| Polycarboxylate superplasticizer has been widely used in concrete field,possessing the advantages of low dosage,high water reducing rate,controllable molecular structure,environmentally friendly and so on.However,with the rapid development of concrete industry,the problems of polycarboxylate superpasticizer in application exposed gradually,the clay existing in the sand restricts the widespread use of polycarboxylate superplasticizer.In this paper,from the molecular structure of superplsticizer,at first,the DM-BC,DM-BB,DMAPS functional monomers were synthesized with dimethyl amino ethyl methacrylate as material,reacting respectively with benzyl chloride,n-butyl bromide,1,3-propyl sulfonic lactone.Then,three kinds of polycarboxylate superplasticizer with low sensitivity to montmorillonite(DM-BC,DM-BB,DMAPS)were prepared using three functional monomers,acrylic acid(AA),isobutene polyoxyethylene ether(HPEG)as monomers,hydrogen peroxide(H2O2)and ascorbic acid(Vc)as initiator,thioglycollic acid as chain transfer agent.The functional monomers and copolymers were characterized by Fourier transform infrared spectrometer(FTIR)and nuclear magnetic resonance hydrogen spectrum(1H NMR)which showed these were the target product.The copolymers were analyzed by gel permeation chromatography(GPC),Thermogravimetric(TG)and differential scanning calorimetry(DSC),cement fluidity.The results showed that the molecular weight of the copolymers concentrated at 30~40 thousand and had high thermal decomposition temperature,and good surface activity.When the superplasticizers with anti-clay had the same dispersing performance on cement as ordinary superplasticizer(PCE),they had better resistance to montmorillonite at the amount of which were 1% and 1.5% than that was 2%.Meanwhile,cationic functional monomers(DM-BC,DM-BB)had more preferable effectthan two kinds of functional monomer(DMAPS).The mechanism between montmorillonite and superplasticizers with anti-clay were analyzed by X-ray diffraction(XRD),infrared spectra(IR),thermogravimetric(TG).The results showed that the characteristic functional groups of superplasticizers were still observed in the montmorillonite adsorbing superplasticizers and the loss rate of thermal weight were increased 8% more than original montmorillonite.These could illustrate superplasticizers were adsorbed into the interlayer of montmorillonite,but the interlayer space of montmorillonite adsorbing superplasticizer with anti-clay was decreased 0.6 nm than that adsorbing ordinary superplasticizer(PCE).The adsorption amount on the surface of cement and montmorillonite were analysized by the total organic carbon(TOC),isothermal adsorption experiment found that the adsorption amount of common superplasticizer on the surface of montmorillonite and cement were 58.843 mg/g and 23.919 mg/g,and the former was 2.5 times of the latter.In addition,the adsorption amount of superplasticizers with anti-clay were36.651 mg,45.794 mg/g and 55.183 mg/g,these were all less than that of common superplasticizer.Dynamic adsorption experiments showed that the adsorption rate curves of different superplasticizers on the surface of montmorillonite and cement could be described by level of adsorption rate equation.The adsorption amount of common superplasticizer on the surface of montmorillonite and cement were 32.469 mg/g and 14.946 mg/g,and the former was 2.3 times of the latter.The adsorption film thickness was detected by X-ray photoelectron spectroscopy(XPS),which stated that the adsorption film thickness of superplasticizers with long side chain on cement were 2 nm.Compared with superplasticizer with short side chain,superplasticizer with long side chain might be in the form of “flat” on the surface of cement.And the adsorption film thickness of superplasticizers with anti-clay on montmorillonite more than that of original superplasticizer,which stated superplasticizers with anti-clay were not easy to interlayer with montmorillonite.The rheological test showed that cement slurry system viscosity increased with the increase of amount of montmorillonite.However,superplasticizers with anti-clay could decrease the viscosity of slurry system containing montmorillonite.From the perspective of compound with sacrificial agent,usingpolyethylene glycol(PEG)as clay adsorbent,the resistant effect of different molecular weight polyethylene glycol at different dosages mixtured polycarboxylate superplasticizer on montmorillonite by the fluidity of cement paste.Meanwhile,polyethylene glycol and mechanism with the suppression of montmorillonite effect on polycarboxylate superplasticizer was analyzed by FTIR,XRD and TOC,etal.The results showed that the fluidity of cement paste had been increased greatly after polycarboxylate superplasticizer mixtured polyethylene glycol at better dosage.When the molecular weight of polyethylene glycol was 1000,the dosage of polyethylene glycol was 0.1% of cement mass,the initial fluidity of cement paste could be increased 40 mm and increased 140 mm after 1 hour.And the reasons why polyethylene glycol could inhibit the negative effect of montmorillonite on polycarboxylate superplasticizer was that polyethylene glycol was priority adsorbed into the interlayer of montmorillonite;polyethylene glycol could decrease the adsorption of montmorillonite on polycarboxylate superplasticizer,and the adsorption quantity was decreased from46.52 mg/g to 37.15 mg/g;polyethylene glycol could inhibit the bibulous dilatability of montmorillonite,and the expansion capacity was decreased from11 mL/g to 8 mL/g. |
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