Study On The Composition Optimization And Performance Of Ballastless Sleeper Concrete

Ballastless sleeper is the important component in various high-speed railway structure.Due to the operating environment and conditions,the ballastless concrete sleeper is not only subjected to the continuous impact load of the train,but also to the rain,freeze-thaw and chemical corrosion,which make the sleeper becoming one of the most vulnerable part in the track structure.Using fly ash,slag powder to replace part of cement is an effective measure to improve the durability of concrete,but it will reduce the early strength of concrete.Due to the special forming and curing process of ballastless sleeper concrete,it is required to a high demanding-strength.Therefore,it is of great significance to study the compound effect and concrete performance of ballastless sleeper concrete with admixtures and synergetic agents that keep both early strength and durability of concrete.In this paper,high active powders A?HP?,fly ash?FA?and slag powder?SS?were selected to raw materials,and the influence of composite admixtures composition on the activity index was studied by simple gravity design method,and its early hydration behavior was studied by isothermal calorimetry.The results revealed that among the three admixtures,the 1d activity index of 30%highly active powder A was the highest,reaching 122%;The 28d activity index of 30%slag powder was the highest,reaching 111%;The activity indexes of fly ash at 1d and 28d were lower than 100%.When admixtures of different components were combined,their activity indexes showed different degree of composite enhancement effect.When high active powder A was mixed with slag powder,both 1d and 28d activity indexes of composite mineral admixtures could reach 118%.The measurement results of hydration heat release rate and heat release were shown as follows:In the age of 7 days,the early exothermic rate and heat release of highly active powder A were the highest,indicating that it had high chemical reactivity.In the 1d age,fly ash and slag powder did not have hydration reaction,only as an inert material,so the slurry had the slow heat release rate and small heat release.After 3d age,the secondary hydration reaction of slag powder is faster than that of fly ash,and the slurry heat release is gradually increased.In the case of mixed admixtures,there was no obvious hydration interaction between the admixtures,so the composite enhancement of the activity index of the composite admixtures comed from the particle effect.The relationship between the composition of composite admixtures and the mechanical properties of sleeper concrete was studied.The effects of rapid chloride ion test and mercury injection on the electric flux and pore structure of concrete were studied.The results revealed that high active powder A enhanced the compressive strength of concrete at different ages.After 28d,fly ash and slag powder greatly improved the compressive strength of concrete.At the age of 180d,the compressive strength of fly ash concrete was the highest,reaching 95.1MPa.At the initial stage of hydration,the compressive strength of ternary concrete showed significant composite strengthening effect.At the age of 180 d,the compressive strength of fly ash and slag powder mixed with concrete was the highest,reaching 91.7 MPa.Both mineral admixtures and composite admixtures significantly reduced the electric flux of concrete.At the age of 28d,the electrical flux of slag-mixed concrete was the lowest,which was 568C;at the age of 60d,the electrical flux of fly ash mixed concrete was the lowest,which was 333C.The electric fluxes of fly ash and slag powder mixed with concrete on 28d and 60d were respectively 604C and 332C,which showed obvious composite enhancement effect.Slag powder and highly active powder A significantly reduced the porosity of slurry,among which the slurry mixed with slag had the lowest porosity,up to 6.4276%.The porosity and pore diameter distribution of composite admixture slurry was lower than that of single admixture.The porosity of 180d mixed slurry of fly ash and slag powder was only 7.8526%.The effects of different types and dosage of synergists?TEA,TIPA,DEIPA?on the compressive strength of cement and composite cement mortar were studied.The effects of synergists on the hydration performance of cement in the early stage were studied by means of XRD,SEM and TG-DTG.The results revealed the synergue promoted the early hydration of C₄AF and C₃A in cement and improved the content of chemical binding water in the slurry at different ages.Therefore,the synergue enhanced the compressive strength of cement mortar.In the experiment,the compressive strength of 0.05%DEIPA mortar on 1d and 90d was the highest,which was 138%and 113%of pure cement mortar respectively.0.05%TEA limited the late hydration of C3S,so the content of chemical binding water in the slurry decreased,reducing the 90d compressive strength of cement mortar by 6.4%.The content of calcium hydroxide in cement slurry was enhanced by 0.05%synergetic agent,so as to promoting the secondary hydration of slag powder and fly ash in composite cement.In addition,0.05%synergistic agent also enhanced the compressive strength of highly active powder A composite cement.The influence of alkanol synergistic agents on the performance of sleeper concrete was studied by compressive strength,rapid chloride ion test,mercury injection and SEM test.The results revealed the 0.05%synergist reduced the 28d compressive strength of concrete,but increased the 90d compressive strength.0.05%TIPA and 0.05%DEIPA improved the 90d compressive strength of concrete of cement and composite cement.The aeration effect of 0.05%synergetic agent leaded to more 200?m large holes in the slurry,so the electric flux of concrete increased for 28 days and its resistance to chloride ion erosion decreased.Synergistic agent accelerated the dissolution of C₄A and C₄AF,promoted AFt to AFm transformation,and improved the pore size distribution of cement slurry.There were many lamellar calcium hydroxide crystals and acicular ettringite crystals on the wall of large pores,which was not conducive to the development of pore structure in the map of SEM.