The fluidity of fly ash–cement paste containing naphthalene sulfonate superplasticizer

Abstract

The zeta potential measurement indicated that the surface potential of fly ash was different from ordinary Portland cement (OPC) in both sign and value. Hence, the Derjaguin–Landau–Verway–Overbeek (DLVO) theory for dispersion–flocculation of heterogeneous particles with different surface potentials was applied to explain the influence of fly ash on the rheology of cement paste containing naphthalene sulfonate superplasticizer. For the fly ash–cement paste without superplasticizer, the sign of zeta potential of fly ash was different from OPC. Thus, the extent of the potential energy barrier between particles was small or even showed negative value, and the change in the rheology of the fly ash–cement paste was mainly dependent on the bulk solid volume of fly ash, which was related to available free water for fluidizing paste. For the fly ash–cement paste with naphthalene sulfonate superplasticizer, fly ash and cement had the same sign and dispersed well due to higher potential barrier. The extent of potential energy barrier depended on the absolute value of surface potential, which was represented by a function of the amount of adsorbed superplasticizer. The bulk solid volume of fly ash also affected the change in flow ability, but the effect of potential energy barrier between particles was superior to that of the bulk solid volume of fly ash.