Residual Strength Research Articles

Porous concrete modification with silica fume and ground granulated blast furnace slag: Hydraulic and mechanical properties before and after freeze-thaw exposure

This study investigates the effects of incorporating silica fume (SF) and ground granulated blast furnace slag (GBFS), both individually and in hybrid combinations, on various properties of porous concrete (PC) were evaluated under room conditions and after freeze-thaw (F-T) cycles. The hardened density (HD), water permeability coefficient (k), apparent porosity (AP), as well as compressive strength (CS), splitting tensile strength (STS), and flexural strength (FS) at 7, 28, and 120 days. Additionally, the impact of SF and GBFS on the mass loss (ML), residual compressive strength (RCS), residual splitting tensile strength (RSTS), and residual flexural strength (RFS) of PC samples subjected to 30, 60, 120, and 180 freeze-thaw (F-T) cycles was analyzed. The findings revealed that the addition of SF and GBFS decreased the AP and k values of PC samples under room conditions. Furthermore, these materials significantly improved the CS, STS, and FS properties of PC samples, especially at the 28-day and 120-day marks, owing to their enhanced pozzolanic activity over time. SF and GBFS also contributed to higher RCS, RSTS, and RFS values in PC samples after F-T cycles compared to the control samples. This was due to their effective gap-filling properties and the formation of additional calcium-silicate-hydrate (C-S-H) gels within the matrix. Additionally, SF and GBFS led to slightly higher RDME values in the C1-C6 samples than in the control samples following F-T cycles. However, SF and GBFS did not have a significant impact on reducing the ML values of PC samples after F-T cycles.

Hysteretic performance of high-strength steel square hollow section T joints considering fracture behavior

The performance of high-strength steel (HSS) welding joints is crucial for tubular structure design. This paper investigates the hysteretic performance of HSS square hollow section (SHS) T joints considering fracture behaviors. The hysteresis and tensile tests of the HSS SHS T joints and a comparative analysis of failure modes and bearing capacity are conducted. Parameter analysis is conducted based on the validated FE model considering fracture and elastoplastic constitutive relationship with a wide range of parameters covered, including the cross-sectional width ratio and the wall thickness ratio between brace and chord, and the width-thickness ratio of the chord, and the seam weld size of the joint connection. The results show that fracture behavior can affect the failure mode and bearing capacity of the joints, and it cannot be ignored in the hysteresis analysis process. The energy consumption capacity and the ductility coefficients increase when β increases from 0.2 to 1.0, τ increases from 0.3 to 1.0 and 2 γ decreases from 40 to 20. Meanwhile, joints’ failure modes and residual strength vary with the above parameters. It is necessary to use the damage fracture constitutive model of steel in numerical simulation.

Preparation of MgO-MgAl2O4 refractories doped with La2O3 and the wetting permeation behavior by alkaline slag

Alkaline slags play a crucial role in modern smelting processes, underscoring the necessity for researching novel refractories and their interaction mechanisms concerning wetting and infiltration. This study investigates the influence of La2O3 doping on the wettability and infiltration behavior between MgO-MgAl2O4 refractories and alkaline slag, introducing a theoretical evaluation method. The study explored the effects of La2O3 doping on the physical properties, mechanical properties, and thermal shock resistance of the samples, as well as the interface reactions between the samples and slag. Results indicate that La2O3 doping from 0 to 3 wt% enhances sintering performance by promoting the formation of LaAlO3, thereby reducing the apparent porosity from 18.25 % to 15.01 % and increasing the bulk density from 2.85 g·cm−3 to 3.34 g·cm−3. Cold compressive strength improves from 166.24 MPa to 178.42 MPa, while the residual strength retention ratio after thermal shock rises from 86.57 % to 88.65 %. Regarding the interface reaction between slag and samples, CaO and SiO2 react with internal MgO in the samples to form low-melting compounds and high-melting solid solutions. These compounds block pores, weaken slag erosion, and enhance the slag resistance of the samples. As the La2O3 doping amount increases from 0 to 3 wt%, the contact angle between the samples and slag increases, resulting in a greater residual volume of slag and a reduced depth of the slag infiltration layer. The penetration depth of the slag gradually decreases from 102.54 μm to 47.84 μm. This study offers new strategies for optimizing the manufacturing process and selection of refractories.

