Usage of LightWeight Concrete in the Construction of Pre-fabricated Structures

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M.Krishna Kanth
S.Sai Kiran
P.N.Srinivasa Raju
Y.Sri Harsha
(Students, Department of Civil Engineering, Vaddeswaram, Guntur (dist) A.P-522502, India)

(Faculty, Department of Civil Engineering, Vaddeswaram, Guntur (dist) A.P-522502, India)

There are a great developments in the recent years like the high-tower buildings, offices, complex structures,or the concrete structures,etc. And the concrete lead for the better performance reducing the self-weight of the structures. As self-weight of the structure is vital for the structural safety. So for this lightweight concrete (LWC) has been used.The use of LWC is increasing for many structural purposes all around the world. LWC is used for fabricated structures which have good thermal insulation,better durability and are lightweight too. The constructional cost is the most important and essential factor for using LWC.The possible advantages of how to design the pre-fabricating structures is briefly scrutinized. The benefits of using this pre-fabricating material , to develop an eco-friendly regime in the environment and to control highly managed disposing of materials is examined.

Keywords: Lightweight concrete, Pre-fabricated materials, Economic Benefits.

Lightweight concrete (LWC) is the materials used to make the prefabricated walls to make it a unit. Lightweight concrete (LWC) has been used successfully in various constructions for many years. The main reason of using LWC for structural purposes is to reduce the self-weight of concrete structures. Reducing the dead load of the structure is very important in earthquake regions.The density of LWC is approximately 80 percent that of normal weight concrete. The density of structural LWC typically ranges between 1440 and 1840 kg/m3, whereas these values vary between 2240 and 2400 kg/m3 for normal weight concrete. Therefore, the most important advantage of using LWC is the possible decrease in the construction costs and the reduction in weight of the structure.


Some characteristics of LWC are as follows:
1.Low density: The density of LWC is much lower than that of ordinary concrete.

2.High strength: The compressive strength of cellular concrete is high enough in relation to its density.

3. Thermal insulation: LWC has a lower thermal conductivity when compared to ordinary concrete.

4. Fire resistance: LWC may protect other structures from the effects of fire due to its low thermal-conductivity.

5. Sound insulation: Sound insulation is better in LWC.

6. Speed of construction: The construction speed could be faster by using LWC in precast construction.

7.Economy: Saving in reinforcement steel and cement could be obtained that result in a reduction in construction costs.

8. Quality control: Prefabrication of LWC units can lead to better quality control in construction.

Coming to the prefabrication where rooms are taken as units i.e the prefabricated units that of Hall units,Bedroom units,Bathroom units and kitchen units. Bedroom units and Hall units need not need any building trades but bathroom units and kitchen units are usually one of the smallest rooms in a dwelling unit. Nevertheless, they are one of the most labour intensive elements to be co-ordinate. It requires the involvement of almost all building trades such as waterproofing finishes, accessories, sanitary wares and plumbing systems. Being subjected to wetting and drying, the construction of bathroom units and kitchen units demands a very high standard of workmanship, especially in the area of waterproofing.There should be a leak found in the floor slab, the amount of time, cost and inconvenience caused could be extensive ,as it often difficult to trace the source defective workmanship or cracks through the structural slab. Rectification work require hacking floor tiles, exposing substrate and re-applying waterproofing membrane.

Prefabricated Bathroom Units (PBU) Types:
Types of Prefabricated Bathroom Units:

1.Precast concrete cell completed with finished wall and floor prior to delivery to site. Bathroom shall be cast as a volumetric concrete cell and pre-finished with floor and wall finishes prior to delivery to site. PBU shall be hoisted to location and the (M&E) Mechanical & Electrical services shall be connected to the mains of the building .

2.Wall panels and floor tray separately lifted and assembled at site. Floor tray shall be lifted to position and set up accordingly.Wall panels shall be lifted and assembled at site.Finally,Ceiling and sanitary fittings shall be assembled accordingly.

3.Wall panels and floor tray were pre-assembled in factory prior to delivery to site. PBU shall be hoisted to location and the M&E services shall be connected to the mains of the building.

4.Floor trays are usually made of Reinforced concrete (RC), Fibre Reinforced Polyester (FRP)[FRP: It is a plastic material that is obtained by impregnating fiber glass with polyester resin and spraying this mixture onto moulds that have the required shapes] or Sheet Moulding Compound (SMC)[SMC is a combination of chopped glass strands and filled polyester resin in the form of a sheet]. Wall panels are commonly made of fibre reinforced polyester, special cement board, sheet moulding compound, galvanized metal sheet as well as sandwich paneling system.

