Effect Of Solidification Research Articles

Effects of curing pathways and thermal-treatment temperatures on the solidification of heavy metal in fly ash by CaCO3 oligomers polymerization

The solidification of the heavy metals (HMs) of municipal solid waste incineration fly ash (MSWI FA) by a calcium carbonate polymer is a novel approach. The effects of different curing pathways and thermal-treatment temperatures on the leaching concentrations of the HMs were investigated by conducting different leaching tests and performing an overall pollution toxicity indices (OPTI) analysis of the leaching data, respectively. The results showed that the solidification efficiencies of the Pb and Zn of FA samples, which could form carbonate-bound states, from the fly ash-CaCl 2 ▪2H 2 O wet carbonation pathway were above 99.5%. The samples from the pathway that involved mixing FA with calcium carbonate oligomers (CCOs) had lower leaching concentrations of Cd and Cr (0 and 0.1112 mg▪L −1 ). With the thermal treatment temperature increasing from 105 °C to 500 °C, the treated FA samples had larger particle sizes, fewer pores, and more compact surface structures covering much more calcite , and the solidification efficiencies of Pb and Zn increased from 64.3% to 98.8% and from 60.2% to 98.9%, respectively. The calcium carbonate structure was decomposed in an acidic leaching agent, so the solidification effects were weakened and even negative. In contrast, the treated FA samples achieved effective solidification of HMs by physical packaging and chemical precipitation in the HT/J 557–2010 standard and the OPTI decreased from 8126.39 to 44.88. Therefore, a nonacidic environment is suitable for the storage or resource utilization of FA samples prepared by this method. • Two different curing methods of MSWI fly ash using CaCO 3 polymer were studied. • Inhibition on heavy metals leaching of 500 °C heat treatment was better than 105 °C. • The leaching characteristics of the samples were evaluated by different standards. • Fly ash samples were subjected to comprehensive heavy metal toxicity assessments.

Heavy metal removal using an advanced removal method to obtain recyclable paper incineration ash

Various agents, including ethylenediaminetetraacetic acid, oxalic acid, citric acid, and HCl, were applied to remove heavy metals from raw paper incineration ash and render the ash recyclable. Among these prepared agent solutions, ethylenediaminetetraacetic acid showed the highest efficiency for Pb removal, while oxalic acid showed the highest efficiencies for Cu, Cd, and As removal. Additionally, three modes of an advanced removal method, which involved the use of both ethylenediaminetetraacetic acid and oxalic acid, were considered for use at the end of the rendering process. Among these three modes of the advanced removal method, that which involved the simultaneous use of ethylenediaminetetraacetic acid and oxalic acid, i.e., a mixture of both solutions, showed the best heavy metal removal efficiencies. In detail, 11.9% of Cd, 10% of Hg, 28.42% of As, 31.29% of Cu, and 49.19% of Pb were removed when this method was used. Furthermore, the application of these three modes of the advanced removal method resulted in a decrease in the amounts of heavy metals eluted and brought about an increase in the CaO content of the treated incineration ash, while decreasing its Cl content. These combined results enhanced the solidification effect of the treated incineration ash. Thus, it was confirmed that the advanced removal method is a promising strategy by which recyclable paper incineration ash can be obtained.

Effect of matrix solidification on the structure formation in electromagnetic suspensions

For suspensions with electromagnetic particles exposed to an external field, we examine the effect of the solidification of the suspending medium on the formation of particle structures, representative of the curing of a photo-reactive resin during stereolithography. To that end, Brownian Dynamics (BD) simulations are examined in which the solidification of the suspending medium can be incorporated by increasing its viscosity in the course of time. For illustrative purposes, it is assumed that the viscosity function is known apriori in explicit and parametrized form, however, experimental data can be used as well. It is demonstrated that one can study the effects of the viscosity increase by a transformation of time, akin to the time–temperature superposition principle, but here also in the presence of thermal noise on the suspended particles. Therefore, instead of performing BD simulations with a continuously increasing viscosity (computationally inefficient), we advocate performing simulations at a constant (low) viscosity and subsequently transform time (nonlinearly) for re-interpretation of the simulation results. So doing, one can predict the formation of particle structures during on-going solidification of the suspending medium. In practice, the viscosity increase is so drastic that further evolution of the particle structure can be considered as arrested after the characteristic transition-time of the viscosity is reached. Semi-quantitative rules of thumb are formulated for the 3D-printing practitioner.Graphical

Study of the Effects on Mn, Pb, and Zn Solidification in Soil by a Mixed Curing Agent of Modified Diatomite.

