Electronic waste plastics (e-waste plastics) have been one of the emerging and fastest-growing waste streams due to the increasing number of generation in waste electrical and electronic equipment ...(WEEE). Given that brominated flame retardant (BFR) materials in e-waste plastics have been the major impediment for recycling treatment, chemical recycling has been proposed as an environmentally friendly method of recycling e-waste plastics for clean fuels production or chemical feedstocks. This paper summarized the current techniques of BFR-plastics recycling with a view to solving energy crisis and the environmental degradation of BFR-plastics. Emphasis was paid on the recent chemical treatment of BFR-plastics, including pyrolysis, co-pyrolysis and catalytic cracking, which are yet to be completely feasible in conversion of BFR-plastics for clean fuels production. Hydrothermal treatment is regarded as a novel high-efficiency technology to recycle BFR-plastics, which can be a potential process for the in situ debromination of oil products. An advanced chemical recycling technique, pyrolysis-catalytic upgrading process, is highlighted. The recycling route of pyrolyzing BFR-plastics prior to catalytic upgrading was intended to obtain high quantity oils, and then the upgrading process of pyrolysis oils was conducted by means of catalytic hydrodebromination with the aim of obtaining bromine-free oils for commercial applications. In short, the integration of pyrolysis with catalytic upgrading process can provide significant economic and environmental options in conversion of e-waste plastics into useful and high-value materials. Further investigations are required to develop the pyrolysis-catalytic upgrading process to become sustainable and commercially viable for clean fuels production.
•Different temperature histories were set to determine the chloride diffusion coefficient of HVFA concrete.•Variations of chloride diffusion coefficient with temperature histories and age were ...revealed.•Relationships between chloride diffusion coefficient with Maturity were obtained.
This paper presents the influence of temperature history on chloride diffusion of high volume fly ash (HVFA) concrete. Four different curing temperature histories, referenced as SDC (standard curing), SMC (steam curing), OC (outdoor curing) and TMC (massive concrete temperature matched curing), were set. Concretes with different replacement levels of fly ash were cast and cured under the four temperature histories, respectively. The variations of compressive strength, porosity and chloride diffusion coefficient with different ages were determined by experiment. SEM and XRD were used to analyze the microstructure and compositions of hydrated pastes. The results show that the performances of fly ash concrete were influenced by temperature histories. And the influence was more obvious with the addition of replacement level of fly ash. For ordinary concrete, higher accumulated temperature at early age got higher compressive strength, better pore structure and lower chloride diffusion coefficient, but had negative effects at later age compared to SDC. For HVFA concrete, it was beneficial for the development of performances. Although the chloride diffusion coefficient was higher than ordinary concrete at early age, it would become small even lower at later age. And higher accumulated temperature promoted this process. In addition, by utilizing the concept of maturity, good power function relations between chloride diffusion coefficient of fly ash concrete and Maturity were obtained at early age.
•We choose two different kinds of simulated concrete pore solution.•The effect of carbonation on chloride-induced steel corrosion depends on the level of carbonation.•The effect of carbonation on ...chloride-induced steel corrosion depends on the kinds of solution.•The cement extract is more suitable to simulate the concrete pore solution.
The influence of carbonation on chloride-induced reinforcement corrosion in concrete has been studied in this work. Two different kinds of simulated concrete pore solutions, i.e. Ca(OH)2+KOH+NaOH solution and cement extract, were applied to carry out the experiment. Different concentration of bicarbonate ions was added to simulate the different level of carbonation and the initiation of pitting corrosion was measured by the open-circuit potential and the corrosion current density obtained from the EIS curves. It has been found that in Ca(OH)2+KOH+NaOH solution, a high HCO3- concentration enhances the stability of the passive film and the corrosion resistance of the steel specimen, while the low concentration of HCO3- ions accelerates the corrosion. However, in the cement extract, the HCO3- concentration always shortens the time-to-initiation of reinforcement corrosion.
The rate at which a nonequilibrium system decreases its free energy is commonly ascribed to molecular relaxation processes, arising from spontaneous rearrangements at the microscopic scale. While ...equilibration of liquids usually requires density fluctuations at time scales quickly diverging upon cooling, growing experimental evidence indicates the presence of a different, alternative pathway of weaker temperature dependence. Such equilibration processes exhibit a temperature-invariant activation energy, on the order of 100 kJ mol
. Here, we identify the underlying molecular process responsible for this class of Arrhenius equilibration mechanisms with a slow mode (SAP), universally observed in the liquid dynamics of thin films. The SAP, which we show is intimately connected to high-temperature flow, can efficiently drive melts and glasses toward more stable, less energetic states. Our results show that measurements of liquid dynamics can be used to predict the equilibration rate in the glassy state.
In this study, an ultrasound-assisted enzymatic extraction (UEE) method was proposed to augment the anti-corrosion performance of the green inhibitor extracted from waste Platanus acerifolia leaves. ...Chemical compositions and anticorrosive properties of UEE extract were characterized via multiple technologies. The adsorption film on the steel surface was characterized via X-ray photoelectron spectroscopy (XPS). The surface information of corroded steel was also analyzed. Results showed that, compared with the ultrasound-assisted alkali extraction (UAE), UEE increased the utilization rate of raw plant materials by 22%∼39%. After optimized via response surface methodology, the maximum yield of UEE extract could reach 27.081 mg/g. Electrochemical results showed, compared with 3% UAE extract, the inhibition efficiency of 3% UEE extract after 72 h in 0.5 M NaCl was increased by 22% while the extraction time was saved by 90%. Microscopic observations also proved that UEE extract can effectively mitigate the corrosion degree where the roughness of steel surface decreased by 63.67%. XPS results revealed that a carbonaceous protecting layer was formed on steel surfaces. The inhibition mechanism analysis suggested that flavonoids and their derivatives were apt to adsorb on the steel surface via chelation and surface physical adsorption, which could block the pathway of chloride attack.
