Search Results (28)

This study investigates the use of cotton ropes (CRs) as a sustainable and cost-effective substitute for synthetic fiber-reinforced polymers for concrete confinement, offering significant environmental benefits such as lower CO₂ emissions and reduced energy consumption. The work evaluates the effectiveness of CR strips for confining concrete, including scenarios with recycled concrete aggregates (ReCA). Compressive strength improvements varied among specimens, with Specimen I-3F showing a 140.52% increase and Specimen II-3F achieving a 46.67% improvement. Strip configurations for Type I recycled aggregate concrete (RAC) outperformed full wraps on Type II RAC, exemplified by Specimen I-3S’s 84.51% improvement. Ultimate strain enhancements ranged from 915% to 4490.91%, driven by the significant rupture strain of cotton rope confinement. For Type I RAC, complete wrapping significantly outperformed strip configurations by 56%, 50%, and 32% in ultimate strength improvement for 1, 2, and 3 layers, respectively. The confinement ratio, varying from 0.10 to 0.70, greatly influenced the compressive behavior, with compressive strength normalized by unconfined strength increasing consistently with the confinement ratio. A minimum confinement ratio of roughly 0.40 is required to achieve an increasing second part in the compressive behavior. The initial parabolic branch was modeled using Popovics’ formulation, revealing an elastic modulus approximately 20% lower than ACI 318-19 predictions. The second branch was described using a linear approximation, and nonlinear regression analysis produced expressions for key points on the idealized compressive curve, enhancing model accuracy for CR-confined RAC. The $R^2$ values for the nonlinear regression analysis performed on experimental results were greater than 0.90. This study highlights the effectiveness of neural network expressions to predict the compressive strength of CR-confined concrete. A strength reduction (ratio of full wrap and strip wrap height CRs) factor of 0.67 was proposed and used for strip-wrapped specimens. It was seen that the neural network models also predicted the compressive strength of partially wrapped specimens with reasonable accuracy using the strength reduction factor. Full article

Background: Routine activated partial thromboplastin time (APTT) and prothrombin time (PT) measurements do not indicate hypercoagulability in patients with acute myocardial infarction (AMI) and acute cerebral infarction (ACI). Methods: Hypercoagulability in patients with AMI or ACI was evaluated using a clot waveform analysis of the APTT or a small amount of tissue factor activation assay (sTF/FIXa). In the CWA, the derivative peak time (DPT), height (DPH), width (DPW), and area the under the curve (AUC) were evaluated. Results: The APTT did not indicate hypercoagulability, but the second DPT of CWA-sTF/FIXa was significantly shorter in patients with ACI than in healthy volunteers (HVs). The first DPH values of CWA-APTT and CWA-sTF/FIXa in patients with ACI and AMI were significantly higher than in HVs. In the receiver operating characteristic (ROC) analyses of ACI or AMI vs. non-thrombosis, the AUC was >0.800 in the DPHs of CWA-APTT and CWA-sTF/FIXa. The AUC of CWA-APTT and CWA-sTF/FIXa in patients with AMI and ACI was significantly higher than in HVs. The AUC/second DPT of CWA-APTT and CWA-sTF/FIXa in patients with AMI and ACI was significantly higher than in HVs. Regarding the ROC analyses of ACI or AMI vs. HVs, the AUC of ROC was higher than 0.800 in the AUC and AUC/second DPT of CWA-APTT and CWA-sTF/FIXa. Conclusions: The AUC/second DPT of CWA-APTT and CWA-sTF/FIXa may be a useful parameter for detecting a hypercoagulable state in patients with AMI and ACI. Full article

