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DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING

UNDERGRADUATE CIVIL PROJECT 2007

Final Year Project Report

Material Testing of

Flax-fibre Reinforced Rammed Earth

Authors:

Jing Siong (John) Cheah

Rohann da Silva

Supervisors:

Dr. Jason Ingham

Kepa Morgan

12 October 2007

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Abstract

This final year research project establishes the material properties of a flax reinforced

earthen wall panel (Uku). The testing conducted ranged from soil gradation analyses to

structural performance tests in compression, bending and shear. This project is a part of the

Uku project, a project to develop a sustainable, accessible and socially acceptable earthen

housing method for rural Maori communities.

In March 2007, a research plan was devised to test the Uku material and establish the95th percentile design strengths for the structural calculations of an Uku test house, to be built

in Rotorua by 2008, and in order to create an Uku design guide.

The tests have demonstrated that the Uku material meets the New Zealand earth

building material performance requirements as specified by NZS 4298:1998 Materials and

Workmanship for Earth Buildings. The test methods followed standard ASTM procedures for

testing soil-cement materials. The design stresses established by this FYP research were

4.6 MPa in compression, 0.18 MPa in flexure and 0.52 MPa in shear. The results had a high

coefficient of variation that has resulted in the adoption of conservative design strengths and

has also outlined the importance of proof testing during construction.

In order to compare the Uku test results with data generated from comparable earthen

research around the world, a soil gradation analysis was carried out and revealed a gravel,

sand, silt and clay fraction of 3.5, 81, 7.8 and 7.7% respectively.

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Acknowledgements

I would like to acknowledge Rohann, my FYP project partner. He has been a easy person to

work, collaborate and share the work with and it is because of this that a lot of research has

been completed this year.

I owe my thanks also to my FYP supervisors Dr. Jason Ingham and Kepa Morgan who have

provided a lot of their time and experience to the project and myself. Their guidance has been

critical to directing the area of research and ensuring that the results obtained are meaningful

and useful.

I would like to acknowledge Hugh Morris, an expert on current earthen research in the world.

He has assisted in the research this year by sharing his wealth of knowledge and experience on

the subject of earthen construction research. Furthermore he has provided many books,

conference proceedings and contacts of earthen researchers both nationally andinternationally.

The many technicians; Mark Byrami and Noel Perinpanayagam in the Civil Materials lab,

Tony Daligan and Hank Mooy in the Test Hall, Mark Liew and Jeff Melster in the

Geomechnics lab and Grant Clendon in the Metalworking lab have been generous with their

time and expertise during all the lab work and not only helped Rohann and I to complete the

testing but made it easier and enjoyable.

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List of Figures

Figure 1 - Closeup of the soil mix .............................................................................................. 4

Figure 2 - Photo of bobcat mixing the soil ................................................................................. 4

Figure 3 - Removing the formwork from the Uku panels .......................................................... 5

Figure 4 - Bag of flax fibres........................................................................................................ 8

Figure 5 - Photo of a cob wall section [22]............................................................................... 13

Figure 6 - Photo of adobe wall construction [26] ..................................................................... 14

Figure 7 - Photo of a rammed earth wall [29]........................................................................... 15

Figure 8 - CAD model of the Wales Institute of Sustainable Education [38] .......................... 19

Figure 9 - Wet sieving through the 600 micron sieve............................................................... 26Figure 10 - Mixing soil for the Hydrometer Test ..................................................................... 28

Figure 11 - Hydrometer Test Setup .......................................................................................... 28

Figure 12 - Bulk density test samples in a vacuum .................................................................. 29

Figure 13 - Sieve stack for the dry sieve analysis..................................................................... 30

Figure 14 - Photo of Jar Test 1 ................................................................................................. 31

Figure 15 - Graph of the Wet and Dry Sieve Analyses ............................................................ 32

Figure 16 - Box plot of Compression Tests.............................................................................. 35

Figure 17 - Photo of the July 31st Compression Samples........................................................ 36

Figure 18 - The compression test setup .................................................................................... 37

Figure 19 - Four point bending test setup ................................................................................. 41

Figure 20 - Failure of H7 in flexure.......................................................................................... 42

Figure 21 - Failure of V1 in flexure.......................................................................................... 42

Figure 22 - Overhead gantry transporting a diagonal shear test panel ..................................... 44

Figure 23 - Photo of the diagonal shear test setup.................................................................... 44

Figure 24 - Tested diagonal shear sample S2 ........................................................................... 45

Figure 25 - Tested diagonal shear sample S3 ........................................................................... 45

Figure 26 - Nine pull-out samples ............................................................................................ 46Figure 27 - Photo of flax fibres clumping together .................................................................. 48

Figure 28 - Failure stress vs development lengths of past research [18, 53]............................ 52

Figure 29 - Diagram of ASTM A944 test setup ....................................................................... 53

Figure 30 - Pull-out test setup................................................................................................... 54

Figure 31 - Pull-out sample BD-B after test ............................................................................ 56

Figure 32 - Photo of the three 3 day strength samples and the three 7 days strength samples. 57

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List of Tables

Table 2-1 Embodied Energy Values [46] ................................................................................. 20

Table 3-1 Results of the Sieve Analyses .................................................................................. 25

Table 3-2 Hydrometer Test Results .......................................................................................... 27

Table 3-3 Results of the Dry Sieve Analysis............................................................................ 30

Table 3-4 Results of the Jar Tests............................................................................................. 32

Table 3-5 Summary of Particle Sizes ....................................................................................... 32

Table 4-1 Summary of Structural Strengths ............................................................................. 34

Table 4-2 Age of Specimens when Tested ............................................................................... 35

Table 4-3 Summarised Results of July 3rd Compression Tests ............................................... 37

Table 4-4 Summarised Results of July 31st Compression Tests .............................................. 39

Table 4-5 Summary of 4-Point Bending Tests ......................................................................... 41

Table 4-6 Summarised Results of the Diagonal Shear Tests.................................................... 43

Table 5-1 Yield Strength of Reinforcing Bar Proof Testing .................................................... 47

Table 5-2 King and Walker's pull-out test results [18, 53]....................................................... 52

Table 5-3 Water Content of the Soil Mix During the Pull-out Test Construction.................... 54Table 5-4 Summarised Results of the Pull-out Tests................................................................ 55

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Table of Contents

1 Introduction........................................................................................................................ 1

1.1 FYP Background ...................................................................................................................3

1.2 Construction of two Uku wall panels ...................................................................................4

1.3 The Uku Research Project ....................................................................................................6

1.3.1 People involved with the Uku project in 2007 .............................................................................6

1.4 The Uku Mix ..........................................................................................................................7

2 Literature Review of Stabilised Rammed Earth ............................................................. 10

2.1 Introduction .........................................................................................................................10

2.2 Earthen Construction..........................................................................................................11

2.2.1 The Benefits of Earthen Construction ........................................................................................11

2.2.2 Development of Earthen Construction Methods ........................................................................ 12

2.3 Limitations of Earthen Structures .....................................................................................15

2.3.1 Seismic Response.......................................................................................................................15

2.3.2 Labour Requirements .................................................................................................................16

2.4 Societal Factors Prompting SRE Development.................................................................17

2.4.1 Resource Scarcity.......................................................................................................................17

2.4.2 Need for large-scale low-cost housing solutions........................................................................17

2.5 Important Developments.....................................................................................................18

2.5.1 New Technology........................................................................................................................18

2.5.2 Earth Building Standards ...........................................................................................................19

2.6 SRE Properties.....................................................................................................................19

2.6.1 High Thermal mass ....................................................................................................................20

2.6.2 Structural properties...................................................................................................................20

2.6.3 Long Service Life.......................................................................................................................20

2.6.4 Low embodied energy................................................................................................................20

2.6.5 Insulation....................................................................................................................................21

2.6.6 Non-toxic, Fire resistant and Pest / Insect resistant....................................................................21

