# Mechanical Characterisation and Shrinkage of Thermoactivated Recycled Cement Concrete
## 4 Conclusions  
In this paper, the fresh and mechanical performance, as well as the long-term shrinkage of concrete produced with total or partial incorporation of thermoactivated recycled cement from waste cement paste and waste concrete, were characterised. For the same workability, concrete with RCP required more mixing water or SP than that with OPC, due to the higher water demand of recycled cement than OPC. Nonetheless, up to 15% RCP incorporation, the workability was not significantly affected and recycled cement concrete could be produced without correcting the mixture composition. The SP was effective in compensating the lower workability of concretes with high amounts of RCP. The concrete density was more affected by the w/b than by the incorporation of recycled cement. However, for over 15% incorporation of RCP, the reduction of workability for the same w/b tended to increase the air entrainment of concrete. Contrary to non-treated waste cement and concrete filler, the recycled cement showed high rehydration capacity, retaining similar binding water than OPC and effectively contributing to improve the mechanical strength of concrete. Overall, for the same w/b, the compressive and tensile splitting strength were not significantly influenced by the substitution of OPC with RCP, even for high incorporation percentages, demonstrating the potential of this more eco-efficient binder as a supplementary cementitious material. The optimum incorporation percentage was attained for up to 15% RCP, with concrete showing similar to better mechanical strength than reference OPC concrete. The performance of thermoactivated recycled cement was significantly affected by its effective dispersion and the fresh concrete workability, which were improved by the addition of SP. In addition, concrete with RCP consistently displayed higher compressive strength at 3 days than that with OPC of equal w/b, which was attributed to the higher surface area and porous nature of RCP, improving the particle cohesion and the nucleation and filler effect at early age. The modulus of elasticity decreased with the increase in the percentage incorporation of RCP, which presents lower hardness and stiffness than OPC. A more significant non-proportional reduction was observed for the addition of more than 15% RCP. The equations suggested in EN 1992-2 [42] for OPC concrete, regarding the estimation of tensile splitting strength and modulus of elasticity, can also be adopted in concrete with recycled cement. Over 15% RCP, the UPV tended to decrease with the amount of RCP, due to the increase in air entrainment and stiffness reduction. The mechanical strength and drying shrinkage were not significantly reduced when RCC was used instead of RCP, especially up to 15% replacement. Thus, the recycled cement derived from waste concrete, according to the patented method developed by the authors, may be as effective as that directly obtained from waste cement paste of equal composition. For the same w/b, the drying shrinkage of concretes followed the same trend of the compressive strength. In concrete with up to 15% RCP incorporation, the lower stiffness of RCP particles and the slightly higher volume of paste were compensated by the development of denser microstructures. For higher amounts of RCP, the trend was inverted. Conceptualization, S.R., J.A.B. and A.C.; methodology, S.R., J.A.B. and A.C.; validation, S.R., J.A.B. and A.C.; formal analysis, S.R., J.A.B. and A.C.; investigation, S.R., J.A.B., A.C. and S.H. ; data curation, S.R., J.A.B. and A.C.; writing--original draft preparation, S.R., J.A.B. and A.C.; writing--review and editing, S.R., J.A.B. and A.C.; project administration, J.A.B. ; funding acquisition, J.A.B. All authors have read and agreed to the published version of the manuscript. This research was funded by the Portuguese Foundation for Science and Technology (FCT) through project PTDC/ECI-COM-28308/2017 and scholarship SFRH/BD/146033/2019. Not applicable.