Cyclic Compression Behavior of Concrete-Filled Hybrid Large Rupture Strain FRP Tube

This paper experimentally investigates the behavior of concrete-filled-fiber-reinforced polymer (FRP) cylinders under cyclic axial compression. The FRP used in this study were either large rupture strain FRP (LRS-FRP) or hybrid LRS-FRP and conventional glass FRP (GFRP). LRS-FRP are manufactured out of polyethylene naphthalate (PEN) and polyethylene terephthalate (PET) obtained from recycled plastics. Hence, they are much cheaper and environment-friendly than conventional GFRP or carbon FRP (CFRP). LRS-FRPs has high tensile rupture strain (usually greater than 5%) compared to 1-2% for GFRP and CFRP. This study presents the results of 4 specimens with different confinement ratios to investigate the behavior of concrete-filled LRS-FRP or hybrid LRS-FRP and GFRP tubes in terms of ductility, ultimate strain, and strength improvement. The results showed that using LRS-FRP significantly improved the ductility of the confined concrete. However, the improvement in strength was limited. The hybrid confinement improves both the ductility and strength

Improvement of adhesive toughness measurement

The double cantilever beam (DCB) method for adhesive toughness measurement was improved by incorporating a sufficiently sharp crack made by a wedge-tapping method. A known route to producing cracks via loading–unloading cycles was proved unreliable because the cycles produced plastic deformation in the adhesive where new cracks propagated. Abnormally high toughness values with large standard deviations were obtained with cracks made by embedding a non-sticky insert. Only instantly propagated cracks made by tapping were sufficiently sharp to produce reproducible, accurate tough-ness measurements. However, toughened resin was insensit

An Investigation of the Mechanical and Physical Characteristics of Cement Paste Incorporating Different Air Entraining Agents using X-ray Micro-Computed Tomography

Improving the thermal insulation properties of cement-based materials is the key to reducing energy loss and consumption in buildings. Lightweight cement-based composites can be used efficiently for this purpose, as a structural material with load bearing ability or as a non-structural one for thermal insulation. In this research, lightweight cement pastes containing fly ash and cement were prepared and tested. In these mixes, three different techniques for producing air voids inside the cement paste were used through the incorporation of aluminum powder (AL), air entraining agent (AA), and hollow microspheres (AS). Several experiments were carried out in order to examine the structural and physical characteristics of the cement composites, including dry density, compressive strength, porosity and absorption. A Hot Disk device was used to evaluate the thermal conductivity of different cement composites. In addition, X-ray micro-computed tomography (micro-CT) was adopted to investigate the microstructure of the air-entrained cement pastes and the spatial distribution of the voids inside pastes without destroying the specimens. The experimental results obtained showed that AS specimens with admixture of hollow microspheres can improve the compressive strength of cement composites compared to other air entraining admixtures at the same density level. It was also confirmed that the incorporation of aluminum powder creates large voids, which have a negative effect on specimens’ strength and absorption.EC/H2020/841592/EU/Ultra-Lightweight Concrete for 3D printing technologies/Ultra-LightCon-3

Numerical Investigation on Hollow Pultruded Fibre Reinforced Polymer Tube Columns

As the axial behaviour of hollow pultruded fibre reinforced polymer (PFRP) profiles is governed by the instability conditions due to the local and global buckling, the determination of the safe load carrying capacity of FRP columns is vital. The compressive performance of PFRP tube depends on many factors such as fibre type, fibre content, and orientation of fibre layers, cross-section, thickness and height of the column member. In this study, concentric compressive testing was conducted using PFRP short columns. Based on the fibre orientation and thickness, the samples were divided into two groups of tubes in a square shape and two groups in a circular shape. The height of columns is designed to keep the slenderness ratio (length/lateral dimension) of 5. The axial behaviour of FRP columns was simulated using STRAND7 finite element software package. The laminate method was followed to define the mechanical properties of the FRP material. Failure was investigated by using the Tsai-Wu failure criterion. The experimental results show that the failure mode of the hollow square tube was either local buckling or corner splitting at the mid-height followed by buckling. Although both types of circular tubes failed in a similar way by crushing one end with high noise, followed by separation of the crushed end into strips, the stiffness and the load capacity of PFRP column was higher for the profiles with fibres oriented close to the axial direction. The numerical results are in close agreement with the peak value of the experimental results. This can be extended to study the effects of all factors that influence the axial behaviour of PFRP columns numerically

