Rigorous characterization of fracture evolution in quasi-brittle materials – such as concrete – requires computationally intensive and, mostly, complex approaches. However, the headway in ...computational power and the efficiency of numerical methods increased the interest in the numerical modeling of concrete fracture. This paper, first, reviews concrete fracture from different perspectives of fracture theories/models based on macroscopic or mesoscopic formulations along with thorough discussions on the existing numerical methods for their solutions. Next, a diverse set of both classical and newly developed experimental concrete fracture tests is compiled and systematically critiqued along with past and evolving literature numerical simulations of the same. This serves as a state-of-the-art benchmark suitable for validating newly emerging numerical models and/or fracture theories. The work, then, discusses the size effect laws controlling the nominal strength of concrete structural elements and analyzed existing studies on the influence of mixture design on the concrete fracture response. Based on the conclusions of the review on numerical models, fracture theories, the compiled experimental benchmarks/tests, and the factors controlling concrete fracture, the literature gap is established and future perspectives highlighted. Finally, the paper develops a series of numerical models based on 3-D adaptive generalized finite element method (GFEM) to validate its ability in simulating mixed-mode concrete fracture trajectories of various benchmarked problems. The GFEM’s superiority in terms of mesh adaptivity, ability to use coarse and unstructured meshes (contrary to the use of expensive discretizations by most of the existing models), as well as resulting in a stable system of the generated equations are established.
•A systematic review of concrete fracture models and experimental benchmarks for models’ exhaustive validation.•Size effect and practical implication of concrete mix-design are highlighted.•The literature lacks fracture tests for mesoscale validation, non-beam test geometries, mode III fracture size effect analysis and 3D-printed concrete.•Independent validation of Bazant’s Model Index for appraising fracture theories is needed.•An adaptive 3D GFEM is validated against a series of mixed-mode concrete fracture tests.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Temperature increased the FRP-concrete bond strength at low humidity within 5 weeks.•Failure mode changed from substrate to adhesive-concrete interface at 100% RH.•Bond strength was lowest (12% ...reduction) under alternating wet/dry cycles.•Epoxy cured at 60 °C changed the failure mode with no effect on bond strength.•Using degraded properties avoided overestimating bond strength of exposed specimens.
Drawing on information obtained via double lap shear tests, this paper discusses FRP-concrete bond behavior following five weeks of exposure to several accelerated hygrothermal conditions. Material tests were also carried out for both dry carbon fibers and the epoxy used in the bond study under similar hygrothermal conditions. The bond-slip relationship for the hygrothermal conditions were developed, and fracture energy calculated for the FRP-concrete bond. The use of degraded material properties obtained from material test coupons under the same exposure conditions prevented overestimation of the FRP-concrete bond fracture energy. Testing revealed that the FRP-concrete bond strength increased as temperature increased at low humidity (dry heat) — a potential consequence of alteration in the epoxy glass transition temperature. The bond strength of concrete with steel slag incorporated was superior at all temperatures and low humidity. In response to continuous or periodic submergence in water, specimen failure mode transitioned from substrate failure to adhesive-concrete interface failure. Alternating two-day wet/dry cycles resulted in a 12% drop of FRP-concrete bond strength. Under low humidity, the FRP dry fiber tensile stress increased as temperature increased (dry heat), while the opposite dynamic was observed in the epoxy coupons.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Size effect validation of a generalized finite element method algorithm for concrete fracture.•Influences of geometry and material properties on LEFM deviation are verified.•Empirical model ...formulated for modification of LEFM to agree with CZM-based concrete fracture.
