Thickness Of Protective Layer Research Articles

Numerical study on the effect of transverse crack self-healing on the corrosion rate of steel bar in concrete

Reinforced concrete is subject to degradation by cracking of the concrete and corrosion of the steel reinforcing bars. This study explores the influence of transverse crack self-healing on the corrosion rate of steel bars by developing a deformed mesh model. The dynamics of transverse cracking and steel bar surface potential distributions are also explored, and parameter sensitivity analysis of the corrosion current density is conducted. The results show that steel bars have a lower surface potential at transverse cracks than in non-cracked areas, which decreases with exposure time. Crack self-healing not only reduces the corrosion rate and surface potential of steel bars but also reduces the rate of chloride-ion diffusion into concrete. Increasing the thickness of the concrete's protective layer is an effective way to slow the corrosion of steel bars.

Corrosion Research and XCT Investigation of RC under Different Artificial Environment Simulation

In this experiment, the common electric accelerated corrosion and drying-wetting cyclic corrosion test are compared, and the influencing factors (diameter of steel and thickness of protective layer) of the two corrosion methods are analyzed. When the constant current density was 100uA/cm2, the cracking time of the protective layer of the wetting-drying test samples was about 4 times that of the electrified test samples. For the two kinds of acceleration experiments, the cracking time of the protective layer increases with the increase of the diameter of the reinforcement and the thickness of the protective layer. Under the condition of accelerated corrosion by electrification, the diameter of reinforcement has a great influence on the cracking time of the protective layer, while the thickness of the protective layer has a relatively small influence. Under the condition of accelerated drying-wetting cyclic corrosion, the thickness of the protective layer has a great influence on the cracking time. The influence of the diameter of reinforcement is not obvious. In addition, we further explored the specimen with XCT. The rust patterns of the two samples are different.

Numerical analysis of simply supported one-way reinforced concrete slabs under fire condition

This paper investigates the mechanical response of simply supported one-way reinforced concrete slabs under fire through numerical analysis. The numerical model is constructed using the software ABAQUS, and verified by experimental results. Generally, mechanical response of the slab can be divided into four stages, accompanied with drastic stress redistribution. In the first stage, the bottom of the slab is under tension and the top is under compression. In the second stage, stress at bottom of the slab becomes compression due to thermal expansion, with the tension zone at the mid-span section moving up along the thickness of the slab. In the third stage, compression stress at bottom of the slab starts to decrease with the deflection of the slab increasing significantly. In the fourth stage, the bottom of the slab is under tension again, eventually leading to cracking of the slab. Parametric studies were further performed to investigate the effects of load ratio, thickness of protective layer, width-span ratio and slab thickness on the performance of the slab. Results show that increasing the thickness of the slab or reducing the load ratio can significantly postpone the time that deflection of the slab reaches span/20 under fire. It is also worth noting that slabs with the span ratio of 1:1 reached a deflection of span/20 22 min less than those of 1:3. The thickness of protective layer has little effect on performance of the slab until it reaches a deflection of span/20, but its effect becomes obvious in the late stages of fire.

Reliability Analysis of Flexural Deflection of Reinforced Concrete Members under Ultra-Low Temperature

Based on the Monte Carlo method, the functional function under the normal use limit state given by the specification introduces the concrete tensile strength of each temperature gradient under ultra-low temperature, and the coefficient of change of concrete elastic modulus. By changing the temperature of the member, the thickness of the protective layer, the bending moment effect ratio, the reinforcement size,the concrete grade and the length of the bending beam. Analyze the reliable index of the deflection control of the flexural member under ultra-low temperature to obtain: When the reinforced concrete flexural member is reduced from normal temperature 20°C to-160°C, the reliable deflection index of the component increases non-linearly, reaches the maximum value at-130°C, and then decreases slightly, the concrete strength grade and the thickness of the protective layer under each temperature gradients have the greatest influence on the deflection control of the bending beam under ultra-low temperature, followed by beam length, steel bar size, load effect ratio,which is different from normal temperature.

