Mortars with thermo activated recycled cement: Fresh and mechanical characterisation

This paper aims to contribute to a better knowledge of the production and rehydration of thermo activated recycled cement (TRC) and its incorporation in cement based materials. To this end, the influence of different factors in the fresh and hardened properties of mortars with TRC was analysed, such as the water/binder ratio, the treatment temperature, incorporation percentage and particle fineness of TRC. Thermogravimetry, X-ray diffraction, isothermal calorimetry, scanning electron microscopy and 29Si nuclear magnetic resonance spectroscopy were carried out to better understand the hydration behaviour and microstructure development of TRC mortars. Optimal rehydration properties and strength development were obtained for recycled cement thermo activated at 600–800 °C. Binders with CEM I 42.5R and 20, 50 and 100% TRC could be framed in the European normative strength classes 52.5, 42.5 and 32.5, respectively. The main obstacles that hinder the application of TRC are its low setting time and high water demand. However, the water demand and setting time were not significantly affected for up to 50% TRC incorporation. Moreover, the mechanical strength was little affected for up to 20% TRC replacement and was only 12% reduced for 50%TRC incorporation. Therefore, TRC proved to be a very promising supplementary cementitious material for cement replacement.