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5.3: Earth materials
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5.3 Book
Houben, H, Guillaud H (1994). Earth
construction : a comprehensive guide, ITPubs, (TH 1421.H6)
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5.3 Earth
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5.3 Earth materials
Kiln dried
Sun dried Stabilised
Unstabilised
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5.3 Earth materials soil
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5.3 Earth materials soil particle size
Pebbles 200mm 20mm
Gravel 20mm 2mm
Course sand 2mm 0.2mm
Fine sand 0.2mm 0.02mm
Silt 0.02mm 0.002mm
Clay - > 0.002mm
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5.3.1 Earth materials Burned bricks
Bricks moulded and then energy(heat) added at 850-1000oC
Clays vitrify (form glasses)
Quality varies with Soil type (mainly clay content)
Firing
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5.3.1 Earth materials Burned bricks
brick bonds
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5.3.1 Earth materials Burned bricks
Advantages and Disadvantages
Advantages Disadvantages
Good compressive strength
Slightly porous permittingmoisture to move
Good thermal capacity
Good fire resistance
Weather (rain) resistant
Poor quality bricks can beused for other purposes no waste
Labour intensive
High fuel consumption (5MJ kg-1 deforestation
Simple kilns produce bricksof varying quality
Lime blowing
Efflorescence
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5.3.1 Earth materials Burned bricks
Clamp kiln
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5.3.1 Earth materials Burned bricks
Clamp kiln
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5.3.1 Earth materials Burned bricks
Clamp kiln - Advantages andDisadvantages
Advantages Disadvantages
They are cheap andstraightforward to build
No permanent structure toinstall and maintain
Can be built next to thesupply of clay and fuel
Low transport costs
Can be left once lit
Good scalability
Can be fired continuously,
Clamps can be fired with a
large variety of fuels
The least energy efficientmethod of firing bricks
Fuel consumption of 2.8 to3.5 MJ/kg fired brick
Labour intensive
Poor quality control a very
Up to 20% of the bricksover or under fired
Slow to fire,
several days to heat upand cool down
Susceptible to the
prevailing weatherconditions
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5.3.1 Earth materials Burned bricks
Bulls trench kiln
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5.3.1 Earth materials Burned bricks
Bulls trench kiln
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5.3.1 Earth materials Burned bricks
Bulls trench kiln - Advantages andDisadvantages
Advantages Disadvantages
More fuel efficiencycompared to periodic kilns
2.5-2.8 MJ.kg
Low initial investment.
High capacity
Demands goodorganization of the brickproduction,
Production cannot easily be
adjusted to fluctuations inthe brick market.
High skill
Moveable chimneys have ashort working life.
Exhaust temperature ishigh, causing a less thanoptimum firing condition
and fuel economy.
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5.3.1 Earth materials Burned bricks
Vertical shaft brick kiln
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5.3.1 Earth materials Burned bricks
Vertical shaft brick kiln
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5.3.1 Earth materials Burned bricks
Vertical shaft brick kiln - Advantagesand Disadvantages
Advantages Disadvantages
Very energy efficient
~1 1.3 MJ/kg
2-3x bulls trench
Low cost
High quality
The kiln is cheap andstraightforward to build,
Very compact
Not effected by variations inthe weather,
Reduced local air pollution
More than one shaft allows for
firing flexibility
Labour requirements are low
Novelty
Requires good quality greenbricks,
Have to be able to withstandbeing stacked 5 meters high in
the firing shaft.
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5.3.2 Earth materials Soil tests Initial
tests
Visual examination
Smell tests
Nibble test
Touch test
Washing test
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5.3.2 Earth materials Soil tests Lustre
test
Cut a slightly moist ball of soil with aknife Shiny surface clayey
Dull surface - silty
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5.3.2 Earth materials Soil tests
Adhesion test
Cut into a slightly moist ball of soilwith a knife Knife penetrates easily low in clay
Soil resists penetration - clayey
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5.3.2 Earth materials Soil tests Water
retention test
A moist ball squeezed into a egg-shaped ballwith just enough water to hold it together
Press the ball into one hand and tap with theother until water forms at the surface
5-10 taps fine sand or course silt 20-30 taps plastic silt or silty clay
No reaction - clayey
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5.3.2 Earth materials Soil tests
Consistency test
Roll an olive-sized ball of moist soil into a threadabout 3 mm If it breaks before 3mm too dry raise water
content
Reroll the thread into a ball and squeeze Hard to crush high clay content
Cracking or crumbling low clay content
Breaks before ball is formed high silt or sandcontent
Soft and spongy high organics - reject
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5.3.2 Earth materials Soil tests
Cohesion test
Squeeze a moist ball of soil into a strip (~12-15mm thickness)
Carefully dangle loose end from fingers
Measure how long it is when it breaks 25-30 cm clayey
5-10 cm low clay content
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5.3.2 Earth materials Soil tests Dry
strength test
Flatten egg sized ball to ~1cm thickness
Allow to dry Break piece between thumb and forefinger
Breaks with difficulty and doesnt crumble clay
Can be easily crushed to powder silty or
sandy clay Pulverised without effort silt or sand with low
clay content
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5.3.2 Earth materials Soil tests Settling
test
Fill jar about 1/3 full with soil and compact slightly
Add water to about 2/3 full. Add a pinch of salt(honest!)
