Earth materials.pdf

8/14/2019 Earth materials.pdf

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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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brick bonds


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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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Clamp kiln


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Clamp kiln


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Clamp kiln - Advantages andDisadvantages


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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Bulls trench kiln


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Bulls trench kiln


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Bulls trench kiln - Advantages andDisadvantages


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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Vertical shaft brick kiln


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Vertical shaft brick kiln


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Vertical shaft brick kiln - Advantagesand 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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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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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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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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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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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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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


Atterberg limits Plasticity index

PI LL PL=


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Atterberg limits chart


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Cohesion test


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Cohesion test chart


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Moisture/density chart


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5.3.3 Earth materials Construction

methods


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methods Cob


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methods Wattle and daub

5 3 3 E h i l C i


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methods - Adobe

5 3 3 E th t i l C t ti


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methods - Adobe


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5 3 3 Ea th mate ials Const ction


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methods Soil suitability for adobe

5 3 1 Earth materials Construction


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methods - Adobe - Advantages andDisadvantages


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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methods Rammed earth


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methods Rammed earth Sitefeatures



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methods Rammed earth charts



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methods Rammed earth -Advantages and 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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methods Compressed blocks


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methods Compressed blocks -Advantages and 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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