超厚料层烧结条件下的钢泥预处理工艺

为了降低钢泥在烧结工序配加时对混合料制粒带来的不良影响,保证超厚料层烧结的料层透气性,天钢联合特钢在实践中开发了钢泥预处理工艺,将钢泥和高炉返矿在料场预先混合、筛分,使得进入配料混合工序的钢泥和高炉返矿粒度稳定在5mm以下。该工艺实施后显著减少了混合料中细粒级(<3mm)物料比例,改善了混合料粒度的稳定性和烧结制粒效果。

轴承滚动体研磨钢泥夹杂物的去除

轴承滚动体在研磨过程中会产生Al_2O_3、SiC等磨料夹杂物而影响研磨钢泥的再利用,因此必须除去。对比了研磨钢泥不同除杂方案的除杂效果,并比较了磁选前钢泥处理方式及磁选强度对去除夹杂物效果的影响。试验结果表明,磁选除杂效果最好,磁选前对钢泥进行湿磨处理,磁选过程中选择较小的磁选强度有利于夹杂物的去除。分析了Al_2O_3、SiC磨料夹杂物杂质不能完全分离的原因,主要是大颗粒钢泥表面存在很多孔洞,使得细颗粒夹杂物镶嵌在内部,难与以钢泥完全分离。

轴承滚动体研磨钢泥废料表面油污去除

轴承滚动体研磨过程中使用一些磨液以起到润滑和冷却作用。磨液为水、油酸以及配加的少量氢氧化钠,因此,钢泥废料表面会吸附上含有油酸和油酸钠的研磨油污,该油污对钢泥废料的后续还原处理生产还原钢粉产生不利影响,必须予以去除。采取400℃蒸馏挥发脱附法对轴承滚动体研磨钢泥废料表面油污的去除进行了研究。通过热重的方式研究了钢泥表面油污挥发脱附的失重情况,得出400℃钢泥表面油污挥发脱附大约需要17.1min,油污的挥发脱附满足二级动力学模型;通过油污蒸馏挥发脱附机理研究,明确油污脱附既要满足热力学条件,同时也受油污蒸汽溢出动力学影响;400℃氩气气氛下油污挥发后碳质量分数由2.89%降至0.76%,钢泥表面油污去除效果较好。

Review of research on interactions between deepwater steel catenary risers and soft clay seabeds

Steel catenary risers （SCR） have become an enabling technology for deepwater environments. A comprehensive review was conducted on recent research that examined interactions between deepwater steel catenary risers and soft clay seabeds. This included the STRIDE （steel risers in deepwater environments） and CARISIMA （catenary riser soil interaction model for global riser analysis） joint jndustry jrogram＇s test data as well as information from existing papers.

Flexural behaviors of steel reinforced ECC/concrete composite beams

An engineered cementitious composite （ECC） is introduced to partially substitute concrete in the tension zone of a reinforced concrete beam to form an ECC/reinforced concrete （RC） composite beam, which can increase the ductility and crack resisting ability of the beam. Based on the assumption of the plane remaining plane and the simplified constitutive models of materials, the stress and strain distributions along the depth of the composite beam in different loading stages are comprehensively investigated to obtain calculation methods of the load-carrying capacities for different stages. Also, a simplified formula for the ultimate load carrying capacity is proposed according to the Chinese code for the design of concrete structures. The relationship between the moment and curvature for the composite beam is also proposed together with a simplified calculation method for ductility of the ECC/RC composite beam. Finally, the calculation method is demonstrated with the test results of a composite beam. Comparison results show that the calculation results have good consistency with the test results, proving that the proposed calculation methods are reliable with a certain theoretical significance and reference value.

Blast Protection Shelter by Using Hollow Steel Filled with Recycled Concrete

Under extreme loading condition,a shelter will provide a safe place to protect people from injury caused by blast wave and fragments.In order to save resource and reuse waste materi-als,a new design concept for blast protection shelter was explored.The new construction was composed of I-section steel panel or C-channel steel panel filled with recycled concrete aggregate.The compaction process of the recycled concrete aggregate filled in the steel construction was ex-perimentally investigated.A single storey shelter based on the proposed design concept was nu-merically simulated by using LS-DYNA software.In the 3D numerical model,three walls were de-signed using I-section steel and one wall using C-channel steel,and all of the four walls were filled with recycled concrete aggregate.The penetration analysis was done by using ConWep.Some penetration tests were also carried out by using a gas gun.It is found that the proposed shelter based on the design concept is effective for blast protection.

