Thermographic non-destructive evaluation for natural fiber-reinforced composite laminates

Natural fibers, including mineral and plant fibers, are increasingly used for polymer composite materials due to their low environmental impact. In this paper, thermographic non-destructive inspection techniques were used to evaluate and characterize basalt, jute/hemp and bagasse fibers composite panels. Different defects were analyzed in terms of impact damage, delaminations and resin abnormalities. Of particular interest, homogeneous particleboards of sugarcane bagasse, a new plant fiber material, were studied. Pulsed phase thermography and principal component thermography were used as the post-processing methods. In addition, ultrasonic C-scan and continuous wave terahertz imaging were also carried out on the mineral fiber laminates for comparative purposes. Finally, an analytical comparison of different methods was give

Tests of continuous concrete slabs reinforced with basalt fibre reinforced plastic bars

yesThis paper presents experimental results of three continuously supported concrete slabs reinforced with basalt-fibre-reinforced polymer (BFRP) bars. Three different BFRP reinforcement combinations of over and under reinforcement ratios were applied at the top and bottom layers of continuous concrete slabs tested. One additional concrete continuous slab reinforced with steel bars and two simply supported slabs reinforced with under and over BFRP reinforcements were also tested for comparison purposes. All slabs sections tested had the same width and depth but different amounts of BFRP reinforcement. The experimental results were used to validate the existing design guidance for the predictions of moment and shear capacities, and deflections of continuous concrete elements reinforced with BFRP bars. The continuously supported BFRP reinforced concrete slabs illustrated wider cracks and larger deflections than the control steel reinforced concrete slab. All continuous BFRP reinforced concrete slabs exhibited a combined shear–flexure failure mode. ACI 440-1R-15 equations give reasonable predictions for the deflections of continuous slabs (after first cracking) but stiffer behaviour for the simply supported slabs, whereas CNR DT203 reasonably predicted the deflections of all BFRP slabs tested. On the other hand, ISIS-M03-07 provided the most accurate shear capacity prediction for continuously supported BFRP reinforced concrete slabs among the current shear design equations

Tensile behaviour of FRP grid strengtheneing ECC composite under a uniaxial loading

As the fibre reinforced polymer (FRP) sheets/textiles strengthening the inorganic cementitious materials technique was presented by some researchers, a few of potential shortcomings, such as penetrating difficultly of cementitious materials to and much brittle of FRP sheets, have been found in recent years. Therefore, a new strengthening system, which was FRP grid strengthening ECC system, in combination with the Engineered Cementitious Composites (ECC) and FRP grid was proposed by the present authors. By applying this system to reinforce the reinforced concrete (RC) beams, the dual strengthening effects can be provided and the intermediate crack-induced debonding failure can also be suppressed by externally bonded the FRP gird reinforced ECC composite layer to the tensile surface of the original RC beams. To investigate the tensile mechanical behaviour of FRP gird reinforced ECC composite layer, six non-strengthened ECC specimens and eighteen basalt fibre reinforced polymer grid (BFRP) strengthening ECC composite specimens (FRP-ECC specimens) subjected to the unidirectional axial tensile loading were conducted in this paper. Three kinds of different thickness BFRP grid were applied to investigate their reinforcement effects. The test results showed that there was no slip at the interface of BFRP grid and ECC substrate significantly. The failure modes were the internal PVA fibers ruptured or pulled out from ECC substrate for the non-strengthened ECC specimens and the rupture of BFRP reinforcements of grid for the strengthened FRP-ECC specimens. The axial stiffness of FRPECC specimens and the ultimate tensile stress and strain were obviously increased after the ECC substrate cracked, which indicated the contribution of the internal BFRP grid reinforcements. Moreover, an analytical model was also presented to predict the stress-strain relationship and the tensile strength of the FRP-ECC specimens and validated through comparison with the rest results

Experimental Studies on Bond Performance of BFRP bars reinforced Coral Aggregate Concrete

As part of this study, has been developed a numerical method which allows to establish abacuses connecting the normal force with bending moment for a circular section and therefore to predict the rupture of this type of section. This may be for reinforced concrete (traditional steel) or concrete reinforced with steel fibers. The numerical simulation was performed in nonlinear elasticity up to exhaustion of the bearing capacity of the section. The rupture modes considered occur by plasticization of the steel or rupture of the concrete (under compressive stresses or tensile stresses). Regarding the fiber-reinforced concrete, the rupture occurs, usually, by tearing of the fibers. The behavior laws of the different materials (concrete and steel) correspond to the real behavior. The influence of several parameters was investigated, namely; diameter of the section, concrete strength, type of steel, percentage of reinforcement and contribution of concrete in tension between two successive cracks of bending. A comparison was made with the behavior of a section considering the conventional diagrams of materials; provided by the BAEL rules. A second comparative study was performed for fibers reinforced section

Experimental studies on the shear capacity of sea sand concrete beams with basalt fiber-reinforced polymer bars

Basalt fiber-reinforced polymer (BFRP) bars can replace steel bars in sea sand concrete structures to prevent the corrosion of steel by chloride ions; thus, sea sand can be directly added to concrete material in construction. Shear tests on 16 sea sand concrete beams with BFRP bars (including ten beams with stirrups and six beams without stirrups) are performed, and their failure modes, shear capacities and influencing factors are analyzed. The results reveal two main failure modes for sea sand concrete beams with BFRP bars: bending failure and shear-compression failure. The shear capacity increases with the concrete strength and stirrup ratio but decreases with an increased shear-span ratio, and the longitudinal reinforcement ratio has an insignificant effect on shear capacity

Bond performance between NSM FRP rods and concrete using ECC as bonding materials

The pull-out test of near-surface-mounted (NSM) FRP (fiber-reinforced plastics) rod from concrete was performed using engineered cementitious composites (ECC) as bonding materials. The feasibility of cementitious materials in NSM FRP strengthened concrete was then analyzed. Carbon FRP (CFRP) rods and Basalt FRP (BFRP) rods with spiral surfaces and diameters of 8 mm were used in the test. The bonding lengths are 5 times and 10 times of the FRP diameter, respectively. Results show that the failure modes of all the specimens using ECC as bonding materials are pull-out of FRP rods with ductile behavior. Moreover, specimens with NSM FRP rods using epoxy are prepared as control specimens to evaluate the feasibility of ECC. For CFRP rods, the pull-out load-bearing capacity of specimens using ECC is 70% and 50% of that in specimens using epoxy for 5 times and 10 times of the FRP diameter, respectively. For BFRP rods, the load-bearing capacity of specimens using ECC is 75% and 55% of that in specimens using epoxy for 5 times and 10 times of the FRP diameter, respectively. Thus, ECC can be applied in NSM FRP strengthened concrete structures as the bonding materials