UNIVERSITY OF NAIROBI SCHOOL OF...

UNIVERSITY OF NAIROBI

SCHOOL OF ENGINEERING

DEPARTMENT OF ENVIRONMENTAL AND BIOSYSTEMS ENGINEERING

PROJECT TITLE: DESIGN OF RAMMED EARTH CONSTRUCTION

FORMWORK AT BANANA HILL IN KIAMBU COUNTY

CANDIDATE NAME: GRIFFINS OCHARO KIMONGE

CANDIDATE No.: F21/36255/2010.

SUPERVISORS NAME: Mr. J. O Agullo

A Report Submitted in Partial Fulfillment for the Requirements

of the Degree of Bachelor of Science in Environmental and

Biosystems Engineering, of the University Of Nairobi

MAY, 2015

FEB 540: ENGINEERING DESIGN PROJECT

2014/2015 ACADEMIC YEAR

F21/36255/2010 I

DECLARATION

I declare that this engineering project (design of rammed earth construction formwork ) is my

work and has not been submitted for a degree in any other university.

SIGNATURE-------------------------------------- DATE------------------------------------

GRIFFINS OCHARO KIMONGE

This project report has been submitted for examination with my approval as University

supervisor.

SIGNATURE---------------------------------- DATE-------------------------------------------

MR. J.O AGULLO

F21/36255/2010 II

DEDICATION

I dedicate this Engineering Design project to my beloved Parents, my siblings and friends for

their kindness and support throughout my undergraduate study.

F21/36255/2010 III

ACKNOWLEDGEMENT

I sincerely thank the almighty God for seeing me through the five years in campus and having

given me good health, mental and physical strength throughout my stay as an undergraduate

at the University of Nairobi.

Special thanks also go to my supervisor, Mr. J.O. Agullo, for his guidance and great

intellectual support.

My gratitude also goes to the able EBE technical staff especially Mr. Bonface Muliro and

Mrs.Annerose Mwangi for the proficient guidance they continuously offered me throughout

this project.

I would also like to thank our hardworking chairman Prof. Eng. Ayub N. Gitau and the entire

staff and student fraternity of the department of Environmental and Biosystems Engineering

for their accompaniment and support.

F21/36255/2010 IV

TABLE OF CONTENTS

DECLARATION ....................................................................................................................... i

DEDICATION .......................................................................................................................... ii

ACKNOWLEDGEMENT ....................................................................................................... iii

LIST OF TABLES .....................................................................................................................v

LIST OF FIGURES ................................................................................................................. vi

ABSTRACT ............................................................................................................................ vii

1.0. INTRODUCTION .........................................................................................................1

1.1. Background ..................................................................................................................... 1

1.2. Problem statement and justification ................................................................................ 2

1.3 Site analysis and inventory ............................................................................................... 2

1.4 Overall objective .............................................................................................................. 5

1.4.1 Specific objectives......................................................................................................... 5

1.5 Scope of work................................................................................................................... 5

2.0 LITERATURE REVIEW ....................................................................................................6

2.1 THEORITICAL FRAMEWORK ......................................................................................13

3.0 METHODOLOGY .......................................................................................................17

4.0 RESULTS AND DISCUSSION ........................................................................................22

4.1 RESULTS AND CALCULATIONS .................................................................................22

4.1.1 Grain size distribution. ................................................................................................ 22

4.1.2 A GRAPH SHOWING GRAIN SIZE ANALYSIS .................................................... 23

4.1.3 Sedimentation analysis ................................................................................................ 24

4.1.4 Atterberg limits results ................................................................................................ 25

4.1.7 Triaxial testing results ................................................................................................. 33

4.3 DISCUSSION OF THE RESULTS ...................................................................................41

4.4 BILL OF QUANTITY .......................................................................................................42

5.0 CONCLUSSION AND RECOMMENDATIONS ............................................................43

5.1 CONCLUSSION ............................................................................................................ 43

5.2 RECOMMENDATIONS ............................................................................................... 43

6.0 REFERENCES ..................................................................................................................44

7.0 APPENDICES ..............................................................................................................45

APPENDIX A: Drawings of modern formwork ................................................................. 45

APPENDIX B: List of Tables .............................................................................................. 46

APPENDIX C: Photos from the lab .............................................................................................. 49

F21/36255/2010 V

LIST OF TABLES

Table B1 Lower limit range for particle size distribution for natural rammed earth

Table B2 Upper limit range for particle size distribution for natural rammed earth

Table B 3 Grading proportion for cement stabilization

Table B4 Lower limit range for particle size distribution for cement stabilization

Table B5 Upper limit range for particle size distribution for cement stabilization

Table 4.1 Grain size analysis of soil at the site

Table 4.3.1 Liquid limit test data

Table 4.3.2 Plastic Limits Test Data

Table 4.5 Water content calculation

Table 4.6.1 Triaxial testing results

Table 4.6.2 Axial strain and unit axial load for sample 1



F21/36255/2010 VI

LIST OF FIGURES

Figure 1.1 A map of Kenya showing the various counties

Figure 1.2 Kiambu county maps showing its sub-counties

Figure 1.3 A Google map extract showing the site location

Figure 4.2 (a) Shows soil S2 sedimentation flask

Figure 4.2 (b) Shows the results of all tests

Figure 4.8 A diagram showing loading conditions of the wall

Figure A 1 Preliminary sketches of modern formwork showing different parts

Figure C 1 Atterberg limits determination in the laboratory photos

Figure C 2. Soil sample taken from the site

Figure C 3. Apparatus for triaxial testing

Figure C 4. Preparing of soil specimen for testing photo

F21/36255/2010 VII

ABSTRACT

The problem of failures and collapse in rammed earth houses has been on the rise leading to

homelessness and lack of decent housing especially at Banana Hill in Kiambu County. It has

also lead to loss of lives. This is as a result of poor construction methods, in correct mixing of

the materials and lack of construction expertise. To help solve such a problem, correct design

of rammed earth formwork while incorporating modern structural considerations can greatly

offer solution.

The overall objective of this project was to design a rammed earth construction formwork

that could be used in construction of rammed earth houses at Banana hill in Kiambu County.

To achieve the above overall objective the following specific objectives were set: to

determine properties of natural and stabilized rammed, to determine the compressive

strength of wood to be used in construction of formwork and to design a rammed earth house

construction formwork that is affordable, portable and long lasting.

I designed the modern formwork to help solve the problem of failures and collapse of

rammed earth houses. Basic elements of modern formwork comprise sheeting material,

against which the earth is compacted, a system of strengthening and stiffening elements

(soldiers and walers), ties and bolts, and inclined props to ensure overall stability. The

supporting members can also comprise steel members and solid timber sections. Steel

through ties connecting the two sides of formwork help stiffen it so as to limit deformation.

At the end of my design project I designed a rammed earth construction formwork that could

be used in construction of rammed earth houses that are affordable, have superior insulation

and require little maintenance and also established the properties of natural and stabilized

rammed earth.

F21/36255/2010 1

1.0. INTRODUCTION

1.1. Background

Construction using Rammed earth that includes use of locally available soils stabilized with

binders such as lime dates back many centuries. Rammed earth structures including walls

have been built in numerous countries since the 1800s (Earth Materials Guidelines, 1996).

Research indicates that the USA and Australia have been the pioneers in using this

sustainable material in building construction (Nelson, 1976). Rammed earth structures utilize

locally available materials with lower embodied energy and wasted materials than traditional

method (Earth Materials Guidelines, 1996).

