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This article uses the interventionist theory of causation, a counterfactual theory taken from philosophy of science, to strengthen causal analysis in process tracing research. Causal claims from process tracing are re-expressed in terms of so-called hypothetical interventions, and concrete evidential tests are proposed which are shown to corroborate process tracing claims. In particular, three steps are prescribed for an interventionist investigation, and each step in turn is shown to make the causal analysis more robust, amongst others by disambiguating causal claims and clarifying or strengthening the existing methodological advice on counterfactual analysis. The article's claims are then illustrated using a concrete example, Haggard and Kaufman's analysis of the Argentinian transition to democracy. It is shown that interventionism could have strengthened the authors' conclusions. The article concludes with a short Bayesian analysis of its key methodological proposals. [ABSTRACT FROM AUTHOR]

Hospital functionality relies not only on the building's structural robustness but also on the seismic performance of its Nonstructural elements, Systems, and Contents (NSC). The objective of this study is to characterize the earthquake‐induced damage to the medical equipment deployed in the full‐scale, five‐story concrete building tested at the University of California, San Diego (UCSD) in 2012 when subjected to Design (DE) and Maximum Considered Earthquake (MCE) levels of demand with Fixed‐to‐the‐Base (FB) support condition. The experimental equipment displacement responses are extracted using the Camera Projection Technique (CPT). Then, sophisticated rolling and sliding models, including instantaneous motion tracking and impact detection are developed to reproduce the equipment behavior obtained from CPT. It was found that CPT was capable of extracting the observed responses and identifying impacts despite the severity of the shaking as long as no significant uplift of the equipment occurred. In addition, both numerical models were capable of reproducing the equipment's displacement trajectories, rotations about the vertical axis (yaw), and impacts as long as no interlocking of the equipment's parts occurred. Moreover, a case study of a partially equipped Emergency Room (ER) was set up to demonstrate that even for low‐intensity motions, the damage to equipment may be significant. Finally, the impact acceleration (a⃗imp$\vec{a}_{imp}$) is proposed as a proxy indicator of damage to medical equipment; however, more functionality tests accompanied by detailed pre‐ and post‐inspections are needed to define robust damage limit states and performance objectives for medical equipment. [ABSTRACT FROM AUTHOR]

The article discusses the test results concerning the compressive strength, water absorption, and frost resistance of concretes produced with three types of cement: CEM I, CEM II/B-M (S-V), and CEM III/A, evaluated after different curing periods (28, 56, and 90 days). Additionally, to assess the effects of the minimum 4% air entrainment recommended by the EN 206 standard, concrete mixes with the same composition but containing an air-entraining admixture used consistently at 0.15% of the cement mass, were prepared. To achieve a more detailed characterization of the concretes, tests on the concrete mixes were also performed, and the physical properties of the concretes, including water absorption, density, and total porosity, were measured. The paper also presents significant results on the pore distribution in the air-entrained concretes, confirming the achievement of very good basic airentrainment parameters in all concretes. Based on the test results, it was found that both the type of cement and the introduction of an air-entraining admixture significantly influence not only the frost resistance of the concretes but also their compressive strength depending on the curing time of the specimens. This is particularly evident in the low-clinker cements CEM II and CEM III. It was observed that in the case of concretes with these cements, it is possible to attain nearly no reduction in compressive strength after undergoing 150 cycles of freezing and thawing following a 90-day curing period. [ABSTRACT FROM AUTHOR]

In this investigation, the bond performance between CFRP and concrete in Near Surface Mounted (NSM) strengthening system using cementitious-based adhesive (CBA) was evaluated at different exposure temperatures. Two types of CBA were used (CBA-A and CBA-B) with and without magnetic water (MCBA-A and MCBA-B). Magnetic device with magnetic strength of 9000 Gauss was used to magnetise the water for 15 mins with a flow rate of 0.1 m3/hr. The bond efficiency was evaluated by performing single-lap shear tests for CFRP laminate embedded in concrete prisms as a near surface-mounted strengthening system. The bond between CFRP and concrete was tested under ambient and high temperatures. The heating regime involves the exposure of NSM CFRP/concrete samples to constant temperature (200°C) for 2 hrs, then the load was applied until failure. In comparison with control samples, an improvement of 40% in the load failure was achieved for specimens strengthened with CFRP using magnetised water in CBA. Within the MCBA samples, higher failure load was conducted for MCBA-B samples when compared with samples of MCBA-A since the latter contain primer in its compositions in which its properties deteriorate by high temperature. All tested samples showed similar failure pattern, which is slippage of CFRP. [ABSTRACT FROM AUTHOR]

This study aimed to utilize the hydration characteristics of cement through wet grinding techniques to efficiently and conveniently prepare a stable C-S-H seed suspension, providing key parameters and a scientific basis for their large-scale production, which ensures the stability of the C-S-H suspension during production, transportation, and application. This preparation aimed to mitigate the adverse effects of high-volume silica fume on the early mechanical properties of high-performance cement concrete. The properties of C-S-H seed were characterized in detail by SEM, XRD, and TD. In the concrete performance test, silica fume was used to replace part of the cement, and different contents of C-S-H seed were added to test its effect on the compressive strength of concrete, with XRD and SEM used to analyze the performance differences. The results show that the particle size and hydration degree of cement no longer developed after 90 min of wet grinding. Polycarboxylate ether (PCE) superplasticizer can increase the fluidity of the crystal C-S-H seed suspension when the content exceeds 1.5%. When the content of PCE exceeded 2%, the C-S-H seed suspension precipitated. Adding 5% C-S-H seed can increase the compressive strength of cement concrete by 10% under the condition of reducing the amount of cement and increasing the amount of silica fume. And Ca(OH)2 (CH) was produced by cement hydration consumed by silica fumes to generate C-S-H gel, by which the concrete became denser with more strength. However, when the amount of C-S-H seed exceeded 7%, the compressive strength of the concrete decreased. [ABSTRACT FROM AUTHOR]

