Control Specimens Research Articles

Effect of Elevated Temperature on Compressive Strength of MICCP and EICCP Biocemented Mortar.

Recently biocementation has got attention of many researchers worldwide as one of the most potent techniques for sustainable construction. Several studies have been carried out worldwide on biocementation by urea hydrolysis. Biocementation by bacterially induced calcium carbonate precipitation by different bacterial species has been among the most widely researched areas in this field. Biocementation has proved efficient in enhancing the strength and durability of cement-based materials. However, no significant work has been carried out to determine the performance of biocemented specimens at elevated temperatures. This study primarily focuses on the effects of high temperatures (300, 450, and 600°C) on the compressive strength of two types of biocemented specimens prepared by using ureolytic bacteria and rich in urease watermelon seeds. The motive behind testing these two types is to know how the enzyme induced or microbially induced react to temperature elevation. Also, the effect of different cooling techniques (viz., natural cooling, water spray cooling and fire extinguishing foam spray cooling) were studied. These cooling techniques were selected so as to check which cooling technique should be preferred in case of fire situation in a cement-based structure. Results show that biocemented specimens can perform very good up to the temperature 300°C as compared to control specimens in terms of compressive strength. At 450°C temperature, there is no significant difference in compressive strengths of control and biocemented specimens. When the specimens were subjected to 600°C, biocemented specimens showed lower strength than control specimens at the same temperature due to denser microstructures. Thus, biocemented cement mortar should not be used in reactors, muffles and ovens where temperature would go above 450°C.

The impact of bleaching using 15% carbamide peroxide on surface properties of CAD-CAM composite structures

This study aims to evaluate the effects of the home bleaching method on the surface microhardness and surface roughness of both polished and unpolished CAD-CAM resin composite materials. A polymer-infiltrated ceramic network (PICN) block, Enamic (VE), along with four resin composite blocks (RCB) (Grandio [GN], Lava™ Ultimate [LV], BRILLIANT Crios [B], and Cerasmart [CS]), were prepared to dimensions of 14 mm × 12 mm × 2 mm and were categorized into unpolished and polished groups (n = 4). Microhardness measurements were conducted using a Vickers microhardness tester (300 gf load for 20 s) at various time points: before home bleaching, after home bleaching with 15% Opalescence for 8 h and for 56 h, 24 h after bleaching, and one month after bleaching. Surface topography was examined using a stylus contact profilometer (n = 4) and a scanning electron microscope (n = 3) at ×40 k magnification. Control specimens from each group were also measured. Data were analyzed using one-way ANOVA, Tukey’s post hoc test, two-way ANOVA and an independent t-test. The polished samples demonstrated a decrease in hardness after 8 h of bleaching, with the most significant reduction observed in VE, followed by GN, LV, CS, and BR. Significant differences were noted between all materials except for CS and LV. After 56 h, VE exhibited the greatest decrease in hardness, followed by GN, LV, BR, and CS, with significant differences between all materials except BR and CS. In the unpolished group, VE showed the highest reduction in hardness after 8 h of bleaching, followed by LV, GN, BR, and CS. After 56 h, the order was VE, LV, GN, CS, and BR, with significant differences observed between all materials except BR and CS. Similar trends in hardness reduction were observed at 24 h and 1 month post-bleaching. Additionally, hardness was significantly reduced after polishing for all materials. Overall, the reduction in hardness was significantly influenced by the type of material, the time, and the interaction between these factors (p < 0.05). Home bleaching using 15% carbamide peroxide significantly decreased microhardness. This effect was more pronounced in unpolished groups and with prolonged exposure. Further studies are recommended to determine the suitable concentration and duration of 15% carbamide peroxide application to ensure its use is safe for CAD-CAM materials.

