Search Results (10)

In the present study, a programme of experimental investigations was carried out to examine the direct uniaxial tensile (and pull-out) behaviour of plain and fibre-reinforced lightweight aggregate concrete. The lightweight aggregates were recycled from fly ash waste, also known as Pulverised Fuel Ash (PFA), which is a by-product of coal-fired electricity power stations. Steel fibres were used with different aspect ratios and hooked ends with single, double and triple bends corresponding to 3D, 4D and 5D types of DRAMIX steel fibres, respectively. Key parameters such as the concrete compressive strength f_lck, fibre volume fraction V_f, number of bends n_b, embedded length L_E and inclination angle ϴ_f were considered. The fibres were added at volume fractions V_f of 1% and 2% to cover the practical range, and a direct tensile test was carried out using a purpose-built pull-out test developed as part of the present study. Thus, the tensile mechanical properties were established, and a generic constitutive tensile stress–crack width σ-ω model for both plain and fibrous lightweight concrete was created and validated against experimental data from the present study and from previous research found in the literature (including RILEM uniaxial tests) involving different types of lightweight aggregates, concrete strengths and steel fibres. It was concluded that the higher the number of bends n_b and the higher the volume fraction V_f and concrete strength f_lck, the stronger the fibre–matrix interfacial bond and thus the more pronounced the enhancement provided by the fibres to the uniaxial tensile residual strength and ductility in the form of work and fracture energy. A fibre optimisation study was also carried out, and design recommendations are provided. Full article

Steel fibre-reinforced concrete (SFRC) consists of short, hooked steel fibres that are randomly distributed and oriented within the cementitious matrix. This paper presents a new analytical load-bounding approach that captures the tensile response of misaligned fibres embedded in the matrix. The contribution of fibres in bridging cracks to provide the required stress transfer relies on the orientation of the fibres in the concrete. Bridging fibres aligned with a crack are less effective than those inclined to it. Therefore, understanding the pull-out behaviour of misaligned fibres is a key factor in quantifying and optimising the design of SFRC in structural applications. In the laboratory, a single-oriented fibre embedded in a solid cylinder of concrete was subjected to a pull-out test, where the axis of the tensile force is aligned with the axis of the cylinder. Based on the observed behaviour, this paper presents a new analytical bounding approach to capture the pull-out response of misaligned hooked-end steel fibres embedded in a concrete matrix. The analysis was based on a transversely isotropic failure criterion assumed for the plasticity that occurs in the cold-drawn fibre. Lower and upper bounds to the loading failure were derived from fibre pull-out and fibre fracture, respectively. The division between bounds depended upon the fibre orientation, fibre diameter and the combined strengths of the steel and concrete. Bounding predictions were drawn from ratios between a fibre’s shear strength and its transverse and axial uniaxial strengths, as found from a novel testing proposal. The two bounds were compared with new data and other experimental results published in the literature. The results showed that the region between the bounds captured the failure loads of embedded fibres with effective load-bearing orientations. A critical orientation was observed at maximum strength. The present interpretation of the plasticity occurring within off-axis, hooked-end steel fibres suggests that it is possible to optimise the strength of concrete using this method of reinforcement. Full article

Flexural strength is an important mechanical property of steel-fibre-reinforced concrete. By designing three-point bending tests of concrete with five specimen heights, three steel fibre types, and two steel fibre mixing methods, the effects of the specimen height, steel fibre mixing method, and steel fibre type on the peak load, effect of size, section characteristics, strain characteristics, and characteristics of the load–displacement curve of concrete specimens were studied. The results show that the peak load of the control group is basically linear with the height of the specimen. After adding three kinds of steel fibres, the peak load of the specimen is greater than that of the control group in the same case. The peak load of the specimen increases by adding three kinds of steel fibres, and the increase is closely related to the height of the specimen. The residual stage of the load–displacement curve of the milling steel fibre and the end hook steel fibre are relatively flat, while the residual stage of the load–displacement curve of the shear steel fibre is relatively large, and the residual load is also greater than the residual load of the shear steel fibre. The specimens in the control group show brittle failure characteristics. As the height of the specimens increases, the failed section of the specimens is smoother. The development of cracks in the steel fibre specimens is more tortuous than that of the control group, showing ductile failure characteristics. Some tensile failure zones are still present where the fibres are densely distributed, and the failure characteristics of the specimens are further explained and proven by the strain characteristics. Full article