2.6.7 Qualitative Properties................................................................................................................. 21

2.7 SRE Construction ................................................................................................................21

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2.8 The Implications of SRE Structures ..................................................................................22

2.8.1 Benefactors of SRE Structures................................................................................................... 22

2.8.2 Current Limitations of SRE Structures.......................................................................................23

2.8.3 Long Term Implications.............................................................................................................23

2.8.4 SRE Research.............................................................................................................................23

2.9 Conclusion............................................................................................................................24

3 Soil Gradation Analysis ................................................................................................... 25

3.1 Wet Sieve Analysis...............................................................................................................26

3.1.1 Hydrometer Test.........................................................................................................................27

3.1.2 Bulk Density Test.......................................................................................................................29

3.2 Dry Sieve Analysis ...............................................................................................................29

3.3 Jar Tests................................................................................................................................31

3.4 Discussion of the soil analyses.............................................................................................32

4 Material Tests................................................................................................................... 34

4.1 Compression cube tests .......................................................................................................35

4.2 Four Point Bending Tests....................................................................................................40

4.3 Diagonal Shear Tests ...........................................................................................................43

5 UKU Reinforcing Bar Pull-out Tests .............................................................................. 46

5.1 Results of the pull-out tests .................................................................................................55

5.2 Discussion of pull-out test results .......................................................................................55

5.3 Failed Cylinder Tests...........................................................................................................57

6 Health and Safety............................................................................................................. 58

7 Future Research............................................................................................................... 58

8 Conclusion........................................................................................................................ 60

9 References ........................................................................................................................ 61

Appendices................................................................................................................................ 64

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Introduction

New Zealand rural Maori communities face significant challenges developing Maori land in

order to adequately provide for their housing needs adequately. The New Zealand Housing

Research Centre (NZHRC) has identified obstacles [1] that are obstructing the provision of

quality and affordable housing developments on rural Maori land. Aid in the form of local

government housing funds, accommodation benefits and boosting state housing around New

Zealand have been limited in their success of providing an adequate standard of living for

rural Maori [1]. Uku, aHarekeke flax-reinforced soil-cement construction technology (Uku) is

a practical solution that is being researched at the University of Auckland to address this issue.

The NZ government has stated that it is important and desirable for individuals and families to

own a house because it provides residents with long term security, independence and control

resulting in a better ability to contribute to society [2]. An increase in the cost of home

ownership over the past 15 years has resulted in a disproportionately high percentage of rural

Maori families living in overcrowded, substandard dwellings [1, 2]. Though many Maori in

these rural communities have expressed a strong desire to own a house it is becoming an

increasingly difficult and frustrating task in terms of overcoming the practical, legal and

financial obstacles of developing on rural Maori land.

A large proportion of Maori land is remote and isolated from infrastructure networks and

amenities like road, power and sewage networks. Due to the undeveloped state of the land,

orthodox construction methods (like timber frame construction) that rely heavily on the

transport of manufactured materials and access to a skilled labour force are not well-suited and

cost effective housing solutions on rural Maori land [3]. Communication between professional

engineers and the Maori community is often another obstacle [3].

Maori land has a complex legal arrangement often with well over 1000 owners. This has made

land development on Maori land a slow and difficult task. In addition to this, some financial

lending institutions discriminate against developments on Maori land due to the inability to

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use inalienable Maori land as a mortgage bond [1]. Financing issues coupled with the

increasing cost of home ownership has effected Maori more than non-Maori because Maori,

on average, have a lower income [2].

Uku has many advantages over conventional construction methods used by rural Maori

presently; for example timber frame construction. The cost and availability of constructing

Uku wall panels in a rural setting is advantageous over conventional methods due to the high

utilisation of locally sourced materials, ability to employ a non-technical labour force and a

minimal need for professional services. Over 90% of the Uku panels is consists of soil.

Depending on the local soil type and gradation, onsite and/or local soils may be used in their

natural state. Other constituents include Harakeke flax fibres (a widely available species of

flax in New Zealand) and an 8% (of dry soil weight) addition of Portland cement. Admittedly

the roof structure is made of timber, steel reinforcing bars are spaced through the earthen walls

and a concrete foundation provides the base but the use of non-local manufactured materials

has been minimized where possible. The Uku panels can be built exclusively with hand tools

and hand powered compacting equipment if required. The Uku research has produced a design

guide that provides a step-by-step method of designing a structurally sound house that satisfies

the NZ earthen standardsNZS4299:1998 Earth Buildings Not Requiring Specific Design [4].

This construction method is unique as it has been developed alongside several Maori

communities in Northland (Taitokerau), the Bay of Plenty (Waiaraki) and on the East Coast

(Tairawhiti) in order to ensure that Uku meets the housing needs of the rural Maori

community adequately and that the rural Maori community is willing to accept and use the

construction method. Two Uku buildings have already been built and had a successful

implementation into the Maori community. Another Uku house is due to be built this year

(2007) in Roitoiti, Rotorua.

Uku differs from other rammed earth construction methods in several ways. The Uku wall

panels are unconventionally thin, featuring a 150 mm thick earthen wall panel as opposed to

280 mm thick as is currently specified in NZS4299:1998 Materials and Workmanship for

Earth Buildings [5]. Conceptually the introduction of flax fibres meshes the soil together and

provides tensile strength within the material. Laboratory testing of Uku material performance

is limited and it was the objective of this final year project to determine the 95% material

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design strengths in compression, flexure and shear. The Uku research project will conclude in

2008, after which the process of implementing and commercialising of Uku will begin with

interested rural Maori communities.

This report details the soil gradation tests of the soil sourced from Sandstone Developments

Ltd in Muriwai, the compression, flexural and shear tests on Uku test samples and the results

of the reinforcing bar pull-out tests.

The following sections of the introduction are included to describe the Uku project

background, objectives and relevant technical details. The contact details of key people in this

project have been included for future reference.

1.1 FYP BackgroundThis year a Final Year Project (FYP) was undertaken by Jing Siong Cheah and Rohann da

Silva under the supervision of Dr. Jason Ingham and Kepa Morgan.

The objectives of the FYP were to:-

Carry out soil analysis in terms of determining the soil gradation profile; Perform material testing in compression, flexure and shear; Conduct component level testing measuring the pull-out strength of reinforcing bars

embedded in the earth panels;

Create an Uku design guide; Use the material values established to refine the structural calculations and design for

the Uku test house located in Rotorua.

The work was split up such that Rohann and I supported each other in all sections but took

ownership of particular objectives. I took charge of the first three objectives and Rohann was

responsible for the final two objectives.

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1.2 Construction of two Uku wall panels

On March 7

th

, 2007 two 2400x1200x150 mm Uku wall panels were constructed at theUniversity of Auckland Test Hall. These walls were built by Brian Morgan, with Roger

Simmons present to provide his expertise and his bobcat in order to mix the soil. The

construction of the walls took just under a day to build; approximately 8 hours with four

labourers. Figure 1 and 2 shows the bobcat mixing the soil.

Figure 1 - Close-up of the soil mix

Figure 2 - Photo of bobcat mixing the soil

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The soil mix used is detailed in section 1.4, with the soil sourced from Sandstone

Developments Ltd which is a quarry located in Muriwai. This quarry is a common source of

soil for earth building around Auckland. The flax fibres were extracted from Harakeke flax

leaves and cut to a length of between 60 and 70 mm. The cutting of the flax fibres was a very

repetitive and time consuming task. Mixing the fibres into the soil with the bobcat achieved a

satisfactory level of soil homogeneity. However concentrations of poorly mixed flax fibres

were still present. The clumping of flax fibres in the teeth of the bobcat and in the mixed soil

were common problems. Two water content tests were conducted on the soil used and showed

a water content of 23%. The formwork (plywood) was removed after seven days, with the

shuttering system (red coloured metal) removed in the days following as shown in Figure 3

below. The walls were left to cure in the university Test Hall.

