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Dramix® Steel – and Synthetic Fibre Reinforced Concrete Which fibre to use for which application and why? INTRODUCTION Fibres for concrete, they appear in all colours, shapes, sizes Specific technical strengths and weaknesses of the different and materials. Today, the majority of the fibres used in concrete fibres, are often less well known, and lead to confusion. The can basically be classified into 3 families: main purpose of this brochure is to offer you an
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  Dramix ® Steel – and Synthetic Fibre Reinforced Concrete Which fibre to use for which application and why? INTRODUCTION Fibres for concrete, they appear in all colours, shapes, sizes and materials. Today, the majority of the fibres used in concrete can basically be classified into 3 families:1. Steel fibres2. Micro synthetic fibres3. Macro synthetic fibresSpecific technical strengths and weaknesses of the different fibres, are often less well known, and lead to confusion. The main purpose of this brochure is to offer you an insight into the technical performance of the different materials. This brochure seeks to answer a question you might have: “Which fibre to use/specify for which application, and why?  Ann Lambrechts Head R&D of Bekaert Building Products  Table of contents  01 Introduction02 Material Properties: what we can learn05 Reinforcement   Plastic shrinkage reinforcement  Drying shrinkage reinforcement & crack control  Load bearing reinforcement in SLS & ULS 08 Creep behaviour09 Fire resistance10 Corrosion resistance10 The right fibre for the right use  1. WHAT CAN WE LEARN FROM MATERIAL PROPERTIES? “Structural use is where the addition of fibres is intended to contribute to the load bearing capacity of the concrete element” Eric Winnepenninckx - Belgian Construction Certification Association (BCCA)  Applicable toWHAT Initial type testing and factory production control by EU certification body System 1Fibres for structural useSystem 3Fibres for other uses Initial type testing by notified labOnly internal factory production control CERTIFICATE (From EU certification body) MANUFACTURER’S DECLARATION Since June 2008, all fibres in EU must comply with standards EN 14889-1 and 2, and be CE labelled. Two levels of attestation are defined: Material Thermal Expansion coefficient λ Melting Point (°C)Creep behaviour in tension (Tg glass transition temperature)(Shrinkage for a temperature decrease of 30°C on a 50 mm long fibre) 12 x 10-6/°C0.018mm12 x 10 -6/°C0.018mm1.5 x 10 -4/°C0.23 mm Young’s ModulusTensile strengthDensityResistance to UV lightCorrosion resistanceTypical length of fibresTypical diameter of fibresBekaert brandsCE label is compulsory in EU –in accordance with +370°C1500°C- 20°C165°C does not reinforce30 000 MPa2 400 kg/m 3 210 000 MPa500 – 2 000 MPa7 850 kg/m3in concrete, and cracks < 0.2 mm30-60 mm0.5 – 1.0 mmDramix ® , Wiremix ® EN14889-13 000 – 10 000 MPa200 – 600 MPa910 kg/m 3 degradation will occur micro:   6 - 20 mm   macro:   30 – 65 mm micro:   0.015 – 0.030 mm   macro:   0.5 – 1.0 mm micro:  Duomix ® macro:  Synmix ® EN14889-2ConcreteSteel Mesh / Steel breMicro / Macro Polymer FibreExtruded polypropylene / polyethylene 2  EN 14889-1 in fact states that structural use is where the addition of fibres is designed tocontribute to the load bearing capacity of the concrete element. The manufacturing process of fibres for structural use should therefore be audited regularly by a certified body. This is not necessary for fibres for other use (non-structural use). A declaration of the manufacturer is sufficient in this case.Concrete and steel have always been complementary: concrete is strong in compression; steel is strong in tension. Concrete protects steel against corrosion as long as the concrete is alkaline, and delays softening of the steel during a fire. Concrete and steel expand/contract equally due to temperature changes (equal thermal expansion coefficient). Only steel fibres, no macro polymer fibres can act as structural reinforcement of concrete for the following reasons:   Polymer fibres melt at 165°C ; in a fire any “reinforcing” effect of the macro fibres fades away as the temperature rises. The Young’s Modulus is 3 - 10 GPa, which is largely insufficient to reinforce  concrete material with a modulus of 30 GPa.  Macro polymer fibres creep  (further elaborated below) (Fig 1)123 -20 o C165 o C T g   glass transition temperature elasticVisco-elasticLiquidNo creepCreep T m   Melting point CE info sheet  According to EN 14889, a minimum performance level must be reached. As such for every fibre for structural use, a minimum dosage is required to have CE marking.Download info sheets at:www.bekaert.com/building B e k a e r t r e c o m m e n d s t o  u s e  a t  l e a s t C E  m i n i m u m d o s a g e !  3  4 Below -20°C , polypropylene/polyethylene are typically elastic with negligible creep. Between -20°C and 165°C , (at ambient temperature), polypropylene/polyethylene is typically visco-elastic, with significant creep. Creep is the increase in extension of a material under constant load. The deformation of the fibre is not only time-dependent, but also temperature-dependent.So creep rises with temperature in the range 20°C to 40°C.Creep of the fibre leads to:ã Unsustainable crack widths (which will widen, over time, under constant loading), thereby adversely affecting the durability of the concrete, serviceability, liquid tightness, ...ã Creep rupture of the fibre, even at stress levels corresponding to the serviceability limit state. Macro polymer fibres are not proven to be a durable reinforcementNo long-term evidence  on durability / ageing on polymer fibre concrete is available . UV-degradation  of macro-synthetic fibres is another cause for concern.Due to the important creep behaviour, it is therefore mentioned explicitly in the Austrian standard- section 1.2.3 - that macro synthetic fibre concrete is not covered  by the design rules on load bearing capacity and serviceability. Tensile strength250006058564069050010001500Time in hours Tests at the Bekaert lab have shown a complete deterioration of the macro-synthetic fibres: 1500 hrs of UV-light  were sufficient to completely embrittle and break the fibres. 4
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