In order to improve the application scale of diatomite in the remediation of heavy metal-contaminated soil in non-ferrous metal mining areas, the preparation of the modified diatomite-combined curing agent and its stabilizing effect on manganese (Mn), lead (Pb), and zinc (Zn) were systematically studied in non-ferrous metal tailing soil in this paper. The results showed that compared with that in natural diatomite (DE), the contents of available Mn in soil treated by acid- and alkali-modified diatomite samples (C-D and Na-D) were 18.82 and 25.93% lower, respectively, and the content of available Zn in Na-D was significantly lower, 6.71%, than that in DE. Further research showed that modified diatomite combined with quicklime (CaO) and hydroxyapatite (HAP) could significantly improve the solidification effect of soil heavy metals. Compared with that in single modified diatomite, the contents of available Mn, Pb, and Zn in the mixed curing agent-treated soil decreased by 23.59–46.32, 5.88–47.93, and 5.37–10.68%, respectively. The final pot test showed that the mixed curing agent of modified diatomite had no significant effect on the growth of plants, but it could reduce the Mn, Pb, and Zn accumulation in the upper and lower parts of plants, which is because the acid-soluble and reducible heavy metals in soil transform into an oxidizable and residual state, which reduces the mobility of heavy metals.

Influence of Different Types of Dewatering Agents on the Solidification Effect and Physical and Chemical Properties of Sediment

In order to study the comprehensive effects of different types of dehydrating agents on the dewatering and solidification of dredged sediments, this study took the dredged sediments of Taihu Lake as the research object and selected microorganisms, polymeric iron aluminum salts, organic polymers, organic-inorganic composites, and aluminum salt microorganisms. These five types of composite dehydrating agents were used to conduct a three-month solidification test on the dredged sediment by means of geotechnical pipe bag solidification. The results of the study showed that the dehydration efficiency of organic polymers and organic-inorganic composite chemicals was better. After one month, the water content of sediment dropped to 61.78% and 63.26%, respectively, which then dropped to 40.56% and 32.16% after three months. Compared with that of the unsolidified sludge, the total nitrogen of the bottom sludge after solidification by the organic-inorganic composite agent was reduced by 74.82%, reaching 591 mg·kg-1, primarily due to the reduction in ammonia nitrogen. The solid sludge contained mainly aluminum-bound phosphorus, calcium-bound phosphorus, and iron-bound phosphorus. Among them, four groups (organic-inorganic composite) had the largest reduction in active phosphorus, with the lowest being 64.3 mg·kg-1. In addition, organic polymer agents had the best curing effect on heavy metals, the comprehensive ecological risk index of heavy metals was reduced by 51.3%, and the leaching toxicity concentration was far below the standard threshold. This study showed that organic polymers and organic-inorganic composite medicaments have a better effect on the dehydration and solidification of bottom sludge and thus have good application prospects.

The evolution of microstructure, micromechanical and magnetic properties of FeCoNiSi alloys solidified under high pressure

A comprehensive study has been conducted on the effects of high-pressure solidification (HPS) on the evolution of microstructures, micromechanical properties, and magnetic properties of FeCoNiSi alloys. As solidification pressure increases(up to 7GPa), FeCoNiSi alloy's columnar grain changes into an equiaxed grain, and the grain size and Ni-rich precipitates are significantly refined. Furthermore, HPS facilitates the conversion of in-coherent matrix/precipitates interface of alloy solidified under atmospheric pressure into semi-coherent, which reduces the pinning effect of phase boundaries on the motion of the magnetic domains and enhances the exchange coupling between matrix and precipitates. As FeCoNiSi alloy solidifying under 7GPa, the maximum magnetic permeability (μ m ) is significantly increased (from 52,600 to 113,000), the inherent coercivity is decreased by 29.5%, and the saturation magnetic polarization( Js ) is increased by 21%. In addition, the high temperature magnetic properties of FeCoNiSi alloys are improved by HPS. Furthermore, HPS produces compressive stress in both the precipitates and matrix, which significantly improved the modulus of precipitates and matrix (i.e. from 171GPa to 215 GPa in matrix),as well as microhardness (i.e. from 5.46 GPa to 10.65 GPa in matrix). Based on the results of these studies, HPS is capable to improve the comprehensive properties of magnetic alloys significantly. • The J s and μ max (H MC ) of FeCoNiSi alloy are increased (decreased) by 21% and 114% (29.5%) after solidified under 7GPa. • HPS produces compressive stress in the precipitates and matrix and significantly improved the modulus and microhardness. • HPS refine the microstructure of FeCoNSi alloy and result in the semi-coherent interface. • The semi-coherent interface enhances the exchange coupling effect between precipitates and matrix.

