Precast technology – everything you need to know
Till a few years ago, workmen hammering away and building structures brick-by- brick, and concrete being poured from huge concrete mixers was a common sight. But, this process has now given way to pre-cast technology.
What is pre-cast technology
Pre-cast concrete means a concrete portion of a structure that is cast and cured at a location that is not the site of construction. Once a precast concrete product is produced and all the undertaken quality controls are satisfactory, the unit is stored until delivery. It is then transported for use at another site.
How is it created?
Pre-cast structures are made in stages that start from engineering and go on to manufacturing of the reinforcement cage, form preparation and pre-pour inspection, concrete placement, curing and stripping, and culminating in post-pour work.
Every pre-cast structure is created using the latest design tools and detailed drawings are created using a 3D computer-aided design (CAD) process. Once the design drawings are approved, they are sent to the factory floor and are used to monitor production.
Manufacturing of the reinforcement cage
The first step of this process is the cutting and bending of the steel reinforcement. These bars are then assembled and tied together to form the reinforcement cage.
Form preparation and pre-pour inspection
Once the form (mould) is ready, the overhead crane is used to lift the cage and place it right in the middle of the form. When one set in done, a certified quality control engineer will conduct a pre-pour inspection to see that the product is in tandem with the original shop drawing. Upon the satisfactory completion of this inspection, the technician will approve the structure to be placed at the site.
A number of raw materials are carefully mixed according to the specific design requirements. There are concrete laboratories that conduct routine tests on raw materials. The concrete also undergoes a variety of additional tests, including a spread test that helps verify whether the mix has the proper flow and there is no segregation of the aggregates.
This approved batch is transported to the product form on the production floor. The concrete is placed into the form and care is taken to allow the concrete to flow without trapping the conduits. Once the form is filled, the top is smoothed off.
Curing and stripping
Once the concrete has settled and has been removed from the form, it is then cured. The product may be covered in tarpaulin overnight to seal in the heat from the hydration process (where the product is constantly doused in water). The controlled environment of the factory enables the product to cure properly and reach the full design strength.
The stripping process involves opening the outer jacket of the form, attaching the lifting devices to the product and lifting it off the form.
Once the product has been removed, it is cleaned and a post pour inspection is conducted. If all design dimensions have been maintained and no visual defects are noted, the quality technician signs it off. The finished product is then transported to the storage area, while care is taken that it receives proper support as it awaits its requirement. When a requirement arises, the product is loaded onto a truck and properly secured to be transported to the site of construction.
Advantages of using pre-cast technology
Structures created with units that have been cast using the pre-cast technology have been known to have superior quality and durability. Pre-cast technology has a plethora of benefits for those using its structures.
Pre-cast structures can bear the brunt of the vagaries of nature and are equally effective in regions with freezing or scorching temperatures. They are also non-combustible and do not melt, thereby eliminating the need of additional fire proofing applications.
The walls built using pre-cast technology turn out smoother than others. These walls are cured at the pre-cast plant and do not depend on variable factors (like weather conditions and availability of labour) that play a major role when work is done at the site. These walls can be painted on directly, or you can adorn them with wallpaper.
Reduced construction time
Pre-cast technology reduces the time required for construction by up to 64%. Since the members are created in plants, they are free from variable factors. This means, large portions of structures can be created in time and delivered to various construction sites to avoid delays.
Reduced labour costs
The use of pre-cast technology reduces labour costs by as much as 60%. This is possible due to the mechanisation of the whole process, where people are required to operate machinery that creates the pre-cast units. The cost of labour reduces by more than half, with a major chunk of the expenses going towards training the operators.