2013
Department of Industrial and Systems Engineering
0303.799.01 – Independent Study
Pedro Cruz Diloné
[“Recommendations to redesign the
base for the arborloo”]
Contents
Abstract ....................................................................................................................................................................................... 4
Introduction ............................................................................................................................................................................... 4
The arborloo ......................................................................................................................................................................... 5
Objectives ............................................................................................................................................................................... 7
Methodology .............................................................................................................................................................................. 7
Materials inventory............................................................................................................................................................ 8
Structures............................................................................................................................................................................. 23
Results ........................................................................................................................... Error! Bookmark not defined.
Conclusions and Recommendations ................................................................. Error! Bookmark not defined.
References ................................................................................................................... Error! Bookmark not defined.
Literature reviewed ......................................................................................................................................................... 30
Appendix A - Sketches ............................................................................................ Error! Bookmark not defined.
Appendix B – Evaluation Table ........................................................................... Error! Bookmark not defined.
Pedro Cruz Diloné, 2013
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List of Figures
Figure 1. Diagram of the use and structure of a conventional arborloo ................................................. 5
Figure 2 Conventional design and dimensions of concrete slabs for arborloos. Left to right, squared,
rectangular and circular bases. .................................................................................................................. 6
Figure 3. Types of conventional rebar reinforced concrete slabs. .......................................................... 9
Figure 4. Schematic of lightweight concrete with composites; in this case, expanded clay pearls. ... 10
Figure 5. Detail of the porosity of cellular concrete................................................................................ 11
Figure 6. Ferrocement wall being cured. ................................................................................................. 11
Figure 7. Sisal fiber panels bonded with polyester resin (top left and right). Bottom image shows
corrugated panel supporting a 200lbs. person ....................................................................................... 13
Figure 8. Corrugated metal sheets used in roofing. ................................................................................ 14
Figure 9. Banana fiber on fixtures for the drying and separation process. .......................................... 15
Figure 10. Various flooring models made from polymers ..................................................................... 20
Figure 11. Variety of manhole covers made from Polymer Concrete. .................................................. 22
Figure 12 Coconut Shell Powder pellets. ................................................................................................. 22
Figure 13. An example of how structural honeycomb stiffens a structure without materially
increasing its weight. ................................................................................................................................ 24
Figure 14. Schematic of dimensions on a structural honeycomb sheet. ............................................... 24
Figure 15. Figure X. Schematics of the modular structures and interlocking designs found in toys.. 25
Pedro Cruz Diloné, 2013
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Abstract
Improving access to sanitation knowledge and technology is one of the most effective and
least expensive ways to prevent life-threatening illness and improve quality of life. Even
when a variety of existing methods are highly effective, they are not reaching the around
40% of the world population without a toilet. As a result millions are affected by
preventable diseases and die every year, especially in developing countries. Pit latrines are
a rather feasible improvement that has already yielded positive results. But the lack of
financial resources, the difficulties of changing long-held unhygienic behaviors, and the low
priority given by leaders are some of the factors that hinder the access and growth of
sanitation. This study uses a function-centered methodology to redesign the base of a pit
latrine with the purpose of achieving a more affordable and accessible sanitation system. A
myriad of materials and structures are explored and 5 concepts are proposed at the end of
the study. These proposals were designed at a conceptual level, but set a baseline for
further recommended studies that can accurately determine a solution.
Introduction
Annually, 1.5 million people die from waterborne illnesses caused by lack of sanitation,
poor water quality and lack of hygiene, most of them children under 5 years old (World
Health Organization/UNICEF, 2009). Improving access to sanitation knowledge and
technology is one of the most effective and least expensive ways to prevent life-threatening
illness and improve quality of life (Fewtrel et al, 2005; Esrey et al., 1991; Tilley et al., 2008).
Even when a variety of existing methods are highly effective, they are not reaching the
around 40% of the world population without a toilet (World Bank, 2008; WHO, 2013; Gates
Foundation, 2013). Most of the regions affected by the deficit in sanitation are developing
countries where around 2/3 of the population has no access to sanitation. In Haiti, for
example, access to Basic Sanitation declined from 45% to 24% between 1990 and 2010
(World Health Organization, 2010). The arborloo provides a solution for the sanitation
crisis dominating Haiti’s rural and urban communities. An arborloo is a simple and
Pedro Cruz Diloné, 2013
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inexpensive sanitation system that consists of a pit latrine that allows for composting
human waste into organic fertilizer. Although Ecological Sanitation –a term to referring to
the controlled recycling the nutrients in excreta for use in agriculture– has been practiced
for centuries, its acceptance on a number of development projects has been limited
(Langergraber et al., 2005). Although the arborloo has yielded positive results in numerous
cases (IRC, 2010; CRS, 2009; Tolessa, 2009), it has the limitation of having a relatively
heavy base, needs to be constructed on site, and requires semi-skilled masonry. The goal of
this research is to redesign the current concrete base of the conventional arborloo through
reengineering its material composition and structure.
The arborloo
The arborloo, invented by Peter Morgan in late 1990’s, is a type of a compost pit latrine
(Morgan, 1998). Compared to other models of compost latrines, like the Blair Latrines or
the Clivus Multrum, the function of the arborloo implies that the latrine itself is moved and
the pit contents remain in place to become the surface for planting a tree. While in use, the
pit is filled with human waste, dirt, leaves and other inputs that control flies and odor, and
provide the environment for decomposition. If the inputs are kept organic and the correct
temperature is achieved for several days then the compost mix will biochemically
transform into fertilizer (Heinonen-Tanski et al., 2005). When the arborloo pit is about 2/3
full, the structure is moved and a layer of soil is placed over the pit contents so a tree can be
planted. The same process can take place again in the new location as seen in Figure 1.
Figure 1. Diagram of the use and structure of a conventional arborloo
Pedro Cruz Diloné, 2013
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Source: http://upload.wikimedia.org/wikipedia/commons/thumb/a/a2/Arborloo-en.svg/500px-Arborlooen.svg.png
The arborloo is best suited to rural areas where there is appropriate soil for digging many
pits and absorbing the contents in the pit. This system is more appropriate for areas that
are not prone to heavy rains or flooding, which may cause the pits to overflow, or areas
where groundwater is not compromised by the contents of the pit leaching into the
reservoir.
The arborloo system consists of 3 functional parts: the structure for privacy, the concrete
slab for surface support, and a pit to intake excreta and organic inputs. In this report, the
concrete slab will be analyzed as an isolated system. As seen in Figure 2-4, the concrete
latrine base is structured with a central hole used to intake human excreta. This concrete
slab must be safe and strong enough to hold user weight, while being light enough to be
moved
by
hand.
Although
previous
practitioners
have
addressed
potential
recommendations on dimensions and lightweight materials (Morgan, 1998; Morgan, 2007;
Hebert, 2010), ergonomics, user perception, and that it may still be too heavy for some
users poses a weakness in the design of the base. Additionally, some of these
recommendations may not be readily available or affordable in developing nations,
specifically in Haiti.
Figure 2 Conventional design and dimensions of concrete slabs for arborloos. Left to right, squared, rectangular and
circular bases.
Source: http://aquamor.tripod.com/ArborLoo1.HTM
Pedro Cruz Diloné, 2013
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Objectives
Specific objectives of this study are:

Generate solutions that improve and expand rural sanitation options for consumers
living on less than $2/day in developing countries.

Conduct research on existing and novel material and shape alternatives for the base
of arborloos.

Propose multiple design options.

Analyze feasibility of options and compare design ideas.

Make technical recommendations.
Methodology
This study uses methods of function-centered review for the collection and interpretation
of available data concerning the design and construction of pit latrine bases. Initiatives
currently and previously developed were studied and assessed to orient the design
process. As an assumption, all proposed designs shall reference the dimensions presented
in Figure 2-5 as acceptable. A variety of materials and structures were explored to generate
alternatives for the conventional latrine concrete base; 16 design prototypes were sketched
and evaluated, and can be seen in Appendix A. Methodologies from reverse engineering
were utilized and methods for brainstorming were explored to segregate design
prototypes.
For the evaluation, 5 criteria were defined:

Light weight (1 or 2 people can pick it up)

Affordability (by the average rural Haitian)

Modularity (pieces that can be acquired separately for later assembly)

Easiness to build (local skills)

Easiness to move (1 or 2 people)
A summary table exhibited in Appendix B uses a rating scale of “+” when the concept
Pedro Cruz Diloné, 2013
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satisfies the criteria and “-” when it does not. It must also be noted that the choices for
material are mostly context specific and based on the local environment, culture and
resources. However, materials outside that description are also explored.
Materials inventory
Incorporating different local materials into the conventional concrete mix (like coconut
shell, plastic bottles, rebar, sisal, banana fiber) presents an opportunity to create a base
with reduced weight and material quantity which makes the arborloo more marketable,
less expensive, and more portable for those living in remote locations. The use of natural
fibers as reinforcement in cement composites has great potential to reduce weight and
cost. Other novel and complex materials were also included to keep the inventory broad.
Although wood is a well-known building material it will not be considered for this
application given the current deforestation crisis in Haiti (McClintock, n.d.) (Picariello,
1997). Using wood would create more demand for the material, which will be detrimental
to current reforestation programs, and importing wood would cause the cost to increase.
The following is a list of materials reviewed.