Ultrasonic non-destructive evaluation of concrete submerged in water is a complex phenomenon that has important implications for the durability and safety of marine structures such as bridges, piers and offshore platforms. The scattering of ultrasonic waves inside concrete materials with aggregate size comparable to the ultrasound wavelength often limits the interpretation of inspection results. To enhance the understanding of ultrasonic wave propagation inside the underwater concrete, numerical simulations using the finite element method (FEM) with the Transient Acoustics-Piezoelectric Interaction application mode of Multiphysics software package have been developed. This study focuses on developing a 2D numerical model to reproduce and illustrate the propagation of ultrasound in seven types of underwater concrete test blocks with various types of inclusions and voids embedded inside it. The B-Scan 2D images of the concrete test blocks were acquired using the simulated data and compared with experimental results acquired using an in-house developed four-channel ultrasonic imaging system. Both simulation and experimental results showed a good resemblance, indicating that B-Scan imaging can be applied to identify and characterise various types of defects and inclusions in underwater concrete structures, providing better assessment of the material than conventional ultrasonic pulse velocity (UPV) method. [ABSTRACT FROM AUTHOR]

This paper analyses the vulnerability of concrete bridges to fire through a comprehensive review and proposes strategies to overcome the fire hazard. As part of mitigation strategies, the application of advanced analysis is illustrated through developing a non-linear transient finite-element model for fire resistance evaluation of prestressed concrete bridge girders. The numerical model is validated using results from fire tests on concrete beams. The model is applied to investigate the effect of girder shape (rectangular and I-shaped sections) and strength of concrete (normal- and high-strength concretes) on the fire resistance of typical concrete bridge girders. Results from the analysis clearly show that fire resistance of high-strength concrete (HSC) girders is lower than that of normal-strength concrete (NSC) girders, which is attributed to its faster degradation of strength and stiffness with temperature. On the other hand, I-shaped girders present lower fire resistance than similar girders of rectangular cross-section due to rapid degradation of its shear capacity. This is mainly the result of slender web widths in I-shaped girders, which results in faster progression of temperatures in the web, leading to early failure under the shear limit state. This problem can be overcome by developing relevant fire mitigation strategies, such as provision of external thermal insulation on girders of critical bridges. [ABSTRACT FROM AUTHOR]

This paper explores the performances of a finite element simulation including four concrete models applied to a full-scale reinforced concrete beam subjected to blast loading. Field test data has been used to compare model results for each case. The numerical modelling has been, carried out using the suitable code LS-DYNA. This code integrates blast load routine (CONWEP) for the explosive description and four different material models for the concrete including: Karagozian & Case Concrete, Winfrith, Continuous Surface Cap Model and RiedeleHiermaiereThoma models, with concrete meshing based on 10, 15, and 20 mm. Six full-scale beams were tested: four of them used for the initial calibration of the numerical model and two more tests at lower scaled distances. For calibration, field data obtained employing pressure and accelerometers transducers were compared with the results derived from the numerical simulation. Damage surfaces and the shape of rupture in the beams have been used as references for comparison. Influence of the meshing on accelerations has been put in evidence and for some models the shape and size of the damage in the beams produced maximum differences around 15%. In all cases, the variations between material and mesh models are shown and discussed. [ABSTRACT FROM AUTHOR]

Copyright of Environmental & Social Management Journal / Revista de Gestão Social e Ambiental is the property of Environmental & Social Management Journal and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to study the shear mechanical properties of rock joint under different unloading stress paths, the RDS-200 rock joint shear test system was used to carry out direct shear tests on concrete joint specimens with five different morphologies under the CNL path and different unloading stress paths. The unloading stress paths include unloading normal load and maintaining constant shear load (UNLCSL), unloading normal load and unloading shear load (UNLUSL), unloading normal load and increasing shear load (UNLISL). The results show that the peak shear strength, cohesion, internal friction angle, pre-peak shear stiffness and residual shear strength of concrete joints under CNL path increases with the increasing JRC and normal stress. Under the UNLCSL path, under the same initial shear stress τ1, instability normal stress σi decreases with the increasing JRC, and normal stress unloading amount Δσn increases with the increasing JRC. Under the same JRC, σi increases with the increase of τ1, and Δσn decreases with the increasing τ1. Under the same JRC and σi, τi is significantly smaller under the UNLCSL path than the CNL path. Under the same JRC, the cohesion under the UNLCSL path is less than the CNL path, and the internal friction angle is higher than that the CNL path. Under the same JRC and σi, τi is the largest under the path of CNL and UNLISL, followed by the UNLCSL path, and τi under the UNLUSL path is the smallest. Compared with the CNL path, the variation range of the specimen internal friction angle is within 3% while the average decrease percentage of the specimen cohesion reaches 37.6% under the UNLCSL path, UNLISL, and UNLUSL. Therefore, it can be inferred that the decrease in cohesion caused by normal unloading is the main reason for the decrease in joint instability shear strength. After introducing the correction coefficient k of cohesion to modify the Mohr-Coulomb criterion, the maximum average relative error after correction is only 3.5%, which is significantly improved compared with the maximum average relative error of 56.9% before correction. The research conclusions can provide some reference for the accurate estimation of shear bearing capacity of rock joints under different unloading stress paths, which is of great significance to the stability evaluation and disaster prevention of rock mass engineering. [ABSTRACT FROM AUTHOR]

Calcined clays (CCs) as supplementary cementitious materials (SCMs) can be a promising option to reduce clinker content and CO2 emissions in eco-friendly concretes. Although CCs as components of composite cements in combination with Ordinary Portland Cement (OPC) and limestone powder (LSP) have attracted industry interest, their use as concrete additives is limited. This study investigates the effects of the addition of CCs on the fresh and hardened properties of industry-standard ready-mixed concretes. Four concrete mix designs, each with three superplasticizer dosages, were tested, resulting in 12 variations. The CCs used, which are typical of 2:1 bentonite clays with low metakaolin content, reflect the clays available in Germany. The results showed that CCs significantly influenced the workability, which could be controlled with a high superplasticizer dosage. Increased CC contents reduced bleeding tendencies, which was beneficial for certain structural applications. Early age strength decreased with CCs, but the 28-day strength exceeded that of pure OPC concretes up to 30 wt% CCs. Resistance to CO2-induced carbonation decreased with higher levels of CCs but was comparable up to 15 wt%. Freeze–thaw damage decreased, and chloride migration resistance improved due to a denser microstructure. The global warming potential (GWP) of the concretes tested is in line with that reported in the literature for concretes made from highly blended cements, suggesting that CCs can improve the sustainability of concrete production. [ABSTRACT FROM AUTHOR]