Optimisation of rubberised concrete with high rubber content: an experimental investigation

This article investigates experimentally the behaviour of rubberised concrete (RuC) with high rubber content so as to fully utilise the mechanical properties of vulcanised rubber. The fresh properties and short-term uniaxial compressive strength of 40 rubberised concrete mixes were assessed. The parameters examined included the volume (0–100%) and type of mineral aggregate replacement (fine or coarse), water or admixture contents, type of binder, rubber particle properties, and rubber surface pre-treatments. Microstructural analysis using a Scanning Electron Microscope (SEM) was used to investigate bond between rubber and concrete at the Interface Transition Zone (ITZ). This initial study led to the development of an “optimum” RuC mix, comprising mix parameters leading to the highest workability and strength at all rubber contents. Compared to a non-optimised concrete with 100% replacement of fine aggregates with rubber, the compressive strength of concrete with optimised binder material and moderate water/binder ratio was enhanced by up to 160% and the workability was improved significantly. The optimisation proposed in this study will lead to workable high rubber content RuC suitable for sustainable high-value applications

Effect of Rubber Heat Treatment on Rubberized-Concrete Mechanical Performance

To eliminate the unfavorable effect of the accumulation of end-of-life car tires on the environment, many studies have been conducted to recycle those tires in concrete as a partial or full replacement of its natural aggregates. However, the produced rubberized concrete suffers from low compressive strength due to low adhesion at the rubber/cement interface. Pre-treating of rubber surfaces before use in concrete is the most effective way to overcome this adverse effect on the concrete strength. Several studies introduced different methods to enhance rubberized-concrete strength through pre-treating rubber particles, especially when using a high content of rubber in concrete. This study presents the results of experimental work on the effect of heat treatment on crumb-rubber–concrete mechanical performance. Rubber contents of 40%, 60% and 80% of sand volume were the variables in this study. Workability, density, compressive strength, and impact resistance were the measurements in this experimental work. The results showed that using saturated-surface dry (SSD) rubber can eliminate the adverse effect on concrete slump when using a high rubber volume or the heat-treated rubber. Using heat-treated rubber at 200 °C for 2 h as 40%, 60%, and 80% displayed compressive strength recoveries of 14.9%, 10.4% and 9.7%, respectively. Heat treatment of 40%, 60%, and 80% rubber contents increased the impact resistance for ultimate failure by 57%, 28%, and 7%, respectively, compared with those of the control mix. The thermal treatment enhanced the impact resistance at ultimate failure by 37%, 28%, and 15%, respectively, for mixes containing 40%, 60%, and 80% rubber contents compared with those of as-received rubber

Displacement and Plastic Hinge Length of FRP-Confined Circular Reinforced Concrete Columns

Confinement of both existing and newly constructed reinforced concrete (RC) columns by fibre reinforced polymer (FRP) has been commonly used in recent decades. This is because of its ability to enhance the shear resistance and the ductility of the RC columns, which are the main parameters that govern the behaviour of RC columns under lateral loading. This paper presents a finite element (FE) model that was developed using the LS-DYNA program aimed at modelling the plastic hinge length (lp) for FRP-confined RC columns. A FE parametric study was conducted to investigate the effect of FRP-confinement on lp. Empirical models were proposed to predict lp and the ultimate drift ratio (δu) for FRP-confined RC columns and the results were compared with similar previous models. The proposed FE model was able to predict the plastic hinge region and lp value which can provide a simple way for designers to investigate the behaviour of FRP-confined columns during the design process. The proposed δu model reduced the average of errors (A) and standard deviation (SD) by 15.1%, 3.9%, respectively, compared to the best predictions by previous models