Characterization and recycling of nickel- and chromium-contained pickling sludge generated in production of stainless steel

Pickling sludge generated during the neutralization of pickling wastewater with calcium hydroxide in stainless steel pickling process was characterized using X-ray fluorescence spectrometry, X-ray diffractometry, scanning electron microscopy, thermogravimetry and differential scanning calorimetry, etc. The major compositions of pickling sludge are CaF2, CaSO4, Me（OH）, （M： Fe, Cr, Ni）, and the content of CaF2 is high in the sludge. The melting point of pickling sludge is about 1350℃ and the viscosity is about 0.14 Pa.s at 1450 ℃, which are comparatively lower than those of normal refining slag. After heat treatment, the contents of sulfur and fluorine in the pickling sludge were reduced, confirming the thermal decomposition of sulfate in the sludge. Fluorine in the sludge is reduced by the gaseous SiF4 and A1F3 generated through the reactions of CaF2 with SiO2 and Al2O3. The preliminary results from the reduction test indicate that the sulfur content in the steel is not affected by the presence of sulfur in the sludge. The recovery of nickel is about 40%, and the chromium content changes marginally due to the protective atmosphere under the reduction condition of chromic oxide. The pickling sludge is a potential auxiliary material for the production of stainless steel.

Simulation and Reasonable Design of Bridge Steel Fenders to Reduce Ship Impacts

Steel fenders are increasingly used for ship-impact resistance structures in the design of navigable bridges. As an important approach to investigating this anti-impact structure effectiveness to reduce influences of vessel impact, simulation analyses are still not perfect yet. So this paper is intended to discuss several issues related to ship collision simulations, including steel constitutive relationship, connections between steel box and pile cap, contacts definition and friction consideration, and the determination of impact waterlines and angles. Consequently based on two examples of ship-steel fender-bridge structure systems, some conclusions about effectiveness and design of fenders to reduce ship impact are drawn.

Axial Compression Behavior and Analytical Method of L-Shaped Column Composed of Concrete-Filled Square Steel Tubes

Based on the characteristics of an L-shaped column composed of concrete-filled square steel tubes, the axial compression experiment and nonlinear finite element analysis were carried out to study the mechanical property of the L-shaped column. The load-displacement curve for the L-shaped column, the deflection and load-strain curves for the mono columns were obtained by the axial compression experiment. The results show that the L-shaped column exhibits a flexural-torsional buckling failure mode. The numerical simulation by the finite element analysis shows that the bearing capacity and failure mode are in accordance with those of the axial compression experiment and the feasi- bility of the finite element analysis is proved. For the calculation of the bearing capacity of the L-shaped column com- posed of concrete-filled square steel tubes, an analytical method is proposed based on the theory of the elastic stability and spatial truss model. The results of the analytical method are in good agreement with those of the axial compression experiment and the finite element analysis.

Quantifying Creep of Concrete Filled Steel Tubes

Using age adjusted effective modulus(AAEM)method,creep of concrete filled steel tube(CFST)member was formulated considering of creep coefficient and aging coefficient.Ten CFST specimens were tested including eight for creep and two for shrinkage.The experimental result was compared with the computed result using AAEM in which the creep coefficient was taken from calibration of ACI model based on experimental result on sealed concrete,and aging coefficient was supplied from relaxation test on sealed concrete specimen.Furthermore,the creep of CFST member was analyzed using author's own subroutine to input concrete properties through user programmable feature(UPF)in ANSYS software.Comparison was made on authors' own experimental database,some existing experimental results,and results from AAEM and numerical analysis.Finally,the conditions of applicability of AAEM method are put forward,and numerical approach to compute creep of CFST specimen is delineated.

Flexural response of reinforced concrete beams strengthened with post-poured ultra high toughness cementitious composites layer

Four-point bending tests were conducted up to failure on eleven reinforced concrete (RC) beams and strengthening beams to study the effectiveness of externally pouring ultra high toughness cementitious composites (UHTCC) on improving the flexural behavior of existing RC beams.The strengthening materials included UHTCC and high strength grade concrete.The parameters,such as thickness and length of strengthening layer and reinforcement in post-poured layer,were analyzed.The flexural behavior,failure mode and crack propagation of composite beams were investigated.The test results show that the strengthening layer improves the cracking and ultimate load by increasing the cross section area.Introducing UHTCC material into strengthening not only improves the bearing capacity of the original specimens,but also disperses larger cracks in upper concrete into multiple tightly-spaced fine cracks,thus prolonging the appearance of harm surface cracks and increasing the durability of existing structures.Compared with post-poured concrete,UHTCC is more suitable for working together with reinforcement.The load?deflection plots obtained from three-dimensional finite-element model (FEM) analyses are compared with those obtained from the experimental results,and show close correlation.

