Spalling Resistance Research Articles

Erosion behavior of arc sprayed FeTi/CrB MMC coating at elevated temperature

A self-developed FeTi/CrB composite cored wire and the commercially available stainless amorphous metal (SH-SAM) cored wire were used to form the composite coatings by arc spraying on 20g steel substrates. The coating composition and microstructure were characterized by energy dispersive X-ray spectra, X-ray diffraction and scanning electron microscope. The high temperature erosion properties of FeTi/CrB and SH-SAM coatings were determined at different impact angles and environmental temperatures. The results show that the matrix phase of FeTi/CrB coating consists of FeCr solid solution, with a certain amount of oxide inclusions and boride hard phase, forming a metal matrix composites (MMC) coating reinforced by ceramic particles. Compared with the SH-SAM coating, the FeTi/CrB coating has lower porosity and higher bond strength. The high temperature erosion rate of FeTi/CrB coating is much lower than that of SH-SAM coating at all experimental conditions. The FeTi/CrB coating exhibits good toughness and high spalling resistance attributed to the hard phase at elevated temperature. By contrast, the SH-SAM coating presents more brittle characteristics. The FeTi/CrB MMC coating presents itself as a potential protective coating for circulating fluidized bed boiler.

Experimental investigation of reinforced concrete and hybrid fibre reinforced concrete shield tunnel segments subjected to elevated temperature

This paper presents a comprehensive experimental study on the comparative behaviour of the reinforced concrete (RC) and the hybrid fibre reinforced concrete (HFRC) shield TBM (Tunnel Boring Machine) tunnel lining segments exposed to fire. The tests were conducted using a newly developed test facility, which is capable of accommodating different mechanical loading and boundary conditions under different fire scenarios. Six RC segments and six HFRC segments were tested to the standard Eurocode HC (Hydrocarbon) curve, while two reference specimens, one for each type, were tested in ambient environment to provide benchmark data. Apart from the spalling resistance, the fire effects on the structural behaviour were investigated under different boundary conditions at the segment ends, including free sliding (no horizontal constraint), total horizontal restraint and controlled horizontal reaction. The vertical load capacities were investigated for both under-fire and post-fire scenarios. The experimental results revealed excellent spalling resistance in the HFRC segments under thermo-mechanical loading, while the RC segments exhibited better structural performance. A combination of RC design (with flexural reinforcement) and the use of hybrid fibres is deemed to be effective in providing good spalling resistance while at the same time ensuring a robust structural behaviour.

Thermal Cycling Assessment of Steel-Based Thermal Barrier Coatings for Al Protection

There is a strong interest from the transportation industry to achieve vehicle weight reduction through the replacement of steel components by aluminum parts. For some applications, aluminum requires protective coatings due to its limited wear and lower temperature resistance compared to steel. The objective of this study was to assess the potential of amorphous-type plasma-sprayed steel coatings and conventional arc-sprayed steel coatings as thermal barrier coatings, mainly through the evaluation of their spalling resistance under thermal cycling. The microstructures of the different coatings were first compared via SEM. The amorphicity of the coatings produced via plasma spraying of specialized alloyed steel and the crystalline phases of the conventional arc-sprayed steel coatings were confirmed through x-ray diffraction. The thermal diffusivity of all coatings produced was measured to be about a third of that of bulk stainless steel. Conventional arc-sprayed steel coatings typically offered better spalling resistance under thermal cycling than steel-based amorphous coatings due probably to their higher initial bond strength. However, the presence of vertical cracks in the steel-based amorphous coatings was found to have a beneficial effect on their thermal cycling resistance. The amorphous plasma-sprayed steel coatings presented indications of recrystallization after their exposure to high temperature.

Microstructure and cyclic oxidation behavior of silicide coating and Si–Al coating on Cr–50Nb alloy

To protect Cr–50Nb alloys from high-temperature oxidation, the silicide diffusion coating and Si–Al coating were produced by pack cementation. The results indicate that the two coatings have three-layer structure and the interfaces are smooth. Uncoated Cr–50Nb alloy occur catastrophic oxidation at the initial oxidation stage at 1200°C. However, the scale spalling resistance of the two coatings are improved significantly, and Si–Al coating exhibits excellent resistance to oxidation. During cyclic oxidation in air at 1200°C for 100h, the weight loss of Si–Al coating is 1.39mg/cm2 and the mass gain is 6.01mg/cm2.

