| The polycarboxylate superplasticizer(PCE)is characterized by a small dosage,a large water reduction rate,a large degree of freedom of structural change of the molecule.It has a wide range of applications in terms of concrete compatibility,reduction of mixing water admixture,overcoming excessive slump loss and improvement of compressive strength of concrete.Therefore,its future applications are very promising.In this thesis,six standard types of PCE were prepared by using isopentenyl polyethylene glycol ether(TPEG-2400)and isobutene polyethylene glycol ether(HPEG-2400)reacted with acrylic acid(AA)through free radical polymerization.It was found through single factor tests that the standard PCE synthesized using the HPEG type had better cement dispersion than the PCE prepared using TPEG.The synthesis scheme:AA:HPEG=4:1 at 60°C.To further improve the dispersion effect,an orthogonal tests were carried out using HPEG-2400,AA and acrylic ester as the main polymerization monomers.That is,at a temperature of 60°C,the acid to ether ratio is 4:1,the ester to ether ratio is 1.5,and the chain transfer agent and initiator are 0.1%and 0.1%of the polyether monomer respectively.The data from infrared spectroscopy(IR),proton nuclear magnetic resonance spectroscopy(~1H NMR)and gel permeation chromatography(GPC)showed that the ester group was successfully polymerized on the PCE molecule.The application results show that an optimum dispersion of 250 mm can be achieved at 0.5%dosing.The reasons for the improvement in cement flowability and dispersion performance were analyzed through performance tests such as zeta potential and surface tension.Finally,the concrete testing data obtained without adding other types of admixtures indicated that the PCE also had a certain viscosity reduction effect.In order to further improve the viscosity reduction effect of concrete,the influence of PCE with different side chain lengths(HPEG-1200,HPEG-1800,HPEG-2400)on the viscosity reduction effect of concrete was explored using HPEG-2400,AA and MA as the reaction system.The structure of the synthesized PCE was confirmed through IR,~1H NMR and GPC.The results of zeta potential(-5.06 m V)and surface tension(60.59m N/m)indicated that PCE prepared using HPEG-1800 had a higher water reduction rate,mainly because the short side chain had a higher degree of freedom,the molecular chain was more relaxed,and sufficient steric hindrance could be provided.Therefore,the cement paste flowability and concrete application testing showed that PCE with shorter side chains had better viscosity reduction effects. |
