A Study On The Sealing Materials For The Cracks In CRTS â…¡ Type Slab Track Structure

Abstract:Slab ballastless track Structure is one of the mian track structure type of high speed railway in china, which is a structure with different layers, including support layer, cement emulsified asphalt mortar layer (Mortar Filling Layer for short), precast concrete slab, fastener and steel rail. Under the action of various environmental factors, different kind of cracks will develop in the slab ballastless track structure during service, which include opening cracks between mortar layer and concrete slab, joint cracks between concrete slabs, cracks in concrete slab and support layer. The width of cracks are relatively small and change dynamically. Literature has shown that cracks have effect on the overall performance of track Structure, more importantly, these cracks accelerate the transport of water into the track Structure. This greatly affect the durability of track Structure. Hence, it is necessary to seal these cracks with sealing metarials. Because of the characteristics of these cracks, the sealing materials should possess high performance in the following features:leak tightness, bonding strength, elastic deformation, durability ect. This paper develops three sealing materials, asphaltic base sealing material, water gel sealing material, hydrophobic sealing agent. Based on a large number of experimental study, the following conclusions can be drawn:(1) There were two asphalt modification methods, which were internal mix method and external mix method, used to conduct asphaltic base sealing material experimental study in the paper. For internal mix method, two different molecular weight polyisobutylene rubber(M-PIB、D-PIB),12-Benzenedicarboxylic acid dimethyl ester (DOP), SBS resin, petroleum resin and terpene resin were mixed with90#heavy-duty asphalt in the melt blending. Testing results showed that the addition of4%(by mass) M-PIB or5%(by mass) terpene resin can obviously improve temperature sensibility, elasticity and adhesive properties of asphalt. For external mix method, polyacrylate emulsion (p-emulsion),3000mesh limestone powder and P·Ⅱ42.5Portland cement were mixed with emulsified asphalt at room temperature. Results showed that the addition of30%(by mass) p emulsion, and10%(by mass) Portland cement can obviously improve deformability, elasticity, stripping resistance ability and Vertical flow resistance ability of emulsified asphalt film. Based on the experimental study, emulsified asphaltic base sealing material made with modified emulsified asphalt by external mix method is a promising material used for sealing the interfacial opening cracks between mortar layer and concrete slab, and joint cracks between concrete slabs in slab ballastless track Structure.(2) Using super absorbent resin as base material, flexible water gel can be made with the modification of polyving akohol, polyacrylamide and Cu2+ion. The water absorption sweelling, cracks sealing and water proof properties of water gel were studied. The influences of saline solution, Dry-wet cycling, rainwater wash and UV-irradiation on the durability of water gel were also studied. Test results showed that, flexible water gel with25times water absorption capacity have the best water absorption swelling ability and cracks sealing ability, which was compounded of CaCl2solution with density of0.01g/L, polyacrylamide with mass fraction of1%and super absorbent resin. Cu2+ion can obviously improve UV-irradiation resistance ability. The flexible water gel developed in this study is a promising sealing material for sealing the interfacial opening cracks between mortar layer and concrete slab, and joint cracks between concrete slabs in slab ballastless track Structure. However, its rainwater wash resistance and weather resistance need further improvement.(3) Three kinds of hydrophobic sealing agent were compounded in this study, which were Stearic acid ethanol solution, Oleic acid ethanol solution and Dimethyl silicone oil carbon tetrachloride solution. Through spraying hydrophobic sealing agent on the surface of Cement mortar specimens and CA mortar specimens, testing contact angle of water on the surface of specimens was evaluated. The effect of spraying density of hydrophobic sealing agent, times of spraying, rainwater wash, UV-irradiation and60℃high-temperature processing on the hydrophobic properties of specimens were studied. The results showed that spraying2%-3%(by mass) of stearic acid ethanol solution on the specimens2times, obvious hydrophobic properties(contact angle great than130°) can be obtained. UV-irradiation and60℃high-temperature processing nearly had no influence on the hydrophobic effect. Field test results showed that hydrophobic sealing agent can provide effective crack sealing and water proof ability for interfacial opening cracks between SL mortar and concrete slab, and the tiny cracks on concrete slab and support layer. The rainwater wash resistance requires further improvement.(4) Through a number of experimental researches and engineering practices, it is indicated that, the basic performance of emulsified asphaltic base sealing material, water gel sealing material and hydrophobic sealing agent can satisfy the crack sealing and water proof requirement of different kinds of cracks on slab ballastless track Structure, the costs are low and the construction is easy. Researches are needed to further improve their technical characteristics. The sealing materials developed in this study can be used for the maintenance for slab ballastless track structure of high speed railway. charts73, tables20, references67.