The soil used for rammed earth building is a widely available resource with little or no side

effects associated with harvesting for use in construction. The soils used are typically subsoil,

leaving topsoil readily available for agricultural uses. Often soil of reasonable quality can be

found close to the location of construction, thus reducing the cost and energy for

transportation. Significant cost savings can be achieved when earth (aggregates or soil) is

used for construction since the material is generally inexpensive and readily available. If the

amount of cement used in rammed earth is carefully controlled, more cost savings can be

achieved. Today more than 30 percent of the worlds population uses earth as a building

material (Anderson, 2000). In addition, rammed provides good thermal mass, with inherent

good heat retention in buildings and cost-savings.

Once the ingredients for rammed earth have been selected, compression or ramming of the

material can be done manually using a tamper. However, rammed earth construction without

mechanical tools can be very time consuming and labor intensive. Buildings constructed

using rammed earth reduces the need for lumber because the formwork is normally removed

and reused. The forms are usually made of form-ply and end panels reinforced and secured

by a system of whalers, strong backs and integrated scaffolding. The face formwork is

secured to end panels.

The rammed earth technology has been used to construct houses in Kenya. This is because

they are cheap to construct and the raw material are readily available. In Kenya rammed earth

houses have been constructed at Banana Hill in Kiambu County and that is where my site is

located.

F21/36255/2010 2

1.2. Problem statement and justification

The problem of failures and collapse in rammed earth houses has been on the rise leading to

homelessness and lack of decent housing especially at Banana Hill in Kiambu County. It has

also led to lose of lives. This is as a result of poor construction methods, in correct mixing of

the materials and lack of construction expertise. To help solve such a problem correct design

of rammed earth formwork while incorporating modern structural considerations can greatly

offer solution.

Formwork is a temporary construction structure intended to support and gives shape to

concrete or rammed earth during the placing and curing phases. Through the use of

permanent formwork it will help solve the high costs of buying or constructing formworks

and also help curb deforestation since the formwork will be made from thin masonry or

brickwork.

1.3 Site analysis and inventory

The proposed project area is in Banana Hill which is a suburb of Karuri town, in the

eastern part of Kiambu County, Central Province of Kenya. The town is situated 2,000 m

above sea level, approximately 20 km north of Nairobi City via Limuru Road by Runda

Estate. It is approachable from an alternate route, the Limuru, Kiambaa/Kiambu and

Ndenderu/Redhill all-weather roads, accessed by the main Limuru road. The project site lies

adjacent to the tarmac road on coordinates -1.17 S, 36.75 E. The area receives an average

annual rainfall of 790 mm (31 in) with average temperatures ranging from 11 C to 29 C in

January and 10C to 26 C in July. Rainfall is bimodal. Long rains occur between April and

May. The cool season occurs between July and August, and short rains occur between

October and November. Clay and sandy soils are the dominant kinds of soil in the area. This

types of soil enables construction of rammed earth house construction. The area has gentle

slopes and ever green ground cover which helps to prevent soil erosion.

(Retrieved fromwww.nema.go.ke/index.php?option=com.)

F21/36255/2010 3

Figure 1. 1: A map of Kenya showing the various counties

(Source: www.guide2kenya.com)

Figure 1.2: Kiambu county map showing its sub-counties

(Source:www.misstourismkenya.org)

http://www.guide2kenya.com/information/53/http://r.search.yahoo.com/_ylt=AwrB8p8vWABVQXEAEQ2jzbkF;_ylu=X3oDMTBxNG1oMmE2BHNlYwNmcC1hdHRyaWIEc2xrA3J1cmwEaXQD/RV=2/RE=1426114736/RO=11/RU=http%3a%2f%2fwww.misstourismkenya.org%2fcontent%2fkiambu%2fpatriq%2f96/RK=0/RS=IpiLtg.cElZBFdVKY5ZUbPXrL88-

F21/36255/2010 4

Figure 1.3: A Google map extract showing the site location

(Source: Google map)

Project site

F21/36255/2010 5

1.4 Overall objective

The overall objective of this project is to design a rammed earth construction formwork that

can be used in construction of rammed earth houses at Banana hill in Kiambu County.

1.4.1 Specific objectives

To achieve the above overall objective the following specific objectives were set:

1. To determine the various properties of natural and stabilized rammed earth

2. To determine the tensile strength of wood to be used in construction of formwork

3. To design a rammed earth house construction formwork that is affordable, portable and

long lasting.

1.5 Scope of work

In my design project I shall mainly concentrate in designing of rammed earth construction

formwork which can be used in construction of rammed earth houses. Various laboratory and

field tests will be performed to come up with a suitable and efficient formwork that will be

used. I will limit myself to rammed earth technology.

F21/36255/2010 6

2.0 LITERATURE REVIEW

There are several important traditional earthen construction methods. These are adobe (sun

dried mud brick) Rammed earth, wattle and daub and cob.

Adobe: It is an Arabic and Berber word and describes bricks that are molded wet and cast

small enough to shrink without cracking. This is the most common traditional earth building

method. The bricks are made with earth, straw (optional) and water, and usually dried in the

sun. Mud plaster is required for protection against weather conditions and frequent

maintenance of the plaster is a must to expand the life of the building. Dry and hot or cold

climates are appropriate for this technique. Selection of soil types, molding and a drying

process are important phases for making adobe bricks. Large bricks are preferred for strength

and easy construction purposes. (Yoldas, 2001).

Rammed Earth: Loam soil that is crumbly, relatively rich in sand content, and of natural soil

humidity is poured in layers into a formwork and slowly compacted. Rammed earth

construction method is advantageous in that it has a longer life. This earth construction

method is mostly preferable in a humid climate because it does not require a curing process.

Its compaction provides higher strength and durability compared to adobe bricks. The

formwork design is the crucial stage of the construction and they are usually made out of

wood. In the traditional method of construction, an iron hammer is used to compact the wall,

but in the modern era hydraulic tools like tampers and mortars to compact and remove the air

lumps. (Yoldas, 2001).

There are also some new tools that are applied to rammed earth construction techniques to

compress the earth more effectively .Steel formwork is used for better surface results.

Normally additives, to improve durability and strength are another improvement of rammed

earth construction technique. This new improved rammed earth construction is also one of the

widely used contemporary rammed earth techniques. (Yoldas, 2001).

Cob: Cob is a combination of sand and clay with straw and water added. Sub-soil can be

used with an even distribution of clay mixed with plant fibers. Clay soils used in cob

construction provide protection against weather conditions. The most critical design

consideration for cob buildings is protection from soaking. Cob walls have ability to absorb

large amounts of water hence, if they stay wet for long time, it weakens the straw and that

weakens the wall. (Yoldas, 2001).

F21/36255/2010 7

Wattle and Daub: Wattle is a woven framework of twigs and daub is a mud covering

applied over framework. It is an easy and simple method of construction. Its section depends

on the wooden part of the construction. This causes the section of the wall to not be thick

enough to supply thermal mass. The disadvantage of this system is that it requires a lot of

maintenance due to the cracks. Cracks are the main reasons of erosion and insects that live in

the walls.

Advantages of rammed earth as a building material

1. It is natural, economical, and available for everyone who has a land and it is ideal for a

do-it-yourself construction. (Ciurileanu&Horvath,2012).

2. It is very good fire resistant. (Ciurileanu&Horvath, 2012).

3. It is environmentally friendly: doesnt consume energy when compared to other

industrialized building materials. For example, stabilized earths embodied energy is of

0.7 Mj/kg and cements embodied energy is of 5.6 Mj/kg. (Ciurileanu&Horvath, 2012).

4. It is available almost anywhere in the world. (Ciurileanu&Horvath, 2012).

5. It preserves timber: it is easy to build with, especially when using a timber frame for load-

bearing and earth mixture as an infill material. (Ciurileanu&Horvath, 2012).

6. It has a high thermal mass: compared to other insulating materials, earth can store the heat

captured during the day and release it in the house during the night after eight hours

(Minke, 2005).

7. It balances air humidity: earth walls absorb the humidity inside the house and maintain an

almost constant air humidity of 50% for an entire year (Minke, 2005).