Study on the axial compression performance of partially prefabricated steel concrete columns after fire

In combination with the advantages of steel reinforced concrete columns, high strength and high performance concrete and precast assembled structures, a new type of partially precast assembled steel reinforced concrete columns (SRHCC) was proposed in this paper. In order to study its post-fire axial compression performance, the finite element analysis software ABAQUS was used to simulate its temperature field under standard fire based on experiments. The results show that the core temperature of the specimen increases with the increase of the thickness of the section steel protective layer and decreases with the increase of the firing time. On this basis, the limit equilibrium theory was used to propose the formula for calculating the residual carrying capacity of SRHCC after fire. The calculated results were close to the test results and tended to be safe.

Constructing ultrathin TiO2 protection layers via atomic layer deposition for stable lithium metal anode cycling

Uncontrollable dendrite growth during the repeated plating/stripping of Li ions induces short cycle life and safety issues, which has severely impeded the practical application of lithium metal battery. It is acknowledged that the solid electrolyte interphase (SEI) is pivotal for Li metal anode stabilization. Here, a lithium metal anode coated with an artificial SEI film as the working electrode is applied. The TiO2 coating layer is firstly demonstrated for the lithium metal anode protection via atomic layer deposition (ALD) method. Thanks to the ultrathin TiO2 layer, dendritic growth is suppressed and the cycling lifetime is significantly improved. Additionally, the thickness of TiO2 protective layer has been further optimized. Comparing with other different thickness TiO2 layer, 5 nm TiO2 layer is found to be the optimized parameter toward capacity, cycling stability and rate capability in both symmetric battery system and full-cell system. The TiO2 layer promoted uniform deposition of Li+ and effectively inhibited the growth of lithium dendrites. Symmetric Li/50TiO2||Li/50TiO2 battery could cycle stably for more than 1600 h at 1 mA cm−2, and more than 500 h at 3 mA cm−2 and 10 mA cm−2 current density. The Li/50TiO2||NCM622 full-cell exhibited better rate performance and long-cycle performance, which capacity retention was increased by 23.3% compared to bare electrode after 100 cycles at 0.5C charge-discharge current density. Furthermore, the inherent working mechanism of TiO2 artificial SEI film has been proposed. This work provides an effective and new alternative method for lithium metal anodes protection, which is critical for the future design of next-generation Li metal batteries under safe operation.

Geological evolution process, mechanism, and application of protective layer in semi-coal and rock face

Under the influence of geological structure, the surrounding rock of semi-coal seam is easy to be loose and fractured, and the repairing rate is high. Therefore, it is of great theoretical and practical significance to study semi-coal seam mining's mechanism and control technology. In this paper, the geological evolution principle of the semi-coal seam is analyzed theoretically. The mechanic's relationship between the mining height of the semi-coal face and the lower coal seam's pressure relief is interpreted. The mechanism of eliminating bad blind areas in non-pillar mining of upper protective seam is analyzed. Through numerical simulation analysis, it is concluded that the expansion deformation rate of a protective layer increases linearly with the increase of mining thickness of the protective layer, and the width of undesirable blind zone of coal seam increases linearly with the rise of protective layer thickness. This paper puts forward the technology of non-pillar mining in the protective seam's semi-coal and rock face. Field industrial test results show that the technology achieves the overall pressure relief and reflection reduction of low permeability and high gas coal seams. The underlying 3 + 4 protective layer achieves the general pressure relief and reflection reduction of low permeability and high gas coal seams. Coalbed methane can be pre-drained up to 18 m3/min with a concentration of 90%.

