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

Introduction

The arborloo

Objectives

Methodology

Materials inventory

Structures

Results

Conclusions and Recommendations

References

Literature reviewed

Appendix A - Sketches

Appendix B – Evaluation Table

List of Figures

Figure 1. Diagram of the use and structure of a conventional arborloo

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

Figure 3. Types of conventional rebar reinforced concrete slabs.

Figure 4. Schematic of lightweight concrete with composites; in this case, expanded clay pearls.

Figure 5. Detail of the porosity of cellular concrete.

Figure 6. Ferrocement wall being cured.

Figure 7. Sisal fiber panels bonded with polyester resin (top left and right). Bottom image shows corrugated panel supporting a 200lbs. person

Figure 8. Corrugated metal sheets used in roofing.

Figure 9. Banana fiber on fixtures for the drying and separation process.

Figure 10. Various flooring models made from polymers

Figure 11. Variety of manhole covers made from Polymer Concrete.

Figure 12 Coconut Shell Powder pellets.

Figure 13. An example of how structural honeycomb stiffens a structure without materially increasing its weight.

Figure 14.Schematic of dimensions on a structural honeycomb sheet.

Figure 15. Figure X. Schematics of the modular structures and interlocking designs found in toys

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 existingmethods are highly effective, they are not reaching the around 40% of the world populationwithout 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 prioritygiven by leaders are some of the factors that hinderthe 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 innumerous 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 ClivusMultrum, 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

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Thearborloo is best suited to rural areaswhere 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.

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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 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 aconcretestructure 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.

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  • Cellular concrete.Thislightweight 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.

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  • 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.

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  • Peter Morgan’sConventional 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 experimentsthat 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 lrvStollmanwith the intention of developing alow 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

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  • 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.

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  • Banana fiber as aggregate of cement. Banana fibercan 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.(SavastanoJr, H., et al., 2005) (Zhu, W. H., et al., 1994)

Figure 9. Banana fiber on fixtures for the drying and separation process.

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  • 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 1

Table 1. Physical and mechanical properties of natural fibers.

Source: Ali, M., 2008. “Natural fibres as construction materials”

Pedro Cruz Diloné, 2013Page 1

  • 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.

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

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  • 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-cementconcrete.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.

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  • 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 12Coconut Shell Powder pellets.

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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.