Flexural behavior of steel reinforced engineered cementitious composite beams

In order to enhance the durability of steel encased concrete beams, a new type of steel reinforced engineered cementitious composite(SRECC) beam composed of steel shapes, steel bars and ECC is proposed. The theoretical analyses of the SRECC beam including crack propagation and stress-strain distributions along the depth of the composite beam in different loading stages are conducted. A theoretical model and simplified design method are proposed to calculate the load carrying capacity. Based on the proposed theoretical model, the relationship between the moment and corresponding curvature is derived. The theoretical results are verified with the finite element analysis. Finally, an extensive parametric study is performed to study the effect of the matrix type, steel shape ratio, reinforced bar ratio, ECC compressive strength and ECC tensile ductility on the mechanical behavior of SRECC beams. The results show that substitution concrete with ECC can effectively improve the bearing capacity and ductility of composite beams. The steel shape and longitudinal reinforcement can enhance the loading carrying capacity, while the ductility decreases with the increase of steel shape ratio. ECC compressive strength has significant effects on both load carrying capacity and ductility, and changing the ultimate strain of ECC results in a very limited variation in the mechanical behavior of SRECC beams.

Replacing Stirrups of Self-Compacting Concrete Beams with Steel Fibers

Based on the investigation of fiber influence on workability of self-compacting concrete (SCC), tests were carried out on two series of SCC rectangular simply supported beams, which were made of hooked steel fibers reinforced concrete with or without stirrups, subjected to four-point symmetrically placed vertical loads. The major test variables are steel fiber contents and stirrup ratios. The results indicate that the ultimate load significantly increases with the increase of fiber content; the addition of ...

Hydration and Mechanical Properties of Portland Cement Blended with Low-CaO Steel Slag

The hydration and mechanical properties of Portland cement blended with low-CaO steel slag were studied and reported. The steel slag was used to replace cement up to 30% and then blended cement powder, paste and mortar samples prepared for the experiment. The quantitative analysis of XRD shows that ettringite formation is greatly reduced by incorporation of steel slag but there was a relatively low reduction of portlandite. Thermal analysis by TG shows that slag injection reduced portlandite content in the cement by at least 50%. Generally, the slag cement pastes required less water to form a workable paste compared to the reference cement, reducing as the slag content was increased. However, the setting times were higher than the reference. The permeability of the blended cement samples were lower than the control. The incorporation of 5% slag could not have an effect on the compressive strength of the concrete. The results confirmed that whilst cements with up to 15% slag content satisfied the strength requirements of class 42.5 N and those containing 20%-30% produce Class 32.5R cement.

The influence of steel slag on the hydration of cement during the hydration process of complex binder

The influence of steel slag,a by-product from the processing of iron to steel,on the hydration of cement during the hydration process of complex binder was studied by calorimetry,X-ray diffraction analysis,and Ca(OH)2 content determination.The results show that steel slag and cement affect each other’s hydration by changing the hydration environment.Steel slag does not react with the hydration products of cement.The dormant period of cement-steel slag complex binder during the hydration is longer than that of cement.The more the adding amount of steel slag is,the longer the dormant period of complex binder will be.The steel slag decreases the early hydration rate of cement.This phenomenon is more obvious with the increment of steel slag addition.However,the steel slag can promote the hydration degree of cement at later ages and the promoting effect becomes more obvious with the increment of steel slag addition and the hydration ages.

Positive and negative shear lag behaviors of composite twin-girder decks with varying cross-section

In steel-concrete composite twin-girder decks, wide concrete slab would undergo significant shear lag warping effect, including positive and negative. Some researchers have investigated the positive shear lag of composite decks by means of one-dimensional line model, while the studies on the negative shear lag have not yet been reported until now. In this study, a new one-dimensional analytical model of composite twin-girder decks is first proposed based on the model proposed by Dezi et al. Besides slab shear lag effect and partial connection at slab-girder interface which have been included in the model of Dezi et al., the particularity of the proposed model relies on its ability to account for variation characteristic of cross-section. Verification of the analytical model is later conducted through comparison of results from the analytical analysis and elaborate FE analysis for a simply supported composite deck with increasing depth and a two-span continuous one with decreasing depth. Finally, three kinds of structural forms of composite twin-girder decks, including cantilever, simply supported and continuous decks, are selected to carry out the analysis of positive and negative shear lag behaviors by means of the analytical model. The influences of cross-sectional variation characteristic and load type on positive and negative shear lag behaviors are mainly investigated. Additionally, a new definition on effective width for considering simultaneously positive and negative shear lag behaviors is proposed. The results from the proposed analytical model and EC4 specification are compared to provide suggestions for designers and checkers. In this study, the proposed analytical model can provide a powerful numerical tool for researchers to conduct the further investigation, and the analysis on shear lag and effective width can assist in design analysis of composite twin-girder decks.