This study focuses on long concrete interfaces tested under cyclic actions, fastened with post-installed industrial steel screws. The overall behavior and the effect of roughness were investigated in three long interfaces, representative of connections between, e.g., a slab and a wall, a beam and a wall, etc. The results were compared with those of short interfaces tested by the authors in previous campaigns. It was observed that rough long interfaces activate their maximum resistance at small values of imposed shear slip. When roughness was reduced, the maximum resistance was also reduced, the corresponding shear slip was increased, and the overall behavior was stable. For large values of the shear slip, imposed at one end of the interface, the shear slips along it tended to be uniform, both in short and long interfaces. The limited embedment length of the screws led to their pronounced pullout. Finally, the asymmetry of resistance between the two loading directions that was observed in short interfaces was alleviated in the long ones, where also the scatter of the results was limited among duplicate specimens. [ABSTRACT FROM AUTHOR]

Concrete is used worldwide as a construction material in many projects. It exhibits a brittle nature, and fibers' addition to it improves its mechanical properties. Polypropylene (PP) fibers stand out as widely employed fibers in concrete. However, conventional micro-PP fibers pose challenges due to their smooth texture, affecting bonding within concrete and their propensity to clump during mixing due to their thin and soft nature. Addressing these concerns, a novel type of PP fiber is proposed by gluing thin fibers jointly and incorporating surface indentations to enhance mechanical anchorage. This study investigates the incorporation of macro-PP fibers into high-strength concrete, examining its fresh and mechanical properties. Three different concrete strengths 40 MPa, 45 MPa, and 50 MPa, were studied with fiber content of 0–1.5% v/f. ASTM specifications were utilized to test the fresh and mechanical properties, while the RILEM specifications were adopted to test the bond of bar reinforcements in concrete. Test results indicate a decrease in workability, increased air content, and no substantial shift in fresh concrete density. Hardened concrete tests, adding macro-PP fibers, show a significant increase in splitting tensile strength, bond strength, and flexural strength with a maximum increase of 34.5%, 35%, and 100%, respectively. Concrete exhibits strain-hardening behavior with 1% and 1.5% fiber content, and the flexural toughness increases remarkably from 2.2 to 47.1. Thus, macro PP fibers can effectively improve concrete's mechanical properties and resistance against crack initiation and spread. [ABSTRACT FROM AUTHOR]

The goal of this research focusing on the burning of coal tailings to produce a lightweight artificial aggregate is to compare the physical-mechanical and durability properties of concrete containing this new type of artificial aggregate with those of the reference concrete. The following parameters are measured on all the samples: compressive strength, volume mass, the static modulus of elasticity in compression, the frost resistance of this new type of concrete, and the resistance to CO2. All the concretes tested with the new artificial aggregate exceeded the characteristic strength values in all the strength classes monitored. The volume mass of the concrete with the new artificial aggregate is tens of percentages lower than that of the conventional reference concrete. The frost resistance of the concrete tested was reliably proven by the non-destructive resonance method. It was also found that at the lower strength classes of concrete, carbonation occurred earlier, but there was no obvious direct relation to the porosity of the new artificial aggregate. The tests performed showed that it is possible to produce high - quality concrete using a new lightweight artificial aggregate produced from coal tailings [ABSTRACT FROM AUTHOR]

The most common methods for the determination of setting times of cements are the various penetration tests. One of the most important of these is the Vicat method, which is the current standard measurement (EN 196-3) to determine the setting time of cement. However, there are alternative methods that can be used to monitor the setting process and eliminate several issues that arise from the Vicat method, such as intermittent measurement, measurability of cement pastes of non-standard consistency, testing mortars and concretes. One such method is semi-adiabatic calorimetry (SAC), which can be an alternative to penetration tests in appropriate circumstances. In this study, determination of setting times of two sources of CEM I 42.5 N cement was observed, using semi-adiabatic calorimetry at different (0.25; 0.27; 0.29; and, 0.31) water to cement ratios (w/c). During our measurements, we observed that the ratio between the setting time of a given source of cement and the time it took to reach the maximum rate of heat development was almost constant for the same cement and w/c ratio, which enables a simple and inexpensive routine measurement of setting times of Portland cement. [ABSTRACT FROM AUTHOR]

Ultra-wideband (UWB) radar is highly effective for nondestructive testing of concrete structures. In this study, we propose a near-field synthetic aperture radar (SAR) signal processing technique using an impulse radio ultra-wideband (IR-UWB) radar to generate high-resolution images of the internal structures of concrete materials. For this purpose, we developed an accurate back-projection (BP) algorithm to compensate for the electromagnetic refraction and attenuation of a radar traveling through a concrete medium. A novel technique was implemented to suppress noisy clutter caused by internal impurities in concrete structures. For the experimental demonstration, concrete structures were constructed with metal bars inside, and the performance of the imaging system was evaluated by measuring the azimuth resolution and signal-to-noise metrics of the generated SAR images. [ABSTRACT FROM AUTHOR]

In Poland, the prevailing protocols for examining the alkali reactivity of aggregates are based on indirect methodologies such as petrographic appraisal, in addition to direct methodologies including the measurement of expansion in mortar and concrete specimens containing the aggregate under investigation. The available research methods exhibit certain deficiencies, which have been mitigated under the experimental conditions delineated in the novel accelerated approach for ascertaining the reactivity of aggregates, otherwise known as the MCPT – Miniature Concrete Prism Test. The methodology of MCPT has the potential to become an alternative for the existing procedures of quality assessment for both fine and coarse aggregates. This work presents the assessment results of the alkaline reactivity of indigenous fine quartz aggregate, examined in accordance with the protocols established by the Polish General Directorate for National Roads and Motorways along together the novel, expedited MCPT methodology. [ABSTRACT FROM AUTHOR]

Research on the durability of structural concrete requires careful selection of aggregates, particularly considering their reactivity to alkali-silica reaction (ASR). The Miniature Concrete Prism Test (MCPT) allows for shortened testing time and eliminates the need for aggregate crushing, making it a practical alternative to other methods. The aim of the research is to evaluate the reactivity of aggregate mixtures with varying mineral compositions. Research results confirm the significant impact of fine aggregates on concrete expansion in the MCPT method in NaOH solution at 60°C. The observed expansion correlates with a reduction in concrete's elastic modulus. [ABSTRACT FROM AUTHOR]

