ARCHITECTURAL GLASS REINFORCED CONCRETE - G R C UK

Feb 2011

ARCHITECTURAL GLASS REINFORCED CONCRETE

passionate about grc

CONTENTS THE HISTORY PAGE 01 THE COMPANY PAGE 02 THE MATERIAL PAGE 04 THE PRODUCTS PAGE 06 THE FINISHES PAGE 08 THE TECHNICAL DATA PAGE 12

Concrete is a material which is strong in compression but weak in tension. As such most structural concrete is reinforced with steel to provide tensile strength. Experiments to reinforce concrete with glass fibre were first carried out in the late 1940’s but were unsuccessful due to the alkaline nature of the cement attacking and breaking down the fibres. The problem was solved in the mid 1960’s with the development of alkaline resistant (AR) glass fibres containing a high level of zirconium dioxide. As with most modern composites the process of blending the fibres throughout the matrix provided substantially increased tensile, flexural and impact strength. This allowed manufacturers to produce very thin (10-15mm) sections with resultant savings in component weight. Glass Reinforced Concrete (GRC) was primarily developed as a cladding material however its introduction coincided with a decline in the UK of this type of construction and a return to more traditional architecture. As a consequence the primary applications of the material in this country were permanent formwork, ducting, modular buildings etc. Throughout the rest of the world GRC became accepted as an expression of architectural design where its combination of light weight and high strength made it the cladding material of choice on some of the most iconic and well known modern construction projects. The Emirates Palace Hotel in Dubai, Repulse Bay in Hong Kong and the 2010 World Cup Stadium in Johannesburg all feature this innovative material. Today the advantages of the material are at last becoming recognised in the UK and GRC cladding is currently being used extensively on projects throughout the country including the Olympic Village in East London.

01

THE HISTORY


GRCUK is one of the country’s leading manufacturers of GRC products. Centrally based in South Yorkshire our Sheffield facility has the capability of producing over 60m2 of high quality GRC every day. We manufacture using two state of the art automated batching and spray plants in either cast premix, sprayed premix or simultaneous spray production methods. Other on site facilities include a full design and detailing centre, along with a fully integrated pattern and mould shop. This allows our engineers, designers and skilled pattern makers to work together as a team, translating ideas into reality. We are also one of the very few GRC manufacturers to operate our own in-house testing laboratory and are fully committed to a frequency of testing well beyond the requirements of all relevant standards and specifications. All finished goods are fully labelled both to assist site installation and provide a full and transparent traceability from the start of the production cycle to despatch from our yard.

02

THE COMPANY

Our plants are fully accredited under the International Glassfibre Reinforced Concrete Association “Approved Manufacturers Scheme” for both spray and premix production methods. As such we are subject to annual assessment of our procedures and testing methodology. Membership of the scheme is recommended by both the National House Builders Council (NHBC) and RIBA NBS Specification H40. The company is an active member of both the International Glassfibre Reinforced Concrete Association and the Concrete Society, with staff serving on the board of both organisations. Whatever your GRC requirements we are totally committed to producing high quality glass reinforced concrete building products and exceeding expectations of customer service.

“The company is committed to producing high quality glass reinforced concrete building products and exceeding expectations of customer service”

03

THE COMPANY


GRC is a composite material manufactured primarily, from hydraulic cement, silica sands, alkali resistant glass fibres, water and other additives. At GRCUK we also include an acrylic polymer in all our mixes to ensure optimum curing and reduce water absorption. Where GRC differs from other precast concretes is the significantly enhanced tensile and bending strengths achieved by the addition of the glass fibre strands throughout the matrix. These characteristics allow components to be cast with profiles as thin as 10mm thus reducing the unit weight by up to 90%.

Unlike other concretes which are classified by compressive strengths GRC is defined by its resistance to flexing or bending stresses. The International Glass Reinforced Concrete Association (GRCA) Specification recognises three grades of GRC, Grade 8, 10 and 18, these being obtained by the characteristic bending strength of the material. The grade of GRC is a function of the fibre content and orientation. A Grade 8 GRC will have a fibre content in the range 2.0%-2.5% whilst a correctly manufactured Grade 18 mix will contain approximately 5% of fibre by weight.