8. Earth is easy to work with using simple tools and less skill. So, it encourages and

facilitates self-help and community participation in house building. (Ciurileanu&Horvath,

2012).

Formwork in rammed earth construction is used as a temporary support during soil

compaction. Like concrete formwork it is required to have sufficient strength, stiffness and

stability to resist pressures it is subjected to during erection, placement of the soil, and

dismantling.

However, unlike concrete, rammed earth formwork can be removed almost immediately

after compaction, enabling much faster re-use. As with in-situ concrete construction efficient

organization of formwork is essential to efficient rammed earth construction. (Maniatidis&

Walker, 2003).

When making a choice of formwork the following general criteria should be kept in mind

F21/36255/2010 8

Strength

The formwork should be able to withstand the outward pressure of the earth during

compaction. Typically pressures during rammed earth compaction are considered to be much

higher than general concrete works, though the area and period of time over which the

pressure acts is typically much less. (Maniatidis& Walker, 2003).

Stiffness

The formwork should be sufficiently stiff to maintain the form without excessive distortion

during compaction. Typically, forms should not deflect more than 3mm over the length

between the ties under full pressure. (Maniatidis& Walker, 2003).

Durability

Formwork must be able to meet the expected number of uses under normal site handling

conditions and appropriate maintenance, without performance deterioration.

(Maniatidis & Walker, 2003).

Adaptability

The formwork should be capable of accommodating variations in the width and layout of the

wall to meet structural and architectural requirements. (Maniatidis& Walker, 2003).

Ease of handling

Formwork must not be too heavy or bulky in order to avoid making assembly difficult and

time-consuming. (Maniatidis& Walker, 2003).

Ease of alignment

Formwork parts should include smooth horizontal and vertical slots, comfortable holes for

bolts and smooth running ties to allow easy and consistent horizontal and vertical alignment.

(Maniatidis& Walker, 2003).

Ease of compaction

The shuttering system should not obstruct the compaction process. (Maniatidis & Walker,

2003).

The basic elements of any formwork system, traditional or modern are:

1. Shutters- the two sides of the form.

F21/36255/2010 9

2. End stops- the boards which close-off the open ends of the formwork.

3. Ties and bolts-these can be either direct through-bolts, cantilever bolts, threaded ties

or ties with wedges.

4. Props or stays- the (fixed or movable) vertical posts used to brace the form.

5. Spacers-bolting often requires spacers in order to set the width of the wall. Spacers

should be softer than the formwork in order to prevent damage to the form faces

6. Wedges-for adjustment of the formwork. (Maniatidis& Walker, 2003).

There are several types of formwork and the selection of the appropriate type of molding

system for each application is important.

Traditional form work

Most of the rammed earth structures around the world have been using the same type of

formwork for centuries with only small variations. This traditional formwork comprises of

two timber shutters usually made out of softwood planks 20-30mm thick (Norton, 1997) and

two end stops the width of the wall held together by timber props and rope ties.

If 20-30mm thick planks are used, the posts can be spaced at 650-700mm centres further

apart. (Maniatidis& Walker, 2003).

In England this formwork was used during the 1920s in Amesbury, although it was later

modified to include hardwood wedges instead of wire ties and was continuous around the

wall plan (Jaggard 1921).In some parts of the world, including Morocco and India

(Popposwamy) the formwork is still in use in its traditional form. (Maniatidis& Walker,

2003).

Modern Formwork

Basic elements of modern formwork comprise sheeting material, against which the earth is

compacted, a system of strengthening and stiffening elements (soldiers and walers), ties and

bolts, and inclined props to ensure overall stability. Suitable sheeting materials include steel,

aluminum, and timber sheeting and planks. As with concrete, the choice of sheeting material

and any pre-treatment applied (i.e. release agent) influence the finish of the rammed earth.

Supporting members can also comprise steel members and solid timber sections. Steel

through ties connecting the two sides of formwork help stiffen it to limit deformation, but

F21/36255/2010 10

leave a hole through the wall that must be filled after stripping and may lead to blemishes in

appearance. A variety of different formwork systems, many based on in-situ cast concrete

formwork systems, have been used for rammed earth. (Maniatidis & Walker, 2003).

SPECIALTY FORMWORK

A) Corner Formwork

Corners are typically easier to build than straight sections, commercial concrete and

Australian formwork systems clip together with standard pieces to allow corners which are in

themselves more stable than are straight sections. Formwork for straight sections is then

connected to existing free standing corner sections and built as filler panels. (Maniatidis&

Walker, 2003).

B) Curved Formwork

Formwork for rounded and curved walls is comprised from same basic components (sheeting

material for shuttering supported by timber or steel soldiers and walers), but requires special

design and is normally more expensive than that for straight wall sections. (Maniatidis &

Walker, 2003).

C) Permanent Formwork

Due to increased cost of formwork, attempts have been made to develop permanent

(sacrificial) formwork techniques. Permanent formwork made from thin masonry or

brickwork. (Maniatidis& Walker, 2003).

Stabilization

Stabilization of the soil is one of the ways of improving the characteristics of a soil. Soil

requires stabilization because the material as found in its natural state is not durable for long-

term use in buildings. Cement and compression are one of the most effective methods of

stabilizing the soil. One can reduce the volume of the voids and connect the particles together

using cement and compaction. This will reduce porosity. This will also help to reduce

swelling and shrinkage percentages as long as production follows the proper procedure.

Mechanical strength, dry and wet compressive strength, will also improve with these

methods.

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Research on durability of cement-stabilized earth walls has tested the durability of the

material against weather conditions. (Maniatidis& Walker, 2003).

Soil stabilization comprises a variety, and often combination, of modification processes to

improve soil properties, including strength and resistance to water. In addition to compaction,

an inherent element of rammed earth construction that seeks to maximize material density,

stabilizing additives can be combined with the natural soil. Additives generally fall into two

classes: those that materially increase strength and reduce moisture absorption; and to those

that reduce moisture absorption and moisture movement but do not appreciably increase

strength (Middleton, 1952).

The use of stabilizers such as cement has derived out of a need to improve wet strength and

erosion resistance in very exposed walls (Houben &Guillaud, 1994).

However, in Australia and USA, cement stabilization has become accepted routine practice in

rammed earth construction irrespective of application. In many situations the use of cement

and other stabilizers can be avoided by good design and construction appropriate to earth

building. (Maniatidis& Walker, 2003).

To optimize the benefits of stabilization then soils should meet a number of requirements.

Soil should be free of humus and plant matter, though under certain conditions, plant matter

like straw can be added, provided it is dry, with no danger of later deterioration (Minke,

2000). In addition soil should mainly consist of sand and fine gravel, with only sufficient clay

for any required cohesive strength and a proportion of silt to act as void filler. (Maniatidis &

Walker, 2003).

The main categories of binders used for earth construction are (Standards Australia, 2002;

Houben &Guillaud 1994; SAZS 724:2001, 2001) Portland cement, lime, bitumen, natural

fibre and chemical solutions such as silicates.(Maniatidis & Walker, 2003).

Cement Stabilization

There various advantages when using cement as a stabilizer. Soil samples gain strength from

both the formation of a cement gel matrix that binds together the soil particles and the

bonding of the surface-active particles, like clay, within the soil (Crowley, 1997). High levels

of cement stabilization improve the surface coating and reduce erosion (Walker, 2000) while

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increasing the cement has a considerable influence in improving the resistance of soils

vulnerable to frost attack (Bryan, 1988).

However there are notable disadvantages using cement. The permeability of most soils is

reduced (ACI Materials Journal Committee, 1990) and hence the natural ability of earth to

allow passage of moisture throughout the soil mass is also significantly impaired.

