Optimization Of Mixture Design And Mixing Process Of The CA Mortar Used In Ballastless Slab Track

Ballastless slab track is the main track in high-speed railway construction.Cement asphalt (CA) mortar is one of the key engineering materials in the structureand its performance directly affects the durability, traveling comfortness and securityof the entire track.At present, many studies about mix proportions of the CA mortar have beenmade and the CA mortar product has been successfully used in practical constructionin China. In this thesis, we mainly focused on the compatibility between the anionicemulsified asphalt and cement, the measurement about how to improve thecompatibility between them, as well as the effects of the nano-thickener and mixingprocess on the performance of CA mortar used in CRTS I and CRTS II ballastless slabtrack on the basis of the present achievements. The results showed that:(1) The compatibility between the anionic bitumen emulsion and cement issimilar to the adaptibility between the superplasticizer and cement. The poorcompatibility is resulted from the competitive adsorption emulsifier by the cementparticle. By appropriately increasing the superplasticizer dosage, adding moreemulsifier or hydrophobic surface-treatment of the cement, the compatibility betweenthe cement and anionic asphalt emulsion can be significantly improved.(2) By incorporating nano-thickener, the consistency and thus the expansion rateof the fresh CA mortars used either in CRTS I or CRTS II ballastless slab track can beeffectively adjusted. For the CA mortar used in CRTS II ballastless slab track, theexpansion rate showed increase at first but decrease later if there is no nano-thickenerincorporation. By using the nano-thickener, the stability of expansion rate can be effectively improved.(3) The mixing process has a great influence on the properties of the fresh andhardened CA mortar used in CRTS II ballastless slab track. While mixing as used inconstruction site, that is to say, mixing the liquid materials (i.e. asphalt emulsion,water and liquid admixture) first, and then adding dry ingredients to mix, the fresh CAmortar prepared is prone to bleeding. However, by using the novel mixing technology,i.e., adding the dry mixes in water containing liquid admixture to mix first, and thenadding the asphalt emulsion for futher mixing, the bleeding of the fresh CA mortarcan be avoided. The bleeding of the CA mortar prepared by using the traditionalmixing method can be effectively prevented by adding nano-thickener.