| Tunnel concrete pavement is easy to be polished and gradually lost the original anti-skid performance under the action of the load,which may cause traffic accident.Repave anti-slip surface with cement mortar is one of maintaining and repairing measure to recover surface function of tunnel pavement.However,the common cement mortar has advantages of brittleness and insufficient toughness,which leads poor adhesion performance with old road surface.Meanwhile,the anti-skid property may decay rapidly under the action of the load and the complex environment of the tunnel,which leads to the failure of the maintenance work.Therefore,it is urgent to prepare new type of anti-slid surface materials with excellent durability performance for maintaining tunnel pavement.According to the special acidic,oil and humid environment of highway tunnels,the modified polyvinyl acetate(P(BA-VAc))latex with excellent water resistance was prepared.The P(BA-VAc)latex was added into the cement mortar,and the modified function on the physical and mechanical properties of mortar was studied.The accelerated polishing tester with three wheels was invented to simulate the wear behavior of automobile tire and anti-slip surface.The durability evaluation system for anti-slide surface of tunnel pavement,which is based on “anti-skid durability,adhesion and chemical resistance”,was presented.The main contents are as follows:The butyl acrelate(BA)was used as modified monomer sodium dodecyl,sulfate(SDS)and octyl phenol polyoxyethylene ether(OP-10)as compound emulsifier,ammonium persulphate(APS)as initiator,and polyvinyl alcohol(PVA)as protective colloid,to prepare modified polyvinyl acetate(PVAc).The P(BA-VAc)latex was prepared by semi-continuous charging method with conversion rate over 97%.The latex particle size distribution,stability and glass transition temperature(Tg)were applied to evaluate the properties of P(BA-VAc)latex.Infrared spectroscopy(IR)and Transmission electron microscope(TEM),and Zeta potential analyzer were conducted to analyze the structure of P(BA-VAc)latex.The results show that BA was good compatible to VAc,which could improve the water resistance and flexibility of polymer film.The modified cement mortar was prepared by P(BA-VAc)latex.Effect of the latex on physical properties was investigated through fluidity,setting time,water-retaining rate and dry shrinkage test.Then the flexural,compressive and tensile strength were tested to evaluate the mechanical properties of P(BA-VAc)modified mortar.The microstructure of the modified mortar was characterized by SEM.The results show that the P(BA-VAc)latex can effectively improve both physical and mechanical properties of cement mortar,and the modified mortar performs well in comprehensive properties when the latex content is in the range of 10% to15%.It is indicated by SEM that the curing films of latex can fill the porous structures in modified mortar,which leads to a bridge connection between the hydrate and aggregate,and therefore,making mortars dense.The tilting coefficient tester and the dynamic friction coefficient tester(DFT)were used to study the anti-skid performance of polymer mortar.The abrasion resistance of anti-skid surface materials was evaluated through cement mortar wear tester,the wet wheel wear tester and the self-developed accelerated polishing tester with three wheels.Then,the anti-slide performance of cement mortar before and after wear is compared.The evaluation method of anti-skid durability of surface materials was put forward.The results show that P(BA-VAc)latex can effectively improve the anti-skid durability of cement mortar.With the increase P(BA-VAc)content,the wear resistance is increased,while the anti-skid property have no obviously change.The effects on anti-slide durability of cement mortar are not similar with the different types of polymer.The P(BA-VAc),styrene-butadiene-styrene and styrene-butadiene(SBR)latex can effectively improve the anti-skid durability of mortar;while chloroprene(CR)and VAE latex do not have obvious modified function.The adhesion strength between polymer mortar and old cement specimen was evaluated by the flexural adhesion test,the “8” tensile adhesion test and the Positest adhesion test,and the applicable environment of these three test methods ware recommended.The effects of different interface treatment methods,interface type and curing methods on the adhesion properties were studied respectively,and the optimum treatment scheme was determined.SEM was used to observe the adhesion condition between the interface between old and new specimens,and X-ray photoelectron spectroscopy(XPS)was conducted to analyze the chemical reaction between the various components of the polymer cement mortar.The results show that P(BA-VAc)latex can significantly improve adhesion strength between polymercement mortar and old cement specimen,and adhesion strength increases with the increase of P(BA-VAc).The Positest adhesion test is suitable to evaluate the adhesion property in the field test,and the laboratory test is recommended to combine with the results of the flexural adhesion test and the Positest adhesion test.It is suggested that roughening and cleaning the surface of old specimen,and smearing the polymer cement slurry with the same proportion as interface agent can strengthen the adhesion between interfaces of old pavement and anti-slide surface.The optimum curing methods is that the specimen after stripping should be placed at curing room with 90% humidity for the early stage,and 60% humidity in later stage.There are some pores in the surface of cement paste,and the part of P(BA-VAc)latex penetrates into that pores.The penetration structure may strengthen the adhesion properties between latex and cement paste.However,the structure of quartzite is too dense for latex penetrating into internal form,and P(BA-VAc)latex just attached to the quartzite surface.The chemical shift are occurred between P(BA-VAc)latex and Ca(OH)2,and SiO2,and the chemical shift between P(BA-VAc)latex and Ca(OH)2 is higher than that of SiO2,which indicates that P(BA-VAc)latex may react slightly with both Ca(OH)2 of hydration products of cement and quartz sand,and the react function of quartz sand is more slighter.After immersed in sulfuric acid,nitric acid,sodium hydroxide,sulfate solution and painted through gasoline,the residual strength ratio of mortar was measured to analyze the corrosion resistance.SEM test was conducted to observe the micro-morphology of modified cement mortar.The main chemical composition of corroded cement mortar was analyzed through XRD test.The results show that the mortar is easy to be corroded by acid solution,while the P(BA-VAc)latex can improve the acid-resistance to some extent.The sulfate-resistance can be increased with the addition of the P(BA-VAc)latex.The mortar with high content of P(BA-VAc)can be used in alkaline environment.The gasoline has little effect on the corrosion resistance.The curing films of latex can fill the porous structures in modified mortar,which prevent the corrosive medium from entering the mortar.Meanwhile,the elastic films can absorb the swelling stress,and reduce the expanded destruction phenomenon,which can improve the corrosion resistance of cement mortar. |
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