We offer Expert Assistance for GRC
CEMCOTEC was set up by Graham T Gilbert who has 50 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 a Member of the GRCA’s sitting on the controlling Council as well as the Publicity and Technical Committees. He also sat on Committee 549 of the American Concrete Institute and assisted in the production of their “State of the Art Report on Premix GFRC”.
From 1969, as a qualified chemist on the original BRE/Pilkington team studying Glassfibre Reinforced Concrete, he helped develop alkaline resistant (AR) glass fibres and there after helped in the commercialisation of Cem-FIL AR fibres which is now used throughout the World. His experiences as part of the team 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]”
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 manufactured by Owens Corning Vetrotex , OCV and sold by CEMCOTEC.
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. Typically, Grade 8 or 10 GRC is achievedPremix GRC properties can be greatly enhanced by the use of 2-layers of AR glassfibre meshes or woven fabrics. MOR and strain capacity in particular are significantly improved sometimes bordering on Grade 18 GRC
Filament Winding Process
Filament winding process was developed for GRP composites but has recently been used to produce Glassfibre Reinforced Concrete GFRC 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 and Australasia.
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
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 acid etching or grit blasting after demoulding or by using a surface retarder on the mould followed by powerwashing. GRC (GFRC) can use coloured sand and/or be pigmented to give a range of coloured finishes or be 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 built UKAS certified Universal M350-5CT testing machine from The Testometric Company Ltd, CEMCOTEC offers routine testing to the GRCA's Method of Testing GRC Part 3 or EN 1170 Part 5 for Limit of Proportionality, Modulus of Rupture, Strain to Failure and Young's Modulus [Elastic Limit]. In addition, assistance can be given in the setting up of testing to all GRCA MOT 1-5 or 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 Full Membership or any internal Quality Assurance procedures.
Glassfibre Reinforced Concrete, GRC, has been used for more than 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. It can also be used to develop unique applications such as filament wound utility poles. The following are some examples of the uses of Glassfibre Reinforced Concrete.
*Architectural Panels *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 suroundsv *Slates, Apex and Stone Roofing *Fireplace surround *Street and Patio Furniture
*Road and Train Noise barriers *Bridge Deck formwork *Water and cable ducting *Sewer Renovation
*Water, Gas and Electric Meter Boxes *Transformer Bases *Electric and Telecom buildings
For more information see Case Studies and the Gallery section.
We also test GRC Samples for Flexural Strength to the GRCA’s Test Method for GRC Part 3.
NOTE. This is now obligatory if you are a manufacturer who wants to be a Member of the GRCA
Please get in touch with us.