Study On Preparation And Properties Of Polycarboxylic Superplasticizer At Low Temperature

Polycarboxylate superplasticizer as one of the concrete admixture, has been widely used and developed in recent years, But with the rapid development of concrete industry, there are some problems exposed gradually. The enormous cost of synthesis of polycarboxylate superplasticizer and the issues of Polycarboxylate superplasticizer are sensitive to mud in the sand restrict the large-scale promotion of Polycarboxylate superplasticizer.In this study, Polycarboxylate superplasticizers were prepared initiated by Fenton reagent at low temperature with Isobutene polyoxyethylene ether (HPEG), acrylic acid (AA), methyl propene sulfonate (SMAS) as raw material. Relationship are discussed respectively between different reaction condition and dispersion of polycarboxylic superplasticizer. The results show that the optimum conditions of synthesis are as follows:H2O2/Fe2+ as initiator, used in an amount of 2% of the total mass of the monomers and m(H2O2):m(Fe2+)=1.2:1, the polymerization temperature was 30℃, n(AA):n(HPEG)=4:1, the dosage of sulphonates was 1.6% of the total mass of the monomers and the chain transfer agent was thioglycolic acid and the dosage is 1.5% of the total mass of the monomers, The results showed that when the dosage of polycarboxylate superplasticizers was 0.3% of cement mass. The initial fluidity of cement paste could exceed 290 mm and exceed 302mm after 1hours together with 0.29 of water cement ratio. The copolymer was analyzed by Fourier transform infrared spectrometer(FTIR), Gel permeation chromatography (GPC), Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The superplasticizer synthesized at low temperature had good thermal stability, the molecular weight of the copolymer concentrated at about 60 thousand and had smaller polydispersity coefficient. Besides the copolymer had good adsorption performance on the cement particles, adsorption amount incresed gradually with the grow of concentration of polycarboxylate superplasticizers.The mechanism of montmorillonite and polycarboxylate superplasticizer were investigated by the tests of fluidity, adsorption amount, X ray diffraction, specific surface area. The results shown that when the dosage of montmorillonite was 2%, the fluidity of cement lost more than half of fluidity compared with the fluidity without addition of Montmorillonite. When the addition of montmorillonite was over 3%, the fluidity would lost completely. The layer spacing of Montmorillonite reacted with polycarboxylate superplasticizer increased 0.37nm compared with blank sample and it appeared the characteristic functional groups of polycarboxylate superplasticizer in the infrared spectrum. In addition, the tests of specific surface area and adsorption results shown that montmorillonite had a huge specific surface area which is about 40 times of the cement, respectively 41.764 m2/g and 1.001 m2/g and the adsorption amount were 111.12mg/g and 34.483mg/g. Therefore, it can be seen that the effect of montmorillonite on the polycarboxylate superplasticizers had two factors, The one is intercalation intercalation, the other is the specific surface area, which causes greatly increases of adsorption amount.At last, In order to improve the adverse effect of montmorillonite on cement slurry mixing with polycarboxylate superplasticizer. A new type of non-branched type superplasticizer (MH) was synthesized by using methyl methacrylate and ethyl methacrylate as monomer, and the best monomer ratio was 2.5:1. The dispersion properties of the non-branched superplasticizer was slightly difference with the comb-like polycarboxylic superplasticizer. The initial fluidity were 280mm and 265mm, and the fluidity were 270mm and 250mm after 60min respectively. The fluidity of cement paste mixed with montmorillonite shown that when the content of montmorillonite is 2%, the loss of fluidity of the comb-like polycarboxylic superplasticizer was 50% after 60min, but the loss rate of non-branched type superplasticizer was only 14.7%. The layer spacing of montmorillonite reacted with new superplasticizer was only 1.40nm not increased significantly. Adsorption measurements shown that the adsorption amount of unbranched superplasticizer and comb-like polycarboxylic superplasticizer on cement particles were very close which were 30.303 mg/g and 34.483 mg/g respectively, but the adsorption amount on montmorillonite particles have difference which are 43.619 mg/g and 111.12mg/g respectively. It can be seen that unbranched superplasticizer has good anti sediment effect. Finally, In order to improve the dispersion of cement with anti sludge agent, the combination of agent and three kinds of slow coagulation components to improve the dispersion performance. Among them, the fluidity of cement with sodium glucose was best and the dosage was 0.03%.