Environmental impact of cement production and reduced ability for recycling of rammed

earth are also significant arguments against widespread use of cement in rammed earth

construction. Less significantly, thermal conductivity, compared to lime stabilized blocks, is

reportedly increased (Adam, 1995).

Lime Stabilization

Though there are few reported examples of lime stabilized rammed earth walls, lime is

included here as potential for future consideration. Much of the data below relates to use of

lime in compressed earth block production. Unlike cement, which works with the coarse

particles of a soil, non-hydraulic lime works with the clay minerals in a soil.

Tests have indicated that there is an optimum lime dosage for a soil beyond which

compressive strength decreases (Norton, 1997). The likely dosages are between 6-12% lime

by dry weight and will increase as clay content increases (Houben &Guillaud, 1994;

Montgomery, 1998; Norton, 1997).

Fibre Stabilization

Fibres are used to improve the thermal performance and bending and tensile strength of soil.

Natural fibres used include straw, sisal fibres and timber. According to Standards Australia

(2002), the ideal soil for fibre stabilization should have a plasticity index between 15% and

35% with the liquid limit from 30% to 50%. One disadvantage of fibre stabilization is that the

compressive strength of soils decreases as the straw content increases (Minke, 2000).

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2.1 THEORITICAL FRAMEWORK

Definition and Classification of Soil

Gravel: Gravel is a small piece of rock. The sizes of gravel ranges between approximately

2mm and 20mm. It forms a stable soil and has mechanical properties that do not change in

the presence of water. It is not preferable to use a large amount of gravel as a building

material because of its lack of cohesion with other materials. (Yoldas, 2001).

Sand: The size of grains of sand range from approximately 0.06 to 2mm. Sand lacks

cohesion when dry, but has a very high degree of internal friction. It displays apparent

cohesion when moistened. Sand is the best ingredient for a good soil-cement brick. (Yoldas,

2001).

Clay: They are the finest particles of the soil. The size of clay is smaller than 0.002mm. Clay

acts as a binder for all larger particles in the mixture. Clay is vulnerable to swelling and

shrinkage when dry. It has a low resistance to deformation in a moist state, but dries out into

very cohesive masses. Clay is difficult to compact when moist. (Yoldas, 2001).

Silt: Silts are fine grains .Their size ranges from 0.002 to 0.06mm. They are unstable in the

presence of water. When dry, silt can be easily pulverized between the pressures of a persons

fiingers. Silt gives the soil stability by increasing its internal friction. Because of their high

permeability silty soils are very sensitive to frost. It is subject to small-scale shrinkage and

swelling. (Yoldas, 2001).

Gravel and sand give the material its strength while clay acts as a binder and silt fulfills a less

clear intermediate function (Yoldas, 2001).

Particle size distribution

Walker and Maniatidis (2003) show particle size distributions recommended for unstabilized

rammed earth given by a wide range of authors. It can be seen that the percentage of clay

varies from a minimum of 10 % to a maximum of 80%, with the same figures for the

proportion of silt. Acceptable ranges of sand range from 5% to 40%.For stabilized rammed

earth the recommended proportions of cement vary from 25% to 40% by volume (Walker

&Maniatidis, 2003).

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Plasticity

Soil plasticity, the ability of a soil to undergo irreversible deformation while still resisting an

increase in loading, is indicated by the plasticity index. The plasticity index is the water

content increase (% of dry weight) required for a soil to pass from a plastic to a liquid state.

Experimentally the plasticity index can be found by estimating the plastic and limits.

(Maniatidis& Walker, 2003).

PI is the difference between the liquid limit (LL) and the plastic limit (PL), and it determines

the extent of the plastic behavior of the properties of the soil. Mathematically, PI = LL PL.

Together, the liquid limits and plastic limits also define the sensitivity of the soil with

changes in moisture content. Soil can also be classified depending on the measure of its

plasticity index and the liquid limits as indicated below; (Mayon, 2009).

1. Soil with PI from 1 to 10 and LL from 0 to 30 is considered to be a sandy soil;

2. Soil with PI from 5 to 25 and LL from 20 to 50 is considered to be a silty soil;

3. Soil with PI greater than 20 and LL greater than 40 is considered to be a clayey soil.

(Mayon, 2009).

A standard method for measuring plastic limit is described in BS 1377-2, 1990. Soil is

screened through a 425 m sieve and dried. On re-wetting soil is rolled out by hand on a flat

surface, usually glass. The plastic limit is defined as the moisture content at which the soil

can no longer be rolled to 3mm diameter thread without breaking. (Maniatidis& Walker,

2003).

The most common method for obtaining the liquid limit is the cone penetrometer method. A

standard 30 angle cone is brought into contact with the soil surface that has been previously

mixed with water. The cone is released and the penetration under gravity at the end of 5 sec is

recorded. This process is repeated for increasing soil moisture content until a semi log curve

of moisture content versus penetration may be produced. From the graph the moisture content

corresponding to 20mm penetration is recorded. This value is the liquid limit.

(Maniatidis&Walker, 2003).

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Compressive Strength

The compressive strength of a soil is a measure of soil bearing, determined by a variety of

tests. (Retrieved from http://www.dictionaryofconstruction.com/definition/unconfined-

compressive-strength-ucs.html)

The compressive strength of rammed earth can be up to 4.3 MPa (620 psi) (retrieved from

http://earthworksmagazine.co.za/features/rammed-earth-ancient-yet-modern/)

The unconfined compressive strength (qu)the load per unit area at which the cylindrical

specimen of a cohesive soil falls in compression is given by:

qu= P/A 3.1

where

P is axial load at failure

A is corrected area which is

1

Ais the initial area of the specimen

is the axial strain which is change in length / original length

(TxDOT Designation: Tex-118-E 2014)

The undrained shear strength (S) of the soil is equal to the one half of the unconfined

compressive strength,

S=

2 3.2

To calculate the axial strain for a given applied load:

= l ls 3.3

where

l is change in length of the specimen as determined from the deformation indicator,

mm

(in.)

Ls is length of specimen after consolidation, mm (in.)

(TxDOT Designation: Tex-118-E 2014)

http://www.dictionaryofconstruction.com/definition/unconfined-compressive-strength-ucs.htmlhttp://www.dictionaryofconstruction.com/definition/unconfined-compressive-strength-ucs.html

F21/36255/2010 16

Water content (w) of a soil sample is the weight of free water contained in the soil expressed

as a percentage of its dry weight. (retrieved from www. wikipedia.org/wiki/Water content)

w =

=

3.4

Degree of saturation (S) is the ratio of the volume of free water contained in the soil to its

total volume of voids. Its often expressed as percentage and has an important influence on

soil behavior.(Retrieved from www.wikipedia.org/wiki/Degree_of_saturation)

S=

3.5

F21/36255/2010 17

3.0 METHODOLOGY

A survey in the area was conducted to know how the local people construct rammed earth

houses. Survey was done through interviewing and administering questionnaires on type of

form work used to support the rammed earth material before compressing and ramming it

using motors or long pieces of wood.

Different soil samples in the study area were collected for laboratory testing to ascertain the

appropriate one to be used in rammed earth house construction. The strength of the timber

used to construct the formwork was also determined by conducting laboratory testing of

tensile strength of the timber used.

Grain size distribution.

This test is carried out by sieve analysis in which the soil is filtered through a series of

standard mesh sieves placed one above the other in the order of decreasing opening size, and

the proportion of material left in each sieve determined. (Mayon, 2009).

Sedimentation analysis.

In sedimentation analysis the soil with coarsest particles will settle first and the soil with the

finest particles the last. Variations in density are measured at regular intervals and at a given

height (density diminishes as the liquid clears).The speed at which the particles settle enables

one to calculate the proportions of the various sizes of particles. (Mayon, 2009).

Atterberg Limits.