Effect of Curing Temperature on Tunnel Fire Insulation of Aerogel Cement Paste Coatings

To further strengthen the protective effect of aerogel cement paste (ACP) coating on self-compacting concrete (SCC) in tunnel fire under the optimal mix proportion, the effect of curing temperature (from 5 to 80 °C, based on site construction curing temperature and surrounding rock temperature) on fire insulation of ACP was investigated. The mechanical properties, thermal conductivity and porosity of ACP were tested. The microstructure of ACP was characterized by means of SEM, XRD and TG/DTG. The results reveal that 50 °C is the optimal curing temperature for ACP with good mechanical properties and fire insulation. Relatively high curing temperature can facilitate hydration and pozzolanic reactions, contributing to the generation of more stable substances (such as C-S-H gels, tobermorite and thenardite, etc). ACP under excessive low curing temperature brings inhomogeneous microstructure with coarse pores, leading to producing wider and longer microcracks when it is exposed to tunnel fire. The microcracks make the heat convection and thermal radiation more significant and thus accelerate the damage of ACP under fire. In case of the less than 7% difference of thermal conductivity, dense microstructure and stable substances are more conducive to strengthening fire insulation of ACP. In practical engineering applications, the thickness of protective layer of ACP can be further optimized when ACP is cured under about 50 °C.

Structural stability of novel composite heart valve prostheses - Fatigue and wear performance

Heart valve replacement is a very effective method to treat severe valvular stenosis or valvular insufficiency. The valve can be divided into the mechanical valve and biological valve according to the main materials of the valve leaflets. The former has good durability, but the patients need to take anticoagulants all their lives, otherwise, thrombosis will occur; the latter has good blood compatibility, and only 3–6 months of postoperative anticoagulation is required, but its durability is lower than the former. Compared with a traditional valve used materials, the fabric composite valve leaflets have both mechanical valve and biological valve advantages, i.e. it can have both good blood compatibility and excellent fatigue resistance. This material is comprised of the internal fabric layer and bilateral external polyurethane layers jointed with adhesive, and it can adjust the flexibility, wear-resistance and fatigue resistance of the valve leaflet through adjusting the thickness of the outer polyurethane protective layer, the weaving method, the fiber diameter and the surface density of the inner ultra-high molecular weight polyethylene (UHMWPE) fabric. In this article, we tested the long-term durability of a fabric composite with its property close to the valve leaflet made of bovine pericardium, to evaluate the material performance loss under long-term fatigue and the wear degree of this material with different polyurethane layer thicknesses. As many as two hundred million cycles of fatigue test and the hydrodynamic performance test before and after the fatigue test proved that the material could withstand a service life of at least five years without structural failure or functional degradation. According to the SEM images after the experiment, it can be predicted that this material can achieve a longer fatigue life.

ТЕНДЕНЦІЇ РОЗВИТКУ РЕАКТИВНОГО ВОГНЕЗАХИСТУ (ОГЛЯД ЛІТЕРАТУРИ)

Purpose. Identification of the main directions of evolution of scientific researches concerning development and improvement of fire protective reactive coatings of intumescent type for steel constructions. Methods. Analysis of literature sources, study and generalization of information, classification and modeling of chemical processes. Results. As a result of the performed researches it has been shown that of all the developed reactive fire protection systems for increasing the fire resistance of steel structures the intumescent composition of ammonium polyphosphate/ pentaerythritol / melamine / polymer is the most widespread and economically justified. To reduce the cost of fire protection measures, it is necessary to improve the coatings of the intumescent type in the following main areas: increasing of fire protection efficiency with a decrease in the thickness of the fire protection layer; prolongation of life time with strengthening of resistance to external factors; reducing the cost of the prescription composition of intumescent paint due to the use of nanomaterials. Scientific novelty. It has been established that nanoclays, nanooxides of metals and silicon, LDH compounds and their analogues should be considered the most promising and multifunctional. The presence of nanomaterials in intumescent compositions allows to increase the environmental parameters of fire-retardant treatment due to the rejection of halogen flame retardants, boron compounds, formaldehyde resins. In addition, the presence of nanocompounds in intumescent coatings significantly reduces smoke in fire. Practical significance. The conclusions obtained from the literature review are of practical importance for the development of new approaches to the design of fire-fighting materials with improved performance through the use of nanomaterials, which provides a strong fire retardant foam char layer and provides rigidity of the insulation frame.

