Low Temperature Properties Research For Carbon Nanofibers And SBS Modified Cement Asphalt Mortar

Cement asphalt mortar (hereinafter abbreviated to CA mortar) is a key material of ballastless track which has great market value and developing prospect because of the overall consturction of high-speed railway and urban rail transit. A high proportion of asphalt are present in the hardened structure of CA mortar, rendering its brittlement more likely to occur when working at low temperature. Then the usage quality of track will be affected under the action of dynamic loads and temperature stress. Therefore, research on the strength and durability of CA mortar in low temperature is of great significance.Improving the properties of asphalt is an effective way to low temperature properties promotion of CA mortar. In this thesis, carbon nanofibers (CNFs) and SBS were adopted to modify original asphalt. Then, both the single modified asphalt and compound ones were used to prepare CA mortar. Respectively, the fluidity, gas content, compressive strength, flexural strength and crack resistance were tested. The influence law of different modifiers and their amounts on working performance, low temperature mechanical properties and anti-cracking performance of CA mortar was studied from testing results and intercomparison. The modification mechanism was preliminary studied by micro-observation methods at the end of this paper.(1) Working performance of single modified fresh mortar deteriorates with the increase of CNFs or SBS; Any increase in CNFs or SBS will decrease the working performance of compound modified CA mortar. In terms of the influence on the working performance of CA mortar, compound modification is more than single modification.(2) Both compressive and flexural strength of single modified CA mortar decrease with the increase amount of SBS, and increase with the increase amount of CNFs.Both compressive and flexural strength of compound modified CA mortar decrease with the single increase of SBS content. And with the singly adding of CNFs, they all first increase and then decrease at any age. The enhancement of compound modification is not good as CNFs single modification, but better than SBS single modified ones.(3) Ratio of flexural and bending energy is respectively adopted to evaluate the low temperature anti-cracking performance of CA mortar. They all indicate that the crack resistance enhanced by SBS or CNFs single modification. Further more, the modified of SBS is stronger than CNFs. As for the compound modified CA mortar, its crack resistance is even better than that of SBS single modified ones (SBS content shoud less than 4%). When the SBS mix amount come up to 4%, the toughness of compound CA mortar decrease with the addition of CNFs.(4) The testing results of SEM and fluorescence microscope show that, the cement paste reduces and asphalt increases with the SBS content increases when the CA mortar is singly modified. In CNFs singly modified CA mortar, the paste increases with the CNFs increases and void also be filled up by CNFs. The low temperature performances change with the modifiers mixing amount in compound modified CA mortar is caused by two changes which refer to the cohesiveness change between asphalt and inorganic materials and the modification effect change.