Climate change increases the risk of coffee yield due to the genotype-dependent effects of water deficit on coffee physiology. The goal of this research was to evaluate how water deficit altered the physiological and growth characteristics of arabica coffee (Coffea arabica L.). Water status, photosynthetic response to CO₂ intercellular concentration (A/C_i curves) and growth parameters were evaluated in seedlings of four genotypes (Catimor ECU 02, Cavimor ECU, red Caturra and Sarchimor 4260). Most of the physiological traits evaluated differed significantly among genotypes. Between control and water deficit plants, significant variations occurred in the A/C_i parameters, showing a wide range of values for net photosynthetic rate, stomatal conductance, and water use efficiency, with decreases ranging from 4 to 74%. Maximum electron transport rate through photosystem II, highest rate of RuBisCO carboxylation, and triose phosphate utilization rate were all strongly decreased by water deficit 61% (red Caturra and Sarchimor 4260), followed by Cavimor ECU (35%) and Catimor ECU 02 (24%). Differences in response to water deficit among genotypes suggest possible genotypic differences in tolerance. The results indicated that Catimor ECU 02 and Cavimor ECU were less sensitive to water deficit, while red Caturra and Sarchimor 4260 were the most susceptible. Full article

The accurate identification of pigments is of principal relevance in the field of cultural heritage conservation and restoration practices. In this preliminary study, a first attempt to set up a procedure for accurate red pigment identification, based on the assessment of the correlations existing between visible reflectance spectrometry (vis-RS) and Raman data, is presented. The proposed approach involved the realization of a library consisting of data acquired on a set of 35 pure red historical pigments supplied by ^©Kremer Pigmente. In particular, vis-RS data, collected through a Konica Minolta CM-2600d spectrophotometer, were registered, together with the position of the Extrema Points (E.P.s) encompassing both the maximum and minimum points of the first derivative of the % spectral reflectance factor (SRF%) curves. Portable Raman spectroscopy measurements were collected by a B&W Tek Inc. portable Raman spectrometer equipped with a 785 nm laser. For each tested pigment, the positions and relative intensities of the characteristic Raman peaks were considered. The library was then tested for the characterization of the red/reddish painted areas of the medieval wall painting located within The Norman Castle of Aci Castello (Catania, Italy), and was shown to be essential for the unambiguous identification of the pigment used. It is worth noting that this study represents the first novel attempt to establish a reliable and efficient methodology for pigment identification, offering promising prospects in reducing uncertainties and ambiguities arising from the application of a single stand-alone approach. Full article

In this work, a new voltammetric procedure for acyclovir (ACY) trace-level determination has been described. For this purpose, an electrochemically activated screen-printed carbon electrode (aSPCE) coupled with well-conductive electrolyte (CH₃COONH₄, CH₃COOH and NH₄Cl) was used for the first time. A commercially available SPCE sensor was electrochemically activated by conducting cyclic voltammetry (CV) scans in 0.1 mol L⁻¹ NaOH solution and rinsed with deionized water before a series of measurements were taken. This treatment reduced the charge transfer resistance, increased the electrode active surface area and improved the kinetics of the electron transfer. The activation step and high conductivity of supporting electrolyte significantly improved the sensitivity of the procedure. The newly developed differential-pulse adsorptive stripping voltammetry (DPAdSV) procedure is characterized by having the lowest limit of detection among all voltammetric procedures currently described in the literature (0.12 nmol L⁻¹), a wide linear range of the calibration curve (0.5–50.0 and 50.0–1000.0 nmol L⁻¹) as well as extremely high sensitivity (90.24 nA nmol L⁻¹) and was successfully applied in the determination of acyclovir in commercially available pharmaceuticals. Full article

An experimental investigation on partially PBO (short of Polyparaphenylenebenzobisthiazole) FRCM (Fiber Reinforced Cementitious Mortar) confined clay brick masonry columns has been conducted. Ten small-scale specimens measuring 445 mm high with a square cross-section of the 250 mm side have been tested under monotonic axial loading until collapse. Two columns were unconfined, while the remaining ones were confined with single-layer PBO FRCM jackets varying the geometric configuration along their height. The vertical spacing ratio sf’/sf, being sf’ and sf the center-to-center and the net spacings between two consecutive jackets, respectively, was considered as the key parameter of the confinement configuration. The failure modes, stress–strain curves and peak axial stress and strain values are reported. The experimental results have been compared to the predictions of models found in the Italian guidelines CNR DT 215/2018 and the American ACI 549-R20 standards. The main aspects analyzed involved (i) the evaluation of the effectiveness of partial confinement on the mechanical response of columns, (ii) the definition of the mechanical and geometrical parameters that influence the structural response of partially confined columns, and (iii) the development of appropriate analytical models for the prediction of the resisting capacity of masonry columns partially confined with PBO FRCM. Full article

