Residual Properties Research Articles

A Review on the Effect of Synthetic Fibres, Including Macro Fibres, on the Thermal Behaviour of Fibre-Reinforced Concrete

The mechanical properties of concrete degrade rapidly when exposed to elevated temperatures. Adding fibres to concrete can enhance its thermal stability and residual mechanical characteristics under high-temperature conditions. Various types of fibres, including steel, synthetic and natural fibres, are available for this purpose. This paper provides a comprehensive review of the impact of synthetic fibres on the performance of fibre-reinforced concrete at high temperatures. It evaluates conventional synthetic fibres, including polypropylene (PP), polyethylene (PE), and polyvinyl alcohol (PVA) fibres, as well as newly emerging macro fibres that improve concrete’s fire resistance properties. The novelty of this review lies in its focus on macro fibres as a promising alternative to conventional synthetic fibres. The findings reveal that PE fibres significantly influence the residual mechanical properties of fibre-reinforced concrete at high temperatures. Although PVA fibres may reduce compressive strength at elevated temperatures, they help reduce micro-cracking and increase flexibility and flexural strength. Finally, this review demonstrates that while conventional synthetic fibres are effective in limiting fire-induced damage, macro fibres offer enhanced benefits, including improved toughness, energy absorption, durability, corrosion resistance, and post-cracking capacity. This study provides valuable insights for developing fibre-reinforced concrete with superior high-temperature performance. Steel fibres offer superior strength but are prone to corrosion and spalling, while PP fibres effectively reduce explosive spalling but provide limited strength improvement. PE fibres enhance flexural performance, and PVA fibres improve tensile strength and shrinkage control, although their performance decreases at high temperatures. Macro fibres stand out for their post-cracking capacity and toughness, offering a lightweight alternative with better overall durability.

Laser-Assisted Surface Modification of TRIP Steels: Chemical and Microstructural Evolution, Residual Stresses, and Micromechanical Properties

AbstractThe use of new lightweight design strategies is implemented in the automotive industry, for applications where high friction forces are present and lubrication systems need to be implemented. Micro-topography modification through laser texturing is an advantageous manufacturing technique that is currently being used by the industry. Combining both ideas, this manuscript aims to analyze the effect of surface modification laser-texturing process on a TRansformation-Induced Plasticity steel. Residual stresses, superficial chemistry, microstructure, and mechanical properties at the submicrometric length scale are investigated. Results show that the intensity and the number of pulses strongly modify the pattern geometry. Also, the pattern distance affects the residual stress state, changing from tensile to compressive stresses for distances higher than 20 µm. Chemical and microstructural changes at the vicinity of the laser may be associated to the fast cooling of the sublimated material around the pattern induced during the laser-assisted surface modification thermal process. Furthermore, the hardness remains stable, and no changes are evident in the bulk material. However, a hardness reduction of around 95 pct in the austenitic value is evident in the pile-up zone around the laser pattern due to (1) the microporosity and defects confined inside the pile-up region and (2) due to the residual chemical composition created during the solidification process, which is rich in iron, chromium, nickel, and manganese and poor in oxygen.

Mechanical properties of discarded shield residue improved by calcium carbide slag and fly ash as subgrade filling.

To utilize discarded shield residue and alleviate the shortage of subgrade filling, industrial wastes such as calcium carbide slag (CCS) and fly ash (FA) were considered to enhance the mechanical properties of the shield residue. A series of laboratory tests, including California Bearing Ratio (CBR) tests, unconfined compressive strength (UCS) tests, moisture content tests, pH tests, water stability tests, and dry-wet cycles tests were performed on discarded shield residue with additive contents. The results show that the UCS and CBR values enhanced significantly with the increase in curing time. However, the moisture content and pH of the stabilized soil exhibited a decreasing trend. The early UCS of CCS-FA stabilized soil is slightly lower than that of QL-FA stabilized soil. After 60 curing days, all stabilized soil exhibited a UCS value exceeding 1.9 MPa. In addition, the CBR values of CCS-FA stabilized soil were more than 8 times higher than those of the original shield residue. Furthermore, the water stability of CCS-FA stabilized soil is slightly better than QL-FA stabilized soil, especially at 7 days and 14 days. As for dry-wet cycles test, after the fifth cycle, the CCS-FA stabilized soil maintained overall integrity. The CCS can effectively replace QL to enhance the mechanical properties of shield residue as subgrade filling.

