Study On Synthesis And Property Of Anti-Clay Polycarboxylate Superplasticizer

Polycarboxylate superplasticizer as a new generation of high performance water reducing agent has the advantages of high water reducing rate,high slump retaining,functional regulation,production and use of energy saving and environmental protection and so on.It has been widely used in various concrete projects.However,there are still a lot of problems in the application of polycarboxylate superplasticizer.The problem that polycarboxylate superplasticizer is too sensitive to the clay composition of aggregate is one of the factors that restrict the popularization and application of polycarboxylate superplasticizer.Clay contains a large number of clay minerals that are harmful to the performance of polycarboxylate superplasticizer.Their adsorption capacity to polycarboxylate superplasticizer is stronger than cement particles,which leads to the decrease in the content of effective polycarboxylate superplasticizer in cement slurry,which reduces the liquidity and liquidity retention of concrete.The method of free radical copolymerization is used in this project.Anti-clay Polycarboxylate Superplasticizer was synthesized with methyl allyl polyoxyethylene ether as macromonomer,acrylic acid as monomer,compound A as initiator and compound B as chain transfer agent.First,the effect of single factor change on the clay resistance of polycarboxylate superplasticizer was explored.The results are as follows: when the synthetic temperature is 72?,the dosage of initiator is 1%,the amount of chain transfer agent is 0.3%,the ratio of acid to ether is 4:1,the anti clay effect of Polycarboxylic Water reducing agent is the best.The addition of methacrylic acid is beneficial to the initial dispersion effect,and the addition of styrene is beneficial to the increase of clay resistance.Then the synthesis process of clay resistant polycarboxylate superplasticizer was optimized by orthogonal test.The effects of ST dosage,compound A amount,compound B dosage,acid and ether ratio,MAA dosage,reaction temperature,drop time and holding time on the effect of Anti-clay were investigated.Two kinds of Anti-clay Polycarboxylate Superplasticizer were finally synthesized,which were No.6 and No.16 respectively.When montmorillonite exists,the initial flow spread of the No.6 water reducer is 290 mm,and the flow spread is 270 mm after 30min;the initial flow spread of No.16 water reducer is 285 mm,and the flow spread after 30 min is 265 mm,which has good initial dispersing and dispersing ability.The molecular structure of polycarboxylate superplasticizer was characterized by IR and the molecular weight and physicochemical properties of polycarboxylate superplasticizer were determined.Through ‘mini slump' test,the effect of clay types and dosage on clay resistance of polycarboxylate superplasticizer was explored.The results showed that montmorillonite was the most harmful to polycarboxylate superplasticizer and the second was mud.Diatomite had the least harm to water reducer.With the increase of clay content,the dispersion retaining of water reducing agent decreases faster than that of initial dispersion.The concrete slump test proves that Anti-clay Polycarboxylate Superplasticizer has better clay resistance than the traditional polycarboxylate superplasticizer.Finally,the adsorption mechanism of clay on polycarboxylate superplasticizer was studied.The results showed that the adsorption capacity of montmorillonite to polycarboxylate superplasticizer was the largest and that of saturated adsorption capacity was 8 times that of mud and 40 times that of diatomite.Montmorillonite has interlayer adsorption on polycarboxylate superplasticizer,mud and diatomite have only surface adsorption on polycarboxylate superplasticizer,which proves that the adsorption amount of interlayer adsorption is much larger than that of surface adsorption.The idea of developing Anti-clay Polycarboxylate Superplasticizer is to prevent polyoxyethylene side chains from intercalating into clay mineral layers.