Shake and leave to settle. Shake again after anhour
Gravel and sand settle after 1 min Silt settles after 30 mins
Clay will take ~ 24 hours
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5.3.2 Earth materials Soil tests Settling
test
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5.3.2 Earth materials Soil tests Sieve
analysis
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5.3.2 Earth materials Soil tests Sieve
analysis chart
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5.3.2 Earth materials Soil tests
Shrinkage test
Grease inside of box
Pack in soil
Measure length of dried pieces after 3days in sun or 7 in shade High shrinkage is bad (aim for
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5.3.2 Earth materials Soil tests Optimal
Water content
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5.3.2 Earth materials Soil tests Optimal
Water content test
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5.3.2 Earth materials Soil tests
Atterberg limits Liquid limit test Casagrande apparatus
Dry soil and weigh
Add some water until soil is a thick paste
Place in apparatus
Make a groove with grooving tool
Turn handle until groove is breached by 13mm
When breach is 13mm after 25 turns, soil is at the liquid limit
Its actually more complex see BS1377
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5.3.2 Earth materials Soil tests
Atterberg limits Liquid limit test
Pack soil in bowel till it is about 8mm deep inthe centre
Make a groove with grooving tool
Tap with hand Soil is at the liquid limit when the gap is
breached by 13mm after 10 taps
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5.3.2 Earth materials Soil tests
Atterberg limits Plastic limit test
Add water to dry soil
Roll about 5g into a ball until it dries and cracks
Divide the sample into two parts and make eachinto a sausage about 6mm
Roll each part to a thread of 3mm If it breaks before 3mm dryer than plastic limit
Remains whole after 3mm wetter than plastic limit
Should break into lengths of about 10mm
Check moisture content by weighing
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PI is the Plasticity
indexLL is the liquid limit
PL is the plastic limit
5.3.2 Earth materials Soil tests
Atterberg limits Plasticity index
PI LL PL=
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5.3.2 Earth materials Soil tests
Atterberg limits chart
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5.3.2 Earth materials Soil tests
Cohesion test
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5.3.2 Earth materials Soil tests
Cohesion test chart
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5.3.2 Earth materials Soil tests
Moisture/density chart
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5.3.3 Earth materials Construction
methods
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5.3.3 Earth materials Construction
methods Cob
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5.3.3 Earth materials Construction
methods Wattle and daub
5 3 3 E h i l C i
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5.3.3 Earth materials Construction
methods - Adobe
5 3 3 E th t i l C t ti
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5.3.3 Earth materials Construction
methods - Adobe
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5 3 3 Ea th mate ials Const ction
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5.3.3 Earth materials Construction
methods Soil suitability for adobe
5 3 1 Earth materials Construction
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5.3.1 Earth materials Construction
methods - Adobe - Advantages andDisadvantages
Advantages Disadvantages
Simple and cheap
Easily worked
Very low energy input
Fire resistant
Good climaticperformance
Unlimited reusability
Environmentally benign
Needs constantmaintenance
Water absorption cancause cracks and evencomplete fluidisation
Low tensile strength bad in earthquakes
Low acceptability formany poor mansmaterial
Low institutional support
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5.3.3 Earth materials Construction
methods Rammed earth
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5 3 3 Earth materials Construction
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5.3.3 Earth materials Construction
methods Rammed earth Sitefeatures
5 3 3 Earth materials Construction
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5.3.3 Earth materials Construction
methods Rammed earth charts
5 3 3 Earth materials Construction
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5.3.3 Earth materials Construction
methods Rammed earth -Advantages and Disadvantages
Advantages Disadvantages
Good compressivestrength
Good surface finish nofurther treatment isusually required
Well understood inmany parts of the world
Very low energy input
Needs a suitable soil witgood grain distribution
Can suffer in rain andrising damp so needs agood foundation (goodpair of boots and a hat)
(Hard) labour intensive
Formwork can be costly
Corners can beproblematic
Must be made on-site
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5.3.3 Earth materials Construction
methods Compressed blocks
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5.3.3 Earth materials Construction
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5.3.3 Earth materials Construction
methods Compressed blocks -Advantages and Disadvantages
Advantages Disadvantages
High compressive strength
Small drying and storagerequirement
Easy transportation
Good surface finish
Good thermal capacity
Good fire resistance
Often lower cost thanburned bricks
Can be made to any shape(interlocking is popular)
Labour intensive
Needs a suitable soil witgood grain distribution
Binders are often necessaryand mix can be critical
Non-traditional, thereforesuspicion and a high cost offailure
Labour intensive
5.3.4 Earth materials Stabilisation why
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o y
stabilise
Clay expansion on wetting
De-lamination of renders Separation of elements such as doors and
windows
Saturation Unstabilised soil has much reduced
(sometimes zero) cohesion when wet
Alternative to good hat and boots
5.3.4 Earth materials Stabilisation
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Stabiliser Nature Method Mode Principle
Without stabiliser Mechanical
minerals
Densification
Create a dense mediumblocking pores andcapillary
inert
fibres
Physical
Reinforcement
Create an anisotropicnetwork, limitingmovement
Cementation
Create an inert matrixopposing movement
linkage Create stable chemicalbonds between claycrystals
Imperviousness
Surround earth particlewith a waterproof film
Waterproofing Eliminate absorption andadsorption
Waterproofers
binderschemical chemical
Withstabiliser
5.3.4 Earth materials Stabilisation
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