5.Both the conventional “S-trap” and the new shallow “P-trap” system can be used for the sanitary plumbing system. The shallow “P-trap” and sanitary pipes have the advantage of being fully encased within the PBU floor tray / slab and connected horizontally to the main sanitary discharge stack in the service duct. This eliminates the exposure of unsightly sanitary pipings under the slab in conventional bathrooms. The maintenance/repairing works can be carried out within the affected unit itself, avoiding the need to disturb the neighbors.

floor trap

Benefits of Pre-fabricated Bathroom Units
(a) Higher quality finishes and low wastage of materials.
(b) Improved productivity of labour on site.
(c) Reduced wet work especially in the bathroom and less cleaning up work on site.
(d) Better quality control in water proofing works in the factory environment.
(e) Maintenance can be carried out with in the unit rather than from neighboring unit.
(f) Higher buildability score.

These benefits translate into substantial savings in the cost of developers, high and consistent quality product for designers and simpler quality control for contractors.

Architectural Design Considerations
Designers could consider the following factors and guidelines during the development stage of a project.

Treatment to external surfaces of PUB’s wall panels.
Some PBU systems may come with complete wall panels ready to receive skin coat and painting. Others would reqire external finishing panels (brickwall, block wall, dry wall, etc.) .

Treatment to the drop in soffit level of the slab.
(Soffit:soffit gives you the opportunity to hide things like wiring, pipes, duct-work and cables that are part of the overall bathroom). In most private residential developments a drop at the entrance of bathroom is incorporated to contain water within the bathroom. Designers are therefore advised to consider the drop at the Soffit level of the slab in the bathroom area. Alternatively a designer may choose to provide a kerb at the bathroom’s entrance to avoid creating a separate floor level.

Location of service ducts and access panel for maintenance.
The location of the access panel is critical to suppliers, and connection of services have to be Predetermined and coordinated with the appointed supplier prior to delivery.


Sanitary plumbing system.
The “P-trap” system refers to “horizontal outlet”(or wall outlet) type of WCs and floor traps.The P-trap WC and floor trap are separately connected horizontally to the main discharge stack at floor level. P-trap system is normally used where the provision of a common discharge pipe below the
slab is not feasible.

The conventional “S-trap”(i.e.vertical outlet)type of WC and floor trap are to pass through the floor slab and connect to a common discharge pipe below the floor slab(i.e.this pipe is within the lower unit) for the connection to the main discharge stack. Access for maintenance of the common discharge pipe is to be provided.

The P-trap can be used in PBUs for the whole construction industry. However,the qualified person is advised to per-consult the sewerage department on the design and layout of the sanitary plumbing system for the PBU and the whole building.

Location of PBU on floor plan
The location of PBU is important to the engineer who is responsible for the hosting of the unit into the building. A detailed study into the building layout,site boundary,constraints,etc., is a per-requisite.

Performance of the wall panel
Developers and designers must be particular in some of the wall paneling systems such that they
may sound hallow.

Types of finishes for the wall and floor
PBU systems must encourage the use of tiled finishing and it is essential that designers discuss
their requirements with suppliers before choosing a PBU system.

Structural design considerations
Weight of the prefabricated bathroom unit When carrying out the structural design of the bathroom tray,the structural engineer would have to consider the weight of the PBU,which could be obtained from the supplier.As a rough guide,the weight of PBU can range from 0.5 to 3 tonnes.

Method of hoisting
Occasionally,the method of hoisting PBUs into a building and the points of lifting are influenced or restrained by the final location of PBUs as such the structural framing system of PBUs may have to be strengthened or modified to suit.

Type of floor trap
There are many methods to connect floor traps to main discharge stacks depends on PBU suppliers. Designers will need to liaise with the suppliers and design the connection details accordingly.For example, if the convention S-trap is to be used,it will be necessary to box out the structural floor slab.

The supplier shall seek approval from the sewerage department on the shallow floor traps.

Shallow floor traps must comply with the following basic requirements:

(a) Depth of water seal shall not be less than 50mm and the parts/partition forming the water seal trap
shall be of an integral part of the trap.
(b) Depth of passage clearance shall not be less than 25mm.
(c) Diameter of waste pipe connection shall not be less than 40mm(or 2 nos.of 25mm waste pipe
(d) Diameter of outlet pipe shall not be less than 75mm.
(e) Floor trap grating shall incorporate with an anti-mosquito device.

