Mechanical characterization of thermal activated low-carbon recycled cement mortars

In this study, low-carbon recycled cement (RC) was produced from thermally activated concrete and cement paste wastes and its incorporation in mortars, as cement replacement, was investigated. The calcination temperatures were defined based on thermogravimetric and X-ray diffraction analysis. Mortars were characterized in terms of their main fresh and mechanical properties (compressive and flexural strength, ultrasonic pulse velocity and dynamic modulus of elasticity). The influence of RC replacement ratio (20%, 50%, 75% and 100%), RC treatment temperature and RC fineness were analyzed. In all tested properties, RC from concrete waste showed significant lower efficiency than that from cement paste waste. The RC rehydration capacity was improved by increasing its fineness and pre-heating temperature. Mortars produced with 100% of 650 °C pre-heated RC were able to attain as high as 8.3 MPa of compressive strength at 28 days, corresponding to about 20% of that found in reference mortars without RC. In addition, mechanical properties were little affected by RC replacement ratios up to 20%. This study shows the efficient rehydration capacity of thermal activated RC and suggests its high potential for the construction industry.