International audienceThis study investigates the effect of adding different types of fibers on the microstructure and the mechanical behavior of cementitious composites, in particular on UHPC. These fibers were distinguished mainly by their differing nature (steel, mineral and synthetic), their dimensions (macroscopic or microscopic), and their mechanical properties. The microstructure of the specimens was examined by using SEM observation and by measuring the porosity, the intrinsic permeability and the P-wave velocity. The mechanical behavior under loading has been studied using a uni-axial compression test which combines the gas permeability and the acoustic emission (AE) measurement. This work focuses on the cracking process under mechanical loading. The experimental results show that the fiber has a relatively slight influence on the compressive strength and elastic modulus of concrete, except for the steel fiber which improves the strength because of its intrinsic rigidity. However, The addition of fiber significantly reduces the lateral strain at peak loading and increases the threshold of initial cracking (σk-ci) and that of unstable cracking (σk-pi). Therefore, the fibers clearly restrain the cracking process in concrete under the mechanic loadin

In this paper, the effect of thermal treatment on physical and mechanical properties of a granitic rock is experimentally investigated. The open porosity, gas permeability, P-wave velocity (and their attenuation), ultimate strength, and Young’s modulus are measured on samples heated at temperatures ranging from 105°C to 600°C. First, results show good correlations between the evolution of physical properties and the amount of the damage induced by the thermal treatment. Second, the mechanical parameters are shown to be dependent on the microcracks’ density in the samples. The effect of temperature on the failure process in granite is also investigated using strain gauge measurements and permeability evolution in a uniaxial compressive test. The results show that the extent of the crack closure stage depends on the initial crack density and that the crack thresholds, which characterize the failure process of the rock under compressive loading, decrease with the thermal treatment.

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Abstract:Oil palm shell is an interesting organic material that can be used as aggregate for concrete. It can help mitigate the environmental problems caused by the concrete industry. We intend to contribute to the knowledge of OPS (oil palm shells) concrete studying the physical mechanic and thermal behavior. Then, this paper presents the results of investigations carried out on the effects of replacing by volume, CGA (crushed granite aggregate) in concrete with OPS. Then, the dry density, apparent porosity, water absorption, electrical resistivity, thermal parameters, flexural strength, compressive strength and static elastic modulus are investigated. Microscopic analysis with an SEM (scanning electron microscopic) is also conducted. The results show that replacing crushed granite aggregate by OPS, increases the apparent porosity of concrete. This makes the concrete lighter and the concrete mechanical strengths lower. SEM analysis indicates that these decreases may be the consequence of a bad bond existing between the cement paste and OPS aggregate. Though, the compressive strength of OPS concrete which is 28 days old is acceptable for structural concrete. OPS concrete is more ductile and has a better thermal behavior compared to CGA concrete.