Study On Fast-hardening Polymer Modified Mortar For Crts Ⅰ And Ⅱ Slab Tracks Filling Layer Repair

CRTS Ⅰ and Ⅱ slab track structures are the main structural types of high-speed railways in China,and various defects have appeared in the structures.The filling layer is the weak part in the CRTS Ⅰ and Ⅱ slab track structures.The standard Q/CR 659-2018 "Repair Mortar for Concrete Structures of High-speed Railway" stipulates that the polymer modified mortar should be used for the repair of filling layer,and the polymer modified mortar should have similar elastic modulus to the original CA mortar and should have high strength at early age.Calcium sulfoaluminate cement is a kind of cement with rapid strength development and small shrinkage deformation,which has been widely used in rapid-repair projects.SBR latex has good compatibility with cement,and it has significant advantages in adjusting the mechanical properties of mortar.Ⅰn this thesis,based on the early performance study of SBR modified calcium sulphoaluminate cement,the mix proportion of two kinds of filling layer repair mortar was designed,and the influence of mixing mode on polymer mortar was studied.The conclusions are as follows:(1)SBR latex has little effect on the setting time of calcium sulphoaluminate cement.SBR polymer particles can reduce the dynamic yield stress of slurry and improve the fluidity of slurry at low dosage(P/C≤20%).However,when P/C≥30%,the dynamic yield stress of polymer cement slurry increases,and the fluidity of cement slurry decreases.With the increase of P/C,the flexural strength of the net polymer cement slurry increases significantly,while the compressive strength decreases gradually.When P/C ≥ 40%,the polymer modified cement presents obvious viscoplastic characteristics.SBR latex is able to refine the pore size of the cement.When P/C≤20%,the SBR polymer can effectively inhibit the shrinkage of polymer modified cement,while when P/C≥30%,the cement shrink sharply.(2)By optimizing expansion agent(N1),retarder agent(tartaric acid)and defoaming agent(polyether,mineral oil),the fast-hardening polymer modified mortars for CRTS Ⅰ and Ⅱ slab track filling layer are prepared respectively.The mix proportion for CRTS Ⅰ slab tracks filling layer is as follows: water-cement ratio is 0.5,sand-cement ratio is 1.5,polymercement ratio is 50%,retarder content is 0.175%,expansion agent content is 8%,defoaming agent content is 0.1%;The mix proportion for CRTS Ⅱslab tracks filling layer is as follows: water-cement ratio is 0.45,sandcement ratio is 2.0,polymer-cement ratio is 20%,retarder content is 0.2%,expansion agent content is 2%,water-reducing agent is 0.16%,defoaming agent content is 0.1%.(3)Mixing process mainly affects the early rheological behavior of polymer mortar,but has little influence on the mechanical properties of polymer mortar.Under the condition of mixing retarder,the increase of mixing rate and mixing time can delay the early hydration and structural build-up of fresh polymer mortar,which is beneficial to the early fluidity.The agglomeration in polymer mortar decreases with the increase of mixing time and mixing rate.Compared with high speed mixing(176rpm),medium and low speed mixing(142rpm and 108rpm)is more beneficial to the stability of bubbles in fresh mortar.As an example,108rpm(10min),142rpm(6-10min)and 176rpm(2-4min)has a considerable dispersion effect in the fast stirring stage.