Basic oxygen furnace slag (BOFs) is difficult to reutilize because it contains excessive free lime, and thus causes serious expansion. For this reason, how to reuse BOF slag has turned out to be an imperative issue in order to meet the concept of a circular economy. The key intention of this research work is to develop a new way to reutilize BOF slag, which due to its high emissivity in the 8–13 µm wavelength range, can be used as a sustainable, passive radiative cooling material. Passive radiative cooling, without the consumption of any energy, achieves the cooling of a surface by reflecting the sunlight and radiating the heat throughout the outer space (not absorbed by the atmosphere). BOF slag is used as a radiative cooling material in geopolymeric coating. This coating possesses an emissivity of 0.95 within the range of 8–13 µm and also has high conductivity, but its gray appearance absorbs too much heat. Therefore, by improving the situation through a double-layer structure, a temperature drop of 5.9 °C was reached compared to non-coated concrete under simulated sunlight, simultaneously with a low heating rate and high cooling rate. Besides, the binding strength between the geopolymeric coating and Portland cement concrete is comparable to two commercial organic paints. It is highly probable that the utilization of BOF slag in geopolymeric coating is energy saving and also feasible for passive radiative cooling applications. Hence, it can greatly decrease indoor temperature and improve the comfort of people living in buildings.
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.
In this study, the feasibility of producing eco-friendly bricks by using geopolymer technology and a waste grinding wheel (WGW) from the grinding wheel industries was investigated. Nowadays, in order to meet industrial needs, for instance, in Taiwan, approximately 500,000 grinding wheels are used annually. That is, a large number of "waste" grinding wheels are produced. Furthermore, few studies have been conducted on the use of WGWs as raw materials in geopolymer applications. The use of geopolymer technology to form bricks can avoid the utilization of clay and cement and even prevent the use of a high-temperature process in kilns. Moreover, it can decrease CO 2 emission and energy consumption and thus, protect the environment. In this study, the following three major factors were considered: press-forming pressure (70 and 100 kgf/cm 2 ), NaOH molar concentration (2 and 4M), and the ratio of binder fineaggregate (1:3, 1:4, and 1:5). Under these conditions, the specimens were tested using the compressive strength test, water absorption test, microstructure analysis, a freezing-thawing test and toxicity characteristic leaching procedure test. The optimal formulation was composed of 1:4 binder fine-aggregate ratio, 4M NaOH concentration, and 100-kgf/cm 2 pressure. Furthermore, we used a WGW and achieved a compressive strength of 50.6 MPa after 28 days, which was greater than 32 MPa and conformed to the Grade A brick standard of National Standards of the Republic of China (13295). In conclusion, this brick fabrication method based on geopolymer technology was not only beneficial to the environment but also improved the efficiency of reutilizing WGW.
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