LOW COST MASS HOUSING USING PRECAST REINFORCED CEMENT CONCRETE WALL PANELS & SLABS Firoz Kamarudeen 1, Dr. Rajesh Kumar G 2, Able Alias 3

1 Master of Technology, Construction Technology & Management, National Institute of Technology, Warangal, Andra Pradesh, India.

2 Professor, Department of Civil Engineering, National Institute of Technology, Warangal, Andra Pradesh, India. 3 Lead Engineer, Nascon Infrastructure Solutions Pvt. Ltd, Cochin, Kerala, India. ABSTRACT: Construction of low-income mass housing projects is a replicated process and is associated with uncertainties that arise from the unavailability of resources. The objective of this research is to give an alternative house construction technology, which exploiting the use of precast reinforced cement concrete wall panels and slabs. In this technique, all precast units are made up of RCC elements thereby wall thickness can be reduced up to 7-8 cm using 8mm welded square mesh, Here all RCC elements itself acts as a load bearing structure, each element in this technique is capable of transferring loads. The dead weight of the structure, foundation plan area and overall cost for the structure alone can be reduced by 50 percentages. Besides these, floor area space can be increased, more strength & less construction time period, more economical & better quality than both conventional brick masonry and ferrocement structure. Keywords: Low cost mass house, Precast RCC thin walls

1. INTRODUCTION

Housing need is one of the most elementary human needs. The need of the houses for the refugee of the tsunami disaster in Aceh in five year ahead reached up to 78,000 units. Not to mention the earthquake that occurred Yogyakarta and Central Java that demolished and devastated 5, 69,825 houses. Apart from that, other various kind of disaster that recently attacked Indonesia has increase the amount of housing needs that is necessary as the action of emergency response.

1.1 Low cost housing Low Cost Housing is a new

concept which deals with effective budgeting and following of techniques which help in reducing the cost of construction through the use of steel wire mesh along with improved skills and technology without sacrificing the strength, performance and life of the structure. There is huge misconception that low cost housing is suitable for only sub- standard works and they are constructed by utilizing cheap building materials of low quality. The fact is that Low cost housing is done by proper management of resources. Economy is also achieved by

postponing finishing works or implementing them in phases. The building construction cost can be divided into two parts namely:

1. Building material cost: 65 to 70 % 2. Labor cost: 65 to 70 %

1.2 Prefabrication as applied to low cost housing (P.K.Adlakha and H.C.Puri, 2002)16

Advantages of prefabrication are: 1. In prefabricated construction, as the

components are readymade, self supporting, shuttering and scaffolding is eliminated with a saving in shuttering cost.

2. In conventional methods, the shuttering gets damaged due to its repetitive use because of frequent cutting, nailing etc. On the other hand, the mould for the precast components can be used for large number of repetitions thereby reducing the cost of the mould per unit.

3. In prefabricated housing system, time is saved by the use of precast elements which are casted off-site during the course of foundations being laid. The finishes and services can be done below the slab immediately. While in the conventional in-situ RCC slabs, due to props and shuttering, the work cannot be done, till they are

removed. Thus, saving of time attributes to saving of money.

4. In precast construction, similar types of components are produced repeatedly, resulting in increased productivity and economy in cost too.

5. Since there is repeated production of similar types of components in precast construction, therefore, it results in faster execution, more productivity and economy.

6. In prefabricated construction, the work at site is reduced to minimum, thereby, enhancing the quality of work, reliability and cleanliness.

7. The execution is much faster than the conventional methods, thereby, reducing the time period of construction which can be beneficial in early returns of the investment.

