Characteristization Of Pore Structures Of Hardened Cement-asphalt Pastes

Cement and emulsified-asphalt mortar (CAM) is a kind of compound material with cement and asphalt. With the rapid development of high speed railway, CAM, a key material of track slab, is widely used in the interlayer of slab track. In the structure of ballastless slab track, CAM interlayer between track slab and concrete base has some main functions including exact adjusting, bracing, damping, buffering deformation. There are abound of closed air pores, capillary pores, which are caused by hydration of cement, and gel pores. For CAM, there are intimate relationships between pore structure and strength, modulus of elasticity, water absorption, shrinkage freezing resistance etc. But currently researches on pore structure of CAM were seldom reported. In this paper, gel pores, capillary pores and air pores of CAB are represented by low-temperature Nitrogen absorption, mercury intrusion method and image method, accordingly qualitative analysis and quantitative analysis of CAB have been done. There were studies on the effect of particle size and aluminite powder content on air pores. The relation was clarified between pore structure parameters and mechanical properties.The conclusions below can be drawn by test results.1) The are some characteristics of CAB such as high porosity,loose structure, substantial circular pore and high connectivity. In a few big pores, hydrate products, CH&C-S-H, are produced in later period, and on the walls of big pores are ball small pore with honeycombs, and that big pores beset small pores.2) There is an increase in air pores of CAB with the increase of mix amount and the decrease of particle diameter of aluminite powder. For usual content of aluminite powder, the range of volume fracture of air pores is the rangeof14.0%～15.3%.3) When age is longer,there is an increase in the specific area of CAB.On the lstday, the specific area of CAB is between180m2/kg and210m2/kg.On the28thday,it is the range of250～310m2/kg. At the age of90d,it goes to310～340m2/kg.The asphalt content affects the specific area of CAB. The A/C rate is bigger and bigger, and asphalt content of CAB is bigger and bigger, and then the specific area of later period is smaller and smaller.5) With the increase in age and the rate of A/C,the amount of gel pores(d<10nm) raises and decrease respectively.The gel porosity is the range of2.17x10-4～2.37×10-4cm3/g at the age of28d;6) The total capillary porosity is the range of15.7%～18.1by BSE image analysis and mercury intrusion method. The capillary porosity becomes smaller as time goes and when the rate of W/C or A/C goes smaller.However the regulation of gel porosity with age and the rate of W/C or A/C is opposite to one above.7)There are some effects of CAB pore-structure parameters on mechanical properties. Smaller the inner capillary porosity of CAB is, and gel pores are more and more, corresponding compressive strength and elastic modulus are higher and higher. When the rate of A/C is smaller and small, specific area is bigger and bigger, and accordingly compressive strength and elastic modulus are bigger and bigger.