Papers by Keyword: Fracture Energy

Abstract: In this study, asphalt concrete (AC) mixtures were modified with polymerized sulfur, using PG58-22 bitumen, and crushed siliceous aggregate. Modifications involved replacing the base binder with 20%, 30%, and 50% polymerized sulfur, compared to a control mix with no replacement. The mixtures were subjected to Single Edge Notched-Beam (SE(B)) fracture tests under mixed mode (I/II) conditions with notch offset value of 48 mm, with temperatures ranging from 0 °C to -20 °C. These tests, focusing on the mixtures' response to mixed mode loading, provided load-displacement curves, enabling the determination of fracture energy. Results indicated an increase in fracture energy for 20% and 30% sulfur-modified mixtures. However, a trend towards increased embrittlement was also observed, as fractures occurred at lower displacements. Significantly, higher sulfur content correlated with similar or decreased mixed-mode (I/II) fracture energy, suggesting an improved resistance to low-temperature cracking for lower replacement percentages.

Abstract: In this research, asphalt concrete (AC) mixtures modified by polymerized Sulfur were prepared. PG58-22 bitumen was used as the base binder for the mixtures along with crushed siliceous aggregate. The base binder was replaced by 20%, 30%, and 50% ratios with polymerized Sulfur in the modified mixtures while the reference mix was fabricated with 0% binder replacement. Single edge notched-beam fracture tests (SE(B)) were carried out in a temperature range of 0 °C to-20 °C on the AC beam specimens. Load-displacement curves were obtained from the experiments and the fracture energy of the mixtures could be determined. It was revealed that modifying the mixtures with polymerized Sulfur could improve the load bearing of the beam specimens as higher peak load values were recorded at fracture. However, fracture failure of the AC beams occurred at lower values of displacement addressing further embrittlement of the mixtures due to replacement of the base binder. Higher contents of polymerized Sulfur in the mixtures resulted in higher magnitudes of fracture energy as a general trend in this research addressing an improved resistance to low-temperature cracking.

Abstract: This study addresses a numerical investigation of the bond behaviour exhibited by an FRCM system when subject to tensile and single direct shear tests. A reinforcement system, based on a polyparaphenylene benzobisoxazole (PBO) bi-directional fibre mesh and a mixed cement-pozzolanic mortar is selected. The system is characterized by the presence of coated glass-fibre yarns and dry polypropylene yarns alternated to the PBO yarns in the warp and weft directions, respectively. The mechanical characterization of composite constituent materials is carried out together with tensile and direct shear tests. Concerning mechanical interpretation of the tests, within a mode II fracture mechanics, and assuming a trilinear cohesive material law (CML), the stress transfer law between the fibre and the matrix is back calibrated from single direct shear test results. The CML obtained is employed into a finite-difference model developed for the purpose. Tensile tests are modelled providing adequate boundary conditions. Results satisfactorily agree with the tested behaviour of the FRCM system.

Abstract: Natural fibre reinforced concrete is been studied for many years as a more sustainable option to current reinforced concrete used in industry. The most common fibre materials currently adopted are steel, glass and synthetic fibres. Apart from the high oxidation and cost, their environmental impact is a serious issue as they are petroleum-based materials. This study assesses the feasibility of replacing polypropylene fibre with hemp and flax fibres. According to the inventory of carbon and energy (ICE) the embodied energy of polypropylene (PP) is 95.4MJ/kg and the embodied carbon is 4.98kgCO2/kg during its lifetime. It represents approximately 3 times more than the estimated values for vegetable fibres. For this, Different concrete mixtures reinforced by 0.5% to 1.0% of hemp, flax and polypropylene fibres were tested, and their post-crack flexural tensile strength, elastic’s modulus, compressive strength and fracture energy were evaluated. The mixtures containing hemp fibres presented properties equivalent to those containing polypropylene under the same proportion. Although both compressive and tensile strength were reduced for the mixes containing flax fibres, the Young’s modulus was 49% smaller and could be an interesting approach for applications that require better elasticity from the concrete, such as industrial floors and structures that may be submitted to impact.

