Chapter 6:
Compressed Stabilized Earth Block (CSEB)
6.1 Introduction
• A compressed earth block (CEB), also known as a pressed earth block or a compressed
soil block
• is a building material made primarily from an appropriate mix of fairly dry
inorganic subsoil, non-expansive clay, sand, and aggregate.
• Forming compressed earth blocks requires dampening, mechanically pressing at high
pressure, and then drying the resulting material.
• There is no clear consensus about the date when man began to use earth construction.
• Some studies mentioned that that the earth for construction has been used for more than
9000 years and some studies mentioned it may have happened over 10,000 years ago.
• the earth construction begin with the beginning with the start of early agricultural
societies, a period whose current knowledge dates from 12,000 to 7000 BC.
• The compressed earth block is the modern descendent of the moulded earth block, more
commonly known as the adobe block.
6.1 Introduction
• The first machines for compressing earth probably date from the 18th century.
• In France, Francois Cointeraux, inventor and fervent advocate of "new pise" (rammed
earth) designed the "crecise", a device derived from a wine-press.
• But it was not until the beginning of the 20th century that the first mechanical presses,
using heavy lids forced down into moulds, were designed.
• Some examples of this kind of press were even motor-driven.
• the turning point in the use of presses and in the way in which compressed earth blocks
were used for building and architectural purposes came only with effect from 1952.
6.2 Merits of CSEB
• A Local Material
-Ideally, the production is made on the site itself or in the nearby area. Thus, it will save the
transportation, fuel, time and money.
• A bio-degradable material
-But let's imagine a building fallen down and that a jungle grows on it: the bio-chemicals
contained in the humus of the topsoil will destroy the soil cement mix in 10 or 20 years?
-CSEB will come back to our Mother Earth!
• Limiting deforestation
-Firewood is not needed to produce CSEB. It will save the forests, which are being depleted
quickly in the world, due to short view developments and the mismanagement of resources.
• Management of resources
-Each quarry should be planned for various utilizations: 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 energy consumption 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.
6.2 Merits of CSEB
• · Cost efficiency
-Produced locally, with a natural resource and semi skilled labour, almost without transport,
it will be definitely cost effective! More or less according to each context and to ones
knowledge!
• An adaptable material
-Being produced locally it is easily adapted to the 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 few weeks. Efficient training centre will transfer the technology in a
week‘s time.
• A job creation opportunity
-CSEB allows unskilled and unemployed people to learn a skill, get a job and rise in the
social values.
• Market opportunity
• According to the local context (materials, labour, equipment, etc.) the final price will vary,
but in most of the cases it will be cheaper than fired bricks.
6.2 Merits of CSEB
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 most adapted equipment for each case.
• Social acceptance
-Demonstrated, since long, CSEB can adapt itself to various needs: from poor income
to well off people or governments.
-Its quality, regularity and style allow a wide range of final house products
6.3 Some limitations of CSEB
• Proper soil identification is required; some soils may not be suitable.
• Ignorance about 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.
• Low social acceptance due to counter examples (By unskilled people, or bad soil &
equipment).
6.4 The Raw Material
-The basic materials required for the production of compressed stabilized earth building
blocks
• Soil
• Stabilizer
• water
6.4.1 Soil
• Soil is the main ingredient of the CSEB.
• Soil characteristics and climatic conditions of an area must be evaluated before
manufacturing soil building blocks..
• All soils are not suitable for every building need particularly CSEB.
• The basic material, -required to manufacture - is a soil containing a minimum
quantity of silt and clay so as to facilitate cohesion.
• It should be much more sandy than clayey.
• Good soil for CSEB contains the following proportion of the four components:
gravel, sand, silt and clay
6.4.1 Soil
• In Nepal the main soils are classified as following five types based on the percentage of the
four components,
1) Black cotton soil
2) Gravely soil
3) Sandy soil
4) Silty soil
5) Clay soil
6.4.1 Soil
• 1. Black Cotton Soil
• Black Cotton Soil have the following common characteristics:
• the colour ranges from dark grey to dark brown,
• pronounced volume change upon wetting and drying, i.e. extreme expansion and shrinkage properties,
• high (35%) clay content (clay is defined as soil fraction containing particle sizes less than 0.002mm).