High temperature performance of recycled fine concrete

The objective of this study is to explore the physical and mechanical behaviour of concretes comprising four different ratios of recycled fine (RF), namely (5%, 10%, 15% and 20%) along with that of a reference concrete (Cref-0%), under three different heating–cooling cycles (200 °C, 400 °C and 600 °C). The thermal properties of concrete during heating and cooling (20 °C – 600 °C – 20 °C) were also investigated. It was determined that the physical properties (mass loss and ethanol porosity) of recycled concrete (RC) with 5% of recycled fine (RC-5%) were similar to those of Cref-0%. At ambient temperatures, the higher the ratio of recycled fines, the lower the residual compressive strength and residual elastic modulus of the recycled concrete. After thermal loading at 600 °C, the residual mechanical properties of all types of concrete were equivalent, regardless of the content recycled fine.

Two-step process to recover metal and mineral residues from municipal solid waste incinerated (MSWI) ashes

The utilization potential of mineral fractions after metal recovery from fly ash and air pollution control residues from a municipal solid waste incineration plant was studied. Chemical leaching using acidic (H2SO4), and alkaline (NaOH) solutions was applied for metal recovery from fly ash and air pollution control residues from a municipal solid waste incineration plant. Subsequently, the feasibility of recycling both untreated and treated samples in cementitious materials was evaluated. This study aims to investigate the influences of chemical leaching on the structures and properties of MSWI residues as well as examine the utilization potential in cementitious materials of mineral residues after leaching, and their environmental risk. The use of acidic and alkaline leachants had good efficiency in critical metal recovery and unvalued/hazardous metal removal: 99 % of As, 72–80 % of Cd, 47–60 % of Zn, Cu, Co or Mn. After leaching, the chemical composition, physical properties, and mineralogical phases of the incinerated residues were substantially modified. The postleaching mineral residues showed potential for use in supplementary cementitious materials with enhanced reactivity and control of hydration kinetics. The compressive strength of cement pastes using 20 % of MSWI residues can obtain 14 MPa after 7 days. Detrimental impacts from potential toxic elements in incinerated residues can be alleviated through chemical leaching.

Machine learning powered predictive modelling of complex residual stress for nuclear fusion reactor design

Fusion In-vessel components, assembled and maintained using laser welding, one of the most promising techniques, exhibit complex distributions of residual stress, microstructures, and material properties. These residual stresses can compromise structural integrity and lifespan of critical components. Although using advanced experimental measurements can evaluate the residual stress for individual case, extending the measurements to massive number of components are costly and time-consuming. Traditional machine learning (ML) models struggle to account for the heterogeneity and anisotropy of these stress distributions. Here, we develop a novel ML framework based on the Eurofer97 steel, the structural material for in-vessel components. The ML framework is trained on high-resolution residual stress data derived from recently-developed evaluation techniques. Combining with microstructures, the model enables prediction of heterogenous and anisotropic residual stress distribution. It successfully predicts the compressive residual stress in fusion zone (∼−200 MPa) balanced by tensile residual stress in heat affected zone (∼300 MPa), aligning closely with experimental results with the R-squared value of 0.989 and the mean square error of 10−4. Unlike experiments that take hours, the ML model provides predictions within seconds. It offers valuable insights into residual stress prediction for various joints, enhancing the reliability and lifetime prediction of in-vessel components.

