Flexural Strength of Innovative Thin-Walled Composite Cold-Formed Steel/PE-ECC Beams

A detailed experimental investigation on the flexural behaviour of an innovative precast composite element combining cold-formed steel (CFS) and engineered cementitious composites (ECC) is presented in this paper. Bonding ECC to the lightweight thin-walled CFS sections enhanced the buckling, bearing, and torsional properties of the composite sections. The proposed composite system will be used as precast flexural members in framed structures with large spans or as a rehabilitation approach for corroded cold-formed and hot-rolled steel flexural members. Simply supported beams with comparatively long spans with span-to-depth ratios of 6.83 and 13.48 were installed back-to-back and tested under a 4-point loading configuration. The behaviour of composite CFS/ECC beams under bending was investigated and compared with the bare CFS sections. Composite CFS/MOR beams incorporating high-strength mortar (MOR) as an ECC replacement were also investigated. The test specimens were divided into three series with sixteen tests in total. Series A (SC300) included six tests utilising 300-mm height SupaCee sections, Series B (C300) included four tests using 300-mm height lipped-Cee sections, and Series C (SC150) included six tests utilising 150-mm height SupaCee sections. The composite CFS/ECC beams exhibited high load-bearing capacities after reaching their plastic section capacities, while the bare CFS beams failed to reach their yield section capacities due to distortional buckling. Composite CFS/MOR beams could not reach their plastic moment capacities due to debonding between MOR and CFS after MOR crushing. The moment capacities of the composite CFS/ECC beams increased up to 140.0% over their duplicate bare CFS sections, while composite CFS/MOR beams showed only a 72.0% increase over CFS sections. Lastly, design equations to predict the moment capacity of composite CFS/ECC beams are presented, based on the experimental results

Mesoscale Analysis of Rubber Particle Effect on Indirect Tensile and Flexural Tensile Strength of Crumb Rubber Mortar

This paper presents a mesoscale model to study the influence of rubber particles on the mechanical performance of crumb rubber mortar (CRM). The indirect tensile and flexural behaviors of CRM with different rubber replacement rates, shapes, and sizes were investigated. Rubber mortar is assumed to be a three-phase material composed of rubber aggregate, a mortar matrix, and an interface transition zone (ITZ). Numerical analysis showed that rubber content was the governing factor affecting the reduction rate of indirect tensile and flexural strength. The effect of the ITZ on the tensile strength of CRM was within one percent, which could be ignored. The influence of rubber particle size was investigated by analyzing CRM models containing five different rubber sizes from 0.86 mm to 7 mm. For each size, six different models with randomly distributed rubber particles were set up. CRM models presented a similar average strength even with different rubber particle sizes. However, the strength variation among the random models became higher when the rubber particle size increased. Numerical results also proved that treating rubber particles as pores in modeling led to negligible errors. Then, a prediction formula after considering the increase in air content is provided. Finally, the accuracy of numerical simulations was verified through a series of experimental studies

Flexural Strength of Innovative Thin-Walled Composite Cold-Formed Steel/PE-ECC Beams

A detailed experimental investigation on the flexural behaviour of an innovative precast composite element combining cold-formed steel (CFS) and engineered cementitious composites (ECC) is presented in this paper. Bonding ECC to the lightweight thin-walled CFS sections enhanced the buckling, bearing, and torsional properties of the composite sections. The proposed composite system will be used as precast flexural members in framed structures with large spans or as a rehabilitation approach for corroded cold-formed and hot-rolled steel flexural members. Simply supported beams with comparatively long spans with span-to-depth ratios of 6.83 and 13.48 were installed back-to-back and tested under a 4-point loading configuration. The behaviour of composite CFS/ECC beams under bending was investigated and compared with the bare CFS sections. Composite CFS/MOR beams incorporating high-strength mortar (MOR) as an ECC replacement were also investigated. The test specimens were divided into three series with sixteen tests in total. Series A (SC300) included six tests utilising 300-mm height SupaCee sections, Series B (C300) included four tests using 300-mm height lipped-Cee sections, and Series C (SC150) included six tests utilising 150-mm height SupaCee sections. The composite CFS/ECC beams exhibited high load-bearing capacities after reaching their plastic section capacities, while the bare CFS beams failed to reach their yield section capacities due to distortional buckling. Composite CFS/MOR beams could not reach their plastic moment capacities due to debonding between MOR and CFS after MOR crushing. The moment capacities of the composite CFS/ECC beams increased up to 140.0% over their duplicate bare CFS sections, while composite CFS/MOR beams showed only a 72.0% increase over CFS sections. Lastly, design equations to predict the moment capacity of composite CFS/ECC beams are presented, based on the experimental results

Axial Compressive Behaviour of Thin-Walled Composite Columns Comprise High-Strength Cold-Formed Steel and Pe-Ecc

A new form of thin-walled composite columns, made of high-strength cold-formed steel (CFS) open sections and thin layers of engineered cementitious composites (ECC), is presented in this paper. The axial behaviour of columns with slenderness ratios (le/r) ranging between 10.08 and 13.86 under concentric loads were experimentally investigated. Twelve column specimens were divided into four groups of bare CFS columns, plain ECC columns, composite columns with SupaCee sections, and composite columns with Lipped-Cee sections. A specific ECC mixture with three PE-fibre contents: 0.75%, 1.75%, and 2.25% by mix volume, was placed in the tested columns in two thin thicknesses of 16.0 mm and 26.0 mm. Additionally, a high-strength concrete (HSC) mixture was utilised in two test columns for comparison with ECC. The results revealed that the composite CFS/ECC columns exhibited enhanced axial compressive capacities up to 2.79 times that of the bare CFS columns. The ductility indices and compressive toughness of the composite CFS/ECC columns were improved to 1.56 and 3.85 times those of the bare CFS columns, respectively. Strength prediction equations were developed based on the experimental observations to estimate the axial compressive capacity of composite CFS/ECC columns susceptible to local buckling

