Low Cost Housing Models for urban and rural areas using Rammed Earth Technique

Abstract

Affordable housing is a term used to describe dwelling units whose total housing cost are deemed “Affordable” to a group of people within a specified income range. In a building the foundation, walls, doors and windows, floors and roofs are the most important components, which can be analyzed individually based on the needs thus, improving the speed of construction and reducing the construction cost. Based on the criteria of design competition jointly organized by Department of Technical Education, Government of U.P. and Department of Civil Engineering, Harcourt Butler Technological Institute, Kanpur. We have attempted to design a low cost housing building using an innovative construction technique called RAMMED EARTH. This documents the construction of a rural house, using rammed earth construction technique. It details our participatory approach and provides technical information about our techniques and the associated costs. We aim to do this through promoting improved and appropriate house building techniques – using cheap, locally available materials, and environmental initiatives such as tree planting. With stronger houses that last longer, households in the end save time and money and are less vulnerable to environmental hazards. The house included some new techniques, we made sure that the household, and builders understood these fully.

Proper housing is one of the basic needs for the millions of people living below poverty line across the world today. Thus, affordable housing and the climate should be compatible with one another so that the inhabitants of a house in a hot climate should have cool living conditions whilst the inhabitants of houses in cold areas have a warm environment in which to live. Mechanical pressed soil products such as blocks and tiles can compete favorably with conventional fired clay bricks and concrete blocks in both quality and durability. Reinforced cement concrete structures are very popular and widely used all over the world today, but its economic value is higher than any other building materials. Thus, there exists a need for more economical and readily available substitute reinforcements for concrete or rammed earth buildings. In some parts of the world, many buildings are constructed only with concrete or mud bricks. This is dangerous in case of seismic activity. Steel reinforcement would be an ideal solution, but cost is a considerable problem. Scientists and engineers are constantly seeking for new materials for structural systems; the idea of using bamboo as possible reinforcement has gained popularity with due course of time. Since time immemorial, bamboo has been used traditionally as a building material throughout the world’s tropical and sub-tropical regions. Bamboo is a renewable and versatile resource, characterized by high strength and low weight, and is easily worked using simple tools. As such, bamboo constructions are easy to build, resilient to wind and even earthquake forces and readily repairable in the event of damage. Thus, locally available bamboo and soil can substantially mitigate the housing problem in rural areas in constructing an efficient, low cost and light weight structures.

Full text

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National Design Competition on low Cost Housing Models for
Urban & Rural Areas in Uttar Pradesh
Jointly organized and prepared by
Department of Technical Education,
Government of U.P.
and
Department of Civil Engineering
Harcourt Butler Technological Institute (HBTI), Kanpur
Name of topic: Design of rammed earth building (Model-2)
Submitted by B.Tech students
SHUBHAM RAJ
SHER MOHAMMAD
RIMA DAS
SHREYA SAHA
Under the guidance of
Dr. Deb Dulal Tripura
Assistant Professor
Department of Civil Engineering
National Institute of Technology Agartala

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1. INTRODUCTION
Affordable housing is a term used to describe dwelling units whose total housing cost are
deemed “Affordable” to a group of people within a specified income range. In a building the
foundation, walls, doors and windows, floors and roofs are the most important components,
which can be analyzed individually based on the needs thus, improving the speed of construction
and reducing the construction cost. Based on the criteria of design competition jointly organized
by Department of Technical Education, Government of U.P. and Department of Civil
Engineering, Harcourt Butler Technological Institute, Kanpur. We have attempted to design
a low cost housing building using an innovative construction technique called RAMMED
EARTH. This documents the construction of a rural house, using rammed earth construction
technique. It details our participatory approach and provides technical information about our
techniques and the associated costs. We aim to do this through promoting improved and
appropriate house building techniques – using cheap, locally available materials, and
environmental initiatives such as tree planting. With stronger houses that last longer, households
in the end save time and money and are less vulnerable to environmental hazards. The house
included some new techniques, we made sure that the household, and builders understood these
fully.
Proper housing is one of the basic needs for the millions of people living below poverty line
across the world today. Thus, affordable housing and the climate should be compatible with one
another so that the inhabitants of a house in a hot climate should have cool living conditions
whilst the inhabitants of houses in cold areas have a warm environment in which to live.
Mechanical pressed soil products such as blocks and tiles can compete favorably with
conventional fired clay bricks and concrete blocks in both quality and durability. Reinforced
cement concrete structures are very popular and widely used all over the world today, but its
economic value is higher than any other building materials. Thus, there exists a need for more
economical and readily available substitute reinforcements for concrete or rammed earth
buildings. In some parts of the world, many buildings are constructed only with concrete or mud-
bricks. This is dangerous in case of seismic activity. Steel reinforcement would be an ideal
solution, but cost is a considerable problem. Scientists and engineers are constantly seeking for
new materials for structural systems; the idea of using bamboo as possible reinforcement has
gained popularity with due course of time. Since time immemorial, bamboo has been used
traditionally as a building material throughout the world’s tropical and sub-tropical regions.
Bamboo is a renewable and versatile resource, characterized by high strength and low weight,
and is easily worked using simple tools. As such, bamboo constructions are easy to build,
resilient to wind and even earthquake forces and readily repairable in the event of damage. Thus,
locally available bamboo and soil can substantially mitigate the housing problem in rural areas in
constructing an efficient, low cost and light weight structures.
1.1 Comparison of bamboo and steel
The strength of bamboo is greater than most timber products, which are advantageous, but it is
approximately half the tensile strength of steel. Bamboo is easily accessible as it grows in almost
every tropical and subtropical region; this lowers the cost of construction and increases the
strength of the buildings that would otherwise be unreinforced. One major problem with bamboo
is that it is highly susceptible to fungal and insects attacks. Bamboo is more prone to insects than
other trees and grasses because of its high content of nutrients. In order to combat this problem,