Soil has various states of consistency including liquid, plastic, or solid. A Swedish researcher

named Atterberg defined these various hydrous states and the boundaries separating them as

limits and indices:

1. Liquid Limits (LL); this is the amount of water expressed as a percentage corresponding to

the point at which the material passes from a plastic state to liquid state.

2. Plastic Limits (PL); this is the point at which the texture passes from being plastic to solid.

(Mayon 2009)

At the liquid limits the soil begins to display some resistance to shearing, and at the plastic

limits it ceases to be plastic and becomes crumbly. PI is the difference between the liquid

F21/36255/2010 18

limit (LL) and the plastic limit (PL), and it determines the extent of the plastic behavior of the

properties of the soil. Mathematically, PI = LL PL. Together, the liquid limits and plastic

limits also define the sensitivity of the soil with changes in moisture content. Soil can also be

classified depending on the measure of its plasticity index and the liquid limits as indicated

below;

1. Soil with PI from 1 to 10 and LL from 0 to 30 is considered to be a sandy soil;

2. Soil with PI from 5 to 25 and LL from 20 to 50 is considered to be a silty soil;

3. Soil with PI greater than 20 and LL greater than 40 is considered to be a clayey soil.

(Mayon, 2009).

Jar test

Take a transparent cylindrical jar or bottle of at least 1/2 liter capacity and fill it at the 1/4

mark with soils and at the 3/4 mark with water, seal the top using your hand or lid, and shake

well. Leave the jar to stand for at least 30 minutes and observe the sedimentation layers. After

resting for about 30 minutes or more, particles in the solution of soil and water will begin to

settle in layers. Coarse material (gravel) will be deposited on the bottom, followed by sand,

then silt, with clay at the top. The depth of each layer approximately gives an indication of

the proportions of each type of material (Houben, 2008).

Cigar Test

Get a ball of mud without gravel. Start to roll it like a cigar. If it breaks before 5 cm more

clay is needed. If it breaks after 15cm there is too much clay in the soil and more sand should

be added. (Mayon, 2009).

Triaxial Compression Test

The Triaxial Compression Test is a laboratory test method that is used to assess the

mechanical properties of rocks and fine-grained soils. It provides a measure of the confined

compressive strength as well as the stress-strain characteristics of rock, soil or other material

specimen. It is most often applied to soil and rock samples to simulate in situ confining

pressures and measure the corresponding strength and deformation characteristics. Triaxial

compression tests performed over a range of confining pressures are used to define a

materials strength envelope. (Retrieved from

www.rocktestinglab.com/?q=triaxial_compression_test.html)

http://www.rocktestinglab.com/?q=triaxial_compression_test.html

F21/36255/2010 19

Procedure for Triaxial Compression Test

1. Place the sampling soil specimen at the desired water content and density in the large

mould.

2. Push the sampling tube into the large mould and remove the sampling tube filled with the

soil.

3. Saturate the soil sample in the sampling tube by a suitable method.

4. Coat the split mould lightly with a thin layer of grease. Weigh the mould.

5. Extrude the sample out of the sampling tube into the split mould, using the sample

extractor and the knife.

6. Trim the two ends of the specimen in the split mould. Weigh the mould with the

specimen.

7. Remove the specimen from the split mould by splitting the mould into two parts.

8. Measure the length and diameter of the specimen with vernier calipers.

9. Place the specimen on the bottom plate of the compression machine. Adjust the upper

plate to make contact with the specimen.

10. Adjust the dial gauge and the proving ring gauge to zero.

11. Apply the compression load to cause an axial strain at the rate of to 2% per minute.

12. Record the dial gauge reading, and the proving ring reading every thirty seconds up to a

strain of 6%.

13. Continue the test until failure surfaces have clearly developed or until an axial strain of

20% is reached.

14. Take the sample from the failure zone of the specimen for the water content

determination (retrieved from http://theconstructor.org/geotechnical/unconfined-

compressive-strength-of-cohesive-soil/3134/)

http://theconstructor.org/geotechnical/unconfined-compressive-strength-of-cohesive-soil/3134/http://theconstructor.org/geotechnical/unconfined-compressive-strength-of-cohesive-soil/3134/

F21/36255/2010 20

PROCEDURE FOR DETERMINING COMPRESSIVE STRENGTH OF WOOD

1. Choose a sample that has appropriate grain features, free of cracks, checks, splits and no

knots larger than 1/8 inch in diameter.

2. For this experiment, be sure the grain runs parallel to the direction of loading. Measure

the height, width, and length of the specimen. Determine the species of sample. Record

this data.

3. Mark the two strain targets 4 inches center-to-center aligned vertically on the centerline

of one of the specimen faces.

4. Place the sample in the center of the loading frame so that the load may be evenly applied

to the specimen.

5. While watching the video extensometers image, carefully align the specimen so the

strain target marks are recognized by the video software (indicated by a small red circle

around each target mark) and in the center of the extensometers horizontal view.

6. Tare the initial strain recorded. When entering information prompted by the data

acquisition software, you should be sure to include a complete description of the test

conditions, including:

a. Lab experiment title,

b. Type of specimen,

c. Load-grain alignment,

d. Length, heath and width, etc., so that when you work on the lab report,

you will have that information available to you. Enter a unique,

descriptive test dataset name.

Once the setup is complete, the load will be applied at a rate of 0.003 inch per inch of the

specimen length per minute. The specimen will be loaded until the proportional limit is

passed. This may occur around 20 kip, depending on the sample species. Photograph the

failed specimen. Accentuate the rupture plane by using a pen or pencil to trace the failure

surface to make it easily seen in the photograph.

(Retrieved from Department of Civil Engineering, Southern Illinois University Edwardsville

on 25/3/2015)

F21/36255/2010 21

BUILDING PROCESS FOR RAMMED EARTH HOUSE

1. First we need to prepare the site once the project is defined and we are allowed to build.

We need to free the space from unwanted vegetation and confine an area where we can

store tools and material to build.

2. Get the soil composition. Preparing the adequate earth mixture can be complicated,

roughly70 percent sand and gravel, 30 percent clay and silt (Easton 2007) .Once we have

the correct mixture of earth in the site, it would be wise to protect it from rain

3. Wet the mixture. The soil needs to be wetted, but not abundantly. If we take a handful of

the mixture and press it, this should not fall apart, but neither stick to the fingers, it should

be almost dry and break if you throw it from a height of one meter. To wet the material is

recommended to spray it, the water content should be between 8-10% in the mixture.

4. Foundations. The foundations or a rammed earth wall are like the ones used for a heavy

masonry wall such as bricks or concrete.

5. Build the formwork. Formwork is a big component in rammed earth buildings, like it is in

concrete works. In the traditional method the formwork consists of two modules of wood

that could be carried by two persons and moved to the next level. Nowadays complex

systems to reduce time and costs are implemented with wood and metal formworks.

These formworks are similar to those used in concrete works.

6. Pour and compact the earth .With rammed earth techniques, moist earth is poured into a

formwork in layers between 12 and 15cm thick, and then compacted by ramming (Minke

2009). The higher the formwork, the more difficult is to maneuver and compress the

mixture.

7. Prefabrication. Rammed earth structures can be load bearing, with a density of two tons

per cubic meter, wall elements are good for sound insulation and thermal mass. The

possibility to create prefabricated elements of rammed earth could facilitate to build

almost all year long, instead of a few months during the summer that the traditional

technique allows. (Escobar,2013)

PROCEDURE FOR CONSTRUCTING FORMWORK

Timber measuring 2 metres length by 0.35 metres width and 0.45 metres height is cut and

joined together at the edges by 40cm bolts to form a rammed earth formwork. Vertical posts

of 0.4 metres area also fixed to brace the formwork. Wedges are also put for easy adjustment

of the formwork. End stops made of timber measuring 0.45 metres by 0.35metres are also put

on the sides of the formwork so as to close off the open end of the formwork.

