Urbanization has influenced the distribution of heat in urban environments. The mutual influence between weather factors and urban forms created by dense buildings intensify human perception of the deteriorating thermal environment in subtropics. Past studies have used real-world measurements and theoretical simulations to understand the relationship between climate factors and the urban heat island effect. However, few studies have examined how weather factors and urban forms are connected to the thermal environment. To understand the influence of various weather factors on urban thermal environments in various urban forms, this study applied structural equation modeling to assumptions of linear relationships and used quantitative statistical analysis of weather data as well as structural conversion of this data to establish the structural relationships between variables. Our objective was to examine the relationships among urban forms, weather factors, and thermal comfort. Our results indicate that weather factors do indeed exert influence on thermal comfort in urban environments. In addition, the thermal comfort of urban thermal environments varies with location and building density. In hot and humid environments in the subtropics, humidity and wind speed have an even more profound impact on the thermal environment. Apparent temperature can be used to examine differences in thermal comfort and urban forms. This study also proved that an urban wind field can effectively mitigate the urban heat island effect. Ventilation driven by wind and thermal buoyancy can dissipate heat islands and take the heat away from urban areas.

In the last decade, waste carbon fiber-reinforced plastic (CFRP) products have not been properly recycled and reused, and they sometimes cause environmental problems. In this paper, the microwave-assisted pyrolysis (MAP) technology was utilized to remove the resin from the CFRP bicycle frame, which was recycled into carbon fiber. A scanning electron microscope (SEM) and single filament tensile test were used to observe and compare the difference between recycled carbon fiber and normal carbon fiber. The mechanical performances of carbon fiber-reinforced concrete (CFRC) were investigated with static and dynamic tests under three different fiber/cement weight proportions (5‰, 10‰, and 15‰). Three different kinds of carbon fiber were used in this study, normal carbon fiber, carbon fiber without coupling agent, and recycled carbon fiber. The experimental program was tested according to ASTM C39-01, ASTM C293, and ACI 544.2R standards for compression, flexural, and impact test, respectively. From the experimental results, addition of 10‰ of carbon fiber into the concrete exhibited maximum compressive and flexural strength. The impact performance of recycled carbon fiber improved the highest impact number compared with normal carbon fiber under different impact energy.

In this study, aggregates in asphalt concrete were partially replaced by basic oxygen furnace slag (BOFS) in proportions of 45 wt.%, 55 wt.%, and 75 wt.%. The thermal performances of the specimens are discussed based on the thermal conductivity, emissivity, and the indoor and outdoor temperature measurements. Consequently, 75 wt.% of the specimen’s aggregates were replaced by BOFS, which had a high emissivity of 0.86 across the sky window. In the indoor and outdoor tests, the temperature change was recorded to estimate the thermal performance of specimens. According to the quantitative calculation, when the substitution of BOFS was higher than 55 wt.%, the specimens had a better radiation cooling ability. Among these specimens, the specimen with the BOFS substitution of 75 wt.% absorbed the most heat inside the body, contributing to less heat remaining in the environment. Furthermore, because Newton’s cooling energy accounted for about 90% of the stored energy within 7 h, the heat dissipation after the seventh hour was primarily radiation cooling, corresponding to the emission across the urban boundary layer. As for the mechanical properties, the stability value, indirect tensile strength, and British pendulum number (BPN) were in line with the specifications under the proper BOFS substitution. In conclusion, BOFS has great applicability in pavements due to its thermal performance and mechanical properties. It not only achieves the goal of urban heat island mitigation by radiation cooling, but also reflects the concept of resource sustainability.

Many studies have shown that paint with reflective heat can effectively reduce the temperature of the building envelope and reduce the future energy consumption of the building. This study inspired the next-generation inorganic geopolymer material (IGM) color paint without volatile matter, which could be applied on concrete surfaces to reduce energy consumption in warm seasons. In this study, a total of five insulating IGM paints, white, red, green, blue, and yellow, were applied to a 50 cm × 50 cm × 12 cm concrete slab top surface. The highest average light reflectance of all the paints was 87.5% of white IGM paint, which was higher than plain concrete (36.4%). The heat flux and surface temperature were examined in the laboratory, and those test results were verified outdoor. The results showed that the IGM paints could effectively reduce the surface temperature and heat flux of the upper and lower surfaces of concrete slabs, and the white colored IGM paint was the best performer among all five colors, whereas the heat storage coefficient ($S_f$) of red, white, yellow, blue, and green IGM painted concrete slabs were 0.57, 0.53, 3.62, 2.95, and 1.91 W·m⁻²·K⁻¹, respectively, lower than plain concrete (24.40 W·m⁻²·K⁻¹). This coefficient was presented to externalize the thermal admittance. The overall measurement results showed that the concrete slab with colored IGM paints had better heat insulation ability than the plain concrete slab, especially in white IGM paint.

In the face of global warming, mitigating the urban heat island effect has become an important concern worldwide. This study applies the principle of buoyancy ventilation formed by sunlight in double skin façades (DSFs) to improve the thermal environment outside buildings by discharging heat through temperature and pressure differences. The study subject is a 15 × 30 × 40 m residential concrete building situated in a subtropical climate. The lower opening of the DSF faces the outdoor environment; heat is absorbed through this opening from the ground environment and then evacuated up to above the urban canopy layer heat island in order to cool pedestrian environments on the ground. We used numerical simulation to analyze the cooling potential of this DSF in summer daytime conditions. The results show that the DSF can successfully transport heat energy and discharge it above the urban canopy layer. Significant cooling effects were observed in both the horizontal and vertical spaces on the leeward side of the building DSF through the passage of surface heat, thereby reducing the load of indoor air conditioning.

The phenomenon related to urban heat islands is becoming severe. Besides the concrete building walls in cities, the urban surface also includes a large amount of asphalt pavement, whose thermal properties play a significant role in influencing the urban heat island. Therefore, it is necessary to examine the thermal characteristics of different asphalt aggregates and to enhance their effect on mitigating the urban heat island effect by applying radiative cooling to the aggregate components. Through indoor scaled experiments, we produced 30 × 30 × 5 cm asphalt concrete specimens, including conventional asphalt concrete (dense mix) and basic oxygen furnace slag (BOF) asphalt concrete with 100% aggregate replacement. The asphalt concrete specimens were heated in an oven until they reached the same temperature as the actual asphalt pavement and then subjected to 24 h radiation heat release cooling observation, to record temperature, humidity, and heat flux. The measured data were then verified against the theoretical values. The results showed that asphalt concrete with BOF aggregate had a higher heat capacity and a more pronounced radiative cooling effect than conventional asphalt. Such properties enable the localized cooling of the surrounding air. The results of this study provide a basis for the development of aggregate asphalt to boost the radiative cooling performance of surface materials and reduce the urban heat island effect.