2. SCOPE OF LOW COST MASS HOUSING The objective of this research focuses to give an alternative house construction technology, which exploiting the use of precast reinforced cement concrete wall panels and slabs. Basically, this research is an explorative research in design and implementation on the building material, prefabricated building components, casting equipment and method, and assembling process. There are a number of significant benefits of using this technology as compared to most traditional construction approaches, the major being:- Speed of construction can reduce the dead weight of the structure

by half More strength & better quality than

conventional brick masonry Low cost Low Level of Skilled Staff Plastering can be avoided Less construction time period

2.1 The elements of project management The project management elements consist of planning, scheduling and controlling (Keizer & Render, 2008)9. The reviews of literature finding are discussed in the following sub-sections.

2.1.1 Project Planning Project planning is the first element in project management. It is the basis of project

management while contractors or home-builders are required to comply with the client’s needs and wants Keizer, 20069; Barley & Saylor, 2001)2. Generally, small project is defined by the length of time it can be completed, i.e. within six (6) months (Rowe, 2000)13. Two common indicators are project delay and financial loss (Badron, 20053; Alan, 2007)2.

2.1.2 Project Scheduling Projects with proper scheduled activities can produce better quality work, cost saving and faster construction periods (Keizer & Render, 2008)9. . Indeed, project scheduling is vital to project execution success and in accomplishing the objectives and goals of a project (Graham, 2006)6. What is equally important is that the contractors adhere to the schedule of projects so that it does not breach the obligation and responsibility of completing the construction of house according to the stipulated time (Al-Kharashe & Skitmore, 2009)14.

2.1.3 Project Controlling Another important element of project management is project control. Its function is to coordinate resources, people, money, equipment, machinery and time into a designated time frame to accomplish project objectives and obtain satisfying performance and results (Keizer, 20069; Tan, 2005; Pinto & Trailer12).

2.2 Why RCC is used? 1. Wall thickness can be reduced up to 8 cm. 2. The dead weight of the structure can be

reduced by 50%. Suppose for a 23cm brick masonry wall, Mass density as per IS 456 = 1.8 T/m3

If Volume = 100 m3

Dead weight = 1.8x100= 180 tons But for a 8 cm thick RCC wall, Mass density as per IS 456 = 2.5 T/m3

Volume = 100x1/3(for RCC wall, thickness reduce by one-third) = 33.33 m3

Dead weight = 33.33x2.5 = 83.33 tons. This light weight property will give the following savings:- Size of foundation and other concrete

elements of the building, if any, will be reduced.

Foundation depth, excavation and backfill will be reduced.

Number of trailers required to transport precast panels is much less.

Erection work can be carried out without the use of heavy equipment.

3. The floor area space can be increased. Saves huge amount of space by reducing

the wall thickness up to 8 cm. Provide significant social and

environmental benefits to the residents. Enables architects more freedom to

design more livable and open spaces through design flexibility.

4. The overall cost can be reduced by 50% for structure alone, Suppose for a 100m3 of 23 cm thick masonry wall, Overall cost comes around 7000 Rs/m3 Total cost = 100x7000 = 7, 00,000 Rs But for a 33.33 m3 of 8 cm thick RCC wall, Overall cost comes around 11000 Rs/m3 Total cost = 33.33x11000= 3, 66,630 Rs

5. Foundation plan area can be reduced by 50%. Generally SBC of black cotton soil= 5 T/m3 Dead weight for 100 m3 of 23 cm thick masonry wall = 180 tons (calculated above) Therefore, Area= load/SBC = 180/5 = 36 m2 But dead weight for 33.33 m3 of 8 cm RCC concrete precast unit is 83.325 tons Therefore, Area = load/ SBC = 80/5 = 16 m2

6. Plastering can be avoided- shutter finished products.

7. Better quality than conventional brick masonry & Ferro cement.

8. More strength. 9. Less construction time period. 10. More economical than Ferro cement.

The problem with Ferro cement construction is the labor intensive nature of it, which makes it expensive for industrial application in the western world. In addition, threats to degradation (rust) of the steel components is a possibility if air voids are left in the original construction, due to too dry a mixture of the concrete being applied, or not forcing the air out of the structure while it is in its wet stage of construction, through vibration, pressurized spraying techniques, or other means. These air voids can turn to

pools of water as the cured material absorbs moisture. If the voids occur where there is untreated steel, the steel will rust and expand, causing the system to fail.

