Relative Residual Strength Research Articles

A Machine Learning Approach to Predict Relative Residual Strengths of Recycled Aggregate Concrete after Exposure to High Temperatures

In recent years, there has been a heightened focus among researchers and policymakers on assessing the environmental impact and sustainability of human activities. In this context, the reutilization of construction materials, particularly recycled aggregate concrete, has emerged as an environmentally friendly choice in construction projects, gaining significant traction. This study addresses the critical need to investigate the mechanical properties of recycled aggregate concrete under diverse extreme scenarios. Conducting an extensive literature review, key findings were synthesized on the relative residual strength of recycled aggregate concrete following exposure to high temperatures. Leveraging these insights, innovative hybrid machine learning models were developed, offering practical equations and model trees for predicting the relative residual compressive strength, flexural strength, elasticity modulus, and splitting tensile strength of recycled aggregate concrete post high temperature exposure. Uncertainty analysis was performed on each model to assess the reliability, while sensitivity analysis was performed to find out the significance of each input variable for each predictive model. This paper presents interpretable models achieving high levels of performance, with R2 values of 0.91, 0.94, 0.9, and 0.96 for predicting the relative residual compressive strength, flexural strength, modulus of elasticity, and splitting tensile strength of RCA concrete exposed to high temperatures, respectively. The unique contribution of the paper lies in the provision of easily applicable equations and model trees, enhancing accessibility for practitioners seeking to estimate mechanical properties of recycled aggregate concrete. Notably, our hybrid machine learning models stand out for their user-friendly nature compared with conventional ML algorithms, without compromising on accuracy. This paper not only advances our understanding of sustainable construction practices but also equips industry professionals with efficient tools for practical implementation.

Deformation analysis of buried subsea pipeline under different pressure-reverse​ fault displacement loading paths

The combined action of subsea seismic faults and pressure loads can cause pipelines to reach the limit state. Consequently, various failure modes, such as global buckling and system collapse, can occur. In this study, the deformation of a buried subsea pipeline under different pressure-reverse fault displacement loading paths is investigated using the nonlinear vector form intrinsic finite element (VFIFE). To quantify the damage to the pipeline and identify its failure modes under accidental reverse fault displacement, the loading path ‘fault displacement → internal/external pressure’ was analysed first. The post-earthquake resumption and reconditioning of unpressurised and pressurised pipelines, respectively, are evaluated based on the performance criteria in terms of strain and deformation. The corresponding loading paths are simplified as ‘ambient hydrostatic pressure → fault displacement → operation pressure’ and ‘operation pressure → fault displacement → external over pressure’. Moreover, the residual bearing capacity, weak position, and possible failure behaviour of the pipeline are comprehensively analysed for all subsequent external overpressures. The results show that the loading paths have a significant effect on structural responses, particularly on the elasto-plastic deformation. The two yield bends of a deformed pipeline under fault displacement are dangerous regions. Their inadequate relative residual strength leads to several successive local collapses and determines the occurrence and direction of buckling propagation during the subsequent external overpressure. The previous internal pressure has a significant influence on the residual capacity and failure modes of the pipeline, particularly the strain hardening effects with the influence of large seismic faults. The critical points of the first local collapse have specific characteristics, and the minimum residual resistance to external over pressure occurs when the maximum flattening parameter is 15% under initial fault displacement. The results of this study can guide the development of seismic design methodologies and engineering practice for buried subsea pipelines.

The Effect of Elevated Temperature on Ordinary Portland Cements

A study was directed to analyze the influence of the different types of Ordinary Portland Cements (OPC) on the hardened cement paste exposed to high temperatures. Hardened cement paste specimens with three types of cement and nine water-cement ratios were investigated and heated to 11 heat steps at 28 days of age. Residual compressive strength and relative residual compressive strength were compared to the unheated results. It was shown that the expected range for the relative residual strength of the different types of OPC up to 400 °C is between 90 and 100%. From the local minimum at 150 °C to the maximum at 300 °C. The CEM I 52.5 type of cement shows the least favorable behavior to the increased (over 400 °C) temperature, according to the results of the residual compressive strengths curves and the newly introduced Integrated Temperature Endurance values after the first water-cement ratio (0.3). Nine water-cement ratios were tested with the favorable types of OPC (CEM I 42.5 and CEM I 32.5). At all water-cement ratios, the residual strength tendencies for the two types of cement were parallel. It has been observed that changes in the water-cement ratio have little to no impact on the relative strength curve's shape or the relationship between strength and the water cement ratio. As a result of our experiments applying simply Ordinary Portland Cement, it is obvious that the CEM I 32.5 type of OPC cement significantly outperformed the CEM I 42.5 type in regards of post-heating strength tendencies.

