Protected Specimens Research Articles

Effect of Heat Treatment on the Microstructural Heterogeneity and Abrasive Wear Behavior of ASTM A128 Grade C Steel.

Microstructural heterogeneities of an ASTM A128 grade C steel subjected to heat treatments and their effect on abrasive wear behavior were investigated. The heat-treatment process involved different austenization times at 1050 °C and quenching media. To characterize the effects of heat treatment on the material's microstructure and mechanical behavior, two microscopy techniques were used: optical microscopy (OM), and scanning electron microscopy (SEM). The chemical composition of the material was obtained using X-ray fluorescence (XRF) optical emission spectrometry. The variation in carbide composition was evaluated using X-ray Energy Dispersive Spectroscopy (EDS). To characterize the mechanical behavior of the steel, hardness measurements and abrasive wear tests were performed after homogenization annealing and quenching treatments. The results showed that the heat-treated samples developed a heterogeneous microstructure, with the presence of austenitic grains and Martensite around the surface of the samples induced by decarburization in both the protected and unprotected specimens. The specimens with lower decarburization presented less formation of Martensite and precipitated carbides, resulting in lower hardness values and higher abrasion resistance (solution treatment at 1080 °C for 1 h + sand protection + brine quenching).

Efficacy of Fire Protection Techniques on Impact Resistance of Self-Compacting Concrete

The present research investigates the behaviour of sustainable Self-Compacting Concrete (SCC) when subjected to high temperatures, focusing on workability, post-fire impact resistance, and the effects of fire protection coatings. To develop environmentally friendly SCC mixes, Supplementary Cementitious Materials (SCM) such as Fly Ash (FA), Ground Granulated Blast Furnace Slag (GGBFS), and Expanded Perlite Aggregate (EPA) were used. Fifty-six cubes and ninety-six impact SCC specimens were cast and cured for testing. Fire-resistant Cement Perlite Plaster (CPP) coatings were applied to the protected specimens, a passive protection coating rarely studied. SCC (unprotected and protected) specimens, i.e., protected and unprotected samples, were heated following the ISO standard fire curve. An extensive comparative study has been conducted on utilising different SCMs for developing SCC. Workability behaviour, post-fire impact resistance, and the influence of fire protection coatings on sustainable SCC subjected to high temperatures are the significant parameters examined in the present research, including physical observations and failure patterns. The test results noted that after 30 min of exposure, the unprotected specimen exhibited a significant decrease in failure impact energy, ranging from 80% to 90%. Furthermore, as the heating duration increased, there was a gradual rise in the loss of failure impact energy. However, when considering the protected CPP specimens, it was observed that they effectively mitigated the loss of strength when subjected to elevated temperature. Therefore, the findings of this research may have practical implications for the construction industry and contribute to the development of sustainable and fire-resistant SCC materials.

Study on the compression performance of RC columns confined with CTRC based on ICCP technology in chloride environment

In this paper, to study the corrosion resistance and compression performance of RC columns confined by carbon textile-reinforced concrete (CTRC) under impressed current cathodic protection (ICCP) technology in a chloride environment, a total of 30 CTRC-confined square columns were examined through axial compression tests. The effects of the parameters such as different protection potentials of ICCP technology, textile ratios, stirrup ratios, and specimen sizes on the bearing capacity and deformation performance were investigated. The experimental results indicated that the corrosion of the reinforcement in the protected specimens in a chloride environment was significantly reduced under the ICCP technology compared to the control columns. In addition, the maximum reduction in the corrosion level (mass loss degree) of the transverse and longitudinal reinforcement reached 96.43 % and 96.30 %, respectively corresponding to a potential of −0.70 V and −1.00 V. The bearing capacity and deformation performance of the CTRC-confined RC columns were significantly improved by using the ICCP technology. The maximum load and nominal effective deformation of the protected columns were increased by 29.87 % and 62.54 %, respectively, corresponding to the potential of −0.70 V. In addition, the compression performance was also found to have been affected by textile ratios, stirrup ratios, and specimen sizes. Finally, semi-empirical and semi-theoretical analytical models for predicting corrosion level and bearing capacity were established and validated through the experimental data. The proposed models exhibited a good correlation with the experimental data of CTRC-restrained RC columns subjected to axial loads under the protection of ICCP technology.