The existence of process zones at crack tips in quasi-brittle materials is responsible for the structural size-dependent fracture strength. Hence, accurate prediction tools should not only be capable of predicting the fracture propagation and its load–displacement attributes, but should render themselves capable of the size effect analysis as well. This paper applies a robust 3-D generalized/eXtended finite element method (G/XFEM) algorithm to fracture propagation in concrete and validates its capability to capture the size effect behavior based on the cohesive zone model (CZM). Equipped with the capability of mesh adaptivity, the framework utilized in discretizing the resulting system of equations allows the adoption of independent representation for the background solid mesh and the fracture surfaces without the need for conformity between the two. The fracture simulations on a series of geometrically similar concrete beams under three-point bending have shown very good agreement with available experimental results in terms of both load–displacement (peak load and post-peak) characteristics and size effect behavior. The study also models the experimental problems using Linear Elastic Fracture Mechanics (LEFM) to investigate the structure’s size threshold below which the applicability of LEFM diminishes. The effect of beam geometry and concrete material properties on the LEFM accuracy is assessed by calculating the deviations between LEFM and bilinear cohesive model solutions. The simulation results show that power functions best describe the effect of beam’s depth and tensile strength, and linear functions best fit the effect of elastic modulus and fracture toughness. Subsequently, the study presents and validates an empirical correlation model that modifies the LEFM solution to predict similar ultimate strength as the CZM in addition to capturing the concrete size effect law successfully.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Given the rise in sustainable use of recycled aggregate concrete (RAC) in new construction, weaker properties may compromise the integrity of structural components, including the slab-column ...connections. Low-strength concrete can be encountered, not only by using weak RAC in new construction, but also in the case of normal concrete in aged and deteriorated historic or conventional structures. To uphold the sustainable use of such materials in critical structural components, the need for restoring the strength via external strengthening using near-surface-mounted (NSM) fiber-reinforced polymer (FRP) bars is presented in this study. The paper experimentally investigates the behavior of NSM FRP strengthening against punching shear failure in slab-column connections produced from RAC and steel fibers with low structural strength. The three variables studied are steel fiber addition, recycled aggregate replacement, and FRP bar material type – Glass FRP (GFRP) versus Carbon FRP (CFRP). Five tests were conducted, utilizing three and two specimens strengthened with GFRP and CFRP bars, respectively. The three GFRP bar strengthened specimens differ in the type of concrete used, namely, ordinary concrete without steel fibers, ordinary steel fiber reinforced concrete (FRC), and RAC without steel fibers. The two CFRP bar strengthened specimens were of ordinary concrete and RAC, both with steel fibers, resulting in recycled aggregate FRC. RCA’s incorporation positively affected the results of the ultimate punching shear, flexural stiffness, and the maximum displacement due to the likely role of the recycled aggregate angularity in resisting the punching shear better. Due to higher flexural stiffness of the NSM CFRP, it entails more likelihood of debonding failure that limits its full utilization in increasing the punching shear capacity compared to that of NSM GFRP. However, both the NSM strengthening materials appear promising in low-strength (f’c ≤ 17 MPa) concrete slabs to reach acceptable capacities. Assessment based on different design code provisions and an analytical model revealed better accuracy of the Critical Shear Crack Theory (CSCT) and the fib Model Code in predicting punching shear capacity for NSM strengthened ordinary concrete column-slab connections, but with some slight deviations when applied to specimens made of RAC.
•RCA from a real CDW plant: Punching shear of NSM FRP+RCA FRC slab-column joints assessed.•Low-strength RCA+NSM FRP outperforms low-strength NA+NSM FRP in punching shear.•GFRP strengthening significantly enhances punching shear capacity over CFRP.•NSM FRP in low-strength NA restores punching capacity to normal-strength levels.•CSCT and fib Code outperform others in NA FRC punching; updates needed for RCA FRC.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract The utility of routine frozen section (FS) analysis for margin evaluation during radical prostatectomy (RP) remains controversial. A retrospective search was conducted to identify RPs ...evaluated by FS over a 5-year period. The potential of FS to discriminate between benign and malignant tissue, and predict final margins was evaluated. During the study period, 71/575 (12.3%) cases underwent FS evaluation of margins, generating 192 individual FSs. Eight FSs were diagnosed as atypical/indeterminate because of significant freezing, crushing and/or thermal artifacts, 11 as positive for carcinoma, and 173 as benign. Two FSs classified as benign were diagnosed as positive for carcinoma on subsequent permanent section. FS sensitivity, specificity, positive predictive value (PV), negative PV and accuracy for diagnosis of prostatic adenocarcinoma were 85%, 100%, 100%, 99% and 99%. Overall RP final margin predictive accuracy was 81%. Positive FS was significantly associated with perineural invasion on biopsy and extraprostatic extension and higher stage disease on RP, but not with the overall final margin status. The high FS accuracy supports its use to guide the extent of surgery. However, FS cannot be used to predict the overall final margin status. Recognition of the histological artifacts inherent to the FS procedure are important to ensure appropriate utilization.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Concrete production entails a high amount of freshwater consumption. Moreover, as heavy-weight concrete production is cost-inefficient for mass structures, such as radiation shielding facilities, the ...need for seawater and other recycled/waste materials to produce sustainable concretes for radiation shielding applications cannot be overemphasized. Hence, this paper investigates the radiation shielding performance of fresh water and seawater-mixed concrete mixes produced using various waste coarse aggregates, including recycled aggregate and electric arc furnace steel slag (EAF-SS). Partial simultaneous replacements of the two coarse aggregate types are also considered. Aimed at addressing material sustainability, a total of ten such concrete mixtures were designed and produced by varying the type of mixing water with different combinations of the normal and waste coarse aggregates while maintaining the cement content and water/cement ratio constants. These mixtures were then tested for their unit weight, compressive strength, and nuclear radiation response through gamma-ray intensity detection. The mixes' compressive strengths ranged from 30.8 to 49.8 MPa, all of which met the specifications for structural concrete. Linear attenuation coefficients were computed based on the radiation experimental results for the different mixes. Three of the specimens passed the minimum requirement to be considered heavy-weight concretes. Regardless of concrete strength, the unit weight of the mixes and the type of water (fresh versus seawater) used for mixing had an impact on radiation shielding performance. The maximum compressive strength was attained in the fresh water-mixed concrete fully incorporating EAF-SS as coarse aggregate – 13% over that of the concrete with natural aggregate. Moreover, the use of EAF-SS enhanced the radiation shielding performance of concrete by 13–19%. Using local seawater improves radiation shielding by 4–5% while pursuing sustainable concrete production for nuclear applications. A mixture's unit weight and chemical composition – particularly the existence of hematite – are crucial factors in the effectiveness of radiation shielding. The variations in gamma-ray transmission reductions between mixtures confirm the feasibility of the materials utilized.