Strength damage mechanism and pore structure evolution of modified Pisha sandstone cement soil with metakaolin

To fully understand the solidification effect of metakaolin (MK) on Pisha sandstone cement soil, unconfined compressive strength (UCS), ultradepth 3D microscopy (U3DM), nuclear magnetic resonance (NMR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests were carried out on the solidified soil. The solidification mechanism of MK was comprehensively analysed from the perspectives of macromechanics, mesostructure and micromechanisms. From the perspective of macromechanics, the damage variable V tended to decrease with increase in MK content, which indicates that the addition of MK helps improve the ability of the solidified soil to resist damage. From a mesoscopic perspective, the addition of MK reduced the average height difference of the surface of the solidified soil. The complexity of the size, number, distribution and shape of pores in the solidified soil was comprehensively analysed based on NMR experiments. With increase in MK content, the proportion of pores with a pore radius >1 µm decreased, whereas the fractal dimensions D T and D 2 increased. XRD and SEM experiments show that the hydration products (calcium aluminate hydrate and calcium silicate hydrate) formed after the incorporation of MK were tightly combined with the soil particles and filled the pores. A grey entropy correlation analysis carried out to analyse the correlation effect of different pore structures on the strength of the solidified soil showed that pore sizes of 0–0.1 µm had a large influence on the UCS. This is a valuable finding on the link between the microstructure and macromechanics of solidified soils.

The impact of intermetallic compound on microstructure, mechanical characteristics, and thermal behavior of the melt-spun Bi-Ag high-temperature lead-free solder

PurposeThis study aims to study the impact of intermetallic compound on microstructure, mechanical characteristics and thermal behavior of the melt-spun Bi-Ag high-temperature lead-free solder.Design/methodology/approachIn this paper, a new group of lead-free high-temperature Pb-free solder bearing alloys with five weight percentages of different silver additions, Bi-Agx (x = 3.0, 3.5, 4.0, 4.5 and 5.0 Wt.%) have been developed by rapidly solidification processing (RSP) using melt-spun technique as a promising candidate for the replacement of conventional Sn-37Pb common solder. The effect of the addition of a small amount of Ag on the structure, microstructure, thermal and properties of Bi-Ag solder was analyzed by means of X-ray diffractometer, scanning electron microscopy, differential scanning calorimetry and Vickers hardness technique. Applying the RSP commonly results in departures from conventional microstructures, giving an improvement of grain refinement. Furthermore, the grain size of rhombohedral hexagonal phase Bi solid solution and cubic IMC Bi0.97Ag0.03 phase is refined by Ag addition. Microstructure analysis of the as soldered revealed that relatively uniform distribution, equiaxed refined grains of secondary IMC Bi0.97Ag0.03 particles about 10 µm for Bi-Ag4.5 dispersed in a Bi matrix. The addition of trace Ag led to a decrease in the solidus and liquidus temperatures of solder, meanwhile, the mushy zone is about 11.4°C and the melting of Sn-Ag4.5 solder was found to be 261.42°C which is lower compared with the Sn-Ag3 solder 263.60°C. This means that the silver additions into Bi enhance the melting point. The results indicate that an obvious change in electrical resistivity (?) at room temperature was noticed by the Ag addition. It was also observed that the Vickers microhardness (Hv) was increased with Ag increasing from 118 to 152 MPa. This study recommended the use of the Bi-Ag lead-free solder alloys for higher temperature applications.FindingsSilver content is very important for the soldering process and solder joint reliability. Based on the present investigations described in this study, several conclusions were found regarding an evaluation of microstructural and mechanical deformation behavior of various Bi-Ag solders. The effect of Ag and rapid solidification on the melting characteristics, and microstructure of Bi-Ag alloys were studied. In addition, the mechanical properties of Bi with different low silver were investigated. From the present experimental study, the following conclusions can be drawn. The addition of Ag had a marked effect on the melting temperature of the lead-free solder alloys, it decreases the melting temperature of the alloy from 263.6 to 261.42°C. Bi-Ag solders are comprised of rhombohedral Hex. Bi solid solution and cubic Ag0.97Bi0.03 IMC is formed in the Bi matrix. The alloying of Ag could refine the primary Bi phase and the Bi0.97Ag0.03 IMC. With increasing Ag content, the microstructure of the Bi-Ag gradually changes from large dimples into tiny dimple-like structures. The refinement of IMC grains was restrained after silver particles were added into the matrix. The inhibition effect on the growth of IMC grains was most conspicuous when solder was doped with Ag particles. As a result, the Vickers microhardness of the Bi-Ag lead-free solder alloys was enhanced by more than 100% ranging from 118.34 to 252.95 MPa. Bi-Ag high-temperature lead-free solders are a potential candidate for replacing the tin-lead solder (Sn-37Pb) materials which are toxic to human and the environment and has already been banned.Originality/valueThis study recommended the use of the Bi-Ag lead-free solder alloys for high-temperature applications.