Small‐scale assessment method for the fire resistance of historic plaster system and timber structures

AbstractThe primary protection against the charring of timber is ensured by protection materials. Today, there are only a limited number of materials given in design codes as fire protection materials for timber. Historic surface finish materials such as plasters have rarely been studied with respect to fire; no design values exist in the current fire part of Eurocode 5. Full‐scale fire testing is costly to assess the fire performance of material combinations, thus this study presents a useful tool that is specifically tailored to evaluate the fire protection ability of materials in small‐scale. A review of conducted tests demonstrate that the cone heater of a cone calorimeter is a dependable device to estimate the charring performance of protected timber specimens as the test results approximate the ones obtained from furnace tests. This work contributes to the assessment of fire resistance performance of various combinations and types of plaster systems found in existing timber buildings that often require an individual approach for an adequate fire risk analysis and design decisions to meet current fire safety regulations with respect to the load‐bearing capacity and compartmentation of building structures. Increased knowledge on the fire protection performance of traditional plasters is believed to facilitate their wider use in timber buildings, primarily to preserve their significance as part of the cultural built heritage.

Effect of elevated temperature on interfacial shear transfer capacity of self-compacting concrete

Interfacial shear stress transfer may occur in structural elements across concrete or between concrete and steel. The fundamental contributing parameters which improve the shear capacities are aggregate grading, compressive strength of concrete, type and area of the interfacial zone, and interfacial reinforcement pattern. During the event of a fire, these parameters are severely affected and mainly depend on the exposure level of the temperature and its duration. In the present investigation, the effect of elevated temperature on the interfacial Shear Transfer Capacity (STC) of Self-Compacting Concrete (SCC) was evaluated using shear (push-off) specimens. SCC was developed using Fly Ash (FA) and Ground Granulated Blast Furnace Slag (GGBFS) as Supplementary Cementitious Material (SCM). The study emphasises the proper understanding of degradation in shear strength of SCC exposed to elevated temperatures. Expanded Perlite Aggregate (EPA) is utilised as a partial replacement for fine aggregate. Also, a thermal protective coating is developed with Cement Perlite Plaster (CPP) for improving the performance of SCC. The European Federation of National Associations Representing for Concrete (EFNARC) guidelines were followed to ensure the workability of the developed SCC mix. Specimens were exposed to 30, 60, 90, and 120 min of heating durations following the International Organization for Standardization 834 (ISO 834) fire rating curve and tested to examine residual compressive strength, mass loss, STC after the natural air cooling process. The SCC specimens with EPA content have exhibited higher residual compressive strength and STC. All the protected SCC specimens coated with the CPP mixture contributed to retaining the original shear capacity by resisting the temperature. An empirical relationship was proposed to predict the residual STC of SCC after exposure to elevated temperature.

Bench-scale fire stability testing – Assessment of protective systems on carbon fibre reinforced polymer composites

Fire resistance testing of components made of carbon fibre reinforced polymers (CFRP) usually demands intermediate-scale or full-scale testing. A bench-scale test is presented as a practicable and efficient method to assess how different fire protective systems improve the structural integrity of CFRPs during fire. The direct flame of a fully developed fire was applied to one side of the CFRP specimen, which was simultaneously loaded with compressive force. Three different approaches (film, non-woven, and coatings) were applied: paper with a thickness in the range of μm consisting of cellulose nanofibre (CNF)/clay nanocomposite, nonwoven mats with thickness in the range of cm and intumescent coatings with a thickness in the range of mm. The uncoated specimen failed after just 17 s. Protection by these systems provides fire stability, as they multiply the time to failure by as much as up to 43 times. The reduced heating rates of the protected specimens demonstrate the reduced heat penetration, indicating the coatings’ excellent heat shielding properties. Bench-scale fire stability testing is shown to be suitable tool to identify, compare and assess different approaches to fire protection.

Experimental Method for Tensile Testing of Unidirectional Carbon Fibre Composites Using Improved Specimen Type and Data Analysis.