Impact performance comparison of carbon fiber reinforced polyamide 6 and fast‐curing epoxy composites manufactured by resin transfer molding

AbstractIn the present paper, we manufactured carbon fiber‐reinforced polyamide‐6 composite (CF‐PA6) by resin transfer molding and compared their impact performance with an equivalent automotive grade epoxy‐matrix composite (CF‐Epoxy). Such comparison is pertinent as the new thermoplastic composite will compete with the traditional thermosetting composite, so impact characterization carried out at the same conditions is necessary for evaluating the possibilities of the new material. The energy dissipation capacity of the CF‐PA6 was 27% higher, the maximum impact‐peak load was 5% smaller, and the damage threshold was similar for both composites. Regarding residual post‐impact properties of samples damaged by a 25 J impact energy, CF‐PA6 retained 62% of its stiffness, 84% of its strength and 67% of its energy dissipation capacity. In contrast, CF‐Epoxy retained 46%, 44% and 40% respectively.Highlights Comparison of impact behavior between CF‐PA6 (RTM) and CF‐Epoxy (RTM). The damage thresholds of both composites were similar (~2.5 J). The penetration and perforation thresholds of CF‐PA6 were 48% and 27% higher. Post‐impact residual property: CF‐PA6 retained 60% of its stiffness.

Effects of layer thickness ratio on residual stress, microstructure and mechanical properties of TiB2-TiC/TiB2-TiN laminated ceramics

Effects of layer thickness ratio on residual stress, microstructure and mechanical properties of TiB2-TiC/TiB2-TiN laminated ceramics

Effect of shrinkage-induced initial damage on the frost resistance of concrete in cold regions

The shrinkage-induced initial damage poses a threat to the frost resistance of concrete in cold regions with low relative humidity (RH). However, the progression of freeze–thaw damage in concrete affected by this initial damage, along with the quantitative relationships among RH, freeze–thaw damage, and the number of freeze–thaw cycles (FTCs), remains unexplored. This study employed combination of experimental and numerical simulation approaches to address these challenges. Experimentally, the freeze–thaw damage of concrete cured at low RH (40 ± 5 %) was compared with that cured at standard RH (95 ± 5 %) after varying FTCs. Results indicated that the former experienced more severe freeze–thaw damage, characterized by increased surface peeling, higher mass loss rate, and greater compressive strength attenuation. For the simulation aspect, a numerical model incorporating cohesive elements was firstly proposed to study the evolution of freeze–thaw damage in concrete cured at different RH under FTCs, of which the rationality was confirmed through experimental data. Additionally, the effect of FTCs and curing RH on freeze–thaw damage was investigated, revealing a negative correlation between freeze–thaw damage and curing RH, resulting in opposite evolution trend for residual mechanical properties of concrete. Finally, the freeze–thaw damage prediction model was proposed based on simulation results, and the error between the predicted and actual values was only 2.1 %, which confirmed that this model can be adopted to accurately assess the freeze–thaw damage degree of concrete cured by different RH after different FTCs. In conclusion, this study aims to better understand the freeze–thaw damage evolution of concrete cured under low RH, which provides a feasible scheme for the frost resistant design of concrete construction in cold regions.

A Correlation Relating the Residual Strength Parameters to the Proportions of Clay Fractions and Plasticity Characteristics of Overburden Sediments from the Open-Pit Mine Drmno

One of the prerequisites for the safe exploitation of surface mines is the stability of the working and final slopes of the mine. In order to ensure this, it is necessary to carry out detailed field and laboratory geomechanical tests of the soil and, based on the obtained results, make calculations related to stability analyses. The results obtained in this way are used for dimensioning the slope of exploitation slopes (excavation). Landslides occur when the ultimate shear strength is reached, and therefore, the adequate definition of shear strength parameters is one of the essential prerequisites for successfully solving the stability problem. Unlike earlier tests in Serbia, when the residual shear strength parameters were determined based on the usual conventional methods (direct shear apparatus, triaxial apparatus), this time, in addition to the direct shear apparatus, a ring shear apparatus was also chosen for testing. The paper shows the method of determining the residual shear strength parameters of high plasticity gray clays and siltstones of roof sediments from open pit mine Drmno, using direct and ring shear apparatus. The results show that the residual angle of internal friction for gray clays obtained with the ring shear apparatus is 9.9–10.8°, and for the siltstone, it is 11.8–12.9°, both of which are lower than the values obtained with the direct shear apparatus. In addition, correlations between the residual parameters of soil shear resistance and some physical indicators (plasticity index, clay content) are provided, showing high correlation coefficients. The proposed correlations should be used only when time and financial constraints prevent the execution of actual tests to determine residual shear strength, as concrete experimental procedures provide a much more reliable assessment of the residual strength properties of the soil.