Temperature Prediction for the Sirius-2c Nuclear Propulsion Fuel Experiment Conducted at the TREAT Facility

This study presents a predictive transient model developed for simulating experiments at the Transient Reactor Test (TREAT) Facility and its application to the Sirius-2c experiments. We introduce an innovative approach to predict control rod motion, reactor power, and specimen temperature during transient experiments using Griffin, BISON, and the stochastic tool packages of the Multiphysics Object-Oriented Simulation Environment. The model provides a blind prediction of the specimen temperature evolution during transient tests given a desired power signal. Initially, our model accurately predicts the transient motion of the control rods to achieve the desired reactor power profile. Subsequently, it predicts the specimen temperature based on the power deposited within the specimen. The simulation results show strong agreement with the measured reactor power and control rod positions; however, the specimen temperature is slightly overpredicted, primarily because of assumptions about surface emissivities. When considering a more accurate set of specimen emissivities, the predicted temperature aligns exceptionally well with the measured values according to post-analysis results. The simulation results will support the design and analysis of the National Aeronautics and Space Administration sponsored Sirius series of experiments for nuclear thermal propulsion applications, and the model can be utilized to assist in the design and optimization of new experiments to be conducted at the TREAT Facility.

Enhancing radiation hardness of microelectronics through stress-relief milling

Single event effects (SEE) in microelectronic devices are predominantly studied from the perspective of electrical charge generation and collection. This study introduces a multi-physics concept by investigating the impact of highly localized mechanical stress in electrically sensitive regions, such as the gate in a transistor. Our hypothesis is that reducing mechanical stress beneath the gate will decrease voltage transients caused by SEE by limiting charge generation and diffusion. To explore this electro-mechanical coupling in relation to SEE, we milled a microscale trench in the substrate beneath a transistor of the LM124 operational amplifier using a focused ion beam, thereby alleviating mechanical stress in the vicinity of the trench. We then perform pulsed laser SEE testing on the stress-relieved transistor and a control specimen without a micro-trench modification. Our experimental results demonstrate a significant decrease in single event transient peak amplitude and collected charge in the stress-relieved device compared to its pristine counterpart under identical pulsed laser conditions. These findings support our hypothesis and suggest that mitigating mechanical stress localizations could inform the design and fabrication of radiation-hardened electronics.

Pathological and Molecular Characterization of Grass Carp Co-Infected with Two Aeromonas Species.

The grass carp (Ctenopharyngodon idella) is highly susceptible to infections caused by Aeromonas species, particularly A. hydrophila and A. veronii. However, the immunological mechanisms underlying co-infection by these pathogens remain largely uncharted. This study investigated the pathogenesis and host immune response in grass carp following concurrent infection with A. hydrophila and A. veronii. Mortality was observed as early as 24 h post-infection, with cumulative mortality reaching 68%. Quantitative analysis demonstrated significantly elevated bacterial loads in hepatic tissue at 3 days post-infection (dpi). Histopathological evaluation revealed severe hepatic lesions characterized by cellular necrosis, cytoplasmic vacuolization, and hemorrhagic manifestations. Comparative transcriptomic analysis of hepatic tissues between co-infected and control specimens identified 868 and 411 differentially expressed genes (DEGs) at 1 and 5 dpi, respectively. Gene ontology and KEGG pathway analyses revealed significant enrichment of immune-related genes primarily associated with Toll-like receptor signaling and TNF signaling cascades. Notably, metabolic pathways showed substantial suppression while immune responses were significantly activated after infected. These findings provide novel insights into the host-pathogen interactions during Aeromonas co-infection in grass carp, which may facilitate the development of effective prevention and control strategies.

Identification of key genes associated with oxidative stress in ischemic stroke via bioinformatics integrated analysis

BackgroundIschemic stroke (IS) is a common cerebrovascular disease. Although the formation of atherosclerosis, which is closely related to oxidative stress (OS), is associated with stroke-related deaths. However, the role of OS in IS is unknown.MethodsOS-related key genes were obtianed by overlapping the differentially expressed genes (DEGs) between IS and normal control (NC) specimens, IS-related genes, and OS-related genes. Then, we investigated the mechanism of action of key genes. Subsequently, protein–protein interaction (PPI) network and machine learning algorithms were utilized to excavate feature genes. In addition, the network between feature genes and microRNAs (miRNAs) was established to investigate the regulatory mechanism of feature genes. Finally, quantitative PCR (qPCR) was utilized to validate the expression of feature genes with blood specimens.ResultsA total of 42 key genes related to OS were acquired. Enrichment analysis indicated that the key genes were associated with oxidative stress, reactive oxygen species, lipid and atherosclerosis, and cell migration-related pathways. Then, 6 feature genes (HSPA8, NCF2, FOS, KLF4, THBS1, and HSPA1A) related to OS were identified for IS. Besides, 6 feature genes and 255 miRNAs were utilized to establish a feature genes-miRNA network which contained 261 nodes and 277 edges. At last, qPCR results revealed that there was a trend for higher expression of FOS, KLF4, and HSPA1A in IS specimens than in NC specimens. Additionally, HSPA8 expression was significantly decreased in the IS specimens, which was consistent with the findings of the GEO database analysis.ConclusionIn conclusion, 6 feature genes (HSPA8, NCF2, FOS, KLF4, THBS1, and HSPA1A) related to OS were mined by bioinformatics analysis, which might provide a new insights into the evaluation and treatment of IS.Clinical trial number: Not applicable.

