Water erosion is one of the major factors for performance degradation of cement asphalt mortar (abbreviated to CA mortar, or CAM). In this paper, the influence of gap depth, coupling effect of water and pressure on the fatigue behavior of CA mortar was investigated. Results indicated that the damage of bonding surface became more seriously with the increase of gap depth, and when the gap depth was 19 to 38% of the structure size, the destruction exacerbated. Results also indicated that CA mortar was damaged more seriously under the coupling effect of water and pressure; the destruction first occurred on the surface between slab track and CA mortar rather than that between concrete roadbed and CA mortar. Timely repair with epoxy resin prevented the further water erosion well, and improved the service life of CA mortar.

The durability, such as chloride ion permeability, freeze-thaw and sulfate attack resistance of ultra-high performance concrete (UHPC) having a large amount, ranged from 42% to 48% by weight of binder, of mineral admixtures including steel slag powder (SS), ultrafine fly ash (UFFA) and silica fume (SF) was studied and the microstructure of selected UHPC compositions was investigated by Mercury porosimetry in this paper. Moreover, the relationship between durability and microstructure of UHPC was analyzed. The mercury porosimetry studies demonstrated the very low porosity and a high proportion of the innocuous pores as well as the very small pore size in UHPCs, whose most probable pore diameter did not exceed 10 nm. This porous structure of UHPCs would definitely enable the material have excellent durability.

In this paper, freezing and thawing resistance of CA mortar was investigated and some influential factors such as the ratio between asphalt emulsion and cement (A/C), cement types, various additives were also explored. Results indicated that a gain of mass was observed for every mixture after the test; mixtures with a higher A/C performed better in terms of higher relative elastic moduli. Mixtures proportioned by partially replacing ordinary Portland cement (OPC) with sulfoalumninate cement (SAC) underperformed in freezing and thawing property. Addition of crumb rubber powder (CRP), redispersible polymer powder (RPP) and organic fiber (FR) improved the resistance of CA mortar to freezing and thawing while that of silica fume (SF) undermined it.

The interfacial properties of reactive powder concretes (RPCs), other known as ultra-high performance concrete (UHPC), containing steel slag powder and ultra fine fly ash are studied in this paper. The microstrctural characterization of interfacial transition zones (ITZs), including the aggregate-cement paste interfacial zone and the steel fiber-paste interfacial zone, is investigated by SEM. The microhardness of the aggregate-paste ITZ and the steel slag-paste ITZ is studied and the bond strength of steel fiber in matrix is tested through fiber pullout tests. The results indicate that the microhardness of the steel slag-paste ITZ is slightly higher than that of the aggregate-paste ITZ, which implies the advantage of the substitution of quartz powder with steel slag powder in preparation of RPCs to some degrees. Moreover, the hardness of these two ITZs is higher than that of the hardened paste. A certain amount of hydration products has been observed exsiting on the surface of steel fiber by SEM and the bond strength of steel fiber-martix is up to 9.3MPa. These interfical properties are definitely critical to obtain high performance of UHPCs containing steel slag powder and fly ash.

Investigation on the continuous dehydration process of calcium silicate hydrate with C/S 1.5 during heating in the air was carried out. Results showed that the heating at 200°C of C-S-H resulted in decreasing basal spacing from 1.2 nm to 1.0 nm, and the basal spacing disappeared as the temperature raised to 400°C. Small amount of the dehydrated calcium silicate hydrate, portlandite and calcite were detectable in the heated sample at 400°C. The phases in the samples heated at 500°C and 650°C are β-C2S, quartz, and calcite. At 800°C and 900°C, α′-C2S, β-C2S, and quartz are main phases in the heated sample.