Risk assessment of Ordovician limestone water inrush in No.9 coal seam of Yangdong coal mine and its prevention and control measures

With the increasing of mining depth, intensity, scale and speed, Ordovician limestone water has become the biggest threat to the safety production of the low group seam. Based on the existing geological data, the hydrogeological characteristics of Ordovician limestone water are analyzed; the risk of Ordovician limestone water inrush is evaluated by using the method of “five maps and double coefficients” and considering the importance of effective protective thickness of floor protective layer in the evaluation results. The results show that there are no non straight through relative safety area (Area I) and non straight type relative risk area (Area II), only non straight type water inrush risk area (Area III) and straight through water inrush risk area (Area IV). According to the evaluation results, the floor grouting reinforcement is directly adopted in Area IV, and the Ordovician limestone may need to be modified in the strong water rich area; in Area III, the grouting transformation of the floor is carried out after the area with water inrush is identified first, but the Ordovician limestone is not needed. Other prevention and control measures should be subsidiary.

The ability of UHPC prepared with unpurified sea sand and seawater to protect embedded steel against corrosion

Preparing concrete with unpurified sea sand and seawater is of great significance for the construction in coastal areas short of river sand and pure water. However, unpurified sea sand and seawater contain a lot of chloride ions which may cause steel corrosion problems. In this paper, unpurified sea sand and seawater are used to prepare ultra-high performance concrete (UHPC), and the potential differences between the steel bars with protective layer thickness of 5mm and 15mm and the Cu/CuSO4 reference electrode under two types of dry-wet cycle and the chloride ion concentrations at different depths from UHPC specimen surface after 40 dry-wet cycles are tested, the UHPC specimens are broken to observe corrosion of embedded steel bars. The results show that UHPC prepared with unpurified sea sand and seawater has good ability to protect embedded steel reinforcement against corrosion under dry-wet cycle conditions in lab.

Effects of coral sand powder and corrosion inhibitors on reinforcement corrosion in coral aggregate seawater concrete in a marine environment

AbstractThis paper investigates the effects of coral sand powder (CSP) and corrosion inhibitors (SBT®‐ZX(V), SBT®‐RMA(II)) on reinforcement corrosion in coral aggregate seawater concrete (CASC) in a marine environment. A reasonable time‐variation model for reinforcement corrosion in CASC is proposed and verified. Based on the time‐variation model and chloride diffusion model, the cracking time and service life of CASC are predicted. The results show that the replacement of cementitious materials by 5% CSP can improve the corrosion resistance of steel bar in CASC. Both SBT®‐ZX(V) and SBT®‐RMA(II) can reduce the corrosion rate of steel bar in CASC, and this effect of SBT®‐RMA(II) is more effective than that of SBT®‐ZX(V). Among all CASC, CASC containing 5% CSP and SBT®‐RMA(II) possesses the best corrosion resistance. The results also reveal that the corrosion current density of steel bar in CASC increases firstly and then decreases over time. The ascending segment of the fitting curves for reinforcement corrosion in CASC conforms to the logarithmic‐type time‐variation model, and the descending segment of the fitting curves for reinforcement corrosion in CASC conforms to the exponential‐type time‐variation model. The cracking time and service life of CASC containing 5% CSP and SBT®‐RMA(II) will reach more than 10 years when the thickness of protective layer is 30 mm.

Chloride threshold value and initial corrosion time of steel bars in concrete exposed to saline soil environments

