THE COMPETITIVENESS OF GRC GLASS REINFORCED CONCRETE
Pilkington Bros first commercially developed GRC in the 1950’s based on original work by the British Government Building Research Establishment. However, the first nation to really be commercially successful on a large-scale was the Americans. Companies such as GRC Lafayette gained worldwide recognition for the work they did in recreating gothic architecture in GRC in cities such as Chicago. They continue to make GRC today. The key characteristic of their product is that they make a 12mm sheet of GRC which is then bonded to a steel frame. The steel frame involves vertical studs. This allows insulation to be placed between the vertical studs with a plasterboard inner lining giving a very neat panel. Their high-rise buildings work on the idea that you erect panels on the building at night and then line and level the panels during the day. This increases speed of construction and of course avoids conflict on use of the crane during the day. They achieve 1.5 hours fire rating with these panels.
The use of GRC in Australia was very much a clone of the American system though that is not to say that every single project is done with a steel frame. Certainly the larger most well known projects utilise that technology. There are one or two notable exceptions such as 120 Sussex Street or the Medical Centre on Camperdown Street, both located in Sydney.
When I attended and spoke at the GRC conference in Istanbul in 2011, I was impressed by the volume of work done in GRC in Turkey and amazed to find that there are over 200 GRC manufacturers based in China. The market is so large there that they have their own Glass Reinforced Cement Association. Besides China, the most dynamic market for GRC in recent years has undoubtedly been the Middle East.
There are a large number of significant GRC manufacturers in Dubai/Abu Dhabi, many of which work on a 24 hour cycle, seven days a week. I have worked with some of them, in particular Fibrex. Minimising the cost of materials is prioritised over minimising labour costs. The introduction of structural steel is a material cost that they don’t wish to consider. As such, nearly all the panels made in the Middle East are GRC skins with integral GRC ribs.
I was recently employed by Watpac Constructions to work with Precast Concrete of Brisbane on the Museum of Contemporary Art Building on Sydney’s Circular Quay. My brief was to provide structural engineering support to achieve the architectural intent of Sam Marshall of Architect Marshall. The panels on the MCA are possibly the largest panels ever made without an integral face joint in the GRC. The final design concluded with the largest panels at 10m x 3.2m, sometimes with a 1500 mm wide return, all within a 200mm front to back panel depth. The connection of GRC to a steel frame creates one major problem; that the steel frame will restrict the shrinkage of the GRC unless appropriately detailed to allow for that movement. Typically GRC shrinks 1.5 mm/m. On a very large panel such as the 10 metre panels, I developed a new connection detail which allowed shrinkage of the panel at either end for a period of time before locking off the GRC to the steel work in order to withstand wind pressures in due course.
You will recall that the traditional American design for steel framed panels positioned the insulation between the steel studs of the frame. The consultant responsible for the BCA regulations on the MCA building prevented the placement of insulation between the steel studs because the resultant configuration failed to provide a percentage coverage which complies with the regulations. This also creates a confused position of a dew point within the panel due to the insulation being present for a large percentage of that area and not for the balance. For this reason, the design on the MCA building had the insulation as a rigid board set behind an impervious membrane on an inner wall with a gap to the outer GRC and its steel frame. The logic of the design was that any condensation would form on the face of the membrane, which is 20-30mm behind the actual steel frame with the GRC attached. The steel frame to the GRC was double dip galvanised due to the ventilation to the cavity and its location close to the harbour’s edge at Circular Quay.
The MCA panels have created a unique final solution which would be impossible without the use of structural steel. However, it also led me to question of the wisdom of immediately adopting a steel frame in conjunction with GRC for every project. The majority of GRC panels should generally not exceed 3/4m wide x 3/4m high. I would suggest that buildings should be schemed in such a way to make the panels of that typical size. For that size, it is more than possible to obtain the necessary strength by means of GRC ribs integrally bonded to the skin. I suggest that GRC should be used in a way that creates a look that is not possible in other materials, and thus increase its commercial viability.
I was recently involved with a Melbourne GRC manufacturer called GRC Environments on the Australian Catholic University extensions in Melbourne. On that project there was a need to create a fair faced GRC finish on both sides of a panel. The panels were blade walls separating units on a continuous balcony. At present, the general process of creating these panels is to have a steel frame with a traditional connection to the GRC on one face, then screw fix a flat sheet of GRC to the return side, patching and filling in the exposed fixings. Further, one also has the awkward connection between the flat sheet and the formed face on the four return edges to consider.
On this particular project, we made the GRC panels in two halves split along the centre line. We then joined them together, carefully detailed for structural adequacy. Therefore, the panels were designed with no steelwork whatsoever with the GRC itself having sufficient strength. A further advancement on this concept is to prestress the panels. This technology was used by me in the early 1990’s with Glenn Industries for the Tax Office Building in Adelaide. The benefit of deleting the steelwork is that one immediately gets rid of the locked in shrinkage between the steel frame and the GRC.
I believe that in a market such as that in Australia where the product struggles competitively, that we should follow the example set by the Middle East and provide more solutions avoiding structural steel. To increase cost effectiveness, the concept of a ventilated cavity wall (as utilised in the MCA design) should be incorporated. The MCA building was able to be sealed off totally based on the internal skin and the addition of the external GRC skin could then take place off the critical path. This requires special fixing techniques and an ability to work to extra tight tolerances but it was achieved on MCA.
To conclude, I recommend to all clients, architects and GRC manufacturers to limit panel size, focus on repetition, focus on creating panel features made commercially viable and possible only in GRC, but to also consider first the use of integral GRC ribs in their design solutions. As ever, please do not hesitate to contact me if I can assist you with any of your projects.
