THE SUPERPLASTICIZER ADSORPTION CAPACITY OF CEMENT PASTES, PORE SOLUTION COMPOSITION, AND PARAMETERS AFFECTING FLOW LOSS

Studies are reported on the interaction of sodium salt of polynaphthalene sulfonate superplasticizer (PNS) with different cement types, its effects on the flow loss, and the chemistry of the pore solution at early time of hydration from mixing to presetting. Six commercial cements displaying a wide compositional range and fineness were selected. Results show that most of the superplasticizer is removed from the pore solution immediately after mixing. The adsorption capacity of the paste is mainly determined by the PNS molecular weight, cement fineness, and C(3)A content. In turn, the rate of flow loss appears to be strongly governed by the ionic strength of the pore solution and marginally to C(3)A content and ettringite formation. Oversulfating the cements by addition of up to 7% of gypsum, reduces the flow loss but within the range of data available, does not enhance the uptake rate of the superplasticizer by the cement constituents.