Preparation And Performance Study Of VPEG Type Polycarboxylic Acid Water Reduce

Polycarboxylate superplasticizer has gradually become a research hotspot in the concrete admixture industry due to its advantages of high water reduction rate,good water retention performance,low dosage and strong designability of molecular structure.However,with the vigorous development of the construction industry,the construction industry’s requirements for the performance of concrete are also increasing.In order to meet its requirements,it is necessary to develop polycarboxylate superplasticizer with higher performance.At the same time,in the current market,most of the preparation process of water reducer requires constant temperature heating（50-80°C）and the synthesis time is long,which increases the energy consumption,time cost and operation cost of the factory in the production process.Macromonomers such as ethylene glycol monovinyl polyethylene glycol ether（EPEG）and4-hydroxybutyl vinyl polyoxyethylene ether（VPEG）with higher activity form p-πconjugates with C=C double bonds due to the oxygen atoms.The strong electron-donating ability makes the C=C double bond easy to break,so the polymerization process has low energy consumption and short reaction time,which can save production costs.In this paper,EPEG and VPEG were used as macromonomers to synthesize functional polycarboxylate superplasticizer.The specific contents and results are as follows:（1）Using EPEG as macromonomer,acrylic acid（AA）as comonomer,thioglycolic acid（TGA）as chain transfer agent,EPEG-type polycarboxylate superplasticizer was synthesized by in-situ modification ofγ-methacryloxypropyltrimethoxysilane（KH570）under H₂O₂/vitamin C（V_C）redox initiation system.The synthesis process was discussed and the properties of the synthesized superplasticizer were characterized.The results showed that the optimum synthesis process was as follows:the reaction temperature was 5°C,the ratio of acid to ether was3:1,the dropping time of A and B was 15 min and 25 min respectively,the amount of H₂O₂ and TGA was 0.4 wt%of EPEG,n（AA）:n（KH570）=10:1.5.The water reducer P（AA10-K1.5）prepared under this condition has the best performance.Its aqueous solution has the highest bubble height and the lowest surface tension.The fluidity of cement paste is large,which can delay the hydration reaction of cement.The compressive strength of cement test block can reach 69.3 MPa at 28 d.（2）Using VPEG as macromonomer,AA as comonomer,TGA as chain transfer agent,VPEG-type polycarboxylate superplasticizer was synthesized by in-situ modification of KH570 in H₂O₂/V_C oxidation-reduction initiation system.The effects of acid ether ratio,dropping time,H₂O₂ dosage,TGA dosage and KH570 dosage on the performance of synthetic superplasticizer were investigated.The most suitable process was as follows:the reaction temperature was 5°C,the acid ether ratio was 3.5:1,the dropping time of A and B was 45 min and 55 min respectively,the initiator H₂O₂ and TGA were 0.5 wt%and 0.4 wt%of VPEG,n（AA）:n（KH570）=10:1.5.The water reducer P（AA10-Si1.5）synthesized under this condition has a higher bubble height and a lower surface tension,which makes the cement suspension have a lower Zeta potential,and can delay the hydration of cement.The cement test block forms a dense pore structure,which significantly improves the compressive strength of the test block,and the compressive strength can reach 70.8 MPa.The comparison between EPEG and VPEG found that VPEG was more suitable for the preparation of polycarboxylate superplasticizer.（3）Using VPEG as macromonomer,AA and hydroxyethyl acrylate（HEA）as main comonomers,TGA as chain transfer agent,VPEG-type polycarboxylate superplasticizer mother liquor PCE-ZZ was synthesized by free radical polymerization under H₂O₂/V_Coxidation-reduction initiation system.The most suitable process was as follows:the reaction temperature was 15°C,n（AA）:n（HEA）:n（VPEG）=1:2.5:1,the amount of TGA and H₂O₂ was0.4 wt%of VPEG,the addition time of A and B material droplets was 60 min and 70 min,respectively.PCE-1 and PCE-2 were prepared by compounding PCE-ZZ and PCE-SS with PCE-JS respectively.Through the comparative study of PCE-1 and PCE-2,it is found that PCE-1 shows more excellent slump retention performance for cement.The fluidity of cement paste at 120 min and 180 min is 305 mm and 270 mm,respectively.The effect of PCE-1 on delaying cement hydration is stronger than that of PCE-2,which can better promote the close arrangement of cement hydration products,thereby improving the compressive strength of cement test blocks.（4）Using VPEG as macromonomer,AA,methacrylic acid（MAA）and sodium methallyl sulfonate（SMAS）as main comonomers,TGA as chain transfer agent,VPEG-viscosity-reducing polycarboxylate superplasticizer PCE-J was synthesized by free radical polymerization under H₂O₂/V_C oxidation-reduction initiation system.The effects of acid-ether ratio,MAA dosage and SMAS dosage on the properties of the synthesized superplasticizer were investigated.The most suitable process was obtained as follows:reaction temperature was 20°C,acid-ether ratio was 3.5:1.The amount of SMAS,MAA,H₂O₂ and TGA was 0.1 wt%,2 wt%,0.7 wt%and 0.6 wt%of VPEG,respectively.The addition time of A and B was 30 min and 40 min,respectively.The PCE-J and the commercially available viscosity-reducing superplasticizer PCE-S were compared and analyzed in terms of cement paste fluidity,concrete viscosity reduction performance（T50time,emptying time）and cement test block strength performance.It is concluded that PCE-J has excellent dispersion performance for cement,cement paste fluidity is as high as 305 mm,and has excellent viscosity reduction effect on concrete.The concrete emptying time and T50time are 4.1 S and 5.7 S respectively,which can significantly improve the compressive strength of cement test blocks.The compressive strength of 28 d cement test blocks is as high as 67.1 MPa.