Compressive Mechanical Properties of a Novel Recycled Aggregate Concrete with Recycled Lightweight Aggregate

A novel recycled aggregate concrete was prepared by replacing the natural aggregate with recycled lightweight aggregate. Subsequently, the mechanical properties and compressive stress-strain constitutive relation of the recycled lightweight aggregate concrete (RLWAC) were explored. For this purpose, the recycled lightweight aggregate (RLWA) replacement ratio (0%, 25%, 50%, 75%, and 100%) was selected as a variable, and the compressive strength of 15 cube and 30 prism specimens was evaluated. The failure morphology of the specimen was subsequently characterized, along with the cubic compressive strength, axial compressive strength, peak strain, ultimate strain, and other performance indices. The influence of the replacement ratio for the specimen indices of the RLWAC was also analyzed. It was observed that the dry apparent density of RLWAC decreased gradually on increasing the replacement ratio. Compared with 0% replacement ratio, a decrease of 6.50%, 11.39%, 21.84%, and 27.54% was observed, respectively. On enhancing the RLWA replacement ratio, the compressive strength, peak strain, and ultimate strain of RLWAC were observed to be gradually reduced. As the replacement ratio was increased from 75% to 100%, the peak strain was noted to decrease the most by about 6.8%. As the replacement ratio was increased from 50% to 75%, the ultimate strain decreased the most by about 14.2%. Based on the experimental findings, the functional relationships of the strength indices and the conversion value of each strength index with the replacement ratio were also established. Finally, based on the model proposed by the existing model, the stress-strain equation of RLWAC was developed, and the fitting results were observed to be in good agreement with the test results.

O08 BIOMECHANICS OF MANUAL, STAPLED, AND MANUAL-STAPLED SUTURES ON FASCIA LATA. TIPS FOR ABDOMINAL WALL SURGEONS

Aim No data on the biomechanical properties of staplers’ use in the repair of abdominal wall defects are available. Our objective is to study prospectively the biomechanical properties of manual, stapled and mixed manual/stapled fascial sutures. Material-Methods Stress/strain tests were performed on 16 human cadaver fascial samples. The data on strength, strain (deformability), Young’s modulus (elasticity), and dissipated energy (toughness modulus) were recorded for each type of suture. Results Stapled and mixed suture showed a significantly higher strength (manual 0.83, stapled 2.10, mixed 2.68 MPa), and a trend towards a higher strain as compared to manual sutures (manual 344, stapled 249, mixed 280%). Stapled and mixed suture were four-fold higher as compared to manual sutures (manual 1.779, stapled 7.374, mixed 6.964 MPa). Manual and mixed sutures showed significantly higher dissipated energy (manual 0.99, vs stapled 0.73, vs mixed 1.35 mJ-mm3). Conclusions Stapled and mixed sutures have better strength performances than manual sutures. On the other hand, stapled and mixed sutures have significantly higher Young’s modulus and lower ultimate strain, showing less deformability, possibly translating in less efficiency in large midline defects, where manual sutures might display higher elasticity. Also, hand-sewn sutures (in manual or over-sewn stapled) appear to increase the ability to absorb mechanical energy, whereas stapled sutures showed to be less tough. Furthermore, an over-sewn stapled suture, as compared to a stapled suture, gains in term of strength, ultimate strain, Young’s modulus, and dissipated specific energy, suggesting the need of over-sewn stapled sutures in case of larger fascial defects.

Effect of Low Temperatures on the Mechanical Performance of GFRC Modified by Low Carbon Cement

Glass fibre reinforced cement (GFRC) is a composite material with great ductility but it undergoes severe strength and ductility degradation with ageing. Calcium sulfoaluminate (CSA) cement is low carbon cement, and more importantly, it exhibits great potential to produce more ductile and durable GFRC. This study focuses on mechanical performance, e.g., compressive strength, stress-strain curve, and freeze-thaw resistance of CSA/GFRC as well as its microstructural characteristics under low temperatures. XRD was applied to investigate the hydration mechanism of CSA cement under −5°C, 0°C, and 5°C. It was found out that low-temperature environments have very little effect on the type of hydration products, and the main hydration product of hydrated CSA cement cured under low temperatures is ettringite. Moreover, low-curing temperatures have an adverse effect on the compressive strength developments of CSA/GFRC but the strength difference compared with that under 20°C reduces gradually with increasing curing ages. In terms of bending performance, both ultimate tensile strength and ultimate strain value indicate considerable degradation with ageing under low temperatures after 14 d. The ultimate strain value reduces to 0.34% at −5°C, 0.39% at 0°C, and 0.44% at 5°C compared with 0.51% for that cured at 20°C for 28 d. The tensile strength of samples cured at −5°C for 28 d is only 15.2 MPa, taking up only 40% of that under 20°C. CSA/GFRC also demonstrated great capability in the antifreeze-thaw performance, and the corresponding strength remains 95.9%, 94.7%, 94.2%, and 94.3%, respectively, for that cured under 20°C, 5°C, 0°C, and −5°C after 50 freeze-thaw cycles. Microstructural studies reveal that densification of the interfilamentary space with intermixtures of C-A-S-H and ettringite is the main reason that causes the degradation of CSA/GFRC, which may result in loss on flexibility when forces are applied, therefore reducing the post-peak toughness to some extent.

