Last time I checked carbon was black. Mixing it with cement to get a darker concrete may be a brain dead idea: you get CO2 sequestration and warmer walls/paveme

Last time I checked carbon was black. Mixing it with cement to get a darker concrete may be a brain dead idea: you get CO2 sequestration and warmer walls/pavements etc if exposed to sunlight. One can avoid that by using it only for no sun exposed elements, but it does complicate things.