Effects of Mixing Sequence of Polypropylene Fibers on Spalling Resistance of Normal Strength Concrete

This paper presents an experimental study on the spalling resistance of normal strength concrete with different mixing sequences of polypropylene (PP) fibers subjected to fire. The mixing sequences of PP fibers in concrete mixture investigated are: (1) mixing PP fibers with fresh concrete; (2) mixing PP fibers with coarse aggregates; and (3) mixing PP fibers with fine aggregates. According to the test results, the degree of concrete spalling is reduced for specimens containing PP fibers at 0.2% by volume in the concrete mixture. The beneficial effect on spalling resistance is maximized when the PP fibers are mixed with fresh concrete and when the PP fibers are mixed with fine aggregates. The results are confirmed using scanning electron microscope (SEM) to investigate the dispersion of PP fibers in hardened concrete. In the case of mixing PP fibers with fine aggregates, smaller amount of superplasticizer is needed to obtain the target slump, and it is therefore recommended for practical use.

Development of a Zirconia-Graphite Refractory for a SEN Application

Zirconia-graphite refractories are generally used in the slag-like zone of the subentry nozzle in continuous casting. A zirconia-graphite refractory has superior thermal shock resistance and corrosion resistance compared to MgO-C and Al2O3-C refractories. The effect of graphite on the zirconia-graphite refractory is not well documented. Therefore, in the present work an attempt has been made to evaluate the effect of graphite on the properties of the zirconia refractory. Graphite can be classified in terms of fixed carbon content and in this work three different types of graphite with varying fixed carbon content were used (99, 94, and 80%). The amount of zirconia was maintained at 82% and that of the graphite at 18%. Other processing parameters and ingredient concentrations were constant throughout the work. Refractory samples were fabricated using the cold isostatic method and refractory samples were coked at 1000°C in a reducing atmosphere. The effect of fixed carbon percentage on apparent porosity, bulk density, spalling resistance, and oxidation resistance were evaluated.

Effect of Cerium on High-Temperature Oxidation Resistance of 00Cr17NbTi Ferritic Stainless Steel

The influence of cerium addition on the isothermal oxidation behavior of 00Cr17NbTi ferritic stainless steel was studied at temperature up to 1,000 °C for 100 h in air. The results show that cerium additions can reduce the grain size of this ferritic stainless steel, improve the diffusion of chromium and decrease the critical concentration of chromium to form protective Cr2O3 layer. With the increasing of cerium addition, the oxide particles become smaller and this can increase the rupture strength and spalling resistance of oxide layers. The transport mechanism through the oxide layer is varied from metal transport outward from steel to principally oxygen transport inward with the increase of cerium content, which leads to the lower oxidation rate and the better scale adherence of 00Cr17NbTi ferritic stainless steel.

고강도 콘크리트의 내화 특성에 관한 기존연구 고찰 및 실험적 연구

본 연구에서는 우선 화재에 노출된 고강도 콘크리트의 내화특성과 폭렬 메커니즘을 규명한 기존 국내외 연구자들의 연구문헌들을 심도 깊게 고찰하였다. 그 후 고온을 받은 고강도 콘크리트에 대한 국내외 연구자들의 주요 실험 변수를 분석하여 가장 최적의 변수를 설정하였으며 이를 토대로 하여 100MPa급 고강도 콘크리트의 내화 특성을 규명하기 위한 내화실험을 계획하였다. 또한 기존 연구의 실험결과를 분석한 결과 폭렬방지에 효과가 있는 것으로 알려져 있는 PP섬유와 친수성 재료로서 시멘트 입자와 부착성능이 우수하고 워커빌리티를 개선할 수 있는 NY섬유를 혼합한 신재료 HB섬유를 섬유혼입률 0.05%로 정해 배합설계에 반영하였다. 이러한 배합설계로 타설한 총 48개의 공시체를 28일 양생기간 후 온도변화 (<TEX>$100^{\circ}C{\sim}700^{\circ}C$</TEX>)에 따른 고강도 콘크리트의 역학적 특성을 분석하기 위해 화재를 받은 후 냉간상태에서의 내화실험을 수행하였으며 이를 통해 고강도 콘크리트의 내화 특성을 분석하였다. This paper reviews past literatures relevant to fire-resistance properties of high strength concrete and investigates spalling mechanism of high strength concrete in fire. First, literatures were reviewed on spalling occurrence and fire-resistance methods. Second, a chemical change of concrete components in an elevated temperature was presented. Finally, the mechanism of the spalling occurrence and spalling resistance were examined in terms of hybrid fiber content. The focus of the experimental study as part of this research is to investigate the effects of fire on the variation of thermal properties of high strength concrete, which tends to be used in super tall buildings. This experimental study was devised to investigate the fire-resistance performance of high strength concrete containing hybrid fibers. A total of 48 test specimens were exposed to high temperature ranging from <TEX>$100^{\circ}C$</TEX> to <TEX>$700^{\circ}C$</TEX>, including room temperature (<TEX>${\sim}20^{\circ}C$</TEX>). Test results provide valuable information regarding fire-resistance properties of strength concrete with 100 MPa or greater.