Impact on HDL and LDL of Hyperlipidemic Rat Models: Designed Solid Self-Nanoemulsifying Drug Delivery Systems with Atorvastatin and Ezetimibe combination

The main purpose of this study was to develop and evaluate solid self-nanoemulsifying drug delivery systems (S-SNEDDs) of Atorvastatin/ Ezetimibe combination to combine the advantages of liquid SNEDDs with those of solid dosage forms and investigate the effect of solidification on both lipid lowering efficiency and the ability to enhance oral bioavailability of included poorly water soluble drugs. Spray dried solid powder was prepared using Aerosil 200 based on its high adsorption capacity and the ratio of liquid SNEDDs: Aerosil was (4:1) due to the smaller droplet size produced after reconstitution compared to other ratios. Surface morphology characteristics and drug-excipients interactions were evaluated via Scanning Electron Microscopy (SEM) and Fourier Transformed Infrared Spectroscopy (FTIR). Crystallinity nature affect drug dissolution so, it was determined by Differential Scanning Calorimetry (DSC) and Powder X-ray Diffraction (PXRD). Pharmacokinetic study investigated the ability of (S-SNEDDS) to improve oral bioavailability of included drugs while, pharmacodynamic study evaluate its efficiency to control serum cholesterol levels compared to pure drugs suspension and liquid SNEDDs. Solid spray dried powder showed very good flowability (3.41±0.23g/s) and rapid dispersion in water with maintaining the self-emulsifying efficiency of liquid formula. Physicochemical evaluation of powder showed spherical separated particles with no significant drug-excipients interactions and drugs are molecularly dispersed or in amorphous state that improve dissolution rate as proven by in-vitro release studies. Pharmacokinetic and pharmacodynamic studies proved that the solidification process had no remarkable effect on the efficiency of liquid formula to enhance oral bioavailability of incorporated drugs and control serum cholesterol level compared to pure drugs suspension. S-SNEDDS was proved as efficient candidate to improve oral bioavailability of Atorvastatin / Ezetimibe combination and control cholesterol serum levels.

Analysis of solidification microstructure and cracking mechanism of a matrix high-speed steel deposited using directed-energy deposition

This study investigated the microstructure and cracking mechanism of a matrix high-speed steel fabricated by direct energy deposition. The combined effect of rapid solidification and chemical composition on microstructure and cracking mechanism during deposition were investigated. Excessive solute segregation into inter-dendritic regions due to rapid solidification caused formation of retained austenite in the inter-dendritic region and formation of α'-martensite in the dendritic region. The excess solute segregation decreased equilibrium solidification temperature and caused formation of low-melting eutectic carbides in the inter-dendritic region. These carbides increased hot-cracking susceptibility, and caused solidification cracking and liquation cracking in the inter-dendritic region. In contrast, tensile residual stress in deposited layers may have caused cold cracking in α'-martensite near the hot crack tips. Cold cracks contributed to growth of macroscopic longitudinal cracks throughout the specimen by bridging the hot cracks formed during solidification or reheating.