Enhancing the mechanical and thermal properties of foam concrete by incorporating glass lightweight microspheres

The inferior mechanical strength and thermal resistance of foam concrete limited its application in thermal insulation engineering. This study focused on enhancing the mechanical strength and thermal resistance of foam concrete by incorporating glass lightweight microspheres (GLM) to partially replace foam. The roles of GLM in foam concrete were investigated through physical, mechanical, and thermal properties tests. The improvement mechanism behind the mechanical strength and thermal resistance was further revealed. Results indicated that the addition of GLM enhanced mechanical strength of foam concrete by promoting hydration reaction, optimizing pore structure, and improving GLM-paste interfaces. The mechanical strength of foam concrete with 20 % GLM increased by about 40 %. Moreover, GLM improved the residual compressive strength after exposure to 800°C, with an enhancement of 39.8 %. The inclusion of GLM reduced the risks of crack formation, densified the paste, and strengthened the foam wall due to its hollow structure, pozzolanic reactivity, melting and filling effects, and the phase transformation of additional C-S-H into well-packed wollastonite. Additionally, GLM with closed and isolated pores reduced the drying shrinkage and water absorption rate of foam concrete. The finding suggests that incorporating an appropriate amount of GLM can produce high-strength, low-density, and thermal-resistant foam concrete.

Impact of corrosion of cast iron tubing on residual strength of mine shaft lining

Impact of corrosion of cast iron tubing on residual strength of mine shaft lining

The effect of in situ-synthesized Y2SiO5 on the thermal shock resistance of Y2O3 ceramic materials

Y2O3 ceramics are increasingly recognized for their excellent vacuum stability and high-temperature chemical stability in the field of functional materials research. However, their poor thermal shock resistance renders them susceptible to spalling and damage during use, thus restricting further applications. To address this issue, the low thermal expansion coefficients of Y2SiO5 materials were leveraged. Through an in situ reaction between SiO2 and Y2O3, a Y2SiO5 phase was generated that induced a thermal expansion mismatch with Y2O3, thereby enhancing the thermal shock resistance of the ceramic. Using Y2O3 fine powder as the primary material, silica sol and nano-SiO2 were selected as reactive silicon sources to prepare Y2O3–Y2SiO5 composite ceramics at 1750 °C. The impact of the different silicon sources and Y2SiO5 phase content on the microstructure, mechanical, and thermal properties of the composite ceramics was studied. The results demonstrated that the in situ formation of Y2SiO5 significantly improved the thermal shock resistance of the composite ceramic. Specifically, increasing the SiO2 content led to a gradual rise in the volume fraction of Y2SiO5 formed between Y2O3 grains, thereby increasing the residual flexural strength and enhancing the hardness and elastic modulus. The low thermal expansion coefficient of Y2SiO5 reduced the overall thermal expansion coefficient of the composite material, thereby improving the thermal shock resistance. Moreover, the thermal expansion coefficient mismatch between the Y2O3 and Y2SiO5 phases induced numerous microcracks within the material, providing thermal stress relief within the microcracks and markedly improving the resistance of the ceramic to thermal shock.

Tensile stress-strain models for steel fiber reinforced concrete

In this study, a simplified analytical multi-linear tensile stress-strain model was introduced to predict the flexural tensile behaviour of steel fiber reinforced concrete (SFRC). Two different tensile stress-strain models namely End Tapered Four Linear Model (ETFLM) and Linear two Step Model (LTSM) were initially selected to study the feasibility. The selected model predictions were validated using experimental results from three-point bending test of SFRC notch beam. However, ETFLM showed better force-deformation behaviour compared to the LTSM. Thereafter, ETFLM was further simplified by incorporating the concrete residual strength characteristics. Finally, a correlation to estimate the residual strength was developed using the steel fiber properties such as strength, geometric characteristics and dosage which makes the proposed simplified model more user friendly.