Novel calcium hexaluminate/spinel-alumina composites with graded microstructures and mechanical properties

Calcium hexaluminate (CA6) was incorporated into the matrix of magnesio aluminate spinel-alumina (MA-A) via infiltration of a porous preform fabricated from α-Al2O3 and MgO powders with a saturated calcium acetate solution and subsequent firing, forming CA6/(MA-A) functionally composites with graded fracture toughness. Actually, the porous preform was partially and perpendicularly immersed (1/4 of its length) in the solution. Owing to the capillary action, the calcium acetate solution was absorbed into the porous preform, and the different absorption distance led to the graded solution concentration in the height direction of the porous preform. The in-situ formation of CA6 conferred graded microstructures, as well as improved mechanical properties on the resultant composites. The CA6 content decreased gradually along the solution absorption direction, i.e., from one end [CA6/(MA-A) region] immersed in solution to the other end [MA-A region], reducing evidently the formation of layered structure along the direction, while increasing gradually the formation of spherical alumina particles. The CA6/(MA-A) region had a better toughness that could prevent the crack propagation and improve the spalling resistance. Meanwhile, the MA-A region could provide structural support, because of the higher Vickers hardness and density.

Compressive behaviour of concrete structures incorporating recycled concrete aggregates, rubber crumb and reinforced with steel fibre, subjected to elevated temperatures

Abstract In this paper, effects of elevated temperatures on the compressive behaviour of rubber crumb and steel fibre reinforced recycled aggregate concrete (RSRAC) are presented. RSRAC is a new concrete material proposed by the authors. In the RSRAC, steel fibre is used to improve the performances of concrete before exposure (e.g. ductility, cracking) and after exposure (explosive spalling) to evaluated temperature, and the inclusion of rubber particles is mainly for the consideration of environment protection and reducing the risk of spalling after exposure to high temperatures. A series of concrete mixes were prepared with Ordinary Portland Cement (OPC), recycled concrete coarse aggregates (RCA) or natural coarse aggregates (NCA), 1% steel fibre (by volume) and rubber particles with different fine aggregate (sand) replacement ratios. The compressive properties, including compressive strength, Young's modulus (stiffness), stress–strain curves and energy absorption capacity (toughness) of the different concrete mixes subjected to elevated temperatures (25 °C, 200 °C, 400 °C and 600 °C), were obtained in accordance to ASTM standards. The results of weight loss and failure modes were recorded and presented in this study. The results showed that both the compressive strength and stiffness of concrete mixes decreased after exposure to elevated temperature, with higher replacement of fine aggregate by rubber leading to lower compressive strength and stiffness magnitude. Nevertheless, rubber crumbs significantly enhanced the energy absorption capacity and explosive spalling resistance.

Comparative impact behavior of four long carbon fiber reinforced concretes

The addition of long carbon fibers (fibers more than 10mm in length) to traditional reinforced concrete is proposed as a method to improve the impact spalling resistance of concrete. A series of experimental tests were conducted to compare the impact resistance of plain concrete (PC), steel reinforced concrete, and four different types of long carbon fiber reinforced concrete (LCFRC) panels. The plain and conventional steel reinforced concrete panels served as control specimens. Of the four types of long carbon fibers tested in this study, the first fiber type consisted of an epoxy-impregnated, bidirectional weave (Type A), while the remaining types consisted of fiber tow with three different variations of a polypropylene support system (Type B). To determine the properties and performance of the LCFRC, experimental testing included a drop weight impact test of the panels as well as a standard ASTM test method for flexural performance of fiber-reinforced concrete. The results from each test in terms of impact energy, time histories of impact load and deflection, strain energy, failure crack pattern, and flexural properties were then compared to one another. This comparison indicated that adding long carbon fibers to concrete increases the post-cracking behavior of the concrete and decreases fragmentation during an impact test. Of the four fibers tested, Fiber Type B3 exhibited the highest performance, absorbing more energy during impact. This result is most likely related to the unique shape of this type of fiber in comparison to the others, which allowed more extensive wetting of the fiber with cement paste and thus improved bond to the cementitious matrix.