Effect of changing the internal structure on the mechanical properties of three-dimensional-printed custom tray material: An in vitro study.

The main challenges to the widespread clinical application of three-dimensional (3D)-printed customized trays include cost and time limitations. This study examined how changing the internal structure of 3D-printed materials used for customized trays affects flexural strength (FS), flexural modulus (FM), manufacturing time, and material weight. Specimens (64×10×3.3mm) were printed using a light-sensitive liquid resin. The internal structures of control specimens were completely filled, whereas the internal structures of test groups comprised vertical bars spaced 1 mm (Test 1) or 2 mm (Test 2) apart. Specimens were weighed and then subjected to a three-point bending test to evaluate their FS and FM. Data were analyzed using one-way ANOVA and Tukey's test, with Weibull analysis applied to FS values. Control specimens had the highestFS (106±4 MPa), while Test 2 specimens demonstrated the highest FM (6101±1407 MPa). No significant differences were found between Test 1 and Test 2 specimens in FS or FM. Test 2 specimens had the lowest mean weight (1440±42 mg). Manufacturing times were 80min for control and Test 1 specimens and 60min for Test 2 specimens. Including spaces in the internal structure of 3D-printed customtray material saves material and manufacturing time while maintaining mechanical properties.

Biodiversity of the Bacterial and Fungal Microbiome and Associated Inflammatory Cytokine Profile in Chronic Rhinosinusitis.

Dysbiosis of the bacterial and fungal microbiome has been increasingly implicated in the pathogenesis of chronic rhinosinusitis (CRS). This study explores the relationship between microbiome and mycobiome biodiversity and type 2 (T2) versus non-type 2 (NT2) inflammation. Mucosal tissues from the ethmoid sinus were collected during endoscopic sinus (CRS) and skull base (controls) surgery between January 2020 and July 2021. Specimens underwent 16S rRNA (bacterial) and internal transcribed spacer (fungal) gene sequencing, along with cytokine analysis using the Luminex assay. Based on cytokine (IL-4, IL-5, IL-13) concentrations and the presence of eosinophils, CRS cases were classified into T2 or NT2 inflammatory profiles. The relationships between CRS endotype and the biodiversity of the microbiome and mycobiome were assessed. Specimens from 92 patients (30 control, 31 CRSwNP, 31 CRSsNP) were included in the analyses. Among 62 CRS cases, 20 exhibited T2 inflammation and 42 exhibited NT2 inflammation. Compared with control specimens, NT2 specimens exhibited significantly lower amplicon sequence variants (mean difference -149, 95% CI [-261, -37], p=0.007), Shannon index (-0.48 [-0.79, -0.16], p=0.002), and Simpson index (-0.003 [-0.005, -0.001], p=0.002) for bacterial alpha diversity. However, no significant differences in bacterial alpha diversity were observed between T2 specimens and controls, or between T2 and NT2 specimens. Fungal biodiversity did not differ significantly across endotype and control groups. Dysbiosis of the sinus bacterial microbiome is more strongly associated with a NT2-mediated inflammatory profile than with a T2-mediated inflammatory profile.

