Seminar report On
THE ROLE OF SOIL CEMENT BLOCKS IN HOUSING SUBMITTED TO VIVESWARAIAH TECHNOLOGICAL UNIVERSITY BELGAUM FOR THE PARTIAL FULFILLMENT OF M-TECH (STRUCTURAL ENGINEERING )
BY B.SUREKHA Reg. No: -
1st Semester M-Tech Structures Under The Guidance of: Asst.Prof.P.M.RAVINDRA Department of Civil Engineering
BANGALORE INSTITUTE OF TECHNOLOGY (Affiliated To Visveswaraiah Technological University) Bangalore-560004
BANGALORE INSTITUTE OF TECHNOLOGY BANGALORE -560004
CERTIFICATE This is to certify that B. Surekha has submitted the seminar report on “THE ROLE OF SOIL CEMENT BLOCKS IN HOUSING” in partial fulfillment of the 1 st semester M-Tech course in structural engineering as
prescribed by the Visveswaraiah Technological University during the academic year 2006-2007, under the guidance of Asst. Prof. P.M.RAVINDRA
Asst.Prof.P.M.RAVINDRA Department of Civil Engineering
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ACKNOWLEDGEMENT I expres express s my deep deep sense sense of gratit gratitud ude e to Asst.Prof.P.M.RAVINDRA , Department of Civil Engineering, BIT, for his guidance and help through out this seminar work. I will remain thankful to all the faculty members of Department of Civil Engineering, BIT for their support during the course of this work. Finally I express gratitude to my parents, fellow students and friends.
B.SUREKHA M-TECH STRUCTURES BANGALORE INSTITUTE OF TECHNOLOGY
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CONTENTS
1.
INTRODUCTION
2.
NEED NEED FOR ALTERN ALTERNATI ATIVE VE BUILDI BUILDING NG MATERI MATERIALS ALS
3.
MANUFACTURING PROCESS
4.
DESIGN CONCEPT
5.
RESULTS, COST ANALYSIS
6.
ADVANTAGE’S AND DISADVANGE’S
7.
WORKS DONE
8.
CONCLUSION
9.
SCOPE FOR FURTHER STUDY
3 4
5
10.
REFERENCES
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1. INTRODUCTION Soil Cement Blocks or Compressed Stabilized earth blocks (CSEB) are dense solid blocks compacted using a machine with a mixture of soil, sand, stabilizer (cement/lime) and water. After 28 days curing, the stabilized mud blocks (SMB) are used for wall construction. Two block sizes (305x143x100mm) and (230x190x100mm) have been standardized. These blocks are 2.5 to 2.8 times bigger in volume when compared with locally available conventional burnt clay bricks. Compressive strength of the block greatly depends upon the soil composition, density of the block and percentage of stabilizer (cement/lime). Sandy soils with 7% cement can yield blocks having wet compressive strength of 3-4Mpa. Higher strength for the block can be obtained by increasing the quantity of stabilizer.
CSEB can be used for wall construction without any new technological problems. They have been successfully used to construct load-bearing wall of several building in the recent past. The mason has to adopt himself to the handling of block of different size. Compared to the normal burnt bricks, stabilized mud block is generally heavier and bigger. The pressed soil block walls require thinner plaster for inside walls and outer walls can be exposed with proper pointing. Also mortar consumption for wall construction will be less. Bigger block size also leads to better wall strength with higher masonry.
The Soil cement blocks can be constructed using cement mortar, lime mortar, lime pozzolana mortar or mud mortar. Mortar selection depends upon the desired wall strength and bond between the mortar and blocks. Lean and low strength mortars can lead to poor bond between mortar and blocks. Normal
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cement mortar of 1:6 proportion has been used in the construction of soil-cement block walls of several buildings. It has been observed that the bond between cement mortar and soil cement block is not as good as that of burnt brick and cement mortar. Smooth surface of pressed soil-cement block and the presence of already hydrated cement leads to poor mechanical and chemical bond. To improve the bonding frogs have been introduced on both faces.