Experimental and numerical analyses of long carbon fiber reinforced concrete panels exposed to blast loading

The addition of long carbon fibers to traditional reinforced concrete is proposed as a method to improve the blast spalling resistance of concrete. A series of tests was conducted to compare the blast resistance of panels constructed with either conventional reinforced concrete (RC) or long carbon fiber-reinforced concrete (LCFRC). Conventional reinforced concrete panels were tested as control specimens. Pressure sensors measured both the free-field incident pressure and the reflected pressure for each panel. Furthermore, a finite element model was created in LS-DYNA to replicate both a control panel and an LCFRC panel to observe whether or not the models could predict the observed damage. Each of the LCFRC panels exhibited less material loss and less surface damage than the control panels. The addition of long carbon fibers significantly increased the concrete's blast resistance and significantly reduced the degree of cracking associated with the concrete panels. The results were also compared to the existing damage level chart (UFC 3-340-02). A comparison of the results indicates that the finite element modeling approach adopted in this study provides an adequate representation of both RC and LCFRC experimental responses. The results can be used in blast modeling with a reasonable degree of accuracy.

Residual mechanical characteristics and spalling resistance of fiber reinforced self-compacting concretes exposed to elevated temperatures

The study presented in this paper concerns the effect that polypropylene fibres have on the properties of SCC of different strength classes when exposed to elevated temperatures. A total of six different SCC and two normal concrete mixtures were produced. The strength classes of the mixtures were C25/30 and C30/37.The specimens produced were placed at the age of 120days in an electrical furnace and the heat was applied with a rate of 5°C/min. The tested temperatures were 300°C and 600°C. Once reached, the maximum temperature was maintained for 1h. Then the specimens were naturally cooled down to ambient temperature in the furnace. The properties measured after heat exposures were the compressive strength, splitting tensile strength, water capillary absorption and ultrasonic pulse velocity.It was noticed that, the spalling tendency was increased for specimens of higher strength class C30/37 irrespective of the mixture type (SCC or NVC). Such an explosive behavior was not observed when polypropylene fibers were added in the mixtures; however, in this case the residual mechanical characteristics of concretes were significantly reduced.

The effect of incorporation of red mud on the properties of clay ceramic bodies

Red mud (RM) by-product of Bayer process was added to clay in different proportions to prepare ceramic bodies and the physical properties of the clay ceramic bodies, bulk density, loss on ignition, sintering shrinkage, water absorption and compressive strength were determined. The optimum preparation condition was determined, and the corresponding influence mechanisms were discussed. Due to the high alkalinity and water absorption, RM obviously influenced the properties of clay ceramic bodies, and the optimum parameters were selected as firing temperature of 1050°C, firing time of 2h and RM content of 20%. During sintering some components of the raw materials transformed into other crystals, and the color changes of ceramic bodies mainly depended on hematite and magnetite. The glass formed at high temperature improved spalling resistance of the ceramic bodies.

Surface initiated rolling contact fatigue based on the asperity point load mechanism—A parameter study

The influence of asperity size, friction and residual surface stress on surface initiated rolling contact fatigue damage was investigated using the asperity point load mechanism. A parametric study was performed in two steps, first with a classic one-parameter-at-a-time approach, then as a 2-level full factorial design. The effect on fatigue initiation, damage size and spalling life for both early and developed spalling damage was examined for a gear application. Simplified response surfaces were derived as an engineering design tool for improved spalling resistance. The parametric investigation suggested that among the investigated parameters, reduced asperity height and local asperity friction will have the largest effect on the crack initiation risk. The simulations agreed with the engineering experiences that reduced surface roughness improves rolling contact fatigue resistance and that improved lubrication lengthens spalling lives and decreases fatigue risk. With compressive residual surface stresses the predictions suggested reduced fatigue risk and substantially decreased depth of individual spalls. Finally, predictions of experimentally observed effects of changing asperity size, friction and residual surface stress on spalling further motivates the asperity point load mechanism as the source behind surface initiated rolling contact fatigue.

