Effect Of Functional Monomer On Polycarboxylate Superplasticizer For Enhancing Clay Tolerance

Polycarboxylate superplasticizers have been extensively studied and applied to concrete,because of their high water-reducing rate,long slump retention and greenness and so on.However,the efficiency of polycarboxylate superplasticizer is limited by clay,especially montmorillonite existing in aggregates.Therefore,it is necessary to enhance the resistance of polycarboxylate superplasticizer to montmorillonite from the perspective of molecular structure design.In this paper,five kinds of polycarboxylate superplasticizers(PST,PCS,PCP,PSM and PSS)for enhancing clay tolerance were synthesized with isobutylene polyoxyethylene ether as macromonomer,acrylic acid as small monomer,copolymerizing separately with styrene,KH570,2-hydroxyethyl methacrylate phosphate,sodium methylallyl sulfonate and sodium p-styrene sulfonate functional monomers.They were compared with water reducer PCE without functional monomer.The copolymers are proved to be the target products,confirmed by infrared spectrum and double bond conversion rate of macromonomer.Relative molecular weight,thermal properties,surface tension and paste fluidity show that the number average molecular weight of the copolymers concentrates at 14 to 21 thousand,and the copolymers have good temperature resistance and a certain surface activity.Resistance of PCP to montmorillonite is best,respectively followed by PCS,PSM,PSS and PST in the presence of montmorillonite(1% by weight of cement).However,when 2% montmorillonite is added,the resistance of PCS to montmorillonite is better than that of PCP.X-ray diffraction was employed to determine interlayer spacing of montmorillonite modified with water reducer.Total organic carbon(TOC)was used to measure adsorbed amount of water reducer on cement or montmorillonite.X-ray photoelectron spectroscopy was used to determine Si2 p photoelectron strength of cement or montmorillonite,further calculating adsorption layer thickness.Zeta potential of cement or montmorillonite modified with water reducer was tested by potential particle size analyzer,investigating adsorption mechanism of water reducer on cement and montmorillonite.There is no significant change in the interlayer spacing of montmorillonite,indicating that no intercalation occurs when water reducer interacts with montmorillonite.Isothermal adsorption results show that the maximum amount of PCE adsorbed on montmorillonite is 115.9408 mg/g,which is about 2.53 times as much as that of PCE adsorbed on cement(45.7824 mg/g).The ratio of maximum amount of water reducer(PCP,PCS and PST)adsorbed on montmorillonite to that of water reducer on cement is less than 2.53.The results of adsorption kinetics show that the adsorption of water reducer on cement or montmorillonite conforms to quasi-secondary adsorption kinetics.The equilibrium amount of PCE adsorbed on montmorillonite is 7.1948 mg/g,which is about 7 times as much as that of PCE adsorbed on cement(1.0137 mg/g).Adsorption layer thickness of PCE on cement is 3.04 nm and that of PCS on cement is the largest,which is 5.10 nm.Adsorption layer thickness of PCE on montmorillonite is 4.47 nm,which is greater than that of PCS and PST on montmorillonite.Zeta potentials of cement and montmorillonite are-1.80 mV and-13.60 mV.As water reducer concentration increases,absolute value of Zeta potential of cement increases and that of montmorillonite gradually decreases,and eventually reaches equilibrium.The absolute values of Zeta potentials of cement and montmorillonite treated with PSM are larger,which are-6.89 mV and-10.26 mV.Rheological results show that cement paste added with water reducer displays the characteristics of the expansion-plastic fluid.When the shear rate is low,the apparent viscosity and shear stress of the cement slurry respectively added with PST,PCS and PCP are all smaller than those of PCE.The apparent viscosity of cement paste increases with the addition of montmorillonite.The apparent viscosity and shear stress of montmorillonite-contained cement paste respectively added with PCS and PCP are all smaller than those of PCE.