This work intends to contribute to the understanding of the influence factors of early hydration of ultrafine cement by focusing on the different fineness, different kinds of hardening accelerators, and different curing temperatures. Isothermal calorimetry, thermogravimetry, and X-ray diffraction (XRD) were performed to compare the hydration and chemical evolution of pastes containing accelerators with different fineness and curing temperatures; meanwhile, mechanical properties and water absorption were tested. The results showed that the cement fineness had a significant effect on the early hydration process; the smaller the cement particle size, the higher the early compressive strength. The 24 h compressive strength of ultrafine cement with a particle diameter of 6.8μm could reach 55.94 MPa, which was 118% higher than the reference cement. Water absorption test results indicated that adding 1% Ca(HCOO)₂ to ultrafine cement can effectively reduce the water absorption, and it was only 1.93% at 28 d, which was 46% lower than the reference cement. An increase in curing temperature accelerated the activation of ultrafine cement in terms of the strength development rate, and the content of Ca(OH)₂ in the ultrafine cement paste could reach 13.09% after being mixed with water for 24 h, which was 22% higher than that of the reference cement.

Gap exists in the interface of cement asphalt emulsion mortar and CRTS I track slab universally, which is more severe at four corners than other parts of the track slab. In this work, the temperature and elevation of CRTS I slab track with and without rail were measured continuously to study the influence mechanism of rail on the gap. The results show that the alternating temperature gradient of track slab is the main reason that causes the gap, and laying rail can efficiently decrease the gap size in the slab track without rail. Compared with the slab track without rail, the maximum elevation occurred at the corner, the maximum gap width and the maximum gap depth of the slab track with rail laid were decreased by 0.45 mm (25.7%), 0.75 mm (46.6%) and 9.5 mm (59.4%), respectively; meanwhile, the disqualification ratio at corners was reduced to 5.9%, which is 50% less than that of the track without rail. When elevation mismatch occurs in adjacent track slabs, a gasket should be placed at rail-bearing bed below the track slab in order to avoid the lower slab being dragged up by the higher slab and the further occurrence of new gap.

In this paper, the corrosion failure mechanism of bearing outer rings for railway freight car wheelset and the wear performance of coatings were systematically analyzed and tested. The results show that the microcells formed by martensite and Fe 3 C in the matrix structure accelerate electrochemical corrosion, which is mainly dominated by Cl -induced localized corrosion. The main components in the rust layer, γ-FeOOH/γ-Fe 2 O 3 , have a loose and porous structure, making it difficult to effectively block the penetration of corrosive media and forming a cycle of "corrosion-infiltrationrecorrosion". In the wear performance tests of different coatings, the weight loss rate of the epoxy coating after friction reaches 0.0616%, that of the phosphating film is less than 0.0019%, and although the thermal spray coating has a higher friction coefficient, its weight loss rate is close to zero, making it suitable for high-load and severe-wear scenarios.

With the large-scale construction of infrastructure such as high-speed railways and the rapid development of building industrialization and prefabricated buildings, the precast concrete industry has ushered in vigorous vitality. However, there are many tricky problems such as high-energy consumption and unstable long-term performance in the existing production technology of steam-cured concrete. Based on the current research on concrete early strength technology, this paper focuses on the early strength performance and greenness evaluation of the reference cement–sulfoaluminate cement (C–SAC) system. The results confirm that when the 30% mineral admixture—60% C–10% SAC system is mixed with the composite early strength agent, the 1 day strength of mortar can reach 38.0 MPa under the condition of 45°C steam curing. The water absorption is 1.1% after 28 days. The carbon emission of the system (32.1%) is lower than that of the reference cement, and the production energy consumption and the initial resource energy are reduced by 14.4% and 8.2%, respectively. This paper provides a promising strategy for the development of low-carbon, and early strength concrete and ultimately provides technical support for the realization of high-quality and green production of precast concrete components.

：To reveal the corrosion mechanism of Zn coating metal components of insulators in the extreme environment of the saline-alkali area, this study takes the insulators, salt blocks, and surface dust of insulators recovered from this area as the research objects, and systematically investigates the causes of Zn coating failure via metallographic laboratory methods. The research results show that: the matrix of both the connector and the steel cap consists of a ferrite-pearlite mixed structure; in the area, Cl⁻ in salt blocks and dust induces local pitting corrosion, while SO 4 2 ⁻ accelerates uniform corrosion; additionally, the components are abraded by salt particles and SiO 2 particles, resulting in a combined effect of chemical erosion and physical abrasion; the Zn coating deteriorates in this environment, forming a loose and porous structure that acts as a channel for transporting corrosive media, thereby accelerating the failure of the components.Keyword：Zn coating; saline-alkali environment; insulator components; corrosion failure