Study On Synthesis Of Polycarboxylate Superplasticizer With Slump-retention And Anti-clay Properties

As a kind of excellent admixture,polycarboxylate superplasticizer has been widely used in high-performance concrete,but it is easily adsorbed by clay minerals with high dispersion layer structure,so it is extremely sensitive to the clay content in concrete.The slump of the fresh concrete prepared by polycarboxylate superplasticizer will be significantly reduced with the increase of the clay content of the aggregate,and its loss rate will be significantly increased.By introducing anti-clay functional monomer,the molecular structure of polycarboxylate superplasticizer has been changed to improve its anti-clay performance.However,based on the normal temperature synthesis process,the anti-clay functional monomers was introduced into the polycarboxylate superplasticizer with slump-retention property to synthesized the superplasticizer with slump-retention and anti-clay properties.There is little research on synthesizing this polycarboxylate superplasticizer.In view of the above,this paper passes the acrylic acid（AA）-methylallyl alcohol polyoxyethylene ether（HPEG-2400）-acrylamide（AM）ternary system at room temperature to synthesize a polycarboxylate superplasticizer with slump-retention.Introducing anti-clay functional monomers with different configurations such as2-acrylamide-2-methylpropanesulfonic acid（AMPS）,dimethyldiallylammonium chloride（DMDAAC）and multi-branched pentaerythritol acrylate（PETA）.The equivalent amount of the macromonomer polyether is substituted,and the molecular structure of polycarboxylate superplasticizer is adjusted to improve the anti-clay performance without increasing the cost.Through the optimization of formula and synthesis process parameters,the named as basic slump-retention polycarboxylate superplasticizer polycarboxylate（PC）was synthesized by using acrylic acid（AA）,methyl allyl alcohol polyoxyethylene ether（HPEG-2400）and acrylamide（AM）at room temperature of 25 ℃ :n（AA）:n（HPEG）=3.5:1,the AM content is 1.16% of the mass of HPEG-2400,and the total mass of the initiator hydrogen peroxide and ascorbic acid accounts for 0.8% of the mass of HPEG-2400（m（H₂O₂）: m（VC）= 3:1）,the chain transfer agent mercaptopropionic acid（MPA）is 0.5% by mass of HPEG-2400.Its polymerization concentration is about 40%.The results of the pure water test with a water-cement ratio of 0.29 indicate that when the PC solids content is 0.16%,the initial fluidity of the cement paste is large,and the 1h fluidity is not lost with time and slightly increased,but the initial fluidity cement-clay slurry was significantly reduced,and the1 hour fluidity loss increased significantly with time,indicating that PC is sensitive to the clay content of cement slurry and poor clay resistance.Under the same conditions as the synthesis conditions of PC,AMPS and DMDAAC were separately or simultaneously incorporated into the PC to synthesize different anti-clay polycarboxylate superplasticizers（A-PC,D-PC,AD-PC）.The results showed that the fluidity of cement paste with AD-PC（synthesized by 1.16 %AMPS and 2.64 % DMDAAC）was more than that of A-PC（1.74% AMPS）or the D-PC（2.64% DMDAAC）.It is further shown that the introduction of AMPS and DMDAAC in the molecular structure is more conducive to improving the anti-clay property of PC.The effects of commercial polycarboxylate superplasticizer（SS-BT）and AD-PC on concrete slump and compressive strength were compared.The results provided that when the clay content was less than or equal 8%,the anti-clay ability of AD-PC was better than that of SS-BT.The two polycarboxylate superplasticizers have the same synergistic effect on the compressive strength of concrete.In the same conditions as the synthesis of PC,the macro-polyether was replaced by 3.8% PETA,and the anti-clay polycarboxylate superplasticizer（P-PC）was synthesized.The test results of pure cement paste and concrete showed: P-PC’s anti-clay performance is better than AD-PC,and P-PC has a slight synergistic effect on concrete compressive strength.The analysis of infrared spectrum and ultraviolet spectrophotometer showed that the polymerization of PC,AD-PC and P-PC was complete,and the anti-clay functional monomer entered the molecular structure of the PC;their adsorption capacity on the surface of clay particles was P-PC<AD-PC<PC.The results show that the less the adsorption capacity of polycarboxylate superplasticizer on the surface of clay particles,the better the anti-clay performance,and the results are consistent with the experimental results of cement paste and concrete.