Preparation and clay tolerance research of a polycarboxylate superplasticizer modified by phosphonate group

Abstract

At present, it is a difficult engineering problem to control the workability of concrete with high clay content sand. A phosphonate group-modified polycarboxylate superplasticizer (PHS-PCE) was synthesized by using 2-(methacryloyloxy) ethyl phosphate (MOEP), isobutyl alcohol polyoxyethylene ether (IPEG) and acrylic acid (AA). Characterization of the molecular structure of PHS-PCE was conducted using Gel permeation chromatography (GPC), Fourier-transform infrared spectroscopy (FT-IR), 31P nuclear magnetic resonance (31P NMR) spectroscopy and elemental analysis measurements, showing successful incorporation of the phosphonate group with high polymer purity. However, owing to the low reactivity of MOEP, approximately 65 wt% monomer was introduced into the copolymer. PHS-PCE exhibited better flowability and stronger retardation effect than the conventional polycarboxylate superplasticizer (C-PCE), attributing to the increased negative charge density and complexing capacity with calcium ion caused by the phosphonate group. Under conditions of clay presence, the maximum variation of PHS-PCE adsorption on cement particle was 18 %, whereas that of C-PCE was 25 %. The phosphonate group in molecule promotes part of PHS-PCE to adsorb on the edges of clay, preventing intercalation and improving the clay tolerance.