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•RC beams failed in flexure while RC beams + CFRP failed in shear.•RC beams + CFRP failure loads are lower than theoretical flexural and shear strengths.•Higher CFRP ratio delaminates ...more and failure load approaches a steady value.•Analytical load–deflection agrees with the experiment up to a certain % of CFRP.•FE modeling captures the behavior and an adjusted capacity model is provided.
This study investigates the shear behavior and debonding characteristics of initially ductile RC beams (failing in flexure when unstrengthened) at the verge of transitioning to a more brittle shear failure upon strengthening using external flexural carbon fiber reinforced polymer (CFRP). Despite the absence of shear CFRP strengthening, various degrees of improvement in the shear capacity were achieved depending on the flexural CFRP amount. However, steeper shear cracks that bypass the stirrups in addition to the nonyielding stirrups results in shear capacities that cannot be reliably predicted using the ACI and other similar codes’ provisions. Instead of adopting capacity models that focus on the shear failure alone or the crack-induced debonding as oneway cause-effect (shear crack-debonding) relationship, a more holistic capacity prediction approach (calibrated with finite element anlaysis) that considers the synergistic effect between the shear failure and the CFRP debonding is provided. Since any enhancement in flexure must be checked against shear, the presented capacity prediction approach could be a more handy means to assess the shear strengthening level needed in such cases where the flexural strengthening is insufficient to achieve the overall structural upgrade sought. The designed beams – i.e. at the verge of changing failure mode with flexural FRP strengthening – and the test program could serve as a bond assessment philosophy in the sense that this upper bound brittle failure mechanism provides more realistic behavior of the crack-induced debonding performance of FRP-strengthened beams. Analytical load–deflection assessment of the tested specimens is also provided.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this work, tri-phase direct dual S-scheme ZnO–V2O5–WO3 heterostructured nanocomposite and pure ZnO, V2O5, and WO3 nanoparticles were synthesized by using a facile co-precipitation approach to ...investigate antibacterial and photocatalytic characteristics of the grown nanocomposite. The physical properties of as-synthesized products were examined by employing characterization techniques such as Scanning electron microscope (SEM), Energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Raman, Fourier transform infrared spectroscopy (FTIR), and UV–vis spectroscopy. The XRD results confirmed the formation of pristine ZnO, V2O5, WO3 nanoparticles and the existence of diffraction peaks related to hexagonal phase ZnO, orthorhombic V2O5, and monoclinic phase of WO3 in ZnO–V2O5–WO3 nanocomposite. The variation in structural parameters was studied by SSP, Scherrer plot, and W–H models. The energy bandgap of nanocomposite (2.63 eV) was calculated from UV–vis spectroscopy, which indicated the usability as a photocatalyst under direct sunlight. FTIR and Raman's spectra also supported the formation of the ZnO–V2O5–WO3 nanocomposite. Spherical and roughly hexagonal morphology were seen in SEM images. EDX analysis has confirmed the existence of Zn, V, W, and O in the nanocomposite. The antibacterial test against Klebsiella pneumonia, Staphylococcus aureus, Proteus Vulgaris, and Pseudomonas aeruginosa bacteria showed higher activity. The photocatalytic performance of the ZnO–V2O5–WO3 nanocomposite (99.8%) was the highest against methylene blue (MB) as compared to pure ZnO (78.8%), V2O5 (85.8%), and WO3 (80.0%) under natural sunlight. The degradation efficiency of ZnO–V2O5–WO3 against cresol red (CR), rhodamine-B (RhB), methyl orange (MO), safranin-O (SO), and methyl red (MR) dyes was 67.0%, 86.6%, 98.0%, 76.8%, and 99.0%, respectively, under direct sunlight in 80 min. Different schematic models are designed to illustrate the photocatalytic reaction mechanism, whereas the separation of charge carriers and enhanced photocatalytic performance can be efficiently explained by S-scheme.
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•Facile synthesis of tri-phase direct dual S-scheme ZnO–V2O5-WO3 heterostructured NC and pure ZnO, V2O5, and WO3 NPs.•SEM, EDX, XRD, Raman, FTIR, and UV–vis was carried out.•The photocatalytic performance was tested against MB, CR, RhB, MO, SO, and MR dyes.•S-scheme is more efficient than other schemes for enhancing photocatalytic activity.•The antibacterial test against different bacteria strain was performed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
