Cast in-situ building systems utilise lightweight prefabricated formwork made of steel/fiberglass/ aluminium in order to replace the existing conventional timber formwork. The objective of Cast-In-Situ Building System is to eliminate and reduce the traditional site-based trades like traditional timber formwork, brickwork, plastering and to reduce labour content. This method is suitable for large numbers of housing units that require repetitive utilisation of formwork.
The formwork can be reused as many times as possible with minimal wastage. Careful planning of cast in-situ work can improve productivity, speed, and total cost (Ismail, 2001). Its advantages over the traditional construction method include, low skill requirement, speedy construction, low maintenance, durable structure and less cost (Badir et al. , 1998)[4. ] (Appendix A – Catalogue) Table form is a large pre-assembled formwork and falsework unit, often forming a complete bay of suspended floor slab.
It offers mobility and quick installation, fewer joints and better surface finishes. The table form method uses separate vertical forms for walls and horizontal table forms for floor slabs. The work is done in two stages. First, the walls are cast, and forms are stripped, the tables are then positioned, and the horizontal slabs are cast. Once the concrete has achieved sufficient strength, the formwork units are lowered, rolled out from underneath of the newly formed slab and moved by crane to the next position. (Appendix B : photo 2)
Tunnel form is one of the most frequently used methods of cellular construction as it is cost effectiveness, productivity and quality benefits are being realised on a variety of developments. Tunnel form usually can be reused for 500 to 1,000 times, and is an effective way to construct buildings that have repetitive elements or layouts, such as hotels, apartment blocks and student accommodation. During the construction process, Tunnel Form allows the contractor to cast walls and slabs in a single operation on a daily cycle.
Every 24 hours, the formwork is moved so that another tunnel can be formed. This cut down the construction time significantly. (Appendix B : photo 3)Prefabricated construction method can be classified into on-site and off-site prefabricated. On-site prefabricated method involves casting structural building elements within site before erecting to actual location. On-site pre-casting provides several advantages over cast in-situ construction. These include mass production of units, cost and time reduction and improved quality of work (CIBD, 1992).
Off-site prefabricated method involves transferring building operations from site to factory. All elements that can be standardised are pre-fabricated in the factory. Prefabrication allows a component to be built whenever convenient, so long as it is delivered to site on time. Normally, this method would involve the assembly of precast elements such as floor slabs, in-filled walls, staircases, etc. into place for incorporation into the main units, columns and beams. This method of construction has reduced the amount of site labour involved in site operations and increased the productivity of the industry.