The attached cement paste in recycled concrete (RC) aggregate leads to its potential reactivity against sulfate ions. Several test methods were evaluated to find a suitable, reliable, and accurate method to evaluate the potential reactivity of aggregates. Different quality RC aggregates were used to apply those methods. The studies included evaluations of concrete cores drilled from source concrete (SC), RC aggregates, recycled mortar bars under different exposures, and RC prisms exposed to external sulfate attack (ESA). The concrete core test allowed qualifying SC as potentially reactive against sulfate in a short time. Tests on recycled aggregates and recycled mortar bars showed variable sensitivity levels. Results from concrete prisms showed an effective reactivity of recycled aggregates when the replacement is higher. [ABSTRACT FROM AUTHOR]

Copyright of Materiały Budowlane is the property of Wydawnictwo SIGMA-NOT and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents a novel framework for assessing the impact of construction defects on bridge deck corrosion-induced deterioration. The model developed quantifies the impact of insufficient concrete cover, damage to the rebar epoxy coating, improper curing technique, and excessive water–cement ratio on the lifespan of concrete bridge decks. Regional variations, including freeze–thaw cycles, carbonation, and deicing salt usage, are also considered in the model. Two applications for estimating deterioration and decrease of condition rating are presented. Simulation results using the model developed reveal a substantial loss of life when these defects occur. This work highlights the importance of proper construction practices in ensuring long-term infrastructure integrity. Moreover, it provides a valuable tool for assessing the impact of these common construction defects on bridge deck deterioration. This tool enables bridge managers to make better-informed decisions regarding repair operations and ask contractors for fairer compensations when defective practices are observed during construction. [ABSTRACT FROM AUTHOR]

The main objective of this research is to investigate experimentally the effect of crushed and uncrushed coarse aggregate on the properties of hardened concrete (compressive strength) by adopting the American Concrete Institute (ACI) and the British Department of Environment (DoE) methods. Concrete mixes were designed, concrete cubes and cylinders were prepared and casted by using DoE and ACI respectively. DoE concrete design method considers both types of aggregates; crushed and uncrushed, while the ACI method does not take into account the effect of uncrushed coarse aggregate in design provisions. Then compressive strength tests of concrete samples were determined at ages of 7 and 28 days full curing period. The results obtained show that ACI gave higher values of compressive strength than that obtained by DoE for M30 and M40 except M25, which resulted in lower values than that obtained by DoE for crushed coarse aggregates. The 7-day compressive strength represents 75% of the 28-day compressive strength for ACI method, whereas in DoE reaching up to 73% and 77% for crushed and uncrushed coarse aggregate, respectively. [ABSTRACT FROM AUTHOR]

In this study, the pore structure and gas permeability of river sand concrete and manufactured sand concrete (mixed with various stone powders) are examined under dry and wet conditions. First, the pore structure of concrete was tested using the mercury-in-pressure (MIP), hydrostatic balance (HB), and nuclear magnetic resonance (NMR) methods. Second, the gas permeability of concrete was measured using the quasi-stationary flow method. Finally, a numerical model was developed based on the relationship between the pore structure and gas permeability. The results indicated that the gas permeability of dry concrete has a quadratic linear relationship with the porosity and volumetric characteristic pore size. The pore structure of partially water-saturated concrete can be corrected using a correction factor and the relaxation rate of the dry material. Finally, a random hierarchical bundle model using the HB–NMR method is proposed. The maximum relative deviation between the predicted and experimental values is 48.28%. [ABSTRACT FROM AUTHOR]

Shotcrete strain in the primary support of a tunnel will produce non-loading strain at an early age due to the influence of its own temperature change, hardening shrinkage, spraying force, and other factors, which means that current strain-monitoring results fail to reflect the real strain, and the strain value after stabilization is high. In addition, tensile strain may be evident in the final result, even exceeding the tensile warning value, but, in actuality, the on-site lining is very stable, with no cracks or damage. Therefore, it is necessary to understand the strain characteristics of shotcrete in the primary support of a tunnel. Based on the long-span tunnel project at Shishan Road Station on the Qingdao Metro Line 6, in situ and indoor pull tests of concrete strain were designed while only considering temperature change, hardening shrinkage, and spraying force. This study shows the following: (1) The strain in shotcrete is greatly affected by temperature changes, hardening shrinkage, and shotcrete force in the first three days, reaching its peak value in the second to third days, while tending to be stable at about the seventh day. (2) The real strain of the shotcrete was tested, and the warning value was adjusted from 90 με to 120 με. (3) The strain value at the third day was taken as the initial value, and the previous monitoring results were revised. The revised results align with the trends shown during real tests performed on-site, providing guidance for tunnel engineering support monitoring. [ABSTRACT FROM AUTHOR]

In order to solve the problems of low tensile strength of composite mortar prone to cracking when reinforced concrete beams are strengthened by traditional methods, this paper proposes a new polyurethane concrete–prestressing wire (PUC–PSW) reinforcement method using polyurethane concrete (PUC) as the wire embedding material. Twelve reinforced concrete T-beams were tested for PUC–PSW flexural reinforcement. These consisted of one unreinforced beam, four PSW-reinforced beams and seven PUC–PSW-reinforced beams. The wire embedding material, wire anchorage form, PUC material depth, amount of wire and loading type were used as variables. The test results show that PUC–PSW reinforcement can significantly increase the yield load and ultimate load of the reinforced beams by 24.1% and 44.6%, respectively, compared with PSW reinforcement. When the load reached 90 kN, the crack widths of PSW-reinforced beam A2 and PUC–PSW-reinforced beam A8 were 0.17 mm and 0.1 mm, respectively. The ability of PUC–PSW reinforcement to limit crack development is better than that of PSW reinforcement, especially after the main beam steel yield. The strength, stiffness and crack-limiting ability of the reinforced beam increase with the PUC thickness of the reinforced layer. [ABSTRACT FROM AUTHOR]