Effect of Chlorpyrifos on the Red Blood Cells Morphology of Common Carp (Cyprinus Carpio): A Hematological Study

Chlorpyrifos, a widely applied insecticide, enters waterways through runoff, affecting a wide range of aquatic species. The environmental impact of chlorpyrifos (CPF), a commonly used organophosphate pesticide, on aquatic organisms remains a significant concern due to its toxicity and persistence in ecosystems. This study evaluates the effects of CPF on the morphology of red blood cells (RBCs) in the common carp (Cyprinus carpio) to better understand its hematological toxicity. Common Carp were exposed to sublethal concentrations of CPF (0, 10, 20, and 30 µL) for duration of seven days. Blood samples were collected and examined for alterations in RBC morphology. Control specimens showed minimal morphological changes which were due to natural conditions, while CPF exposure induced a concentration-dependent increase in cellular abnormalities, including double nucleated cells, nuclear displacement, cell deformation, and fragmentation. The highest CPF concentration (30 µL) resulted in severe RBC damage, including nuclear pyknosis, loss of cell integrity, and necrosis. These findings suggest that CPF exposure leads to significant erythrocyte damage, which may compromise overall fish health and survival. The results underscore the need for stringent environmental monitoring and regulation of pesticide use to mitigate its detrimental effects on aquatic life.

Bacillus subtilis as a Novel Biological Repair Technique for Alkali-Activated Slag Towards Sustainable Buildings

Rebuilding using outdated methods and tearing down the buildings would have a negative impact on the environment without lowering carbon dioxide emissions or increasing sustainability. This study presents a novel approach to repair that considers environmental and sustainable factors. In contrast to conventional repair methods, the use of Bacillus subtilis as an external biological repair technique could offer a novel and sustainable solution, especially when used on alkali-activated slag (AAS) concrete. By breaking down urea into carbonate and ammonium, alkaliphile bacteria can precipitate calcium carbonate. In an environment rich in calcium, the bacteria’s opposing cell wall (CO32−) draws in positive calcium anions, which result in the formation of calcite crystals. The pores and crevices in the concrete are filled with these crystals. Incorporating bacteria into the fresh mixing of AAS ingredients is contrasted with using Bacillus subtilis culture in the water curing medium for pure AAS specimens. The effectiveness of both approaches was evaluated. Direct administration of Bacillus subtilis during mixing has a superior outcome regarding mechanical qualities rather than biological therapy, although their effective healing capability in closure of the crack width is similar. The enhancement in compressive and flexural strengths reached 51% and 128% over the control specimens. On the other hand, the healing rate reached nearly 100% for crack widths ranging from 400 to 950 µm. Furthermore, additional studies in this field led to some inferred correlations between the mechanical and durability aspects following healing.

Flexural and Shear Strengthening of High-Strength Concrete Beams Using near Surface Basalt Fiber Bars

Strengthening of reinforced concrete (RC) structures has become a primary challenge in civil engineering. Different materials and procedures have been used in order to repair or strengthen RC structures. In this research, the NSM-Basalt Bar (NSM-BFRP) technique was used to strengthen high-strength reinforced concrete beams in flexure and shear. Twelve beams were designed, constructed, and tested under four-point loads. Six of them were designed to have insufficient longitudinal steel reinforcement to make sure that the failure would be a flexural failure in the control beam. Whereas, the other six specimens were designed to have insufficient transverse steel reinforcement to make sure that the failure will be a shear failure in the control beam. All RC beams were strengthened using NSM-BFRP with different configurations except control specimens. The load deflection curve, the cracking pattern and the failure mode were evaluated. The experimental results reveal that NSM-BFRP bars significantly enhance the ultimate load capacity of high-strength concrete beams, with flexural capacity improvements of up to 33.33% and shear capacity enhancements of up to 63.5%. However, the use of BFRP bars also led to a shift in failure modes from flexural to shear, particularly in specimens with increased flexural reinforcement. The findings suggest that while NSM-BFRP bars are highly effective in strengthening concrete beams, careful consideration of the reinforcement configuration is necessary to avoid premature shear failure and ensure balanced structural performance.