This paper presents an experimental method for tensile testing of unidirectional carbon fibre composites. It uses a novel combination of a new specimen geometry, protective layer, and a robust data analysis method. The experiments were designed to test and analyze unprotected (with conventional end-tabs) and protected (with continuous end-tabs) carbon fibre composite specimens with three different specimen geometries (straight-sided, butterfly, and X-butterfly). Initial stiffness and strain to failure were determined from second-order polynomial fitted stress–strain curves. A good agreement between back-calculated and measured stress–strain curves is found, on both composite and fibre level. For unprotected carbon composites, the effect of changing specimen geometry from straight-sided to X-butterfly was an increase in strain to failure from 1.31 to 1.44%. The effect of protection on X-butterfly specimens was an increase in strain to failure from 1.44 to 1.53%. For protected X-butterfly specimens, the combined effect of geometry and protection led to a significant improvement in strain to failure of 17% compared to unprotected straight-sided specimens. The observed increasing trend in the measured strain to failure, by changing specimen geometry and protection, suggests that the actual strain to failure of unidirectional carbon composites is getting closer to be realized.

Influence of ring size on corrosion inhibition potential of environmental sustainable cycloalkyltriphenylphosphonium based ionic liquids: Computational and experimental demonstrations

Background: Corrosion mitigation potential of environmental sustainable cycloalkyltriphenylphosphonium based ionic liquids, namely, cyclopentyltriphenylphosphonium bromide (CPTPB), cyclohexyl triphenylphosphonium Bromide (CHTPB), differing in the size of cycloalkyl rings was demonstrated for mild steel corrosion in 0.5 M H2SO4.Methods: Electrochemical (EIS and PDP), surface (SEM and AFM) and computational modelings (DFT and MDS).Findings: Results suggest that CHTPB containing cyclohexyl ring exhibits superior inhibition potential as compared to the CPTPB containing cyclopentyl ring. CPTPB and CHTPB exhibit highest protection potential of 99.36% and 99.52%, respectively at 10−2 M. Both the inhibitors are mixed type of inhibitors. Potentiostatic polarization (PP) study showed that passivation was observed only at lower concentrations due to a synergistic effect. Adsorption mechanism of CPTPB and CHTPB was best explained using the Langmuir adsorption isotherm. Surface morphologies of protected metallic specimens were greatly enhanced due to the formation of protective film by CPTPB and CHTPB. MDS and DFT based computational analyses were support the experimental outcomes.

SRB-mediated corrosion of marine submerged AISI 1020 steel under impressed current cathodic protection

Metallic corrosion is a recurrent and costly problem to almost every industry; therefore, prevention strategies might be well-defined on a case-by-case basis. Commonly, cathodic protection (CP) is the world’s most widely-adopted technique to guarantee the integrity of buried or submerged structures from corrosion. However, as current potential values are dependent on metal-structure and environmental features, the target shall be well-identified; otherwise, the intended effect will not be reached. In seawater, a protective current potential of −800 mVAg/AgCl is recommended by technical standards, while a more negative potential (−900 mVAg/AgCl) is the suggested criterion for the control of corrosion induced by sulfate-reducing bacteria (SRB), even though without proper scientific support. Thus, this study focused on evaluating the efficiency of different cathodic protection potentials (−800, −900 and, −1000 mVAg/AgCl) on inhibiting SRB-mediated corrosion of AISI 1020 steel. Both unprotected and impressed current cathodically protected steel specimens were exposed to indigenous microorganisms in seawater for 7 days. The Most Probable Number (MPN) enumeration of sessile aerobic heterotrophic bacteria, acid-producing bacteria and, sulfate-reducing bacteria was performed at the beginning and at the end of the assays. Also, the reducing activity of hydrogenase-positive SRB strains was measured. Although the microbial colonization was greater on unprotected steel surfaces than on the cathodically protected ones, biofilm quantification of CP specimens did not show important differences regardless of the potential. However, hydrogenase-positive SRB counts increased with the reduction of CP potential value, promoting an increase in the number and depth of pits on specimens protected at −1000 mVAg/AgCl when compared with those protected at −800 mVAg/AgCl and unprotected ones.