The Effect of Clay on the Shear Strength of Microbially Cured Sand Particles.

Microbial solidification of sand has obvious effects: energy-saving and environmental protection. It is a green and sustainable soil consolidation technology with low energy consumption, which meets the needs of high-quality development of modern economy and society. However, when clay is doped in sand, clay has an uncertain influence on the effectiveness of the microbial solidification of sand. Therefore, triaxial consolidation undrained tests before and after microbial solidification of sands with different clay content are carried out in this paper. The effects of clay content on the solidification effect of sands are compared and analyzed. The variation laws of shear strength, unconfined compressive strength, internal friction angle and the cohesion of sands with different clay content before and after microbial solidification are discussed. The failure modes of sand samples were studied and the influence mechanism of clay on the microbial solidification of sand was revealed from a micro perspective. The test results show that the failure strain and unconfined compressive strength of microbial-induced calcium carbonate precipitation (MICP) treated samples increase first and then decrease with the increase in the clay content. The unconfined compressive strength is the highest when the clay content is 9%, and the samples with low clay content (3~9%) can still retain good integrity after being destroyed. As the content of clay in the sand–clay mixture increases, the internal friction angle of the sample decreases and the cohesion increases. After MICP treatment, the internal friction angle and cohesion of the sand increase first and then decrease with the increase in clay content. There are three main contact modes between sand-clay-CaCO3. When clay content is low, clay plays a filling role. The contact mode between sand-clay and CaCO3 is mainly between sand particles and calcium carbonate and between clay particles and calcium carbonate. When clay content is high, the contact mode between particles is mainly between clay particles and calcium carbonate. Higher clay content wraps sand particles, prevents contact between calcium carbonate and sand particles and reduces the strength of sand.

The Effects of Portland and Sulphoaluminate Cements Solidification/Stabilization on Semi-Dynamic Leaching of Heavy Metal from Contaminated Sediment

Cement-based solidification/stabilization technology is widely applied in the treatment of heavy metals in river sediment because it is an effective treatment, with the advantages of saving time and being economically and environmentally friendly. In this study, the heavy metal polluted sediment in Shanghai Fuxing Island Canal was used as the raw material, the cement solidified form was prepared by adding 10% Portland cement or sulphoaluminate cement, and semi-dynamic leaching tests were carried out on the solidified forms. In this study, we compare two types of cements as metal conditioners and curing agents aiming to determine the more economical and effective way to utilize river sediments. The results showed that the compressive strength of Portland cement solidified form (PSF) increased with an increase in curing time, which could reach 0.75 MPa after 28 days and met the requirements of general subgrade engineering. The compressive strength of sulphoaluminate cement solidified form (SSF) reached 0.35 MPa after curing for 1 day, however, it decreased later. The semi-dynamic leaching test results showed that the mobility of Cu and Cd in the cement solidified form was low, and the migration mechanism of heavy metals was mainly diffusion. The mobility of heavy metals in the PSF was lower than in the SSF, thus, the PSF had a better solidification effect and was more suitable for treating heavy metal-contaminated sediment.

Simulation on the fragmentation characteristics of molten core materials in SFRs using modified MPS method

Fragmentation characteristics of molten metallic materials interacted with liquid sodium during core disruptive accidents (CDAs) in SFRs is essential to the evaluation of the severe accident development tendency. In this paper, a modified MPS method is proposed to simulate the fragmentation process of molten core structure material (316 stainless steel) under different dropping modes. The simulated fragments size distribution for the single droplet is consistent with the experimental results under relative low thermal condition, with the solidification and deformation effect being the dominant factors. With increasing thermal and hydrodynamic conditions, the fragments sizes decrease rapidly. For continuous droplets, the fragmentation is accelerated and enhanced under high thermal conditions due to the collision between the droplets if the time interval is short. For the jets, the sodium is observed to be entrained in the melt as well as the continuous cone structure, which are consistent with the experiments and mechanism analysis.

