Preparation Of A Novel Shrinkage Reducing Polycarboxylate Superplasticizer And Its Primary Properties

In this paper,the fluorocarbon surfactant which has the strongest surface activity was selected as the shrinkage reducing monomer.A novel fluorinated shrinkage reducing polycarboxylate superplasticizer（FS-PCE）was prepared.By studying the influence of synthesis conditions on the primary properties of fluorinated shrinkage reducing polycarboxylate superplasticizer,an optimal synthesis parameters were determined as follows:The reaction temperature is 80℃,the monomer dropping time is 2 h,the retention time is 2 h,the monomer concentration is 50%,the ratio of each monomer is n（TPEG）:n（AA）:n（fluorinated shrinkage reducing monomer）=1:4.5:1.Six kinds of shrinkage reducing polycarboxylate superplasticizers with different fluorinated shrinkage reducing monomer were prepared by the optimal synthesis conditions.The effects of the number of fluorine atoms in the shrinkage monomer and the methyl of its hydrophilic head on the performance of FS-PCEs were investigated.The molecular structure was characterized by gel permeation chromatography（GPC）,infrared spectroscopy（FTIR）and ¹⁹F nuclear magnetic resonance spectroscopy(¹⁹F NMR).It is proved that the fluorinated shrinkage reducing monomers are successfully introduced into polycarboxylate superplasticizer.The water-reducing performance of FS-PCEs were tested by the cement paste fluidity and the mortar water-reducing rate,the shrinkage of cement paste and mortar were used to evaluate its shrinkage performance,and whether FS-PCEs have the negative impact on strength was investigated.It is concluded that the mortar water-reducing rate of FS-PCEs is about 30%.When the mortars at same fluidity,FS-PCE can improve the strength of mortar.The six kinds of FS-PCEs all exhibitis the ability to reduce the shrinkage of cement-based materials.In this paper,the mechanism of FS-PCE was studied by surface tension of FS-PCE solution,Zeta potential on cement particles,cement hydration heat and XRD analysis.The result shows that 6 kinds of FS-PCE has strong surface activity,especially the FS-PCE with hexafluorobutyl acrylate or dodecafluoroheptyl acrylate,when its solution concentration is 5 wt.%,the surface tension of the solution was reduced to 43mN/m.The FS-PCE has increased the absolute value of the zeta potential on cement particles.The FS-PCE has delayed the hydration of cement.And FS-PCE has promoted the formation of calcium hydroxide and ettringite.