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it becomes necessary to treat bamboo to protect it from the environment. Steel does not have this
problem but it also needs to be coated in order to protect it from rusting. Bamboo is very light in
weight compared to steel. Due to its low modulus of elasticity, bamboo can crack and deflect
more than steel reinforcement under the same conditions. These aspects put bamboo on the list of
viable construction materials. These properties, when combined, suggest that bamboo will make
a fine addition to the current selection of materials, but it is necessary that people in general be
made more familiar with its strengths and weaknesses. The relatively low modulus of elasticity
of bamboo can cause elasticity problems in respect of the following:
Cracking and deflection: A bamboo-reinforced element will crack and deflect perhaps 50%
more than a steel reinforced element of equivalent sect.
Quantity of reinforcement: Ten times more bamboo is required in an equivalent steel
reinforced section, i.e. 5% of the cross sectional area compared with 0.5% for steel.
1.2 Treatment of bamboo
As the bamboo is often attacked by fungus and termites, hence it should be treated chemically
according to IS 401 (2001) with Copper-Chrome-Boron (CCB) solution confirming to IS 9096
(2006). Its durability varies with the type of species, age, conservation condition, treatment, and
curing. Curing should be initiated when bamboo is being cut in the bamboo grove. The
recommended preservation technique for bamboo poles/splints used in construction is “hot-
dipping” of air-dried culms. The cheapest and most-effective preservative is a mixture of coal tar
creosote and fuel oil (50:50 by weight). Apart from these, the splints should also be treated for
water-resistance. Asphalt or coal tar emulsion is considered the best option to provide adequate
water resistance to the splints. However, an excess of asphalt might reduce the bonding between
the splint and the earth.
2. RAMMED EARTH
Rammed earth is an ancient construction technique, which has recently gained renewed interest
due to varied sustainable benefits. In this technique, moisten soil (stabilized or unstabilized) is
filled in a temporary formwork (wooden or steel) and compacted/rammed into successive layers
of ~10 to 12 cm thick by means of rammer. After compaction of every couple of layers
(equivalent to height of formwork), the formwork is raised (if necessary) at higher level and the
process is continued until the desired construction is completed (Fig.1). Soil, sand, gravel and
stabilizer (cement, lime, asphalt etc.) are the major constituents for unstabilized and stabilized
rammed earth constructions. The soil suitable for rammed earth construction will generally have
less clay (≤ 30%) and sand content ranging from 70 - 80%. The moisture content of the rammed
earth mix just prior to compaction shall be within 3% of the optimum moisture content for
maximum dry density compaction. Fig. 2 shows unstabilised rammed earth building, Weilburg in
Germany.
Some of the major advantages of rammed earth constructions are:
• Low cost of materials and locally available
• Low energy and transportation costs
• Low fire risk and non-combustible
• Virtually sound proof
• Durable

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• Maintains a balanced indoor climate without extremes of temperature
• Flawless surface and flexibility in wall thickness and plan; and
• Non-requirement of high skilled workers etc.
Its disadvantages include:
• Loss of strength of unstabilised walls on saturation
• Construction recommendation in hard soil and non-flooding areas etc.
Fig.1 Rammed earth wall construction
Fig. 2 Unstabilised rammed earth building, Weilburg, Germany
3. DESIGN OF RAMMED EARTH BUILDING
Plan and elevation has been made strictly as per the guidelines of IS 8888 part 1: 1993 for
housing for low-income group (LIG).