Dynamic plastic behavior of single and nested rings under lateral impact

This paper aims to investigate the dynamic plastic behavior of single and nested circular rings traditionally used as energy absorbers. The response characteristics of these structures are experimentally and numerically determined when they are subjected to high rate lateral impacts. It should be emphasized that a gas gun is employed in order to conduct experimental tests in which a load cell is utilized to measure the force-time response at the distal end. Furthermore, the finite element software LS-Dyna is employed to obtain numerical results in which the Johnson-Cook constitutive equation is used to take into account the strain rate and hardening effects. It is revealed that employed single rings as energy absorbers are absorbing input energies while transmitting small amounts of forces particularly peak loads to protected specimens or occupants. Moreover, it is determined that circular rings having smaller thicknesses and greater inner diameters are much more efficient energy absorbers. However, it is found that single rings have low energy absorption capacity leading to high peak loads for high input energies. It is shown in the presented paper that nested rings can be used as suitablealternatives since they can absorb much more energy and transmit much fewer forces compared to single rings.

Efficiency of Impressed Current Cathodic Protection in Repaired Reinforced Concrete

—Corrosion attack in reinforced concrete and thus contribute to degradation of concrete influenced by aggressive environment, represent a great concern in relation to the durability of reinforced concrete structures. In this respect, an interesting need is required that is patch repair with additional protection known as ICCP method to prolong the serviceability of the concrete structures. However, details inspection is crucial to understand the effect of different repairing materials and chloride content towards application of ICCP. To clarify this issue, non-protected and protected test specimens were prepared, and analyzed up to 175 days of protection. The result reveals that, reference specimen was found as most corroded specimen unable to obtain 100 mV depolarization at 56 days installation compared to repaired ones. However, all specimens show only greater depolarization values beyond 129 days of installation. To clarity further effectiveness of ICCP system to the studied specimens, time-dependence within 24 hours disconnecting CP current has been carried out and depolarization values was recorded every 4 hours interval. In the final analysis, all specimens are satisfying the CP criteria by obtaining depolarization potential ranging 100 to 250 mV at 4 and 24 hours monitoring period. Index Terms— corrosion attacks, reinforced concrete, repaired concrete, repairing materials, impressed current

Carbon nanotube protected composite laminate subjected to lightning strike: Interlaminar film distribution investigation

A kind of interlaminar film with carbon nanotubes inserted into polyether ketone with cardo was used for lightning strike protection of composite laminates. The distribution of the interlaminar film was investigated by experimental and numerical methods. Artificial lightning strike tests were conducted for 12-film carbon nanotube and traditional surface silver coating protected specimens. Then corresponding finite element models (FEMs) were established to analyze the lightning strike effect and validated by the experimental results. Based on the FEMs, the number, distribution and thickness of interlaminar film were investigated in order to obtain equivalent protection effect with the traditional surface silver coating. The results show that only the first two layers were damaged for the surface silver coating protected specimen, while 5 layers were ablated for the 12-film protected specimen. Lightning strike damage area of the laminate protected with 5-film carbon nanotube is almost the same as that of the laminate protected with 12-film carbon nanotube. Compared with traditional surface silver coating protection, one film protection with thickness of 360 μm can make the laminate to obtain equivalent damage depth, 54.8% smaller damage area and 58% less additional weight. And reparability of the laminate is better than that of the laminate protected with 5 interlaminar films.

Specimen representation on the prediction of artificial test lightning plasma, resulting specimen loading and subsequent composite material damage

Preceding work has established that artificial test lightning plasma and composite test specimen damage can be modelled. However, no work has studied the impact of specimen representation in the modelling of the plasma and the resulting impact on specimen composite damage. Herein four distinct specimen designs have been modelled, with a magnetohydrodynamic FE multiphysics model employed to simulate the plasma and a FE thermal-electric modelling approach used to predict composite material damage. For the test arrangements modelled herein it has been found that specimen representation has limited impact on plasma global structure, even with significant change in specimen properties (e.g. from copper to epoxy). However, noteworthy variation in the local specimen surface loading is witnessed with specimen property change (e.g. epoxy to carbon reinforced epoxy), with peak magnitudes for surface pressure, velocity, current density and temperature changing by up to 88%. Such variation in local specimen surface loading does significantly vary the prediction of composite material thermal damage depth (up to 1200%) and surface damage area (up to 1314%). Moreover, this work, for the first time, provides predictions for the thermal damage suffered by both protected and unprotected composite specimens exposed to test standard Waveform B.