• This clay fraction is composed mainly of montmorillonite, a group of soils often found in drier tropics. Its
structure allows water molecules to enter between the layers causing expansion or shrinkage,
•  the liquid limit (LL) ranges between 47% and 93%,
•  the plastic limit (PL) ranges between 26% and 50%,
•  the plasticity index (PI) ranges between 13% and 58%,
•  the linear shrinkage ranges between 8% and 18%.
• Due to the high plasticity of these soils they can be difficult materials to handle when mixed with water.
• Nevertheless, black cotton soil is a popular building material since it covers large areas in Kathmandu Valley.
• However, due to the high clay content and the presence of expandable clay minerals in this soil type, the life
span of buildings made from black cotton soils
• is normally short (approximately 15 years on average), and so there is continuous need for repair.
• In recent years it has been recognized that further study of the properties and characteristics of black cotton
soils and their potential for use in the building industry is necessary.
6.4.1 Soil
• 1. Black Cotton Soil
6.4.1 Soil
• 2. Gravely Soil
• It is composed of unconsolidated rock fragments that have a general
particle size range and
• include size classes from granule- to boulder-sized fragments. A coarsegrained soil is classed
• as gravel if more than half the coarse fraction by weight is retained on a
Number 4 sieve. Gravely soil have the following common characteristics:
equivalent diameter size (mm) : > 2 mm
• Sieving, with mesh size # 8 to 10 mm, is indispensable to remove coarse
gravel.
• - A maximum of 15% to 20% by weight of gravel passing the screen will
be allowed.
• - The maximum size for the gravel passing through the sieve will be 10
mm.
• - If the soil is too gravely, mix with it another soil, which is more clayey.
• - The minimum cement stabilization will be 4% by weight, if the clay
content is not less than 15 %.
• - The average cement stabilization will be 6% by weight.
6.4.1 Soil
• 3. Sandy Soil
• Sand is naturally occurring granular material composed of finely divided
rock and mineral particles.
• The composition of sand is highly variable, but most common constituent
of sand is silica (silicon dioxide, or SiO2, usually in the form of quartz.
• Sandy soil have the following common characteristics:
• Equivalent diameter size (mm): 0.05 - 2 mm
• very coarse 1 - 2 mm
• coarse 0.5 - 1 mm
• medium 0.25 - 0.5 mm
• fine 0.1 - 0.25 mm
• very fine 0.05 - 0.1 mm
• Sieving, with mesh size # 10 to 12 mm, is only required to loosen, aerate
the soil and break up lumps.
• - Do not sieve in a very windy area, especially if the soil is dry, so as not
to loose the fine clay.
• - The minimum cement stabilization will be 5% by weight.
• - The average cement stabilization will be 6-7% by weight, if the clay
content is not less than 15%.
6.4.1 Soil
• 4. Silty Soil
• Silt is granular material of a size somewhere between sand and clay
whose mineral origin is quartz and feldspar.
• Silt may occur as a soil or as suspended sediment (also known as
suspended load) in a surface water body.
• Silty soil have the following common characteristics: equivalent diameter
size (mm) 0.002 - 0.05 mm.
• A slight crushing might be required and sieving, with mesh size # 6 to 10
mm, is required.
• - Adding some coarse sand (10 to 20 %) might be needed to give more
skeletons to the soil, only if the clay content is not less than 20%.
• When the silt content is high (more than 25- 30%) and the sand very fine
(0.06 to 1mm), adding coarse sand and a clayey soil will improve the
structure.
• - The minimum cement stabilization will be 6% by weight.
• - The average cement stabilization will be 7-8% by weight.
6.4.1 Soil
• 5. Clayey Soil
• Clay is a general term including many combinations of one or more clay
minerals with traces of metal oxides and organic matter.