STABILIZED MUD BLOCK
AURAM HALLOW INTER LOCKING BLOCKS (295)
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Blocks produced by the Auram Press 3000
Auram equipment equipment for for earth construct construction ion A wide range range of equipment equipment for for building building with earth has been been researched researched and developed from the very outset. It ranges from presses for compressed earth blocks, quality control devices for block making, handling equipment, hand tools,
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scaffolding, and rammed earth equipment. To date, this equipment has been sold mostly in South Asia and Africa. Meanwhile, the AURAM Press 3000 has
become renowned as one of the best presses available worldwide, and machines are being sold worldwide: in USA, Europe and Middle East.
2. NEED FOR ALTERNATIVE BUILDING MATERIALS Demand for new buildings as well as the cost of building construction is growing at a steady pace. Bricks, cement, steel, timber, plastics, glass, are some of the commonly used conventional materials. Manufacture of such conventional materials requires expenditure of energy in various forms, and the manufacturing processes are detrimental to the environment. The use of traditional building techniques mud walls, thatch roofs require frequent repairs. Use of conventional materials alone to satisfy the demand for new buildings, can drain the available energy resources and cause environment degradation. This clearly indicates the need for energy efficient, environment friendly, economical alternative building materials and technologies. Centre for ASTRA (Application of Science and Technology to Rural Areas) was formed in the Indian Institute of Science, Bangalore, has developed alternative building technologies looking at utilisation of local materials and reducing energy consumption to achieve cost reduction. Indian construction industry is one of the largest in terms of economic expenditure, volume of raw materials/natural resources consumed, volume of materials and products manufactured, employment generated, environmental impact etc. Large variety of materials are manufactured and consumed in the construction industry. Production levels and energy expenditure of some of the building materials consumed in bulk quantities are given in Table 1.
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Table 1.
Volume and energy consumption of building materials in India (2003)
Total energy expenditure on bricks, cement aluminium and structural steel consumed in bulk quantities is 1684 × 106 GJ per annum. It has been estimated that 22% of green house gas (GHG) emissions is contributed by the construction sector in India1. There is an ever-increasing demand for building materials. For example demand for houses has doubled in about two decades from 1980 (Figure 1)
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200 HOUSING SHORTAGE 180
HOUSING STOCK NO OF HOUSE HOLDS
160
140
120 S N O I L L I M N I
100
80
60
40
20
0 1975
198 0
19 85
1990
1995
2000
2005
YEAR
Figure-1
3. MANUFACTURING PROCESS 3.1 Soil Suitability and Stabilization for CSEB Not every soil is suitable for CSEB in particular. Topsoil and organic soils must not be used. Identifying the properties of a soil is essential to create, at the end good quality products. Not every soil is suitable for earth construction and CSEB in particular. But with some knowledge and experience many soils can be used for producing CSEB.
A soil contains contains four components: components: gravel, gravel, sand, silt silt and clay. clay. In concrete, concrete, the binder of gravel and sand is cement. In a soil, the binder is silt & clay. But silt and clay are not stable in water. Thus, the aim of stabilization is to stabilize silt
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and clay against water, so as to give lasting properties with the minimum of maintenance.
Figure-2
3.2 Soil identification and stabilization The points to be considered while analyzing the property of soil: a) Grain size distribution, to know the quantity of each grain size. b) Plasticity characteristics, to know the quality and properties of the binders (clays and silts).
c) Compressibility, to know the optimum moisture content, which will require the minimum compaction energy for the maximum density. d) Cohesion, to know how the binders bind the inert grains. e) Many stabilizers can be used. Cement and lime are the most common ones. Others, like chemicals, resins or natural products can be used as well. The selection of a stabilizer will depend upon the soil quality and the project requirements: Cement will be preferable for sandy soils and to achieve quickly a higher strength. Lime will be rather used for very clayey soil, but will take a longer time to harden and to give strong blocks.
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The average stabilizer proportion is rather low : Cement stabilization = 5% average. The minimum is 3% and the maximum is 8% Lime stabilization = 6% average. The minimum is 2% and the maximum is 10% .