Glass fiber-reinforced polymer (GFRP) of high performance, as a relatively ideal partial or complete substitute for steel, could increase the possibility of adapting structures to changes in harsh weather environments. While GFRP is combined with concrete in the form of bars, the mechanical characteristics of GFRP cause the bonding behavior to differ significantly from that of steel-reinforced members. In this paper, a central pull-out test was applied, according to ACI440.3R-04, to analyze the influence of the deformation characteristics of GFRP bars on bonding failure. The bond–slip curves of the GFRP bars with different deformation coefficients exhibited distinct four-stage processes. Increasing the deformation coefficient of the GFRP bars is able to significantly improve the bond strength between the GFRP bars and the concrete. However, while both the deformation coefficient and concrete strength of the GFRP bars were increased, the bond failure mode of the composite member was more likely to be changed from ductile to brittle. The results show members with larger deformation coefficients and moderate concrete grades, which generally have excellent mechanical and engineering properties. By comparing with the existing bond and slip constitutive models, it was found that the proposed curve prediction model was able to well match the engineering performance of GFRP bars with different deformation coefficients. Meanwhile, due to its high practicality, a four-fold model characterizing representative stress for the bond–slip behavior was recommended in order to predict the performance of the GFRP bars. Full article

Alkali-activated concrete is an eco-friendly construction material that is used to preserve natural resources and promote sustainability in the construction industry. This emerging concrete consists of fine and coarse aggregates and fly ash that constitute the binder when mixed with alkaline activators, such as sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃). However, understanding its tension stiffening and crack spacing and width is of critical importance in fulfilling serviceability requirements. Therefore, this research aims to evaluate the tension stiffening and cracking performance of alkali-activated (AA) concrete. The variables considered in this study were compressive strength (f_c) and concrete cover-to-bar diameter (C_c/d_b) ratios. After casting the specimen, they were cured before testing at ambient curing conditions for 180 days to reduce the effects of concrete shrinkage and obtain more realistic cracking results. The results showed that both AA and OPC concrete prisms develop slightly similar axial cracking force and corresponding cracking strain, but OPC concrete prisms exhibited a brittle behavior, resulting in a sudden drop in the load–strain curves at the crack location. In contrast, AA concrete prisms developed more than one crack simultaneously, suggesting a more uniform tensile strength compared to OPC specimens. The tension-stiffening factor (β) of AA concrete exhibited better ductile behavior than OPC concrete due to the strain compatibility between concrete and steel even after crack ignition. It was also observed that increasing the confinement (C_c/d_b ratio) around the steel bar delays internal crack formation and enhances tension stiffening in AAC. Comparing the experimental crack spacing and width with the values predicted using OPC codes of practice, such as EC2 and ACI 224R, revealed that EC2 tends to underestimate the maximum crack width, while ACI 224R provided better predictions. Thus, models to predict crack spacing and width have been proposed accordingly. Full article

Elevated CO₂ concentration (eCO₂) generally increases plant growth by improving photosynthesis, but it is unclear whether eCO₂ can alleviate the negative effects of elevated temperatures, especially in high-temperature years. Manipulative experiments with elevated [CO₂] and temperature were conducted in North China to understand the effect of elevated CO₂ concentration and temperature on wheat. The photosynthesis, A_n–PAR and A–C_i curve parameters, growth period, biomass, yield component, and yield of wheat were investigated under different [CO₂] (around 400 and 600 ppm) and temperatures (ambient temperature and ambient temperature +2 °C) for 3 years by using controlled chambers. Results showed that elevated temperature significantly shortened the growth period and decreased the yield and biomass of wheat. Elevated [CO₂] significantly increased the maximum net photosynthetic rate (A_nmax) but reduced the maximum carboxylation rate (V_cmax) and the maximum electron transport rate (J_max). The extremely high temperature during the grain filling period in 2019 exerted a serious negative impact on wheat production. Elevated [CO₂] stimulated photosynthesis, increased kernel number per spike, and extended the duration of the grain filling period, which consequently increased biomass and grain yield under elevated temperatures in normal years (2018 and 2020). Although the combination of CO₂ and temperature reduced photosynthesis and biomass, it also alleviated the negative impact of elevated temperatures on grain yield to some extent under extremely high temperature during the grain filling period in 2019. The mitigative effect of eCO₂ under extreme high temperature is limited, and planting early-maturing cultivars or increasing the genotypes of kernel number per spike help to escape the extreme high temperature of the critical growth period. Full article

