Preparation Of Viscosity-reducing Polycarboxylate Superplasticizer And Its Primary Properties

By researching and developing viscosity-reducing agents,this paper is aimed to concretes,mainly the mixtures of ultra high-strength and ultra high-performance concrete with low water-cement（binder）,which are too viscous and cause difficiluty in construction,especially pumping.This study selected monomers with multiple acrylates such as isoprene tetraacrylate,trimethylolpropane triacrylate,hexanediol diacrylate as branched monomers,and grafted multiple molecular chains of PCE to prepare a series of viscosity-reducing polycarboxylate ethers（VR-PCEs）with long-arm structure,by the free radical polymerization reaction.And the structure has changed from traditional comb-shaped to new-type topological structure.The orthogonal experimental design method and the average value method was used to study the influence of polymerization process parameters on the basic performance of VR-PCEs,and the optimal parameters were determined as follows:the monomer ratio is n _TPEG:n _AA:n _An:n _TGA:n _APS=15:50:1.0:2.7:4.2,concentration is 30%,reaction temperature is 65℃,monomers adding time length for 2.5h,followed by a cooling process until to the room temperature,where n,TPEG,AA,An,TGA,APS are denoted the amount of monomers,methallyl polyoxyethylene ether,acrylic acid,crosslinking monomer,thioglycolic acid,ammonium persulfate,respectively.Using the optimized synthesis process parameters,three branched monomers as noted are used as the"core"to prepare VR-PCEs,while PCE without branched monomers are used as the control group to explore the influence of molecular conformation on the performance of VR-PCEs and PCE.The molecular structure was characterized by gel permeation chromatography（GPC）,infrared spectroscopy（FTIR）,nuclear magnetic resonance（¹H NMR）.The results showed that except for A₂-PCE,the conversion rates of the other three products were over 80%.Reference to the national and industrial standards,the performance of the slurry mixed with the VR-PCEs and PCE was tested analysed.By experiments on cement paste fluidity,paste viscosity,setting time,mortar water-reducing rate and its viscosity test,concrete slump flow test,the ability of VR-PCEs to improve the workability of fresh cement-based materials was evaluated.By testing the flexural/compressive strength of mortar and concrete,the effect of VR-PCEs on the mechanical properties of cement-based materials was revealed.The results showed that the cement-based materials mixed with the VR-PCEs has higher fluidity and well dispersity retention,and water-reducing rate is up to 30%;when the water-cement ratio is the same,paste or mortar with VR-PCEs performed lower viscosity than blank,however,when keep slump is equal and paste and mortar with VR-PCEs has lower water,resulted higher viscosity;the VR-PCEs can extend setting time in both boundary conditions,the retarding effect is obvious,and the initial and final setting time can be prolonged by 2h and 3h;the strength of the mortar is positively correlated with the degree of branching of VR-PCEs,therefore,the mechanical performance of the A₄-PCE group is better,which can increase the flexural/compressive strength of mortar in each age by 20%when slump is equal.In order to explore the mechanism of the VR-PCEs with new topological structure,this study further tested the Zeta potential of the cement particle surface,the surface tension of solution with different concentation,the heat of hydration and hydration products.The research results showed that the absolute value of the Zeta potential on the surface of cement particles was changed by VR-PCEs,which played its roles by the combination of electrostatic repulsion,steric hindrance,adsorption and dispersion,changing of solid-liquid surface energy,etc.The VR-PCEs can delay hydration process,and changed mineral composition of paste at different ages.Meanwhile,VR-PCEs changed the morphology of the hydration products,which changes the structural density of the specimens at different ages.