11. Shuttering can be avoided As the components are readymade, self supporting, shuttering and scaffolding is eliminated with a saving in shuttering cost.

2.3 Panels shape and sizes There are five types of precast panels (refer fig.1) used for constructing a single unit in this alternative technology. They are:-

1. Rectangular wall panel (1mx0.5m x0.08m)- Rectangular wall panels are reinforced units, for load bearing applications as either external or internal walls in a wide variety of low and medium rise buildings. Male (4.8cmx2.3cm) and female sockets (5cmx2.5cm) are provided at ends for connecting each panel properly without having any change in dimensions. These male and female sockets are sealed using aluminium tower bolt of 100mm. Panels are designed in such a way it can lay in either vertical or horizontal positions. Bar diameter = 8mm ф@120 mm spacing square mesh.

2. L-shaped panels (3mx1mx0.15m) - L-shaped panels are placed in corners for load transfer from slabs. This type of panels serves as a column in conventional framed structure. In this type of panels, concrete haunch (0.15m x 0.15m) is provided at the bending portion in order to increase the moment of inertia there by to decrease slenderness ratio. Only female sockets (5cm x 2.5cm) are provided on L-shaped panel, such that male sockets of each wall panels are attached firmly to the female sockets of L-shaped panel properly without affecting its dimensions. These male and female sockets are sealed using aluminium tower bolt of 150 mm. Bar diameter = 8mm ф@75 mm spacing square mesh (refer tab.1).

3. T-shaped panels (3m x 2m x .15m) - T-shaped panels are placed in corners for load transfer from slabs. Concrete haunch (0.15m x 0.15m) is provided at the bending portion. Only female sockets (5cm x 2.5cm) are provided on T-shaped panel, such that male

sockets of each wall panels are attached firmly to the female sockets of T-shaped panel properly. Sockets are sealed using aluminium tower bolt of 150 mm. Bar diameter = 8mm ф@75 mm spacing square mesh (refer tab.1).

4. Lintel beam (2.1mx0.3mx0.15m) - Lintel beam act as a continuous beam over rectangular wall panels in order to fix all panels in a straight line. Male (4.8cm x 2.3cm) sockets are located on sides, in order to fix inside the female sockets of L-panels or T- panels while female sockets (5cm x 2.5cm) sockets of lintel beam are located on above and below. Bar diameter = 2-12mm ф (top), 3-16mm ф (bottom), stirrups= 8mm ф@75mm c/c spacing (refer tab.1).

5. Slab (3.2m x .5m x .08m)- precast concrete slabs are arranged depending upon the room dimensions. Male (2.3cm x 4.8cm) and female sockets (5cm x 2.5) are provided at

ends. Bar diameter: 8mm ф@75 mm spacing (1º), 8mm ф@ 120 mm spacing (2º).

3. CONSTRUCTION METHODOLOGY Precast concrete is a construction product produced by casting concrete in a reusable mold or form which is then cured in a controlled environment, transported to the construction site and lifted into place. Construction sequence involves:- 3.1 Site clearing: The construction process involves a large amount of materials and employees who are often working on a tight schedule. If any roots or stumps of trees are met during excavation, they shall also be removed.

3.2 Supply of steel moulds: The advances in casting technology were made possible through the continued development of high performance moulds. Using one steel mould we can construct large number of panels (refer tab.2).

Mould shape No of moulds Cost Rectangular 20 Rs 9,600.00/ea

L-shape 3 Rs 45,000.00/ea T-shape 3 Rs 90,000.00/ea

Lintel beam 4 Rs 9,500.00/ea Slab 12 Rs 12,000.00/ea

Figure 1. Precast panel shape & sizes

Table 1. Specifications of all types of panels Table 2. Number of steel moulds used with cost

3.3 Excavation: All excavation work shall be carried out by mechanical equipments unless, in the opinion of Engineer, the work involved and time schedule permit manual work.

