Optimising Concrete Precasting
Optimising Concrete Precasting

Optimising Concrete Precasting

Precast concrete technology adds value and reduce cost of the project as compared to cast in-situ built.

In India, there is a huge demand for housing which neither the cities nor the housing sector is prepared for. The construction industry is also facing problems such as shortage of skilled labour, poor workmanship, low productivity and quality of construction plus time and cost overruns, to name a few. Using precast (pre-engineered pre-cast) concrete method improves the speed of construction and saves huge cost.

Concept of precast construction includes those buildings, where the majority of structural components are standardised and produced in bulk quantity which, later, together with other pieces, becomes part of a larger structure. These precast concrete elements are prepared, cast and hardened at specially-equipped plants with a permanent location in plants at project site or in a location away from the building site, and then transported to the site for assembly.

In order to get the best result from the precast concrete technology, experienced precast architects or structural engineers are required, along with well-trained and experienced erection crews are also must to carry out the site work with utmost satisfaction. Precast concrete products do not need any finishing (such as plastering) on site. By using coloured aggregates and form liners beautiful patterns can be achieved on facades/outer load bearing walls of building.

The precast concrete building technology can be efficiently and effectively used for townships, affordable and low-cost mass housing, IT/ITES parks and SEZs at a much competitive cost and on-time schedule to be adopted in the construction sector of India.

Advantages of precast concrete elements
  • Production in controlled environment results in high quality of factory-made strong durable products
  • Repetition of standard precast elements will lead to cost reduction
  • Plastering on precast walls and floor slabs is not needed because of smooth finishing
  • Production can continue in any weather condition
  • Better health and safety standards as compared to the conventional construction methods
  • Project can be better planned, managed and controlled. High speed can be achieved
  • Fast construction, less manpower required on site, and no shuttering required on site
  • Door and window frames can be installed in the wall panels before erection
  • Electricity conduits, pipes and boxes can be embedded in precast panels
  • Large span floor system leads to more flexibility as internal columns are avoided
  • Thin precast walls and facade panels increase the carpet area and reduced self-weight, increased life load
  • Precast concrete is a durable material, which requires less maintenance
  • Precise reinforcing during prefabrication saves steel
  • Precise consumption of all material used
  • Precast plant at site can reduce transportation distance and increase speed of erection

Precast concrete technology adds value and reduce cost of the project as compared to cast in-situ built versus precast:

  • Construction time cost = 50-60 per cent
  • Labour numbers on site cost = 50-60 per cent
  • Waste material on site cost = 40-45 per cent
  • Cost due to less snagging = 40-50 per cent
Indiapreacast.com gives full support for complete range of precast plants and machinery for manufacturing all types of precast concrete elements, including that of affordable/mass housing (even for on-site plants) like:
  • Load bearing hollow core planks
  • Lightweight non-load bearing wall panels, boundary wall, etc.
  • Can manufacture panels at project site
  • Saves transportation and government taxes
Project investment for 100 x 600 mm: Less than Rs 1 crore at Indiaprecast plant. European plants: Rs 8-12 crore. Project requirement: Land required: 1.5 acre plus, having length to width ratio 5:1. Power: 50 Kw is required for only wall panel production. Water: 10,000 liters per day. Labour: Average skilled labours 12 to 15. Raw Material: Cement, sand, aggregate 6 to10 mm/LECA: 2 to 10mm. Speed of Extruder m/c. -1.6 m/min.
Plant capacity: 400 m2/12 hours shifts.

Plants for pallet circulating system (PCS)/carousel system
In hi-tech and high-capacity computer controlled pallet circulating system/carousel system, the production of solid and sandwich elements is highly flexible. The system has been optimised for production of elements up to 12m in length and 4m in height. The employees specialise on individual working steps and are therefore more reliable and competent at their supervising workstations.

Production pallets are transported between the workstations using two side shifters, two concrete spreaders supplying concrete in either grey or coloured form, two vibrating units ensure that the concrete is compacted correctly and power trowels are used to guarantee smooth surfaces, insulated curing racks with 30 places provide the ideal conditions for element curing. A plotter, cleaning and oiling equipment and tilting station all serve to boost the efficiency of the system.