Researches on Ecological Solidification and Melioration Effects of Plants on Silty Soft Soil

Dredged soil from river and lake is a typical silty soft soil, which has a high potential for farmland utilization. However, the newly dredged soil generally has high water content and poor engineering properties, therefore, it must be dehydrated and solidified before utilization. The traditional dehydration and solidification methods have disadvantages such as high energy consumption and secondary pollution risk. A method of soil solidification and amelioration by using plants is explored in this research. Four species of Pennisetum hydridum, Sorghum bicolor × Sorghum sudanense, Typha angustifolia, and Zea mays, were used as the research objects, planted in silty soft soil. The solidification and amelioration effects of different plants were studied by observing the changes in soil mechanics and physicochemical properties before and after the experiment. The results showed that: all the four tested species showed soil solidification effects in different degrees, the Pennisetum hydridum with 0.5m planting distance showed the best effect. The four tested species increased the soil organic matter content in varying degrees, among which the mix-planting of Pennisetum hydridum and Typha angustifolia showed the best effect. Pennisetum hydridum can increase the soil alkaline hydrolyzable nitrogen(AH-N) content, Typha angustifolia can simultaneously increase the soil available phosphorus and available potassium content. In addition, the four tested species showed varying degrees of amelioration effects on physical properties. The Pennisetum hydridum shows the best amelioration effect, followed by Sorghum bicolor × Sorghum sudanense. In summary, it is feasible to use plants to solidify and ameliorate silt soft soil, which is beneficial to realize the resource utilization of dredged soil, especially suitable for agricultural land use.

Performance evaluation of a high-performance offshore cementing wastes accelerating agent

Abstract This article reports a quick-setting agent named AS-G1. In the current offshore oil exploitation, there are usually wastes mixed with the drilling fluid, completion fluid, cement slurry, etc. To protect the marine environment, offshore construction workers need to weakly solidify these wastes so that they can be transported to land for disposal. The accelerating agent can reduce the fluidity of offshore cementing wastes and achieve the effect of solidifying wastes. Compare the time for the three cement slurries to lose fluidity with the addition of accelerating agents. Evaluate the setting time of cement slurry under the action of the accelerating agent after adding two drilling fluids. The solidification effect of this kind of accelerating agent on cementing waste is verified. It can be applied to waste treatment in oil fields.

Synthesis of inherently helical nanofibers: Effects of solidification of electrified jet during electrospinning

AbstractIn this paper, a helical fiber was fabricated through electrospinning by increasing the vapor pressure of the solvent, increasing the conductivity of the polymer solution and forming an uneven electrical field distribution around the jet. Fiber morphology during electrospinning of a dielectric polymer solution was observed to dramatically change from straight to helical due to rapid solidification of the jet as vapor pressure of the solvent increased. A similar effect was observed with conductive solutions prepared by adding large amounts of metal ion to the polymer solution. The addition of metal ion induced strong electrical stresses, causing the electrified jet to rapidly solidify in the early stage of electrospinning. Simulations revealed that the jet near the nozzle tip was subject to a strong electrical field due to increased charge density. The thickness of the emerging fiber was rapidly reduced with fast and simultaneous solidification, resulting in helical nanofibers. In addition, by using the asymmetric spinnerets, an uneven electric field distribution around jet was generated, maximizing the fiber curvature and increasing the helical fiber ratio.

Effect of WC content on laser cladding Ni-based coating on the surface of stainless steel

Ni-based cladding coatings with WC weight percentage of 5%, 7.5% and 10% were prepared on the surface of 0Cr17Ni12Mo2 stainless steel by Raycus RFL-C1000 laser, and optical microscope, scanning electron microscope, energy spectrum analyzer, X-ray diffractometer, microhardness instrument, electrochemical analyzer, friction and wear test machine and wear track measuring instrument were used to characterize the microstructure and properties of the coatings. The results showed that the coating microstructure was mainly composed of cellular crystals and columnar crystals，and due to the combined effects of convection and rapid solidification of laser in the molten pool, WC granules were unevenly distributed and had "agglomeration" effect. With the increase of WC content, the nucleation core in the coatings saw an increase, and the degree of grain refinement raised. In addition, the coatings obtained higher thermodynamic stability and microhardness with the increase of WC content. However, as the number of unevenly distributed WC granules acting as primary batteries added, the tendency of corrosion reaction was enhanced and the corrosion rate increased initially, followed by a decrease. Owing to the influence of solid solution strengthening, dispersion strengthening and surface defects such as cracks and pores, the wear volume and friction coefficient of the coating showed a trend of first growing and then dropping with the increase of WC content.