Treating Waste with Waste: Activated Bauxite Residue (ABR) as a Potential Wastewater Treatment.

Bauxite residue (or red mud) is a highly alkaline waste generated during the extraction of alumina. As a result of the substantial accumulation of bauxite residue in tailings facilities, there is a growing interest in exploring the potential for reusing this material for other purposes. The main objective of this study is to evaluate the use of activated bauxite residue (ABR) for remediating oil sands process-affected water (OSPW) and as a supplement to municipal wastewater treatment through bench-scale, proof-of-concept studies. The ABR is produced through a reduction roasting process that alters the physicochemical properties of bauxite residue, resulting in the generation of potentially effective adsorbent media. The treatment performance via chemical and biological activity removals (cytotoxicity, estrogenicity, and mutagenicity) was also assessed. For OSPW, ABR treatment resulted in the effective removal of recalcitrant acid-extractable organics (AEOs), with kinetics following the pseudo-second-order and comparable adsorption capacity to other waste materials (e.g., petroleum coke). ABR also effectively reduced the estrogenicity and mutagenicity of OSPW, albeit cytotoxicity increased at higher dosages, possibly due to some components leaching out of the material (e.g., metals). For municipal wastewater, ABR treatment reduced fecal coliform concentrations (>99%), total phosphorus (up to 98%), total ammonia-nitrogen (63%), estrogenicity (nondetectable), and mutagenicity (nondetectable), especially in the primary effluent. The ultimate end use of ABR is for the recovery of valuable metals (especially iron) and as a construction material, but additional work is needed to optimize the dosage (currently in the g/L range) and maximize the use of ABR as an adsorbent prior to its subsequent uses.

Application of shot peening to improve fatigue properties via enhancement of precipitation response in high-strength Al-Cu-Li alloys

This paper investigates the role of a hybrid treatment considering severe shot peening as a pre-treatment to age-hardening in enhancing the fatigue properties of an advanced high-strength Al-Cu-Li alloy. The alloy was subjected to severe shot peening with a combination of two different heat treatment regimes, aiming for microstructural modification to promote precipitation of heterogeneously nucleating phases. The effects of different treatments based on combined aging and severe shot peening on residual stresses, hardness, microstructural characteristics, and fatigue properties were evaluated and critically discussed. The results have shown that in the case of heat treatment regimes at which the formation of heterogeneously nucleating T1 precipitates occurs, the application of severe shot peening prior to aging results in significant refinement of strengthening particles, enhancing the fatigue properties in the short and medium fatigue lifetimes.

Prediction of compression after impact strength from surface profile of low-velocity impact damaged CFRP laminates using machine learning

Recently, Composite materials have been increasingly used in various actual structures, leading to active research on their damage and residual material properties. Therefore, the residual compressive strength of carbon fiber reinforced plastic subjected to low-velocity impacts has been considered. In particular, we determined the complexity of impact conditions that can occur in practical applications and the difficulty of obtaining internal damage information from experimental specimens. In addition, we applied machine learning to investigate the essential features calculated from surface profile data after the impact tests. This learning revealed that features representing changes in the contour of the specimen surface had high contributions. Therefore, the surface damages, such as fiber breakage and major matrix cracks, also influence the CAI strength.

Post-fire residual mechanical properties of Q460GJ steel under different pre-tensile stresses

Previous studies on the post-fire mechanical properties of steel were conducted with unstressed state, without considering the influence of pre-stress which subjected to structures in reality. In this article, the post-fire residual mechanical properties of Q460GJ steel under different pre-tensile stresses were studied. The stress-strain curve, elastic modulus, yield strength, ultimate strength and fracture elongation of Q460GJ steel after different elevated temperatures heating are analyzed in detail. The experimental results are compared with that of Q460 steel and S460 steel in the existing literatures. At last, the predictive equations of post-fire mechanical properties of Q460GJ steel under different pre-tensile stresses are established. Q460GJ steel still maintains good ductility after elevated temperature heating, which increases the possibility of reuse of Q460GJ steel element after fire. The Q460GJ steel has better post-fire ductility than that of Q460 and S460 steels. The predictive equations for the post-fire residual mechanical properties for Q460GJ steel under different pre-tensile stresses were proposed. The variation coefficients of yield strength for Q460GJ steel under different pre-tensile stresses after 20 min different elevated temperatures heating were within 0.065. The findings should have a great significance to providing theoretical support for design of reusing or restoring steel building after fire.

