Waste resources recycling in controlled low-strength material (CLSM): A critical review on plastic properties.

The exponential growth of waste generation is posing serious environmental issues and thus requires urgent management and recycling action to achieve green sustainable development. Controlled low-strength material (CLSM) is a highly flowable cementitious backfill material with self-consolidating properties. The CLSM efficiency during construction and final performance at the site depends on its plastic properties. Plastic properties are responsible for workability, pumpability, stability, and lateral pressure on adjacent soils. This paper presents a critical review to date on the use of waste materials and/or by-products and their impacts on the plastic properties of the CLSM. Extensive previous studies demonstrated that the basic properties and content of waste materials as well as the amount of water in the mix design, play a dominant role in determining the plastic properties of CLSM. The discussed plastic properties of CLSM include flowability, bleeding, segregation, and hardening time, which are found to be inter-related. Proper mix design adjustment to accommodate the use of waste materials is possible to produce sustainable CLSM with acceptable plastic properties. Additionally, the discussion and analysis presented in this paper could provide a basis for future research advances and the development of sustainable CLSM prepared with waste materials.

Lead Isotopic Compositions of Selected Coals, Pb/Zn Ores and Fuels in China and the Application for Source Tracing.

Lead (Pb) pollution emission from China is becoming a potential worldwide threat. Pb isotopic composition analysis is a useful tool to accurately trace the Pb sources of aerosols in atmosphere. In this study, a comprehensive data set of Pb isotopes for coals, Pb/Zn ores, and fuels from China was presented. The ratios of 206Pb/207Pb and 208Pb/206Pb in the coals were in the range of 1.114-1.383 and 1.791-2.317, similar to those from Europe, Oceania, and South Asia, but different from those from America (p < 0.01). The Pb/Zn ores had 206Pb/207Pb and 208Pb/206Pb in 1.020-1.183 and 2.088-2.309, less radiogenic than the coals. Leaded gasolines showed similar Pb isotopic compositions to Pb/Zn ores, with unleaded gasolines and diesels being mixed sources. The average Pb isotopic ratios of gasolines and diesels were significantly different (p < 0.01) from those of coals in China, leading to the possibility to discriminate Pb in fuels from in coals. Urban aerosols demonstrated similar Pb isotopic compositions to coals, Pb/Zn ores, and fuels in China. After removing the leaded gasoline, the Pb in aerosols is more radiogenic, supporting the heavy contribution of coal combustion to the atmospheric Pb pollution.

Use of Alkali-Activated Slag as an Environment-Friendly Agent for High-Performance Stabilized Soil.

Discharged slag not only occupies a large amount of land for disposal, but also causes serious environmental pollution. The use of alkali-activated slag (AAS) instead of cement as a soil-stabilization agent is beneficial for industrial waste disposal and energy conservation, which complies with the concept of green and low-carbon sustainable development in the construction industry. In this study, the compressive strength, water permeability coefficient, chloride migration coefficient and sulfate resistance of alkali-activated slag-stabilized soil (AASS) were evaluated, and compared with those of cement-stabilized soil (CSS). The hydrated crystalline phases and microscopic pore structures were analyzed by X-ray diffraction, electrochemical impedance spectroscopy (EIS) and mercury intrusion porosimetry (MIP) tests, respectively. The results indicate that, compared with CSS, AASS exhibits a higher compressive strength, lower water permeability, chloride migration coefficient and better resistance to sulfate attack, with the optimum dosage higher than 10 wt.%. The results of the MIP analysis show that the addition of AAS reduces the porosity by 6.47%. The combined use of soil and AAS proves to be a viable and sustainable method of waste utilization and carbon emission reduction in the construction industry, which provides a practical path towards carbon peaking and carbon neutrality.

Upcycling of wastes for sustainable controlled low-strength material: A review on strength and excavatability.

In recent decades, the use of controlled low-strength material (CLSM) in densely populated cities has increased. CLSM is designed for future excavation with great fluidity, appropriate early strength, and low final strength. CLSM mixtures exhibit variable strength properties and performance due to the distinctive features of wastes (i.e., combustion residues, industry slags, and construction and other solid wastes) produced from various sources. CLSM should increase early strength quickly enough to allow traffic to resume within a few hours while maintaining a low strength for future re-excavation. It is suggested that the initial mixture design for each waste reported in the literature be changed until the combination meets the application standards defined in ACI 229R-13. The effects of adjusting other ingredients (i.e., cement, water, and admixtures) in the wastes incorporated into CLSM mixtures on the strength and re-excavatability properties are also detailed and discussed in this review. From practical and economic perspectives, the supply of materials in the waste streams, transport distance, and material properties and cost are important aspects to consider before their introduction to the construction industry.

The Effect of Seawater on Mortar Matrix Coated with Hybrid Nano-Silica-Modified Surface Protection Materials.