Figure 3 - Removing the formwork from the Uku panels

The wall panels were used to create all the Uku material test samples for the FYP project

which included compression cubes, beams to be broken in four-point bending and diagonal

shear samples.

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1.3 The Uku Research ProjectThe Uku project began in 2003. A research grant of $1,139,000 NZD was provided by the

Foundation of Research, Science and Technology (FRST). The project will conclude on the

31st

of January, 2008.

The Uku project has three objectives.

To:-

develop the technology for the earth-fibre composite material; optimise the technology for adoption by the end user; build full scale trials and commercialise the technology.

1.3.1 People involved with the Uku project in 2007

Throughout the duration of the project several key people have been involved.

University of Auckland Staff

Kepa B Morgan

[email protected]

Associate Dean Maori

Senior Lecturer

Hugh W Morris

[email protected]

Senior Lecturer

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Dr. Jason M Ingham

[email protected]

Deputy Head of Department (Research)

Associate Professor

Colin Nicholas

[email protected]

Designer in Residence

Uku FYP students in 2007

This year (2007) three fourth year civil engineering students have done a Final Year Project

(FYP) on the Uku project.

Jing Siong Cheah ([email protected]) has analysed the soil gradation anddetermined the compressive, flexural and shear design strengths of the Uku material.

Rohann da Silva ([email protected]) has used the design strengthsestablished and created an Uku design guide. He has also performed the structural

calculations for the Uku test house, due to be completed in 2008, on the foreshore of

Lake Rotoiti, Rotorua.

Laura Devcich ([email protected]) has conducted thermal testing on the Ukumaterial and performed a life cycle analysis of the construction process. She was also

involved with the thermal testing of the Uku test house in Rotorua.

The contact details of earthen contractors that are aware / involved with the Uku project arelisted in the appendices.

1.4 The Uku MixThe Uku mix (by weight) that has been used this year for all the Uku wall panels and the

reinforcing bar pull-out samples is

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91.25% (Moist) soil (w/c = ~25%)

0.075% Flax fibres

8% Portland cement

A typical mix batch was made up of one full tractor bucket of soil (~250 kg), mixed with half

a bag of Portland cement (20 kg), 200 g of flax fibres (cut to 60-70 mm) with water added

such that the soil passes the drop test as specified in NZS 4298:1998 Materials and

Workmanship for Earth Buildings [5]. A photo of the flax fibres used in construction is shown

below in Figure 4.

Figure 4 - Bag of flax fibres

Uku mixes Past and Present

The proportion of flax fibres used has varied as different researchers conducted their research.

From July to November, 1997 Gregor Haab completed research optimising the fibre

reinforced soil-cement mix. His research concluded that the optimal recipe was 9% cement

and 0.75% fibre content cut to 64 mm lengths [6]. It should be noted that the flax fibre content

used this year is 10% of the amount of fibre recommended in Haabs research.

Research in 2006 by Micheal Segetin at the University of Auckland used flax fibre contents of

0.6% and 0.8%. Segetins research recommended that a flax fibre content of 0.6% be adopted

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due to difficulties in preparing and mixing the flax fibres into the soil mix [7]. The fibres in

Segetins research were coated with paint and the actual fibre contents tested were 0.32% and

0.43% respectively.

The reason for adopting a flax fibre content of 0.075% in 2007 can be attributed to practical

aspects. It is a very tedious task to extract and prepare the flax fibres. Mixing the fibres into

the soil in a homogeneous manner is also difficult and adds tremendously to the physical

labour required.

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2 Literature Review of Stabilised Rammed Earth2.1 IntroductionStabilized Rammed Earth (SRE) construction is a recent development in a series of earthen

construction improvements dating back several millennia. Earthen construction methods were

among the first man-made solutions for housing. Rammed Earth (RE) structures have been

dated to at least 7000 BC in Pakistan [8]. Adobe construction was used by the citizens of

Jericho by 8000 BC and cob construction pre-dates adobe construction further still [9]. Many

historic earthen heritage structures remain standing today, like the east end of the Great Wall

of China which is made of rammed earth [10]. Though there are many large earthen landmark

structures demonstrating the merits of earthen architecture, the most influential impact of

earthen technology has been in housing and in particular, low-cost housing. Presently earth

structures house a third of the worlds population [11]. Though earthen construction remains

the most popular method of construction, the use of earthen structures has not been without

disadvantage.

Past experience has revealed that RE exhibits a brittle mode when subjected to earthquake

loads [12]. Earthquakes in developing countries result in the collapse of villages and towns

incurring thousands of human casualties each year. In 2003 more than twenty-six thousand

people died as a result of the earthquake in Bam, Iran [13]. The 2005 Pakistan earthquake

incurred in excess of eighty-two thousand casualties. 2.8 million people lost their homes [14].

The areas with earthen structures that are most vulnerable to natural disasters are poorer

developing nations that are limited in their ability to provide and ensure good earthen

construction practice.

New materials and understanding is being applied to earthen methods and has resulted in

recently developed earthen construction solutions that are gaining attention as viable building

alternatives like SRE construction. The application of additives and improved methods has not

only addressed historic seismic and moisture limitations of earth but has made SRE a

competitive and attractive building method. Standardized construction methods and laboratory

testing of SRE structures has provided a much needed element of reliability and predictability

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to the material. Features of SRE buildings include good air quality, minimized indoor

temperature fluctuations throughout the year and good acoustic properties [15]. Home owners

of SRE buildings report qualitative advantages like a solid feel to the house and a sense of

security. A growing number of individuals are seeking alternatives to conventional building

methods [16].

In recent decades there has been a change of public opinion in the way earthen building

solutions are perceived. Individuals, communities and national governments are beginning to

explore and accept the possibilities of implementing SRE solutions on a large scale. Large

research projects can be found in the UK assessing SRE as a housing solution [17]. Earth

building standards covering SRE construction have been developed in many countries

including the US, Germany, Australia and New Zealand. The use of SRE is greatest in

developing Asian and African nations but is growing in popularity around the world [18].

SRE has the potential to be a globally sustainable building alternative to modern construction

materials. The factors that make SRE technology a possible alternative include its low-cost,

locally sourced material, simple equipment requirements and the ability to use non-technical

labour while still being able to meet modern building standards and provide a high qualityattractive building with a service life estimated between 200 and 600 years [19]. As resources

become scarce and the global need for buildings (low-cost housing in particular) increase,

sustainable solutions like SRE will gain significant recognition as an alternative structural

material that has the potential to provide sustainable global housing solutions at a reasonable

cost.

2.2 Earthen Construction2.2.1 The Benefits of Earthen ConstructionIt is estimated that a third of the worlds population lives in earthen structures, with the

majority located in the developing world. For many millennia earthen structures have been the

most common building solution in the world and it is still true of earthen structures today. The

reasons why earthen construction has remained so widely used is due to the factors that are

listed below:-

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Material availability In nearly every human settlement there is an accessible sourceof earth material.

Low-cost Earth material is abundant and everywhere. It requires minimal materialmodification and is locally sourced.

Easy to work It can be built using simple hand powered tools. Simple and intuitive It can be built without design guides and technical training Strength It can provide adequate strength for domestic housing purposes. High thermal mass During hot days the earth keeps the building cool by absorbing a

high amount of energy and keeps the building warmer at night as it slowly releases the

heat gained.

Durable Earthen structures last a long time (with low maintenance requirements). Sustainable practice The use of earth to build structures over the past ten thousand

years has not resulted in a depletion of the earth resource.

2.2.2 Development of Earthen Construction MethodsEarthen construction has been used for thousands of years and has developed progressively

through several changes in earthen construction methodology, each with advantages and

limitations. Stabilized Rammed Earth (SRE) is a result of continued refinement of earthen

construction methods and possesses similarities with traditional methods. SRE is a

construction system based on RE but with cement additions and an improved material

performance. A brief overview of earthen construction technology begins with cob

construction.