To investigate the impact of freeze–thaw damage on the mechanical properties of concrete, this study utilized Python in combination with ABAQUS 2016 to generate a two-dimensional meso-scale model of concrete. Uniaxial compression tests were conducted on the concrete after freeze–thaw cycles to study the evolution of its mechanical properties. Using "relative compressive strength" as a variable, the relationships between this variable and the parameters of the freeze–thaw damage model were determined, leading to the establishment of the freeze–thaw damage model and the simulation of compressive tests on concrete after freeze–thaw cycles. This study also explored the changes in the mechanical properties of concrete with variations in ITZ parameters and coarse aggregate content. The conclusions drawn are as follows: A comparison with experimental data showed that the model ensures that the relative error of each mechanical property parameter does not exceed 7%, verifying the model's rationality. Increasing the ratio of ITZ parameters improved the mechanical properties of the ITZ, enhancing the overall mechanical performance, but had almost no effect on the elastic modulus. Compared to ratios of 0.7 and 0.8, concrete with a ratio of 0.9 showed slower rates of decrease in compressive strength and elastic modulus and slower rates of increase in peak compressive strain after freeze–thaw cycles. The increase in coarse aggregate content had a similar effect on the strength and freeze–thaw resistance of concrete as the ratio of ITZ parameters. Concrete with a coarse aggregate content of 60% exhibited slower rates of change in mechanical properties after freeze–thaw cycles. [ABSTRACT FROM AUTHOR]

A torsional strength model for prestressed concrete beams was proposed considering the initial crack angle, principal stress angle, and longitudinal strain, which are affected by the axial stress induced by the effective prestress. The use of the torsional effective thickness was also proposed to calculate the torsional strength of prestressed concrete beams by considering the effect of prestress. The shear element in the torsional member was simplified under the assumption that the principal tensile stress and principal compressive strain were negligible in the ultimate state. The torsional strength was determined when the principal compressive stress or shear stress at the crack surface in the shear element reached the failure criterion according to the multipotential capacity model, which considers concrete crushing and aggregate interlocking as the main resistances to the applied load. The proposed strength model was verified using test specimens collected from existing experimental studies. The proposed model accurately evaluated the torsional strength of prestressed concrete beam specimens, regardless of the key variables of the prestressed concrete specimens, where the mean value of the tested results to the calculated torsional strengths was 1.123, and the corresponding coefficient of variation was 17.7% for 104 prestressed concrete beam specimens, while the ACI 318-19 torsional design method gave the mean and coefficient of variation of 0.880 and 24.3%, respectively. [ABSTRACT FROM AUTHOR]

In extremely cold regions with frequent extreme weather conditions, coupled factors make concrete corrosion by garbage landfill leachate become more complicated. Although previous studies have characterized the effects of individual factors, the mechanisms of coupled effects under specific conditions require further research. Therefore, this study analyzed the individual and coupled effects of landfill leachate, salt solution, and freeze–thaw cycles. The corrosion mechanism of landfill leachate was explained by analyzing the mechanical properties, surface morphology, and microstructure of the concrete. The individual factor tests showed that landfill leachate affected the performance of concrete more significantly than salt solution in the short term. In the immersion tests, the strength of concrete specimens corroded by landfill leachate was always minimized throughout the process, and the compressive and flexural strengths of concrete in landfill leachate decreased by 6.40% and 7.83%, respectively. In the coupled tests, freeze–thaw cycles amplified the effect of landfill leachate on concrete, exhibiting more severe damage than that with only landfill leachate. After four test cycles, the compressive strength of the concrete in the coupled test group decreased by 22.5%, 19.7%, and 31.3% and the flexural strength decreased by 40.2%, 26.7%, and 46.3%, respectively. Through surface morphology and microstructure analyses, we found that the inorganic salt ions in the landfill leachate reacted to form expansive ettringite and gypsum, which initially optimized the internal structure of the concrete but caused severe damage in the later stage. Concrete corrosion by landfill leachate was significantly enhanced under the influence of freeze–thaw cycles. The experimental results of this study provide basic data and theoretical support for designing and protecting concrete buildings in extremely cold environments. Practical Applications: The deterioration of concrete buildings in landfills by landfill leachate corrosion has received widespread attention, and this problem is pronounced in cold regions. This study selected landfill leachate, salt solution, and freeze–thaw cycles as the corrosion conditions for the concrete corrosion test under one-factor conditions. At the same time, landfill leachate and salt solution were coupled with freeze–thaw cycles for the concrete corrosion test. The severity of concrete damage was compared by the changes in mechanical properties and microscopic morphology of the concrete during the test. The results of the one-factor corrosion test showed that the landfill leachate would cause more damage to the concrete in the short term. Meanwhile, the coupled-factor corrosion test results showed that freeze–thaw cycles amplify concrete corrosion by landfill leachate, resulting in a significant reduction in the mechanical properties of concrete and damage to the internal structure. In addition, the study characterized the mechanism of action of landfill leachate corrosion on concrete. This could also provide theoretical support for constructing and protecting concrete structures in landfills in cold regions. [ABSTRACT FROM AUTHOR]

In this study, Recycled Concrete Aggregate (RCA) was employed as a sandwich technique around the geogrid to enhance the pullout resistance of the geogrid in clayey backfills. Large-scale pullout tests were conducted on three configurations: geogrid-reinforced clay, geogrid-reinforced RCA, and geogrid sandwiched between layers of RCA, aimed at investigating pullout resistance and deformation. The experiments encompassed two different geogrid types (designated as G1 and G2), varying normal pressures ranging from 10 to 50 kPa, and RCA layers with thicknesses of 40, 80, 160, and 320 mm. Results from the experiments revealed that the inclusion of RCA layers around the geogrid substantially enhanced pullout resistance, with improvements ranging from 1.5 to 3 times compared to clay specimens. Optimal RCA thicknesses were determined in order to enhance soil-geogrid bonding and pullout resistance. For G1 geogrid, a thickness of 160 mm (equivalent to replacing 25% of clay volume with RCA) was identified as optimal, while for G2 geogrid, an 80 mm thickness (equivalent to replacing 15% of clay volume with RCA) was found to be sufficient. These thicknesses were established to achieve over 80% of the pullout force compared to full RCA specimens. • Large-scale pullout tests were performed on two types of geogrids. • Recycled Concrete Aggregate (RCA) was utilized at various thicknesses within a sandwich technique to enhance geogrid pullout resistance in clayey backfills. • The optimum thickness of RCA layer in sandwich technique was determined. [ABSTRACT FROM AUTHOR]