Analysis of Residual Post-Impact Compressive Strength of Composite Laminates Under Hygrothermal Conditions

Analysis of Residual Post-Impact Compressive Strength of Composite Laminates Under Hygrothermal Conditions

Justification for the use of modified concrete for foundations of overpass supports

Introduction. The article discusses the possibilities and prospects of using modified concrete for the foundations of overpass supports. The aim is to study the effect of various additives on the sulfate resistance of the foundations of bridge supports and overpasses. Materials and methods. To achieve this goal, tests of reinforced concrete samples were carried out with the introduction of various additives into the concrete mixture. As part of the study, a MasterLife® WP 3760 modifying additive was selected. Using this additive, experiments were conducted with an accelerated assessment of the effect on the sulfate resistance of concrete based on general-purpose Portland cement. In accelerated tests, the sulfate resistance of concretes with the studied additive was performed in comparison with concretes of the same composition prepared on sulfate-resistant and general-purpose Portland cement without additional additives. The water-cement ratio in all tested formulations remained constant. Results. Samples made of general construction cement with the addition of MasterLife® WP 3760 after performing the specified test cycles in a sulfate medium showed a decrease in compressive strength by 3 % from their initial values. The residual strength of concrete samples with MasterLife® WP 3760 additive was 97 %, which exceeds the resistance of concrete to sulfate-resistant cement, the remaining strength of which is 94 %. The MasterLife® WP 3760 additive is a substance that significantly reduces the permeability of concrete due to "blockage" by particles of the substance or neoplasms of pores and capillaries of concrete, these substances due to physical and chemical processes lead to homologation, a decrease in the permeability of concrete, and, as a result, an increase in frost resistance and corrosion resistance. Conclusion. As a result of the action of the MasterLife® WP 3760 additive, the corrosion resistance of concretes and mortars increases, including resistance to sulfate aggression, by reducing water permeability. Thus, it becomes possible to eliminate cracks in concrete with an opening width of up to 0.4 mm and extend the durability of concrete.

Magnesium sulphate resistance of fly ash one-part geopolymers: Influence of solid alkali activators on physical, mechanical and chemical performance

The commitment to promoting circular economy and durable construction materials has led to the advocacy for one-part geopolymer (OPG), as an eco-friendly substitute for traditional ordinary Portland cement (OPC). Solid alkali activator is the fundamental component of OPG and significantly influences the sulphate resistance. To identify the types of solid alkali activators best suited for the development of sulphate-resistant OPGs, OPGs activated with Na2SiO3 (M-OPG), Na2SiO3+Na2CO3 (MC-OPG), Na2SiO3+NaOH (MH-OPG) and Na2SiO3+NaAlO2 (MA-OPG) were exposed to 5 % and 10 % of MgSO4 solutions for 28 days. The fine pore structures of MH-OPG and MC-OPG mitigated deterioration from the more concentrated MgSO4 solution, resulting in higher residual compressive strengths after exposure to the 10 % MgSO4 compared to the 5 %. Exposure to the 5 % MgSO4 solution resulted in strength deterioration for M-OPG, MH-OPG and MC-OPG due to the discontinuity of the aluminosilicate structure, as evidenced by the diminished Q4(3Al) sites. Conversely, the MA-OPG exhibited a 24.1 % increase in compressive strength, accompanied by the emergence of sodium magnesium aluminium silicate hydrate ((N,M)-A-S-H) gel. Hence, Na2SiO3+NaAlO2 should be acknowledged as the primary candidate for solid alkali activators in the development of sulphate-resistant OPGs.