An experimental study on the shear behavior of dune sand reinforced concrete (DSRC) deep beams was conducted to determine the feasibility of using dune sand (DS) in engineering. Nine DSRC deep beams were designed and thoroughly analyzed for failure modes, diagonal cracks, and load–deflection curves in this study. The results showed that the shear strength and ductility of DSRC deep beams increased when the DS replacement rate was 30%, but the opposite effect occurred when the DS replacement rate was 50%. To analyze the differences in the effects of the DS replacement rate, shear span-to-depth ratio, concrete strength, and stirrup ratio on the shear strength of DSRC and normal reinforced concrete (NRC) deep beams, a total of 227 shear experimental tests of NRC deep beams were conducted. Furthermore, four national codes were evaluated and compared based on experimental data. The evaluation results showed that the four codes underestimated the shear strength of DSRC and NRC deep beams. Among them, ACI 318–11 provided more reliable predictions for both NRC and DSRC deep beams. It is in this regard that a new empirical model for predicting the shear strength of DSRC deep beams is proposed, in which a reduction coefficient of the DS replacement rate is incorporated. The verification results indicates that the predicted results of the proposed model are in good agreement with the experimental results. Full article

PBL stiffeners, made of thin-walled steel plates with circular openings and welded to the steel tube of a square concrete-filled steel tubular (CFST) column, can improve the combined effect effectively by co-carrying axial compressive forces and confining the concrete core. A numerical simulation study based on the previous test was conducted to study the ultimate strength of the CFST stub column with PBL stiffeners. Finite element models of CFST with different stiffeners were made and verified by the test results of typical failure modes and load–strain curves of specimens. The parameter study was conducted, including PBL stiffener detailing (i.e., material strength, stiffener thickness, opening diameter, and opening spacing). Finally, based on the study and analysis results, an ultimate bearing capacity prediction formula was proposed, which can reasonably predict the bearing capacity of a square CFST column with longitudinal or diagonal stiffeners, while the methods in ACI, BS5400, EC4, AIJ, and DBJ were more conservative. Full article

Repair materials have been developed in this research by adding micro-synthetic fibers in cement-based mortar. In addition, accelerator is incorporated in the mortar to obtain high early strength of the repair materials. Their shrinkage behavior is of interest. This study aims to determine the shrinkage of the micro-synthetic fiber-reinforced mortar and propose models to reflect their shrinkage behavior. The results show that rapid developments of shrinkage are observed at an early age where the 3-day shrinkage already attains about 40–50% of the 84-day shrinkage value. Moreover, after 14 days of age the shrinkage curves tend to approach the asymptotic value. The ACI 209.2R-08 and CEB-MC 90-99 models do not reflect the shape of the shrinkage curves of the micro-synthetic fiber-reinforced mortar. Therefore, this research proposes a modified ACI 209.2R-08 and CEB-MC 90-99 that can describe the shrinkage behavior of the micro-synthetic fiber-reinforced mortar. The accuracy of the modified models has been confirmed quantitatively using the method of best fit line, residual analysis, and coefficient of error. Full article