GRC was invented in the 1950s through the Building Research Establishment in the UK. Pilkington Bros Ltd were the original company to release the product into the market but it has been further developed in many regions since that time,particularly in the USA. it has been used for a variety of different purposes. Not all have proved to be commercially viable.
Those uses of GRC can be summarised as follows:
- It can be used for the façade on a new building.
- It can be used to renovate as a over-cladding on an old façade on an existing building.
- It can be used as permanent formwork on which you pour concrete thereby gaining a very durable long term soffit surface to your slab.
- It can be used to form sculptured structures such as the 37 metre high Merlion on Sentosa Island, Singapore or The Big Ram, The Big Prawn and The Big Oyster in Australia.
- It can be used for awnings or sunscreens on the face of a building.
- It can be used for in ground or above ground drainage chambers; oil or grease separators.
- It can be used for robust on the ground service ducts , planter boxes or even street furniture.
- Computer flooring systems.
What are the advantages of GRC?
The advantages of GRC can be listed as follows:
It is typically made in a thickness of around 12mm. To this will be added perhaps a steel support frame or GRC integral ribs. This typically gives a panel weight less than 50 kilograms a sq metre. You compare that with conventional reinforced concrete which weighs 360 kg per sq m from a 150mm panel. This means that the GRC panel will be seven times lighter.
GRC can achieve a fire rating. A single skin of GRC can achieve a fire rating of up to 1.5 hours. Greater fire rating can be achieved by introducing a Styropor [polystyrene beads, sand and cement] core to create a sandwich panel which can then give you a fire rating up to 3 hours.
It is an extremely durable product. GRC has the compressive strength of 70mpa concrete which therefore makes it a perfect material for an exposed application and has a durability far better than reinforced concrete because it has no steel which is the general cause of concrete cancer.
GRC is made in a mould so one can create any shape you wish within reason, dictated only by available support and design analysis. In fact the biggest restriction on the successful commercial use of GRC has been the fact that people to often try to emulate solutions possible in a different material instead of aiming for a solution which is unique to the ability of the material. More recent developments in technology now allow the GRC product to be used in a full structural application.
Improved energy footprint of the building achieved through the use of GRC.
What are the disadvantages of GRC?
1. The material is relatively fragile and requires great care in transportation and erection.
2. It is a labour intensive product and therefore is not cheap to manufacture.
3. It is very important to rationalise design to maximise the possibilities of repetition.
Some key points that one should think about when utilising GRC?
1. Innovative design techniques utilising prestressing allows very thin elements of GRC to span large distances.
2. The lightweight nature of GRC enables it to be a very successful material for the use of over-cladding on existing buildings. Generally, engineers will allows a 25% increase in load on existing building foundations subject to appropriate investigation and justification of the existing structure. The lightweight nature of GRC allows this to be added on the existing façade subject to appropriate detailing without the need for expensive strengthening.
3. A very recent innovative development with GRC has been to design a new building utilising an inner skin to seal the building which can be done more rapidly than waiting for the final external skin to be added to the building. Thereafter, the external GRC skin is added off the critical path. We recommend the GRC is used generally as a rain screen with a ventilating cavity between the inner and outer skin. Recent developments have allowed a fixing technique to be developed which does not require internal access to the rear of the GRC panels.
Who makes GRC in Australia?
There are 5 major manufactures of GRC is Australia.
Asurco have been manufacturing GRC in Australia since the 1980s. The company is headed up by Mr Des Pawelski and they are based in Adelaide.
Precast Concrete in Brisbane makes all manners of precast which also includes GRC. That company is headed up by Mr Ian Coulter, Mr Col Ginger and Mr David Raetz. They recently completed the MCA project in Sydney.
GRC Environments who has been established since 2006 has already built a substantial reputation in its home town of Melbourne. Their most prestigious project to date is the Australia Catholic University project in Melbourne which is nearing completion.
Mascot Engineering which is headed up by Mr Brian Taylor and has been making all manner of precast GRC pits since the 1980s. This company is based in Sydney. Mascot Engineering products are now available all over Australia. They specialise in pits and chambers including planter boxes.
Quattro Design Solutions. This is another company that originally specialised in draining chambers but has enlarged its portfolio to include building facades. They are currently involved in the addition of a GRC façade to a prestigious residential project in Bellevue Hill Sydney.
If you are looking for design assistance in relation to GRC, then the most experienced design engineer in Australia is RH Consulting Engineers based in Sydney. Their principal, Charles Rickard, has been designing GRC since the 1980s and was the Technical Secretary for the original publication of the National Precast Concrete Association of Australia’s document entitled GRC Manufacture and Design. RH Consulting Engineers offer free tender support subject to a written agreement on the basis that the project goes ahead in GRC then their fee is incorporated in the costing. RH Consulting not only support GRC manufacturing companies but also architects and clients who are looking at different design options. The fee arrangement for that service is assessed on a job by job basis.
To conclude – Why GRC?
The key points are these:
There are 5 manufactures in Australia who are able to provide a competitive professional service in a tender situation The material is lightweight and can be added to existing buildings.
The building is lightweight and can be used for all manner of different product such as draining chambers, planter boxes.
The product is not cheap to make. One needs to maximise repetition but more importantly, look for a finish in GRC that cannot be achieved in a different material.
There are no limitation on the different textures, features can be built into GRC.
The product is incredibly durable. The absence of aggregate in the mix means that the lines of the panels are very sharp and the surface of the panels can be very smooth.
The product can provide an immediate upgrade to an existing building as well as improving significantly the energy performance of that building.
Besides the 5 major manufacturers of the product design support is available from RH Consulting Engineers in Sydney.