2013

Department of Industrial and Systems Engineering 0303.799.01 – Independent Study

Pedro Cruz Diloné

[“Recommendations to redesign the base for the arborloo”]

ContentsAbstract........................................................................................................................................................................................... 5

Introduction.................................................................................................................................................................................. 5

The arborloo............................................................................................................................................................................ 6

Objectives.................................................................................................................................................................................. 8

Methodology................................................................................................................................................................................. 8

Materials inventory...............................................................................................................................................................9

Structures............................................................................................................................................................................... 24

Results...........................................................................................................................................................................................26

Conclusions and Recommendations................................................................................................................................28

References................................................................................................................................................................................... 29

Literature reviewed...........................................................................................................................................................34

Appendix A - Sketches............................................................................................................................................................35

Appendix B – Evaluation Table..........................................................................................................................................43

Pedro Cruz Diloné, 2013 Page 2

List of Figures

Figure 1. Diagram of the use and structure of a conventional arborloo.................................................6Figure 2 Conventional design and dimensions of concrete slabs for arborloos. Left to right, squared, rectangular and circular bases..................................................................................................................7Figure 3. Types of conventional rebar reinforced concrete slabs.........................................................10Figure 4. Schematic of lightweight concrete with composites; in this case, expanded clay pearls.....11Figure 5. Detail of the porosity of cellular concrete...............................................................................12Figure 6. Ferrocement wall being cured.................................................................................................12Figure 7. Sisal fiber panels bonded with polyester resin (top left and right). Bottom image shows corrugated panel supporting a 200lbs. person......................................................................................14Figure 8. Corrugated metal sheets used in roofing................................................................................15Figure 9. Banana fiber on fixtures for the drying and separation process...........................................16Figure 10. Various flooring models made from polymers.....................................................................21Figure 11. Variety of manhole covers made from Polymer Concrete...................................................23Figure 12 Coconut Shell Powder pellets.................................................................................................23Figure 13. An example of how structural honeycomb stiffens a structure without materially increasing its weight................................................................................................................................25Figure 14. Schematic of dimensions on a structural honeycomb sheet................................................25Figure 15. Figure X. Schematics of the modular structures and interlocking designs found in toys. .26

Pedro Cruz Diloné, 2013 Page 3

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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

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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.

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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.

Source: http://aquamor.tripod.com/ArborLoo1.HTM

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Figure 2 Conventional design and dimensions of concrete slabs for arborloos. Left to right, squared, rectangular and circular bases.

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

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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.

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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.

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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).

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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 Page 12

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 Page 13

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)

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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)

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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)

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Table 1. Physical and mechanical properties of natural fibers.Source: Ali, M., 2008. “Natural fibres as construction materials”

Pedro Cruz Diloné, 2013 Page 18

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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.

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

Table 2. Typical Compressive Yield Strength and Compressive Modulus of Polymers

Polymer TypeCompressive Yield

Strength (MPa)Compressive

Modulus (GPa)ABS 65 2.5

ABS + 30% Glass Fiber 120 8

Acetal Copolymer 85 2.2Acetal Copolymer + 30% Glass Fiber

100 7.5

Acrylic 95 3Nylon 6 55 2.3Polyamide-Imide 130 5Polycarbonate 70 2Polyethylene, HDPE 20 0.7

Polyethylene Terephthalate (PET)

80 1

Polyimide 150 2.5

Polyimide + Glass Fiber 220 12

Polypropylene 40 1.5Polystyrene 70 2.5

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

Pedro Cruz Diloné, 2013 Page 22

Figure 10. Various flooring models made from polymers

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)

Pedro Cruz Diloné, 2013 Page 23

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

Pedro Cruz Diloné, 2013 Page 24

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

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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.

Pedro Cruz Diloné, 2013 Page 26

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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