Effects of post-fire curing on the mechanical properties of cement composites containing carbon black nanoparticles and multi-walled carbon nanotubes

Concrete elements exposed to fire can partially recover strength and stiffness if recured in water or in a moist environment. This paper reports a pioneering investigation of the influence of post-fire curing on residual mechanical properties and microstructure of cement mortars containing different concentrations of carbon-black nanoparticles (CBN) or multi-walled carbon nanotubes (MWCNT). A total of 84 specimens were subjected to various maximum exposure temperatures (200, 400, or 600 °C) and post-fire curing (water-recuring for 1 day followed by air-recuring for 27 days). X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectrometry (EDS) were used to investigate the microstructure of different types of specimens. Experimental tests were carried out to determine the compressive strength, static modulus of elasticity, and dynamic modulus of elasticity of rehydrated specimens. Nanofillers enhanced the strength recovery of composites exposed to temperatures up to 400 °C, since they improved rehydration reactions. In this case, the rehydration process provided values of relative residual strength and elastic modulus factors higher than 85%. Composites containing 0.4% MWCNT and 3% CBN presented the best strength and stiffness recovery. Therefore, small contents of carbon nanomaterials provided additional nucleation sites for dehydration products to sediment and being rehydrated. Moreover, water adsorbed by the nanomaterials during the water-recuring process was used later to provide greater rehydration. Composites containing 1.2% MWCNT and 9% CBN presented lower mechanical properties recovery, as high contents of nanomaterials made it harder for water to reach decomposed C-S-H gel, hindering the development of rehydration reactions. After 600 °C, lower relative residual factors were obtained, but always higher than 40%. It happened because nanofillers were not able to provide those rehydration improvements, since their thermal decomposition started at about 500 °C.

Effect of elevated temperature on the mechanical strength of glass mortar

This experimental study aimed to investigate the elevated temperature behavior of glass powder (GP) as a partial replacement of Portland cement. The residual compressive strength is an essential consideration for the sustainability of newly introduced supplementary cementitious material at elevated temperatures. For this study, the powder of waste glass was used to replace portland cement in the proportion of 0%, 10%,20%, and 30%. For fundamental understanding, the compressive strength test was carried out on samples after exposure to high temperature with two different cooling regimes. The experimental result reveals that the mortar mix with cement replaced by 20% GP for both cooling conditions retained more relative residual strength and showed sound behavior compare to the reference sample. The mortar sample with 20% glass powder replacement shows better performance with lower strength loss for both cooling regimes. For air cooling samples, the average strength loss was 27.0% compared to 31.2% of the reference sample. In water cooling samples, the average strength loss was 25.4% compared to the 30.7% reference sample. The two distinct temperature ranges were observed regarding the effect of glass powder replacement on mortar strength under elevated temperature. For temperature above 400 °C average strength loss was 38.62% in the mortar with glass powder and 35.60%in reference sample for water cooling condition. Similarly, for air-cooling samples, the average strength loss was 51.8% compared to 48.90% of the reference sample. Therefore, the lesser strength loss of mortars containing glass powder may be related with their low calcium hydroxide content.

The impact of time on the heat resistance of self-compacting high-performance concrete incorporated with recycled martials

The influence of time on the mechanical behavior of concrete after exposure to elevated temperatures has been studied. Twenty-one self-compacting high-performance concrete mixtures with different incorporation amounts of coarse recycled concrete aggregate (RCA) and three unprocessed waste powder materials have been tested at age of 270 days for residual compressive and flexural strength after exposure to fire. The results have been compared to the results for the same concrete, which have been studied at age of 90 days. A new parameter has been introduced for comparing the responses of concrete to elevated temperatures at different ages; this parameter was the “heat resistance” which expresses the total area under the curve of the relative residual strength (compressive or flexural) after exposing to six temperature degrees (20, 150, 300, 500, 600, and 800 °C). The results showed that the age of concrete has an influence on the response of concrete to elevated temperatures. The heat resistance of compressive strength enhanced with age but the concrete behaved with a tendency different to that at the age of 90 days. The heat resistance of flexural strength has not been affected or slightly decreased but not with more than 10% to that at the age of 90 days. The used waste powder materials were unprocessed waste fly ash, waste cellular concrete powder and waste perlite powder; they proved that using any of them up to 15% as a replacement for cement with 0% or 25% of RCA enhanced the concrete resistance for the fire with time. The main two reasons for changing of residual strength with the time were the changing of water content and the proceeding of hydration of the binder. In general, long ages testing properties of concrete simulate the real behavior of concrete structures accurately.