The fire resistance of construction materials is an essential part of safety requirements in the construction industry. In this work, experimental investigations were conducted to understand the thermal behaviour, spalling, transfer characteristics, strength, and microstructures of self-cured high-strength plain (HSGC) and steel-fibre-reinforced geopolymer concrete (S–HSGC) under severe fire scenarios with peak temperatures of 275, 560, and 825 °C; the peak was maintained for a period of 120 min after reaching it. Forty-eight standard cylindrical specimens for each mixture were prepared to test and analyse their time–heat response, gradients, visual appearance, spalling, density change, water absorption, and compressive strength before and after fire exposure. Additionally, Scanning Electron Microscopy (SEM) along with Energy Dispersive X-ray Analysis (EDX) were utilised to analyse the internal structures and phase transformations. The thermal analysis showed that no cases of explosive spalling were recorded during sample exposure to various fires, while the used hook-end steel fibres had an influence on the considered test variables. The sample cores almost reached the target heat, and the thermal saturation degree at the peak ranged from 55 to 97%. The experimental findings also revealed slight surface cracking after exposure to 560 °C fires, while the surface cracking was more obvious for specimens exposed to 825 °C. Moreover, the residual compressive strength of the S–HSGC at various fires was noticeably 10.20% higher than that of the HSGC. Also, state-of-the-art research data were used to discuss the prediction model’s performance. The SEM and EDX results showed that the self-cured geopolymerization process was effective and successful in producing gels, in addition to the significant phase transformations in microstructures at different fires. This study presented sophisticated data on the behaviour of HSGC and S–HSGC exposed to fires up to 825 °C. Full article

Concrete is the central pile for the infrastructure that maintains civilisation and human life. The concrete industry faces many challenges, including improving mechanical properties, eco-friendliness, and durability. In this context, the present study focuses on evaluating and modelling themechanical properties of engineered concrete, namely slurry-infiltrated fibrous concrete (SIFCON). The main experiments will be devoted to measuring and modelling the failures of slabs made from SIFCON under two loading systems, namely static and impact loading systems. The model was developed using a non-linear finite element analysis. The experiments considered the influence of the geometry of the reinforcement steel fibres (hook-end fibres, microfibres, and combined hook-end and microfibres), sizes of fibres, and slab dimensions. The outcomes of this investigation showed that increasing the slab’s thickness enhances the load-bearing capacity of the SIFCON slab, and the microfibres and combined hook-end and microfibres improved the load-bearing capacity of the slab compared to the hook-end fibre. Generally, it was noticed that the outcomes of the experiments agreed with the modelling outcomes. Nevertheless, it was noticed that experimentally measured axial deformation was more significant than the predicted axial deformation. In summary, the difference between experimental and modelling outcomes was 1.1–10.2%, with a standard deviation of 0.0264. Based on the excellent ability of SIFCON to resist impacts and dynamic loads, it is recommended to be used in pavements, military structures, nuclear reactor walls, and in areas subjected to high bending moments, such as corner connections subjected to opening bending moments. Full article

The proper disposal of used rubber tires has emerged as a primary concern for the environment all over the globe. Millions of tires are thrown away, buried and discarded every year, posing a major environmental concern owing to their slow decomposition. As a result, it is advantageous to use recycled waste rubber aggregates as an additional building resource. Recycling crushed rubber would lead to a long-term solution to the problem of decreasing natural aggregate resources while conserving the environment. This study examines the impact strength variability and reliability of preplaced aggregate concrete containing crumped rubber and fibres. Ten different mixtures were prepared by replacing natural aggregate with crumped rubber (5, 10, 15 and 20%). The crumped rubber was pretreated by the water with sodium hydroxide dilution for 30 min before usage. Hooked-end steel fibres were used at a dosage of 1.5%. The compressive strength, impact strength, impact ductility index and failure pattern were examined and discussed. In addition, a statistical method called Weibull distribution is used to analyze the scattered experimental results. The results showed that when the crumb rubber content was raised, the retained first cracking and failure impact numbers increased. As a result of substituting crumb rubber for 20% of the coarse aggregate in plain and fibrous mixes, the percentage development in first crack and failure was between 33% and 76% and 75% to 129%, respectively. Full article

