| Polycarboxylate superplasticizer（PC）is an indispensable part of concrete.Introducing silane groups into the molecular structure of PC can improve their properties and endow them with novel functions.In this study,two silane-modified PC were synthesized by using the silane coupling agentγ-methacryloxypropyl trimethoxysilane（KH570）and vinyltriethoxysilane（VTEO）,ethylene glycol monovinyl polyethylene glycol ether（EPEG）,and acrylic acid（AA）as other reaction monomers.The structure of the silane-modified PC was characterized by FT-IR,EDS,1H NMR and GPC.The effects of monomer ratio,different dosage,storage time and flexural compressive strength of two kinds of silane-modified PC on the dispersion ability of cement paste were studied.The effect of silane-modified PC on hydration products of cement was analyzed by XRD.Finally,the structure analysis and comparison of the two kinds of silane-modified PC and non-silane modified PC were carried out to compare their dispersion ability,sulfate resistance and rheological properties.The results are as follows:（1）The silane-modified PC with KH570 was synthesized by copolymerization using KH570,EPEG and AA as reactive monomers,H2O2and Vc as redox initiator systems,and 3-mercaptopropionic acid（MPA）as chain transfer agent.By adjusting and optimizing the molar ratio of the three monomers,it can be seen that when the ratio of the three reactive monomers is n（EPEG）:n（AA）:n（KH570）=1:4.2:0.3,the dispersion performance of PC on the cement paste is the best.Through FT-IR,EDS and 1H NMR,it is known that the silane structure has been introduced into the molecular structure of PC.The molecular weight and distribution of PC were determined by GPC.By using the single factor method,it can be seen that when the superplasticizer dosage is 0.2%,the net slurry fluidity remains stable within 120 minutes,exhibiting excellent dispersion performance and dispersion retention.However,due to the existence of alkoxy group in KH570,the dispersibility of this type of silane-modified PC decreases with the extension of storage time.According to the flexural compressive strength of cement mortar and the analysis of cement paste hydration products,the early strength is low,and the later strength is improved;Compared with the non-silane modified PC,silane-modified PC with KH570 added into the cement paste at the age of 24h causes less formation of hydration products AFt and Ca（OH）2,while at the age of 72h,the formation of AFt and Ca（OH）2increases,indicating that silane-modified PC with KH570 has a certain retarding effect on early cement hydration.（2）Using VTEO,EPEG,and AA as reaction monomers,H2O2and Vc as redox initiator systems,and 3-mercaptopropionic acid（MPA）as chain transfer agent,a series of silane-modified PC with VTEO were synthesized by adjusting the molar ratio of VTEO to AA,n（VTEO）:n（AA）.The FT-IR,EDS and 1HNMR analysis of SP(EPEG1-AA4.20-Si0.30)showed that the polymer had reacted and the silane structure had been grafted into the molecular structure of PC.According to the investigation of the content of silane-modified PC with VTEO,the dispersion performance is the best when the content of water reducer is 0.2%.According to the comprehensive analysis of fluidity,flexural compressive strength and XRD of cement mortar,silane-modified PC with VTEO can promote the early hydration of cement.（3）The two synthesized silane modified PC were compared with non silane-modified PC with VTEO reducing agents P(EPEG1-AA4.20-Si0.30),SP(EPEG1-AA4.20-Si0.30),and P(EPEG1-AA4.50-Si0).The negative influence of sulfate on the three PC is investigated through the fluidity,flexural compressive strength and rheological properties of the slurry,and the order is P(EPEG1-AA4.20-Si0.30)<SP(EPEG1-AA4.20-Si0.30)<P(EPEG1-AA4.50-Si0). |