Carbon fiber–reinforced polymer–steel composite bars (C-FSCBs) and coral sea-sand aggregate seawater concrete (CSSC) are attractive choices as construction materials for island and atoll engineering construction. Understanding the bond behavior between the C-FSCB and CSSC is crucial for evaluating the mechanical properties of C-FSCB-reinforced CSSC structures. In this study, the bond–slip behavior between the C-FSCB and CSSC was experimentally assessed via pullout tests. The influence of various factors on the bond behavior was discussed, and the bond mechanism between the C-FSCB and CSSC was analyzed. The results indicate that, unlike steel bars, the low rigidity of fiber-reinforced polymer caused surface fiber stripping (i.e., shear damage) of the C-FSCB after interface slip, consequently reducing the squeezing fragmentation of concrete between the ribs. As the diameter and bond length of the C-FSCB increased, the bond strength decreased. Compared to specimens with C-FSCBs, the bond strength of specimens with steel bars of the same diameter increased by 17.9%. The degree of coarse aggregate fracture at the CSSC interface in the splitting failure was much higher than that of normal concrete. Based on existing research data, a formula for calculating the bond strength of C-FSCBs in CSSC has been established to determine the anchorage length of C-FSCBs, and the calculated values accurately predicted the test values. [ABSTRACT FROM AUTHOR]

Concrete compressive strength testing is crucial for construction quality control. The traditional methods are both time-consuming and labor-intensive, while machine learning has been proven effective in predicting the compressive strength of concrete. However, current machine learning-based algorithms lack a thorough comparison among various models, and researchers have yet to identify the optimal predictor for concrete compressive strength. In this study, we developed 12 distinct machine learning-based regressors to conduct a thorough comparison and to identify the optimal model. To study the correlation between compressive strength and various factors, we conducted a comprehensive analysis and selected blast furnace slag, superplasticizer, age, cement, and water as the optimized factor subset. Based on this foundation, grid search and fivefold cross-validation were employed to establish the hyperparameters for each model. The results indicate that the Deepforest-based model demonstrates superior performance compared to the 12 models. For a more comprehensive evaluation of the model's performance, we compared its performance with state-of-the-art models using the same independent testing dataset. The results demonstrate that our model achieving the highest performance (R2 of 0.91), indicating its accurate prediction capability for concrete compressive strength. [ABSTRACT FROM AUTHOR]

The capacity of the circumferential joint of the precast concrete segmental tunnel lining (PCTL) structure in terms of shear performance principally includes the dowel action by connector/bolt as well as friction force, and it is a vital parameter to assess the mechanical response of the circumferential joint. Further, as there was no analytical model available for precise estimation of a circumferential joint in terms of the shear‐bearing capacity considering the dowel action of the bolt in the presence of axial/normal force, therefore in this investigation, an analytical model has been proposed to estimate the shear‐bearing capacity of the circumferential joint. Furthermore, the analytical model's precision and accuracy were validated via large‐scale experimental investigation on a circumferential joint of PCTL. Upon comparing analytical model outcomes with experimental results, absolute error varied between +5% and −9%, with an average value of the coefficient of friction at the yield point of the bolt. Moreover, the formation of hinges on the side of the bolt within the segment was considered a failure of the circumferential joint. Additionally, the parametric investigation revealed that with just a 1% change in axial force, the diameter, pre‐tightening, and yield strength of the bolt and concrete strength improved by 2.85%, 1%, 0.27%, 0.26% and 0.17% shear‐bearing capacity of the circumferential joint respectively. Axial force variation greatly influences the shear‐bearing capacity of circumferential joint followed by diameter, pre‐tightening, yield strength of the bolt, and concrete strength. Conclusively, with analysis of axial force distribution around the ring for the tunnel, the proposed model has been applied to a full ring to estimate shear bearing capacity. [ABSTRACT FROM AUTHOR]

In order to study the influence of synthetic polycarboxylate superplasticizer on the performance of mechanical sand concrete used in the construction project of Dalian Bay Subsea Tunnel, according to different production processes and different cases of synthetic polycarboxylate superplasticizer, the content of mechanical sand stone power and the adaptability of different mud content were studied, and the application effect in practical engineering was explored. Regarding the concrete construction mix ratio of the main structure of the Dalian Bay Subsea Tunnel construction project, the influence of stone powder content on the physical properties of mechanism sand concrete was tested. The test results show the slump decreases with the increase of stone powder content. At the same time, in order to ensure the same slump and 1 hour slump loss, the dosage of water reducing agent needs to be appropriately increased with the increase of stone powder content. When the content of stone powder reaches a certain limit, the portion of stone powder should be calculated into the cementitious material to determine the actual amount of superplasticizer used in the mix proportion. Through practical engineering applications, the concrete treated with EPEG process polycarboxylate superplasticizer exhibits good slump retention and workability, and has good adaptability. [ABSTRACT FROM AUTHOR]

Utilization of large aggregates can promote energy conservation and emissions reductions, and large aggregates have been widely used in hydraulic concrete. The failure criterion for concrete material utilizing large aggregates forms the basis for constitutive models and structural design. However, the concrete failure criterion with respect to large aggregates has never been researched. To this end, the authors first conducted a series of triaxial compressive tests on concrete specimens with scaled aggregates. On this basis, several 3D mesoscopic numerical models were established with different aggregate gradations and used to simulate the triaxial compressive behaviors of hydraulic concrete after the models had been verified by experimental results. The results showed a pronounced aggregate-gradation effect on triaxial compressive behaviors, and concrete mixes with larger aggregates usually have higher compressive strength, especially under conditions of higher confinement. The normalized peak strength can increase by up to 23.49%. Finally, based on the available testing data, the strength criterion in different constitutive models is discussed and modified to allow more accurate simulation of the dynamic responses of and damage to fully graded concrete structures. This result can provide a theoretical basis on which construction entities can optimize the mix proportions of fully graded concrete and detect the failure modes of concrete structures. [ABSTRACT FROM AUTHOR]

