Precast construction is the manufacturing of products in a pre-made cast or mould and then, after being cured in a controlled environment, transporting it to the construction site for final assembly. Prefabricated construction is the assembly of pre-made components for construction of structures required for the use, and then transporting these complete or semi complete assemblies to the final location.
Prefabricated buildings are cost-effective. The amount spent on the materials required is cut down. The orders can be customised as per the quantity. The transportation of these products also become easy as the individual components, rather than a hefty final assembly, needs to be transported to the final site for the installation.
Prefabricated construction offers flexibility and better control in the process of building the components. The size and dimension of the assemblies can be customised as per requirements. Both of these construction types have their advantages and disadvantages.
It can be inferred that places where cost-effectiveness, flexibility, and shorter construction times are needed, prefabricated construction is advisable. Precast constructions are opted for projects requiring a better durability, quality, and a sturdy structure.
As the construction cost increases in this booming economy, labour shortage in construction, and site access limitations the need for innovative and cost effective systems as well as automated processes is being sought by the industry. Precast construction seems to be a promising alternate to conventional construction in an industry that yearns for innovation.
Prefabrication in India
Prefabrication in India began with the emergence of the Hindustan Housing Factory. The company was developed by the first Prime Minister of India, Jawaharlal Nehru, as a solution to the housing crisis that resulted from the influx of refugees from West Pakistan in the 1950s. The Hindustan Housing Factory pioneered the production of pre-stressed concrete railway sleepers to replace dilapidated wooden sleepers on Indian Railways. The company changed its name shortly thereafter to reflect the diversity of its operations. It is now known as the Hindustan Prefab or HPL. The government-run company prefabricates primarily precast concrete for architectural and civil projects throughout greater India.
When HPL began it was intended to produce low-income housing solutions for the deficit in India. Precast wall panels and frame members such as beams and columns provided a much needed set of tools to erect quick structures for mass housing. The most difficult technology transfer obstacle for the HPL has been the cost of machinery and materials for production. Since the government could not recoup the return on investment for the factory through housing production, prefabrication from HPL began to service other markets including higher end civil jobs and larger public and hotel buildings.
It was found that the transportation cost alone was equal to the cost of manufacturing the prototype of a prefab house. Therefore the model was economically unviable for India. The solution to low cost prefabricated housing must overcome the obstacle of transport costs. Prefabricating regionally might better serve developing countries. Majority of buildings are relatively simple and do not require the complexity of systems coordination and parameters available in the software. There are many thinkers who are suggesting that additional tools be developed for the South American method of project delivery. This would be a software system that allows for more flexibility in the process for projects that require less information.
This is likewise an issue in other developing countries, especially India. With the increase of developing countries having digital products such as computers, the technology providers must consider culture specific tools.
Prefabrication technology has not been transferred as easily when compared with other technologies because it is a production technology or knowledge based and not a consumption technology or product based. Technology transfer of prefabrication is not as pertinent to architects as it is to manufacturers of building products. Precast construction has a wide scope to establish itself in infrastructure. However, the challenge lies in the fact that cities are highly populated, and traffic is increasing day by day. Precast is the best suitable option, as it does not hinder the traffic flow with construction taking place at a faster pace. The governing authorities must thereby encourage precast in infrastructure tenders.
As the efforts to transform cities to smart cities are gaining momentum in the country, precast satisfies the requirements like underground services, subways, tunnels, roads, pavements, flyovers etc.
A classic example of precast concrete in day today life is railway sleepers. It is a type of railway sleeper made out of steel reinforced concrete. Reinforced cement concrete (RCC) and pre-stressed concrete sleepers are now replacing other types of sleepers. Interest in concrete railway sleepers increased after World War II following advances in the design, quality and production of pre-stressed concrete. They have a longer life than wooden sleepers, and they need less maintenance, resulting in lower ongoing costs and fewer track closures.
Advantages of R.C.C. sleepers
Concrete sleepers have long life, generally 40 to 60 years
These are free from natural decay and attack by insects' etc.
These sleepers require fewer fittings
Track circuiting is possible in these sleepers
These sleepers provide more lateral and longitudinal rigidity as compared to other sleepers
The maintenance cost is low
Due to higher elastic modulus, these can withstand the stresses due to fast moving trains
J J Flyover
Perhaps the most important inter-national innovation in transport construction to be enrolled has been the use of precast concrete segmentation techniques. First pioneered in Germany in the 1950s, Dar Consultants reintroduced it to Mumbai in 2002 to build the J. J. Hospital flyover. This allows flyovers to be built without bulky scaffolding enabling construction to proceed over busy existing roads and densely populated neighbourhood. Connections into international networks have been made and strengthened not only through the construction of transport projects but through their design and technological rendering. The overall management of transport projects and systems in Mumbai has also become closely integrated into international standards and codes. As S. L. Dhingra, then Professor in Transportation System Engineering at Indian Institute of Technology, Mumbai suggests, the MSRDC's (Maharashtra State Road Development Corporation) style of functioning is not very different from the way infrastructure projects are executed abroad" (interview, 2009). This is evident in the design, typography and placing of new road signs along Mumbai's expressways over the last decade, which contrasts to the situation in 1993.
Pune based B. G. Shirke Construction Technology Private (BGSCTPL), formerly known as B. G. Shirke & Company, that was established in 1944 by its Chairman, BG Shirke. BGSCTPL is credited being first few, who pioneered and patented the "3-S" system in India - a system using partial pre-cast structural components, such as dense concrete hollow core columns, dense concrete partially pre-cast beams, lintels, staircases, etc., and commonly known Siporex blocks and slabs. BG Shirke did many mass housing jobs with prefab technology in the mass housing segment.
There have been many other applications like electric poles used for rural electrification are made of reinforced concrete. Spun pipes, asbestos corrugated sheets, manhole covers are other examples of precast technology. The list of products will extend depending our engineering innovation.
The housing deficit in urban India is approximately 18.78 million houses
About 95 per cent of the deficit is in EWS and LIG sector (As per GoI reports)
It is estimated that actual figure might be in the range of 40 million houses
based on studies conducted by various private agencies
As per HFA policy, need to construct 9,400 million sq ft in six years (2016-2022)
It means 1,600 million sq ft every year
Implementation of PMAY: A challenge
There is a great scope of standardising the houses coming under PMAY across India. But majority of the projects under PMAY scheme are being built using conventional method of construction due to which, the inherent advantage that these projects can offer in terms of repetitions and huge volume turnover remain unexploited. In addition, these large scale projects constructed using conventional methods complicates the project management in terms of speed and quality of the management in terms of speed and quality of the construction. The construction of 9,400 million sq ft spread across 200 urban centres cannot be completed within time and quality unless we adopt industrialised building construction (precast/prefab construction technology).
- VIKAS DAMLE