Seminar report

On

THE ROLE OF SOIL CEMENT BLOCKS IN HOUSING

SUBMITTEDTO

VIVESWARAIAH TECHNOLOGICAL UNIVERSITYBELGAUM

FOR THE PARTIAL FULFILLMENT OF M-TECH (STRUCTURAL ENGINEERING)

BYB.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 TECHNOLOGYBANGALORE -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 1st 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.RAVINDRADepartment of Civil Engineering

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ACKNOWLEDGEMENT

I express my deep sense of gratitude 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 FOR ALTERNATIVE BUILDING MATERIALS

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

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 INTERLOCKING BLOCKS (295)

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Blocks produced by the Auram Press 3000

Auram equipment for earth construction

A wide range of equipment for building with earth has been 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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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 four components: gravel, sand, silt and clay. In 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% 1 20Cement 4% 1 25Cement 3% 1 33

Lime 5% 2 24Cement 2.5% 1 40

Lime 3% 2 40Cement 8% 2 25

Cement 3.5% 1 25Lime 2% 1 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: The proportion of water should be approximately

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

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Ks : Reduction factor due to slenderness ratio

Ke : Reduction factor due to eccentricity of loads

s : Basic compressive stress in masonry

Table:3

Sl no Masonry Details Burnt bricks

From (NBC code)

Soil-cement Blocks

(from tests)

1 Compressive

strength(N/mm2)

5 2.51

2 Basic stress for cm

1:6 (sb)N/mm2

0.35 0.43

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 weight of the wall = 2(1.0mx0.23mx3.0m)x20 KN/m2 = 27.60 KN

b) Dead weight of floor and roof slab

= 2(0.15x1x4/2m+4.3/2m+0.23) 24 KN/m3 = 31.53 Kn

c) Live load of floor

= 1mx(4+4.3)/2 x 2 KN/m2 = 8.30 KN

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d) Live load of roof

= 1m x (4+4.3)/2 x 1.5 KN/m2 = 6.22 KN

Total Load = 73.66 KN

Compressive stress developed at the base of the wall

= 73.66 KN/ 230 mmx100mm = 0.314N/mm2

Assume soil cement block strength of 2.5 N/mm2 and the wall is built using 1:6cm

Basic compressive stress in masonry =sb = 0.43N/mm2

(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/mm2

0.314 N/mm2

Hence the central wall of building should be 23cm thick soil cement block

constructed in 1:6 cement mortar, of 2.5N/mm2 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 /M2)

Pollution emission(MJ)

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4.9 times less than wire cut bricks 2.4 times less than wire cut bricks15.1 times less than country fired bricks

7.9 times less than country firedbricks

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 %

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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 %

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

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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

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 m3 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, 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.

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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

According to the local context (materials, labor, equipment, etc.) the 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

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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.

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. 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,

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which promotes indigenous and sustainable development. Today, Auroville can

show a wide variety of earthen projects: public buildings, schools, apartments

and individual houses.

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

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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.

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.

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Table: 6

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.

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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!

Appendix:

Brick: An object (usually of fired clay) used in construction, usually of rectangular

Shape whose largest dimension does not exceed 300mm.

Block: A larger type of brick not necessarily made of fired clay, but stabilized in

Some Way, sometimes with central cores removed to reduce the weight.

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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 process that compresses the soil by applying a 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 mixture of rock particles ranging from 0.06mm to 2 mm in 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

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 D E Montgomery & Dr T H Thomas March 2001

Sustainable building technologies B. V. Venkatarama Reddy

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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 Centre – INDIA

Alternative Building Technologies,

The Indian Institute of Science, Bangalore

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