Valorisation of recycled concrete sands in cement raw meal for cement production

The demolition of old structures in concrete generates materials which can be recycled in the form of aggregates for new concrete, thus preserving natural resources. These recycled concrete aggregates are composed of natural elements bounded with hardened hydrated cement paste. The fine fraction (sands and fillers) is however more difficult to reuse than aggregates because it contains a high proportion of cement paste which absorbs a lot of water. The recycling of these products in the cement process is an interesting alternative way. In this paper, the possibility to use recycled concrete and fine material from de-dusting process of crushing platform for demolition concrete as alternative raw material for cement production was investigated. After a full chemical characterization of the recycled concrete sands and fines (XRF, XRD, DTA-TGA.), several cement rawmixes were prepared by substituting partially or fully clay or marl. The generated clinkers have been characterized by different analytical techniques (TGA/DTA, XRF, XRD, SEM.). If the chemical composition of the raw is well balanced, the substitution of one of the cement raw meal components by recycled concrete sands does not affect the clinker. However, the free lime content may vary, including the initial quartz content of the recycled concrete sands used.