• Clayey soil have the following common characteristics: equivalent
diameter size (mm): < 0.002 mm
• Crushing might often be required and sieving, with mesh size # 6-10 mm,
is required.
• - Adding a lot of sand (30 to 40 % ) is most the time needed to reduce the
plasticity and to
• give some skeletons.
• - The minimum cement stabilization will be 7% by weight and the
average cement
• stabilization will be 8%.
• - Lime stabilization can be used instead of cement. The minimum will be
8 % and the
• average will be 9% by weight of lime. Then, the adjunction of sand will
be reduced.
• - A combination of cement-lime stabilization, can give good results.
• For example: 3% cement + 5% lime + sand as needed.
6.5 Soil Stabilizers
• Modifying soil properties by adding another material to improve its durability is called soil stabilization.
• When a soil is successfully stabilized one or more of the following
• -effects will be evident strength and cohesion of the soil will increase,
• - permeability of the soil will be reduced, the soil will be made water repellent,
• - the durability of the soil will increase, soil will shrink and expand less in dry and wet conditions.
• The chemical admixtures such as lime, cement, and/or fly ash are widely used as a mean of chemically
transforming unstable soils into structurally sound construction foundation.
• There are several methods of soil stabilization widely used to improve construction quality.
6.5 Soil Stabilizers
• 6.5.1Mechanical stabilization
• This involves tamping or compacting the soil by using a heavy weight to bring about a reduction in the air void
volume, thus leading to an increase in the density of the soil.
• The main effects of compaction on the soil are to increase its strength and reduce its permeability.
• The degree of compaction possible, however, is affected greatly by the type of soil used, the moisture content
during compaction and the compression effort applied.
• Best results can be obtained by mixing the correct proportions of sand and clay in a soil.
• More recent developments for roads and embankment construction have led to compacting soil with vibrating
rollers and tampers.
• Tampers and block-making presses are also used for single storey constructions. The major drawback of
mechanically compressed stabilized earth blocks is their lack of durability especially in places of moderate to high
rainfall.
• Manual stabilization or compaction methods vary from foot treading to hand tamping equipment, with
compacting pressures varying between 0.05 to about 4MN/m2.
• Mechanical equipment may achieve compacting pressures of several thousand MN/m2.
6.5 Soil Stabilizers
• 6.5.2 Cement stabilization
• Ordinary Portland cement hydrates when water is added, the reaction produces a cementitious gel that is
independent of the soil.
• This gel is made up of calcium silicate hydrates, calcium aluminate hydrates and hydrated lime. The first two
compounds form the main bulk of the cementitious gel, whereas the lime is deposited as a separate crystalline solid
phase.
• The cementation process results in deposition between the soil particles of an insoluble binder capable of
embedding soil particles in a matrix of cementitious gel. Penetration of the gel throughout the soil hydration process
is dependent on time, temperature and cement type.
• The lime released during hydration of the cement reacts further with the clay fraction forming additional
cementitious bonds.
• Soil-cement mixes should be compacted immediately after mixing in order not to break down the newly created
gel and therefore reduce strengthening.
• The basic function of cementation is to make the soil water-resistant by reducing swelling and increasing its
compressive strength.
• Cement is considered a good stabilizer for granular soils but unsatisfactory for clays.
• Generally cement can be used with any soil type, but with clays it is uneconomical because more cement is
required. The range of cement content needed for good stabilization is between 3% and 18% by weight according to
soil type.
6.6 Soil Testing
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Laboratory analysis of the raw material is always necessary for large-scale production of
compressed stabilized earth blocks. For small-scale production, however, it is not essential to
employ sophisticated tests to establish the suitability of a soil. Simple field tests can be
performed to get an indication of the composition of the soil sample. Such tests are discussed
briefly below.
a) Visual Identification:
Dry soil is examined with the naked eye to estimate the relative propertions of the sandy and fine fraction.
Large stones, gravel and coarse sand are removed in order to facilitate the evaluation.
Look a humid or dry soil
A gravely soil contains big pieces
A sandy soil contains coarse particles
A silty soil is thin, with small lumps
A clayey soil is very thin, with big lump
6.6 Soil Testing
• b) Smell Test:
• The soil should be smelt immediately after removal.
