Arabian Business   December 05, 2009   by Alison Luke  

As 2010 approaches, many firms are re-evaluating their working methods in order to maximise their efficiency prior to any potential upturn in the construction sector. Value engineering is thus becoming a common phrase, with off-site prefabrication one of the key factors being considered for this process.

Off-site prefabrication can be applied to many elements of a building. And, while a wide variety of materials and products can be used in the process, one of the most successful is concrete. So what is the uptake of precast concrete products in the Middle East and how is the material being used?

"Precast concrete was introduced to this part of the world more than ten years ago and has rapidly grown in popularity," reports Dubai Precast general manager Matti Mikkola.

The use of precast concrete products peaked in 2007-08, as did the construction sector in general, however its rise in use was not simply down to a stronger construction market. "Along with a rapid increase in the construction sector, the precast business managed to gain an increasing market share from the conventional structural systems," reports Mikkola.

Precast concrete in use

There is a vast range of applications for precast concrete within the construction industry, many of which are installed for a project's operational purposes.

"Sanitary and storm sewers, box culverts, catch basins, pump/lift stations, septic tanks, exterior grease interceptors, water storage tanks, wet wells, electrical and communication vaults and many other products all play a pivotal role in maintaining a clean, healthy, productive environment. The main components of these systems typically consist of precast concrete," explains Xtramix International Precast's precast operations manager Dr Tomasz Ciesielski.

In addition, precast concrete can be used to provide larger structural components such as walls, frames and floors. The basic concept remains the same: at a factory location in advance of being needed on a project, concrete is poured into shaped casts to form individual components.

These are then transported to the construction site when required and connected together to form the final structure. One very visible, large-scale use of precast concrete currently underway is the Dubai Metro project; however it is also being used extensively in the region for many other less prominent projects.

"A large majority of projects done with precast are housing projects; these comprise of many types of low-rise buildings, including labour accommodation, hostels and housing projects," reports Mikkola. "The repetitive nature of these projects makes precasting them a wise decision as it reduces the amount of manpower required; the components are produced in a factory where the efficiency is higher and only a small amount of labour is required for the installation at site," Mikkola explains.

The second largest sector for precast use is commercial buildings, including offices and shopping malls. "Some precast products are very efficient for [providing] long spans such as those required in shopping malls and car parks," explains Mikkola. "The architect is able to provide large open spaces, which are the requirement in modern malls," he adds.

"Architectural precast concrete provides architects with an exciting medium when designing facades for a wide range of buildings, from healthcare facilities to shopping malls, commercial office buildings to sports stadiums," adds Ahmad E'Wida, quality assurance/quality control manager and precast operations manager's assistant, Xtramix International Precast.

"Precast concrete frames involve an entire structure being fabricated off-site. In addition, structural components can be supplied for incorporation into a structure on-site," adds E'Wida. Such precast building frames can be used to simultaneously achieve both structural and decorative design requirements as it is possible to achieve a variety of concrete mixes and finishes under factory conditions.

Precast walls are suitable for central cores and lift shafts in addition to internal and external building walls. Mainly used for domestic properties, precast walls can be load-bearing or partition only, depending on the client needs. "Precast walls offer the advantages of speed of construction, smooth surface finishing, acoustic insulation and fire resistance," explains E'Wida.

Floors can be totally or partially precast according to project requirements. E'Wida explains: "Partially precast floors are composed of a precast part and a cast in-situ part; both parts work together at the final stage to achieve the composite structural capacity." With fully precast floors, a series of parts are cast at the factory then connected on site, with the longitudinal joints grouted; in some cases a further structural topping screed is cast in-situ.

Benefits and challenges

So should you use precast components for your next project? There are a number of advantages and disadvantages to consider when making the decision whether to use precast and if you do so, to what extent.

"The advantages [of using precast concrete] are higher [final build] quality due to the factory production environment; higher efficiency; lower manpower requirement on site; and definitely faster construction speed," states Mikkola.