Axial Bearing Mechanism of Post-Grouted Piles in Calcareous Sand

Post-grouted piles, as a foundation form for large-span and large-scale structures on calcareous sand, are expected to provide a high bearing capacity, but research on the response of post-grouted piles subjected to axial load in calcareous sand is still in the exploratory stage. In this paper, a model test is constructed for static pressure piles in calcareous sand under axial loading. The response of axial compressive piles, with and without post-grouting, in calcareous sand were investigated, and the test results were compared with those of axial compressive piles, with and without post-grouting, in siliceous sand. The influence of post-side-grouting on the response of a single pile subjected to axial compressive load in calcareous sand and its bearing mechanism were further analyzed. The results show that the change in shaft resistance, caused by the lateral extrusion of calcareous sand, is less than the negative effect caused by particle breakage during pile driving, so single piles without post-grouting in calcareous sand exhibit weaker axial bearing behavior than that in siliceous sand. A single pile with post-side-grouting in calcareous sand can provide a higher bearing capacity by increasing the shaft resistance and tip resistance compared with a single pile without post-side-grouting, and the increased ratio of the bearing capacity of piles, after grouting in calcareous sand, is better than that of piles in siliceous sand. Post-side-grouting can not only strengthen the surrounding soil by the solidification effect of injected cement grout, but it can also have a strengthening effect on the tip resistance. In addition, ideal-geometry grouting has more obvious advantages in improving the bearing behavior of pile foundations than annular point grouting, and higher stability in improving the bearing properties of pile foundations is evident for ideal-geometry grouting. Therefore, it is suggested that a directional grouting device should be adopted in actual projects in the future to form a more stable pile-soil interaction system and to expand the application prospect of pile foundations in calcareous sand.

Eco-friendly treatment for MSWI bottom ash applied to supplementary cementing: Mechanical properties and heavy metal leaching concentration evaluation

This paper reports a green method for treating municipal solid waste incineration bottom ash (MSWI-BA, MB), which is named Ce-wet grinding. The MSWI-BA can be used as a part of the cement for construction engineering after this treatment. The effects of wet grinding time on the mechanical properties and fluidity properties of municipal solid waste incineration bottom ash-ordinary portland cement (MB-OPC) were studied. Then the mechanism of heavy metals of toxic leaching concentration and chemical speciation in MSIW-BA was discussed in detail. The test results show that citric acid (CA) and ethylene diamine tetraacetic acid (EDTA) are added in wet grinding water can reduce the content of heavy metals in MSWI-BA. This method reduces the toxic leaching content of heavy metals and improves the solidification effect of cement on heavy metals. In addition, Ce-wet grinding increases the iron-manganese oxide binding state and carbonate bound state of heavy metals, which improves the stability of heavy metals. Ce-wet grinding can also reduce the particle size of MSWI-BA and enhance the mechanical properties of MB-OPC. This study provides an environment friendly idea for the MSWI-BA used as an admixture in cement, and it reduces the pressure of garbage treatment in garbage dumps.

Harmless treatment technology of phosphogypsum: Directional stabilization of toxic and harmful substances

Phosphogypsum is one of the typical by-products of phosphorus chemical industry. As a strategic industry related to the national livelihood of China, phosphorus chemical industry has accumulated and produced a significant amount of phosphogypsum. In general, phosphogypsum contains approximately 80%–95% calcium sulfate dihydrate, and less than 5% toxic and harmful elements. In this paper, toxic and hazardous components in phosphogypsum were efficiently solidified and stabilized by highly targeted solidification and stabilization technology. Calcium carbide slag or lime was used as an alkali-base neutralizer of phosphogypsum, and polymeric ferric sulfate or polymeric aluminum chloride as a directional solidification stabilizer to analyze the leaching toxicity of the mixed powder in 1, 3, 5 and 15 days. The experimental results demonstrate excellent solidification and stabilization effect with the leaching pH of 6–9, the leaching concentration of P, F and heavy metals of less than 0.5 mg/L, 10 mg/L and 0.1 mg/L, respectively, which meets the requirements of relevant international standards. Mechanistic analysis indicates that the solidification and stabilization of toxic and hazardous substances in phosphogypsum is perfectly achieved owing to the generation, adsorption and encapsulation of insoluble substances. This technology can reduce the costs and difficulty in the phosphogypsum treatment, and has extensive application potentials.