The influence of steel slag with high Al_2O_3 content on the initial hydration of cement

The initial hydration of steel slag with high Al2O3 content and its influence on the initial hydration of cement were investigated in this study.Steel slag with high Al2O3 content may contain much calcium aluminate mineral but very little gypsum.The steel slag hydrates much more quickly than cement in the initial hydration period,producing many flake products which have a great influence on the fluidity,initial setting time,and adsorption level of superplasticizer of paste.Replacing part of cement by steel slag with high Al2O3 content can change the hydration condition of calcium aluminate mineral of the cement by decreasing the gypsum to calcium aluminate mineral ratio,resulting in accelerating the hydration rate of calcium aluminate mineral in the initial hydration period.Paste containing steel slag with high Al2O3 content has a shorter initial setting time,higher adsorption level of superplasticizer,and greater loss in fluidity than the pure cement paste.

Durability of calcium sulfoaluminate cement concrete

Calcium sulfoaluminate cement(CSAC),first developed in China in the 1970 s,has received significant attention because of its expansive(or shrinkage-compensating)and rapid-hardening characteristics,low energy-intensity,and low carbon emissions.The production and hydration of CSAC(containing ye’elimite,belite,calcium sulfate,and minors)have been extensively studied,but aspects of its durability are not well understood.Due to its composition and intrinsic characteristics,CSAC concrete is expected to have better performance than Portland cement(PC)concrete in several aspects,including shrinkage and cracking due to restrained shrinkage,freeze-thaw damage,alkali-silica reaction,and sulfate attack.However,there is a lack of consensus among researchers regarding transport properties,resistance to carbonation,and steel corrosion protectiveness of CSAC concrete,all of which are expected to be tied to the chemical composition of CSAC and attributes of the service environments.For example,CASC concrete has poorer resistance to carbonation and chloride penetration compared with its PC counterpart,yet some studies have suggested that it protects steel rebar well from corrosion when exposed to a marine tidal zone,because of a strong self-desiccation effect.This paper presents a succinct review of studies of the durability of CSAC concrete.We suggest that more such studies should be conducted to examine the long-term performance of the material in different service environments.Special emphasis should be given to carbonation and steel rebar corrosion,so as to reveal the underlying deterioration mechanisms and establish means to improve the performance of CSAC concrete against such degradation processes.

Seismic behavior of precast concrete coupled shear walls with engineered cementitious composite (ECC) in the critical cast-in-place regions

The seismic performance of precast reinforced concrete （RC） coupled shear walls is significantly influenced by coupling beams and the beam-to-wall joints during large deformations into plastic ranges. This study investigated the use of engineered cementitious composite （ECC） in the cast-in-place beam-to-wall joints and the upper regions of the composite coupling beams as an innovative method to improve the seismic performance ofprecast RQ coupled shear walls. Two 1/2-scale precast coupled shear walls were tested under reversed cyclic loading and seismic behavior in terms of failure characteristic, mechanical characteristic value, load-displacement hysteresis curves, load-displacement envelope relationship, stiffness degradation, ductility and energy dissipation capacity were evaluated. Research results show that the substitution of concrete with ECC in the critical cast-in-place regions proved to be an effective method to improve the seismic performance of the two-story spatial of precast RC coupled shear walls.

Theoretical modeling of steel reinforced ECC column under eccentric compressive loading

Fiber reinforced cementitious composites(ECC) are a class of advanced composites with strain hardening and multiple cracking behaviors. Substitution of concrete with ECC can significantly improve the seismic resistance and durability of the infrastructures. In this paper, it is proposed to use ECC as the matrix of frame columns for improving its load carrying capacity, ductility, and avoiding the brittleness of concrete. Based on the assumption of plane remaining plane and constitutive models of materials, theoretical models for calculating the load-carrying capacity of the steel reinforced ECC columns under small and large eccentric compression are proposed. With the parameters of the constitutive models from the existing experimental data, the relationship between ultimate axial load and moment capacities is also derived with the proposed models. To verify the validity of the proposed theoretical models, finite element analysis with the software of ATENA is conducted to simulate the mechanical behavior of the steel reinforced ECC columns under eccentric compressive loading. The calculation results from the theoretical models show good consistency with the simulated results, indicating that the proposed models are feasible and reliable for design. Finally, based on the theoretical models, the effect of the ultimate tensile strain and compressive strength of ECC, longitudinal reinforcement ratio on the load carrying capacity of the steel reinforced ECC column are comprehensively studied.