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Fig. 3 Plan and elevation of proposed rammed earth building
Here in this report a model has been proposed having the following specifications:
• Plinth area = 30.8 m
2
• Plinth height = 300 mm
• Depth of foundation = 400 mm
• Wall thickness = 300 mm
• Wall height from plinth level = 2600 mm

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3.1 Wall
Thickness of wall = 300 mm
Fig. 4 View of rammed earth building
The rammed walls have been reinforced with bamboo splints of dimensions 20 mm × 30 mm @
500 mm c/c in horizontal direction and bamboo splints of dimensions 30 mm × 30 mm @ 450
mm to 500 mm c/c in vertical directions to ensure its high strength and durability.
Percentage of shear reinforcement provided in vertical direction considering the plan area of
walls = (55 × 30 × 30 × 100) / (7.38 × 10
6
) = 0.671 %
Where,
Plan wall area = 7.38 m
2
Number of bamboo splints of dimensions 30 mm × 30 mm in vertical direction along the plan
wall area = 55
Percentage of shear reinforcement provided in horizontal direction (calculation for a single wall)
= (6 × 20 × 30 × 100) / (2600 × 300) = 0.46 %
Here,
No. of bamboo splints of dimension 20 mm × 30 mm in horizontal direction in each wall = 6.

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Fig. 5 Bamboo reinforced rammed earth wall
3.2 Calculations
1) Available Data
a) Specified compressive strength rammed earth, f
m
= 8MPa
b) Overall height of wall, H = 3.3 m
c) Unit weight of GCI sheet = 0.056KN/m
2
and wood = 4.41 KN/cum
d) Weight of rammed earth wall = 442.7475 KN
e) Unit weight of rammed earth wall (w) = 18.85 KN/m
3
f) Thickness of wall, b = 0.3m
2) Seismic Dead load
a) Weight of roof = 0.056 × 49.614 + 4.41× 0.6063 = 5.4513 KN
b) Weight of zinc coating = 49.614× 0.275× 9.81 = 0.13385 KN
c) Weight of wood used in doors and windows = 1.532 KN
d) Weight of wall = 23.48793× 18.85 = 442.7475 KN
Total weight of building, W = 449.892 KN
3) Seismic and site data
a) Zone factor, Z = 0.36 (Seismic zone V)
b) Importance factor, I = 1 (occupancy importance factor)
c) Response reduction factor, R = 3
d) Soil type = Type 1 (Medium soil sites)
e) Natural period of building (IS 1893 Part 1 - 2002)
T = 0.09 h/√D = 0.09 x3.3/√5.6 = 0.1255 and 0.1266 (for 5.5 m base dimension)
f) D = Base dimension of building at plinth level in meter, along considered direction of the
lateral force.
g) Design spectral acceleration, S
a
/g = 2.50

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h) Design base shear coefficient, A
h
= (Z I S
a
)/ (2 R g) = (0.36 x 1 x 2.5)/ (2 x 3) = 0.15
i) Base shear, V
B
= A
h
W = 0.15 x 449.482 = 67.42 KN
4) Reinforced Rammed Earth
Allowable compressive stress in rammed earth, Fa = 0.25× f
m
= 0.25×8 MPa = 2 MPa
Allowable bending stress in rammed earth, F
b
= 1.25×2 = 2.5 MPa
Allowable tensile stress in bamboo strip, f
s
= 230 MPa
Distance between the centre lines of splints from end of wall, de = 0.3/2 = 0.15 m
Provide 30 x 20 mm cross sectional splints of bamboo @500 mm c/c, as horizontal
reinforcement. Percentage of shear reinforcement provided = (6 × 20 × 30 × 100) / (2600 × 300)
= 0.46 %
Similarly, Provide 30 x 30 mm cross sectional reinforcement in vertical direction. Percentage of
shear reinforcement provided = (55 × 30 × 30 × 100) / (7.38 × 10
6
) = 0.671 %
Minimum shear reinforcement to be provided as per IS code recommendation in horizontal
direction = 0.0384 %.
Minimum shear reinforcement to be provided as per IS code recommendation in vertical
direction= 0.0768 %
As the sum of percentage of splints in both directions is more than 0.2%, hence the design is OK.
3.3 Lintels
Lintels have been provided at every opening as per the recommendations of IS 13827: 1993 i.e.
the bearing length (embedment) of lintels on each side of an opening should not be less than 300
mm. Hence, keeping this in mind the bearing length of 300 mm has been provided oh both side
of the opening.
The lintel is pre-casted reinforced concrete in proportion 1:2: 4 (M15) with stone aggregate of
nominal size 20 mm and mild steel bars (Fe 250) as tension reinforcement.
Fig. 6 (a) Lintel on an opening in wall and (b) cross section of concrete lintel
1
2
0 mm

