Precast Concrete

WHEN used as a construction system, precast concrete offers several advantages that range from improved quality to safer, long-lasting structures, says the Riyadh-based Al Rashid-Abetong (ARA), which has been serving the Saudi market for more than three decades.

The advantages of precast construction, coupled with the inherent benefits of concrete, provide a superior building material that has been proven the world over for several decades.

“Precast systems offer significant savings in construction, thanks to earlier completion dates, inbuilt fireproofing, reduced formwork, scaffolding, reduced wet trades and increased budget control,” says Munir Sultan, assistant sales and marketing manager.

“Also, fast-track procurement and construction can minimise capital costs by reducing financing costs and securing earlier rental income,” he points out.

The precast frame package typically includes columns, beams, floors, wall panes, stairs, landings, and balconies – all of which have an inbuilt fire protection.

According to Sultan, builders can derive benefits of using precast concrete right from the construction stage. These include:

• Savings: These are generated through reduced requirements for formwork, access scaffolding and less reliance on wet trades. The reduced requirement for site supervision by the main contractor also saves money. Compared to cast in-situ concrete, the following percentages of savings can be expected: 75 per cent in terms of formwork and scaffolding, and 90 per cent for wet concrete.

• Lower labour requirements: Compared with cast in-situ structures, site labour is reduced by between 50 per cent and 80 per cent. Also, work for the following trades is reduced by between 30 per cent and 50 per cent, depending on finishes.

• Speedy construction: High-speed construction and tight schedules are primary considerations in most building projects and are areas where precast concrete excels. Factory production means that there is less weather dependency. To take full advantage of precast construction, the design of the building should maximise on the repetition of precast units.

• Quality: Precast units are manufactured in factory conditions that are governed by strict manufacturing controls, ensuring clients receive high quality products that are aesthetically superior and that deliver high performance. Factory production ensures increased accuracy and quality of finish.

• Safety: Once precast floor slabs are installed they provide a safe working platform for site operatives. Simultaneously installing precast stairs offers safe and easy access between floors.

• Control: Greater project control can be seen from a completion/project management perspective and from a cost control perspective.

• Stability: Some of the prestressed precast elements act compositely with an in-situ structural screed (topping), combining the benefits of precast and in-situ construction.

• Reduced waste: The systems significantly reduce the amount of waste materials produced on site.

• Fire resistance: Precast concrete has its own inbuilt fire resistance properties, which is present throughout the whole construction phase. Fire resistance is typically achieved without the application of additional sprays or linings. This is an important innate advantage over steel structural solutions. This intrinsic property either totally eliminates or greatly reduces the need for additional fire protection and the associated costs including insurance premiums.

“Clients and owners can rest assured that the system is based on proven technology. Precast frame design incorporates proven designs and methodologies which have been developed over many years,” Sultan says.

They can also benefit from the system’s acoustic properties and air-tightness. Precast structures meet the highest standards for resistance to sound transmission. Test figures show the airborne sound insulation of 150-mm-thick concrete floor is 50 db, according to him.

“Also, air infiltration in precast buildings is minimal because of the relatively small number of joints in the construction. This factor, combined with the thermal mass of concrete, provides excellent thermal performance,” he says.

The longevity that is built into precast components through the use of special concrete mixes means there is almost no maintenance and replacement, compared to other building systems.

Another major advantage is the larger clear spans precast concrete systems offer. “Reducing the numbers of columns is critically important in developments such as showrooms, malls, function halls and car parks,” Sultan comments. “Longer spans and shallower construction depths can be obtained by using prestressed concrete beams and floors.”

Longer spans is also ARA’s forte, as it is an area where the company is capable of delivering the most advanced precast system, using the Swede Beam system.

“The unique Swede Beam system is a proven technology for more than 30 years, delivering superior advantages over other building methods when very long span, column-free structures are critical to a project,” he says.

Sultan continues: “When the Swede Beam system is complemented with insulated precast concrete walls, the structure will require 44 per cent less energy to heat and 32 per cent less energy to cool than framed buildings. The system also offers greater resistance to natural disasters and ensures durability and better acoustic performance, leading to a more comfortable indoor environment.”

Engineering of precast buildings, based on client’s conceptual design, forms part of the ARA’s scope of services. The company has more than 60 engineers to support its clients in developing  quality buildings that are highly rated, both structurally and architecturally.

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