Experimental study on insulative properties of intumescent coating exposed to standard and nonstandard furnace curves

SummaryThis paper reports the results of an experimental study on two types of intumescent coating exposed to the ISO834 standard fire and three nonstandard fire curves. The nonstandard fires were all less severe than the standard fire. A total of 72 intumescent coating protected steel specimens were tested. The expanded thickness of intumescent char was measured, and the pore feature was observed. Constant thermal conductivity for each specimen was calculated based on the measured steel plate temperature. Thermogravimetric analysis (TGA) test was carried out, and the results show that more gas is trapped within the coating due to better matching of thermal behaviour between gas evolution and polymer viscosity as the rate of heating increases. The constant effective thermal conductivities for the intumescent coating under the nonstandard fires were 65% (type‐W) and 35% (type‐S) higher than that under the standard fire, which resulted in an overestimation of the coating failure time up to 15 and 11 minutes, respectively. Therefore, it is sometimes insecure to use results from standard fire tests guiding the design of coating thickness for steel elements under nonstandard fire conditions.

Pre and post-fire mechanical properties of structural steel and concrete in steel-concrete composite cellular beams

This paper presents an experimental investigation into possible variations of mechanical properties of structural steel and concrete in composite cellular beams exposed to ISO 834 fire and cooled down phases. Four full-scale fire tests were performed on protected and unprotected beams under assumed service loads. Tensile stress-strain behavior of steel coupons taken from the beams and compressive strengths of concrete cores taken from the reinforced concrete slabs are studied. Material coupon tests for steel are carried out as per TS EN ISO 6892-1. As for the concrete, compression tests were conducted. Coupon test results reveal that, after fire testing, a maximum reduction ratio of 65% in ultimate strain is obtained for the unprotected beam samples. This indicates that the reductions in the mechanical properties of steel in the protected beams are much less when compared to those of the unprotected beams. It is also found that the maximum increase in post-fire strength/pre-fire strength ratios for concrete is 11% for the unprotected beam, while a 20 % decrease is recorded for water based protected cellular beam. For the protected specimens, the RC slabs were exposed to higher temperatures, and the compressive strength of concrete after testing was lower than that of the unprotected beam slabs.

Lightning Damage Testing of Aircraft Composite-Reinforced Panels and Its Metal Protection Structures

In order to investigate the lightning damage behavior of an aircraft carbon fiber/epoxy composite-reinforced panel and its protection structures, four types of panels were selected to carry out a lightning experiment. Panels were without protection, with a full-sprayed aluminum coating, a local-sprayed aluminum coating, and a full-embedded copper mesh filling, respectively. Their surface and internal damage was detected via ultrasonic C-scanning. Results showed delamination damage for the protected and unprotected specimens due to substantial lightning Joule heat, thermal shock, and internal explosion. The aluminum coatings and the copper mesh had good shielding performance against anti-lightning strike damage. The protection method with a full-sprayed aluminum coating is more effective compared with the other two methods. This study is valuable to investigate the protection effectiveness of metal covers when aircraft composite structures are struck by lightning.

Active and passive protection of steel reinforcement in concrete column using carbon fibre reinforced polymer against corrosion

This study aims to investigate the efficiency of active and passive protection of the pre-corroded steel reinforcement in reinforced concrete (RC) columns using an externally bonded carbon fibre reinforced polymer (CFRP) wrap. Active protection is a novel technique used to impede corrosion achieved by employing the CFRP wrap as the anode of the impressed current cathodic protection (ICCP). Passive protection denotes the anti-corrosion behaviour of the CFRP fabric. Nine reinforced concrete columns with different degrees of corrosion (theoretical mass losses of 1%, 3%, and 6%) were prepared and then treated with different protection methods (non-protection, passive protection, and active protection) by exposing them to wet–dry cycles. By measuring the steel potential, linear polarization, and electrochemical impedance spectroscopy (EIS) of all investigated specimens, the efficiency of active protection was found to be closely related to the degree of the pre-corrosion of the protected specimens. Furthermore, the efficiency of active protection decreased with time, which may be attributed to the deterioration of the CFRP anode and CFRP/concrete interface. Passive protection was proven to be effective in every case, however, it can only slow down the corrosion process but cannot stop the elicited corrosion response.

