Influence Of Cement Type On The Properties Of Cement-Asphalt Composites

Abstract:CA mortar composed of Portland cement, emulsified asphalt and fine sand is used as placing mortar for the cushion layer in CRTS I and CRTS II slab track structure of high-speed railway. The calcium leaching from CA mortar cushion layer will happen under the action of water in service, which increases the porosity and reduces the strength of CA mortar. Thus, CA mortar will deteriorate much faster under the action of high-speed train dynamic load, which directly affect the ride performance and security of high-speed train. Therefore, the calcium leaching of CA mortar is of great significance.Changing the varieties of cement or reducing the content of calcium hydroxide is an effective way to reduce or inhibit calcium leaching of CA mortar. In this paper, Sulphoaluminate cement, High-aluminate cement, Portland cement doped silica fume, cationic and anionic emulsified asphalt are used to prepare cement-emulsified asphalt paste and mortar, respectively. The flowability, mechanical properties and volume stability of these cement-asphalt composites are studied. The main conclusions are as follows:(1) Adopt J type funnel to test the flowability of cement-asphalt composites. The results show that:when asphalt cement ratio A/C is the same, the flowability of cement-asphalt composites prepared by Sulphoaluminate cement is poor while the High-aluminate cement-asphalt composites have good flowability and the mortar would not segregate and delaminate; the composites prepared by anionic emulsified asphalt has better flowability than that of composites prepared by cationic emulsified asphalt; the flowability decreases with the increases of A/C or the decreases of W/C. The difference of flowability is connected to the difference of surface properties of cement particles and emulsified asphalt particles and the difference of solid volume fraction.(2) Hydrostatic balance is used to measure the volume change of the composites during setting and hardening progress.The results show that:1) The shrinkage process of Sulphoaluminate cement-asphalt composites within24hours present slow shrinkage, rapid shrinkage and stable shrinkage three stages. The volume shrinkage occurs mainly in the first two stages which usually take less than3hours. Emulsified asphalt type has little effect on the24-hour shrinkage which increases with the increases of A/C or the decreases of W/C.2) The volume shrinkage of High-aluminate cement-asphalt composites within24hours also present slow shrinkage, rapid shrinkage and stable shrinkage three stages. The duration of the first two stages increase along with W/C and A/C.The addition of LiCl eliminates the slow shrinkage stage of the composites mixed by anionic emulsified asphalt and which enter rapid shrinkage stage as soon as mixed. Due to the retarding effect of anionic emulsifier, the shrinkage of composites prepared by anionic emulsified asphalt within24hours are less than that of composites prepared by cationic emulsified asphalt while the shrinkage after24hours of the former is greater than that of the later.The shrinkage decreases with the increases of A/C or the decreases of W/C.3) The volume shrinkage and its regularity of cement-asphalt composites are related to the hydration of cement and the physical structure of the composites. The shrinkage mainly results from the chemical shrinkage of cement and the interface interaction between cement hydrates and asphalt.(3) Sulphoaluminate cement-asphalt composites and High-aluminate cement-asphalt composites have high early strength and the strength gain mainly in7days, then it grows very slowly. Strength and elastic modulus decreases with the increase of W/C. The flexural strength and28-day elastic modulus of the composites decrease linearly with the increase of the A/C.(4) The flowability of Portland cement-asphalt mortar decrease with the increase of dosage of silica fume. The shrinkage increase along with silica fume dosage, especially increases the shrinkage of hardened mortar. The3-day strength of CA mortar decreases with the increase of dosage of silica fume while7-day,28-day strength and the28-day elastic modulus increases along with the dosage of silica fume.The influence of silica fume on the properties of CA mortar is associated with its specific surface area and pozzolanic effect.