D. Fakhri; M. Hosseini; M. Mahdikhani
Abstract
Fracture toughness is an important concrete property that controls crack extension and concrete fracture. Concrete is the most widely used material in civil engineering containing the most conventional and cheapest materials. Accordingly, cracks and fractures may cause irreparable damages. To this end, ...
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Fracture toughness is an important concrete property that controls crack extension and concrete fracture. Concrete is the most widely used material in civil engineering containing the most conventional and cheapest materials. Accordingly, cracks and fractures may cause irreparable damages. To this end, fibre-reinforced concretes have been recently constructed in order to overcome the aforementioned weaknesses. Crack propagation and fracture toughness of various concrete specimens are analyzed by the straight notched Brazilian disc (SNBD) test. The specimens are conventional concrete lacking micro-silica and limestone powder, and those containing various volume percentages of fibers including the concrete specimens containing 0.35% individual polypropylene (PP) fibers, 0.35% individual glass fibers, concrete specimens containing 0.17% PP and 0.18% glass fibers, and concrete fibers containing 0.1% PP and 0.25% glass fibers. Micro-silica has replaced 10 wt% cement in all fiber-reinforced concrete specimens, and limestone has replaced 5 wt% cement. Crack extension from the pre-existing cracks in the specimens and mode I, mode II, and mixed-mode fracture toughness are calculated. The BD test is performed on the specimens at the crack inclination angles of 0°, 15°, 28.83°, 45°, 60°, 75°, and 90°. The experimental results show the initiation of wing cracks at angles less than 60° (0 < α < 60°) from the tip of the pre-existing cracks. The crack growth and propagation path approach the loading direction by continuing loading. However, the cracks are initiated at a distance of d from the crack tip at angles larger than 60°. The observed distance is larger in the fiber-less specimens than in the fiber-reinforced specimens. The concrete specimens reinforced by 0.17% PP and 0.18% glass hybrid fibers containing micro-silica and limestone powder showed the highest mode I, mode II, and mixed-mode fracture toughness compared to the other concrete specimens.
M. Hosseini; D. Fakhri
Abstract
The purpose of this work is to investigate the possibility of using mine wastes in the improvement of concrete properties. This research work investigates the physical and mechanical properties of the concrete specimens. These concrete specimens include concrete-lacking fibres, micro-silica and limestone ...
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The purpose of this work is to investigate the possibility of using mine wastes in the improvement of concrete properties. This research work investigates the physical and mechanical properties of the concrete specimens. These concrete specimens include concrete-lacking fibres, micro-silica and limestone powder (C), concrete-containing glass fibres without micro-silica and limestone powder (GC), concrete-containing micro-silica and limestone powder without fibres (CML), and concrete-containing glass fibres, micro-silica, and limestone powder (CGML). The physical and mechanical properties including the effective porosity, longitudinal wave velocity, water absorption, unit weight, tensile strength, uniaxial compressive strength, triaxial compressive strength, cohesion, and internal friction angle are investigated. The results obtained show that adding glass fibres to the concrete (GC) improve its properties compared to the fibre-less concrete (C). However, the properties of GC are improved significantly less than CGML. The Brazilian tensile strength and uniaxial compressive strength of GC increase by 13.6% and 10.95% relative to C. The Brazilian tensile strength and uniaxial compressive strength of CGML increase by 21.8% and 45.94% relative to C. Finally, it can be concluded that adding the micro-silica and limestone powder to the glass fibre concrete as well as the use of mine wastes also significantly improves the properties of the concrete.