Slump loss control of cement paste by adding polycarboxylic type slump-releasing dispersant

A polycarboxylic type slump-releasing dispersant, which is a copolymer of maleic anhydride and acrylic acid (MA-co-AA) with an average molecular weight of 800, was used to compensate the slump loss of cement paste by naphthalene sulfonated formaldehyde condensate (NSF). The different ratios of MA-co-AA to NSF were added to the target CaCO3 particles or cement paste to evaluate adsorptive properties, dispersive stability, zeta potential, slump loss, and rheological behavior with time elapsed. The mixing of MA-co-AA with NSF resulted in the increase of adsorption amount of dispersant per unit weight of CaCO3 particle, but there were no differences in the zeta potential. The result for 20 wt% of MA-co-AA showed an excellent control effect of slump loss of cement paste and increasing apparent viscosity. The optimum dosage of NSF containing 20 wt% of MA-co-AA (NM-2) for the control of slump loss was between 1.0 and 1.5 wt% by cement weight for paste with water-to-cement ratio of 0.35. The optimum dosage of NM-2 depended on the water-to-cement conditions to obtain the effective slump loss control of cement paste. From the results of this research, the slump loss of cement paste could be controlled effectively by the addition of 1.0 to 1.5 wt% of the copolymer containing 20 wt% of MA-co-AA mixed with NSF. (C) 1999 Elsevier Science Ltd. All rights reserved.