Effect of aggregate size on spalling of geopolymer and Portland cement concretes subjected to elevated temperatures

This paper presents a study on the effect of aggregate size on spalling of concrete in fire. Three concretes with completely different chemical compositions and strengths were investigated, namely, geopolymer concrete and high strength and normal strength Portland cement concretes. The effect of aggregate size was found to be the same regardless of the type of concrete. The concretes containing 10mm aggregates spalled while the ones with 14mm did not spall. Since this effect is the same in geopolymer and Portland cement concretes, it is independent of binders’ chemical compositions. This paper shows that the degree of spalling has a good correlation to the fracture process zone length, which increases with increasing aggregate size; this in turn reduces the flux of kinetic energy from pore pressure and thermal stress that is released into the fracture front and thereby improves the spalling resistance.

Effects of Silica Fume Addition on the Spalling Phenomena of Reactive Powder Concrete

The explosive spalling of high-strength concrete due to fire is a problem that has garnered increasingly widespread attention, particularly the explosive spalling of reactive powder concrete (RPC). For years, based on the vapor pressure mechanism, the addition of fibers has been demonstrated to be somewhat effective in protecting against spalling. However, relevant experiments indicate that fibers are not effective for dense concrete, which is a challenge for the simple vapor pressure mechanism in providing spalling resistance for RPC. The authors found that silica fume plays an important role in the explosive spalling of RPC. Thus, four classes of RPCs with different ratios of silica fume were prepared, and the spalling phenomena and the inner temperature distribution during heating were investigated. The results show that silica fume content has a prominent effect on the spalling process of RPC.

The Wear Mechanism Comparison between MgO-Based Chrome-Free Brick and MgO-Cr&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Brick in the Lower Part of RH Vacuum Degasser

The damage and improvement mechanism of rebonded MgO-Cr2O3 brick and MgO-ZrO2 brick used in the lower part of RH vacuum degasser were studied. The results show that the main damage of rebonded MgO-Cr2O3 brick is structure spalling because of the penetration of slag. MgO-ZrO2 brick has characteristics of high direct-bonding degree, small air permeability and making the viscosity of penetrated slag increased by means of ZrO2 absorbing CaO in slag to form CaZrO3 or ZrO2 solid solution, which make the degree of slag penetration decrease and improve the structure spalling resistance. MgO-ZrO2 brick has the defect of poor thermal shock resistance in use, the incorporation of MgO-rich spinel into MgO-ZrO2 brick significantly improved both thermal shock resistance and hot modulus of rupture because of the formation of eutectoid structure of grain-refining spinel and zirconia, which also improved structure spalling resistance because air permeability was decreased to 5% of MgO-ZrO2 brick

Deformation behavior and spalling fracture of a heterophase aluminum alloy with ultrafine-grained and coarse-grained structure subjected to a nanosecond relativistic high-current electron beam

The results of a comprehensive experimental–theoretical investigation of the deformation behavior, regular features and mechanism of spalling fracture in an Al–Mg–Li–Zr heterophase aluminum alloy with ultrafineand coarse-grained structure subjected to a nanosecond high-current electron beam with the power density 7·109 W/cm2 are presented. The patterns of formation and propagation of a shock wave are discussed, and so is the behavior of the respective reflected wave, once the former is reflected from the back surface. Common regularities of variation in the thickness of the spalled layer and its plastic deformation degree are observed in the cases of ultrafine- and coarse-grained structure. It is shown that spalling resistance of the Al–Mg–Li–Zr heterophase alloy is controlled by the ultrafine-grained structure formed in the spalling zone under the tensile wave rather than by the initial grain structure.

Geopolymer and Portland cement concretes in simulated fire

High-strength Portland cement concrete has a high risk of spalling in fire. Geopolymer, an environmentally friendly alternative to Portland cement, is purported to possess superior fire-resistant properties. However, the spalling behaviour of geopolymer concrete in fire is unreported. In this paper, geopolymer and Portland cement concretes of strengths from 40 to 100 MPa were exposed to rapid temperature rises, simulating fire exposures. Two simulated fire tests, namely rapid surface temperature rise exposure test and standard curve fire test, were conducted. In both types of test, no spalling was found in geopolymer concretes, whereas the companion Portland cement concrete exhibited spalling. This can be attributed to different pore structures of the two concretes. The sorptivity test found that geopolymer concrete had a significantly higher sorption, therefore more connected pores, than Portland cement concrete when compared at the same strength level. Hence, it is suggested that the water vapour can escape from the geopolymer matrix quicker than in Portland cement concrete, resulting in lower internal pore pressure. The paper concludes that, when compared at the same strength level, the geopolymer concrete possesses higher spalling resistance in a fire than Portland cement concrete due to its increased porosity.