Comparative study of Steel-FRP, FRP and steel reinforced coral concrete beams in their flexural performance

In this paper, a comparative study of Carbon Fiber Reinforced Polymer (CFRP) Bar and Steel-Carbon Fiber Composite Bar (SCFCB) reinforced coral concrete beams are made through a series experimental tests and theoretical analysis. The flexural capacity, crack development and failure modes of CFRP and SCFCB reinforced coral concrete were investigated in detail. They are also compared to ordinary steel reinforced coral concrete beams. The results show that under the same condition of reinforcement ratio, the SCFCB reinforced beam exhibits better performance than those of the CFRP reinforced beams, and its stiffness is slightly lower than that of the steel reinforced beam. Under the same load condition, the crack width of the SCFCB beam is between the steel reinforced beam and the CFRP bar reinforced beam. Before the steel core yields, the crack growth rate of SCFCB beam is similar to the steel reinforced beam. SCFCB has a higher strength utilization rate, about 70% -85% of its ultimate strength. The current design guidance was also examined based on the test results. It was found that the existing design specifications for FRP reinforced normal concrete is not suitable for SCFCB reinforced coral concrete structures

Reinforced silica-carbon nanotube monolithic aerogels synthesised by rapid controlled gelation

This work introduces a new synthesis procedure for obtaining homogeneous silica hybrid aerogels with carbon nanotube contents up to 2.50 wt.%. The inclusion of nanotubes in the highly porous silica matrix was performed by a two-step sol–gel process, resulting in samples with densities below 80 mg/cm3. The structural analyses (N2 physisorption and SEM) revealed the hierarchical structure of the porous matrix formed by nanoparticles arranged in clusters of 100 and 300 nm in size, specific surface areas around 600 m2/g and porous volumes above 4.0 cm3/g. In addition, a relevant increase on the mechanical performance was found, and an increment of 50% for the compressive strength and 90% for the maximum deformation were measured by uniaxial compression. This reinforcement was possible thanks to the outstanding dispersion of the CNT within the silica matrix and the formation of Si–O–C bridges between nanotubes and silica matrix, as suggested by FTIR. Therefore, the original synthesis procedure introduced in this work allows the fabrication of highly porous hybrid materials loaded with carbon nanotubes homogeneously distributed in the space, which remain available for a variety of technological applications

Bond–slip Behavior of Fiber-reinforced Polymer/concrete Interface in Single Shear Pull-out and Beam Tests

It has been assumed that the fiber-reinforced polymer/concrete interface is subjected to in-plane shear condition when intermediate crack debonding failure occurs. Therefore, the single shear pull-out test results are often used to predict the intermediate crack debonding failure in beams. In this study, the behavior of fiber-reinforced polymer-strengthened concrete beams and single shear pull-out specimens were studied experimentally and numerically. The bond–slip behavior of the fiber-reinforced polymer/concrete interface was obtained by single shear pull-out and beam tests. In all beam specimens, a concrete wedge located at the edge of the notch detached with the fiber-reinforced polymer debonding failure. This phenomenon shows that the initiation of debonding is due to a diagonal crack formation close to the major flexural/shear crack inside the concrete. The diagonal crack formation is due to a local moment at the tip of the notch. This causes the different stress state and slip of the fiber-reinforced polymer/concrete interface of beam specimens from that of the pull-out specimens. It is found that the bond–slip relation obtained from the pull-out test does not represent the bond–slip relation of the fiber-reinforced polymer/concrete interface in the fiber-reinforced polymer-strengthened concrete beams, and it cannot be directly used for predicting the load capacity of the fiber-reinforced polymer-strengthened concrete beams

Design and evaluation of three-phase fibrous composite structures

Study reveals composite combination evaluations for boron binder reinforcements for unidirectly reinforced boron/epoxy, glass binder reinforcements for unidirectionally reinforced boron/epoxy, and glass binder reinforcements for unidrectionally reinforced glass/epoxy

Improved method for producing metal-reinforced ceramics

Vacuum impregnation process produces metal-reinforced ceramics with only 3 percent void space volumes. Method may be used to produce metal-reinforced ceramics for high temperature or structural applications such as furnace supports and armor

Large deviations in the reinforced random walk model on trees

In this paper, we consider the linearly reinforced and the once-reinforced random walk models in the transient phase on trees. We show the large deviations for the upper tails for both models. We also show the exponential decay for the lower tail in the once-reinforced random walk model. On the other hand, the lower tail is in polynomial decay for the linearly reinforced random walk model.Comment: 20 page

Transition from glass to graphite in manufacture of composite aircraft structure

The transition from fiberglass reinforced plastic composites to graphite reinforced plastic composites is described. Structural fiberglass design and manufacturing background are summarized. How this experience provides a technology base for moving into graphite composite secondary structure and then to composite primary structure is considered. The technical requirements that must be fulfilled in the transition from glass to graphite composite structure are also included

Production of circular polymer-glass fabric composites

Potentially automated pultrusion technique has been provided for production of curved, glass-reinforced polyimide, epoxy, and graphite reinforced structures. Specially designed apparatus has been manufactured for production of curved structures

Post crack flexural toughness in steel fabric and fibre reinforced concrete beams

The purpose of the paper is to provide independent research and evaluate manufacturers’ claims that structural polypropylene fibres provide satisfactory crack control reinforcement and compare the test results from macro synthetic polypropylene fibres against steel fabric reinforced concrete, extensively used as a crack control medium in concrete ground bearing floor/hardstanding slabs where tensile forces are likely to occur. Three concrete beam types were produced, plain, steel reinforced and fibre reinforced, and a comparative study was undertaken of post crack flexural toughness. The procedure used was to manufacture steel A 142 fabric and macro fibre reinforced concrete beams to provide load, deflection data, toughness indices and was compliant with, ASTM C1018 -97, [ASTM, 1997] using a three point loading arrangement. The data was representative of what might occur in a floor slab. The findings of the paper is that A1 42 steel fabric reinforcement as used in slabs was more effective in producing toughness and residual strength when directly compared to the performance of structural polypropylene fibre reinforced concrete. When small post crack forces are encountered within the concrete matrix, polypropylene macro fibres are suitable for crack control. The paper makes direct comparisons between known and widely used crack control using steel fabric, and the use of low modulus polypropylene macro synthetic fibres as a crack control medium

Reinforced structural plastics

Reinforced polyimide structures are described. Reinforcing materials are impregnated with a suspension of polyimide prepolymer and bonded together by heat and pressure to form a cured, hard-reinforced, polyimide structure