Rebar with concrete. The use of rebar steel rods embedded into concrete is the
most practiced method to reinforce concrete. Concrete can withstand compressive
strength, but not tensile strength; rebar is used to absorb the tensile, shear, and
sometimes the compressive stresses in a concrete structure achieving a more
resistant structure. (Encyclopedia Britannica, 2013) Figure 3 shows different
arrangements of rebar reinforced concrete applied to slabs.
Pedro Cruz Diloné, 2013
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Figure 3. Types of conventional rebar reinforced concrete slabs.
Source: (Jiravacharadet, 2012)

Lightweight composite concrete: it is a novel product that mixes concrete with
foam combined with either lightweight aggregates and/or admixtures (such as fly
ash, silica fume, clay, synthetic fiber reinforcement, and high range water reducers
(aka superplasticizers)). The compressive strength and overall physical properties
of an aggregate are correlated to the cement content and the fiber content used in
the mix. Results from GeckoStone® showed a compressive strength in cellular
concrete at 105pcf has achieved over 7,500 psi on their formula (GeckoStone®,
2013). A study from Kurugol et al., 2007 investigated the relationship between
various composite properties and the mixtures used to produce lightweight
concrete, and showed that the most effective fiber volume is at a 0.75% fraction.
Pedro Cruz Diloné, 2013
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Figure 4. Schematic of lightweight concrete with composites; in this case, expanded clay pearls.
Source: http://whatwow.org/lightweight-concrete/

Cellular concrete. This lightweight concrete can be achieved by distributing
microscopic air cells into a mixture of neat cement or cement & sand mixture.
LightConcrete, LLC reported the obtainment of cellular concrete with properties of
weight of 220 kilograms per cubic meter [l4 lbs. cubic foot] to 1,922 kilograms per
cubic meter [120 lbs. cubic foot] and compressive strengths that vary from 0.34
megapascals [50 psi] to 20.7 megapascals [3,000 psi]. A High Performance version
was also produced by working with the densities of the materials leading to a
substantial reduction in the dead weight of a structure. 0.028 cubic meters [one
cubic foot] of foam in a matrix replaces 28.30 kilograms [62.4 lbs.] of water, or 0.028
cubic meters [one solid cubic foot] of aggregate weighing 74.84 kilograms [165 lbs.
per cubic foot]. (LightConcrete LLC, 2003).
Pedro Cruz Diloné, 2013
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Figure 5. Detail of the porosity of cellular concrete.
Source: http://soa.utexas.edu/matlab/search/materials/details/t/product/id/3420

Ferro-cement. This building material is made from a structure of wire reinforced
with a mixture of sand, water, and cement producing a thinner and lighter material
than poured concrete. It has been widely used as a low cost alternative building
material. Davis, n.d. proposes an improved model that uses “chicken wire” wire
mesh as the wiring structure.
Figure 6. Ferrocement wall being cured.
Source: http://www.ruralize.com/Genes%20Projects/ferrocement/ferrocement%20garden%20bed.html
Pedro Cruz Diloné, 2013
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
Peter Morgan’s Conventional mix. Consists of 1 Portland cement: 4 river sand and
enough water to achieve a consistent thick mixture (No quantity specified, just
needs to be able to hold the form of a ball by hand). Gravel or stones that are
available can be added to the sand and cement to replace a proportion of the
cement. (Morgan, 1997)

Coconut shell as aggregate of cement. The use of coconut shell to obtain a lighter
concrete has been studied and referred as useful for most supporting tasks.
(Gunasekaran, K. et al, 2013a, b) have made comparative experiments that
determined, among other properties, an adequate load factor against failure for
reinforcement ratios up to 3.14%, low modulus of elasticity (3-Co, 2010) (Ali M.,
2012).

