Study On The Modified Synthesis And Application Of Polycarboxylic Acid Superplasticizer

Water reducing agents(superplasticizers)are one sort of the indispensable components of concrete.Polycarboxylate superplasticizers(PCEs),a new generation of superplasticizers,have become a hot spot in the field of concrete admixture at home and abroad because of its high water reducing rate,low dosages and facile molecular structure design.The dispersing effect of PCEs on cement mainly takes place on the surface of cement particles through chelating effect between carboxylic groups of superplasticizers and Ca2+ of cement particles.The side chain of polyethylene glycol can provide larger steric hindrance to disperse cement particles.Because of strong sensitivity of PCEs to clay in the mixture,the scientific relationship between the water reducing performance and the amount of clay(such as montmorillonite)needs to be investigated.With the development of science and technology and the need of rapid construction,the concrete pouring mode has changed from traditional hoisting construction to pipeline transportation.Therefore,how to get real-time information of cement in pipeline transportation is also an urgent problem to be solved.In this paper,a series of polycarboxylate superplasticizers with different side chain lengths and different carboxylic acid densities were synthesized.The effects of the side chain lengths on the dispersion properties,the retention properties and the sensitivity to clay are studied.PCEs with better properties are further chemically modified.Zeta potential,total organic carbon(TOC),X-ray photoelectron spectroscopy(XPS)and X-ray diffraction(XRD)are used to study the dispersion and water reducing mechanism of polycarboxylate superplasticizer.(1)Allyl polyethylene glycol ether(APEG)with different molecular weight and acrylic acid(AA)are polymerized via free radical polymerization to synthesize polycarboxylate superplasticizer with different side chain lengths and different carboxylic acid densities.For PCEs with the same side chain length,effect of carboxylic acid density on the performance was tested by means of mini slump tests.Then,effects of side chain length on the dispersion properties,the retention properties and the sensitivity towards the clay are investigated.Through TOC,Zeta potential,XPS measurements,adsorption behaviors,including adsorption capacity,zeta potential changes and adsorption layer thickness,are studied.XRD and TOC are employed to respectively investigate the layer spacing and adsorption of water reducing agent on montmorillonite to explore its clay resistance.The results show that:PCEs with longer side chain have better dispersion performance,but the retention performance and clay resistance become poorer.Hence,PCEs with moderate side length and better comprehensive performance are selected for further chemical modification of side chain,in order to improve its dispersion performance.(2)It is found that reaction to Ca2+ of sulfonic acid groups is similar to that of carboxylic acid groups,which can act on the surface of cement particles.More functional group can improve the adsorption and the dispersing performance.Thus,APEG with polymerization degree of 10 is employed to react with sulfamic acid under the condition of urea as a catalyst to obtain APES.APES 10-3 is then obtained by free radical polymerization of APES and acrylic acid.The dispersion performance,retention properties and sensitivity towards clay is tested.The adsorption behavior between APES 10-3 and cement particles,and the intercalated effect of APES 10-3 towards montmorillonite are studied by TOC,Zeta potential,XPS and XRD analyses.The results show that:APES 10-3 with sulfonic acid groups effectively increasing the adsorption onto cement particles.Both the adsorption capacity and adsorption layer thickness are improved,which further enhances the dispersing performance and retentions performance,whereas decreases the sensitivity towards clay.(3)Further modification on PCEs with better comprehensive performance is carried out.A monomer 4-(N'-methyl-1-piperazinyl)-n-hydroxyethyl-1,8-naphthalenedicarboxylic acid allyl ammonium chloride(denoted as N)containing naphthalic anhydride groups with fluorescence property is firstly synthesized.Then,free radical polymerization among N,APEG 10 and acrylic acid are conducted to obtain APEG10-3-N.The dispersion properties,dispersing retention ability and clay resistance of APEG10-3-N are systematically tested.The adsorption behaviors between APEG10-3-N and cement particles,as well as the intercalated effect of APEG10-3-N towards montmorillonite,are investigated by TOC,Zeta potential,XPS and XRD analyses.The results show that:APEG 10-3-N has significantly enhanced dispersing retention ability and clay resistance.At the same time,APEG10-3-N with good fluorescence intensity even at lower concentration can be further used for on-line monitoring of cement.