Concrete structures frequently manifest diverse defects throughout their manufacturing and usage processes due to factors such as design, construction, environmental conditions and distress mechanisms. In this paper, a multilevel convolutional neural network (CNN) combined with array ultrasonic testing (AUT) is proposed for identifying the locations of hole defects in concrete structures. By refining the detection area layer by layer, AUT is used to collect ultrasonic signals containing hole defect information, and the original echo signal is input to CNN for the classification of hole locations. The advantage of the proposed method is that the corresponding defect location information can be obtained directly from the input ultrasonic signal without manual discrimination. It effectively addresses the issue of traditional methods being insufficiently accurate when dealing with complex structures or hidden defects. The analysis process is as follows. First, COMSOL-Multiphysics finite element software is utilized to simulate the AUT detection process and generate a large amount of ultrasonic echo data. Next, the extracted signal data are trained and learned using the proposed multilevel CNN approach to achieve progressive localization of internal structural defects. Afterwards, a comparative analysis is conducted between the proposed multilevel CNN method and traditional CNN approaches. The results show that the defect localization accuracy of the proposed multilevel CNN approach improved from 85.38% to 95.27% compared to traditional CNN methods. Furthermore, the computation time required for this process is reduced, indicating that the method not only achieves higher recognition precision but also operates with greater efficiency. Finally, a simple experimental verification is conducted; the results show that this method has strong robustness in recognizing noisy ultrasonic signals, provides effective solutions, and can be used as a reference for future defect detection. [ABSTRACT FROM AUTHOR]

The water–cement ratio significantly affects the mechanical properties of concrete with changes in porosity serving as a key indicator of these properties, which are correlated with the ultrasonic wave velocity and energy evolution. This study conducts uniaxial compression tests on concrete with varying water–cement ratios, analyzing energy evolution and ultrasonic wave velocity variations during the pore compaction stage and comparing damage variables defined by dissipated energy and ultrasonic wave velocity. The results indicate the following findings. (1) Higher water–cement ratios lead to more complete hydration, lower initial porosity, and a less pronounced pore compaction stage, but they deteriorate mechanical properties. (2) In the pore compaction stage, damage variables defined by dissipated energy are more regular than those defined by ultrasonic wave velocity, showing a nearly linear increase with stress (D = 0~0.025); ultrasonic wave variables fluctuate within −0.06 to 0.04 due to diffraction caused by changes in the pore medium. (3) In the pre-peak stress stage, damage variables defined by ultrasonic wave velocity show a distinct threshold. When the stress ratio exceeds about 0.3, the damage variable curve's growth shows clear regularity, significantly reflecting porosity changes. In conclusion, for studying porosity changes during the pore compaction stage, damage variables defined by dissipated energy are more effective. [ABSTRACT FROM AUTHOR]

One of the most important factors influencing concrete durability is permeability. Permeability testing is conducted according to certain standards to measure the water permeation in concrete. After the test, the concrete specimens should be positioned under the concrete breaker jack and split into two sections to measure the permeability. In general, it is difficult to use the majority of permeability tests to determine concrete permeability in situ. As a result, the permeability and compressive strength of concrete with various strength classes were measured in this study by using the novel "cylindrical chamber" and "friction transfer" tests. Permeability-reducing admixtures, including Fibrous microsilica gel and waterproof, were used in several specimens that were subjected to 0, 50, 100, and 150 freezing and thawing cycles. A cylindrical chamber device can quantitatively display the permeation volume and rate of any liquid into concrete. By comparing the results of the nondestructive cylindrical chamber test with the standard destructive test, it was observed that there is a 97.6% correlation coefficient between the results. This correlation coefficient demonstrates the high accuracy of the cylindrical chamber test in measuring water permeability within concrete without the need for sample breakage. Furthermore, by comparing the results of the friction transfer test with the standard destructive test, a 94.2% correlation coefficient was observed. This correlation coefficient indicates the high accuracy of the friction transfer test in assessing the compressive strength of concrete without the need to break the concrete. In addition, the process of rising permeability rate has a greater value for low cycles. However, it progressively becomes smoother for higher cycles, in such a way that, on average, the permeation volume increased by 71% in the first 50 cycles, 21% in the second 50 cycles, and only 8% during the third 50 cycles. In concrete specimens without additives, the value of permeability rate increases under freezing and thawing cycles by approximately 36% and 19%–22% in specimens containing permeability-reducing admixture. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to propose and numerically assess different ways of discretising a very weak formulation of the Poisson problem. Design/methodology/approach: We use integration by parts twice to shift smoothness requirements to the test functions, thereby allowing low-regularity data and solutions. Findings: Various conforming discretisations are presented and tested, with numerical results indicating good accuracy and stability in different types of problems. Originality/value: This is one of the first articles to propose and test concrete discretisations for very weak variational formulations in primal form. The numerical results, which include a problem based on real MRI data, indicate the potential of very weak finite element methods for tackling problems with low regularity. [ABSTRACT FROM AUTHOR]

The use of simulated solutions is a common practice in corrosion studies to assess easily and quickly the corrosion behaviour of materials in real situations. In this context, it is frequent to substitute tests performed in concrete or mortar with tests performed in porous‐like solutions. Particularly, to simulate carbonated concrete, different carbonated porous‐like solutions (CPS) are found in the literature. However, it is not known whether the use of these solutions accurately predicts the behaviour of steel bars embedded in carbonated concrete. In the present work, a comparison between the corrosion behaviour of carbon steel in carbonated mortar and in different CPS was performed. It was found that none of the CPS studied in the present work adequately simulate the corrosion behaviour of the steel in carbonated mortar, but the CPS containing high concentrations of carbonates/bicarbonates is the only one that provides corrosion rates close to those obtained in carbonated concrete. [ABSTRACT FROM AUTHOR]

By combining time-frequency images and deep learning models, the nonlinear ultrasound signals can be classified, detected, and predicted, using the nonlinear coefficient as a fundamental label for training deep learning models. This integrated approach enables quantitative identification and real-time monitoring of concrete damage, promoting the widespread adoption of nonlinear ultrasonic techniques in engineering applications. As a basis, the relationship between damage variations and nonlinear coefficients is discussed by performing nonlinear ultrasonic damage testing on concrete specimens with different crack lengths and angles. The testing signals are converted into time-frequency images using the short-time Fourier transform and the continuous wavelet transform, and both types of images are combined for data augmentation and input into the deep learning model for training, with nonlinear coefficients serving as labels for the time-frequency images. The MobileNetV2, VGG16, and ResNet18 deep learning models are trained separately on time-frequency image datasets for the length specimens, the angle specimens, and the length-angle specimens, and the performance of the different models is evaluated and compared. The results show that all three models have accuracy rates above 94%, indicating good identification performance. Finally, with the example, the nonlinear coefficients of the testing signals are compared with the labels of the nonlinear coefficients in the time-frequency images identified by the deep learning model, which confirms the high accuracy of damage identification by the deep learning model. [ABSTRACT FROM AUTHOR]

