Using waste concrete as a replacement for natural limestone to produce cement clinker

Four samples of waste concrete with crushed limestone as coarse aggregate were collected from four different demolition sites. Each sample was crushed into particles which were then screened by sieves to remove smaller particles of given size. The residue was retained for use. Most of the residue was the crushed limestone; it was used to replace natural limestone as the calcareous raw material to produce cement clinker. These four clinker samples were compared with the similar Chongqing Lafarge cement clinker and some selected Portland cements on the market. The comparison results of XRD indicated that the XRD characteristic apex of the four principal compounds in the usual cement clinkers, C3S, C2S, C3A and C4AF, are strong enough in the clinkers produced by the waste concretes. All the free CaO content in the clinkers produced by the waste concretes was less than 1%, meeting the requirement of a given Chinese standard. It can be used to prepare Portland cements with strength grade of 52.5. The experimental results offer theoretical and technological guidance for efficiently reusing waste concretes.

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