<Expert Assistance with GRC>
CEMCOTEC was set up by Graham T Gilbert who has 40 years experience with Glassfibre Reinforced Concrete and now offers this knowledge to the GRC industry. He is a Chartered Chemist, M.R.I.C. and the Chairman of the GRCA's Publicity Committee. He is also a member of the American Concrete Institute sitting on Committee 549 who have recently produced a "State of the Art Report on Premix GFRC".
As part of the original BRE/Pilkington team studying Glassfibre Reinforced Concrete, he helped develop alkaline resistant (AR) glass fibres and helped in the commercialisation of Cem-FIL AR fibres which is now used throughout the World. His experiences include the development of GRC (GFRC) production techniques and equipment through to market development starting in the UK and expanding across Europe, the Middle East and North America.
"This is a unique kaleidoscope of technical, practical and geographic knowledge about GRC [or GFRC in North America]"
CEMCOTEC specialises in offering new or existing GRC manufacturers independent advice on
AR fibre suppliers and their product range including pros and cons of these products.
The special glass fibre needed to reinforce concrete was developed by Pilkington in conjunction with the British Building Research Station. This resulted in the commercialisation of the first ever alkali resistant fibre which was branded Cem-FIL. This is still one of the leading AR fibre for Glassfibre Reinforced Concrete, GRC. This is now sold by Owens Corning Vetrotex , OCV
Another AR fibre is manufactured in Japan under the trade name ARG fibre and is sold by NEG. Recently, the Chinese have also developed versions of AR fibre mainly for home consumption but also for export.
Care has to be taken that the minimum quantity of Zirconium is above 16% otherwise long term performance will be affected.
The classic E-glassfibre used with resin systems CANNOT be used for concrete since the lime developed as concrete sets totally detroys this type of glassfibre so it is NOT suitable for Glassfibre Reinforced Concrete.
Simultaneous Spray Process
In the simultaneous chopping/spraying process, continuous AR glassfibre is passed through a specially developed spray head, cut into 25-35mm strands and sprayed out. A wet sand:cement mix is pumped to this spray head and the two materials deposited simultaneously into a mould. Successive 4-6mm [1/4”] layers are sprayed and roller compacted to form a typical 12-15 mm thick (½”] panel. The compaction removes air, helps bond and ensure a good quality finish.
The simultaneous spray process can be manual or automated. Spray process allows flexibility in manufacturing complex architectural shapes as well as producing a high strength product. Consequently, architects around the globe commonly design and specify architectural shapes manufactured using the spray process which is typically referred to as Grade 18 GRC [or GFRC]
AR glass fibres are pre-chopped by the manufacturer to 6 ->35mm length. 2-4% w/w is blended into a wet sand:cement mix. Traditionally this was done using a high speed shaft mixer but conventional pan & paddle mixes are now frequently used provided the correct admixtures are used to help dispersion. This mix is then placed into a mould either by hand-plastering, pouring or sprayed via a specially developed peristaltic pump. The premix process typically yields a three-dimensional random orientation of fibres. Consequently, premix products are not as strong as simultaneous sprayed ones but the process has the advantage of ease of production and a lower level of skill required to manufacture the end product.
Filament Winding Process
Filament winding process was developed for GRP composites but has recently been used to produce Glassfibre Reinforced Concrete poles.
Continuous AR fibre strands are passes through a specially modified mortar mix before being wound onto a mandrel. Up to 25% of AR fibre can be incorporated by this method yielding an ultra-high strength form of Glassfibre Reinforced Concrete with tensile strengths higher than 300 MPa [50,000psi] and flexural strengths as high as 200 MPa [30, 000psi]. Mainly used for the production of poles in the USA.
Admixtures for Glassfibre Reinforced Concrete, GRC or GFRC, can help enormously both in production and with final properties. In production they can make the casting or spraying easier and faster and either retard or accelerate the setting time. They can improve the quality of the finish and additives can also improve the compressive and bending strength of GRC (GFRC) products. For further information see "Admixtures for GRC" in Downloads
Glassfibre Reinforced Concrete, GRC produces a hard dense matrix giving excellent surface finishes when the correct mix and casting techniques are used. It can be a simple ex-mould finish either by spraying on mist coat (to eliminate air bubbles) or an exposed finish. This is achieved by using a surface retarder on the mould or acid etching or grit blasting after demoulding. GRC (GFRC) can be pigmented to give a range of coloured finishes or painted. During production, a wide range of stone imitation mixes can be applied to the mould before the Glassfibre Reinforced Concrete is poured, laid or sprayed resulting in a natural, stone like appearance when the product is demoulded. This can be exposed or polished to extend the aesthetic range.
Using a purpose bult Universal testing machine from The Testometric Company Ltd, CEMCOTEC can ofer routing testing of GRC to EN 1170 Part 5 for Limit of Proportionality, Modulus of Rupture, Strain to Failure, Young's Modulus [Elastic Limit] and I5/I10 for impact. In addition, assistance can be given in the setting up of testing to EN 1170 Parts 1->4. This information can be used to confirm compliance for Grades 8, 10 or 18 GRC and as part of any application for the GRCA's Approved Manufacturers Scheme or any internal Quality Assurance procedures.
Glassfibre Reinforced Concrete, GRC, has been used for nearly 40 years in most parts of the World. GRC is usually precast in a factory and applications range from all types of cladding panels and architectural features through to permanent formwork, street and garden furniture and civil engineering products such as water and cable ducting. The following are some examples of the uses of Glassfibre Reinforced Concrete.
*Prefabricated & Modular Buildings
*Overcladding & Remodelling
Architectural Mouldings and Cast stone replacement [1/3 the weight]
*Captital and column covers
*Corbels and Cornices
*Sills, copings and door surounds
*Slates, Apex and Stone Roofing
*Street and Patio Furniture
*Road and Train Noise barriers
*Bridge Deck formwork
*Water and cable ducting
*Water, Gas and Electric Meter Boxes
*Electric and Telecom buildings
For more information see Case Studies and the Gallery section.
In addition, CEMCOTEC can supply the polymer used to simplify the production and improve the properties of GRC See About Polymers