•Chloride diffusion behavior associated with four common cations is studied.•The model considering multi-phase reactions and ionic interactions is improved.•The improved model is applicable for more ...common situations.•Two important factors influencing the binding capacity are analyzed.
In the previous paper, a model considering multi-phase reactions and ionic interactions was created to describe the diffusion behavior of chloride ions in concrete immersed in NaCl and CaCl2 solutions. In this paper, more experimental tests and numerical simulations are conducted to improve the model and to study the influence of cation type on chloride diffusion behavior in concrete. In the experimental part, the total and the water-soluble chloride concentrations are determined after 180days of immersion in the NaCl, KCl, MgCl2 and CaCl2 solutions. The test results show that the chloride binding capacities associated with the four cation types decrease in the order Ca2+>Mg2+>Na+≈K+ while the apparent diffusion coefficients of them decrease in the order K+≈Na+>Ca2+>Mg2+. In the numerical part, the equations of magnesian ions are newly considered so that the improved model can be applicable for more cation types. Based on the improved model, the chloride binding capacity of concrete in natural diffusion process is a complicated function concerning with many factors, among which the cation type and the contact duration are significantly important.
Natural hydraulic lime (NHL) as a building material has been widely used to restore the historic structure. However, the slow growth rate of strength and durability limits its engineering ...application. In this work, the NHL-based mortars were pretreated by lithium silicate (LS) solution impregnation and surface spraying. The results show that the compressive strength, surface hardness, and freeze-thaw cycle (FTC) resistance of NHL-based mortar were greatly improved after LS pretreatment. Specifically, the compressive strengths of the sample increased by about 32.7–52.0%. LS was sprayed on the sample’s surface (about 0.2 kg/m2) and the surface hardness increased by up to 10 grades. Compared with the control samples, the weight loss of treated samples decreased by about 31.6–43.8%. A rehydration process to generate the hydrated calcium silicate gel (C-S-H) was observed between calcium hydroxide (CH) and LS, which can decrease the sample’s porosity and form a silicate coating on the surface. With an increase in the concentration of LS, the macropores (50–10,000 nm) content decreased, while the mesopores (10–50 nm) and nanopores (less than 10 nm) increased. This work reveals that the LS pretreatment provides a potential route to improve NHL-based mortar’s mechanical properties and durability.
•Focus was placed on effect of electro-deposition on microstructures of concrete.•Electro-deposition exerted negligible influences on mineral compositions of samples.•Electro-deposition improved ...overall compactness of samples.
The electro-deposition technique can be used to repair cracks in reinforced concrete. Inevitably, this treatment affects the physical and chemical properties of the reinforced concrete. However, scant research has focused on the effect of electro-deposition on the microstructures of concrete. This study investigated the changes in the compositions and morphology of reinforced concrete with cracks after electro-deposition treatment. The results showed that the electro-deposition treatment exerted negligible influences on the mineral compositions of mortar specimens. However, the overall compactness of mortar was significantly improved with a reduction in the total porosity and refinement in the most probable pore size. Microstructure observation revealed that deposits, such as Mg (OH)2 and ZnO, were distributed and accumulated on the interface between aggregates and hardened cement paste, which contributed to the improvement in the overall compactness of the mortar samples.
A novel polymeric microcapsule was designed and synthesized using perfluoropolyether silane (PFPE-silane) as a superhydrophobic core material and ethyl cellulose (EC) as a shell material. The effects ...of the stirring rate and the core-to-shell ratio on the synthesized microcapsules were investigated. The physicochemical properties of the polymeric microcapsules were evaluated using scanning electron microscopy, fourier transform infrared spectroscopy, thermogravimetric analysis, laser particle size analysis, and wettability analysis. The results showed that when the stirring rate was 650 rpm and the core-to-shell ratio was 1:1, well-distributed and uniformly dispersed microcapsules could be obtained. The results also indicated that the prepared polymeric microcapsules were spherical particles with micropores on the surface, and they had an average particle size of 165.71 μm. The EC shells could effectively prevent the thermal decomposition of PFPE-silane during cement hydration, and the PFPE-silane also exhibited excellent hydrophobicity. The specially designed structure of this polymeric microcapsule suggests its potential for enhancing the corrosion resistance of reinforced concrete structures.
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Cracking is a recurring defect that typically arises during the construction and service periods of cementitious materials. Self-healing based on stimuli-responsive microcapsules has ...shown to be a cutting-edge technology to make cementitious materials sustainable. Despite the reported implementation of microcapsules in various fields, the strategies toward self-healing of cementitious materials via embedding microcapsules remain a significant challenge. Given this, a review concentrating on the healing exploration of cementitious materials assisted by self-healing stimuli-responsive microcapsules is conducted to bridge the gap. Special attention is given to the encapsulation designs and preparation processes, followed by capsules’ response mechanisms and healing processes. In particular, application scenarios, challenges and future prospects of self-healing stimuli-responsive microcapsules for cementitious materials are summarized and proposed in detail for the first time. This review attempts to better grasp the future research direction of this field, which provides new perspectives for addressing the cracking issue of cementitious materials.
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