F21/36255/2010 22

4.0 RESULTS AND DISCUSSION

4.1RESULTS AND CALCULATIONS

4.1.1 Grain size distribution.

Table 4.1 Grain size analysis of soil at the site

Sieve

number

Diameter

of the sieves

(mm)

Mass of

Empty

Sieve

Mass of

Sieve and soil

Retained (g)

Soil

Retained (g)

Percent

Retained

Percent

Passed

4

4.75 429.0 457.5 28.5 5.7 94.3

10 2 399.5 444.0 44.5 8.9 85.4

20 0.85 511.0 596.5 85.5 17.1 68.3

40 0.425 291.5 345 53.5 10.7 57.6

60 0.25 461.0 518.0 57.0 11.4 46.2

140 0.125 447.0 481.0 34.0 6.8 39.4

200 0.075 272.0 295.0 23.0 4.6 34.8

Pan 0 254.0 428.0 174.0 34.8 0.0

F21/36255/2010 23

4.1.2 A GRAPH SHOWING GRAIN SIZE ANALYSIS

Diameter of sieves in mm

Per

cen

tage

pass

ing

F21/36255/2010 24

4.1.3 Sedimentation analysis

Figure 4.2 (a) shows soil S2 sedimentation flask

Figure (b) shows the results of all tests

.

F21/36255/2010 25

4.1.4 Atterberg limits results

4.1.4.1 Liquid limit test data

Table 4.3 showing liquid limit test data

Test No. 1 2 3 4 5

Mass of empty

can (M1 )g

30.2 30.4 30.6 30.4 30.6

Can + moist

soil(M2) g

42.8 47.1 42.0 45.2 40.4

Can + dry

soil(M3) g

40.7 44.4 40.0 42.8 38.4

Moisture

content %

20 19.3 21.3 19.3 25.6

No. of blows

(N)

40 35 25 15 10

Moisture content %, W % = [(M2 M3)/ (M3 M1)] X100

For test no. 1

W% = [(42.8-40.7)/ (40.7-30.2)] X100

= (2.1/10.5) X100= 20%

For test no. 2

W %=[( 47.1-44.4)/ (44.4-30.4)] X100

= (2.7/14) X100

=19.3%

For test no. 3

W% = [(42.0-40.0)/ (40.0-30.6)] X100

= (2/9.4) X100

=21.3%

F21/36255/2010 26

For test no.4

W% = [(45.2-42.8)/42.8-30.4)] X100

= (2.4/12.4) X100

=19.3%

For test no.5

W% = [(40.4-38.4)/38.4-30.6)] X100

= (2/7.8) X100

=25.6%

Liquid Limit (LL) is the moisture content that corresponds to N = 25 blows = 21.3%

4.1.4.2 Plastic Limits Test Data

Can No. 1 2 3

Mass of can, M1 (g) 30.8 31.0 30.9

Mass of can + moist soil,

M2 (g)

50.3 58.4 54.3

Mass of soil + dry soil, M3

(g)

47.6

54.5 51.0

Moisture content % =

{[(M2 M3)/(M3

M1)] X 100}

16.07 16.60 16.42

Moisture content % = {[(M2 M3)/ (M3 M1)] X 100}/3

Moisture content % for sample 1= [(50.3-47.6)/47.6-30.8)] X 100

= (2.7/16.8) X 100

=16.07 %

Moisture content % for sample 2= [(58.4- 54.5)/ (54.5-31.0)] X 100

= (3.9/23.5) X 100

=16.60%

Moisture content % for sample 3= [(54.3-51.0)/ (51.0-30.9) X 100

= (3.3 /20.1) X 100

=16.42%

F21/36255/2010 27

Average Moisture content % for the soil = {[(M2 M3)/ (M3 M1)] X 100}/3= Plastic limit

of the soil

= (16.07+16.60+16.42)/3

=16.36%

Hence the plastic limit of the soil =16.36%

Plasticity index= liquid limit plastic limit

=21.3-16.36

= 4.96

Results of Atterberg limits test for 2 % cement.

Liquid limit was found to be 44.6

Plastic limit was found to be 35.9

Plasticity index =LL-PL =44.6-35.9 = 8.7

y = 0.9493x - 23.193

-20.0

-10.0

0.0

10.0

20.0

30.0

40.0

50.0

10 100

Mo

istu

re C

on

ten

t (%

)

NO. OF BLOWS

LIQUID LIMIT CHART

F21/36255/2010 28




Plasticity index= LL-PL =44.6-36.1 =8.5

y = 0.1181x + 13.746

0.0

10.0

20.0

30.0

40.0

50.0

10 100

Mo

istu

re C

on

ten

t (%

)

NO. OF BLOWS

LIQUID LIMIT CHART

F21/36255/2010 29




Plasticity index = 10.2

y = -0.0151x + 41.929

0.0

10.0

20.0

30.0

40.0

50.0

10 100

Mo

istu

re C

on

ten

t (%

)

NO. OF BLOWS

LIQUID LIMIT CHART

F21/36255/2010 30

Summary for the Results of Atterberg limits test percent of cement to the total Weight

Results of Unconfined Compression Strength Test

Percent of cement to the total Weight

12 %

cement

6%

cement

2%

cement

0%

cement

44.6 44.6 44.6 44.6 Liquid Limit

34.4 36.1 35.9 28.6 Plastic Limit

10.2 8.5 8.7 16.1 Plasticity Index

12 %

cement

6%

cement

2%

cement

0%

cement

2week

strength

(kN/m2)

1week

strength

(kN/m2)

2week

strength

(kN/m2)

1week

strength

(kN/m2)

2week

strength

(kN/m2)

1week

strength

(kN/m2)

strength

(kN/m2)

Cube

Number

4030 2900 3100 2550 3420 2450 1180 1

3750 2700 3550 2600 3260 2350 1230 2

3890 2800 3325 2575 3340 2400 1205 Average

F21/36255/2010 31

Results of Unconfined Compression Strength Test

4.1.5 Degree of saturation calculation

S= Vv

Vw

S=26.4cm3 /66cm3

= 40%

0

500

1000

1500

2000

2500

3000

3500

4000

4500

0 2 4 6 8 10 12 14

Com

pre

ssiv

e S

tren

gth

(k

N/m

2)

% of Cement

Compressive Strenght vs. % of Cement

1 week

2 week

F21/36255/2010 32

4.1.6 Water content calculation

Sample NO: 1 2 3

Can NO: G21 G22 G23

Weight of Can+ Moist

soil [W 1] g

164.15

137.2

131.5

Weight of Can+ Dry

soil [W2]g

135.64

114.6

108.7

Weight of can.

[Wc]g

23.4

24.2

18.22

Weight of water.

[W w] g

28.51

22.6

22.8

Weight of Dry soil.

