Figure 1: Precast 3D Element processRapid urbanization and the surging construction activities, along with diminishing labour has pushed leading players to adopt mechanized and precast methods of construction.
The 3D modular standardized precast (onsite / offsite) pre-finished elements, specifically in the toilet and/or kitchen areas is an alternative that promises transformative improvements in time, cost, quality, health and safety. It involves the production of 3D precast and prefinished modular toilet/kitchen units in controlled factory conditions, prior to their transportation to site.
It eliminates the problems inherent in 2D large panel-based construction by minimizing the number of joints and connections, which are the root cause of leakages, seepages, and lack of ductility in the conventional precast construction.
Government of India has already directed the use of 3D Technology to speed up housing construction with huge demand for houses, possibly with lowest price, and in the least possible time. For high-rise construction, lateral load resisting is a requisite, therefore india is adopting a shear wall system and moving away from conventional column, beam and slab based construction since the past decade.
Precast Technology: Current Scenario in India
Precast Technology is being used in India majorly by private players since the last 10 years or so by setting up their own 2D Precast Panel Production facilities at developed cities in India. Most of the production facilities are configured to produce large panels, hollow-core slabs, and solid slabs. During this period, approximately 100 million sqft of precast concrete construction was carried out, which is not even 2% of the total size of the construction industry.
Figure 2Even though Precast Concrete Technology offers some distinct advantages like time saving and better quality of construction, it is not popular, despite its potential, in India (so far). Now a day’s precast readymade elements are widely adopted for the hybrid system of construction (combination of cast in situ load bearing vertical elements and precast slab elements). So far, 70% of overall Precast Buildings constructed in India belong to EWS, LIG and Slum Rehabilitation Housing projects funded by respective state governments, but there is also need for adoption of Precast Technology in large-scale private projects as well.
Figure 3: 3D MouldsShortcomings of 2D precast technology
The reasons for 2D conventional precast construction being not so popular in India are:
High Indirect cost: The initial capital investment and plant maintenance are high for setting up a precast plant near or at site. This method of construction requires big players, large-scale projects, or speed of construction from 1 million sq.ft built up area per annum to a maximum of 3.5 million sq.ft built up area per annum.
Expensive Connections: Higher cost of joints & connections and of hardware items like grout, sealants, connecting loops, temporary props, scaffolding etc.
Higher Crane cost: 2D Precast Construction involves about 15-20 number of elements per apartment which require more cranes for erection, for which the expense is high.
Non-Standard Architectural Plans: There is lack of understanding and exposure for most architects regarding Precast Technology. There is also lack of standardisation in the plans which indirectly impacts the technology. This leads to negative and a mixed perception by the stakeholders in the construction industry, so there is resistance to adoption of the technology.
Laborious & Time-Consuming Finishing Work: Even though the completion time of a structure’s completion is vastly improved, the saving of time for the overall project is not so significant as the finishing work still involves a lot of trades and labour.
Figure 4a: Production process of the 3D ElementsAdvantages of Out-of-Box Construction Approach
An Out of Box construction approach is a revolutionary method in building construction; it involves use of 3D Modular precast, prefinished Toilets and/or Kitchen units (Pods) produced offsite in a controlled environment. These Pods can be easily standardised accross different apartment sizes and projects. The architectural plan and structural frame is made considering these 3D Pod Modules as primary vertical and lateral load- resisting systems and other rooms such as the living room, bedroom etc are configured around this basic core.
Lower Indirect cost: Due to standardisation of kitchen and toilet units (wet areas), standardised modules are formed in moulds etc. which can be used in multiple projects with a lot of repetition in the moulds.
Scalability: The Out of Box construction approach does not necessarily need high project volume. This system is highly scalable where speed of construction can be as low as 300 apartments per annum to a maximum of 25000 apartments per annum.
Cost Optimization: This is achieved due to the minimum number of joints/connections, up to 50% reduction in crane cost due to less number of elements per apartment, reduction in transportation cost due to optimum use of trailer capacity, reduced temporary supports/props, cost-effective solutions for reduced handling of elements, reduced manpower due to increased automation, and optimum infrastructure requirement.
Improved structural Performance of Building: Use of Monolithic 3D Units improves the structural behaviour due to box action and offers better ductility.