Saline soil is widely distributed in Western China. Its main components have the characteristics of high concentration and many kinds of ions, which pose a serious threat to the service life of reinforced concrete in this area. Therefore, it is of practical significance to determine the initial corrosion time and the chloride threshold value (CTV) of steel bars. In this research, the electrochemical impedance spectroscopy (EIS) method was used to determine the initial corrosion time and the CTV of steel bars immersed in saline soil simulation solutions, and the influence of sulfate and other ions on the initial corrosion time and the CTV of the steel bars was analyzed, as well as the influence mechanism. Based on Fick's second diffusion law, considering the time-dependencies of the chloride diffusion coefficient and the surface chloride content, a prediction model for the initial corrosion time of a steel bar in concrete was established. The results showed that compared with the solution containing only chloride and the solution containing low concentration of sulfate, the initial corrosion time of steel bars in saline soil simulation solution was significantly longer, and the CTV was lower. The sulfate had an obvious inhibited effect on the diffusion of chloride, the corrosion products of sulfate could fill the pores of concrete, affect the microstructure of the transition zone and concrete resistance, and caused the initial corrosion time of the steel bars to increase. other ions in the simulation solution also inhibited the diffusion of chloride, HCO3− ion reduced the pH value of concrete pore solution and made the CTV of steel bars decrease. The prediction model established in this research was in good agreement with the actual situation, which can provide experimental evidence for the service life prediction of reinforced concrete structures in a saline soil environment. In order to prolong the initial corrosion time of the reinforced concrete in a saline soil simulation solution, in addition to increasing the thickness of the concrete protective layer, other anti-corrosion measures were also needed.

Design of Concrete Building Structure in Marine Corrosion Zones

Zhao, H.R., 2020. Design of concrete building structure in marine corrosion zones. In: Al-Tarawneh, O. and Megahed, A. (eds.), Recent Developments of Port, Marine, and Ocean Engineering. Journal of Coastal Research, Special Issue No. 110, pp. 266–270. Coconut Creek (Florida), ISSN 0749-0208.Building structures in offshore areas are extremely susceptible to chloride ion erosion in seawater or marine atmospheric environment, causing problems such as corrosion and swelling of steel rebar, spalling of concrete protective layer, etc., reducing the service life of the structure, and increasing the maintenance and operating costs of the structure. This paper attempts to enhance the design concrete building structures in the marine corrosion zones from the two aspects of durability and service life. To this end, it summarizes the principles of chloride ion erosion of reinforced concrete structures in coastal areas based on existing research, and explores the destruction mechanism of reinforced concrete structures under the action of chloride ions and external loads. Finally, the new method suitable for durability design of reinforced concrete structures in marine corrosion zone was proposed. The study found that the chloride-induced corrosion to the structure in the marine environment can cause the corrosion of the steel bars and accelerate the corrosion rate; a time-varying reliability model of the reinforced concrete structure was proposed; the increase in the thickness of the steel protective layer in the concrete can effectively improve the durability and service life of the structure. The research findings provide a theoretical basis for the durability design of concrete structures in offshore environments or marine corrosion zones.

Heat transfer and ablation of carbon/carbon composites based on multi-field coupling

With the development of hypersonic technology, the demand for thermal protection material is continuously increasing. Carbon/carbon composites are widely used as thermal protection materials in the nose and in the leading edge of hypersonic vehicles owing to their high latent heat and good resistance to high temperatures. The flow field around the aircraft affects the heat transfer and ablation of carbon/carbon composites, changing the thickness and shape of the thermal protection layer. The ablation of carbon/carbon composites alters the flow field distribution, thus conversely affecting the ablation of carbon/carbon composites. To predict the heat transfer and ablation of carbon/carbon composites, a multi-field coupling model was established to predict the transient temperature distribution, ablation rate, and ablation profile of carbon/carbon composites in hypersonic aerothermal environments. The thermochemical non-equilibrium effects of the flow field, heat transfer of the material, and ablation of the material surface were considered in the modeling. The wall temperature and heat flux in the stagnation area change significantly. The initial heat flux is higher and the stagnation heat flux at 1 s is 17.22 MW·m−2. As time passes, the wall temperature increases, the temperature gradient in the stagnation area decreases, the heat flux decreases, and the stagnation heat flux at 30 s is 10.22 MW·m−2. As the temperature of the stagnation area is high, the material at the surface reacts actively and the ablation is more serious, whereas only a small amount of ablation occurs on the side of the model. The shape of the material model changes after the ablation, the leading-edge radius increases, and the ablation depth at the material stagnation point is 17.47 mm at 30 s. The results show that, in the hypersonic aerodynamic thermal environment, the carbon/carbon composites have a certain ablation recession, which leads to change in the external flow field and thermal load. The multi-field flow-heat-ablation coupling model can be used to predict the response of thermal protection materials, which can provide some reference for the design of thermal protection systems.