Effect of curing temperature on the behaviour of UHPFRC at elevated temperatures

Ultra-high performance fibre reinforced concrete is one of the construction materials that is still in need of more research to evaluate its performance under fire, particularly regarding explosive spalling. In this study, the effect of curing temperature on the fire resilience of ultra-high performance fibre reinforced concrete (UHPFRC) has been tested. In particular, the influence of cold (20 °C) and hot (90 °C) water curing temperatures on the performance of UHPFRC exposed to elevated temperatures has been investigated. Beams, cured in cold water and in hot water were tested under the standard ISO 834 heating regime. The test results showed that the beam cured in hot water spalled significantly more than the beam cured in cold water. The study further investigated the influence of curing temperature on the residual strength of UHPFRC (containing both steel and polypropylene fibres). The cube elements were heated at eight selected temperatures between 200 °C and 900 °C. The cold-cured concrete exhibited higher relative residual strength at all temperatures. The results further showed that UHPFRC have high strength retention up to 600 °C. The residual peak strength for both the cold and the hot-cured occurred at 400 °C.

Contribution of acrylic fibre addition and ground granulated blast furnace slag on the properties of lightweight concrete

The experimental investigation concerning the mechanical performance, drying shrinkage and residual strength upon heat exposure of acrylic fibre reinforced lightweight oil palm shell concrete (OPSC) containing ground granulated blast furnace slag (GGBS) is reported. The addition of 0.1% acrylic fibres in OPSC containing 20% GGBS was found to be the most effective in enhancing the tensile strength. The addition of acrylic fibres in OPSC was also found to reduce the 60-day drying shrinkage strains by up to 10% and improve the relative residual strength by up to 23%. Generally, the OPSC containing 20% GGBS had superior performance among the investigated hardened OPSC properties, except for the residual strength upon heat exposure, in which mixes with 70% GGBS achieved lower strength loss.

Study on Residual Splitting Tensile Strength of HFCC after High Temperature

This paper presents the results of the splitting tensile strength of high fly ash content concrete (HFCC) after high temperature and analysis the degraded rules of the residual splitting strength subjected to high temperature and the replacements of cement by fly ash. The specimens were prepared with three different replacements of cement by fly ash 30%, 40% and 50% by mass and were tested after exposure to high temperature 250, 450, 550 and 650°C and room temperature respectively, compared with ordinary Portland cement concrete. The results showed that the splitting tensile strength sensitively decreased with the high temperature increased. Furthermore, the presence of fly ash was effective for improvement of the relative strength. The relative residual splitting strength of fly ash concrete was higher than those of ordinary Portland cement concrete except 30% fly ash replacement. Based on the experiments results, the alternating simulation formula to determine the relationship among relative residual strength, high temperature and fly ash replacement is developed by using regression of results, which provides the theoretical basis for the evaluation and repair of HFCC after high temperature.

Influence of Cooling Methods and Standing Time on Different Aggregate Concrete Strengths after Elevated Temperature

After heated to high temperature, the strength test of concrete cube specimens made by siliceous and calcareous coarse aggregates was carried out. We analyzed the influence of cooling methods and standing time on concrete compressive strength respectively. The test results show that the compressive strength is generally decreased with increase in temperature. The relative residual strength of calcareous aggregate concrete is higher than siliceous aggregate concrete at higher temperature, so siliceous aggregate concrete has more significant fire resistance than calcareous aggregate concrete. Between 200°C and 550°C, the cooling methods have a great influence on concrete strength. The minimum of concrete strength appears at the 28th day after elevated temperature for both calcareous aggregate concrete and siliceous aggregate concrete in air cooling condition, whereas the minimum appears at the first week in water cooling condition. In addition, concrete strength values become steady with the lapse of time after the fire.

