Municipal solid waste incineration (MSWI) has been widely used due to its benefits in reducing waste and recovering energy. However, MSWI fly ash and bottom ash are increasing rapidly, causing harm to human health and the environment. This paper discussed the production process, physical and chemical properties, leaching properties, pretreatment methods, and applications of fly ash and bottom ash. By summarizing the previous literature, it is found that MSWI fly ash and bottom ash have mechanical properties similar to natural aggregate. Many beneficial attempts have been made in cement concrete aggregates, ceramic raw materials, and highway engineering materials. Due to concerns about the leaching of heavy metals in fly ash, its application in highway engineering is limited. The application of bottom ash in asphalt pavement is rare because of the side effect on the performance of asphalt mixture. Considering the solidification effect of cement on heavy metals and the low cost of fly ash and bottom ash, the application in cement-stabilized macadam base has broad application prospects. This is beneficial to reduce the construction cost and promote the process of waste incineration, especially in developing countries.

Greenhouse gas emission has been a serious problem for decades. Due to the high energy consumption of traditional construction and building materials, recycled aggregate and other environmentally-friendly materials or recycled materials have been researched and applied. The treatment and reuse of construction and demolition waste (CDW) is a good way to reasonably distribute the renewable resources in the urban city. The recycled aggregate can be used in road engineering, geotechnical engineering and structural engineering. The combined use of natural aggregate and recycled aggregate may possess better performance in real constructions. This paper investigates the mechanical performance, micro-mechanism and CO2 footprint assessment of NAM (natural aggregate mortar) and RAM (recycled aggregate mortar). Compressive strength test, flexural strength test, XRD and SEM, and CO2 emission evaluation were conducted and analyzed. The results indicate that NAM depicts better compressive strength performance and RAM has higher flexural strength. The XRD and SEM patterns illustrate that the ettringite and C-S-H are the most important role in shrinkage-compensating mechanism, which is more obvious in RAM specimens. The proportion of CaO and MgO hydrated into Ca(OH)2 and Mg(OH)2 is also a key point of the volume expansion through the curing period. Finally, the CO2 emission of NA is higher than RA per unit. This indicates that utilizing recycled aggregate over other conventional resources will reduce the energy consumption, and hit the mark to be environmental-friendly.

No abstract

Foundation pit excavation is common in urban construction, while safety evaluation is always significant in every specified project. The soil material properties, groundwater level, excavation method, supporting structure, monitoring points’ arrangement, and so on distinguish from one site from another. Thus, many studies have looked into the safety and reliability of designated projects. This paper was based on the co-construction underground tunnel project of a deep foundation pit excavation in Suzhou, China. This paper aimed to perform a safety evaluation on this foundation pit by means of numerical simulation for parameter influence analysis, as well as scientific comparison with in-site monitoring data. To minimize the energy consumption and contribute to the carbon neutrality, a brief energy consumption analysis was also conducted. The results indicated that the maximum deformation of the foundation pit bottom is 4.5 cm and the deformation of the foundation pit is within the allowable range. The maximum horizontal displacement of each excavation is approximately at 10 m to 12 m of the diaphragm wall and the largest deformation is 28 mm. The maximum ground settlement is less than 16 mm, which confirmed the safety during excavation. It is ideal that the above deformation law will provide a reference for similar projects. Furthermore, this research simulated and monitored the whole cycle of foundation pit excavation, and contributes to savings in energy consumption and limiting of carbon emissions.

Carbon emission is one of the main causes of global climate change, thus it is necessary to choose a low-carbon method in the contaminated soil remediation. This paper studies the adsorption ability of ZVI on Pb(II) contaminated soils under different working conditions. The removal efficiency of Pb(II) was 98% because of the suitable ZVI dosage, log reaction time and low initial solution concentration. The whole balancing process was much fast according to the pseudo-second-order kinetic and Freundlich isothermal model. Moreover, sequential extraction procedure (SEP) showed Pb(II) was transformed from Fe/Mn oxides-bound form to residual form in Pb(II) contaminated soils. From scanning electron microscopy (SEM), Brunauer-Emmett-Teller method (BET) and X-ray diffraction (XRD) results, it was confirmed that zero-valent iron (ZVI) stabilizes Pb(II) pollutants mostly through the combination of chemical adsorption and physical adsorption. The economic and carbon emission assessments were used to compare the cost and carbon emissions of different methods. The results show that ZVI adsorption has excellent economic benefits and low carbon emission.