Cob structures are made by mixing soil, water and straw into a dough-like mixture that is

shovelled or thrown into place. One layer is built at a time and is left to set. The next layer is

placed on the next suitable day. The surface of the cob is trimmed to shape and tapers up the

height of the building. The walls are typically around 450-600 mm thick [20, 21]. Cob

construction is illustrated in the Figure 5 below.

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Figure 5 - Photo of a cob wall section [22]

Cob construction is simple, low cost and does not require a technically skilled labour force. Byusing cob construction, unique shapes and curves can be achieved [23]. Some disadvantages

of cob include high weather dependence during construction, high variations in material

performance and long build durations.

Adobe construction developed from cob and is similar to a masonry construction system. The

building system created a more uniform earthen structure than cob. Although adobe

construction uses a wet soil mix like cob, it does not experience as much shrinkage as cob due

to most of the soil shrinkage occurring as the brick dries in its mould. The disadvantages of

adobe include a high labour and space requirement to form, transport and place the adobe

bricks. The planes of weakness created by the weaker mud mortar joints make the adobe

structure particularly susceptible to seismic loads.

Adobe construction consists of two stages. The first stage involves creating the sun dried

adobe bricks and the second is laying the adobe bricks in layers with intervening layers of mud

mortar in-between [24]. A typical adobe brick measures 250 mm x 360 mm x 100 mm. The

final adobe wall thickness depends on the environment and the size of the structure being

built [25]. A photo of typical adobe construction is illustrated in Figure 6 below.

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Figure 6 - Photo of adobe wall construction [26]

The development of rammed earth (RE) followed on from cob and adobe and featured a few

distinct differences. The RE method allowed significantly faster construction with less

dependence on the weather and the seasons, when compared to cob and adobe. Cob layers and

adobe bricks require adequate exposure to the sun to evaporate the moisture in the soil mix

and set the material. RE construction is built in monolithic sections which improves seismic

resistance by creating a material of uniform strength and by eliminating weak joints [27]. One

disadvantage of RE is a large labour requirement. Traditionally, soil compaction was done by

hand. Rammed earth continued to develop and many materials have been added to the soil

mixture with some success. In 1562, an RE construction system called Pis de terre was

developed and was first used in Lyon, France. It consequently became a name used

synonymously with rammed earth. The method allowed rammed earth walls to be built at a

thickness of 500 mm [28].

Soil compaction gives the RE material durability and structural strength. Many heritage

structures still standing today used rammed earth construction. Some examples are the east

end of the Great Wall of China and the Potala Palace in Lhasa, Tibet [10]. RE construction has

been identified all around the world and is likely to have been independently developed by

many different civilisations at different times. Dating methods have shown that RE

construction was used as early as 7000 BC in Pakistan [8]. A photo of a rammed earth wall is

shown in Figure 7 below.

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Figure 7 - Photo of a rammed earth wall [29]

A revival brought on by a growing demand for sustainable building methods has renewed

interest in stabilized rammed earth (SRE) construction. Building codes and guidelines advising

on SRE construction have been developed around the world in countries including the US,

Germany and Australia. The majority of countries standardizing SRE construction specify

walls thicknesses of approximately 300 mm. The New Zealand Earth Building standard

NZS 4299:1998 specifies a minimum thickness of 280 mm [30]. 300 mm SRE construction is

the current international standard.

2.3 Limitations of Earthen Structures

Earthen structures are not without weaknesses and in the past, before the knowledge and

ability to address these limitations had been developed, it was usually poorer countries with

scarce alternative building materials that continued to use earthen construction as their main

construction method instead of making the transition to modern building materials like steel,

concrete and timber. Two of the main limitations of earthen structures are the seismic response

and labour requirements.

2.3.1 Seismic Response

Past earthquakes have demonstrated that traditional earth structures perform poorly when

subjected to seismic loads. This is due to the low strength in flexure and tension in traditional

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earthen structures that induce a brittle mode of failure. The variability of the soil and the heavy

mass of earthen structures are also contributing factors. The implications can be illustrated by

the 2001 earthquakes in El Salvador. Eleven hundred people lost their lives and in excess of

one hundred and fifty thousand earthen buildings were severely damaged [31]. Earthquakes

occurring in South America, India, Pakistan and many parts of Africa still incur large death

tolls due to poor design and inadequate earthen construction methods.

The presence of straight weak mortar joints in adobe make it particularly vulnerable to seismic

loading [32]. While cob and rammed earth do not have these joints, the variability of the soil

combined with high material mass and brittle behaviour have restricted these methods of

construction to low structures with thick walls. RE heritage structures in Argentina with

600 mm to 1000 mm thick walls have stood through centuries of earthquakes while

surrounding structures have collapsed [15].

SRE structures are able to provide adequate seismic resistance. The addition of cement in SRE

increases the tensile and compressive material strengths of the SRE by binding the soil

together and earthen building standards provide design guidelines that ensure a seismically

resistant structural system by specifying required connection details and minimumreinforcement requirements. The adoption of modern design requirements for seismic

response and a standardised SRE construction methodology has resulted in the construction of

structurally efficient and safe SRE structures.

2.3.2 Labour RequirementsEarthen construction methods often require a large amount of labour to prepare, mix,

transport, lift and place the soil mixture. It is particularly the high labour requirements that hasmade earthen construction undesirable to use in developed nations, especially compared to

other building methods. Labour costs in traditional (hand compacted) RE construction are

estimated at 60% of the total project costs [33].

SRE construction methods use machinery and tools which greatly reduce the labour

requirements of construction and increase construction speed however there is an increase the

overall cost. It is common to use a bobcat to mix and lift the soil, and pneumatic rammers to

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compact the soil mixture. With modern machinery and tools, a SRE structure can be built with

two people preparing the soil and two people compacting the soil [16].

2.4 Societal Factors Prompting SRE DevelopmentIn recent decades interest in sustainable building methods has resulted in a revival of SRE

technology, after a period of declining use in favour of materials like concrete and steel. The

societal factors prompting SRE technology include resource scarcity and the need for large-

scale low-cost housing brought on by the current global housing shortage [34].

2.4.1 Resource Scarcity Nearly every modern construction material requires significant raw material inputs,

manufacturing and transportation. The increasing demand for construction materials can be

seen in rising steel prices, large scale deforestation and the industries in Auckland transporting

aggregate in from the Waikato due to a depletion of local aggregate sources in the Auckland

region [35]. The energy required in manufacturing materials like steel, concrete and timber is

high. There is also a heavy reliance on oil to transport the materials large distances from the

raw material source, through the manufacturing and distribution processes, and finally to the

building site. With peak oil production predicted to occur as early as 2013, the costs of many

materials can be reasonably expected to increase soon [36].

SRE uses a large proportion of locally sourced materials that require minimal processing. Soil

is a cheap, abundant and easy to work material with adequate structural properties. SRE relies

on the transportation of soil from a quarry, manufacture of rebar, and includes a (5-10%)

proportion of cement, but will comparatively suffer less from future resource and energy

issues due to low proportions of high energy materials.

2.4.2 Need for large-scale low-cost housing solutionsThere is a global housing shortage occurring around the world. The ability to make or afford a

house that provides basic human needs is not available to many millions of individuals today.

This is especially true in poor and developing nations [34]. The problems include the cost of

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housing, the availability of materials, machinery and space, the skill level of the available

work force, environmental factors and resources, the rate of population growth and

urbanization, and conflict. A housing solution that addresses these limitations and is capable

of being implemented on a large scale is needed.

SRE construction addresses many of the above criteria. The use of SRE construction does not

require a technically trained labour force. Machinery can be replaced by manual labour (e.g.

hand tamping the soil) and most material inputs can be acquired locally and cheaply. The

provision of a design guide would provide an accessible, low-cost housing solution that is

simple, safe and sustainable enough to house billions of people around the world.