• If it smells musty it contains organic matter. This smell
will become stronger if the soil is heated.
• For the soil identification in field the following point
should considered
 It should not smell rotten
 It should not smell musty
 It should smell agreeable
• c) Touch Test:
• After removing the largest grains, crumble the soil
rubbing it between the fingers and the palm
• The soil is sandy if a rough sensation is felt and has no
cohesion when moist.
• The soil is silty if it gives a lightly rough sensation and is
moderately cohesive when moistened.
• The soil is clayed, if, when dried, contains lumps or
concretions which resist crushing and if becomes plastic
when moistened.
6.6 Soil Testing
• d)Sedimentation test
• To obtain a more precise idea of the nature of each soil fraction,
a simplified sedimentation test can be carried out in the field.
• The apparatus required is straight forward:
- A transparent cylindrical glass bottle with a flat bottom and a
capacity of at liter with a neck wide enough to get a hand in and a
lid to allow for shaking.
- Fill the bottle to one-third with clean water. Add approximately
the same volume of dry soil passed through a 6mm sieve and add a
teaspoonful of common salt.
- Firmly close the lid of the bottle and shake until the soil and
water are well mixed. Allow the bottle to stand on a flat surface
for about half an hour.
- Shake the bottle again for two minutes and stand on level surface
for a further 45 minutes until the water particles fall more slowly
and as a result, it will get deposited on top of the larger size
particles.
• Two or three layers will emerge, with the lowest layer containing
fine gravel, the central layer containing the sand fraction a and
hence percentages, of each fraction can be determined.
6.6 Soil Testing
• e) Adhesion test
• Compact a ball of moist soil so that it does not stick to the
fingers and insert a spatula or knife.
• If the spatula penetrates it with difficulty, and soil sticks to it
upon withdrawal, the soil is extremely clayey.
• If the spatula can be pushed into it without great difficulty but a
bit of soil remains on the knife upon withdrawal the soil is
moderately clayey.
• The spatula can be pushed into the mass without encountering
any resistance at all, even if the spatula is dirty upon withdrawal
the soil contains only a little clay
6.7 Block Production process
6.8 Sieving
• Soil contains various sizes of grain, from very fine dust
up to pieces that are still too large for use in block
production.
• The oversized material should be removed by sieving,
either using a built-in sieve, as with the pendulum crusher,
or as a separate operation.
• The simplest sieving device is a screen made from a wire
mesh, nailed to a supporting wooden frame and inclined at
approximately 45o to the ground.
• The material is thrown against the screen, fine material
passes through and the coarse, oversized material runs
down the front.
• Alternatively, the screen can be suspended horizontally
from a tree or over a pit.
• The latter method is only suitable in the case where most
material can pass through easily otherwise too much coarse
material is collected, and the screen becomes blocked and
needs frequent emptying.
6.9 Proportioning
• Before starting production, tests should be performed to establish the right proportion of soil, stabilizer and water for
the production of good quality blocks.
• The proportions of these materials and water should then be used throughout the production process.
• To ensure uniformity in the compressed stabilized earth blocks produced, the weight or volume of each material used in
the block making process should be measured at the same physical state for subsequent batches of blocks.
• The volume of soil or stabilizer should ideally be measured in dry or slightly damp conditions. After establishing the
exact proportion required of each material, it is advisable to build a measuring device for each material.
• The dimensions of each measuring box should be such that their content, when full, is equivalent to the proportion
which should be mixed with other materials measured in other gauge boxes.
• Alternatively, a simple gauge box may be used for all materials. In this case, the amount of material for the production
of a given batch of blocks may be measured by filling and emptying the gauge box a number of times for each separate
material.
• For example, a batch of blocks may require ten gauge boxes of soil for one gauge box of stabilizer. Water may be
measured in a small tank or container. It is advisable to mix enough materials to allow the block-making machine to
operate for approximately one hour. Thus, the volume of the mixed material will depend on the hourly output of the block
making equipment.
