Precast Concrete Floor, Wall and Frame Construction Process

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Primary elements of precast concrete construction consists of frame, walls and floors. Precast concrete provides time and cost benefit to the project and better quality control than on-site concrete construction. Precast concrete construction has many advantages over cast-in-situ concrete structures as well as steel, wood, & masonry structures. It provides faster and more efficient construction process. This system has its own characteristics which influence the layout, span length, construction depth, stability system, etc. to a greater or less extend. Theoretically, all joints between the precast concrete units can be made in such a way that the completed precast structure has the same monolithic concept as a cast-in-situ structures. However, precast concrete construction is very labour intensive and costly. If the full advantages of precast concrete are to be realized, the structure should be conceived according to its specific design philosophy. Long spans, appropriate stability concept, simple details, etc. Designers should from the very outset of the project consider the possibilities, restrictions & advantages of precast concrete, its detailing, manufacturer, transport, erection & serviceability stages before completing a design in precast concrete.

Properties of Precast Concrete Construction

Following are the few Properties of Precast Concrete Construction Process:

• Enables faster programmed times - not affected by weather or labour shortages.
• Improves buildability - early enclosure of dry envelope enables follow-on trades to start sooner.
• Produces a high standard of workmanship in factory conditions - reduces potential for accidents, addresses on-site skill shortage.
• Has a high quality finish that can be left exposed - concrete's thermal properties can be exploited in low-energy buildings.

Functions of Precast Concrete Construction

Primary Functions

• Keep water out
• Prevent air leakage
• Control light
• Control radiation of heat
• Control conduction of heat
• Control sound

Secondary Functions

• Resist wind forces
• Control water vapor
• Adjust to movement
• Thermal & moisture expansion/contraction
• Structural movements
• Resist fire
• Weather gracefully
• Easy to install

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. Precast concrete provides

• Complete thermal protection
• Continuous air/vapour barrier
• Effective rain screens
• Superior lifespan
• Reduced construction schedule and on-site labour
• High quality control standards
• Numerous finish options and colours

Precast Concrete Frame Construction

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. Frames can simultaneously achieve both structural and decorative design requirements - a wide variety of mixes, colours and finishes can be accommodated. Architecturally-finished precast structures can be left exposed to exploit concrete's high thermal capacity in a building's "green" energy management system.

Construction Process

Precast concrete frames are cast in the same way as precast concrete cladding, but as they are designed as structural elements have heavier reinforcement than is required for non-structural cladding. Elegant connections are required between columns and beams to transfer considerable forces without adversely affecting the visual appearance of the frame.

Benefits of using Precast Concrete Frames:

Precast concrete frames:

• Enable faster programme times - not affected by weather or labour shortages.
• Improve buildability - structure is fabricated off-site for rapid erection on-site
• Produce a high standard of workmanship in factory conditions - reduces potential for accidents, addresses on-site skill shortage.
• Have a high quality finish that can be left exposed - concrete's thermal properties can be exploited in low-energy buildings.

Precast Concrete Wall Construction

Precast concrete walls are used for internal & external walls, lift shafts, central cores etc. Precast wall system are mostly used in domestic construction, both for individual housing & for apartments. The solution can be considered as the industrialized form of cast in-situ walls or classical brick or block masonry walls.

• The precast walls can be load bearing or only partition walls. The surface of the elements is smooth on both sides & ready for painting or wallpapering.
• Precast walls offer the advantage of speed of construction, smooth surface finishing, acoustic insulation & fire resistance.

Precast Concrete Floor Construction

Types of precast concrete floors

• Hollow core floors
• Ribbed floors
• Concrete roof elements
• Massive slab floors

The principle advantages of precast floors are speed of construction, absence of scaffolding, large variety of types, large span capacity, & economy. Precast floors can also be classified according to their manufacture into totally & partially precast floors. Totally precast concrete floors are composed of units, which are totally cast at the plant. After erection, the units are connected to the structure & the longitudinal joints are grouted.In some cases a cast in-situ structural topping screed is added. Partially precast concrete floors are composed of a precast part & a cast in-situ part. Both parts are working together at the final stage to achieve the composite structural capacity. The main totally precast floor & roof types are described hereafter.

Advantages of Precast Concrete Process

Precast concrete process provides following advantages:

• Structural efficiency
• Flexibility in use
• Optimum use of materials
• Speed of construction
• Quality consciousness
• Adaptability
• Protection of the environment

Advantages

• Precast concrete construction is less expensive than real brick.
• Does not require an extensive footing like a real masonry wall. Can be reset should it ever shift.
• More durable than real masonry - no mortar joints to let water in.
• Installs quickly and easily - most can be done in one day.
• Maintenance free - No need to paint or periodically replace slats as you would with wood fences.

Disadvantage

• System building is less flexible in its design concept than purpose-mode structures
• Most design briefs can be fulfilled without too much modification to the original concept
• Structural connection between the precast concrete units can present both design & contractual problems

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