2.5 Important DevelopmentsThere are several important developments that have occurred within SRE construction that

have popularized SRE structures and made SRE construction a competitive building solution

on a global scale.

2.5.1 New TechnologySRE construction has benefited from the invention of various materials, machinery and

equipment. The use of mechanical rammers and tractors has greatly reduced the labour

requirement to mix, lift and compact the earth. Portland Cement was invented in 1824 and is a

key ingredient in SRE construction [37]. SRE contains between 5 -10% cement. Compressive

strengths up to 15 MPa have been achieved. The addition of cement also improves the

materials durability against moisture ingress, erosion by rain and frost attack. New formwork

solutions were an important development and have resulted in better SRE wall finishes,

improved construction speed, reduced labour requirements and allowed the construction of

wall sections that are curved and higher than was previously achievable using traditional

rammed earth formwork systems [16]. The Wales Institute of Sustainable Education campus

(due to be completed at the end of 2007) features a circular 7.2 metre high SRE lecture theatre

that seats 200 people [38]. A CAD model is shown in Figure 8.

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Figure 8 - CAD model of the Wales Institute of Sustainable Education [38]

2.5.2 Earth Building Standards

In recent decades many governments have published earth building standards including the

US, Australia, Germany, Spain and New Zealand. In New Zealand three earth building

standards were published on November 14th

, 1998. They are listed below.

NZS 4297:1998 Engineering Design of Earth Buildings [39] NZS 4298:1998 Materials and Workmanship for Earth Buildings [40] NZS 4299:1998 Earth Buildings Not Requiring Specific Design [30]

These standards specify comprehensive requirements and guidelines during design and

construction of an earthen structure. The availability of earth building standards provides

greater public accessibility to SRE technology gives the building method credibility and

promotes public acceptance.

2.6 SRE Properties

SRE is a structural and sustainable alternative building material with unique desirable

attributes that can be exploited with good design. The material aspects of SRE are presented

below.

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2.6.1 High Thermal massRammed earth has a high thermal mass between 0.65 - 0.85 kJ/kg [41]. Water has a thermal

mass of 1.9kJ/kg and most other building materials are between 0.4 and 0.6 kJ/kg [42]. This property allows the material to absorb heat during the day and slowly release it during the

night. This has the effect of averaging the outdoor temperature fluctuations. With good passive

solar design the need for heating and cooling throughout the year will be greatly reduced. SRE

features a dry density between 1750 kg/m3

to 2100 kg/m3

[43, 44].

2.6.2 Structural propertiesSRE has been proven to reach compressive strengths of 15 MPa and is adequate for use in

multi-storey construction. One example is a five storey SRE hotel in Queensland, Australia

[18, 28].

2.6.3 Long Service LifeRE and SRE structures last a long time. RE structures in Fujian, China are over one thousand

years old and are still in use [45]. A SRE structure is estimated to last two to six centuries if it

is well designed and maintained [19].

2.6.4 Low embodied energySRE has a low embodied energy due to low transportation and manufacturing requirements.

Embodied energy is a value indicating how much energy is needed to create the material. The

embodied energy of SRE is significantly lower than other modern building materials as shown

in the Table 2-1 below.

Table 2-1 Embodied Energy Values [46]

Material MJ/kg

Stabilised rammed earth 0.7

Insitu concrete 1.9

Kiln dried sawn softwood 3.4

Galvanised Steel 38

Aluminium 170

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2.6.5 InsulationRammed earth insulation levels vary with wall thickness. The thermal resistivity of rammed

earth is relatively low and thicker walls are required to compensate. An SRE wall thickness of300 mm has been deemed by NZ [30], Australia [46] and the US [47], among many other

countries, to provide an acceptable level of thermal insulation.

2.6.6 Non-toxic, Fire resistant and Pest / Insect resistantSRE does not have or emit any toxic gasses during its construction or its service life. As a

result SRE homeowners enjoy a good indoor air quality. The material is inert, highly fire

resistant and does not attract or support pests and insects [19, 28].

2.6.7 Qualitative PropertiesSRE structures have qualitative advantages. David Easton, an expert in rammed earth

technology, describes a feeling of permanence in a rammed earth house [16]. Homeowners

have expressed a solidness and sense of security in an earthen house. The density of the walls

also creates a good acoustic resonance and sound proofing between rooms [15].

2.7 SRE ConstructionThe construction advantages of SRE are in the low prerequisites and ease of construction.

Local materials can be used and labour can be trained on-site. The construction process is

listed below:

1.

Set up the formwork

2. Mix the soil to the appropriate proportions. Before compaction the soil mix should beat the optimum water content and within the following gradation limits:-

15-30 % clay 20-55 % silt 45-80 % sand 5-10 % cement [8, 40]

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3. Place soil into formwork in 100-150 mm layers [28].

4. Compact the soil using an appropriate mechanical rammer and/or a hand rammer.Adequate compaction is reached when the formwork rings.

5. Repeat steps 3 and 4 until the desired wall height has been reached.

6. Remove the formwork. This can occur as soon as compaction has been completed.

2.8 The Implications of SRE Structures2.8.1 Benefactors of SRE StructuresMost SRE is built in the developing world, especially in Asia and Africa, but it is gaining

popularity in many developed nations, notably countries including the US and Australia [18].

SRE technology is common practice in parts of Australia [46] and in the last few decades

hundreds of high-class SRE structures have been constructed around the world [8].

Many areas of the developing world do not benefit from SRE structures because the

technology is not available in a usable form, locals resist adoption of the unfamiliar building

methods and/or because the tools, formwork and cement are not easily accessible.

In the developed world SRE structures remain predominantly a novel housing solution. One

reason is the costs that are attributable to availability and scale of construction. It costs more to

build an SRE structure than a conventional structure. In North America an SRE house costs 15

to 20% more than a timber house to build [48]. Public resistance against earth buildings and a

limited public recognition of SRE as a structural building solution also limits the spread of the

technology [49]. Currently, rammed earth makes up a small portion of the residential market

and there are few experts and contractors that are able to undertake such jobs.

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2.8.2 Current Limitations of SRE StructuresSRE is still gaining recognition as a sustainable building method. It is important to recognise

that SRE construction is an earthen construction method and that there are several otherearthen construction methods that share similar advantages. SRE construction may not be the

best building solution in all regions. There are many adequate and well established building

materials used in construction and until the sustainability of the construction method becomes

a significant factor and/or oil prices go up, the advantage of using SRE technology over other

building materials will not be enough to bring about a large change in conventional building

methods.

2.8.3 Long Term ImplicationsIf SRE technology gains widespread acceptance and becomes a major construction method

there will be many long term implications. These include a reduction in CO2 emissions from

the building sector due to minimal manufacturing requirements and local material sources.

Poor and developing nations are likely to benefit from the quality and safety of low-cost SRE

housing. The natural material properties also provide thermally efficient buildings and

sustainable long-term housing solutions.

2.8.4 SRE ResearchAs a new technology, not much testing has been performed and there are many aspects of the

technology that are still not well explained and understood in a scientific sense. One area of

research looks at the effect of alternative binders. The SRE soil mix contains 5-10% cement

content which is usually Portland cement. Portland cement production produces a lot of CO2,

has a high embodied energy and is not readily available in many rural, poor and undeveloped

regions. Improving the seismic response of SRE is another important area of research. The

use of post-tensioned steel reinforcement [50] and fibre-earth composite technology [7] to

improve the ductility and tensile strengths are some examples of current research in SRE

technology.

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2.9 Conclusion

SRE construction is a sustainable building method that has the potential to be competitivelyand beneficially used in poor and rich nations alike. SRE has improved seismic resistance by

improving material strength and adhering to earthen design standards. It has also reduced

labour requirements, improved the materials durability and allowed for safe and efficient

structural design without sacrificing the elements of earthen construction that are foundational

to the continuing widespread use of earthen construction methods, like simplicity, availability

and ease of construction.