Pre-Finishing of 3D Pods: The 3D Toilet/Kitchen pods can be delivered with all internal finishes like tiling, partition walls, dado, etc. and with all internal cosmetic fittings, which ultimately saves in lead and lift of finishing material and labour.
Leak-proof wet areas: Water leakage risk is eliminated due to monolithic casting of slab and walls in the kitchen and toilet areas. Sunk requirements etc. are possible with this system.
Figure 4b: Production ProcessStructural Design, Production, Logistics and Erection
At the preliminary design stage, structural framing has modularisation of the toilet/kitchen units by configuration, sizes, dimensions and weight of units finished and un-finished, and transportation and erection considerations. Structural integrity of 3D elements with remaining structure is detailed properly to establish a high degree of ductility and emulative design.
Especially horizontal joints (wall to wall joints) between 3D units are designed to transmit the axial, moment and shear forces due to gravity and lateral loads. These are designed for eccentricity as per the building code requirements. Horizontal joints with wall connections are designed to avoid complications during erection and to achieve speed of construction. Horizontal joints between 3D units and structure must ensure the floor diaphragm action. The 3D units and layout is laterally connected and designed such that horizontal forces can effectively be transferred to the buildings laterally load resisting system.
Although 3D Pods are monolithic, the connections with other elements are detailed with peripheral and internal ties as per the robustness and codal provisions.
Figure 5: Transportation and Stacking of 3D Pod ElementsProduction of 3D Precast Elements
Production of 3D precast elements can be done through special 3D Moulds. These elements are cast with slab and walls without conical shape by using hydraulic collapsible inner mould. Moulds are fabricated in steel with comprehensive design to withstand the handling and production process for the lifetime required.
3D Moulds are equipped with concrete vibrators and heating system to accelerate the curing of the concrete or by steam curing as per the requirement. Concrete is self-compacting concrete. Complete reinforcement cage of the Pod is placed into the base mould; MEP and cast in accessories are placed and concreting is done after quality inspection. The production process depends on the Pod with top or bottom slab. Pod with top slab can be cast in one pour and Pod with bottom slab can be done in stages, as required. After initial strength, the Pod is dispatched to the finishing yard.
Production of 3D Pods should satisfy the production tolerances in terms of length, cross sectional dimensions, squareness, straightness, twist, flatness and diagonal measurements as per the codal provisions.
Figure 6: Erection of 3D Pod ElementsLogistics
3D Pods can be handled using special lifting frames designed to lift the elements. Precast Pods with bottom slab can be handled with stationary base throughout the process of multiple stations in the production facility. Typically, precast concrete elements are de-moulded and lifted from their casting position to the storage yard and delivered to site, once they reach the required strength. If the elements have not gained their full design strength, they would be more susceptible to damages during handling. Two 3D Pods can be stacked one above the other to reduce the storage area. Transportation of 3D elements of quantity 1 or 2 can be decided based on the weight of the elements and can be fully utilised for the trailer capacity.
Erection
Precast 3D Pods must be installed with special attention to their alignment during erection. Proper access with platform has to be provided with all safety measures. Connection of elements using mechanical splice, preferably grouted couplers, eases the erection. Grouted splice connections help to align the 3D Pod in the least possible time since the projection length of the bar is less. Most of the erection instruments can be eliminated like push pull props, propping anchors etc. Steel frame is only used to handle and erect 3D Pods, and there must be proper planning of the order and progress of modular erection sequence from the production to supply to site. Erection tolerances have to be followed as specified in the code.
Figure 9: Typical floor plan and Unit plan (LHP Ranchi)Out-of-Box Construction by Innovela
Innovela has been part of many medium- and large-scale projects by offering structural design services. Ongoing projects include the Suraksha city and the Light House GHTC project in Ranchi.
Figure 10: Typical 3D Pod Element for Kitchen and Toilet (LHP Ranchi)Conclusion
The fast-growing construction industry of India is mired in problems such as shortage of skilled workers, reduced productivity, and uncertainties in delivery cycle. It is also stuck with 2D construction, assembling numerous elements, and sealing multiple joints, which pose many challenges during construction. Now, several 3D pilot projects are underway, many mock-ups have been done, and private players are also slowly adopting the technology.