Figure-3 .Production stabilized mud blocks using a manual press
3.3 Production a. Preparation The soil will have o be sieved through a 5mm sieve to remove gravel, roots and clay lumps. If there are too many lumps of clay, the soil may be spread in a thin layer (about 15cms thick) on level ground and about 15% moisture sprinkled on the lumpy soil. The soil may be left in that condition for a day and then the lumps may be broken on softening of the soil.
b. Mixing stabilizer and moisture Table -2 : The stabilizer percentage is specified is by weight . Stabilizer &% by Weight
Volume of stabilizer in scoops
Volume of soil in scoops
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Cement 5% Cement 4% Cement 3% Lime 5% Cement 2.5% Lime 3% Cement 8% Cement 3.5% Lime 2%
1 1 1 2 1 2 2 1 1
20 25 33 24 40 40 25 25 30
When the stabilizer percentage is specified, we normally mean percentage by weight. However in practice it is necessary to convert this ratio to a volume percentage. When
cement is the stabilizer the weight proportion and
the volume proportion (in bulk) turn out to be the same. Lime stabilization is being carried out, the weight and volume proportions are different, the correspondence between the two is presented in table 2 for the various combinations.
Dry mixing: For 5% soil cement block, measure out 20 scoop of sieved and prepared soil, such that it forms a thin layer on the ground, measure out one scoop full of cement and spread it thinly on the top of soil. Now mix the soil and cement thoroughly till the presence of neat cement cannot be detected visually. This mixing is done preferably when the soil is dry. Addition of moisture: moisture: The proportion proportion of of water should should be approximate approximately ly close to the field optimum moisture content. Water to be mixed should be about 10% of the total weight of dry mix. Assuming that the dry soil contains 5% of moisture, the water should be added gradually. The soil cement mixture and moisture must be thoroughly mixed with hand and checked for optimum moisture content. This can be easily determined by making a ball of the moist soil in the palm of your hand. The soil should not stick in this process.
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The soil has to be prepared in batches for block pressing. When cement is used, as the stabilizer the quantum of moist soil prepared at a time must be less than or equal to 25 scoops. Larger batch size means that the last few blocks will be pressed after the initial setting of cement. This will lead to poor strength gain. c. Block pressing: Lift the toggle lever till it is vertical and touches the frame of the machine. Open the lid and place the bottom plate of the machine in the mould. Take a of scoop of moist soil mixed with stabilizer and weigh it in a pan balance. The soil weight should be 9kgs for a 10cms thick block (it will be 7.25 kgs for a 8cms thick block)
Fill the mould with the soil, pushing the narrow end of the scoop deep into the mould and shaking the soil by an up and down motion of the scoop. Care must be taken to prevent the soil from falling outside the mould. Press all the soil into the mould and close the lid with a forceful action. This will lead to the initial compaction of the top of the mud block. Lock the lid in position using the screw jack provided for the purpose. Press the block by pulling the toggle down. If necessary two persons can press the toggle lever. The person operating the end of the lever can use his bodyweight in pulling the lever down. Under no circumstances should 3 persons press the lever. The block pressing is complete only when the lever touches the first fulcrum at the bottom of the frame. If this does no happen, the block thickness will be more than the specified value.
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Release the screw jack and open the lid. The toggle lever may now be pressed further down using the first fulcrum and then the second fulcrum. The block is now ejected. Slide the block along with the bottom plate and stack it edgewise. The plate may now be taken out. The second bottom plate may be inserted into the mould and the process is repeated. d. Curing The mud blocks stabilized with cement or lime must be cured for 21 days by a gentle sprinkling of water. It is preferable to use a garden rose-can for the sprinkling. Under no circumstances should a jet of water from a hose should be used. The top of the stack of blocks must be covered by straw or gunny cloth to prevent evaporation of water. The stacking may be done in a shaded area to assist curing.
4. DESIGN CONCEPT
Concept for wall Design: The masonry design can be carried out using specifications and design guidelines given by National Building Code (2).