There are impending resource shortages and a current need for large-scale low-cost housing

solutions. SRE technology is capable of contributing to the global housing solution. SRE can

be made with low-cost, universally available, renewable materials and caters for people

needing low-cost housing, but is also competitive in the upmarket housing sector.

The application of new machinery and construction systems during SRE construction and the

support provided by recent earth building standards around the world has played an important

role in improving the viability and recognition of SRE as a viable alternative building

material. The future implications of this technology are vast and will be determined by how

the world responds to future material and energy challenges. Research is ongoing and

continually improves and validates SRE technology as a good alternative building material.

The merits of SRE construction position it well to make a significant positive impact on the

lives of untold numbers of people around the world in the future.

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3 Soil Gradation AnalysisThe soil used for the construction of the Uku wall panels in March was sourced from the

Sandstone Developments quarry in Muriwai. The soil gradation and in particular the

proportion of clay, which is a critical component in earth building, was not accurately

established. It was decided that testing of the Muriwai soil was needed in order to establish the

soil gradation profile, so that the results obtained this year can be correlated to past research,

both domestic and international, and to provide a benchmark for future material testing using

different soils located around New Zealand.

The summarised results of the sieve analyses is listed in Table 3-1 and will be referred to in

the sections following.

Table 3-1 Results of the Sieve Analyses

Wet Analysis Hydrometer Dry Analysis

Sieve size % passing % passing % passing

7.0 mm 100.00 100.0

4.75 mm 96.5 97.9

3.35 mm 91.5 92.2

2 mm 84.3 83.0

1.18 mm 78.7 74.6

600 m 68.7 53.0

425 m 58.0 37.6

300 m 46.6 22.4

212 m 35.2 11.4

150 m 26.2 5.6

90 m

63 m 13.8

47.5 m 13.7

34.9 m 12.2

25.2 m 11.2

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18.3 m 9.8

13.6 m 9.0

9.7 m8.5

7.0 m 8.0

5.0 m 7.7

3.5 m 7.5

2.7 m 7.3

1.5 m 7.3

1.3 m 7.0

1.0 m 7.0

3.1 Wet Sieve Analysis

In the absence of any previous soil testing, NZS4402:1986 specifies that a full wet sieve

analysis needs to be conducted. NZS4402:1986 Test 2.8.1 Standard method by wet sievingwas

carried out. The results are shown above in Table 3-2.

A photo of the soil being washed through a 600 m sieve is shown in Figure 9 below.

Figure 9 - Wet sieving through the 600 micron sieve

The proportion of fines (passing 75 m) was 15.5%. NZS4402:1986 specifies that for soils

with a fines content of greater than 10% a hydrometer test is required.

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3.1.1 Hydrometer TestA hydrometer test following NZS4402 Part1:1980 2.9.4 Test 9 (D) Subsidiary Method for

Fine Soils (Hydrometer method) was conducted to determine the fines part of the wet sievegradation curve. The results are presented in Table 3-2 below.

Table 3-2 Hydrometer Test Results

Sieve size % passing

of fines

47.5 m 99.6

34.9 m 88.3

25.2 m 81.4

18.3 m 71.4

13.6 m 65.4

9.7 m 61.9

7.0 m 58.0

5.0 m 55.9

3.5 m 54.1

2.7 m 53.3

1.5 m 52.8

1.3 m 50.7

1.0 m 50.7

The last reading was taken at 1 m 50 hours after the first reading and the experiment stopped

at that point. From the 31st

hour (1.3 m) to the 50th

hour (1.0 m) the change in the

hydrometer level was unnoticeable.

Figure 10 and 11 below, is a photo of the mixer used to prepare the soil for the Hydrometer

test and the test setup.

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Figure 10 - Mixing soil for the Hydrometer Test

Figure 11 - Hydrometer Test Setup

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3.1.2 Bulk Density Test

In order to complete the hydrometer test a value for the bulk density of the fines material in

the soil was needed. A bulk density test as defined by NZS 4402:1986 Test 2.7.2

Determination of the Solid Density of Soil Particles was conducted on the fines extracted from

the Muriwai soil and was completed on the 25th July, 2007. Two bulk density samples were

tested, giving a bulk density value at 23oC of 2724.7 kg/m

3and 2730.4 kg/m

3respectively.

The bulk density value adopted for the fines extracted from the Muriwai soil was 2728 kg/m3.

Figure 12 shows the soil suspension being placed in a vacuum chamber.

Figure 12 - Bulk density test samples in a vacuum

The bulk density test was a tedious experiment to carry out and allowed small margins of

error. If the two bulk density values differed by 20 kg/m3

the test would have to be repeated.

Thankfully both results obtained differed by only 5.7 kg/m3.

3.2 Dry Sieve AnalysisA dry sieve analysis was conducted to compare with the wet sieve analysis to determine if the

results were consistent and also if the gradation of the soil could be accurately determined

using a dry sieve analysis rather than a wet sieve analysis in future tests. The stack of sieves

used is shown in Figure 13 below.

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Figure 13 - Sieve stack for the dry sieve analysis

The dry sieve analysis was considerably quicker and simpler to conduct as it was able to be

automated by placing the soil on the top sieve in a stack of sieves and placing it in the shaker

cupboard for 5 minutes. In the dry analysis conducted the sieving was done in two parts

because the shaking cupboard was not big enough to accommodate all the sieves at the same

time. The results are summarised in Table 3-3.

Table 3-3 Results of the Dry Sieve Analysis

Sieve size % passing

7.0 mm 100.00

4.75 mm 97.85

3.35 mm 92.20

2 mm 82.99

1.18 mm 74.62

600 m 52.96

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425 m 37.57

300 m 22.35

212 m11.43

150 m 5.59

3.3 Jar Tests

A common soil composition field test that is currently employed by some earth builders is the

jar test. The purpose of this test is to give a rough indication of the fractions of gravel, sand,

silt and clays present in the soil. Photo of all the first jar tests is shown in Figure 14 below.

Figure 14 - Photo of Jar Test 1

The tests is conducted by filling a jar (approximately 1 L) a third full with soil. The jar is filled

with water and the jar is shaken thoroughly and left to settle until the water is clear again. The

soil will settle in layer, and though the division are not distinctive, the layers are clear and can

be correlated with particular soil components. The height of each layer is measured against the

whole layer of soil and converted to a percentage.

Three jar tests were performed and their results are presented in Table 3-4 below

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Table 3-4 Results of the Jar Tests

Jar Test 1 Jar Test 2 Jar Test 3 Average

Coarse 61% 70% 67% 66%

Silt 14% 10% 8% 11%

Clay 25% 20% 26% 24%

3.4 Discussion of the soil analyses

A summary of the sieve analyses is included in Figure 15 and Table 3-5 below.

Figure 15 - Graph of the Wet and Dry Sieve Analyses

Table 3-5 Summary of Particle Sizes

Wet Analysis Dry Analysis Jar Tests

Gravel 3.5% 2.1%

Sand 81% > 92% 66%

Silt 7.8% - 11%

Clay 7.7% - 24%

Wet Sieve

Dr Sieve

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Inadequacy of the Dry Sieve Analysis

The soil tests also reveal that the dry sieve analysis is not suitable for grading the type of soil

that is being tested. This is due to the inability to accurately sort and measure the smaller silt

and clay particles. From the results shown in Table 3-1 and Table 3-6 it is clear that the wet

sieve analysis measured a significantly higher fines contents (passing 75 m). Though the

smallest sieve used in the dry analysis was a 150 m sieve, already 94.1% of the soil had been

retained. The higher fines content measured during the wet sieve analysis is not

surprising because of several reasons. Firstly there was considerably more handling involved

in the wet sieving process. The soil was worked gently through each sieve individually with a

glass rod and a strong stream of water. It is possible that some of the soil particles would have

been broken into smaller particles during this process. In the dry analysis, the mechanical

shaking was not sufficient to dislodge the finer and/or cohesive particles attached to larger

grains. The presence of water would have been an important aid during the wet sieving

process to help dislodge fine and/or cohesive particles that were attached to larger soil

particles.

