Research On Synthesis And Slump Retention Properties Of Polyether Grafted Polycarboxylate Superplasticizer

Polycarboxylate superplasticizer （PC） is the new generation of high-performancewater-reducer after naphthalene series water-reducers. With many virtues, such as low dosage,high water-reducing, high slump retention ability and no pollution, PC can be used in cementsystem to meet the requirement of high-performance concrete in various engineering projects.In recent years, as the need for the construction of sustainable development in China, PC hasbeen widely applied in the key projects and the public projects. It represents the mostadvanced technique product of addictive material of concrete and becomes a hot researchtopic of chemical admixture. Therefore, it will dominate the market of water-reducers in5years as expected.PC can be synthesized by free-radical polymerization of various unsaturatedmonomers. PC with different structures can be obtained by molecular design andreaction controlling, e.g. choosing different monomers, choosing the ratio of variousmonomers and adjusting the reaction process. In this paper, a series of PC weresynthesized with allyl alcohol polyethylene glycol （APEG,EO=45）,2-acrylamide-2-methylpropane sulfonic acid（AMPS）, maleic anhydride（MAL） and acrylic acid（AA） asmonomers, and using ammonium persulfate（APS） as an initiator. To determine theoptimum process of PC, various reaction conditions for PC were intensively investigated,such as reactant concentration, temperature and the molecular ratios of monomers. By theL9（34） orthogonal experiment, the best synthesized condition was obtained. And the effect ofdifferent additives on dispersion retention of cement and slump retention of concrete werestudied. Moreover effect of above synthesized conditions on air-entraining performance andadsorption characteristics of PC was further investigated.Results show that the HX-PC with high dispersing ability can be obtained by adjustingthe dosage of monomers.The optimum reaction conditions are as follows. The ratio ofnAPEG:nAMPS:nAA:nMALis1:0.12:3:2.4, the reactant concentration is40⁵0%, thetemperature is80℃and the dosage of APS is0.2%. When HX-PC was used in cementsystem with W/C ratio of0.29and dosage of0.2%, the initial paste fluidity of cement was255mm, and changes in paste fluidity with elapsed time was243mm in30min, whichpossesses better dispersing and dispersion retention abilities.As bad workability and serious slump loss of PC applied in concrete, the effect ondispersion retention in cement of PC compounded with additives P、G and T has been studied.Results show that additive P is best improving dispersion retention ability of PC. When PC was used in cement system with W/C ratio of0.29and dosage of0.2%, reasonable dosage ofadditive G is equal and below5%, additive T5%and additive P4%.When PC was appliedin concrete compounded with additives G、T、Aand P, results show that additive P is bestimproving workability of concrete. PC compounded with additive P can remarkably decreaseslump loss. PC compounded with3%T,1%A and6%P possesses better workability andslump retention ability in concrete, while the dosage of PC is0.21%.Air-entraining performance and setting time of PC were studied. Results show that all ofthe PC synthesized in lab have certain air-entraining performance, PC synthesized by differentreactant concentration possess best air-entraining performance and PC synthesized bydifferent dosage of APEG possess best bubble maintaining ability. When nAPEG:nMALis1.0:0.64，PC possesses best air-entraining performance and retards46min of final setting timeof cement.Absorption kinetics of PC on cement particle surface was studied. The results show thatthe process of absorption kinetics meets the Langmuir adsorption rate equation. Adsorptionrate constant k and activation energy Eαwere0.01594min^-1（30℃） and17.9647kJ·mol^-1,respectively. Thermodynamics results showed the adsorption capacity of PC increased astemperature increased. The thermodynamics parameters were obtained as followed:ΔHad=-24.788kJ·mol^-1，ΔSad=0.050kJ·mol^-1·K^-1, ΔGadθ=-39.886kJ·mol^-1（30℃）, from which,we knew the adsorption was spontaneous exothermic process.XPS results show thattemperature made the adsorption layer get thicker which fit the results of adsorption capacity.