6.10 Mixing
• In order to produce good quality blocks, it is very important that mixing
be as thorough as possible.
• Dry materials should be mixed first until they are of uniform color, then
water is added and mixing continued until a homogeneous mix is obtained.
• Mixing can be performed by hand on a hard surface, with spades, hoes,
or shovels.
• It is much better to add a little water at a time, sprinkled over the top of
the mix from a watering can with a rose spray on the nozzle.
• The wet mix should be turned over many times with a spade or other
suitable tool.
• A little more water may then be added, and the whole mixture turned
over again. This process should be repeated until all the water has been
mixed in.
• A concrete mixer, even if available, will not be useful for mixing the wet
soil, since the latter will tend to stick on the sides of the rotating drum.
• If machinery is to be used for mixing, it should have paddles or blades
that move separately from the container. Hand-mixing methods are often
more satisfactory, more efficient and cheaper than mechanical mixing, and
are less likely to produce small balls of soil that are troublesome at the
block moulding stage.
6.11 Moulding CSEB
• To manufacture blocks of uniform size and density, special precautions must be taken to mould with the same
amount of mix for each compaction by using a small wooden box as a measuring device.
• To facilitate development of the pressed blocks and to ensure good neat surfaces it is advisable to moisten the
internal faces of the machine which can be applied with a rag, brush or spray.
• (Mould immediately the mix: within 20 minutes)
6.11 Moulding CSEB
• Aurum 3000
• Aurum 3000 machine is hand press machines.
• The machine consists of a frame, an interchangeable mould, a reverse toggle lever.
• Other accessories include scoops and bottom plates.
• The machine is mounted on the ground and secured in position using sand bags or stones. Measured quantity
of this mixture is poured in the die of predefined shape and dimensions and is compressed by pulling the lever
by hand.
• Then the compressed block is ejected from the die. The wet compressed blocks are stacked in rows.
• Special Features of Aurum press 3000:
•  High output from the automatic opening: 1000
• strokes/day.
• = 125 Blocks/Hour (plain full size blocks)
•  Handling of the press with 3 men. Mix preparation and block stacking with 4 men.
•  High and adjustable compression ratio from 1.6 to 1.83
• (1.77 for 9 cm height)
•  Micro adjustment of compression ratio.
•  Double compression with the folding back lid.
•  Rollers to move the press on site. Only 2 men are
• needed.
•  Block height adjustable with ring spacers: 2.5 cm and from 5 to 10 cm.
•  Micro adjustment of block height: 0.5mm accuracy
6.12 Curing
• To achieve maximum strength, compressed stabilized earth blocks need a period of damp curing, where they are kept
moist.
• If the block is left exposed to hot dry weather conditions, the surface material will lose its moisture and the clay particles
tend to surface cracks on the block faces.
• In practice, various methods are used to ensure proper curing. Such methods include the use of plastic bags, grass,
leaves, etc. to prevent moisture from escaping.
• The required duration of curing stabilizer is used.
• With cement stabilization, it is recommended to cure blocks for a minimum of three weeks.
• The curing period for lime stabilization should be at least four weeks.
• Compressed stabilized earth blocks should be fully cured and dry before being used for construction.
6.13 Quality Control
• Compressed stabilized earth building blocks are usually larger in size than traditional burnt bricks. A typical block size is
240 x 140 x 90mm. The exact amount of stabilizer necessary must be established for any particular project. The fraction of
cement usually varies between 5% to 8% by weight.
• Golden rules
• - To create a joyful atmosphere where everybody is conscious of the quality required and check the blocks.
• - Check the production at every stage (see the production cycle).
•  The pile must remain covered 2 days with a plastic sheet
•  Stacking the fresh block
•  Cover immediately every row with a plastic sheet.
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- Check the quality of the compression with the pocket penetrometre, always for the first block of every mix.
- Check the height with the block height gauge, always for the first block of every mix.
- Follow the production daily. Record the outputand dates...
- Check weekly or monthly, the production with the field block tester (after 28 days).