Abstract: Fibre-reinforced concrete (FRC) is widely employed in the construction industry, with assorted fibre types being used for different applications. Typically, steel fibres give additional tensile strength to the mixture, while flexible fibres may be used in large sections, such as floor slabs, to control crack width and to improve the handling ability of precast sections. For many reasons, including durability concerns, environmental impact, thermal performance, etc, alternatives to the currently available fibres are being sought. This study examines the potential of using basalt fibres, a mineral and natural material, as reinforcement of concrete sections in comparison to steel fibres and plain concrete mix. Mixes were tested containing 0.5% and 1.0% of basalt fibres measuring 25mm length, 0.5% of the same material with 48mm length and steel fibres measuring 50mm by 0.05%, 0.1%, 0.15% and 0.2% of the concrete volume. For the mechanical performance analysis, the 3-point bending test was led and the fracture energy, Young’s modulus and tensile strength in different moments of the tests were calculated. When compared to the control mixtures and the steel-fibre-reinforced concrete, the mixes containing basalt had a reduction in their elastic modulus, representing a decrease in the concrete brittleness. At the same time, the fracture energy of the mixtures was significantly increased with the basalt fibres in both lengths. Finally, the flexural strength was also higher for the natural fibre reinforced concrete than for the plain concrete and comparable to the results obtained with the addition of steel fibres by 0.15%.

Abstract: Fracture energy (G_f) studies provide us with means to assess the variation in ductility of concrete. This paper presents the results of fracture energy studies conducted on 18 mixes of M60 Grade concrete consisting of rubcrete (0%, 5%, 10%, 15% of crumb rubber), steel fibre reinforced rubcrete (0.25%, 0.5%, 0.75%, 1% steel fibres and 0% and 15% crumb rubber) and polypropylene fibre reinforced rubcrete (0.1%, 0.2%, 0.3% polypropylene fibres and 0% and 15% crumb rubber) using three-point bend beam tests on 60 × 100 × 500 mm specimens as per TC 50 FMC (1985). Results indicated an enhancement of fracture energy with an increase in rubber content.

Abstract: The paper shows results of microscale experimental tests performed on cement paste specimens fabricated by focused ion beam milling. The specimens are prepared in the form of cantilever beams and loaded in bending by nanoindenter. The dimensions of specimens are in the order of a few micrometers which corresponds to the single phase size. Intact and notched specimens with a stress concentrator are tested. Tensile strength and fracture energy are derived for the hydration product by analyzing the nanoindentation data and with the aid of analytical and numerical modeling. Although small number of tests is performed good correlation of the results is reached with respect to the available literature and molecular dynamic simulations.

Abstract: One of main raw materials for monolithic refractory is calcium aluminate cement which provides CA6 hexagonal plate-like microstructure with self-toughening properties and fracture resistance. In the present study, in-situ CA6 was formed by using sintered alumina mixing with alumina cement in stoichiometric composition to achieve 100 mass% and 50 mass% of CA6 in alumina monolithic refractory with 2 mass% of silica addition. Samples were fired from 1400-1500°C for 5 h and characterized for physical and mechanical properties. The results showed that both samples could not obtain CA6 content as expected and apparent porosity did not exhibit in the same tendency. However, only proper amount of CA6 content could gain proper amount of apparent porosity which is the main effect of mechanical properties. Especially the formation of CA6 lower than 50 mass% with the presence of low melting phase caused low apparent porosity and led to high fracture toughness and effective fracture energy.

Abstract: This article deals with the experimental investigation of residual mechanical properties of refractory composite after the action of various thermal loading. Specimens with dimension 40 × 40 × 160 mm were produced from composite containing basalt fibres and aggregate, aluminous cement and metakaolin. Different group of specimens were exposed to various temperatures 105 °C, 200 °C, 300 °C, 400 °C, 500 °C and 600 °C for three hours. Different temperature caused various changes in chemical composition of concrete that can result into decrease of mechanical properties. Bulk density, flexural strength, compressive strength, fracture energy and dynamic modulus of elasticity were investigated after each type of thermal loading. After the action of 600 °C all investigated residual properties achieved lowest values. Based on performed experiments we can conclude that the main decrease of mechanical properties take place after the action of 400 °C.

Abstract: This study deals with experimental determination of tensile properties of cement paste hydration products at micro-scale. Cantilever micro-beams with length of about 16 µm and pentagon cross section with micrometer dimensions were fabricated by focused ion beam milling on hydrated cement paste samples. Nanoindentation was used for evaluating elastic properties while tensile properties were derived from beam bending tests. Displacement controlled micro-scale tests give access to both tensile strength and estimates of fracture energy based on the load-displacement curves measured with the nanoindenter. The mean tensile strength and the fracture energy of inner hydration product were assessed as 791 MPa and 16.7 J/m², respectively. The huge difference of the micro-scale properties when compared to macroscopic values comes from the scaling properties of concrete.