Study On Synthesis And Slump Retention Properties Of Polycarboxylate Superplasticizer

Polycarboxylate superplasticizer(PC) as a new generation of high performance water reducing agent, has many virtues,such as low dosage, high water-reducing, high slump retention ability and no pollution. In recent years, with the national requirements for the construction of sustainable development, PC has been widely applied in the key projects and the public projects. It has become a hot research topic of chemical admixtures..In this paper, according to the principle of molecular design, using aqueous solution free radical copolymerization reaction, a series of PC were synthesized with TPEG-2400, acrylic acid(AA) as polymerization of monomers,methyl allyl sulfonate(MAS) as a chain transfer agent, and ammonium persulfate(APS) as an initiator. In this paper, using the single factor analysis method study the effect of different concentration, polymerization temperature and monomer ratio on the dispersing performance of polycarboxylate superplasticizer. Then using several kinds of mineral admixture equivalent substitute cement, to study the influence of different mineral admixtures on the dispersing performance of polycarboxylate superplasticizer. Then study on the performance of polycarboxylic superplasticizer mixing with other kinds of water reducing agent. Finally, in order to improve the performance of polycarboxylate superplasticizer, using hydroxypropyl acrylate esterification on the modification, and testing the influence of modification of polycarboxylate superplasticizer on cement paste, mortar and concrete performance.Research shows that, the carboxyl group density is the main factor affecting the PC water reducing agent of initial dispersion performance, the polycarboxylate superplasticizer initial dispersion performance increases with the increase of the carboxyl group density. With the polymer concentration, reaction temperature, dosage of chain transfer agent and dosage of chain initiator increased, synthesized polycarboxylate superplasticizer initial dispersibility increases at first and then decreased. Through the analysis of the test to get better synthetic process of water reducing agent are as follows: the ratio of n(AA):n(TPEG-2400) is 3.5:1, the reactant concentration is about 45%, the reaction temperature is 65℃,the dosage of MAS is 5% and the dosage of APS is 2%. The synthesized polycarboxylate superplasticizer possesses better dispersing and dispersion retention abilities. In the esterification modified test, when the hydroxypropyl acrylate replace rate is 30% for synthesis of polycarboxylate superplasticizer, the initial dispersion is good, and later the fluidity with elapsed time is increasing. when the hydroxypropyl acrylate replace rate is 35% for synthesis of polycarboxylate superplasticizer, the initial dispersion performance is poor, but the fluidity with elapsed time increased obviously after 1h and 2h.With the increase of dosage of fly ash, initial fluidity of cement mortar mixed with PC and the fluidity is generally presents the increasing trend. With the increase of mineral powder dosage, initial fluidity of cement mortar mixed with PC and the fluidity is both present a more obvious increasing trend. With the increase of dosage of silica fume, initial fluidity of cement mortar mixed with PC and the fluidity were appeared largely reduced. Polycarboxylate superplasticizer mixed with Aliphatic superplasticizer has a good effect. Polycarboxylate superplasticizer mixed with Sulfamic acid salt water reducing agent has a general effect. Polycarboxylate superplasticizer mixed with naphthalene superplasticizer has a bad effect.