Non-destructive testing (NDT) techniques are crucial in making informed decisions about reconstructing or repairing building structures. The SonReb method, a combination of the rebound hammer (RH) and the ultrasonic pulse velocity (UPV) tests, is widely used for this purpose. To evaluate the compressive strength, C S , of the concrete under investigation, the ultrasonic pulse velocity V p and the rebound index R must be mapped to the compressive strength C S using a suitable conversion model, the identification of which requires supplementing the NDT measurements with destructive-type measurements (DT) on a relatively large number of concrete cores. An approach notably indicated in all cases where the minimization of the number of cores is essential is to employ a pre-existing conversion model, i.e., a model derived from previous studies conducted in the literature, which must be appropriately calibrated. In this paper, we investigate the performance of Gaussian process regression (GPR) in calibrating the pre-existing SonReb conversion models, exploiting their ability to handle nonlinearity and uncertainties. The numerical results obtained using experimental data collected from the literature show that GPR calibration is very effective, outperforming, in most cases, the standard multiplicative and additive techniques used to calibrate the SonReb models. [ABSTRACT FROM AUTHOR]

Concrete is widely utilized across various industries as a containment material. One essential property related to its performance is permeability, which determines its ability to allow the passage of gases or liquids through its pores and capillaries and even the transmission of aggressive agents. This study focused on investigating the permeability of gases with varying atomic weights and molecular volumes, such as helium, nitrogen, oxygen, and argon, to pass through concrete. The primary objective was to determine the significance of variation in permeability and to evaluate and differentiate their behavior. To achieve this, concrete test specimens were employed, and factors such as cold joint impact, gas pressure, and specimen saturation levels were considered. Throughout the study, changes in weight, specimen humidity, resistivity, and ultrasonic pulse velocity were monitored. The findings suggested that within concrete, the variation in permeability for these gases is negligible. By utilizing the acquired data, the present study estimated the permeability of hydrogen through mathematical models based on gas pressure and concrete thickness. These insights contribute to a deeper comprehension of concrete gas permeability and its potential impact on improving hydrogen containment. [ABSTRACT FROM AUTHOR]

Rubber-foamed concrete demonstrates exceptional toughness, a low elastic modulus, and significant sensitivity to density. It is necessary to parameterize the density mix of rubber-foaming concrete to meet engineering design requirements. Density-mix design methods for foaming concrete rely mainly on empirical knowledge or trial-and-error approaches. In this paper, with numerous parametric tests and regression analysis based on general principles for density-mix designs applicable to both foamed and rubber-foamed concretes, the key design parameters, such as volume correction coefficient, rubber size effect coefficient, and water-reducing agent effect coefficient, have been proposed in order to optimize their respective densities more accurately. The tests demonstrated an optimal water-to-cement ratio of 0.45, corresponding to a volume correction factor of 1.027. Incorporating rubber particles and water-reducing agents has a more significant effect on the cement-paste volume. Controlling fluidity in the 200 to 300 mm range is crucial when designing foamed concrete with varying densities. The regression equation accurately predicts the paste's measured volume and wetting density by incorporating volume corrections, size, and water reduction effect coefficients. By employing a foam excess coefficient of 1.1 and a mass coefficient of 1.25, the dry and wet density error of foam concrete is less than 5%. A comprehensive framework for optimizing mix design in terms of density is provided for applications in foamed concrete and rubber-foamed concrete, facilitating researchers in designing mix ratios for additional novel mixture-based foamed-concrete applications. [ABSTRACT FROM AUTHOR]

Vietnam's seaport system currently includes 298 ports with 588 wharves (a total length of approximately 92,275 m), which is vital in developing Vietnam's marine economy. The piled pier, a type of wharf structure, is widely used and accounts for up to 90%, while the remaining 10% is made up of other types of wharf structures, such as gravity and sheet pile quay walls. Most wharves have been operating for over 10 years and some for even more than 50 years. Noticeably, wharves are highly vulnerable and degrade rapidly due to many factors, especially heavy load impacts and severe environmental conditions. Additionally, wharves have a higher risk of deterioration than other inland infrastructure, such as buildings and bridges. Consequently, determining a wharf's health is an important task in maintaining normal working conditions, extending its lifecycle, and avoiding other severe damage that could lead to dangers to the safety of vehicles, facilities, and humans. Moreover, regulated quality inspections usually include only simple inspections, e.g., displacement, settlement, geometric height, and tilt; the visual inspection and determination of dimensions by simple length-measuring equipment; concrete strength testing by ultrasonic and rebound hammers; and the experimental identification of the chloride ion concentration, chloride diffusion coefficient, corrosion activity of rebar in concrete, and steel thickness. These testing methods often give local results depending on the number of test samples. Therefore, advanced diagnostic techniques for assessing the technical condition of piled piers need to be studied. The impact vibration test (IVT) is a powerful non-destructive evaluation method that indicates the overall health of structures, e.g., underground and foundation structures, according to official standards. Hence, the IVT is expected to help engineers detect the potential deterioration of overall structures. It is fundamental that, if a structure is degraded, its natural frequency will be affected. A structure's health index and technical condition are determined based on this change. However, the IVT does not seem to be widely applied to piled piers, with no published standard; hence, controversial issues related to accuracy and reliability still remain. This motivates the present study to recommend an adjusted factor (equal to 1.16) for the health index (classified in official standards for other structures) through numerical and experimental approaches before officially applying the IVT method to piled piers. The current work focuses on the health index using the design natural frequency, which is more practical in common cases where previous historical data and the standard natural frequency are unavailable. This study also examines a huge number of influencing factors and situations through theoretical analysis, experience, and field experiments to propose an adjusted indicator. The results are achieved with several assumptions of damages, such as the degradation of materials and local damages to structural components. With the proposed adjusted indicator, the overall health of piled piers can be assessed quickly and accurately by IVT inspections in cases of incidents, accidents due to collisions, cargo falls during loading and unloading, or subsidence and erosion due to natural disasters, storms, and floods. [ABSTRACT FROM AUTHOR]