Sisal fiber with bioresins or polymers. Sisal fibers are stiff fibers extracted from
an agave plant with considerable strength and ability to stretch. The use of sisal
fibers along with bioresins or polymers was first conceived by lrv Stollman with the
intention of developing a low cost and light weight building material for houses.
Four tests were performed to study sisal panels: Tension (breaking stress 1,500psi
and Elasticity Moduli 1x106 psi), Compressive (compressive strength 100 psi), Shear
test (above avergae), and Bending test (held 480lbs or 75lbs/m2 without bending).
(Ledward, N. & Blowers, E., 2012) (Chambers, C. and Chaplin, R, 2010).
Pedro Cruz Diloné, 2013
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Figure 7. Sisal fiber panels bonded with polyester resin (top left and right). Bottom image shows corrugated panel
supporting a 200lbs. person
Source: http://www.flickr.com/photos/sisalhouse/

Sisal fiber as aggregate of cement. Due to the physical properties of natural fibers,
these can be added to cement in order to achieve tensile strength increase in
concrete. Although studies were found on the use of a variety of natural fibers (some
are detailed in this paper), no studies were found in the use of sisal fibers. Sisal is of
particular interest due to its availability in Haiti (Mongabay, 2013) and its potential
for use. (Ghavami et al., 1999) (Ali, 2012)

Corrugated metal panels. Corrugated metal sheets are widely used in the building
of structures like roofing, decking, siding and flooring. Corrugated metal panels are
available in a variety of materials such as copper, zinc, aluminum, and galvanized
iron, due to its fire resistance and weathering ability. The design of the corrugated
panel of the sheet provides greater stiffness and rigidity compared to flat sheets.
Thus, the strength of the panel depends on the design of the corrugation pattern and
the material used. (Wakeland, H, 1958).
Pedro Cruz Diloné, 2013
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Figure 8. Corrugated metal sheets used in roofing.
Source: http://www.rosselliroofingandsiding.com/metal-roofing-corrugated.htm

Banana fiber as aggregate of cement. Banana fiber can be used as a viable
resource to produce composites to reinforce cement. Banana fiber is obtained from
the pseudo-stem of banana plant. In a study by Mukhopadhyay, S. et al (2008),
pulped banana fiber, at a loading of between 8 and 16% by mass, resulted in
composites with flexural strengths in excess of 20 MPa. Addtionally, at a fibre
loading of 14% by mass, the flexural strength is 24·92 MPa and the fracture
toughness value is 1·74 kJm−2. (Savastano Jr, H., et al., 2005) (Zhu, W. H., et al.,
1994)
Pedro Cruz Diloné, 2013
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Figure 9. Banana fiber on fixtures for the drying and separation process.
Source: http://www.agrarianworld.com/wpcontent/uploads/2012/10/383335_526977953985519_874703641_n.jpg

Other vegetable fibers as aggregate of cement. Other non-conventional natural
fibers which presence is abundant can be considered as a material. Table 1 is extract
from another research where a number of studies on natural fibers were reviewed
and synthetized. Palm, sisal, jute, sugarcane bagasse, banana and fibers from other
plants
are
Pedro Cruz Diloné, 2013
analyzed
in
the
table.
(Ali,
2012)
Page 15
Table 1. Physical and mechanical properties of natural fibers.
Source: Ali, M., 2008. “Natural fibres as construction materials”
Pedro Cruz Diloné, 2013
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
Polymers. Polymers are used in numerous applications in our everyday life.
Processed from petroleum, polymers are relatively simple, quick and cheap to
manufacture in large quantities. Polymers with relatively high compressive
strength and flexural strength are the most promising for the purpose of this
research. Table 1 shows a list of polymers with their typical compressive strength
and moduli.
Figure 10. Various flooring models made from polymers
Sources: http://partywarehouse.co.nz/hire/images/marquee%20flooring.jpg; https://encryptedtbn2.gstatic.com/images?q=tbn:ANd9GcSULs9oL0L7_MFX013HNelpHQaSblcq0eg91f1qQlXaO_DWve6mnQ,
http://kids.woot.com/offers/brik-a-blok-30-piece-set
Table 2. Typical Compressive Yield Strength and Compressive Modulus of Polymers
Compressive Yield
Strength (MPa)
65
Compressive
Modulus (GPa)
2.5
120
8
85
2.2
100
7.5
95
55
130
70
20
3
2.3
5
2
0.7
80
1
Polyimide
150
2.5
Polyimide + Glass Fiber
220
12
40
70
1.5
2.5
Polymer Type
ABS
ABS + 30% Glass Fiber
Acetal Copolymer
Acetal Copolymer +
30% Glass Fiber
Acrylic
Nylon 6
Polyamide-Imide
Polycarbonate
Polyethylene, HDPE
Polyethylene
Terephthalate (PET)
Polypropylene
Polystyrene
Source: http://www.matweb.com/reference/compressivestrength.aspx

