Mode I fracture toughness of fibre reinforced concrete (original) (raw)
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This The influence of fibre reinforcement on crack propagation in concrete was studied. Thirty-five double torsion specimens, made with three types of fibres (fibre glass , straight steel fibres and deformed steel fibres) were tested. The variables were the fibre volume and size of the fibres. The test results indicated that the resistance to rapid crack growth increased somewhat with increasing fibre content up to about 1.25%-1.5% by volume. The degree of compaction had an enormous effect on the fracture properties .The fracture toughness increased with fibre content up to about 1.25% by volume, and then decreased , due to incomplete compaction. It was found that in this test geometry, fibres did not significantly restrain crack growth. It was also observed that once the crack had propagated down the full length of the specimen, the system changed from a continuous system to a discontinuous system, consisting of two separate plates held together by the fibre reinforcement. Different types of fibres did not significantly affect the fracture toughness.
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Geopolymer concrete (GPC) is currently a hot research area. This work aims to study the fracture behavior of beam specimens with and without steel reinforcement and cast with different binders. Forty-eight notched-beams with dimensions of 100×150×1000 mm were used and tested in three-point bending loads. Different variables taken into consideration mainly, notch height (0, 50, 75 mm), reinforcement ratio (0%, 17%), replacement ratio of fly ash with cement (0%, 20%, 30%, 50%) in GPC, replacement ratio of cement with fly ash (0%, 50 %) in Portland cement concrete (PCC), polypropylene fibers content (0%, 0.5%, 0.75%). were studied. The loaddeflection, and crack mouth opening displacement (CMOD) were considered as the characteristic responses at various stages of loading. Fracture Toughness (K IC), Fracture Energy (G F), Characteristic Length (Ɩ ch), Brittleness (B), J-Integral (J IC) were calculated to evaluate the fracture behavior of the beam specimens without reinforcement. Whereas, brittleness number (N P), dimensionless number (S), and the ratio of plastic moment / critical moment (M P /M F) were calculated to evaluate the fracture behavior of the beam specimens with reinforcement. The results revealed that, the GPCs exhibit similar behavior and fracture properties that those determined in PCCs. Hence, the inclusion of polypropylene fibers to different concrete mixtures noticeably enhanced their fracture properties, while the brittleness was reduced with the increase of the polypropylene fibers content.
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Polyolefin fibre reinforced concrete (PFRC) has become an attractive alternative to steel for the reinforcement of concrete elements mainly due to its chemical stability and the residual strengths that can be reached with lower weights. The use of polyolefin fibres can meet the requirements in the standards, although the main constitutive relations are based on the experience with steel fibres. Therefore, the structural contributions of the fibres should be assessed by inverse analysis. In this study, the fibre dosage has been fixed at 6kg/m³ and both self-compacting concrete and conventional concrete have been used to compare the influence of the positioning of the fibres. An idealized homogeneous distribution of the fibres with such fibres crossing from side to side of the specimen has been added to self-compacting concrete. The experimental results of three-point bending tests on notched specimens have been reproduced by using the cohesive crack approach. Hence, the constitu...
Fracture behavior of polymeric fiber reinforced lightweight structural concrete
Materials Research, 2014
A study has been made of the effect of short randomly dispersed polypropylene fibers on the fracture behavior of lightweight structural concrete. Using unnotched and precracked beams subjected to bend loading, it was possible to determine the toughness factor TF and to estimate specific J integral parameters, namely J IC and J Max corresponding to the onset of fracture initiation and to the attainment of ultimate load, respectively. The results have indicated a considerable improvement in the fracture behavior associated with the presence of fibers. More specifically this improvement was manifested by a 400% increase in both TF and J IC .
Modelling of the fracture toughness anisotropy in fiber reinforced concrete.PDF
Steel fiber reinforced concrete is potentially very promising material with unique properties, which currently is widely used in some applications, such as floors and concrete pavements. However, lack of robust and reliable models of fiber reinforced concrete fracture limits its application as structural material. In this work a numerical model is proposed for predicting the crack growth in fiber reinforced concrete. The mixing of the steel fibers with the concrete usually creates nonuniform fibers distribution with more fibers oriented in horizontal direction, than in vertical. Simple numerical models of fiber reinforced concrete require a priori knowledge of the crack growth direction in order to take into account bridging action of the fibers, which depends on the fibers orientation. In proposed model user defined elements are used to calculate the bridging force during the course of the analysis when the crack starts to grow. Cohesive elements were used to model the crack propagation in the concrete matrix. In cohesive zone model the cohesive elements are embedded between all solid elements to simulate the arbitrary crack path. The bridging effect of the fibers are modeled as nonlinear springs, where the stiffness of the springs is defined from experimentally measured pull-out force and the angle between the fiber and crack opening direction.