Fatigue enhancement of concrete beam with ECC layer
Introduction
Concrete, composing of cement, water, fine and coarse aggregates, is widely used in civil engineering construction. The brittle behavior of concrete, especially under tensile loading, is one of its major limitations. With the low toughness of concrete, cracks can propagate rapidly to result in failure at a low ultimate strain (around 0.01%) without warning. In order to improve the failure behavior, fiber reinforced concrete (FRC) is made by adding discrete short fibers into the concrete matrix. Fibers used currently include steel, glass, carbon and polymer fibers. These fibers act as bridges across the cracks to delay their propagation. Thus, a more ductile failure mode with a significant softening response could be attained.
Development of FRCs started in the 1970s. At that time, only glass fiber and steel fiber were investigated. During the past 10 years, with the development of micromechanical models, properties of fiber, matrix and fiber/matrix interface have been tailored to produce cementitious composites that exhibit a pseudo-strain hardening behavior similar to that of metals. These composites are called Engineered Cementitious Composites (ECC) [1]. With effective crack bridging provided by the fibers, failure of ECC occurs with the formation of multiple cracks that are very fine (the crack opening at ultimate strain is normally below 100 μm). The ultimate tensile strain can reach a value as high as 2–6%, which is 200 to 600 times greater than that of concrete.
A typical mix of PVA–ECC contains about 2% of PVA fibers. Also, the binder content is often above 1000 kg/m3. As a result, the cost of PVA–ECC can be 4 to 5 times that of normal concrete [2]. In order to achieve better economy, ECC should be used selectively in parts of a structure where their advantages can be fully exploited.
The flexural fatigue performance of concrete is important for many applications such as highway and airfield pavements, bridge decks and pavement overlays. Consider a plain concrete beam subjected to cyclic flexural load. The first crack will form when the maximum principal tensile stress exceeds the cracking strength of the material. Crack propagation will initially occur at a slow rate, and increase rapidly with crack size. The number of cycles to failure is hence governed by the ‘small crack’ regime, when crack propagation is slow. Once the crack propagates beyond a certain size, it will grow very rapidly and failure occurs after a small number of additional cycles. Following this argument, mechanisms that can delay crack propagation at an early stage should be particularly effective in extending the fatigue life. The incorporation of an ECC layer (which possesses very high resistance to crack growth) on the tensile side of the concrete beam (where cracks will initiate) may hence be a cost-effective alternative to improve the fatigue performance of a concrete beam.
The fatigue performance of beams made entirely of ECC has been investigated in the past [3], [4]. As expected, the ECC beams exhibited significantly higher fatigue life than plain concrete members. In the present investigation, layered ECC/concrete beams will be made with two different ECC layer thickness. Both monotonic and fatigue flexural tests will be performed. As control specimens, plain concrete members are also cast and tested. The test results, including the number of cycles to failure and the growth of deflection with cyclic loading, will be compared for various cases and discussed.
Section snippets
Specimens, materials and mix
Fatigue behavior of layered ECC–concrete beam was investigated through conducting four-point cyclic bending tests. In each batch, six specimens with dimensions 100 × 100 × 500 mm were cast. Among the specimens, three of them were tested under static flexural load; another three were tested under fatigue flexural load. The strength values obtained in the static tests were used to determine the range of fatigue loading when conducting the bending fatigue tests. The mix constituents and their mix
Layered ECC–concrete beam under static flexural loading
Static load-deflection curves for the different kinds of beams are displayed in Fig. 4. The values of compressive strength for the materials in each batch are given in Table 4. In Table 5, the static flexural strength (or modulus of rupture) of the beams is compared. The average flexural strength of concrete beam was 4.4 MPa. With the addition of ECC, the average flexural strength increased to 5.2 MPa for the 25 mm ECC layer and 6.3 MPa for the 50 mm layer. The percentage of strength
Conclusion
A thorough experimental investigation on the static and fatigue behaviors of ECC layered composite beam was performed through the conduction of four-point bending tests. From the static tests, it was found that the application of a layer of ECC on the tensile side of a flexural concrete beam increased its flexural strength and the degree of improvement increased with the thickness of ECC applied. From fatigue tests, it was found that the application of a layer of ECC was very effective in
References (11)
- et al.
Monotonic and fatigue performance of engineered fiber reinforced cementitious composite in overlay system
Cement and Concrete Research
(2002) - et al.
Experimental study of the fatigue behaviour of high strength concrete
Cement and Concrete Research
(1996) - et al.
Fatigue life prediction of plain and fiber reinforced concrete under flexural load
International Journal of Fatigue
(1999) Engineered cementitious composites–tailored composites through micromechanical modeling
- Y.N. Cheung, Investigation of Concrete Components with a Pseudo-ductile Layer. MPhil Thesis, Hong Kong University of...
Cited by (76)
Peridynamic model of ECC-concrete composite beam under impact loading
2024, Engineering Fracture MechanicsExperimental investigation on the seismic behavior of composite steel plate shear wall restrained by ECC panels
2023, Engineering StructuresExperimental investigation of interfacial shear behavior between Engineered Cementitious Composite and normal concrete
2023, Case Studies in Construction MaterialsMinimizing the crumb rubber effects on the flexural behaviour of the layered RC beams cast using rubberized concrete with or without recycled tire steel fibers
2023, Construction and Building MaterialsChloride penetration resistance of engineered cementitious composite (ECC) subjected to sustained flexural loading
2023, Materials Today Communications