Polymer concrete. This material consists of a concrete mix where polymers are
used as supplements or as a substitute of cement. Polymer concrete is characterized
by its resistance against quick freezes, thaws, salts, chemicals, fertilizers, heavy
impact and abrasion, which makes them suitable for structures where heavy traffic
is present (driveways, sidewalks, others). The types include polymer-impregnated
concrete, polymer concrete, and polymer-Portland-cement concrete. Studies from A.
A. Alzaydi et al. (1990) show that, polymer concrete with a resin content of 8% and
cured at 110 °C for about 7 days, developed an ultimate compressive strength of 37
M Pa. For certain mixes, Polymer Concrete achieved the same or surpassed the
compressive strength of conventional Portland Concrete.
Pedro Cruz Diloné, 2013
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Figure 11. Variety of manhole covers made from Polymer Concrete.
Source : http://www.tvcinc.com/underground-equipment/polymer-concrete-amr-covers/

Coconut Shell Powder in polymers.
This patented material is commercially
available as Coconut Shell Powder by Natural Composites, Inc ©. Made from coconut
shell it works as functional filler for thermoplastics. Within its features are:
increases mechanical properties such as stiffness at a lower cost typical petroleumbased resin, eight savings compared to mineral fillers, and it also repurposes unused
coconut shell. (Natural Composites, Inc © 2012)
Figure 12 Coconut Shell Powder pellets.
Source: http://www.naturalcompositesinc.com/products.html
Pedro Cruz Diloné, 2013
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Structures
Base structures are in the scope of this analysis because it plays a part in portability and
ergonomics of the arborloo base. In order to reach the goals described in previous
sections of this report, modularity and reduction of thickness to decrease weight are the
focal points for the exploration of structures. By focusing on these features, feasibility in
transportation, maintenance and safety can be efficiently approached. Structures found
in nature (biomimicry) were also used as an inspiration, specifically honeycombs and
spider webs. Assembly features and structural design of toys (Legos, Tinker Toy, K’nex,
Lincoln Log, Brik-a-Blok, and others) were also reviewed to complement modularity of
the design.

Steel Reinforced Concrete slabs. Using rebar, steel rods, to reinforce concrete is
probably one of the most common practices in the construction of slabs for
arborloos; Especially in Haiti, where concrete and rebar are the main materials of
construction. Additional to providing tensile strength to concrete, steel
reinforcement is largely practiced and simple to place, reduces cracking, allows to
reduce the thickness of the concrete, provides necessary temperature and shrinkage
protection as well as crack width control. Figure 2 shows the dimensions and shape
of conventional concrete slabs used in arborloos; Figure 3 shows different
arrangements of steel rods to achieve reinforced concrete slabs. (Reiterman, n.d.)
(Prieto-Portar, 2008)

Structural Honeycomb: lightweight and resistant material typically made of
phenolic and available commercially. Structural Honeycomb is made primarily by
expanding substrate material on which adhesive node lines have been printed.
There are metallic and plastic options to structural honeycomb. It is commercially
known for its low weight, toughness and sound dampening characteristics. Since it
is a patented and commercialized product, it has a costly acquisition cost. (3M,
2013)
Pedro Cruz Diloné, 2013
(HexCel
Composites,
2013)
Page 23
Figure 13. An example of how structural honeycomb stiffens a structure without materially increasing its
weight.
Source: http://www.hexcel.com/Resources/DataSheets/Brochure-DataSheets/Honeycomb_Attributes_and_Properties.pdf
Figure 14. Schematic of dimensions on a structural honeycomb sheet.
Source: http://www.hexcel.com/Resources/DataSheets/Brochure-DataSheets/Honeycomb_Attributes_and_Properties.pdf

Modular design + interlocking. One of the advantages of modular structural
design is that it allows organizing a complex structure into a set of much simpler
Pedro Cruz Diloné, 2013
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components. Additionally, modular design allows for simple assembly and
disassembly, which consequently simplifies adding or removing components.
Moreover, modular components can be acquired in different times making the
whole system easier to finance.
Figure 15. Figure X. Schematics of the modular structures and interlocking designs found in toys
Brik-a-blok (Top, source: http://kids.woot.com/offers/brik-a-blok-30-piece-set), Lincoln Log (Bottom left,
source: http://www.orwellloghomes.com/lincoln-log-profiles.jpg), and TinkerToy (Bottom right, source:
http://www.orwellloghomes.com/lincoln-log-profiles.jpg)
Pedro Cruz Diloné, 2013
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