| With the development of China's infrastructure construction,cement and concrete admixture technology grow rapidly under the promotion of energy conservation activities,construction of green resource-saving and environment-friendly society by our government In cement industry,97%of energy is wasted during the process of cement grinding.So,grinding aid is widely use because of its remarkable energy saving effect.During use of cement grinding aids,it can be found that the instable quality of traditional cement grinding aids,compatibility issues with concrete materials,and durability with concrete materials has not been solved.Meanwhile,high clay content,and high dust content of concrete aggregates gravel severely restrict the function of concrete admixtures,which brought great difficulties to the concrete construction and safety hazards.The shortcomings resulted from separation research between cement grinding aids and water reducing aids due to industrial chains division is more and more apparent.Therefore,the development of a polymer cement concrete admixtures with a good cement grinding effect and solving"anti-mud" issue of the concrete admixture become very important.The main research results are as follows:The effects of reaction temperature,reaction time,monomers ratio,initiator dosage on PCCA grinding effect were studied.In our study,polymerization of monomers included acrylamide,maleic anhydride,vinyl polyether(relative molecular weight:380,600,1200,2400),respectively,with thioglycolic acid as a chain transfer agent and hydrogen peroxide and vitamin C as initiator(molar ratio of 4.5:1).It is concluded that the synthetic conditions of PCCA with best grinding performance are as follows:reaction temperature is 30?3 5? and the reaction time is 3.5h with the amounts of initiator,maleic anhydride,acrylamide as 20%,20%,9%,respectively.In order to study the effect of molecular structure changes of PCCA on its performance,PCCA with different groups and relative molecular weight were prepared by the way of molecular structure design,and the polymerization mechanism was put forward as well.With Specific surface area,particle size distribution and mobility of cement grinding as criterions of cement grinding effect,grinding effects of PCCA were estimated though experiments herein:the same content PCCA with different grinding time,same grinding time with different content PCCA,and parallel comparisons with traditional cement grinding aids.The results showed that:PCCA exhibited excellent grinding effect,grinding cement agglomeration disappeared,liquidity increased,particle size distribution narrowed and specific surface of cement increased significantly.The ratio of anionic groups and nonionic groups,nonionic branched chain length and the relative molecular weight of PCCA molecular structure on grinding effect were studied.The results showed that:ratio of anionic groups and nonionic groups has an optimal ratio,the shorter length of branched nonionic,the smaller of relative molecular mass,the better of PCCA grinding effect.It can be deduced that the grinding effect of PCCA was caused by the combined actions including chemical adsorption,induced cracking,and dispersion effect and shielding effect.The effect of PCCA on cement hydration was studied by the tests of cement setting time,hydration heat release rate,the initial conductivity hydration,hydration products change and strength of mortar to cement,respectively.The results showed that longer initial and final setting time of cement,lower ratio of harmful pores to less harmful pores,and more promotion of late hydration products compared with cement without PCCA.Moreover,PCCA has the function of set-retarded in the views of hydration heat release rate and conductivity tests.With the ratio of anionic groups in the molecular structure of PCCA increased,fluidity of cement paste increased first and then decreased,but the cement mortar strength is proportional to the ratio of anionic groups.In the water-reducing rate test of concrete,concrete water-reducing rates were 16%under aliphatic water-reducer and naphthalene superplasticizer water-reducer withl.4%,separately;but concrete water-reducing rates were 31.5%and 16.5%under polycarboxylate water-reducer and PCCA water-reducer with same 0.5%.It was found PCCA had an excellent "shielding" effect on Kaolin by the method of testing the methylene blue value of river sand with 11.89%Kaolin(by weight)after mixing 3250PPM PCCA as admixture.Furthermore,the testing also showed that the smallest molecular weight of PCCA had the best "shielding" performance on clay by the method of testing the methylene blue value of river sand with 6%clay(by weight)after mixing different molecular weights of PCCA as admixtures.The initial slump and extension of concrete with PCCA as admixture was bigger,but 1h liquidity losses was smaller compared with concrete with only polycarboxylate(such as commercial anti-sludge:glycerol and polyethylene glycol-300)as admixture.In addition,the initial slump of concrete get to the best performance when PCCA and polycarboxylate were simultaneously added.While the fluidity of concrete showed superior when PCCA was added after polycarboxylate.In order to evaluate the effects of PCCA on durability of concrete,a series of tests including freeze-thaw,sulphate resistance,chloride penetration resistance were carried out with mass loss and dynamic elastic modulus as criteria.The results showed that concrete with PCCA has better freeze-thaw resistance performance,and less mass loss and more dynamic modulus with more addition of PCCA in sulphate resistance testing,whereas concrete with PGA-1 had better chloride penetration resistance performance.In our study,the other purpose is to evaluate the compatibility of PCCA with lignin-based aliphatic water reducer(co-produced from black liquor and aliphatic superplasticizer graft),aliphatic superplasticizer,naphthalene and polycarboxylate super:plasticizer in the view of cement standard consistency water,cement setting time,paste fluidity,and concrete initial fluidity,the strength of concrete,concrete microstructure.It was found that PCCA exhibited excellent compatibility from the view of reducing water consumption of cement standard consistency,extending the cement setting time,improving the application effect of water-reducer.The main innovations are as follows:A new polymer cement concrete admixture(PCCA in short)was developed in order to resolve the issues fundamentally,which exist in the field of grinding aids and concrete admixtures.The synthesis process was determined.The polymerization mechanism of PCCA was put forward according to free radical polymerization mechanism,and their structures were designed by the way of molecular structure design.By researching the corresponding relation between molecular structure and cement grinding effect,grinding mechanism of PCCA was provided,which resulted from joint effects of chemical adsorption,induced cracking,desperation and shielding.By researching the impact of PCCA on concrete performance with high content of clay or rock flour,the "anti-mud" mechanism of PCCA was put forward. |
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