“Recommendations to redesign the base for the arborloo”
2013Department of Industrial and Systems Engineering 0303.799.01
– Independent StudyPedro Cruz Diloné
[“Recommendations to redesign the base for the arborloo”]
ContentsAbstract5Introduction5The
arborloo6Objectives8Methodology8Materials
inventory9Structures24Results26Conclusions and
Recommendations28References29Literature reviewed34Appendix A -
Sketches35Appendix B – Evaluation Table43
List of Figures
Figure 1. Diagram of the use and structure of a conventional
arborloo6
Figure 2 Conventional design and dimensions of concrete slabs
for arborloos. Left to right, squared, rectangular and circular
bases.7
Figure 3. Types of conventional rebar reinforced concrete
slabs.10
Figure 4. Schematic of lightweight concrete with composites; in
this case, expanded clay pearls.11
Figure 5. Detail of the porosity of cellular concrete.12
Figure 6. Ferrocement wall being cured.12
Figure 7. Sisal fiber panels bonded with polyester resin (top
left and right). Bottom image shows corrugated panel supporting a
200lbs. person14
Figure 8. Corrugated metal sheets used in roofing.15
Figure 9. Banana fiber on fixtures for the drying and separation
process.16
Figure 10. Various flooring models made from polymers21
Figure 11. Variety of manhole covers made from Polymer
Concrete.23
Figure 12 Coconut Shell Powder pellets.23
Figure 13. An example of how structural honeycomb stiffens a
structure without materially increasing its weight.25
Figure 14. Schematic of dimensions on a structural honeycomb
sheet.25
Figure 15. Figure X. Schematics of the modular structures and
interlocking designs found in toys26
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 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
Source:
http://upload.wikimedia.org/wikipedia/commons/thumb/a/a2/Arborloo-en.svg/500px-Arborloo-en.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
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 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.
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.
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).
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
· 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).
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).
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)
Figure 9. Banana fiber on fixtures for the drying and separation
process.
Source:
http://www.agrarianworld.com/wp-content/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 analyzed in the table. (Ali, 2012)
Pedro Cruz Diloné, 2013Page 2
Table 1. Physical and mechanical properties of natural
fibers.
Source: Ali, M., 2008. “Natural fibres as construction
materials”
· 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.
Sources:
http://partywarehouse.co.nz/hire/images/marquee%20flooring.jpg;
https://encrypted-tbn2.gstatic.com/images?q=tbn:ANd9GcSULs9oL0L7_MFX013HNelpHQaSblcq0eg91f1qQlXaO_DWve6mnQ,
http://kids.woot.com/offers/brik-a-blok-30-piece-set
Figure 10. Various flooring models made from polymers
Table 2. Typical Compressive Yield Strength and Compressive
Modulus of Polymers
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.
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
petroleum-based 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
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) (HexCel Composites, 2013)
Figure 13. An example of how structural honeycomb stiffens a
structure without materially increasing its weight.
Source:
http://www.hexcel.com/Resources/DataSheets/Brochure-Data-Sheets/Honeycomb_Attributes_and_Properties.pdf
Figure 14. Schematic of dimensions on a structural honeycomb
sheet.
Source:
http://www.hexcel.com/Resources/DataSheets/Brochure-Data-Sheets/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 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)
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Polymer Type
Compressive Yield
Strength (MPa)
Compressive
Modulus (GPa)
ABS652.5
ABS + 30% Glass Fiber1208
Acetal Copolymer852.2
Acetal Copolymer +
30% Glass Fiber
1007.5
Acrylic953
Nylon 6552.3
Polyamide-Imide1305
Polycarbonate702
Polyethylene, HDPE200.7
Polyethylene
Terephthalate (PET)
801
Polyimide1502.5
Polyimide + Glass Fiber22012
Polypropylene401.5
Polystyrene702.5