Residual and damage properties of recycled brick powder-UHPFRC after high temperature

This research explores the impact of temperature, Recycled Brick Powder (RBP) replacement rates, and cooling methods on the mechanical characteristics of Ultra-high-performance fibre reinforced concrete (UHPFRC). Additionally, the material morphology and pore structure at elevated temperatures are thoroughly examined through Scanning Electron Microscope (SEM), X-ray diffraction (XRD), and mercury intrusion (MIP) tests. The findings reveal a pattern in the behavior of residual compressive strength, splitting tensile strength, and residual fracture energy as the target temperature increases. Initially, these properties increase and then decrease. Specifically, a threshold temperature of 400 °C is identified for compressive strength. For splitting tensile strength, threshold temperatures under natural cooling and water cooling are 400 °C and 200 °C, respectively. The threshold temperatures for residual fracture energy at substitution rates of 30%, 0%, and 50% with RBP are determined to be 400 °C, 200 °C, and 200 °C, respectively. when the RBP content is 30%, UHPFRC shows superior mechanical performance during the entire heating process. The performance under water cooling is weaker than that under natural cooling. Additionally, this study also proposed the evaluation and calculation models of residual compressive strength, residual splitting tensile strength and residual fracture energy considering the influence of simulated fire temperature.

A novel stacking ensemble learner for predicting residual strength of corroded pipelines

Accurately assessing the residual strength of corroded oil and gas pipelines is crucial for ensuring their safe and stable operation. Machine learning techniques have shown promise in addressing this challenge due to their ability to handle complex, non-linear relationships in data. Unlike previous studies that primarily focused on enhancing prediction accuracy through the optimization of single models, this work shifts the emphasis to a different approach: stacking ensemble learning. This study applies a stacking model composed of seven base learners and three meta-learners to predict the residual strength of pipelines using a dataset of 453 instances. Automated hyperparameter tuning libraries are utilized to search for optimal hyperparameters. By evaluating various combinations of base learners and meta-learners, the optimal stacking configuration was determined. The results demonstrate that the stacking model, using k-nearest neighbors as the meta-learner alongside seven base learners, delivers the best predictive performance, with a coefficient of determination of 0.959. Compared to individual models, the stacking model also significantly improves generalization performance. However, the stacking model’s effectiveness on low-strength pipelines is limited due to the small sample size. Furthermore, incorporating original features into the second-layer model did not significantly enhance performance, likely because the first-layer model had already extracted most of the critical features. Given the marginal contribution of model optimization to prediction accuracy, this work offers a novel perspective for improving model performance. The findings have important practical implications for the integrity assessment of corroded pipelines.

One-part alkali activated binder activated by sodium metasilicate and ternary-factored sustainability of structural block

This work was designed to develop an one-part alkali-activated binder (AAB) which has obvious advantages over two-part for industrial manufacturing. In experimentation, ground granulated blast furnace slag (GGBS) was activated by anhydrous sodium metasilicate (SMS) by varying the content from (8 to 16 %). The physico-mechanical performance was evaluated at different ages, and the specimen selected exhibited higher strength than ordinary Portland cement (OPC). Then, the durability of developed AAB and OPC was evaluated by obtaining residual strength under sulphate and acidic environment exposure for up to 56 days. It was concluded that 12 % SMS resulted in 44.7 and 56.0 MPa at 7 and 28 days, respectively. The proposed binder is compared with a geopolymer-based binder, and several advantages are reported over counterparts. Under sulfate exposure of 56 days, about 28 % reduction in residual strength was observed for AAB, and it was only 8.3 % for OPC. However, comparable strength at all ages was observed for both binders under acidic exposure. A low-strength structural block was developed using a low dosage of SMS (8 − 10 %) and 50 % sand. The w/AAB ratio was reduced from 0.30 to 0.15, and a static pressure of 20 MPa was employed on a resh matrix. The block with low-SMS (8 %) fulfills the structural requirement defined by ACI and ASTM for concrete and fired clay brick, respectively. Furthermore, it was compared with a distinguished database of geopolymer-based structural blocks regarding strength, CO2 emissions, and cost. Consequently, the GGBS based AAB structural blocks disclose the least CO2 emissions and the lowest cost as well as the adequate strength.

