Research on a mix design method of self-compacting concrete based on a paste rheological threshold theory and a powder equivalence model

Abstract

This work studied a mix design method of self-compacting concrete (SCC) containing limestone powder (LP) or fly ash (FA) or both. The addition of LP or FA or both was shown to reduce the water/powder volumetric ratio (Vw/Vp) and the superplasticizer/powder mass ratio (SP%) and increase the SCC flowability. The reason for these phenomena is that powders such as LP and FA have ball bearing effect, filler effect and adsorption effect, which play a larger role in paste than in SCC owning to the relative percentage of LP or FA or both decreasing after adding aggregates. The different role limit the applicability of the paste rheological threshold theory, which results in the self-compacting paste (SCP) zone not accurately matching the SCC zone. A powder equivalence model was proposed to solve the influence of the above three effects on this zone mismatch. LP and FA can be converted to equivalent cement through equivalence coefficients based on the SCC flowability. The equivalence coefficients of LP by volume and by mass are 0.75 and 0.6, respectively. The equivalence coefficients of FA by volume and by mass are 0.50 and 0.38, respectively. Based on the equivalence coefficients from the experiments, LP and FA were mutually used in SCCs with the coefficients unchanged. The result shows that the equivalent SCP zone for the addition of LP and FA coincide partly with the SCC zone.