Jar Test and the Wet Sieve Analysis

The results obtained from the jar test are considerably different from the wet sieve analysisresults, especially with respect to the clay content (24% and 7.7% respectively). Some of the

difference can be explained by the determination of an arbitrary height for each distinctive

layer in the jar test however this does not adequately explain the 17% difference in clay

content indicated between the jar tests and the wet sieve analysis. A more likely explanation is

that the particle sizes, where the jar tests shows a clear transition to another particle size, does

not occur exactly at 4.75 mm (for sand) and 75 m (for silts) and 5 m (for clays) as specified

by ASTM D422 sieve designations. As a result the jar test it is not technically correct to label

separate layers as clay, silt and sand however the tests usefulness to earthen construction

should not be discounted as it provides a practical, albeit crude and technically incorrect, field

test of the soil.

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4 Material TestsOne of the primary objectives of the FYP project this year was to determine the 95

thpercentile

design strengths of the Uku material in compression, flexure and shear. Using the Uku wall

panels constructed in the March, testing methods and samples for all three material tests were

planned and executed. The details of each test are detailed in their respective sections. The

results are summarised in Table 4-1 below.

Table 4-1 Summary of Structural Strengths

Method of

Test

Number of

Samples Tested

Average Strength

(MPa)

95% Design Strength

(MPa)

Coeff. of

Variance

Compression 33 7.6 4.6 23.7%Flexural 8 0.35 0.18 28.9%

Shear 3 0.73 0.52 17.0%

Compliance with NZ Earth Building Standards

The NZ Earth building standard NZS 4298:1998 Materials and Workmanship for Earth

Buildings specifies that rammed earth material used for construction needs to exceed 1.3 MPa

in compression and 0.25 MPa in flexure. As shown in Table 4-1, the measured compressive

strength of the Uku material easily meets the criteria, with an average compressive strength of

7.6 MPa. The material also passes in flexure with all seven horizontal beams failing at a

flexural strength greater than 0.25 MPa. The reason why the design strength was below 0.25

MPa was due to the spread of the results and the low number of flexural tests conducted.

Age of Specimens

The curing time before testing for the compressive, flexural and shear tests were not defined

by standard periods but rather by practical considerations like when there was space in the lab

and during holidays when there was time to conduct experiments. For the purposes of this

research project the strengths of the material was assumed to have reached a constant value.

For the purposes of future research in this area the age of specimens for each test are listed in

Table 4-2 below.

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Table 4-2 Age of Specimens when Tested

Event Age of Specimens (d)

Construction of wall panels 0

Compression tests July 3rd 117

4-point bending tests 132

Compression tests July 31st

145

Diagonal Shear tests 161/162

4.1 Compression cube testsThis year 33 Uku test cubes, 125 mm in each dimension, were tested using the standardconcrete test machine located at the University of Auckland Civil Materials Laboratory. Box

plots of the compression tests are shown in Figure 16.

Figure 16 - Box plot of Compression Tests

The compression tests were conducted in two sets with 12 being tested on the 3rd of July and

21 being tested on the 31st of July. The first 12 cubes were cut out of the Uku wall panels and

were tested in all three axes to give an indication of the materials compressive strength and

6.0

6.1

5.9

7.4

7.4

7.3

8.8

8.2

8.7

4 5 6 7 8 9 10 11 12

Compressive Strength (MPa)

July 3rd

Tests

July 31st

Tests

Average

Lower Quartile Upper QuartileMedian

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the anisotropy of the material. The 21 cubes in the second set were made from the failed beam

specimens and they are shown in Figure 17.

Figure 17 - Photo of the July 31st Compression Samples

The compression tests were guided by ASTM D1633-00 Standard Test Methods for

Compressive Strength of Moulded Soil-Cement Cylinders. The reason that cubes were tested,

rather than cylinders, was because the coring machining uses a wet cut. It was decided that wet

cutting the Uku material would affect its performance and needed to be avoided. As a result, a

diamond tipped circular saw blade was purchased and this allowed the Uku wall panels to be

dry cut into cubes. A photo of the test setup is shown in Figure 18 below.

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Figure 18 - The compression test setup

July 3rd

Compression Tests

The first set of compression cubes was separated into three groups, one set for each axes. The

specimens were allocated to each group depending on the samples best test faces. The

summarised results of the tests are included in Table 4-3. Full test data is included in the

Appendix.

Table 4-3 Summarised Results of July 3rd Compression Tests

Specimen Orientation of Test Stress (MPa)

C1 Vertical Compression 5.7




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Vertical Average 7.1

C3 Width Compression 7.3



Width Average 8.0

C6 Depth Compression 6.8



Depth Average 7.5

TOTAL Average 7.4

The results of the July 3rd

compression test indicated that vertical compression was more

variable and possibly weaker than loading in the other two directions, although more

compression tests will need to be conducted in order to make a credible statement. The

compression results are similar in all directions and this may indicate that the material is

isotropic even though the earth mix was rammed in layers. The overall coefficient of variance

for the twelve tests is 22.7%

July 31st

Compression Tests

Twenty one 125 mm compression cubes was made out of the failed 4-point bending test

samples. These compression samples were considerably easier to cut because the beams had a

cross section of 125 mm x125 mm. All 21 samples were tested in the vertical axis. The results

are collated in the below Table 4-4.

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Table 4-4 Summarised Results of July 31st Compression Tests

Specimen Stress (MPa)

H1A 8.2

H1B 9.1

H1C 8.8

H2A 6.1

H2B 6.7

H2C 8.5

H3A 5.2

H3B 5.2

H3C 6.5

H4A 7.3

H4B 5.5

H5A 7.5

H5B 7.3

H5C 10.5

H6A 6.0

H6B 5.3

H6C 7.7

H7A 11.2

H7B 9.9

H7C 11.2

V1A 7.5

Average 7.7

The results of the July 31st

compression tests produced a similar result to the July 3rd

compression tests in terms of average compressive strength (+0.261 MPa) and coefficient of

variance (+1.7%).

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Table 4-5 Summary of 4-Point Bending Tests

Specimen

Modulus of Rupture

(MPa)

H1 0.40

H2 0.29

H3 0.28

H4 0.31

H5 0.36

H6 0.27

H7 0.55

Horizontal Average 0.35

V1 0.14

KEY: H Horizontal Specimen, V Vertical Specimen

The horizontal flexural tests all met the flexural stress as specified in NZS 4298:1998

Materials and Workmanship for Earth Buildings of 0.25 MPa. The vertical flexural strength

was low, as predicted. However this was not deemed to be a problem due to the presence of

steel reinforcing that will span the height of the Uku walls. A photo of the four point bending

tests is shown in Figure 19.

Figure 19 - Four point bending test setup

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The effect of the flax fibres

The addition of flax fibres was clearly illustrated between the failure of the horizontal and

vertical flexural tests. In the vertical sample the crack that formed upon failure was large and

retained no strength. In the horizontal samples the crack that formed upon failure was of the

order of a couple of millimetres and continued to provide a residual, albeit low, flexural

strength as the flax fibres were pulled out of the soil matrix. Figures 20 and 21 show flexural

horiztonal (H7) and vertical (V1) samples after they have failed. The crack formed in the

vertical sample was significantly larger.

Figure 20 - Failure of H7 in flexure

Figure 21 - Failure of V1 in flexure

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4.3 Diagonal Shear TestsShear testing was conducted on the Uku material using three 1200x1200x150 mm samples

that were cut out of the Uku wall panel. The testing method followedASTM E519-02 Standard

Test Method for Diagonal Tension in Masonry Assemblages. The results are summarised

below in Table 4-6. Full test data is included in the Appendix.

