GRC has a long history of being used for architectural cladding. In recent years, its popularity has increased dramatically, as more and more architects realise the potential of this versatile material.

Recently, the term ‘UHPC’ has been used in specifications, in some cases incorrectly, and often the material properties requested are the same as GRC.

Photo Credit: Sebastien LE DEROUT

Ultra High Performance Concrete

Over the past decade or so, various types of Ultra-High Performance Concrete (UHPC) have been developed and can be used to produce impressive-looking architectural panels. UHPC uses dense particle packing, combined with fibre reinforcement and an exceptionally low water:cement ratio to achieve very high strength, density and durability. The exact requirements of UHPC are not well defined, but it is generally agreed that it should have a minimum compressive strength of 150MPa.

UHPC was initially developed for structural use and has been used extensively in the USA as surface overlays in road applications where its durability is an advantage, particularly in places with aggressive climates. It has also been used to make concrete girders for bridges. Perhaps the most famous application of this type is the 115m-long UHPC footbridge at the Mucem Museum in Marseille.

Ductal, a product from LafargeHolcim, is possibly the most well-known brand of UHPC and many prestigious projects have been completed using it.

Glassfibre Reinforced Concrete

Glassfibre Reinforced Concrete (GRC / GFRC) is a cement-based composite material reinforced with alkali-resistant (AR) glass fibres. The integration of these alkali-resistant fibres boosts its flexural, tensile, and impact strengths, enabling the manufacture of products that are both durable and lightweight.

Such qualities have positioned GRC as the material of choice across various fields, notably in architectural and civil engineering applications.

Many spectacular projects have utilised this versatile material to great effect. Examples include the Elizabeth Line in London and the 1000 Museum in Miami – both demonstrating how GRC can streamline construction processes and form remarkable structures that exhibit a range of impressive mechanical properties.

From production equipment to raw materials, we’ve got the knowledge and expertise to answer your GRC enquiry

Comparison

Although the two materials have very different properties and manufacturing methods, there are some similarities between GRC and UHPC which can lead to some confusion:

• ‘Both materials have a high cement content’ – GRC is typically made with 1:1 sand:cement ratio; UHPC is generally similar.
• ‘Both use fibres as reinforcement’ – GRC uses alkali-resistant glass fibres, whereas UHPC can incorporate organic, metallic, or glass fibres.

Drawbacks

A major drawback of some UHPC mixes is that they are highly viscous and can only be used in poured applications, making certain shapes much more difficult to produce than by sprayed processes, normally requiring complex, closed moulds. As a result, AR-glass-fibre-reinforced concretes, using the principles of UHPC, have now been developed – which can be sprayed with standard GRC equipment – to create high performance GRC.

Fibre Technologies International has been testing high-performance GRC mixes for use with specially adapted Power-Sprays equipment and has had some positive results. These do not have the same properties as true UHPC’s, but manufacturers claim they offer improved properties over standard GRC and fit somewhere inbetween GRC and UHPC in terms of strength and durability.

These improved matrices help to mitigate the problem of uncertainty when specifying GRC. Although GRC standards are well established, differing materials, production methods and quality control can lead to appreciable differences in material characteristics when supplied from different suppliers. UHPC-based mixes offer an engineered, standardised product where there are fewer variables, giving specifiers confidence that the properties they require will be achieved. However, these standardised products come at an increased cost; the nature of UHPC means that particle sizes, the admixtures used, and mix procedures have to be tightly monitored, which requires a high level of quality control few companies are capable of.

On the other hand, for the vast majority of projects where GRC panels are specified, properly produced GRC is more than sufficient and there would be no benefit from a material with a higher strength and cost.

GRC vs UHPC

For manufacturers already familiar with GRC production, using a new product can add an extra level of complexity, as many mixes require slightly different mix and spray procedures to that of ordinary GRC. Whereas GRC uses very few materials (sand, cement, water, AR glass fibres, and admixtures), the enhanced versions require additional materials with smaller particle sizes (eg. silica fume) and often require more carefully selected sands. In many parts of the world, these can be difficult to obtain, particularly with a high level of consistency.

UHPC’s demonstrate enhanced flexural and compressive strengths, thus they can be used for both architectural and structural components. High-performance GRC, on the other hand, cannot be used for structural components and there are still unanswered questions as to how much of an advantage these offer over ordinary GRC. For example, if a panel could be made 15mm thick with GRC, using a material that is 50% stronger would still require a panel of at least 12mm thick – quite possibly thicker – once tolerances, etc. are taken into account.

High-performance GRC mixes are not yet proven, but development work is ongoing and there is the potential of a new ‘middle-ground’ material, which gives enhanced properties, without some of the drawbacks of traditional UHPC’s.

If you’re searching for the materials and equipment you need to produce high-quality Glassfibre Reinforced Concrete, we’re here to help. Click the links below to view our product range or get in touch with our expert team today:

info@power-sprays.co.uk