Recovering hydrated cement paste in new mortar as supplementary cementitious material

The old hydrated cement paste in concrete waste is only partially hydrated. An efficient activation is required to liberate the unhydrated cement core surrounded by hydrates. This work innovated in the development of optimal mechanical activation techniques for recovering hydrated cement paste and using it as supplementary cementitious material in new mortar. The effect of recovered hydrated cement paste in the new mortar was compared to inert fillers, and a k-factor was calculated based on late compressive strength. The most efficient method for liberating the active cement core and activating the residual cementing properties was grinding in a planetary mill with a low concentration of grinding aids. Recovered cement fines reached higher compressive strength values than inert fillers and equivalent values to cement at later ages. The increment in compressive strength after 28 days indicated late hydraulic activity due to the high content of belite in the residual cement.