Synthesis And Performance Of Amphoteric Superplasticizer Used In Concrete

Polycarboxylate-type superplasticizers (PC) become more and more popular due to better controlling of concrete slump loss and higher water-reducing ability than the other kind of superplasticizers. Up to now, most superplasticizers belong to anionic polymers. Others, such as amphoteric or cationic admixtures are seldom reported.The surfaces of cement particles exhibit both negative and positive. 3CaO·3Al₂O₃·CaSO₄ (C₄A₃S|ˉ) is positiv while 2CaO·SiO₂ (C₂S) is negative.It can be inferred the adsorption capacity of the traditional anionic superplasticizer was very limited and adsorption saturation would be improved by amphoteric superplasticizer. The dispersing effectiveness and dispersing retation of APC were much better than those of anionic superplasticizers.In this paper, a novel amphoteric superplasticizer(APC) was prepared by solution copolymerization from maleic anhydride, allyl polyethylene glycol and methacryloxyethyltrimethyl ammonium chloride. The optimal condition on preparation was determined with the help of orthogonal experiment.The initial flow of paste of OPC with APC was used as index. The optimum condition on preparation is the molar ratio of MA, APEG(with 7 ethylene oxide units) and DMC was chosen as 5.5:1.5:0.5 and the dosage of KPS was 5.0 wt.%. The reaction was continued for 1.5 h at 80℃.APC characterized by FTIR spectra, Liquid chromatography and surface tention. Besides, Effect of factors on perforamces of APC in OPC and SAC was investigated. It was shown that perforamces of APC in OPC was different with that of APC in SAC. Adsorption and Zeta potential were also tested for investigating the the main mechanism for APC in OPC and SAC. Results indicated that steric repulsion between the cement particles carrying adsorbed polymer molecules is the main mechanism for dispersion.A commercial anionic superplasticizer were also used for assessing the performances of APC. Adsorption and mechanical performance were tested. It was shown the adsorption of APC in OPC was larger than that of commercial anionic superplasticizer while mechanical performance of APC was a little lower than commercial anionic superplasticizer. The experimental would be improved in further. Both adsorption and mechanical performance of APC in SAC were much better than that of commercial anionic superplasticizer. APC was compatible with SAC.