Damage parameters and crack morphology in high strength concrete BBR9 under dynamic uniaxial compressive loading: An experimental study

In recent years, there has been significant growth in the use of high-strength concrete (HSC) in structures designed to withstand extreme events such as collisions, terrorist attacks, and earthquakes. Continuum damage mechanics has been utilized to develop constitutive models that can capture the damage evolution in concrete materials under such conditions. These models must be validated against experimental data obtained under controlled laboratory conditions. Yet, no experimental dataset currently exists that accurately quantifies the damage evolution and its influence on the residual mechanical properties of HSC. The present study aimed at investigating the damage initiation, progression, and morphology of HSC-Baseline Basic Research Mixture 9 (BBR9) when subjected to dynamic uniaxial compressive loading. A Kolsky compression bar system was implemented to introduce distinct damage states in the HSC-BBR9 specimens. Thereafter, the partially damaged specimens were tested to quantify their residual mechanical properties. Accordingly, stiffness-based and strength-based constitutive damage parameters were adopted to propose an indirect quantification of the damage state based on the deterioration of mechanical properties. In addition, the X-ray micro‐computed tomography (micro-CT) technique was utilized to extract measurements of 3D crack networks (e.g., crack volume and surface area) that provide a direct quantification of the damage state based on microstructural evidence. The results demonstrated that the HSC-BBR9 material can maintain its residual mechanical properties into the post-peak regime. In the initial stages of damage, stiffness and strength deteriorate at a proportional rate; however, as damage accumulates, the rate of stiffness degradation increases. Moreover, correlations between constitutive damage parameters and 3D crack measurements were established.

Integrated Control of Thermal Residual Stress and Mechanical Properties by Adjusting Pulse-Wave Direct Energy Deposition.

Directed energy deposition with laser beam (DED-LB) components experience significant residual stress due to rapid heating and cooling cycles. Excessive residual tensile stress can lead to cracking in the deposited sample, resulting in service failure. This study utilized digital image correlation (DIC) and thermal imaging to observe the in situ temporal evolution of strain and temperature gradients across all layers of a deposited 316 L stainless steel thin wall during DED-LB. Both continuous-wave (CW) and pulsed-wave (PW) laser modes were employed. Additionally, the characteristics of thermal cracks and geometric dislocation density were examined. The results reveal that PW mode generates a lower temperature gradient, which in turn reduces thermal strain. In CW mode, the temperature-stress relationship curve of the additive manufacturing sample enters the "brittleness temperature zone", leading to the formation of numerous hot cracks. In contrast, PW mode samples are almost free of cracks, as the metal avoids crack-sensitive regions during solidification, thereby minimizing hot crack formation. Overall, these factors collectively contribute to reduced residual stress and improved mechanical properties through the adjustment of pulsed-wave laser deposition.

The influence of chloride-sulfate attack history on the residual mechanical properties of concrete after high temperatures

The influence of chloride-sulfate attack history on the residual mechanical properties of concrete after high temperatures

Experimental investigation on the post-fire mechanical properties of YSt-355FR (0.1 % Mo) low-alloyed fire-resistant steel