Surface treatment technology is an effective method to reinforce the durability of concrete. In this study, cement-based materials containing industrial solid wastes were modified by hybrid nano-silica (HN), then applied as a novel surface protection material (SPM-HN). The effect of SPM-HN on surface hardness of mortar matrix exposed to seawater was investigated. Further, the microstructure was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and mercury intrusion porosimetry (MIP). The results show SPM-HN could significantly enhance the surface hardness of matrix in seawater curing, and the rebound number is increased by 94%.The microstructure analysis demonstrates that the incorporation of HN inhibits the formation of ettringite, thaumasite, and Friedel's salt. In addition, thermodynamic modeling shows the incorporation of hybrid nano-silica could generate more C-S-H, and decrease the maximum volume of Friedel's salt when SPM is exposed to seawater. This research indicates SPM-HN can be applied as a concrete protective layer in the marine environment.

Highly-efficient green photocatalytic cementitious materials with robust weathering resistance: From laboratory to application.

The combined use of nano-TiO2 with cementitious materials offers an environmentally-friendly way to combat the air pollution problem. However, a trade-off between a high efficiency and a robust weathering resistance has often to be made for most of the attempted nano-TiO2 incorporation methods. This paper developed a simple and effective "spraying" method to coat nano-TiO2 particles on the surface of concrete surface layers (CSL). The results showed that the NOx removal rate of the samples increased with an increase in both the concentrations of nano-TiO2 solutions and the number of times of the spraying action. And the conditions for preparation of the Spray AB (the CSL were first sprayed with the 30 g L-1 TiO2-solution 20 times, followed by mechanical compaction, and for another 20 times after the compaction) were found to be optimal in terms of NOx removal performance and weathering resistance. The Spray AB was superior to the 5% TiO2-intermixed samples with respect to photocatalytic NOx removal ability. Compared with TiO2-dip-coated samples, the Spray AB samples had better and robust weathering resistance. A case study on the factory-fabricated green Eco-blocks (produced by the laboratory-developed spray method and the conventional intermix method) was performed. Examination and comparison on their respective photocatalytic NOx removal further verified the advantages of the spray method over the intermix method.

Mechanistic study on the combination of ultrasound and peroxymonosulfate for the decomposition of endocrine disrupting compounds.

The effectiveness and synergistic mechanisms of combining ultrasonic process (US) with peroxymonosulfate (PMS) were investigated using Bisphenol A (BPA) and Dimethyl Phthalate (DMP) as the model pollutants. Synergy between US and PMS improved the degradation of target pollutants, and PMS was found to play a dual role. The optimum dosage of PMS and the extent of efficiency promotion were found to depend on not only the ultrasonic frequency but also on the hydrophobicity of target pollutants. The scavenger quenching experiments and electron paramagnetic resonance analysis indicated that OH was responsible for DMP degradation in both US and US/PMS processes. The chemical probe experiments also proved that activation of PMS could increase the production of OH while excess PMS consumed the available radicals. Furthermore, it was found for the first time that the constituent salts of KHSO4 and K2SO4 in the commercial Oxone also made considerable influence on US/PMS process. It was also found that the combination of US and PMS showed more pronounced synergistic effect for treating DMP at lower concentrations. Higher efficiency was achieved at more acidic condition and similar efficiencies were obtained at pH range of 5.1 ~ 8.12. DMP degradation pathways were found to be the OH addition to the aromatic ring and hydrogen absorption at the aliphatic chains with and without the presence of PMS, but much better mineralization capability was obtained in the presence of PMS than ultrasonic degradation alone.

Enhanced Optical Absorption and Interfacial Carrier Separation of CsPbBr3/Graphene Heterostructure: Experimental and Theoretical Insights.

Controlling effective separation of carriers at the interface is a key element to realize highly efficient halogenated perovskite-based optoelectronic devices. Here, a comprehensive study of interfacial properties for CsPbBr3 nanocrystals (NCs)/graphene heterostructure is performed by the combination of theoretical and experimental methods. Enhanced visible light absorption is observed experimentally in the CsPbBr3 NCs/graphene heterostructure. The strong photoluminescence quenching phenomenon and improved photoresponse prove the efficient interfacial charge transfer from the perovskite CsPbBr3 NC layer to the graphene side. Significantly, theoretical calculations suggest that an intrinsic built-in electric field, pointing from graphene toward CsPbBr3, promotes the separation of photoinduced carriers at the CsPbBr3 NCs/graphene interface and simultaneously inhibits the recombination of electron-hole pairs. Thus, the high optoelectronic performance can be obtained in the CsPbBr3 NCs/graphene heterostructure, as shown in our experiment. Moreover, the CsPbBr3 NCs/graphene heterostructure exhibits smaller effective mass than that of CsPbBr3 NCs, indicating that the heterostructure does possess a high carrier mobility, which can further accelerate the separation of photogenerated carriers. Furthermore, the calculated results reveal that, accounting for the presence of the stronger built-in electric field, larger band bending value, and smaller effective mass, the PbBr2/graphene interface can realize the separation of the photoinduced carriers more effectively than the CsBr/graphene interface and thus more efficiently facilitate electron transfer from the perovskite optical absorber side to the graphene electronic transport side. Our findings provide valuable insight into perovskite/graphene-based photodetector devices via the interface engineering project.