Table 4-6 Summarised Results of the Diagonal Shear Tests

Specimen Shear Stress (kPa)

S1 716

S2 860

S3 612

Average 729

Preparation of the tests

The test setup required two steel shoes to be manufactured as specified in ASTM E519-02

Standard Test Method for Diagonal Tension in Masonry Assemblages. The metal shoes were

placed on each diagonal of the earthen sample and used to load the sample. The shoes were

manufactured by the metal workshop at the University of Auckland. Each shear sample

weighed approximately 750 kg and was moved around with the assistance of the overhead

gantry. Care needed to be taken with the overhead gantry to avoid damaging the samples while

they were being transported, due to the heavy loads involved. A photo of the gantry lifting one

of the shear samples is shown below in Figure 22.

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Figure 22 - Overhead gantry transporting a diagonal shear test panel

The test setup was assembled on the strong floor in the Test Hall. The samples were

instrumented with a displacement gauge measuring the vertical displacement against the

applied load as shown in Figure 23.

Figure 23 - Photo of the diagonal shear test setup

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Method of Failure

All three shear samples failed in a brittle manner. Signs of cracking could not be identified

before the brittle failure occurred. The samples all split down the vertical diagonal as

expected. Due to the magnitude of the forces involved and the large self-weight of the

samples, the flax fibres did not provide any observable residual strength. The brittle failure of

the samples emphasized the need to place reinforcing bars through the material. Figure 24 and

25 show sample S2 and S3 put together after failure. A clear line of failure can be seen along

the loaded diagonal.

Figure 24 - Tested diagonal shear sample S2

Figure 25 - Tested diagonal shear sample S3

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5 Uku Reinforcing Bar Pull-out Tests

Reinforcing bar pull-out tests were conducted to determine the bond pull-out strengths of

straight deformed reinforcing bar and 90o

bent deformed reinforcing bar in 150 mm thick Uku

flax-fibre reinforced rammed earth wall panels. The bond strength of two deformed

reinforcing bar geometries, straight and 90o

bend, were tested with varying development

lengths to determine the failure mechanism and the optimal reinforcing bar development

length needed to yield a Grade 300 12 mm reinforcing bar constructed insitu into an Uku wall

panel. The constructed pull-out specimens are shown in Figure 26 below.

Figure 26 - Nine pull-out samples

Justification for test and test specimens dimensions

Designs and plans were drawn up for a full scale house that will be built in Rotoiti in 2007

using Uku flax-fibre reinforced rammed earth wall panels. The (original) reinforcement

detailed for the Uku wall panels consists of 90

o

bent reinforcing bars with a vertical

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development length of 600 mm (150 mm horizontal leg) extending into the wall panel from

the top (anchored into a concrete ring beam) and bottom (anchored into the concrete nib

wall) [51].

Reinforcing bars used

Grade 500 12 mm deformed reinforcing bars were used in all tests. The reinforcing bars were

proof tested in tension according toASTM A370 Method for Testing Steel Reinforcing Bars.

Grade 300 reinforcing steel was the intended reinforcing bar grade used and the grade that was

ordered. However proof testing of the reinforcing bars that were ordered (through

PlaceMakers) showed clearly that the reinforcing bars were Grade 500. The proof testing was

conducted after the samples were built. The proof testing results are included in Table 5-1

below.

Table 5-1 Yield Strength of Reinforcing Bar Proof Testing

Member Yield Strength (MPa)

Reinforcing Bar 1 526.3



Pull-out samples built

On the 10th

of August, 2007, nine pull-out samples were constructed and are detailed below:-

3 @ (150ST-600) Straight reinforcing bars with a long (~600 mm) development lengthembedded in a 700x700x150 mm Uku panel;

3 @ (150BD-600) 90o bent reinforcing bars with a medium (~400 mm) developmentlength with a 150 mm horizontal leg embedded in a 700x700x150 mm Uku panel;

3 @ (150BD-350) 90o bent reinforcing bars with a short (~300 mm) developmentlength with a 150 mm horizontal leg embedded in a 700x700x150mm Uku panel.

Bolded length is the minimum value defined in NZS 4299:1998

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Soil Mix Preparation

The preparation of the soil mix earlier this year in March 2007 revealed a significant problem

arising in achieving a homogeneous soil mixture, particularly with respect to dispersing the

flax fibres throughout the mixture. The flax fibres had a tendency to clump together and did

not mix well. The teeth of the bobcat further exacerbated the problem as the fibres

accumulated in the machines joints. The final tested samples showed regions of dense flax

fibre congregation that acted as planes and regions of weakness as shown in Figure 27.

Figure 27 - Photo of flax fibres clumping together

Past research by Segetin [7] on mixing flax fibres has found that the flax fibres separate better

from each other when slightly dirtied by the Uku soil mixture. Several methods of mixing the

soil have been previously investigated, ranging from hand mixing, using rotary hoes, concrete

mixers and tumble mixers. Hand mixing and using the tumble mixer performed the best in

terms of achieving a homogeneous soil mix. Segetin identified a method of improving the

quality of mixing the flax fibres into the Uku soil mixture by pre-mixing the cement and dry

soil, then taking a small portion of the mix to create a slurry to which the flax fibres would be

added [7]. The slurry would then be gradually mixed with the remaining mass of pre-mixed

soil. The pull-out samples will emulate this soil mixing process during construction. A soil

source below optimal moisture content is needed to compensate for the addition of the water

slurry so that the soil overall will not be significantly above its optimal moisture content.

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This procedure was used during the pull-out test sample construction and was found to be not

so practical or beneficial on a larger scale. Segetin performed his mixing in a 10 L tumble

mixer whereas the pull-out construction was mixing 250 kg of soil per batch. The additional

time required to mix the soil was likely to have detrimentally affected the soil mix due to the

increased delay between adding the cement and placing the soil. The delay was due to the

need to perform the extra steps for soil preparation and to mix the soil.

The flax fibres were cut to a length of 60-70 mm. A fibre length around this range was shown

to provide the optimal balance between achieving a good tensile response without creating

significant problems in terms of separating the fibres and creating a homogeneous soil

mixture [7].

Construction Method

To ensure a good level compaction, each samples was compacted in five layers, between

100 mm to 150 mm thick, in line with standard rammed earth construction practice [28]. Each

layer was mechanically compacted equally over the length of the sample using a mechanical

rammer in the open spaces and using the hand rammer along the formwork walls and aroundthe reinforcing bars.

The samples were left in the formwork at room temperature for three days to ensure that the

samples did not dry too quickly and crack. After three days the formwork was removed and

the samples were left to cure for a further 25 days in the University of Auckland Test Hall.

The samples were tested at their 28 day strength.

Formwork

In order to facilitate the construction of high quality samples without delay the formwork was

built (rather than wait for the use of the formwork system used for the construction of the earth

panels in March 2007, that was located in Rotoiti, Rotorua awaiting the building consent for

the Uku test house). Roger Simmons, a professional earth builder, was contracted and offered

his own shuttering (formwork) system which was adapted to build the pull-out samples.

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A wall height of 1200 mm was chosen to allow the formwork to guide the mechanical and

hand rammers at the higher layers. Two separate sets of formwork were used with two rows in

each set. This was required due to the need to resist the high lateral pressures on the formwork

during compaction.

Reinforcing bar embedment lengths

In 2001, Walker and Dobson conducted pull-out tests on deformed and plain reinforcing bars

in cement-stabilized rammed earth. The deformed reinforcing bars were shown to have up to

twenty times higher bond pullout strengths than plain reinforcing bars [18]. The bond pullout

strengths of deformed reinforcing bars were dictated by the shear strength of the rammed earth

material and the friction created by the outer perimeter of the deformed reinforcing bar ribs.

Plain reinforcing bar bond pullout strengths were determined by the extent of adhesion to the

rammed earth and friction. The pull-out strength of plain bars is significantly lower than

deformed bars and will not be cons

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