Fire-resistant steel (YSt-355FR (0.1 % Mo)) has become the most utilized structural steel due to its superior performance at elevated temperatures compared to traditional structural steel at both the material and structural levels. However, its performance after exposure to fire remains questionable. This study investigates the post-fire performance of cold-formed fire-resistant steel at the material level. A total of 132 steel coupons and 84 Charpy test specimens were exposed to temperatures ranging from 100°C to 1000°C. These temperature-exposed steel coupons were subjected to four different cooling conditions: furnace cooling (FC), air cooling (AC), water-jet cooling (WJC), and water cooling (WC). Tensile tests were performed on the cooled steel coupons to obtain post-fire stress-strain curves, from which the residual mechanical properties were determined. Charpy impact tests were also conducted on the cooled steel specimens to obtain impact energies and identify the fracture patterns. Key observations regarding the post-fire behavior of fire-resistant steel in terms of strength, deformability, stiffness, and toughness parameters were made. Both the exposure temperature and the cooling condition significantly influence the post-fire performance of fire-resistant steel. Fire-resistant steel demonstrates superior post-fire behavior compared to traditional structural steel. Constitutive equations were proposed to predict the mechanical properties of fire-resistant steel under various post-fire conditions, and a sound reliability analysis was performed to examine the reliability of the predicted design parameters compared to the test results. The findings presented in this paper are significant as no prior investigation has assessed the post-fire performance of fire-resistant steel; thus, they may encourage the steel construction industry to prefer fire-resistant steel over traditional structural steels and promote the reuse of temperature-exposed fire-resistant steel for sustainable construction.

Thermomechanical properties and microstructure of concrete made with recycled concrete aggregates after exposure to high temperatures

AbstractUsing recycled concrete aggregates (RCA) in concrete has emerged as a promising solution to produce concrete with reduced environmental impact and adequate performance. However, a deeper understanding of the thermal and mechanical behavior of concrete made with RCA is still needed for further application in real structures. The present paper addresses one of the crucial issues for structural concrete: its behavior after exposure to high temperature. Four concrete mixes are studied: a reference concrete made with natural aggregates (NA), two concretes including 40% and 100% of coarse RCA as a direct replacement (DR) for coarse NA, and a concrete made with 100% of coarse RCA relying on a strength‐based replacement (SBR). The SBR concrete mix was designed to achieve the same performance (28 days compressive strength and slump) as the reference concrete. All specimens were exposed to temperatures of 200, 400, and 600°C. After cooling, samples were evaluated for residual mass loss, thermal, and mechanical properties. Microstructural quantitative analyses were conducted over several square millimeters to show that interfaces between the old and new cement pastes, peculiar to concrete made with RCA, do not further promote fracture development. The results show that after exposure to high temperatures, the thermal and mechanical performances of concrete made with RCA are reduced in the same manner and extent as in concrete made with NA. When the RCA‐based concrete is designed to achieve similar performance as concrete with NA at room temperature (SBR), the residual thermomechanical behavior is similar between both concretes.

Evaluating the fire resistance potential of functionally graded ultra-high performance concrete

Relevant standards stipulating the concrete surface temperature less than 380 °C and the defects of UHPC prone to fire spalling both limit the direct application of UHPC in specific tunnel fire prevention occasions. In view of this, a two-layered functionally graded ultra-high performance concrete (FGUHPC) was proposed in this paper, where lightweight aggregate concrete (LWAC) serves as the fire-resistant layer and UHPC functions as the structural load-bearing layer. The results showed that LWAC can control its backfire surface temperature to meet the standard requirements under a thickness of 40 mm, and the residual mechanical properties of UHPC before 400 °C were comparable to those at ambient temperature. The straight shear test was adopted to evaluate the FGUHPC interfacial bond strength. The results showed that the interfacial strength of FGUHPC reaches 3.05 MPa at ambient temperature, which is close to or even slightly higher than that of homogenous LWAC. When FGUHPC was treated at 1200 °C for 2h, FGUHPC can still maintains its integrity with its interfacial strength 120.0 % higher than that of LWAC. Compared to the homogenous UHPC member, FGUHPC composed of 40 mm LWAC and 120 mm UHPC effectively avoided explosive spalling, and maintained the interface temperature at around 200 °C. After static loading failure of the post-fire FGUHPC member, the two layers of concrete still remained bonded without delamination, and the loss in load-bearing capacity was less than 20 %. Finally, the design method of FGUHPC members under elevated temperature was discussed.