Manufacturing and Modeling of Hybrid Polymer Composites by Using Multiple-nonlinear Regression Analysis

In this study, artichoke stem particles (AS) and wollastonite mineral (W) were used as an organic and inorganic fillers in order to improve the mechanical properties of polypropylene (PP). In this regard, PP-based composites containing AS and W were produced as non-hybrid and hybrid materials using a high-speed thermokinetic mixer. Mechanical properties of polymer composites were investigated by the tensile test. Experimental results reveal that the highest elastic modulus for PP-W and the highest tensile strength for PP were obtained while the lowest ultimate strain value was gained using PP-W-A. Then, multiple nonlinear regression analysis was employed to determine the effect of weight ratios of wollastonite mineral and artichoke stem particles in polypropylene on elastic modulus, tensile strength and ultimate strain. Experimental results were expressed second order (tensile strength), third order (elastic modulus) and fourth order (ultimate strain) mathematical models. The results show that the proposed models have well fitted with the experimental results. The coefficient of determination (R2) values were found between 0.95 and 1 in all models. Also, boundedness check control of the proposed models which gives information about whether models are realistic or not was carried out by calculating the maximum and minimum values produced by the relevant model.

Transverse shear properties of fiber reinforced polymer bars with different reinforced phases

In this study, a total of 105 shear specimens of fiber reinforced polymer bars with different reinforced phases, including the glass fiber, the hybrid of carbon fiber with glass fiber, and the hybrid of steel wire with glass fiber, were prepared to systematically investigate their transverse shear properties. The surface configuration of specimens, the performance characteristics and distribution pattern of reinforced phase were mainly regarded as variables. The results showed the shear strengths of glass fiber reinforced polymer bar specimens increased from 247.9 MPa to 263.5 MPa as the rib depth changed from shallow ribs to deep ribs, and their ultimate strain decreased from 0.374 to 0.328 with the increase in rib spacing from 8 mm to 16 mm. The shear strengths of carbon/glass hybrid fiber reinforced polymer (C/G HFRP) bar specimens declined from 247.4 MPa to 226.3 MPa as the distribution pattern of carbon fiber changed from centralized distribution to dispersed distribution. The shear strength of C/G HFRP bars decreased from 256.5 MPa to 247.4 MPa as the ratio of glass fiber to carbon fiber ranged from 0:1 to 1:4, and increased from 138.7 MPa to 214.8 MPa for steel wire/glass HFRP bars as the volumetric fraction of steel wire replacing glass fiber increased from 0 to 33.3%. This indicated that the surface configuration of specimen, the distribution pattern of fiber, and the performance characteristics of reinforced phase have great effects on the ultimate strain and shear strength of FRP bars, respectively.

Effect of reduced graphene oxide on mechanical behavior of an epoxy adhesive in glassy and rubbery states

The mechanical behavior of an adhesive, in neat state and reinforced with up to 0.5 wt% of reduced graphene oxide (RGO) was investigated here. Tests were done at temperatures between the ambient temperature and the glass transition temperature ( Tg[Formula: see text] of the adhesive. Using a metal mold, cured plates of the neat and RGO reinforced epoxy adhesive were prepared. The adhesive powder and the bulk dumbbell-shaped specimens, obtained from cured adhesive plates, were subjected to differential scanning calorimetry (DSC) and tensile tests, respectively, to obtain the Tg as well as mechanical properties of the adhesives. The results indicated that adding RGO up to 0.5 wt% increased the glass transition temperature, the modulus of elasticity, and the strength of the adhesive. It was found that the presence of RGO reduced the adhesive’s strain at the break at the ambient temperature. However, at high temperatures, near the Tg, the ultimate strain of RGO-reinforced adhesives decreased slightly when compared to the ultimate strain of the neat specimens. This explains the reduction in toughness at ambient temperature obtained by adding RGO and the increase at high temperatures. Finally, the failure morphology of the neat and RGO-reinforced adhesive specimens was investigated using microscopic imaging of the specimens’ failure cross-sections, which supported and justified the experimental observations.

Stressstrain state of cast-in-place and precast structure with loaded cast-in-place element

The paper presents the strength analysis of cast-in-place and precast structures in accordance with regulatory documents, which require clarifications, since the properties of such structures distinguish them from conventional reinforced concrete structures. These properties include the beginning of the deformation process, ultimate strain, physical properties, and others. The strength analysis of cast-in-place and precast structure is conducted with regard to these properties.The proposed analysis is based on the load-bearing capacity exhaustion of deformed concrete or reinforcement and allows considering the different time of involvement in the deformation process of cast-in-place and precast structures as well different stress and strain properties of concrete. The experimental data are in good agreement with theoretical calculations.

Experimental investigation of the mechanical behavior of glass fiber/high fluidity polyamide-based composites for automotive market

In this work, we examine the relationships between the microstructure and the mechanical properties of glass fiber–reinforced polyamide 6,6 composite materials ( V f = 54%). These materials made by thermocompression incorporate different grades of high fluidity polyamide-based polymers and two types of quasi-UD glass fiber reinforcement. One is a classic commercial fabric, while the other specially designed and manufactured incorporates weaker tex glass yarns (the spacer) to increase the planar permeability of the preform. The effects of the viscosity of the polymers and their composition on the wettability of the reinforcements were analyzed by scanning electron microscopy observations of the microstructure. The respective influences of the polymers and the spacer on the mechanical performance were determined by uniaxial tensile and compression tests in the directions parallel and transverse to the warp yarns. Not only does the spacer enhance permeability but it also improves physical and mechanical properties: tensile longitudinal Young’s modulus increased from 38.2 GPa to 42.9 GPa (13% growth), tensile strength increased from 618.9 MPa to 697 MPa (3% growth), and decrease in ultimate strain from 1.8% to 1.7% (5% reduction). The correlation of these results with the damage observed post mortem confirms those acquired from analyses of the microstructure of composites and the rheological behaviors of polymers.