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Compact Reinforced Composite CRC is the designation for a special type of Fibre Reinforced High Performance Concrete with high strength (150-400 MPa) developed by Aalborg Portland A/S. Because of a large content of steel fibres the matrix is very ductile and that makes it possible to utilise rebars much more effectively without having large cracks under service conditions. The size of the fibres and the largest grains of the matrix dictate the distance between reinforcing bars and the cover layer to the reinforcement, both of which have to be optimised in the slender structures, which can be produced with CRC. This is the reason for typically using a mortar composition for CRC and for using short fibres. Often a cover layer of 10-15 mm and a similar distance between individual bars are used. With the high fibre contents, CRC is especially suitable for pre-cast applications, but in-situ cast concrete with 6% by volume of fibres has also been produced - for joints between slabs made in conventional concrete - using a poker vibrator for compaction. For these applications a premix called CRC JointCast is usually supplied. CRC has been the subject of a number of research projects investigating mechanical properties as well as durability and fire resistance. This information is necessary in order to be able to use CRC for structural applications, as this type of material is not covered in existing standards and codes of practice. Mechanical properties depend on type of aggregate, curing, content and type of fibres, reinforcement etc., but they will typically be in a range of: |
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150-400
MPa
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100-300 MPa |
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50-100 Gpa |
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2700-3500 kg/m3 |
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CRC - developed in 1986 at Aalborg Portland, Denmark - is a special concept for high performance concretes, where ductility is achieved through incorporation of a large content of short, stiff and strong steel fibers (typically 3-6 vol.%). This ductility combined with high compressive strength (150-400 MPa) and exceptional durability makes it possible to utilize a large amount of reinforcement, thus giving new structural possibilities compared to conventional concrete. The properties of CRC are often indicated as a range, as the properties depend on type of aggregate, fiber type and content and type of main reinforcement. E.g. for compressive strength a range of 150-400 MPa is given, as a strength of 150 MPa measured on cylinders is achieved with quartz aggregates, but with calcined bauxite aggregates and heat curing a compressive strength of more than 400 MPa can be achieved. The typical mix composition - which could be called the standard composition - of CRC includes a binder with a large content of micro silica, a water/cementitious materials ratio of 0.16, quartz sand up to 4 mm and 6% by volume of steel fibers with a length of 12.5 mm and a diameter of 0.4 mm. This typical composition will give a compressive strength of 150 MPa and a bending strength - or modulus of rupture - of the matrix of 25 MPa. This composition can be mixed and placed with standard equipment, whereas some of the more exotic compositions - such as mortars with 12% by volume of small steel fibers - would require special equipment. CRC is used for slender structures such as balcony slabs, walk-ways and staircases or structures where special properties are required such as high strength lining blocks for mines — typically as precast products - but a special application of CRC is for in-situ cast joints between precast members.
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