In addition, a number of construction site issues can be addressed. "The potential for accidents is reduced; programmes are not affected by weather or labour availability; and it addresses on-site skill shortages," explains E'Wida. "Buildability of the structure is improved and a potential early closing of the building envelope means that follow-on trades can begin work earlier, reducing the overall build programme," he adds.

The high quality finish possible in precast concrete products also means that such components can be left exposed in the final building or covered with little or no additional on-site preparation needed. "Because precast concrete products typically are produced in a controlled environment, they exhibit high quality and uniformity. Variables affecting quality typically found on a job site, such as temperature, humidity, materials quality and craftsmanship, are nearly eliminated in a plant environment," stresses Ciesielski.

The relatively better strength and durability of precast to poured in-situ concrete should also be considered. "The strength of precast concrete gradually increases over time, whereas other materials can deteriorate, experience creep and stress relaxation, lose strength and/or deflect. The load-carrying capacity of precast concrete is derived from its own structural qualities and does not rely on the strength or quality of the surrounding backfill materials," Ciesielski explains.

There are also some less positive points that should be considered when determining the potential benefits of precast concrete for a project. "The system building is less flexible in its design concept than purpose-mode structures; plus structural connection between the precast concrete units can present both design and contractual problems," warns E'Wida.

"Each project is different," reminds Mikkola. "For some types of buildings, precast is always the cheaper solution; for example, with long-span parking buildings the structure will be cheaper, much faster to build and the final quality is very high," he adds.

Sustainable construction

One of the primary considerations with any product or material currently being applied to Middle East construction projects is its sustainability or contribution to ‘green' building. Precast concrete meets these demands in several ways.

Firstly, precast concrete products have been shown to have a service life of more than 100 years, with the potential for the precast elements to be dismantled following the lifetime of a building and reused for future applications. "This needs to be considered in the design from day one, however we think that one day that will be a major consideration," predicts Mikkola.

In addition, the product can be used to contribute to reducing operational energy use in a building. E'Wida explains: "Architecturally-finished precast structures can be left exposed to exploit the concrete's high thermal capacity in a building's green energy management system."

The future of precast concrete?

What is the future for precast concrete use in the Middle East? Will buildings be designed to enable its use and maximise long-term value engineering or will the economic downturn see a fall in demand for the forseeable future?

In order to truly maximise the benefits of the product, traditional design and construction methods may need to be reviewed. "If the full advantages of precast concrete are to be realised, the structure should be conceived according to its specific design philosophy," stresses E'Wida.

"Often the buildability of a project is not considered in the initial stage; the architect has a free hand. During the last few years especially, the building's external shape and design has been the main criterion for the architect and the developer," explains Mikkola. "Buildability, especially using precast components, would require quite a bit more initial consideration than is often locally done," adds Mikkola.

"Designers should from the very outset of the project consider the possibilities, restrictions and advantages of precast concrete, its detailing, manufacturer, transport, erection and serviceability stages before completing a design in precast concrete," adds E'Wida. "Most design briefs can be fulfilled without too much modification to the original concept," he stresses.

The current economic climate is acting against the uptake of the product reports Mikkola: "The precast industry is faced with an additional problem in this [current economic] scenario," reports Mikkola. "All contractors have a large surplus of workers and in order to keep these workers, some are willing to choose less efficient work methods to complete the projects.

Time is seldom an issue anymore and won't be for the near future. Currently there is a huge volume of precast capacity in the market; much beyond what will be needed in the next one to two years," he adds.

However, in the long-term the use of precast concrete is sure to feature more prominently in the market. "Pre-fabrication has a great potential to respond to new market demands," stresses E'Wida. "The possible solution lies not only within the classical advantages related to working conditions, technology and speed of construction, but also in new developments of materials such as high performances and self-compacting concrete, green concrete buildings systems," he concludes.