Effect of Concrete Compressive Strength on the Bond Performance of Flexural Prisms Externally Strengthened with CFRP Laminates

This paper presents a study from an ongoing research project on the bond performance of flexural prisms strengthened using carbon-fiber-reinforced polymer (CFRP) laminates. The primary objective is to evaluate the effect of normal-strength concrete (NSC – 30MPa) and high-strength concrete (HSC - 50MPa) on the bond performance of plain concrete prisms notched at the mid-span and strengthened using CFRP laminates. Six of the twelve plain concrete prisms were strengthened using CFRP laminates, while the remaining prisms were unstrengthened to serve as control specimens. After achieving 28 days of curing in standard lab conditions, all prisms were tested under a four-point bending test. The ultimate mid-span deflection, maximum and ultimate strains at the mid-span, strain distribution at different positions along the length of the laminate, and bond/shear stress versus slip were analyzed to evaluate the bond performance of flexural prisms. The average ultimate load-carrying capacities and mid-span deflection of the NSC and HSC groups were 31.33 and 35.02 kN and 0.55 and 1.54 mm, respectively. The average CFRP strain values at the mid-span corresponding to the ultimate load were 5005 and 3544 με for the NSC and HSC groups, respectively. The maximum attained bond-stress values for NSC and HSC groups were 1.71 and 1.42 MPa, respectively. The corresponding values for slip at maximum bond stress are 0.27 and 0.24 mm for the two groups, respectively. It was concluded from the study that the concrete compressive strength has minimal effect on the flexural bond performance of concrete prisms externally bonded with CFRP laminates.

Rolled Soft Actuators Based on P(VDF‐TrFE‐CTFE) Electrospun Nanofibers

This study presents a novel rolled dielectric elastomer actuator, based on Poly(vinylidene fluoride‐trifluoroethylene‐chlorotrifluoroethylene), i.e., P(VDF‐TrFE‐CTFE), nanofibers that are fabricated by means of an electrospinning process. The soft actuator is realized by rolling a mat of two active layers, interleaved with two electrodes. The active layers are mats of P(VDF‐TrFE‐CTFE)‐based nanofibers, embedded in an elastomeric matrix of polydimethylsiloxane (PDMS). The electrodes are made of a mixture of carbon black and PDMS, bonded to the active layers by electrostatic adhesion force. The effects of the nanofibers in the soft actuators are investigated. Specimens of the soft actuator are realized that differ in the thickness of the nanofibrous mats used for the active layers, that is, 60 and 120 μm. An electromechanical characterization is performed to analyze and measure the axial force and axial displacements of the soft actuators when different electric fields are applied to the specimens in the transversal direction. The experimental results show that the presence of P(VDF‐TrFE‐CTFE)‐based nanofibers enhances the force‐to‐weight ratio of the soft actuators by up to 43.5%, and the energy density by up to 12.9%, compared to a control specimen with the active layer made of PDMS only.

Seismic performance enhancement of brick masonry walls by retrofitting with nominal RC bands: a study of diagonal compression tests

In-plane performance of un-reinforced brick masonry (URBM), retrofitted with nominal Reinforced Concrete (RC) bands, was investigated under diagonal compression tests using full-scale and half-scale specimens. The retrofitting technique is cost-effective, reliable, simple, easily implementable, and minimally intrusive. Six URBM wall specimens (three full-scale and three half-scale) served as control specimens, and similarly, six (three full-scale and three half-scale) were retrofitted with RC bands. All specimens were tested under diagonal compression in a computer-controlled servo-hydraulic universal testing machine using displacement-controlled scheme. Data on applied force and corresponding wall displacements were recorded. Responses of retrofitted specimens were compared with control specimens in terms of strength, deformation capacity, and failure patterns. Retrofitted specimens exhibited progressive damage due to ductile failure, showing a significantly increased deformation capacity and providing sufficient warning time before collapse. However, control specimens showed sudden catastrophic collapse due to sliding of bed-joints. Overall, retrofitted specimens demonstrated a significant enhancement of ductility. Next, a semi-empirical prediction formula for diagonal load capacity was established through macro-modelling approach and subsequent regression analysis to capture experimental results. From results, the proposed retrofitting scheme provides a promising solution for seismic risk reduction of existing deficient masonry structures in rural areas of the Indian subcontinent and elsewhere.

Role of Myofibroblasts in the Repair of Iatrogenic Preterm Membranes Subjected to Mechanical Stimulation.

