Vijay Shah, Managing Partner, India Precast, talks about the process of making precast concrete shapes, with a focus on the challenges that accompany the production.

Tell us about the process of casting concrete in shapes.
Precast concrete products are made through pouring either wet cast or dry cast concrete into moulds, which are then hardened and removed to be dispatched. These moulds could be from concrete posts, pillars, columns, slabs etc. This benefits the construction process as it can be difficult to manoeuvre or create the right shapes and sizes by pouring the concrete on site.

The process of making precast shapes involve:

• Build a form. The inside of the form defines the shape that is being created. This form is then filled up with cement and is kept to dry and harden.
• Clean the mould before adding cement to it. The mould should be lined with materials or chemicals that allow for the hardened concrete structure to retrieve from it.
• Cement or concrete mix is then created to be poured into the moulds for setting. We use a variety of concrete grades like M25, M30, M35, M40, and M45 for this mix. The mould poured in cement is left alone for 24 hours to harden and removed once set.
• Once set, a hard mould is either broken or the cast is retrieved from a soft mould by shaking, which is ready to be transported to the location of construction or building activity.

What are the standard sizes and shapes of precast made by your organisation?
Our organisation makes various types of precast elements like:

Solid load bearing floor slabs, load bearing walls, facades, sandwich wall panels and cladding panels
Floor and roof slabs, made from prestressed load bearing hollow concrete slab and ribbed slab. Floors or roofs are also made from half floor slab or semi-finished floor slab with
lattice girder.
Precast stair cases, balcony, toilet pods, lift shafts and water tanks
Prestressed lintel, frames, beams, column and double tee beam
Internal partition walls, made from light-weight hollow core wall panels instead of AAC blocks or bricks
Sandwich walls, beams, columns, I-Beam, tee beam, lintel, footings, boundary walls, retaining walls, fencing poles, U-drainage or trench, box culvert, jersey barriers, covers, paver blocks etc.

Explain the moulds used to make these shapes. Do you customise moulds?
Concrete moulds are moulds that are used to shape the concrete you are working with. The concrete will adopt the shape of the mould as it cures. Concrete moulds are used to give concrete its finishing shape. Moulds are of various types (refer table below). We customise the moulds as per requirements.

S. No. Mould type Uses

1. Conventional moulds Ribbed slabs, beams, window panels, box type units and special elements
2. Battery moulds Interior wall panels, shell elements, roof and floor slabs
3. Tilting moulds Exterior wall panels where special finishes are required on one face or for sandwich panels
4. Long line prestressing beds Double tees, ribbed slabs, piles and beams
5. Extrusion machine Roof slabs and hollow core slabs