Notations Pb
:
Brick or block strength
Pm
:
Masonry unit strength
Pw
:
Masonry Wall strength
e
:
Eccentricity of loading
h
:
Masonry efficiency = Pm/Pb
Ks
:
Reduction factor due to slenderness ratio
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Ke s
: :
Reduction factor due to eccentricity of loads
Basic compressive stress in masonry
Table:3 Sl no
Masonry Details
1
Compressive
2
strength(N/mm2) Basic stress for cm
Burnt bricks
Soil-cement Blocks
From (NBC code)
(from tests)
5
2.51
0.35
0.43
1:6 (sb)N/mm 2
Design calculations of the most critical central wall are for a ground and first floor building is illustrated below.
Let the wall thickness be 230mm Consider a wall width of 1.0m Loads a) Self weigh weightt of the wall wall = 2(1.0mx0. 2(1.0mx0.23mx 23mx3.0 3.0m)x20 m)x20 KN/m KN/m 2
= 27.60 KN
b) Dead weight weight of of floor floor and and roof slab = 2(0.15x1x4/2m+4.3/2m+0.23) 24 KN/m 3
= 31.53 Kn
c) Live Live loa load d of of floo floor r = 1mx(4+4.3)/2 x 2 KN/m 2
= 8.30 KN
d) Live Live load load of roof roof = 1m x (4+4.3)/2 x 1.5 KN/m 2
= 6.22 KN
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Total Load
= 73.66 KN
Compressive stress developed at the base of the wall = 73.66 KN/ 230 mmx100mm
= 0.314N/mm 2
Assume soil soil cement block strength strength of 2.5 2.5 N/mm 2 and the wall is built using 1:6cm Basic compressive stress in masonry = sb = 0.43N/mm 2 (Based on laboratory tests on masonry prisms)
Then Permissible compressive stress in the wall = sb x Ks x Ke = 0.43 x 0.845 x 1.0 = 0.363 N/mm 2
0.314 N/mm 2
Hence the central wall of building should be 23cm thick soil cement block constructed in 1:6 cement mortar, of 2.5N/mm 2 wet compressive strength.
5. TEST RESULTS, COST ANALYSIS
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Table: 4 Energy effectiveness Cost is too often limited only to the monetary value. It is understandable and one can remember that in Auroville a cubic meter of CSEB is around 23.6 % cheaper than a cubic meter of country fired bricks. But the energy approach should be integrated: some studies have shown that, in the Indian context,
building a m² of masonry with CSEB consumes 5 times less energy than a m² of wire cut bricks masonry and 15 times less than country fired bricks.
Ecological comparison of building materials Compressed stabilized earth blocks are more eco-friendly than fired bricks. Their manufacture consumes less energy and pollute less than fired bricks Table: 5 Energy consumption (Kg of CO2 /M 2)
4.9 4.9 tim times es less less than than wire wire cut cut bri brick cks s 15.1 times less than country fired bricks
Pollution emission (MJ)
2.4 2.4 tim times es less less than than wire wire cut cut bri brick cks s 7.9 times less than country fired bricks
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Source 1998 – Development Alternatives for Indian Context.
Figure - 4
This (FIG 4.) graph shows the change in compressive strength with extra pressure and extra cement. For the low pressure samples (1 and 2 MPa) as the cement content doubles the strength also doubles. For the higher pressure samples the fractional increase in strength for the same increase in cement is greater. This clearly indicates that the effectiveness of the cement present increases as the level of compaction is also increased.
Cost effectiveness
CSEB are generally cheaper than fired bricks. This will vary from place to place and especially according to the cement cost. The cost break down of a 5 % stabilized block will depend on the local context. In India with manual equipment (AURAM press 3000), it is usually within these figures: Labor: 20 - 25 % Soil & sand: 20 - 25% Cement: 40 - 60 % Equipment: 3 - 5 %
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In Auroville, a finished m3 of CSEB wall is generally: 48.4 % cheaper than wire cut bricks and 23.6 % cheaper than country fired bricks.
The strength of a block is related to the press quality and the compression force, and to the quantity of stabilizer. This implies that to reduce the cost of a block one should try to reduce the quantity of cement but not the cost of the labor with unskilled people. One should also not cut down the cost of the press with cheap quality machines, which would not last long and would not give strong blocks.