[Ws]g

112.24

90.4

90.48

Moisture content %

W=[Ww/Ws]100

25.4

25.0

25.2

Moisture content % w=

Moisture content % w for sample 1

= 28.51/112.24

= 25.4%


=22.6/90.4

=25.0%


=22.8/90.48

=25.2%

Average moisture content = (25.4+25.0+25.2)/3

=25.2%

F21/36255/2010 33

4.1.7 Triaxial testing results

Table 4.1.7 showing triaxial testing results

Elapsed

time

Deformation

Dial

Axial strain

Area(mm^2) Proving Ring

Dial

Applied

axial load

Unit Axial

load

(min) L,(mm) (L/L) A/(1-) (mm) (N) (kpa)

0 0 962.11 0 0 0

1 0.5 0.007 962.79 2.333 7 7.721

2 1 0.013 974.67 8 24 24.624

3 1.5 0.02 981.74 10 30 30.558

4.24 2 0.0263 988.9 13.333 40 40.449

5.49 2.5 0.0329 994.84 14.333 43 43.223

6.49 3 0.04 1002.2 15.333 46 45.899

7.49 3.5 0.046 1008.5 16 48 47.595

8.35 4 0.0526 1015.53 16.667 50 49.235

9.29 4.5 0.0592 1022.65 17.333 52 50.848

10.24 5 0.0658 1029.88 18.333 55 53.404

11.21 5.5 0.0724 1037.2 19.333 58 55.92

11.19 6 0.079 1044.64 19.667 59 56.479

12.23 6.5 0.0855 1052.11 19.667 59 56.078

13.42 7 0.0921 1059.71 21.667 65 61.338

14.42 7.5 0.0987 1067.47 22 66 61.828

15.4 8 0.1053 1075.34 22 66 61.376

16.39 8.5 0.1118 1083.21 22 66 60.93

17.32 9 0.1184 1091.52 22 66 60.466

18.26 9.5 0.125 1099.55 22 66 60.134

19.4 10 0.1316 1107.91 22 66 59.572

20.42 10.5 0.1382 1116.4 22 66 59.119

F21/36255/2010 34

Table 4.1.7.2 showing axial strain and unit axial load for sample 1

Axial strain Unit Axial load

(L/L) Kpa

0 0

0.007 7.721

0.013 24.624

0.02 30.558

0.0263 40.449

0.0329 43.223

0.04 45.899

0.046 47.595

0.0526 49.235

0.0592 50.848

0.0658 53.404

0.0724 55.92

0.079 56.479

0.0855 56.078

0.0921 61.338

0.0987 61.828

0.1053 61.376

0.1118 60.93

0.1184 60.466

0.125 60.134

0.1316 59.572

0.1382 59.119

F21/36255/2010 35


Axial strain, Unit Axial load

L/LO (kpa)

0 0

0.0007 5.712

0.013 16.416

0.02 19.353

0.0263 21.253

0.0329 24.124

0.04 27.939

0.046 29.251

0.0526 30.526

0.0592 31.291

0.0658 32.043

0.0724 33.745

0.079 35.419

0.0855 36.118

0.0921 36.803

0.0987 36.535

0.1053 37.198

0.1118 36.927

0.1184 36.653

0.125 35.469

0.1316 33.4

0.1382 32.247

F21/36255/2010 36


Axial strain, Unit Axial load

h/ho (N)(Kpa)

0 0

0.0007 11.425

0.013 19.494

0.02 23.428

0.0263 27.325

0.0329 30.156

0.04 31.93

0.042 31.863

A graph of axial strain against unit axial strain load for sample 1, 2 and 3

The compressive strength of unstabilized rammed earth was found to be 0.45Mpa whole for

stabilized rammed earth was found to be 6.2 Mpa which complied with the theoretical values.

-10

0

10

20

30

40

50

60

70

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16

a graph of axial strain against unit axial load for sample 1,2 and 3

Unit Axial load Kpa Axial strain L/LO Unit Axial load (kpa)

Axial strain, h/ho Unit Axial load (N)(Kpa)

F21/36255/2010 37

4.1.8 COMPRESSIVE STRENGTH OF WOOD

After a laboratory experiment the compressive strength of mahogany wood was found to be

6,460 psi (pound per square inch)

4.1.9 STABILIZED RAMMED EARTH CALCULATIONS

In the case of stabilized rammed earth where cement is used, the section of the wall directly

underneath the applied load is taken into consideration to calculate quick and approximate

compression capacity.

Figure 4.8 A diagram showing loading conditions of the wall

The load is applied via the steel plate 500 mm long along the mid span of the wall.

Area of concrete taking the load

AC = steel plate length x width of concrete panel x 2

= 500 mm x 40 mm x 2 = 40,000 mm2

fc = 65.6 MPa

Point load applied from jacking at failure

P = fc x A

= 65.6 N / mm 2 x 40,000 mm2 = 2.624 x 10 6 N = 2624 kN

F21/36255/2010 38

Theoretical Mass of concrete =

[(2m x 0.63m x 0.04m) x 2+ (0.15m x 0.27m x0.63m) x2] x 2400 kg/ m3 =364.39 kg

Mass of soil = 602.62 kg

Mass of the wall = measured mass of soil + theoretical mass of concrete =

= 602.62 kg + 364.39 kg = 963.01 kg

Soil Density = soil mass/ soil volume= 602.62 kg/3.178m3

=1915kg/m3

Mass of the test specimen = 963.01 kg,

Volume of test specimen = 2m x0.63m x 0.35m+0.15m x0.63m x0.27m=0.467m

Average density =

=

963.01

0.467 =2062.1 kg/m3 =20.23 kN/m3

Load on wall at the bottom of the ground floor, foundation level

Wall self weight

Wall height = 2.7 m x 2 floors = 5.4 m

Wall self weight = floor height x wall thickness x average density of wall

= 5.4 m x 0.35 m x 20.23 kN / m3

= 38.23 kN /m

Slab load

Assume concrete slab for the first floor 300 mm thick

Assume slab spans 8 m between load bearing walls one of which is the wall considered. 4 m

is

taken by the wall considered.

Slab weight = half slab span x slab thickness x concrete density

= 4 m x 0.3 m x 24 kN / m3

= 28.8 kN / m

Connecting Reinforced Concrete Beam on the top of the wall

Assuming beam depth 180 mm

F21/36255/2010 39

UDL = 24 kN / m3 x 0.18 m x .35 m = 1.5 kN / m

Roof Load

Total pressure from roof self weight = 75 kg / m2. The load includes roof tiles, structural

timber, insulation, ceiling battens and plaster ceiling - taken from span book, timber

promotion council

Assume roof spans 25 m across from exterior wall to exterior wall, therefore one wall carries

12.5 m worth of load which is half a span.

UDL=75/29.81/2

1000 12.5 =8.89kN/m

Floor finishes

=4 m 1 kN / m2 = 4 kN / m

Ceilings and services = 0.3 kN / m2 x 4 m = 1.2 kN / m

Partitions

= 1 kN / m2 x 4 m = 4 kN / m

Total Dead Load, G = 38.23 + 28.8 + 1.5 + 8.89 + 4 + 1 + 4= 86.42 kN / m

Live Load, Q = 3 kN / m2 x 4 m = 12 kN / m

Ultimate Limit State = G + Q

= 1.2 x 86.42 + 1.5 x 12 = 121.7 kN / m

F21/36255/2010 40

4.2.0 CALCULATION OF CHARACTERISTIC COMPRESSIVE STRENGTH OF

CONCRETE

Standard Cylinder Compression Test

Mass: 3.750 kg

Diameter:

Top average =100.34 mm

Middle average =100.22mm

Bottom average=100.15mm

Average Diameter = 100.35+100.22+100.15

3 =100.235mm

Concrete Strength Calculation

Load applied = 517622.75 N + Cylinder Self Weight

Cylinder weight =3.750 kg x9.81m/s2 =36.7875 N

Load =517622.75 N+36.7875 N= 517659.5375

F21/36255/2010 41

4.3 DISCUSSION OF THE RESULTS

From the grain size experimental results, it was found out that there was 5.7 % gravel, 59.5 %

sand and 34.8% fine (silt + clay) in the soil which is ideal for rammed earth house

construction. This also matches the theoretical values. This was obtained by plotting a graph

of percentage passing versus diameter of sieves in mm

From the sedimentation analysis it was observed that the coarsest soil particles will settle first

and the finest last. It was evident that gravel since it has the is the coarsest particles settles

fast whereas clay settles last since it has the finest particles. It was also observed that the

speed at which the particles settle enables one to calculate the proportions of the various sizes

of particles.