Cast Premix As the name suggests cast premix is a process where the fibres are added to the concrete slurry during the mixing process. To achieve this chopped fibres are used which are carefully blended with the concrete matrix using accurate and computer controlled weighing systems. The mix is then poured or pumped into a mould using very similar methods to precast concrete. Moulds are generally two part to create hollow core items. Because the mix is required to be relatively fluid, fibre content is at the low end of the scale. The lower strength of the material means it is generally only suitable for smaller architectural features such as cills, heads etc.

Sprayed Premix Although this method of manufacture again uses pre blended fibres the mix is sprayed into open moulds. The spray can be directed to the vertical sides of the mould thus removing the need to manufacture complex closed moulds. The material strength is slightly increased over cast premix due to fibre orientation. A further advantage is that de-moulding and reassembly times are reduced making the process more cost effective in certain applications.

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THE MATERIAL

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Simultaneous Spray This method of production was the first to be developed and is still the most widely used throughout the USA, Australia, Middle East, Europe and the Far East. When designing large scale GRC components it remains the only practical method due to the significantly higher bending strengths attained. All our simultaneous sprayed GRC complies with Grade 18 classification. These higher strengths are all a function of the much higher fibre content and a lower water/cement ratio. Because of the increase in fibre content it is impossible to pre-mix the fibres which have to be introduced to the slurry using specially developed concentric gun spray delivery systems. The combination of the slurry and fibres (which are chopped in the gun from a continuous glass fibre roving) are simultaneously sprayed into open moulds. Each layer is compacted by hand until the desired thickness is achieved. During production continual testing on both the wet and cured GRC is essential to ensure the correct ratio of slurry/fibre is being achieved. Using this method GRC panels as large as 6-8 m2 can be produced. Because of the high fibre content a “face coat” layer without fibres must be applied. As this can contain decorative aggregates, sands and pigment a wide variety of colours and textures can be produced.

THE MATERIAL


Architectural Dressings Architectural dressings, usually in natural or cast stone, are part of the UK’s building heritage. Both private or commercial developments in either traditional or contemporary styles all benefit from designs featuring this type of product. However the use of these components can present builders with various problems, primarily: Items are heavy and difficult to lift. Units are easily damaged during transportation and site installation.

Dressings manufactured from GRC can help alleviate or completely eliminate these problems. Because of the ability to cast with hollow cores, weight is reduced substantially and most components can easily be handled by one or two operatives without the need of expensive lifting equipment. This offers significant advantages, particularly on commercial developments using large section profiles. The effect of blending fibres throughout the matrix and the increased cement content result in a material which is significantly more resistant to impact than traditional cast stone. Only a very severe impact will damage high quality GRC and in such situations the binding effect of the fibres ensure that any repairs required are minimal. Because of the component’s reduced weight, support and restraint systems need not be as substantial as those required for heavy cast stone and concrete products. This of course can translate into significant cost savings. GRC units can often be retro fitted which not only take the items away from the critical build path but also reduce the chances of any damage, scuffing etc. by secondary trades.

THE PRODUCTS

Cladding Panels/Rain Screen Systems Cladding panels manufactured from GRC offer several advantages over those manufactured from precast concrete or other forms of rain screen cladding such as terracotta or fibre cement board. Precast panels are primarily used to replace natural stone thus reducing cost. Once installed these components are virtually indistinguishable from panels cut from quarried Portland or other stone. They do however offer no weight advantages which mean that support and restraint systems have to be very substantive. In addition heavy lifting equipment has to be used to place the units. GRC panels are manufactured as hollow core units thus reducing item weight considerably. Although in appearance they look identical to natural or precast stone installation costs are reduced significantly. In addition, concrete or steel framed structures can be designed from the outset to carry less dead load, thus reducing costs even further. A further benefit over traditional pre cast is the elimination of any risk of corrosion of the reinforcement. The material can also be used as an external rain screen cladding. Unlike most other such products, reveals and returns can be formed within the moulded face of the product if required.