We examined the role of myofibroblasts in regulating Cx43 and collagen structure in iatrogenic preterm amniotic membrane (AM) defects subjected to mechanical stimulation. Preterm AM specimens were collected from women undergoing planned preterm caesarean section after in utero intervention for correction of spina bifida by open fetal surgery (n=4 patients; preterm delivery at 34+0weeks to 35+0weeks). Control specimens taken 5cm away from the open fetal surgery defect site were compared with wound edge AM. In separate experiments, the effects of mechanical stimulation and co-treatment with Cx43 antisense on matrix and repair proteins were examined. Specimens were immunostained to detect αSMA and Cx43 in myofibroblasts and counterstained with DAPI to quantify nuclei shape. The direction of collagen fibrils in the wound edge region was examined by SHG imaging. Markers for matrix (collagen, elastin, GAG), inflammation (PGE2) and repair (TGFβ1) were examined by RT-qPCR and biochemical assays. In iatrogenic preterm AM specimens, the diameter of the open fetal surgery defect ranged between 3.5 and 7.5cm. At the wound edge of the open fetal surgery defect, αSMA positive myofibroblasts had deformed nuclei and showed abundant Cx43 localized in the cell bodies or formed plaques. In the fibroblast layer, collagen had degenerated in some regions or had polarity near the wound edge. In preterm AM defects, mechanical stimulation and Cx43 antisense increased the levels of collagen and elastin but not GAG or PGE2 release. Mechanical stimulation increased Cx43 and TGFβ1 gene expression. In open fetal surgery defects, myofibroblasts were elongated with collagen fibrils that either degenerated or had polarity. Whilst cells produced substantially higher Cx43 in the fibroblast than in the epithelial layer, they formed plaques, which may prevent migration and delay healing. Mechanical stimulation of preterm AM enhanced matrix repair proteins and the mechanotransduction should be explored to understand how Cx43 contributes to membrane integrity.

Effects of antifreeze admixtures on masonry performance at subfreezing temperatures

Concrete brick prisms prepared with Type S masonry mortar that included sodium nitrite and/or nanocellulose as potential antifreeze admixtures were cured for 28 days at −10 °C before measuring compressive and flexural bond strengths. Addition of sodium nitrite allowed masonry prisms cured at −10 °C to reach 88% and 86% of the compressive and flexural bond strengths, respectively, of control specimens cured at room temperature. Nanocellulose was only effective when used in combination with sodium nitrite, improving the compressive and flexural bond strengths by an additional 3% and 27%, respectively. Results are primarily attributed to the ability of the sodium nitrite to lower the freezing point, allowing hydration to continue in subfreezing conditions, as confirmed by results of companion tests on mortar samples. Both additives also reduced the required w/ c ratio and porosity. The findings offer a sustainable alternative to energy-intensive protective heating methods, potentially lengthening the construction season into colder periods.

EXPLORING THE USE OF PALM KERNEL SHELL AND PALM FIBRE AS SUSTAINABLE AGGREGATES IN CONCRETE

Palm kernel shells and palm fibres are leftover materials from the palm oil industry. However, they are not fully utilized and encounter disposal issues, particularly in Malaysia where they are produced in large quantities. This research aims to enhance sustainability and reduce palm waste disposal in Malaysia by exploring the potential of substituting palm waste for conventional aggregates. Six experiments were carried out to assess both the physical properties (including density, UPV, and water absorption) and mechanical properties (such as compressive strength, flexural tensile strength, and splitting tensile strength). The results indicate that a 35% palm kernel shell substitution is optimal, and it was able to produce a concrete specimen of 18 MPa cube strength, approximately 40% lower than the control specimen's 30 MPa. Despite this reduction, the strength is adequate for structures such as driveways, footings, and footpaths. The flexural and splitting tensile strength were the highest, at 4.99 MPa and 2.36 MPa, respectively. This batch also exhibited the best physical properties with a density of 2149 kg/m3, UPV of 3828 km/s, and water absorption of 9.31%. Additionally, the research also concludes that the addition of palm fibre in concrete tends to increase tensile strength by about 6%.

