Synthesis Of Gemini Quaternary Ammonium Salt And Improvement Of Mud Resistance Of Polycarboxylate Superplasticizer

Polycarboxylate superplasticizer is widely used in engineering concrete such as bridges and buildings due to its environmental protection,high water-reducing rate,and easy adjustment of molecular structure.At the same time,it overcomes the disadvantages of low water-reducing rate of the first-generation lignin series,environmental pollution in the production process of the second-generation naphthalene series water-reducing agent and low strength of concrete,etc.However,it has been found that it is sensitive to the mixed clay on the gravel in the concrete,especially the montmorillonite in the clay.The montmorillonite is a layered crystal layer structure which is easy to absorb water and polycarboxylate superplasticizer,so that the free water in the slurry and the effective polycarboxylate superplasticizer adsorbed by the cement are reduced,which affects the fluidity of the cement paste.Therefore,it is great significance to study the high-performance polycarboxylate superplasticizer resistant to clay.In engineering applications,the negative effects of montmorillonite on the slurry are generally inhibited by washing sand and gravel,high-volume water reducing agent and synthetic anti-clay type polycarboxylate superplasticizer.However,these methods have the disadvantages of destroying sand and gravel grading,bleeding segregation,rapid slump loss,and unsatisfactory anti-clay effect.In this paper,based on competitive adsorption and selective adsorption,two series of gemini quaternary ammonium salts were synthesized,and the quaternary ammonium salts were used as an anti-clay agent in combination with a polycarboxylate superplasticizer to discuss the effect of quaternary ammonium salts on the fluidity of cement slurries containing montmorillonite.In the experiment,trimethylamine or triethylamine and 1,3-dibromopropane were used as reactants to synthesize two kinds of diquat quaternary ammonium salts?labeled as G-KN1,G-KN2?by quaternization.Secondly,three kinds of diquat quaternary ammonium salts with different linkages were synthesized by reacting triethylaminewith1,4-dibromobutane,1,5-dibromopentaneand p-dibromobenzyl?labeled as G-KN3,G-KN4,G-KN5?.The structure of the gemini quaternary ammonium salts were characterized by FT-IR and ¹H NMR,all of which were the target products.The fluidity and rheological results show that when cement particles are replaced by 3%montmorillonite,the fluidity of cement slurry is the most improved after compounding with G-KN5 and RS-1.When the amount of G-KN5 was 0.1‰,The initial value is 265 mm,which is 95mm higher than that of the blank group.At the same time,the viscosity of the slurry is reduced,which is in accordance with the Herschel-Bulkley???28??₀?10?K?ⁿ?equation and is expressed as an expanding plastic fluid.The swelling ratio of the montmorillonite adsorbed by the quaternary ammonium salt was determined by the light transmittance.The results showed that the swelling ratio of the montmorillonite adsorbed by the quaternary ammonium salt was decreased.The hydrophilicity of montmorillonite was evaluated by contact angle.The results showed that the hydrophobicity of montmorillonite after adsorption of the quaternary ammonium salt was enhanced.The interlayer spacing of montmorillonite after adsorption of RS-1 and gemini quaternary ammonium salt was determined by X-ray diffraction.The results showed that the interlayer spacing of montmorillonite adsorbed by gemini quaternary ammonium salt was relatively increased,indicating that the gemini quaternary ammonium salt is adsorbed between the montmorillonite layer and the surface.The adsorption thermodynamics and kinetics of RS-1/G-KN5 by cement/montmorillonite were determined by total organic carbon.The results of adsorption thermodynamics indicated that the saturated adsorption capacity of montmorillonite and cement particles to RS-1 was 100 mg·g^-1 and 47.61 mg·g^-1at 298 K,the adsorption capacity of montmorillonite to RS-1 was more than twice that of cement,indicating that montmorillonite was more susceptible to adsorption of RS-1 under the same conditions;The saturated adsorption capacity of montmorillonite particles to G-KN5 was 27.93 mg·g^-1 at the same temperature,while the cement does not adsorb diquat quaternary ammonium,and the temperature rise is not conducive to the adsorption of RS-1 and G-KN5 on the surface of cement and montmorillonite particles.The adsorption kinetics showed that the adsorption of G-KN5 on the surface of montmorillonite accorded with the quasi-first-order kinetic equation,which was physical adsorption.Secondly,the adsorption results on the surface of montmorillonite by the compounding system indicate that there is competitive adsorption on the surface of montmorillonite in the RS-1 and G-KN5.The zeta potential of cement/montmorillonite before and after adsorption of RS-1/G-KN5 was measured by potentiometric particle size analyzer.The results showed that the zeta potential of montmorillonite decreased from-18.6 to-29.74 mV after adsorption of RS-1,and cement particles adsorbed RS-1 decreased from-3.2 to-11.24 mV,the montmorillonite increased more than the absolute value of the zeta potential of cement particles;While the zeta potential of montmorillonite adsorbed by the G-KN5 increased from-18.6 mV to-0.35 mV,and the zeta potential of the cement particles remained basically unchanged.Indicating that G-KN5 selectively adsorbed on the surface of montmorillonite,which makes G-KN5 achieve the desired anti-clay effect.