In this study, the impact of steel fibres and Silica Fume (SF) on the mechanical properties of recycled aggregate concretes made of two different types of Recycled Coarse Aggregates (RCA) sourced from both low- and high-strength concretes were evaluated through conducting 60 compressive strength tests. The RCAs were used as replacement levels of 50% and 100% of Natural Coarse Aggregates (NCA). Hook-end steel fibres and SF were also used in the mixtures at the optimised replacement levels of 1% and 8%, respectively. The results showed that the addition of both types of RCA adversely affected the compressive strength of concrete. However, the incorporation of SF led to compressive strength development in both types of concretes. The most significant improvement in terms of comparable concrete strength and peak strain with ordinary concrete at 28 days was observed in the case of using a combination of steel fibres and SF in both recycled aggregate concretes, especially with RCA sourced from high strength concrete. Although using SF slightly increased the elastic modulus of both recycled aggregate concretes, a substantial improvement in strength was observed due to the reinforcement with steel fibre and the coexistence of steel fibre and SF. Moreover, existing models to predict the elastic modulus of both non-fibrous and fibrous concretes are found to underestimate the elastic modulus values. The incorporation of SF changed the compressive stress-strain curves for both types of RCA. The addition of steel fibre and SF remarkably improved the post-peak ductility of recycled aggregates concretes of both types, with the most significant improvement observed in the case of RCA sourced from a low-strength parent concrete. The existing model to estimate the compressive stress-strain curve for steel fibre-reinforced concrete with natural aggregates was found to reasonably predict the compressive stress-strain behaviour for steel fibres-reinforced concrete with recycled aggregate. Full article

The most researches on steel-concrete-steel (SCS) sandwich slabs are to control the cracking of concrete core along with losing weight, and shear connector type. In this study, the behaviour of SCS slabs with bi-directional corrugated-strip shear connectors (CSC) was investigated. One of the most important practical problems of CSCs in SCS slabs is lack of access for another end welding to the second steel faceplate. In this research, plug weld was proposed to provide partial welding of the other end of CSCs to a steel plate. For this reason, three slabs were manufactured using the normal concrete core as a control sample and lightweight concrete (LWC) core with and without steel fibres. The behaviour of these slabs was compared with the behaviour of SCS slabs with J-hook and stud bolt connectors from previous researches. The specimens were tested under a concentrated block load as quasi-statically. Based on the load-displacement relationship at the centre, failure modes, loading capacity, energy absorption, and ductility showed acceptable behaviour for CSC system slabs. There was also a good agreement between the ultimate flexural strength based on experiments and previous research relationships. Full article

This study investigates the fracture properties of high performance cementitious composites (HPCC) with four different types of fibres and with volume fraction content 3%. The four fibres are steel hooked end (S), polypropylene crimped (PP), basalt chopped (B), and glass (G) fibres. The tests were carried out in accordance with the RILEM recommendations. In order to examine the fresh properties of HPCC the slump flow tests were performed. Twelve fibre reinforced HPCC beam specimens with notch were cast and tested using central point loading experiments. In addition, experimental tests of the compressive strength and splitting tensile strength were carried out. The test results made it possible to obtain representative fracture parameters, such as the equivalent strengths, residual strengths, and fracture energy of fibre reinforced HPCC. The S fibre specimens showed the best performance in terms of workability, compressive strength, tensile splitting strength, and fracture energy at large deflection. On the other hand, G fibre specimens exhibited the best performance in terms of flexural strength, equivalent flexural strength at higher deflection, and residual flexural strength at lower deflection. In terms of equivalent flexural strength at lower deflection and residual flexural strength at higher deflection, basalt fibre specimens performed the best. On the contrary, polypropylene fibre reinforced beam specimens revealed the highest deflection capacity. Full article

Addition of steel fibres to concrete is known to have a significant positive influence on the mechanical properties of concrete. Micro polypropylene (PP) fibres are added to concrete to improve its performance under thermal loads such as in case of fire by preventing the phenomena of explosive spalling. An optimum mixture of steel and micro PP fibres added to concrete may be utilized to enhance both the mechanical and thermal behaviour of concrete. In this work, systematic investigations were carried out to study the influence of elevated temperature on the mechanical properties and physical properties of high strength concrete without and with fibres. Three different mixtures for high strength concrete were used, namely normal concrete without fibres, Steel fibre reinforced concrete and Hybrid fibre reinforced concrete having a blend of hooked end steel fibres and micro PP fibres. The specimens were tested in ambient conditions as well as after exposure to a pre-defined elevated temperature and cooling down to room temperature. For all investigated concrete mixtures the thermal degradation of following properties were investigated: compressive strength, tensile splitting strength, bending strength, fracture energy and static modulus of elasticity. This paper summarizes the findings of the tests performed. Full article