Concept of a carousel system

  • Concrete elements are produced on work tables (pallets)
  • Pallets are transported to the working stations, shuttering, reinforcement, concreting and compaction
  • After the curing time of eight hours at the curing places the finished elements will be removed and the empty pallet will be transported to the next working station
  • There are various methods for making affordable/mass/EWS/LIG housing by precast technology. Some of the most comm-only used are:

Method A
Suitable for ground up to fourth floor. Advantage of this method is that it is very low on investment

  • Plinth, beam and column - made from cast-in situ.
  • Floor and roof - made from precast, pre-stressed load bearing hollow core concrete slab/planks. (120mm thick slab x 600/1,200 mm width depending on requirement and design) along with structural screed of 50 mm.
  • External walls - made from hollow core non-load bearing lightweight interlocking wall panels 120/150 mm thick x 600 mm width or from AAC block/hollow block/solid Block. All to be plastered from inside and outside.
  • Internal partition - made from hollow core non-load bearing lightweight interlocking wall panels (100 mm thick x 600 mm width length to cut as per requirement from long slab only skim coat plaster required)
  • Other items made from molds include staircase, balcony mold, lift shaft and waterproof toilet pods

Method B 

Suitable ground up to 13th floor. Advantage of this method is that it is average on investment.

  • Solid load bearing outer wall are precast (160/200 mm thick other dimension as per design). No beam and column. Made by plants for pallet circulating system with central shifter or by plants for pallet in-line - vibrated and tilted by mobile shuttle.
  • Floor and roof - made from precast, pre-stressed load bearing hollow core concrete slab/planks. (150/200/250 mm thick slab x 1,200 mm width depending on the requirement and design) along with structural screed of 50 mm.
  • Internal partition - made from hollow core non-load bearing lightweight interlocking wall panels (100 mm thick x 600 mm width length to cut as per requirement from long slab only skim coat plaster required).
  • Other items made from molds include staircase, balcony mold, lift shaft and waterproof toilet pods.

Method C
Suitable for ground up to 23rd floor. Advantage of this method is: fast construction but little high in investment as compared to above.

  • External walls solid load bearing type of 160/200/250 mm thick depending on the requirement and design. Made by plants for pallet circulating system with central shifter or by plants for pallet in-line - vibrated and tilted by mobile shuttle.
  • Floors/roof from half floor slab/semi-finished floor slab (up to 3 m width x 10 m long x 40/60 mm thick) made with lattice girder/truss for floor and roof. Plants for filigree/half floor slab with lattice girder on long line casting bed. (Including pre-stressed)
  • Internal partition walls - made from hollow core non-load bearing lightweight interlocking wall panels (100 mm thick x 600 mm width length to cut as per requirement from long slab only skim coat plaster required).
  • Other items made from molds include staircase, balcony mold, lift shaft and waterproof toilet pods.
  • Precast, pre-stressed load bearing hollow core concrete slab used for floor and roof are made by extrusion process on steel bed/concrete bed. Size available from 120 x 600 mm, 150 x 1,200 mm, 200 x 1,200 mm, 250 x 1,200 mm, 300 x 1,200 mm, 380 x 1,200 mm. The span depends on the load, steel reinforcement and thickness of the slab.
  • Hollow core non-load bearing lightweight interlocking wall panels for making partition walls are made by extrusion process on concrete bed/or automatic plant. Size available from 100 x 600, 120 x 600 mm, 150 x 600 mm. Most commonly used is 100 x 600 mm.

About the AUTHOR:
Vijay Shah
is a Consultant for Precast Plant and Machinery and its technology.áHe is a mechanical engineer, having 40 years of experience and more than eight years in the precast industry.'He has visited major precast plant manufacturers and their clients in the world.

Web: www.indiaprecast.com

He can be contacted on:

Email: sogovijay@hotmail.com

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