Accelerating effect of low replacements of carbonaceous materials in cement paste and mortar

Abstract

This study investigated the effect of incorporating small amounts of carbonaceous materials in cement paste and mortar systems at a low dosage. The materials studied include industrial graphite, natural graphite, carbon black, activated charcoal, and decolorized charcoal. The effect of this material on cement hydration through different techniques such as compressive strength mortar, TGA, SEM, isothermal calorimetry, rheology, and calcium isotherm adsoprtion. These tests studied the influence of carbonaceous materials’ properties on cement hydration. With the exception of industrial graphite G1, the carbonaceous materials showed an acceleration of setting after 1 day by favoring the nucleation of hydrates, reducing the porosity, and improving the mechanical properties. On the other hand, traces of this acceleration are no longer visible beyond 28 days. The accelerating effect of different carbons sources appears to be less dependent of crystallinity, mineralogy, or particle size, but rather on surface chemistry and the quality of particle dispersion.