2,513 research outputs found

    Polypropylene fibres within concrete with regard to heat induced spalling and reduction in compressive strength

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    The paper examines the effect of various polypropylene fibre additions (Types 1 and 2 and different fibre volumes) to concrete with regard to explosive spalling when subject to high temperatures similar to that experienced in building or tunnel fires. The pilot study used to determine an appropriate heat source for the test showed concrete to be a significant insulator and fire protection for structural members. Explosive spalling was shown to be reduced with the use of polypropylene fibres but the final compressive strength of concrete was significantly reduced and had little residual structural value after a 2 hour period of heating

    Post crack flexural toughness in steel fabric and fibre reinforced concrete beams

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    The purpose of the paper is to provide independent research and evaluate manufacturers’ claims that structural polypropylene fibres provide satisfactory crack control reinforcement and compare the test results from macro synthetic polypropylene fibres against steel fabric reinforced concrete, extensively used as a crack control medium in concrete ground bearing floor/hardstanding slabs where tensile forces are likely to occur. Three concrete beam types were produced, plain, steel reinforced and fibre reinforced, and a comparative study was undertaken of post crack flexural toughness. The procedure used was to manufacture steel A 142 fabric and macro fibre reinforced concrete beams to provide load, deflection data, toughness indices and was compliant with, ASTM C1018 -97, [ASTM, 1997] using a three point loading arrangement. The data was representative of what might occur in a floor slab. The findings of the paper is that A1 42 steel fabric reinforcement as used in slabs was more effective in producing toughness and residual strength when directly compared to the performance of structural polypropylene fibre reinforced concrete. When small post crack forces are encountered within the concrete matrix, polypropylene macro fibres are suitable for crack control. The paper makes direct comparisons between known and widely used crack control using steel fabric, and the use of low modulus polypropylene macro synthetic fibres as a crack control medium

    Improving the performance of concrete using 3D fibres

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    This paper examines whether 3D fibre reinforcement can improve the toughness and flexural strength of concrete, when compared to equal dosage of straight steel fibres. This work was carried out to determine structural qualities that may lead to potential enhanced performance when concrete is subjected to a bomb blast and in addition the same structural qualities may act as a safety measure in earthquake situations. The majority of injuries caused from bomb attacks are a result of fragmented building components energised by the blast wave, therefore it is vital to reduce fragmentation of concrete. It is known that fibre reinforcement can reduce fragmentation of concrete by increasing energy absorption. A three point beam test was conducted on two batches of beams reinforced with straight steel and 3D fibres respectively, so that flexural strength and post crack toughness could be calculated and compared. A paired comparison test was carried out between the straight steel fibres and the 3D fibres. 3D and straight steel fibres were also embedded in cubes, so that pull out testing could be conducted and compared for the two fibre types. 3D fibre reinforced samples proved to have a higher flexural strength and post crack toughness than straight steel samples. 3D fibres also had a much higher pull out value. After testing, 3D fibres continued to span the rupture plane after initial crack formation during 3 point bend testing, which held together the concrete matrix. These findings suggest 3D fibre reinforced concrete would perform better as a blast protection material when compared to straight steel fibre reinforced concrete, as the results show 3D fibres produce tougher concrete that hold together fragments after loading

    Synthetic fibres and steel fibres in concrete with regard to bond strength and toughness

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    The ability of fibre reinforced concrete composites to absorb energy has long been recognised as one of the most important benefits of the incorporation of fibres into plain concrete” (Golpalaratham and Gettu 1995). Steel and synthetic fibres have been used in concrete floor slabs with success in providing crack control. Slab design using synthetic fibres relies heavily upon manufacturers design guidance whereas steel fibres have better developed independent design guides available to assist their correct use (The Concrete Society 2007a). This paper examines the pull out values of both steel and Type 2 synthetic fibres embedded in concrete and equates their dosage when used in beams to provide near equal toughness values, thus providing the designer with a synthetic/steel fibre ratio by mass of fibre addition for equal performance. According to Nataraja, et al (2000), the most common method to measure toughness, is to use the load-deflection curve. One of the most widely used load-deflection tests has been ASTM 1018, which was used herein to evaluate the post crack toughness; by stating toughness as independent indices and residual strengths based upon the deflection at the formation of the first crack in the beam in relation to fixed points of further deflections under load. The ASTM test was chosen as it has been widely used and it is readily understood by many readers. The research demonstrates that near equal post crack toughness can be achieved in concrete beams using steel and synthetic fibres, at different doses

    Concrete manufacture with un-graded recycled aggregates

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    Purpose – The purpose of this paper is to investigate whether concrete that includes un-graded recycled aggregates can be manufactured to a comparable strength to concrete manufactured from virgin aggregates. Design/methodology/approach – A paired comparison test was used to evaluate the difference between concrete made with virgin aggregates (plain control) and concrete including recycled waste. Un-graded construction demolition waste and un-graded ground glass were used as aggregate replacements. With regard to concrete, compressive strength is widely used as a measure of suitability as being fit for purpose. Therefore compressive strength was mainly used to compare the different concrete batches; however density was measured across the range of samples. Findings – The findings show that a lower average compressive strength is achieved when compared to the plain control sample manufactured with virgin aggregates. Correct particle packing may not be achieved and grading of aggregates is essential prior to mix design. The recycled aggregate was highly variable in terms of the fine particle content, which affected the water demand of the concrete. Practical implications – This manufacturing practice is considered necessary because of the current trend in using waste products in concrete to replace binders and aggregates; thus reducing the impact on the environment and use of finite natural resources. The research shows the risk of mixing concrete using a simple aggregate replacement without careful aggregate grading and adjustments to the mix design. Originality/value – The paper examines 100 per cent ungraded aggregate replacement with glass and demolition waste

    The effect of polypropylene fibres within concrete with regard to fire performance in structures

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    Purpose – The purpose of this paper is to examine the effect of various polypropylene fibre additions (types and volume) to concrete with regard to explosive spalling when subject to high temperatures similar to those experienced in building or tunnel fires. Design/methodology/approach – Medium strength concrete was manufactured with varying proportions of polypropylene fibres. Plain control samples were used to determine the original concrete strength and this was used as a benchmark following high temperature heat tests to evaluate the surface condition and final compressive strength. A pilot study was used to determine an appropriate heat source for the test. This was three Bunsen burners, however sufficient heat could not be generated within 150mm concrete cubes and the concrete was shown to be a significant insulator and fire protection for structural members. The concrete test cubes were tested in a saturated condition which may reflect conditions where concrete is used in an external environment and thus is subject to soaking. Findings – One hundred and fifty millimetre concrete cubes with and without fibres were placed into a furnace at 1,000°C. Explosive spalling was shown to be reduced with the use of polypropylene fibres but the final compressive strength of concrete was significantly reduced and had little residual structural value after a two hour period of heating. Research limitations/implications – As the concrete tested was saturated, this condition provided a worst case scenario with regards to the build up of hydrostatic and vapour pressure within the cube. A range of percentage moisture contents would produce a more evenly balanced view of the effects of fibres in concrete. A single grade of concrete was used for the test. As the permeability of concrete influences the rate at which steam can escape from the interior of a saturated concrete cube, testing a range of concrete strengths would show this aspect of material performance with regard to spalling and final residual strength. Further research is recommended with regard to moisture contents, strengths of concrete and a range of temperatures
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