Bacillus cereus GS-5 immobilized sintered fly ash lightweight aggregate for strength, durability, and autonomous crack healing in bacterial concrete

This paper investigates the impact of ureolytic bacteria, specifically Bacillus cereus GS-5 immobilized sintered fly ash lightweight aggregate, on the self-healing, strength, and durability characteristics of the bacterial concrete. Different concentrations of bacterial cells (105 to 107 cells/mL) were used, and a part of conventional aggregate was replaced by microbe immobilized lightweight aggregate as part of producing concrete mixes. Various systematic tests, such as compressive strength, water absorption, rapid chloride permeability, and self-healing capability, were conducted after defined time intervals. The results of the experiments demonstrated that the compressive strength of the bacterial concrete increased by an average of 25.65% as compared to the control specimens. A simulated crack width of 0.5mm was successfully effectively healed in the specimen by microbial induced calcium carbonate precipitation. The SEM images confirmed the precipitation, structure, and dispersion of the calcium carbonate crystals, whereas XRD analysis revealed the formation of the calcite crystalline phases within the calcium carbonate crystals. Calcite precipitation resulted in reduced porosity of the bacterial concrete, which was confirmed by reduced chloride permeability (5% - 17%), water permeability (29% - 60%), and water absorption (3% - 32%) with respect to the control specimen. It has been concluded that Bacillus cereus GS-5 immobilized sintered fly ash lightweight aggregate would serve as an effective concrete admixture, providing advantages such as self-healing of cracks, better durability, and improved mechanical performances.

Experimental Investigation on the Effectiveness of EB-CFRP Confinement of Elliptical Concrete Columns

This paper presents the results of an experimental study involving 20 tests performed on elliptical concrete columns confined with externally bonded carbon fiber-reinforced polymer (EB-CFRP) laminates. The study aimed to evaluate the effects of elliptical aspect ratio (A/B) as well as confinement rigidity (number of EB-FRP layers) on confinement effectiveness. The experimental program consisted of one series of control concrete columns (unstrengthened) and three additional series, each one strengthened with one, two and three layers of EB-CFRP sheets, respectively. Furthermore, each series considered five elliptical aspect ratios (A/B) ranging from 1.0 to 1.6. Following compressive concentric tests until failure, the results were analyzed to characterize the confinement level with an increasing number of EB-CFRP layers as a function of the elliptical aspect ratio. The results show considerable enhancements in compressive strength and in the ductility of the confined columns. Furthermore, this improvement is amplified as the number of EB-CFRP layers increases, indicating a proportional relationship between the compressive strength and the number of CFRP layers. It is found that the ultimate strength of EB-CFRP-confined columns with three layers reached up to 130% compared to the control specimens. However, increasing the elliptical aspect ratio reduced the compressive strength and ductility of confined columns. This study investigated the relation between the CFRP hoop and axial strains and the elliptical aspect ratios. Moreover, through comparison, the results reveal that the prediction models proposed by the Canadian standards S806-12 and S6-19 do not capture the negative effect of the elliptical aspect ratio in confined concrete columns.

Numerical Response of Concrete-Filled Steel Tubular (CFST) Columns Externally Strengthened with FRP Composites Subjected to Cyclic Loading

The ultimate load-carrying capacity of concrete-filled steel tubular (CFST) columns exposed to monotonic loadings can be greatly increased by strengthening those columns, and the occurrence of the steel tube's outward buckling can be postponed. The current research aims to study the possibility of improving the structural characteristics of CFST columns exposed to cyclic loadings in terms of lateral load capacity and absorbed energy by strengthening them with different patterns of fiber-reinforced polymer (FRP) sheets. The ABAQUS software was used to create a three-dimensional (3D) non-linear finite element model (FEM) to simulate the behavior of FRP-strengthened CFST columns exposed to monotonic and cyclic loadings. After ascertaining the accuracy of the proposed model's results in successfully predicting failure patterns and lateral loads compared to the experimental results of tested specimens available in the literature, the model was used to create a parametric study. The parametric study focused on the impacts of the thickness, location, and length of the strengthening sheets on the failure pattern, lateral load-carrying capacity, stiffness, cumulative energy, absorbed energy, and viscous damping factor of the CFST columns exposed to cyclic loadings. The results revealed that the un-strengthened specimen displayed a maximum lateral load of 185 kN and a viscous damping factor of 45.2% at a lateral drift of 5.7%. On the other hand, strengthening the CFST column using five layers of FRP sheets exhibited the highest lateral load of all investigated columns (50% more than the un-strengthened specimen). Additionally, at a lateral drift of 5.7%, the decrease in viscous damping factor of CFST specimens due to strengthening using 1, 2, 3, 4, and 5 layers of FRP sheets with respect to the control specimen was 7.9%, 14.9%, 20.8%, 27.7%, and 30.3%, respectively.