Experimental research on the mechanical properties of gypsum breccia with different water content

This paper deals with the influence of water content on the mechanical properties of gypsum breccia with different initial water contents. The experimental research was taken on the GDS (geotechnical digital systems) tri-axial experiment system by strain rate control. The mechanical properties, including stress-strain curves, peak deviator stress, relative residual strength, elastic modulus, Poisson’s ratio, angle of internal friction and cohesion of gypsum breccia, were studied by experiment. The results showed that the water content has obvious influence on the mechanical properties of gypsum breccia. With increasing of water content, the angle of internal friction and cohesion of gypsum breccia decrease linearly. Meanwhile, the stress-strain curves go through from the declining, hump curve to the strain hardening curve. At the same confining pressure, the peak deviator stress and elastic modulus decrease exponentially, while Poisson’s ratio increases linearly with the increasing of the water content. At the same water content, with increasing of the confining pressure, the peak deviator stress, elastic modulus and the peak deviator stress increase trend but Poisson’s ratio decreases at a lower water content. While at a high water contents, the Poisson’s ratio doesn’t change much. It shows that water content plays an important role in the process of changing from the brittleness to plastic for the mechanical properties of gypsum breccia.

Fatigue residual strength of circular laminate graphite–epoxy composite plates damaged by transverse load

The research dealt with the relation between damage and tension–tension fatigue residual strength (FRS) in a quasi-isotropic carbon fibre reinforced epoxy resin laminate. The work was organized in two phases: during the first one, composite laminates were damaged by means of an out-of-plane quasi-static load that was supposed to simulate a low velocity impact; in the second phase, fatigue tests were performed on damaged and undamaged specimens obtained from the original composite laminates. During the quasi-static transverse loading phase, damage progression was monitored by means of acoustic emission (AE) technique. The measurement of the strain energy accumulated in the specimens and of the acoustic energy released by fracture events made it possible to estimate the amount of induced damage and evaluate the quasi-static residual tensile strength of the specimens. A probabilistic failure analysis of the fatigue data, reduced by the relative residual strength values, made it possible to relate the FRS of damaged specimens with the fatigue strength of undamaged ones.

Mechanical behaviors of concrete combined with steel and synthetic macro-fibers

In this paper, hybrid fibers including high elastic modulus steel fiber and low elastic modulus synthetic macro-fiber (HPP) as two elements were used as reinforcement materials in concrete. The flexural toughness, flexural impact and fracture performance of the composites were investigated systematically. Flexural impact strength was analyzed with statistic analyses method; based on ASTM and JSCE method, an improved flexural toughness evaluating method suitable for concrete with synthetic macro-fiber was proposed herein. The experimental results showed that when the total fiber volume fractions (<TEX>$V_f^a$</TEX>) were kept as a constant (<TEX>$V_f^a=1.5%$</TEX>), compared with single type of steel or HPP fibers, hybrid fibers can significantly improve the toughness, flexural impact life and fracture properties of concrete. Relative residual strength RSI', impact ductile index <TEX>${\lambda}$</TEX> and fracture energy <TEX>$G_F$</TEX> of concrete combined with hybrid fibers were respectively 66-80%, 5-12 and 121-137 N/m, which indicated that the synergistic effects (or combined effects) between steel fiber and synthetic macro-fiber were good.

Predicting Residual Strength in Unsaturated Concrete Exposed to Sulfate Attack

Deleterious damage that manifests in cracking and strength loss due to expansion and exfoliation often occurs when hardened concrete is exposed to sulfates. For a degradation-free service life, modeling sulfate attack is as important as considerations for strength and stability in concrete. This paper focuses on modeling the impact of gypsum as a constitutive durability product responsible for strength loss in concrete due to sulfate attack. The model blends the calculation of coupled moisture-sulfate transport processes with quantitative simulation of chemical reactions involving sulfates, moisture, and an incipient portlandite phase in concrete. Account is taken of variations in sulfate and moisture diffusivities to reflect microstructural changes when a portlandite matrix is stoichiometrically transformed to gypsum. Implementation of the model to both water-saturated and unsaturated concretes is numerically achieved according to standard Galerkin procedure in the finite-element sense. Contrary to expectations, simulation results for the case of initially unsaturated specimens before immersion in a sulfate solution are not significantly different from the initially saturated condition. Calculations of global relative residual strength predicated on degradation profiles generated by the model showed good agreement with postsulfate-immersion-test residual strength data.

Effect of Mixture Composition on Relative Strength of Highly Flowable Underwater Concrete

Concrete used for underwater repair is often proportioned to spread readily into place and self-consolidate, and to develop high resistance to segregation and water dilution. A study was conducted to determine the effect of the dosage of antiwashout admixture, water-cementitious materials ratio (w/cm), and binder composition on the relative residual strength of highly flowable underwater concrete. Two types of antiwashout admixtures and 4 binder compositions were used. Results indicate that for a given washout mass loss and slump flow consistency, greater relative residual strength can be secured when the dosage of antiwashout admixture is increased, the w/cm reduced, and a binary binder with 10% silica fume substitution or the ternary binder are employed.