6. ADVANTAGE’S AND DISADVANTAGE’S ADVANTAGES OF CSEB:
A local material Ideally, production is made on the site itself or in the nearby area. Thus, it will save transportation, fuel, time and money. A bio-degradable material Well-designed CSEB houses can withstand, with a minimum of maintenance, heavy rains, snowfall or frost without being damaged. Their strength and durability have been proven since half a century. But let’s imagine a building fallen down and that a Jungle has grown on it: the bio-chemicals contained in the humus of the topsoil will destroy the soil cement mix in 10 or 20 years… And CSEB will come back to our Mother Earth... No other building material can do that. Limiting deforestation
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Firewood is not needed to produce CSEB. This will save forests, which are being depleted quickly in the world, due to short view developments and mismanagement of resources. Management of resources Each quarry should be planned for various utilisations: water harvesting pond, wastewater treatment, reservoirs, landscaping, etc. It is crucial to be aware of this point: very profitable if well managed… Disastrous if unplanned! Energy efficiency and eco friendliness Requiring only a little stabilizer the embodied energy in a m 3 can be from 5 to 15 times less than a m³ of fired bricks. The pollution emission will also be 2.4 to 7.8 times less than fired bricks.
Cost efficiency Produced locally, with a natural resource and semi skilled labor, almost without transport, transport, it will be definitely cost effective, more or less according to each context and to ones knowledge. An adapted material Being produced locally it is easily adapted to various needs: technical, social, cultural habits. A transferable technology It is a simple technology requiring semi skills, easy to get. Simple villagers will be able to learn how to do it in a few weeks. An efficient training centre can transfer the technology in a week’s time. A job creation opportunity CSEB allow unskilled and unemployed people to learn a skill get a job and rise in the social scale. Market opportunity
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According to the local local context context (materials, (materials, labor, equipment, equipment, etc.) the final final price will vary, but in most cases it will be cheaper than fired bricks. Reducing imports Produced locally by semi skilled people, no need to import from far away expensive materials or transport over long distances heavy and costly building materials. Flexible production scale Equipment for CSEB is available from manual to motorized tools ranging from village to semi industry scale. The selection of the equipment is crucial, but once done properly, it will be easy to use the best-adapted equipment for each case.
Social acceptance Demonstrated, since long, CSEB can adapt itself to various needs, from poor income groups to well off people or government needs. Its quality, regularity and style allow a wide range of final house products. To facilitate this acceptance, banish from your language “stabilized mud blocks” , when speaking of CSEB. Often people associate in their minds the name mud with poor building material.
DISADVANTAGES •
Proper soil identification is required or lack of soil.
•
Unawareness of the need to manage resources.
•
Ignorance of the basics for production & use.
•
Wide spans, high & long building are difficult to do.
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•
Low technical performances compared to concrete.
•
Untrained teams producing bad quality products.
•
Over-stabilization through fear or ignorance, implying Outrageous costs.
•
Under-stabilization resulting in low quality products.
•
Bad quality or un-adapted production equipment.
7. WORKS DONE 7.a BUILDING WITH EARTH IN AUROVILLE Since the beginning of Auroville, various experiments have been made with earth building, with mixed results. The creation of the Auroville Building Centre/Earth Unit in 1989, and the construction of the Visitors’ Centre, started a new era in earthen architecture. This Visitors’ Centre of 1200 m² was granted the “Hassan Fathy Award for Architecture for the Poor” in 1992. 1992. Built of compressed stabilized earth blocks, it demonstrated the potential of stabilized earth as a quality building material. Since then, the value of earth as a building material has been acknowledged for its economic advantage, as well as its comfort and quality, which promotes indigenous and sustainable development. Today, Auroville can show a wide variety of earthen projects: public buildings, schools, apartments and individual houses.
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7b. Building with arches, vaults and domes This R&D seeks to increase the span of the roof, decrease its thickness, and create new shapes. Vaults and domes are usually built with compressed stabilized earth blocks, which are laid in “free spanning” mode, without using a formwork. This technique was previously called the Nubian technique.