Mechanical behavior of unsaturated soils from suction controlled ring shear tests

The shear strength behavior associated with a large shear deformation of both the fine- and coarse-grained unsaturated soils is important in interpreting and forecasting the initiation and movement of landslides. For this reason, a suction-controlled ring shear apparatus was designed by introducing modifications to the conventional Bromhead ring apparatus extending the axis translation technique. A series of suction-controlled ring shear tests were performed on fine- and coarse-grained unsaturated soil specimens subjecting to large shear deformation. The experimental results are presented and interpreted for highlighting: (i) the shear stress/void ratio-shear displacement relationships; (ii) the envelopes of the residual shear strength; (iii) the void ratio, water ratio and degree of saturation of the fine-grained soil specimens sheared to the residual state under different net normal stresses and matric suctions. These results provide valuable information toward understanding and interpreting the behaviors of landslides in unsaturated soils that experience the first failure and the reactivation along a pre-sheared slip surface.

Comparison of post-impact residual strength ratio between hybrid filament-wound cylinder and hybrid plate specimen

The filament-wound (FW) cylinders possess numerous benefits as a high-pressure storage device but are susceptible to impact loads. The presence of post-impact residual strength in an operating FW cylinder has the potential to accelerate the onset of failure. Ensuring the structural integrity and safety of the equipment requires thorough impact testing, which can be expensive and time-consuming, resulting in limited use. This article presents an innovative and cost-effective approach for conducting low-velocity impact testing on a hybrid Al/CFRP filament-wound cylinder by utilizing a simple hybrid Al/CFRP plate specimen. The main focus is to conduct low-velocity impact testing on both types of specimens, followed by post-damage testing that includes tensile tests on the hybrid plate specimen and burst tests on the FW cylinder. The results of laboratory experiments were compared to explicit and implicit numerical models conducted in a broad spectrum of impact energy range and found to be consistent. Using a parameter known as the post-impact residual strength ratio, it is possible to determine the expected impact loading conditions on the hybrid plate specimen that are equivalent to those experienced by the FW-cylinder. This low-cost impact testing method offers a practical and feasible solution to ensure the dependability and safety of FW cylinders throughout their operational lifespan.

Effectiveness of TRC jackets for the strengthening of concrete columns after elevated temperatures: Experimental and analytical investigation

Textile reinforced concrete (TRC) materials with high strength and excellent heat resistance might considerably enhance the performance of structures under thermal conditions. This study examined thirty concrete columns, each reinforced with varying TRC configurations, and subjected them to different high-temperature scenarios. Axial compression experiments were subsequently carried out to assess the impact of TRC on concrete's performance at elevated temperatures. Key variables in these tests included different textile layers (0–4 layers), and a temperature range extending from room temperature to 800 °C. The application of TRC was found to facilitate more gradual failure progress during compression tests. In contrast to the unconfined specimens, whose stress-strain curves exhibited a parabolic pattern, those reinforced with TRC displayed a hardening segment at temperatures up to 400 °C. The presence of TRC jackets significantly improved the compressive strength, the ultimate axial strain, and the energy dissipation, both at room temperature and after high-temperature treatments. Furthermore, this paper proposed an innovative model for estimating the residual strength of TRC-confined cylinders after being exposed to various temperatures. This model accounted for the impact of high temperature on the residual bearing capacity of unconfined cylinders, the modulus of elasticity for fibers, and the confinement effectiveness coefficient.

