A novel kind of concrete superplasticizer based on lignite graft copolymers

A novel superplasticizer was synthesized by grafting 2-acrylamido-2-tert.butyl sulfonic acid (ATBS) and acrylic acid (AA) monomers onto a lignite backbone using free radical copolymerization technique. Different molar ratios of ATBS:acrylic acid were tested to investigate the influence of the acrylic acid content on the dispersing performance of the graft copolymer. The synthesized polymers were characterized relative to their molecular properties and their dispersing performance in cement. It was found that especially the graft copolymer with an ATBS:acrylic acid molar ratio of 1:0.15 exhibits high dispersing force, long slump retention, high sulfate tolerance and only minor cement retardation. The polymer is more effective than industrial grade BNS. Successful grafting of the monomers was confirmed by size exclusion chromatography and measurement of the adsorbed layer thicknesses.