Synthesis of sodium alginate-polycarboxylate superplasticizer and its tolerance mechanism on montmorillonite

Sodium montmorillonite (MMT) is a major mineral component of clay in manufactured sand which is an economical aggregate in concrete. Its lamellar structure has a negative effect on an important concrete admixtures polycarboxylate superplasticizer (PCE). In this study, sodium alginate (SA), a polysaccharide, was grafted with an unsaturated amide, having a double bond structure, to synthesize the acrylamide modified sodium alginate (Ugi-SA) through the Ugi reaction. Then, Ugi-SA, acrylic acid (AA), and isopentenol polyoxyethylene ether (TPEG) were used to synthesize sodium alginate-polycarboxylate superplasticizer (SPCE) by free radical copolymerization. The structures of Ugi-SA and SPCE were determined by gel permeation chromatography (GPC) and Fourier transform infrared (FT-IR). The fluidity of the montmorillonite (MMT) cement paste with SPCE and the traditional polycarboxylate superplasticizer (TPCE) was investigated. Furthermore, the adsorption behavior of SPCE on MMT was measured by X-ray diffraction (XRD), thermogravimetric analysis (TGA), total organic carbon analyzer (TOC) and the tolerance mechanism of SPCE on MMT was discussed. The FT-IR and GPC results showed that Ugi-SA and SPCE were synthesized successfully. The initial fluidity test results indicated that SPCE had a better dispersion effect and MMT tolerance than TPCE. TGA, TOC and XRD tests showed that the adsorption of SPCE on MMT was much lower than that of TPCE. This study demonstrated that the SA structure of SPCE appears to exhibit a large steric hindrance, which prevents the intercalation of SPCE into MMT.