Understanding the positive effects of silica fume on the high-temperature resistance and water resistance of magnesium oxysulfate cement

This study aims to improve the high-temperature resistance and water resistance of magnesium oxysulfate cement (MOSC) through introducing silica fume (SF). The residual strength of MOSC after exposure to high temperatures of 200 °C, 400 °C, 600 °C and 800 °C was tested. The softening coefficient of MOSC after immersion in water for 28 days was used to evaluate the water resistance. The results revealed that SF enhanced the high-temperature resistance of MOSC at temperatures exceeding 200 °C. For SF-MOSC system, prolonged exposure to high temperature of 400 °C could further promote the transformation of partial MgO to M-S-H gel. This phenomenon extremely increased the residual compressive strength of SF-MOSC. Although the residual strength of MOSC and SF-MOSC decreased sharply at 600 °C, the SF-MOSC still displayed a better high-temperature resistance performance. At 800 °C, the MgO in SF-MOSC could have a solid-solid reaction with silicon source to generate forsterite with high melting point. Additionally, SF exhibited favorable filling effects in MOSC and could restrict the conversion of MgO to Mg(OH)2, which also promoted the crystallization of 5Mg(OH)2·MgSO4·7H2O (5·1·7 phase). The decreased Mg(OH)2 after immersion in water and further generation of partial 5·1·7 phase contributed to the enhancement of MOSC’s water resistance in this study.

Research on improving the flexural performance of alkali-activated geopolymer cemented coal gangue through layered addition of fibers

The brittle characteristics of geopolymers during failure seriously hinder their practical engineering applications. To improve the toughness of low-energy alkali-activated geopolymer cementing coal gangue (AGCCG), the flexural performance of alkali-activated geopolymer cementing coal gangue (AGCCG) was enhanced by layering polypropylene fibers. Based on DIC digital speckle technology, the four-point flexure test of AGCCG was carried out, and the strength formation mechanism of the material was analyzed in depth by combining SEM-EDS and XRD. 3D visualization and analysis of the inside of the specimen with the help of CT scanning technology. The internal crack evolution law of the sample was illustrated by PFC numerical simulation. The results showed that the crack formation threshold, peak flexural strength and residual flexural strength of the specimens reached a local maximum at 3 % NaOH doping. With the increase of NaOH dosage, the cementitious product becomes more and more dense and homogeneous, and the area of void defects in the hydration product within the field of view becomes smaller and smaller. The peak bending strength of specimen B4-#4 is 79.43 % of that of specimen B5-#1–4, in which the cost of specimen B5-#1–4 is four times of that of specimen B4-#4, and the way of fiber assignment in specimen B4-#4 is more reasonable when considered together. The layered addition of fibers has a directional strengthening effect on the mechanical properties of geopolymer, and the overall addition of fibers can improve the overall strength and toughness of geopolymer. The numerical simulation results basically coincide with the macroscopic test results, and are consistent with the progressive damage law of the specimens obtained from the numerical scattering test. The results of the study can provide a theoretical basis for improving the bearing capacity of geopolymer and optimizing its structural performance. As well as reducing the impact of solid waste on the environment and improving the efficiency of resource use.

From Mg(OH)2 to lightweight closed-pore MgO refractory aggregates: The role of NiO additive

MgO refractory aggregates with high closed porosity were prepared using light-burned MgO and Mg(OH)2 with adding NiO additive. The evolutions of microstructure and pores and their effects on the properties were investigated. The introduction of NiO effectively enhanced growth of MgO grains and transformation of large open pores into small closed ones, attributing to the lattice distortion caused by MgxNi1-xO solid solution formation. Due to the occurrence of more closed pores and lattice distortion, thermal insulation performance was improved significantly. Moreover, the formed circular closed pores and MgxNi1-xO could absorb thermal stress, lower thermal expansion coefficient and induce crack deflection, thus effectively enhancing thermal shock resistance. The specimen with 4.0 wt% NiO showed the best performance, with a median pore diameter of 5.69 μm, closed/apparent porosity of 9.4 %/3.6 %, thermal conductivity of 9.9 W/(m·K) (500 °C), flexural strength of 68.5 MPa, and residual flexural strength of 10.8 MPa after thermal shock.

Investigating the effect of Nylon 6.6 electrospun nanofiber mats and punch—Die clearance on the damaged area and residual strength of punched glass/epoxy composite laminates

Investigating the effect of Nylon 6.6 electrospun nanofiber mats and punch—Die clearance on the damaged area and residual strength of punched glass/epoxy composite laminates