compressive strength of the concrete mixes, a high variation of the thermal conductivity with the RA used in concrete production was also observed. The different types of RA have quite different compositions, with the incorporation of distinct percentages of concrete, ceramics, glass, wood, and other materials. Hence, considering that these wastes have different thermal conductivity, the concrete mixes were expected to have different thermal behaviour. The concrete mixes produced with fine RA from Vimajs displayed the best results, with a 42% decrease in their thermal conductivity coefficients when compared to the RC. The lower thermal conductivity of concrete with RA is due to the lower density and thermal conductivity of these aggregates. On the other hand, the change of the thermal  
Figure 14: Variation of the thermal conductivity with the compressive strength.  
behaviour it is also due to the higher porosity of these RA and of the corresponding concrete itself. The results obtained in the compressive strength test carried out at 28 days also confirm that the different composition of the RA used strongly influences the strength and durability of the concrete mixes produced with these aggregates.  
The use of RA from Vimajas resulted in a much higher reduction of compressive strength at 28 days (43.4%), when compared to the RC, than that observed with the use of RA from Ambilei (23.9%). This variation, together with the analyses carried out through Scanning Electron Microscopy, shows that the concrete mixes with RA from Vimajas have the highest porosity.  
Finally, it was concluded that the choice of the size of the RA used does not seem to significantly influence the quality of the concrete mixes regarding their thermal performance.  
This research was supported by the ICIST-CERIS Research Centre of IST, University of Lisbon, by FCT (Portuguese Foundation for Science and Technology), and Secil.  
[PERSON], [PERSON] and [PERSON] conceived and designed the experiments; [PERSON] performed the experiments; [PERSON] and [PERSON] analyzed the data; [PERSON] contributed analysis tools; [PERSON] wrote the paper.  
The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.