Concrete-filled steel tubes present excellent structural and constructional performances because they ideally combine the advantage of concrete and steel tube. Thus, they are widely used in civil infrastructures. However, they inevitably suffer from either hard compacting or high costs. Thus, convenient and rapid construction for compacting concrete and cost saving are the urgent challenges for concrete-filled steel tubes. Therefore, this study investigates filling a thin-walled steel tube with self-compacting concrete to solve the challenges presented by traditional concrete-filled steel tube columns, such as poor compacting performance and high costs. This experimental study tests self-compacting concrete-filled thin-walled steel tube (SCCFTST) columns under concentric compression from loading to failure. Effects of wall thickness of the thin-walled steel tube on the failure modes, load-deformation behaviors, and the ultimate loads of the SCCFTST columns are comprehensively investigated. The ultimate loads between experiments and their calculated values in terms of design codes are also compared. The results suggest that buckling on thin-walled steel tube surface is the typical failure mode. The amount of local buckling increases with decreasing wall thickness, and the decreasing rate of the load-deformation curves in the descending branch decreases by increasing the wall thickness, as well as the ultimate load increasing with increases wall thickness. The ACI and CECS are the most conservative and accurate design codes, respectively, for predicting the ultimate load. Therefore, the SCCFTST columns can be used as structural components in civil infrastructures and their peak loads can be calculated using design codes for conventional concrete-filled steel tube columns. However, modification measures must be taken while predicting the ultimate loads of the SCCFTST columns by design codes. The experimental results of this paper can contribute towards the application of SCCFTST columns in practice. Full article

With the increased interest in the inherent fire resistance of organic insulators, various precast concrete insulation panels have been developed. However, precast concrete insulation panels still have structural and fire resistance problems resulting from a low composite action and unclosed cross-sectional details. To improve composite action and fire resistance, this study proposes the closed cross-sectional details of insulator panels with lightweight aggregate concrete, insulation material, and wire mesh. The objective of this study is to examine the flexural–shear performance of precast lightweight concrete panels with closed cross-sectional details developed for exterior cladding with high insulation capacity. Six full-sized insulation panels were tested under two-point top loadings. The main investigated test parameters to vary the moment–shear ratio of the insulation panels were the amount of the shear reinforcement and shear span–effective depth ratio. Test results indicate that the insulation panels with moment–shear ratios of 2.60 or higher were governed by shear, indicating that the longitudinal bars remained in an elastic state until the peak load of the insulation panels was reached. Thus, an increase in the moment–shear ratio of the insulation panels led to more brittle failure characteristics. Meanwhile, the insulation panels governed by flexure exhibited plastic flow performance in the applied load–deflection curve and well-distributed cracks. In particular, the maximal flexural moments of insulation panels with moment–shear ratios of 0.75 or less were higher than those calculated from the equations specified in ACI 318-19, indicating that the composite action was fully exerted. Overall, the developed insulation panels with cross-sectional details must be designed to a have moment–shear ratio of 0.75 or less to fulfil the ductile response under extreme lateral loads and exert full composite action. Full article

The ordinary Portland cement (PC) manufacturing process emits toxic carbon dioxide into the environment. Minimizing cement consumption in the construction industry is a major scholarly priority. This paper studies the comparison of reinforced Portland cement concrete and geopolymer concrete beams, in which rice husk ash (RHA) is used as a partial replacement for cement. The study aims to determine the optimum mix proportion of Portland cement concrete with RHA (PC-RHA) and geopolymer concrete with RHA (GC-RHA) for compressive strength that meets the requirements for normal strength concrete of 18, 25, and 32 MPa and compares to ones of the control PC without RHA. Then, the load behaviors and the failure modes of the reinforced PCC beam and reinforced GC beam using RHA as partially PC (PC-RHA beam and GC-RHA beam) were investigated. The obtained experimental load capabilities were also compared to ones predicted by the equation for designing reinforced concrete beams developed by ACI Committee 318. According to the test results, the compressive strength of the PC-RHA and GC-RHA decreased when there was a higher proportion of RHA replacement in the concrete. In terms of the structural behavior, all the PCC, PC-RHA, and GC-RHA beam curves are bilinear up to the first crack load and before the yield load, then become nonlinear after the yield load of the beam specimens. The maximum crack width of the GC-RHA beam was less than that of the PC-RHA beam. Furthermore, the GC-RHA beam was more ductile than the PC-RHA beam. Finally, the ACI equation provides reliable predictions with a margin of error of 4 to 7%. This concludes that the experimental load capabilities of the PC-RHA beam and GC-RHA beam were consistent with the ACI design equation. Full article