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3.4 Design of Lintel
Effective cover = 30 mm
Dead Load on each lintel = 3.05 KN/ m
2
Live load as per IS 875 Part 2: 1987 = 0.75 KN/ m
2
Minimum reinforcement to be provided as per IS 456: 2000 = (0.85 × b × d) / f
y
= 224.4 mm
2
Maximum reinforcement to be provided as per IS 456: 2000 = 0.04 b × d = 2640 mm
2
Reinforcement as per calculation for singly reinforce beam = 30 mm
2
Thus, minimum reinforcement is provided as per IS guidelines.
Hence, 3 bars of diameter 10 mm is provided as tension reinforcement.
3.5 Foundation
Fig. 7 Foundation
The depth of foundation below the existing ground level is 400 mm. First trench is cut as per
dimensions and then earth is rammed subsequently in layers as per rammed earth construction
procedure. The foundation has been designed considering the soil strata to be firm. It is as per the
recommendation of IS 13827: 1993.

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3.6 Roof
Fig. 8 Roof truss
Roof truss members are built up of wood having cross sectional dimensions 50.8 mm × 101.6
mm as shown in above fig. with dark line. Mainframe, which is supported on wall, has cross
sectional dimension 152.4 mm × 203.2 mm as shown in above fig. with red lines.
Overlapping length of GCI sheet shall not be less than 150 mm or at least two corrugations.
Galvanized Corrugated Sheet (GCI) of 0.63 mm thickness with zinc coating not less than 275
g/m
2
is laid on the wooden truss.
Total length of wood in truss = 117.47 m
Total volume of wood = 0.6063 m
3
or 21.414 cubic feet.
Total area of GCI sheet required including overhangs = 49.61 m
2
Total volume of GCI sheet = 31.257 m
3
Overhangs on sides = 600 mm
Overhangs on front and back = 315 mm

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3.7 Toilet
In this model toilet (WC) is separate with internal dimension of 1000 mm × 1000 mm. It has two
pits each having diameter 800 mm and depth of 6000 mm. This kind of toilet design has an
advantage that when first pit is filled up, the flow of excreta has to be diverted to the second pit
as both pits are connected to one single pour flush toilet. Twin-pit toilets have a high
convenience- when emptying one pit, people use second pit.
Fig. 9 Details of toilet

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4. ESTIMATE BASED ON TRIPURA SCHEDULED RATES (TSR) - 2011
Item
No.
Description of Work
Quantity
Unit
Rate
Total Cost
01.
Earthwork in excavation in all kinds of soil over
areas (exceeding average depth of 400 cm, 600
mm in width as well as 24 sqm. on plan ) including
disposal of excavated earth lead up to 50 m outside
the periphery of the area and lift up to 1.5 m,
disposed earth to be levelled and neatly dressed.
23.
5
Cum
1100
25850
.00
02.
Providing, hoisting and fixing up to floor five level
precast reinforced cement concrete work in string
courses, bands, copings, bed plates, anchor blocks,
plain window sills and the like including the cost
of required centring, shuttering, finishing smooth
with 6mm thick cement plaster 1:3 (1cement: 3
fine sand) on exposed surfaces complete, but
excluding cost of reinforcement with cement
concrete 1:2:4 (1cement: 2 fine sand: 4 graded
stone aggregate 20mm nominal size).
0.66
Cum
9531.50
6
290.79
03.
Cost of bamboo, 70 mm dia., 7 m long, for both
horizontal and vertical reinforcement
10
Nos
.
100
1000
.00
04.
Wood work
Roof truss (Jam)
Doors and windows (Jam)
0.6063
0.4633
Cum
cum
19883.70
19883.70
12055.49
9212.12
05.
Calculation for GCI sheets
0.63 mm thick with zinc coating not less than
275gm/m
2
49.61
S
qm
.
607.30
30
128.153
06.
Twin pit
–
pour flush latrine as per Prama
Neerja
Ayaala
1
each
7257.00
7257.00
07.
Providing and lying flat brick flooring in cement
mortar including cement slurry etc. complete. In
cement mortar 1 : 5 ( 1 cement : 5 fine sand )
23.42
S
qm
.
387.60
9
077.
6
0
08.
Reinforcement for R.C.C. work including
straightening, cutting, bending, placing in position
and binding all complete up to floor five level.
Mild steel and Medium\Tensile steel bars.
5.207
kg
60.90
317.106
Total = Rs. 101188.26 /-