3.4 Making of precast panels: The production process for Precast Concrete is performed on ground level, which helps with safety throughout a project. There is a greater control of the quality of materials and workmanship in a precast plant rather than on a construction site. Financially, the forms used in a precast plant may be reused hundreds to thousands of times before they have to be replaced, which allow cost of formwork per unit to be lower than for site-cast production. 3 stages of precast construction are: Casting – includes mesh placing inside steel

mould, fixing of embedded parts, concrete pouring,

Curing - Steam curing - a process for hardening concrete, cement, and mortar that involves exposure to warm steam. Materials subjected to this hardening technique tend to cure more uniformly and also much more quickly than those hardened via other processes.

Formwork removal.

3.5 Storage of panel & installation: Working with the precast concrete panels is not like working with plywood or other building materials. They are bulky and very heavy. Plan for how many panels you will need, and have them ready for when a crane can be available. You will also have to determine the different elements like windows, doors, and interior walls. The walls will require use of a crane to lift the precast walls off of the delivery truck and into the correct spot for installation.

Once the plinth belt is built and level, you will need to bring the crane into position to lift the panel off the truck and position it to start the wall. First of all, Place the L-shape precast concrete panels on a corner of a wall so that you have a definite starting point (refer fig.2). Use the crane and set the first wall into place. This wall will need to be braced with 2 by 4's on either side to keep it upright and vertical. L-shaped panels are placed in corners for load transfer from slabs. This type of panels serves as

a column in conventional framed structure. Then place T-shaped panels on all the junctions. T-shaped panels are placed in corners for load transfer from slabs. Use the crane again for placing heavy T-shape panel. This should be at a right angle to the first so that the braces can be removed and the wall will have a stable starting point. The next wall should form a 90 degree angle to the first and will make it possible to remove the braces. In both panels, male and female sockets are sealed using aluminium tower bolt of 150mm. Then place rectangular wall panels in between corner L-panels and junction T-panels. Once you have set a few concrete panels into position along your wall, it is a good idea to take the time to seal them with a waterproof sealer or bolt them with aluminium tower bolt of 100 mm. After you have a few panels set, and sealed, you can continue to erect with lintel beam panels, square panels and slab panels. Take your time and make sure that they form a tight seal. Finally precast concrete slabs are arranged depends upon the room dimensions.

Figure 2. Construction stages

4. COMPARISON When comparing precast RCC walls to brick, there are several issues need to be considered including the ease of installation process, time, cost and quality. Ease of Construction One of your main concerns will be the procedure required to erect the retaining wall. The construction will be much easier using precast concrete. Laying brick is more labor intensive, and requires skill working with mortar whereas the wall can be constructed in one go with precast concrete. Strength Concrete retaining walls are extremely strong and actually increase in strength as time goes on and the concrete continues to cure. Precast concrete structures can have a useful life of 100 years or more. Durability Concrete lasts for years. Prestressed concrete panels are very durable due to their high load capacity. Concrete walls also resist the adverse affects of repeated thawing and freezing in colder climates. Blocks and panels produced from denser concrete will also provide greater resistance to water infiltration and dampness. Ease of Installation Once the initial footings are dug and poured, concrete retaining walls are relatively easy to install. If you are building a concrete block wall, spending the time to level the first row of blocks will make the rest of the installation a snap and will provide the eye pleasing results you are looking for. Safe Everybody knows that concrete does not burn! Not only is the structural stability maintained for longer periods, but concrete construction prevents the spread of the fire from one building to another. It is sufficiently strong to resist impacts, blasts and natural catastrophes like earthquakes, tornadoes and floods. 4.1 Cost analysis: After constructing 50 houses(refer tab.3), Precast RCC technique costs Rs 3.33 crore while Conventional brick masonry costs Rs 3.77 crore. Difference in cost = 3.77 cr – 3.33 cr = .44 cr.

