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

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

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

Cigarette filter material and polypropylene fibres in concrete to control drying shrinkage

Due to a reduction in demand for cigarette filter material (North East UK), significant quantities have arisen that have little commercial value. The filter manufacturers have been looking for another outlet for their product and polypropylene fibre replacement in concrete was considered. The purpose of adding Type 1 polypropylene fibres (BS-EN14889) to concrete is to control plastic shrinkage and reduce bleeding. A paired comparison test was carried out to examine concrete cured under extreme conditions of heat and air flow. This micro climate would cause uneven drying due to surface evaporation and internal stresses within the concrete matrix and as a consequence of this instigate drying shrinkage cracking. Type 1 micro polypropylene fibres have known properties to control drying cracking and the performance of concrete with polypropylene fibres was compared against plain concrete and concrete with cigarette filter material. The findings showed that when cigarette filter material and Type 1 polypropylene fibres were compared together their performance was very similar and showed less drying shrinkage cracks than plain concrete

Improving the performance of concrete using 3D fibres

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

Bacterial crack repair to concrete

This study has demonstrated the potential S. pasteurii and consequently MICP holds in improving the integrity of finish to concrete, without the use of chemical based sealants. This is part of an ongoing range of experimental work designed to find an effective way of using bacteria as a cementitious repair agent

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

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

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

Comparative thermal performance test for GGBS and OPC concrete mixes

The research investigates the effect of heating two concrete types and profiles to evaluate the most effective material during diurnal heating and cooling cycles. Plain and finned concrete slabs were manufactured from concrete with a 100% - PC binder (CEM 1) and a binder using 50% - PC and 50% GGBS (CEM 111). The slabs were subject to mainly radiative heat for a 7.5 hour daytime period and left to cool for 16.5 hours. Comparative readings were taken to measure the temperature difference between the two types of concrete during heating and cooling. The findings showed concrete manufactured with GGBS had a lower heat build up and release when compared to concrete manufactured with 100% CEM 1 binder. The research was limited to one comparative test at a single concrete strength with a single water cement ratio, and 50% GGBS cement replacement. Various GGBS cement replacement percentages could be tried to evaluate heat build up and release. Further research on U and Y values are also worthy of further investigation. Thermal mass could be improved thus reducing the need to use energy intensive air conditioning systems