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8. CONCLUSION: The high-density compressed and stabilized soil block seems to be a reasonable Contender in low-cost building materials. It requires less energy than all of the available competitors and slightly less cement than most of them. Variants on the CSEB can reduce the cement still further making it even more acceptable to a wider range financial capacity. Furthermore the ability for the CSEB to utilize local materials and be manufactured either on-site or very locally makes the material more suitable to cottage industries and self-build schemes. The table below summarizes the different possible variants that can be accomplished with the CSEB and how each one performs with reference to the unmodified CSEB. By combining several of these variants into a single block the material can theoretically achieve a tolerable cement requirement, (less than 15kg/m²), without excessive energy consumption. The tall, hollow, interlocking block as described below even uses less cement then the clamp fired bricks . As this is one of the more common and more wasteful methods of making satisfactory building materials, this confirms that this variant of CSEB is a real contender.
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Many different variants of the CSEB have already been successfully made. However, the author is not aware of any specific manufacturer that can produce the tall, hollow, Interlocking CSEB variant that seems so frugal in its cement use. It is hoped that the application of compaction by impact can yield such a material without the addition of expensive machinery but has yet to be confirmed.
Tests need to be conducted to see if such a variant of CSEB can indeed be made successfully. Following that it would need to be tested to determine whether or not it exhibits the necessary level of durability for use in the humid tropics. If these proved successful, then a pilot scheme would need to be implemented to disseminate the information and necessary technology to a suitable area where low-cost housing is needed.
Table: 6
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9. TOWARDS THE FUTURE Building with earth is definitely an appropriate, and cost and energy effective technology. Obviously one has to know the material and master its disadvantages, which normally are variations in the soil quality and hence the block quality, shrinkage cracks, lower strength than high quality fired bricks or concrete, production of the blocks on site, etc. Since half a century, research and development has proved the potential of earth techniques. Earth can be used as a quality and modern building material almost everywhere in the world. One of the main key points for a general revival and dissemination of earth techniques is respect for Nature and the management of resources. The Earth is Sacred and any soil for building is a precious material. Don’t waste it. To avoid waste earth, separate the piles of topsoil from the building soil. Don’t mix waste building materials with it. Use rubble from building sites for filling basements rather than good soil. Don’t spoil quarry holes by dumping in garbage.
Building with earth has a great past, but also a promising future everywhere in the world. Don’t miss it!
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Appendix: Brick: An Brick: An object object (usually of of fired clay) clay) used in construction construction,, usually of of rectangular rectangular Shape whose largest dimension does not exceed 300mm. Block: A Block: A larger type type of brick not necessarily necessarily made of fired clay, clay, but stabilized stabilized in Some Way, sometimes with central cores removed to reduce the weight. Cement: Ordinary Portland Cement (OPC). Clay: The finest of the particles found in soil, usually of less than 0.002mm in Size and possesses significant cohesive properties. Concrete: The finished form of a mixture of cement, sand, aggregate and water. Dynamic Compaction: A Compaction: A process that compresses compresses the soil by applying applying a series series of Impact blows to it. Fines: General category of silts and clays. Green Strength: The strength present in a freshly formed block prior to curing. Sand: A Sand: A mixture of of rock particles particles ranging ranging from 0.06mm 0.06mm to 2 mm mm in diameter. diameter. Silt: Moderately fine particles of rock from 0.002mm to 0.06mm in size. Soil: Material found on the surface of the earth not bigger than 20mm in size, not including rocks and boulders and predominantly non-organic. If soil is to be used for building material it must not contain any organic material and it can be a natural selection of particles or a mixture of different soils to
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attain a more suitable particle distribution. Stabilized soil: Soil, which has been stabilized (treated to improve structural characteristics) by using one or more of the following stabilization techniques: mechanical, chemical and physical.
References: Minimising the cement requirement of stabilized soil block walling Author: Mr Mr D E Montgomery Montgomery & Dr Dr T H Thomas Thomas March 2001 2001
Sustainable building technologies B. V. Venkatarama Reddy Department of Civil Engineering & Centre for Sustainable Technologies, Indian Institute of Science, Bangalore 560 012, India
Earthen Architecture for sustainable habitate and Compresses stabilized earth block technology. Satprem Maïni, Architect, Director of the Auroville Earth Institute Auroville Building Building Centre Centre – INDIA
Alternative Building Technologies, The Indian Institute of Science, Bangalore
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