Hence, an amount of 44 lakh rupees can be saved by using this new technique. In other words, with this amount another 6 houses can be constructed.

4.2 Duration analysis Considering the durations of Precast RCC technique and Conventional brick masonry for the first 10 houses (refer tab.4), conventional technique takes around 339 days (nearly 1 year) while Precast RCC technique requires only 85

Table 3. Cost incurred till 25 phases

Figure 3. Line chart showing breakup point

Table 4. Duration v/s No of houses

days (nearly 3 months), around 9 months can be saved with this new technique.

5. CONCLUSION After constructing 10 houses (5 phases), the break up point (refer fig.3) is found after constructing 8 houses (4th phase). Cost at this stage of precast RCC structure is only Rs 61,27,276, while on the other side, conventional structure costs around Rs 61,82,624. After constructing 50 houses, it is found that cost of precast RCC house/ unit is Rs 6,66,000 while conventional brick masonry house/ unit cost around Rs 7,54,000. Considering the duration point, around 9 months can be saved with the help of this new technology.

References:

1. ACI Committee 318, “Building Code Requirements for Structural Concrete (ACI 318-02) and Commentary (ACI 318R-02),” American Concrete Institute, Farmington Hills, MI, 2002.

2. Alan (2007), Construction Project Management. USA: Prentice Hall.

3. Barley & Saylor, (2001). Professional Construction Management. USA: Mc Graw Hill.

4. Badron (2005). Materials handling system simulation in precast viaduct construction: modeling, analysis and implementation. J Constr Eng Manag 2008;134(4):300–10.

5. Garg R.K., `Sustainable Human Settlements and Cost Effective Housing Technologies.‟ BMTPC

6. Graham, A., & Dainty, A. (2007). Perspectives of UK house builders on the use of offsite modern methods of construction. Journal of Construction Management and Economics ,25, 183-194.

7. Halpin DW, Riggs LS. Planning and analysis of construction operations. USA: John Wiley & Sons, Inc.; 1992

8. Hurd, M. K., “Precast Concrete Homes for Safety, Strength, and Durability,”PCI JOURNAL, V. 39, No. 2, March- April 1994, pp. 56-72.

9. A.K. Keizer & Render, (2009). `Hand Book of Low Cost Housing.‟

10. Omar O. A framework for planning and optimizing low-income housing projects using computer simulation. MSc Thesis, Cairo University, Egypt; 2009

11. Peter, B, & Butler, D. (1973). Building cost control Techniques and Economic. London: William Heinemam Ltd.

12. Pinto, J. K. & Trailer, J.W. (1999). Essentials of project control. Pennsylvania, USA: Project management institute, Inc.

13. Row (2000). Fifth Edition, Precast/Prestressed Concrete Institute, Chicago, IL, 2000.

14. Skitmore & Al-Kharashe.,(1996) “Full Scale Testing of Precast Concrete Sandwich Panels,” ACI structural Journal, V. 94, No. 4, July-August 1997, pp. 354-362.

15. Standards and Specifications for Cost Effective Innovative Building Materials and Techniques.‟ BMTPC.

16. P.K.Adlakha and H.C.Puri, (2002). Study on Low Cost Incremental Housing for UP State.‟ BMTPCD, Adlakha and Associates.

17. Rinku Taur & T. Vidya Devi (2002), low cost housing, CBRI report 1999-2000

18. VanderWerf, P. A., and Ridsdale, C., “Concrete Floor Systems in Residential Construction,” Concrete Construction, March 1998, pp. 34-38.

19. Zamini & Bachan, (2008). Be a successful Building Contractor (3rd ed.). USA: McGraw Hill Inc.