Structural Performance of Novel Thin-Walled Composite Cold-Formed Steel/PE-ECC Beams

A novel form of thin-walled composite beams has been developed by bonding cold-formed steel (CFS) and engineered cementitious composites (ECC). Apart from the superior material strength and ductility of CFS and ECC, the proposed CFS/ECC composite system also benefits from the lightweight concept of thin-walled sections and improved buckling performance due to the ECC restraints on CFS. An experimental study, utilising cold-formed steel sections with a yield strength of 450 MPa and engineered cementitious composites with an ultimate tensile strength of 7 MPa, was conducted to investigate the improvement of the innovated structural system over the traditional CFS structures. Two series of composite CFS/ECC beams, namely, short- and long-span Series, were prepared and tested to monitor the shear and flexural behaviours of the novel composite system. Three locations of thin-layered ECC; outside, inside, and in–out of the CFS section were proposed to determine the perfect composite action between ECC and CFS. The load capacity of the composite beams (ECC—in composite beams) increased to eight times those of the bare CFS members in the short-span Series and up to four times in the long-span Series. The failure modes of the novel composite beams were more ductile compared to the bare CFS. Numerical modelling was conducted and validated using the results obtained from the experimental study. This FE model was employed in a small-scale parametric study to investigate the influence of beam spans on the structural behaviour of the composite CFS/ECC beams

Novel approach to improve crumb rubber concrete strength using thermal treatment

The concept of using crumb rubber as a partial replacement of natural aggregate in concrete to produce rubberised concrete and reduce environmental impacts has been a subject of research for many years. A plethora of studies have investigated various methods to improve the rubberised concrete strength using different pre-treatment methods for the rubber particles and/or using other additives for general concrete strength enhancement. However, the efficiency and applicability of these methods have been quite inconsistent and in some cases in conflict with each other. This study presents a novel approach to pre-treating crumb rubber particles using thermal treatment at 200 °C before incorporation into concrete. Heating time, rubber size, and rubber content were the variables in this experimental investigation. Scanning electron microscope (SEM) investigation was carried out on both as-received and thermally-treated rubber particles, as well as crumb rubber concrete (CRC) specimens. The results showed promising enhancements in concrete performance compared with the previous work findings. At 20% rubber content using size #40 mesh thermally-treated rubber, the compressive strength recovered by 60.3%

Electrochemically Reduced Carboxyl Graphene Modified Electrode for Simultaneous Determination of Guanine and Adenine

<div><p>An electrochemically reduced carboxyl graphene modified glassy carbon electrode (ERCGr/GCE) was prepared from a carboxyl graphene modified glassy carbon electrode (CGr/GCE) and employed for the simultaneous determination of guanine and adenine. The ERCGr/GCE showed an enhanced voltammetric response toward the oxidation of guanine and adenine compared with the CGr/GCE because the conductivity and electrochemical active surface area increased during the reduction process. The voltammetric peak current was linearly dependent on guanine and adenine concentration over the ranges of 0.5–10 and 2.5–50 µmol L⁻¹, respectively. The detection limits were 0.15 µmol L⁻¹ for guanine and 0.10 µmol L⁻¹ for adenine in 50 µmol L⁻¹ phosphate buffer at pH 6.86. Determination of guanine and adenine in thermally denatured herring sperm DNA showed that the ratio of guanine/adenine was 0.758 demonstrating practical application of the ERCGr/GCE.</p></div

Small Molecule-Initiated Light-Activated Semiconducting Polymer Dots: An Integrated Nanoplatform for Targeted Photodynamic Therapy and Imaging of Cancer Cells

Photodynamic therapy (PDT) is a noninvasive and light-activated method for cancer treatment. Two of the vital parameters that govern the efficiency of PDT are the light irradiation to the photosensitizer and visual detection of the selective accumulation of the photosensitizer in malignant cells. Herein, we prepared an integrated nanoplatform for targeted PDT and imaging of cancer cells using folic acid and horseradish peroxidase (HRP)-bifunctionalized semiconducting polymer dots (FH-Pdots). In the FH-Pdots, meta-tetra­(hydroxyphenyl)-chlorin (m-THPC) was used as photosensitizer to produce cytotoxic reactive oxygen species (ROS); fluorescent semiconducting polymer poly­[2-methoxy-5-((2-ethylhexyl)­oxy)-<i>p</i>-phenylenevinylene] was used as light antenna and hydrophobic matrix for incorporating m-THPC, and amphiphilic Janus dendrimer was used as a surface functionalization agent to conjugate HRP and aminated folic acid onto the surface of FH-Pdots. Results indicated that the doped m-THPC can be simultaneously excited by the on-site luminol–H₂O₂–HRP chemiluminescence system through two paths. One is directly through chemiluminescence resonance energy transfer (CRET), and the other is through CRET and subsequent fluorescence resonance energy transfer. In vitro PDT and specificity studies of FH-Pdots using a standard transcriptional and translational assay against MCF-7 breast cancer cells, C6 glioma cells, and NIH 3T3 fibroblast cells demonstrated that cell viability decreased with increasing concentration of FH-Pdots. At the same concentration of FH-Pdots, the decrease in cell viability was positively relevant with increasing folate receptor expression. Results from in vitro fluorescence imaging exhibited that more FH-Pdots were internalized by cancerous MCF-7 and C6 cells than by noncancerous NIH 3T3 cells. All the results demonstrate that the designed semiconducting FH-Pdots can be used as an integrated nanoplatform for targeted PDT and on-site imaging of cancer cells