What is GRC?

Glass Fibre Reinforced Cement or GRC is a composite with alkaline resistance fibre acting as reinforced elements randomly distributed throughout a mixture of cement and silica sand. GRC is unlike reinforced concrete where steel is placed as reinforcing element in a mixture of cement and aggregates.

The fibre material used is Alkali-resistant glass (ARG) fibres which contain about 20% of zirconia which is necessary for resistances to alkaline.

The alkali resistance of glass fibre (ARG) is determined mainly by the zirconia content in the glass. The higher the zirconia, the greater the alkali resistance.
A common substitute for the glass fibre is the E-type glass fibre. However, when comparing the E-glass fibre with the alkali resistance glass fibre, the ARG is more durable as shown in the comparison of alkali erosive attack in ARG fibre and E-type glass fibre before and after being immersed in saturated cement solution at 80°C as shown below.

Comparison of Alkali Erosive Attack in ARG Fibre and E-Type Glass Fibre

ARG Fibre
ARG Fibre

As manufactured

Held at 80°C for 200 hours in saturated cement solution
E-Glass Fibre
E-Glass Fibre

As manufactured

Held at 80°C for 200 hours in saturated cement solution

The GRC composite is a concrete like material that combines the flexural and tensile strength of glass fibre with the compressive strength of cement mortar. GRC is a high modules' fibre composite material that displays an associated high tensile, impact strength.

The blend of glass fibre with cement and sand mix creates a thin concrete like material that displays some very useful and interesting properties:-

  • light weight
  • high impact strengths
  • high tensile; flexural strengths
  • mouldability
  • fire resistance
  • sound reduction properties
  • low water penetration
  • high resistance to crack development
  • vandal resistance

Mechanical Properties of GRC

Properties Hand or Machine Spray (MPa) Premixed (MPa)
Poisson's Ratio:
Ultimate Strength (MOR) 20-30 10-14
Elastic Limit (LOP) 7-11 5-8
Direct Tensile:
Bending Over Point (BOP) 5-7 4-6
Ultimate Tensile Strength (UTS) 8-11 4-7
Shear:
In-plane 8-11 4-7
Interlaminar 3-5 NA
Compressive Strength 50-80 40-60
Impact Strength 10-25 10-15
Elastic Modulus 10-20 10-20
Dry Density 1.9-2.1 1.8-2.0

 


Uses of GRC

Since the introduction of GRC in the late 1960s, extensive ad well proven design parameters regarding loading, fixing, and handling etc. have been established. GRC is used principally for architectural purposes. It offers the architect/designer a unique and unrivalled opportunity to express individuality, interpretation and creativity in a way not offered by other materials.

GRC presents architects and engineers with a material from which the most ambitious designs can be created. It can be moulded to form modern futuristic designs or to replicate traditional historic features. GRC can be painted, faced with fine aggregates, coloured or simply left with a natural white or grey, smooth or textured finish.

Application and advantages of GRC panels are highlighted below:-

  • ability to reproduce fine surface details – ideal for simulated stone or slate
  • light weight – thus reducing transport and erection cost
  • ability to be moulded into completed shapes – especially for building renovations or restoration work
  • reduce loading on building due to light weight – leads to reduction in structural and foundation cost
  • Thin section GRC ’sprayed’ panels provides a cavity for insulation and electrical, mechanical, communications ductings

GRC cladding panels can be designed as wall units, window wall units, spandrels, mullions, column coverings, cornices. Shapes can be designed to suit modular planning of building. GRC is especially suited as fascia panels, sun screens, roofing and interior feature panels.

GRC panels can be produced with a face mix of conventional concrete with decorative aggregates. A wide range of surface finishes may be achieved using exposed aggregate face mixes, colour pigment, white cement, tile surface. In terms of creative architectural design, the architect/designer can choose from deep reveals to complex rectilinear and curvilinear shape, such as short radius curves, wide sweeping arcs or 90 degrees angles. GRC offers the architect/designer a wide latitude for free architectural expression.

GRC is used to produce beautiful architectural mouldings and features. Whilst often cast with thicknesses in excess of 12 mm, these products remain easy to handle and erect, and presents to the architect or engineer an unrivalled freedom for creative design. Using glass fibres, GRC does not suffer from corrosion of the reinforcement.

Seating, planters, receptacles, kiosks, bollards, signs, statues and fountains, to name but a few, all benefit from being made in GRC with its ability to tailor shape, form and surface finish and to be aesthetically compatible with the chosen environment.

GRC also provides theme park and zoological architects with a medium through which they can turn dreams into reality. Many of the world’s largest theme parks and zoos use GRC to create rockscapes, replica buildings, simulated environments for animals, and much more.

A retrospect of GRC works can be found here.

Manufacturing GRC

GRC is produced in two basic processes; the Spray method and the Pre-mixed process. The method chosen is dictated by factors such as strength requirements, size and type of panel. Typical products made with spray method include architectural claddings, channels, tanks, facade elements, ducting, permanent formwork. Pre-mixed process is more suited for products such as sunscreens, planters, slates and tiles, drainage components.

Spray Method
The spray method is able to produced GRC panels that has a typical section thickness of between 10mm to 15mm. This is done with specialist mixing/spray machine. It is a very versatile technique for the production of high strength components of a simple or complex nature. Typical formulation for the spray process is as follows :-

Material Content
Cement, Sand, Water, Plasticiser 95%
Glass Fibre 5%
Forton Polymer VF774 5% of cement weight

Pre-mixed
The production of GRC by pre-mixed process is closely similar to the manufacture of precast concrete. Pre-mixed process produces GRC panels is usually relatively thicker than spray method. However, this technique offers typical sections and details that are smaller and finer than that of conventional precast reinforced concrete. Typical formulation for the premixed process is as follows :

Material Content
Cement, Sand, Water, Plasticiser 97%
Glass Fibre 3%
Forton Polymer VF774 5% of cement weight

The manufacturing process can be summarized using the following schematic diagram
(source: NEG ARG Fibre. Advantages of NEG ARG Fibres. Nippon Electric Glass (1999))

 

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