Structural Regulation of Magnetic Polymer Microsphere@Ionic Liquids with an Intermediate Protective Layer and Application as Core-Shell-Shell Catalysts with High Stability and Activity.

A novel ionic liquid immobilized on a magnetic polymer microsphere catalyst is reported in this paper. The obtained core–shell–shell catalyst consisted of magnetic nanoparticles (MNPs) as the core, catalytic inert St-co-DVB as the intermediate protective layer, and cross-linked polyaryl imidazole ionic liquids as the active catalytic layer located at the outermost [Im[OH]/MNPs@P(St-DVB)@P(VBC-DVB)]. This catalyst exhibited a high ion-exchange rate (64.65%), high saturation magnetic strength, and excellent acid and alkali corrosion resistance. In the catalyzed Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate, the conversion of benzaldehyde maintained at 92.1% during six times reuse. Optimizing the materials of the protective layer and regulating the thickness of the inert protective layer decreased the corrosion ratio of MNPs in acidic media from 44.82 to 0.44%. Adjusting the thickness of the catalytic layer realized excellent catalytic activity (97%) and high magnetic response performance. In summary, introducing an inert protective layer to the structure of ionic liquids immobilized on the magnetic polymer microsphere catalyst, regulating its thickness, and optimizing its structure achieved a catalyst with high activity, excellent stability, and easy magnetic separation.

Моделирование глубины проникновения дизельного топлива в защитную песчаную подушку

When deploying a temporary fuel storage warehouse, the primary source of soil contamination by oil products is technological losses related to the leakage of isolation valves. To protect the soil from contamination, containers are placed on a layer of sand. The thickness of the sand layer depends on the volume of possible losses. The purpose of the work is to model the depth of diesel fuel penetration into the protective layer of sand bed. The method of performing the experiment imitated a high rate of fuel penetration in the form of droplets onto the protective layer. The article considers the mechanism of fuel penetration into sand and factors, determining the penetration depth. It is established that the mechanism of fuel penetration into the protective layer has two stages, on each of which the penetration depth and rate of fuel distribution are different. The maximum penetration depth is reached on the first stage and depends on the quantity of fuel. The author developed the model, which allows the determination of the thickness of the sand bed protective layer with known granulometric particle composition necessary for the prevention of diesel fuel penetration into soil.

BRDF characterization of Al-coated thermoplastic polymer surfaces

In this paper, we present a combined morphological and optical characterization of aluminum-coated thermoplastic polymer surfaces. Flat plastic substrates, obtained by means of an injection molding process starting from plastic granules, were coated with ultra-thin aluminum films evaporated in vacuo, on top of which a silicon-based protective layer was plasma deposited in order to prevent oxidation of the metal reflective surface. Different sample treatments were studied to unravel the influence of substrate chemistry, substrate thickness, aluminum and protective layer thickness, and surface roughness on the actual optical reflectance properties. Bidirectional reflectance distribution function measurements, corroborated by surface morphological information obtained by means of atomic force microscopy, correlate reflectance characteristics with the root-mean-square surface roughness, providing evidence for the role of the substrate and the thin films’ morphology. The results unravel information of interest within many applicative fields involving metal coating processes of plastic substrates as an example in the case of automotive lighting.

Residual Bearing Performance of RC Beam Supporting Column Joint after Fire

In this paper, the residual load bearing performance of RC beam supporting column joint after fire is studied. Using the finite element analysis method, considering the influence of heating time, the thickness of the longitudinal reinforcement protective layer and the additional reinforcement, the bearing performance of the beam supporting column joint specimen after fire is analyzed respectively. The results show that the shorter the duration of high temperature, the smaller the change rate of the deflection of the beam supporting column joint under static load, and the lower the deformation of the beam supporting column joint under load can be reduced by the setting of additional steel bar, which plays a beneficial role in the residual bearing performance of the joint.