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Typical cladding section showing GRC panel spanning SSL to SSL

THE PRODUCTS


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The base colour of our GRC is virtually identical to that of naturally occurring Portland Stone. We can however utilise iron oxide pigments to achieve virtually any colour a customer may require. These include sandstone, bath stone and slate grey amongst many others. In addition many of our products are available in a range of finishes as shown. We can also, working in conjunction with our trade partners, Reckli GmbH and University of Derby, produce GRC panels with photo imaging transfer or complex repeating patterns and textures.

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F00 F03

THE FINISHES

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THE FINISHES


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THE FINISHES

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Pattern Finish F19

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Photo Image Finish

THE FINISHES


CHARACTERISTIC PROPERTIES

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THE TECHNICAL DATA

Property Unit Premix Spray

Dry Density Kg/m3 1800-2200 1800-2200

Water Absorption % 8-13 8-13

Apparent Porosity % 16-25 16-25

Compressive Strength Mpa 40-50 50-60

Bend over Point (BOP) MPa 3-5 4-6

Ultimate Tensile Strength (UTS) MPa 3-6 8-12

Limit of Proportionality (LOP) MPa 6-10 7-12

Modulus of Rupture (MOR) MPa 8-14 18-30

Interlaminar Shear MPa N/A 3-5

In-Plane Shear MPa 4-6 7-12

Impact Strength KJ/m2 7-12 15-20

Thermal Conductivity W/mK 0.5-1 0.5-1

Fire Classification A2 A2

Component Precast GRC

1405x140x150 Cill 56Kg 22Kg

1405x215x100 Head 63Kg 24Kg

1000x215x100 Band Course 45Kg 17Kg

1000x365x150 String Course 114Kg 25Kg

1200x1200x100 Cladding Panel 302Kg 72Kg




WEIGHT COMPARISONS (approx)

Notes: All characteristic properties are indicative only. Specific test data is available from our Technical Department on request. Approximate weights are based on a precast density of 2100Kg/m3. Weights of cast and natural stone will be similar.

Useful Information Available from www.grca.co.uk International Glassfibre Reinforced Concrete Association Specification 2010 Practical Design Guide for Glassfibre Reinforced Concrete 2005 Practical Fixing Guide for Glassfibre Reinforced Concrete Parts 1 & 2 2010

Available from www.bsi.org BS EN 1169 General rules for factory production of glass– fibre reinforced cement BS EN 1170 1:1998 Measuring the consistency of the matrix “Slump test” method BS EN 1170 2:1998 Measuring the fibre content in fresh GRC “Wash out test” BS EN 1170 3:1998 Measuring the fibre content of sprayed GRC BS EN 1170 4:1998 Measuring bending strength “simplified bending test” BS EN 1170 5: 1998 Measuring bending strength “complete bending test method” BS EN 1170 6:1998 Determination of the absorption of water by immersion and the determination of the dry density BS EN 1170 7:1998 Measurement of extremes of dimensional variations due to moisture content BS 8297:2000 Design and installation of non-loadbearing precast concrete cladding

Available from www.pci.org Recommended Practice for Glass Fiber Reinforced Concrete Panels Fourth Addition 2001

OTHER USEFUL WEB SITES www.grconline.com

www.grctesting.com © Glass Reinforced Concrete UK Ltd 2011 Not to be reproduced in whole or part without the express permission of the author. Whilst every care has been taken in the preparation of the document to ensure that any advice, recommendations or information is accurate, no liability or responsibility of any kind is accepted in respect of Glass Reinforced Concrete UK Ltd

Glass Reinforced Concrete UK Ltd, 1-3 Redwood Court, Campbell Way, Dinnington, Sheffield. S25 3NQ T: +44 1909 566911 F: +44 1909 569399 E: [email protected]

www.grcuk.com

ARCHITECTURAL GLASS REINFORCED CONCRETE - G R C UK

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