Dimensioning and labeling system
It is imperative that designers use the internal coordinating dimensions in multiplies of 0.5M(where M is equivalent to 100mm)for the length,breadth and width of the bathroom, when designing the bathroom layout .To support the application of modular system, the size and layout of the PBUs should be standardized in specific incremental dimension.Walls are 50mm thick and tiles or marbles are applied to the walls with a special adhesive.Reinforced concrete floor slab shall be 100mm thick,laid to fall with waterproofing membrane.

Installation of Prefabricated Bathroom Units
The installation procedures for prefabricated bathroom units varies from system to system. Designers must liaise with suppliers for specifying PBUs in their projects.

The general rules are:
1. All loose concrete and debris such as loose timber and nails shall be removed. Surfaces shall be prepared and made good before reeving the unit.

2. Contingency discharge pipe should be cast in the structural slab as an outlet pipe for seepage of water through the PBU, even though most PBUs are water proffed prior to delivery.

3. Debris in pipe shall be removed to avoid choking sanitary discharge pipes/stacks.

4. With the preparation works complete, care should be taken to prevent damage to PBUs when hoisting the unit to the respective floor level.

5. Palletiser could be used to transport PBUs. Final position shall be adjusted using pneumatic jacks and leveling shims.

6. Electrical wires shall also be connected to the main switch of the building.

7. The gap between the bottom of the PBU and the structural slab shall be packed with non-shrink grout around the perimeter .

8. If one of the PBUs walls panels is exposed or formed part of the external wall or faced, much care should be taken to prevent water seepage or migration.

Environmental Sustainability:

To develop an Eco-friendly regime throughout the manufacturing process.
We can control highly managed and effective disposing of the management procedures.

Energy Saving:
The exhaustion of the natural resources and relevant regulations are changing the approach to building process.


In this study the Usage of LightWeight Concrete in the Construction of Pre-fabricated Structures is discussed. Possible advantages and benefits are obtained both in design and construction stages. Lightweight concrete can be an alternative to the heavy weighted concrete for prefabrication production, enhance green construction, reduce dead load and speed of construction. While comparing with other construction this type of pre fabrication construction cost is low. Prefabrication take advantage of controlled manufacturing conditions to improve the onsite conditions, reduce onsite labor congestion,increase the amount of ground level work, and reduce the overall amount of onsite construction. Prefabrication usually shorten the project duration and may reduce the overall project cost, while increasing craft productivity, improving quality, and reducing labour rates. Prefabrication may reduce the environmental impact of construction and increase worker safety. The skill level required for prefabrication workers is no different than traditional stick-build construction.

1. Properties of Cast-In-Place Concrete and Precast Concrete Blocks Incorporating Waste Glass Powder.
The Open Construction and Building Technology Journal, 2009, 3, 42-51 1874-8368/09 2009 Bentham

2. Pelletized fly ash lightweight aggregate concrete a promising material.
Journal of Civil Engineering and Construction Technology Vol. 3(2), pp. 42-48, February 2012.

3. A Target Benchmark of the Impact of Three-Dimensional Parametric Modeling in Precast Construction.
Journal of the Precast/Prestressed Concrete Institute (Submitted 5/25/2004, Accepted 2/15/2005).

4. Studies on Prefabricated cage Reinforced Steel-concrete composite beams.

5. Productivity Improvement of Pre-cast Concrete Installation.
Jordan Journal of Civil Engineering, Volume 3, No. 2, 2009.

6. CONCRETE DURABILITY Through High Volume Fly ash Concrete (HVFC) A Literature review.
International Journal of Engineering Science and Technology Vol. 2(9), 2010, 4473-4477.

7.Geopolymer Concrete with Fly Ash.
Second International Conference on Sustainable Construction Materials and Technology.June28-June 30,2010.

8.The Performance Evaluation of Lightweight Concrete Piles on UTHM’s Soft Soil Under Static and Dynamic
Loading Tests.
International Journal of Integrated Engineering (Issue on Civil and Environmental Engineering)

We at are thankful to Er Sai Kiran for submitting the research paper on “Usage of Light Weight Concrete in the Construction of Pre-fabricated Structures” to us. We are hopeful that this will be of great use to all other civil engineers who are looking to know more about Prefabricated Structures.

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