This paper intends to contribute to a better knowledge of the production and rehydration of thermoactivated recycled cement and its incorporation in cement-based materials. To this end, the influence of the treatment temperature on the properties of recycled cements and recycled cement pastes was assessed by means of a wide array of tests. Anhydrous recycled cement as well as the resulting pastes were characterized through density and particle size, water demand and setting time, thermogravimetry, X-ray diffraction, field emission gun scanning electron microscopy, isothermal calorimetry, ²⁹Si nuclear magnetic resonance spectroscopy, flowability, mechanical strength, mercury intrusion porosimetry and scanning electron microscopy. The treatment temperature had a significant influence on the dehydration and hydration of recycled cement, essentially resulting in the formation of C₂S polymorphs of varying reactivity, which led to pastes of different fresh and hardened behaviors. The high water demand and the pre-hydration of recycled cement resulted in high setting times and low compressive strengths. The highest mechanical strength was obtained for a treatment temperature of 650 °C.

This paper investigates the mechanical and shrinkage behaviour of concrete with recycled cement (RC) thermoactivated from waste cement paste and waste concrete. Overall, compared to ordinary Portland cement (OPC), for the same water/binder ratio, the mechanical strength and ultrasonic pulse velocity were not significantly influenced by the incorporation of RC. The elasticity modulus decreased with the addition of RC and the shrinkage tended to increase at high RC content. The incorporation of up to 15% RC allowed the production of workable concrete with identical shrinkage and similar to higher mechanical strength than concrete with only OPC. RC proved to be a very promising more eco-efficient supplementary cementitious material.

The urgent need to tackle the effects of global warming has led to a worldwide compromise and ever-more demanding regulations. In this respect, as an important greenhouse gas emitter, the cement industry has to implement major changes in its production processes to achieve future goals. In this perspective, low-carbon eco-efficient cement, such as the thermoactivated recycled cement from concrete waste (RCC), seem to be a promising alternative to current carbon-intensive binders, such as ordinary Portland cement (OPC). This study aimed to demonstrate the potential contribution of RCC to the reduction in the environmental impacts of the cement industry, by means of a comparative life cycle assessment of three production methods of this binder (wet (WM), dry (DM) and air clean (ACM) methods) and OPC. Overall, RCC WM did not turn out to be a good alternative to OPC, essentially owing to the amount of fuel and electricity required for washing and drying the particles before the magnetic separation. On the other hand, RCC DM and RCC ACM proved to be promising alternatives to RCC WM and OPC, with a relevant reduction in all impact categories.