The liquid limit experiment was also done the laboratory for the five samples collected at the

site. Each moisture content obtained was recorded after calculation. From theory it is known

that Liquid Limit (LL) is the moisture content that corresponds to N = 25 blows. In my case

the liquid limit was found to be 21.3%.For plastic limit it was found to be 16.36 and hence

the plasticity index can be obtained by subtracting the plastic limit from the liquid limit

which is 21.3-16.36 which give 4.94.This test was for natural rammed earth.

For stabilized rammed earth, in this cement is added to soil to increase its mechanical

strength, the results were different. For 2% the liquid limit was found to be 44.6 whereas

plastic limit was found to be 35.9.The Plasticity index 8.7.for 6% cement Liquid limit was

found to be 44.6, plastic limit was found to be 36.1, Plasticity index was 8.5.for 12% the

Liquid limit was found to be 44.6 while the plastic limit was found to be 34.6 hence the

Plasticity index was 10.2.

Degree of saturation for the soil was calculated and obtained to be 40%.traixial testing of the

soli was performed so as to obtain the shear stress of the soil and enable me to obtain the

compressive strength of the soil. The various parameters were determined and were tabulated.

After a laboratory experiment the compressive strength of mahogany wood was determined

to be 6,460 psi (pound per square inch)

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4.4 BILL OF QUANTITY

S/N ITEM DESCRIPTION UNIT COST (KSH)

1 Timber Mahogany timber 2 m *0.5 m 1500

2 Bolts and ties Steel bolts 40 cm

long for formwork

4 pieces 200

3 Wedges Mild steel wedges 4 pieces 350

4 Labour - - 1000

TOTAL 3050

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5.0 CONCLUSSION AND RECOMMENDATIONS

5.1 CONCLUSSION

The objective of the project was achieved successfully since a rammed earth construction

formwork was designed to be used in rammed earth house construction in Banana Hill area in

Kiambu County. The form work designed was portable, affordable and strong enough to

resist outward pressure during compaction.

Moreover the various properties of natural and stabilized rammed earth were determined and

known through laboratory experiments. The values got matched with the theoretical values.

Tests were carried out to figure the most suitable % of cement to be added to the silty clay to

produce good rammed earth. It was found that the most appropriate % of cement is in range

of 2%.

Plasticity index decreases with cement added to the clay soil. However, 2% of cement is

enough for reducing plasticity index. Plastic limit increases as cement is added to the clay,

but the value does not change with changing % of cement. Liquid limit was found to be

unaffected with quantity of cement.

Regarding compressive strength it is noted that as the amount of cement increase the strength

does not increase predominantly. It seems that 2% of cement by weight would produce good

strength rammed earth. In addition to that as time increases rammed earth gain more

strength.). After a laboratory experiment the compressive strength of mahogany wood was

found to be 6,460 psi (pound per square inch).

5.2 RECOMMENDATIONS

Construction of sample elements form rammed earth such as blocks or walls. Testing their

strength as whole unit, such as wall, columns or beams should be done also inspect their

insulation to temperature and acoustics be inspected.

I recommend in the future the constructors or architects to design and use the column

formwork in construction of rammed earth formwork since the column formwork bracing

performs two functions namely: to withstand results of forces acting on either the column

formwork or bracing. The forces may be wind and impact and also to maintain the accuracy

of the column form position and plump so that it is within tolerance.

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6.0 REFERENCES

1. Minke, G. (2000). Earth Construction Handbook: The Building Material Earth in

Modern Architecture. Southampton, Boston: WIT Press.

2. Walker, P. (2000). Review and experimental comparison of erosion tests for earth blocks,

in Proceedings 8th International conference on the study and conservation of earthen

architecture, pg 176-181.

3. Vasilios Maniatidis & Peter Walker (2003). A Review of Rammed Earth Construction for

DTi Partners Innovation Project.

4. David Martnez Escobar (2013).Building with rammed earth in a cold climate master

programme design for sustainable development Chalmers university of technology

Gothenburg, sweden masters thesis

5. Cenk Yoldas (2000). A prototypical (school) design strategy for soil-cement construction

in Afghanistan.

6. Gabriela-Teodora Ciurileanu &Ildiko Bucur Horvath (2012).The use of cement stabilized

rammed earth forbuilding a vernacular modern house

7. Elizabeth, L. & Adams, C. (ed.) (2000). Alternative Construction: Contemporary Natural

BuildingMethods. New York: John Wiley & Sons.

8. Houben, H., & Guillaud, H. (1994). Earth Construction: A Comprehensive

Guide.Southampton Row, London: Intermediate Technology Publications.

9. Anderson D.W. (2000). Rammed earth construction. Retrieved May 21, 2009, from

Ashlandctc: http://webs.ashlandctc.org/jnapora/hum-faculty/syllabi/trad.html

10. Earth Materials Guidelines (1996). Retrieved 2009, from greenbuilder:

http://www.greenbuilder.com/sourcebook/EarthGuidelines.html#Rammed.

11. Nelson W. (1976). Compressed earth blocks. Retrieved 2009, from Network earth:

http://www.networkearth.org/naturalbuilding/ceb.html

12. Retrieved from http://theconstructor.org/geotechnical/unconfined-compressive-strength-

of-cohesive-soil/3134/)

13. retrieved from www.rocktestinglab.com/?q=triaxial_compression_test.html)

14. retrieved from http://www.aboutcivil.org/tension-test-tensile-strength-test.html

http://webs.ashlandctc.org/jnapora/hum-faculty/syllabi/trad.htmlhttp://www.greenbuilder.com/sourcebook/EarthGuidelines.html#Rammedhttp://www.networkearth.org/naturalbuilding/ceb.htmlhttp://theconstructor.org/geotechnical/unconfined-compressive-strength-of-cohesive-soil/3134/http://theconstructor.org/geotechnical/unconfined-compressive-strength-of-cohesive-soil/3134/http://www.rocktestinglab.com/?q=triaxial_compression_test.html

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7.0 APPENDICES

APPENDIX A: Drawings of modern formwork

Figure A.1: Drawings of modern formwork showing different parts.

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APPENDIX B: List of Tables

Table B1: Lower limit range for particle size distribution for natural rammed earth

Table B2: Upper limit range for particle size distribution for natural rammed earth

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Table B3: Grading proportion for cement stabilization

Table B 4: Lower limit range for particle size distribution for cement stabilization

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Table B5: Upper limit range for particle size distribution for cement stabilization

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APPENDIX C: Photos from the lab

Figure C 1: Atterberg limits determination in the laboratory photos taken by me on

11/3/2015 10:30 am

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Figure C 2: Soil sample taken from the site at 27/4/2015

Figure C 3: Apparatus for triaxial testing machine taken at 27/4/2015

Figure C 4: Preparing of soil specimen for testing. Photo taken at 27/4/2015

DECLARATIONDEDICATIONACKNOWLEDGEMENTLIST OF FIGURESABSTRACT1.0. INTRODUCTION1.1. Background1.2. Problem statement and justification1.3 Site analysis and inventory1.4 Overall objective1.4.1 Specific objectives1.5 Scope of work

2.0 LITERATURE REVIEW2.1 THEORITICAL FRAMEWORK3.0 METHODOLOGY4.0 RESULTS AND DISCUSSION4.1RESULTS AND CALCULATIONS4.1.1 Grain size distribution.4.1.2 A GRAPH SHOWING GRAIN SIZE ANALYSIS4.1.7 Triaxial testing results

4.3 DISCUSSION OF THE RESULTS4.4 BILL OF QUANTITY5.0 CONCLUSSION AND RECOMMENDATIONS5.1 CONCLUSSION5.2 RECOMMENDATIONS

6.0 REFERENCES7.0 APPENDICESAPPENDIX A: Drawings of modern formworkAPPENDIX B: List of TablesAPPENDIX C: Photos from the lab

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