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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.

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This paper characterises the thermal conductivity of structural lightweight aggregate concrete with strength classes ranging from LC12/13 to LC55/60 and density classes from D1·6 to D2·0. The thermal conductivity of concrete is assessed by a transient test method, taking into account different types of lightweight aggregate and binder, as well as different water/binder ratios. The influence of the concrete constituents on its thermal conductivity is analysed and relations between this thermal property and both the density and water content of concrete are established. It is shown that the thermal conductivity of structural lightweight aggregate concrete can be half that of normal weight concrete of similar composition. A high exponential correlation between thermal conductivity and density of concrete is achieved. On average, thermal conductivity decreases about 0·6% per each 1% increment in aggregate porosity, 8·3% per each 50 l/m3 increment in coarse aggregate volume and 3–9% per each reduction of 1% by weight in water content.

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