The experimental behavior of CFRP-strengthened reinforced concrete slabs with fire protection systems subjected to standard fire exposure

PurposeThis paper aims to evaluate fire resistance of carbon fiber-reinforced polymer (CFRP)-strengthened concrete slabs in two forms of unprotected and protected against fire.Design/methodology/approachTo achieve the objective, an unstrengthened and two CFRP-strengthened concrete slabs were first subjected to increasing gravity loading until failure. Subsequently, the unstrengthened concrete slab was placed on a furnace and was subjected to a constant service gravity load and then, the temperature of the furnace was increased according to a standard temperature–time curve until the failure of the slab occurred. This slab was strengthened by CFRP with two different amounts and then, in two cases of unprotected and protected against fire, was tested in accordance with the aforementioned method.FindingsThe gravity test results revealed that CFRP strips bonded to concrete slabs increased the load-bearing capacity considerably. So, this method can be suitable for flexural strengthening of concrete slabs. The fire test results showed that because of more load-bearing capacity and subsequently increase in service gravity load, the strengthened concrete slab failed in a short time due to the lack of CFRP resistance against fire. By contrast, the protected specimens resisted the fire in a considerable time. In addition, it was revealed that details of fire protective coating had an important effect on fire resistance duration.Originality/valueIt is notable that in the literature, there is a lack of data on the fire endurance of fiber-reinforced polymer-strengthened concrete slabs alone without any fire protection system. Furthermore, the applicability and effectiveness of a new kind of spray mineral fire protective coatings was evaluated.

Ventilator-Associated Pneumonia in Pediatric Traumatic Brain Injury.

Ventilator-associated pneumonia (VAP) is a common occurrence among intubated pediatric traumatic brain injury (TBI) patients. However, little is known about the epidemiology, risk factors, and microbiology of VAP in pediatric TBI. We reviewed a cohort of 119 pediatric moderate-to-severe TBI patients and identified 42 with VAP by positive protected bronchial brush specimens. Location of intubation, severity of injury, and antibiotic administration within 2 days after injury were not associated with VAP. Most treatments for elevated intracranial pressure were associated with increased risk of VAP; however, in a multi-variable analysis barbiturate coma (hazard ratio [HR], 3.2; 95% confidence interval [CI] 1.4-7.3), neuromuscular blockade (NMBA; HR, 3.4; 95% CI 1.6-7.3), and use of a cooling blanket for euthermia (HR 2.4; 95% CI 1.1-5.5) remained independently associated with VAP. Most VAP (55%) occurred prior to hospital Day 4 and only 7% developed VAP after Day 7. Methicillin-sensitive Staphylococcus aureus (34%), Haemophilus influenzae (22%), and Streptococcus pneumoniae (15%) were the most common organisms, comprising 71% of isolated pathogens (36% of infections were polymicrobial). Patients with VAP had significantly longer intensive care unit and hospital stays, as well as increased risk of chronic care needs after discharge, but not mortality. VAP is a common occurrence in pediatric TBI patients, and early empiric therapy for patients requiring barbiturate infusion, NMBA, or use of a cooling blanket could mitigate morbidity.

Analysis of the Durability of Lightweight Concrete Protected by an Acrylic Layer in an Aggressive Acid Environment

When exposed to adverse conditions the concrete must be protected so as to maintain absorption at acceptable levels. This paper presents the assessment of a lightweight expanded clay concrete protected by an acrylic layer exposed to an aggressive environment. The specimens were prepared with 370kg/m3 of cement and the water-binder ratio of 0.50 corresponds to the value established in NBR 6118 types for concrete subjected to highly aggressive environments. The concrete produced presented specific mass of 1,600kg/m3, dry consistency and compressive strength of 25MPa. Visual inspection shows that the protected specimens of lightweight concrete presented a clear reduction of the loss of cohesion of the grout caused by the attack as well as lower water absorption and mass loss. The acrylic layer assessed as a surface protector presented a good adherence level to the substrate and efficiency since it reduced the penetration of the aggressive agent, thus minimizing degradation and increasing durability of the lightweight expanded clay concrete.