Wenyu Li

Cementitious materials prepared by the ice-templating method appear to have difficulty simultaneously possessing good mechanical properties and an oriented microstructure with microchannels. Surface micro-ceramicization of TiB₂ and the decomposed products of cement hydrates at high temperatures can be regarded as in situ solid–solid reactions involving oxygen, thereby enhancing mechanical properties. This study investigates the mechanical property changes in cement paste with different water-to-cement ratios containing 25% TiB₂ micron powder before and after high-temperature treatment. Cementitious samples are prepared using both freeze-casting (F-CAST) and regular casting (R-CAST) methods with and without the heating post-treatment. The average compressive strength of samples with a W/C of 0.65 prepared by the freeze-casting method at −60 °C with a heating post-treatment is much larger than that of samples prepared by the regular casting method with and without the same heating process. The freeze-casting process for preparing cementitious composites with TiB₂ not only reorders the distribution of water molecules but also redistributes the concentrations of the TiB₂ particles and the main hydrates in the frozen samples. Due to the concentration increase near ice crystal channels within the samples, led by the freeze concentration effect, the new products are formed and cover the channel surfaces after high-temperature treatment. This enhances both the overall and internal properties of the cement-based TiB₂ composite material. The variation in TiB₂ content within the specimens is of paramount importance.

The contradiction between the threshold values of carbon nanomaterials in cement-based materials for enhancing electrical, magnetic, and mechanical properties appears irreconcilable in previous studies. Reducing the numerical differences of these thresholds of carbon nanomaterials in cement-based materials is a straightforward approach to resolving the predicament. Flash graphene powder (FGP) with varying dosages is used to prepare the modified Portland cement paste in this work. Hydration heat release behaviours and the morphologies of hydrates are significantly impacted due to the unique turbostratic graphene layers. The percolation threshold of FGP in paste approximates its thresholds for enhancing the strength and absorption of electromagnetic waves (EMWs), which is 0.50 wt.% of cement. The compressive and flexural strength values of samples with 0.50 wt.% FGP increased by 59.5% and 22.4%, respectively, compared with the blank sample. The minimum EMWs loss value of the sample with 0.50 wt.% FGP is −12.2 dB with an effective absorption bandwidth value of 7.76 GHz in the EMWs frequency between 2 and 18 GHz. The smaller Portlandite crystals are associated with better conductive and impedance-matching properties, resulting in significantly improved EMWs absorption in the Ku band. This work proposes a possible solution that involves using FGP to replace normal graphene, thereby alleviating the contradiction and reducing the gaps in the graphene thresholds in cement paste and enhancing mechanical and electrical conductivity and EMWs absorption properties.

With the rapid expansion of urban areas, short naturally ventilated traffic tunnels (NVTTs) have become prevalent in modern cities. However, their enclosed design and inadequate ventilation often lead to the accumulation of vehicle emissions, especially during peak traffic periods, which poses significant threats to public health. Previous studies have shown that airflow in such tunnels is caused by ambient crosswinds (ACWs), which contribute to the dilution of pollutants. Based on this, a geometrical model including traffic tunnels belonging to a complex traffic system of the Second Ring Road in Wuhan City was established, followed by a mathematical model describing the fluid flow and pollutant transformation. The current flow characters and pollutant dispersion mechanism of CO and NO_X were analyzed. Among them, the number and speeds of vehicles are measured to calculate the strength of the pollutant source. Then, the data was set as the initial contaminant source strength in Ansys Fluent 14.0 to compute the pollutant dispersion of the whole domain. The results indicate the following: (1) The airflow direction inside the tunnel varies with changes in ambient wind direction and wind speed. Specifically, variations in ambient wind direction result in changes in airflow direction in both tunnels. In contrast, changes in wind speed do not affect the airflow direction in both tunnels; only in the downstream tunnel does the airflow direction change with increasing westward wind speed. By comparison, in the upstream tunnel, the airflow direction remains unchanged regardless of the westward wind speed; (2) Pollutant accumulates along the downstream airflow in both the tunnels; (3) The mass fraction level of contaminate stratification differs along the tunnels. The pollutant tends to form y-component layering near the upwind opening and x-component stratification at the downwind opening of the two tunnels.

The increasing demand for sustainable development and carbon neutrality highlights the need to improve the energy efficiency of infrastructure, particularly in highway service areas. This study explores the application of green roofs as a low-carbon technology to reduce energy consumption across buildings located in different climate zones in China. A combination of theoretical modeling and simulation-based analysis was used to evaluate various green roof configurations in five representative cities: Harbin, Beijing, Wuhan, Guangzhou, and Kunming. The results show that green roofs can reduce annual building energy consumption by up to 2.02%, depending on climate and plant species. For example, fern roofs in Guangzhou reduced heating demand by 16.35%, while grass roofs in Wuhan lowered the daytime roof surface temperature by 31.82 °C. Furthermore, optimizing the building orientation to 60° led to energy savings of up to 7.73% in Kunming. These findings suggest that tailored greening strategies based on regional climate can effectively improve building energy performance and support the development of sustainable service infrastructure.