Development of pavement blocks using waste PET bottles

TABLE OF CONTENTS

DECLARATION

DEDICATION

ACKNOWLEDGEMENT

ABSTRACT

TABLE OF CONTENT

LIST OF TABLES

LIST OF FIGURES

CHAPTER ONE
INTRODUCTION
1.1 Background to the Study
1.2 Problem Stateme
1.3 Main objective
1.4 Specific objectives
1.5 Scope of the study
1.6 Justification

CHAPTER TWO
LITERATURE REVIEW
2.1 Concrete
2.2 Concrete pavement blocks
2:2:1 Properties of concrete pavement block
2:2:2 Specification requirements of a good concrete pavement block
2:3 Polymers
2:4 Polymer modified concrete
2:4:1 Polymer impregnated concrete
2:4:2 Polymer cement concrete
2:4:3 Polymer concrete
2:5 Interactions between polymer and cement
2:6 Polyethylene terephthalate (PET)
2:6:1 Properties of polyethylene terephthalate (PET)
2:6:2 Polyethylene terephthalate (PET) in concrete work
2:7 Solid waste management in Ghana

CHAPTER THREE
METHODOLOGY
3.1 Materials
3.1.1 Cement
3.1.2 Fine Aggregates
3.1.3 Quarry dust
3.1.4 Polymeric Material
3.1.5 Water
3.1.6 Sulphuric Acid,H2SO4
3.2 Equipment
3.3 Preparation of Samples
3.3.1 Mix Proportion
3.3.2 Mixing, Casting, Curing for complete replacement of cement with PET
3.3.3 Mixing, Casting, Curing for partial replacement of quarry dust with PET
3.4 Test conducted
3.4.1 Compressive strength, ASTM C39 (2014)
3:4:2 Water absorption test, ASTM (936)
3:4:3 Effects of H2SO4 on the weight of dry pavement blocks

CHAPTER FOUR
RESULTS AND DISCUSSION
4.1 Results.
4:2 Discussions.
4:2:1 Compressive strength ASTM C39 (2014)
4:2:2 Water absorption test
4:2:3 Effect of sulphuric acid on the weight of pavements

CHAPTER FIVE
CONCLUSION AND RECOMMENDATION
5.1 Conclusion
5.2 Recommendations

REFERENCES

APPENDIX

Miscellaneous Tables

DECLARATION

Abbildung in dieser Leseprobe nicht enthalten

DEDICATION

I dedicate this thesis to my grandmother; Madam Georgina Mirekua, to my mother; Abena Nyamekye and also to each and every person who has offered me advice, love, care and support throughout this programme. I love you all.

ACKNOWLEDGEMENT

First and foremost, I give all thanks and praise to the Almighty God for providing me with the strength and wisdom to complete this undergraduate program. I am deeply indebted to my supervisor Prof. Johannes. A. M. Awudza for his guidance, support and encouragement throughout the completion of this thesis. I am grateful to Mr. Antwi of Civil Engineering Structures Lab. I am grateful to Owura for his immense support and guidance throughout the period I spent at his construction site. I am also grateful to Mr. Michael Baah Mensah and sister Selina for their guidance throughout my work. Finally, from the deepest of my heart, I would like to thank Madam Georgina Mirekua and the family for their care, support and encouragement. God bless you all.

ABSTRACT

The use of waste plastics in concrete pavement block is a partial solution to the environmental and ecological challenges associated with the use of plastics. The aim of this research is to reduce environmental pollution by using waste PET bottles to produce pavement blocks. In this study, Voltic bottles were first used to replace cement in the production of pavement blocks. The polymeric material was first shredded and melted in an aluminum container at a temperature range of 250 ºC - 260 ºC and the quarry dust and sand were added in their respective ratios. In another set of studies, the waste Voltic bottles were used as a partial replacement for quarry dust in the manufacturing of pavement blocks. The cleaned waste plastics bottles were first cut into flakes and then incorporated into the concrete mixture. Test conducted involved the effect of sulphuric acid on the weight of pavement, its water absorption and compressive strength. In the first studies, when PET bottles were used to replace cement, the results obtained had the compressive strength almost the same as that of the control sample which contain no plastic. The percentage water absorbed was less and it also had good resistance for acid. In the second studies when PET was used to replace quarry dust partially, the compressive strength was a little bit lower than the control. Its water absorption was less and it also had good resistance to acid. From the above findings, PET pavement blocks have a good strength and can therefore be used for any construction work.

Keywords: Water absorption, waste Voltic bottles, Acid test, Compressive strength

LIST OF TABLES

Table 2.1 Properties of PET

Table 3.1 Chemical composition of ordinary Portland cement

Table 3.2 Control mix ratio

Table 3.3 Mix ratios of blocks for complete replacement of cement

Table 3.4 Mix ratio of blocks for partial replacement of quarry dust

Table 3.5 Compressive strength of various mix proportions of the control specimen

Table 3.6 Compressive strength of specimens with complete replacement of cement with PET

Table 3:7 Compressive strength for Pavements made with partial replacement of quarry dust with PET polymer

Table 3:8 Water absorption test for control pavement

Table 3.9 Water absorption test for complete replacement of cement with PET polymer

Table 3:10 Water absorption for pavement made with partial replacement of quarry dust with PET

Table 3:11 Effects of sulphuric acid on the weight of the control pavement blocks

Table 3:12 Effect of sulphuric acid on complete replaced PET pavements

Table 3:13 Effects of sulphuric acid on partial replacement of PET pavement

LIST OF FIGURES

Figure 2.1 A standard pavement block for construction

Figure 2.2 Production of polyethylene terephthalate

Figure 3.1 Shredded Voltic bottles

Figure 3.3 Hydraulic compressive machine

Figure 4.1 Pavement blocks made with complete replacement of cement with PET

Figure 4.2 Pavement blocks made with partial replacement of quarry dust with PET

Figure 4.3 Compressive strength for control specimen

Figure 4.4 Compressive strength for complete replacement of cement with PET

Figure 4.5 Compressive strength for control and complete replacement of cement with PET

Figure 4.6 Compressive strength for partial replacement of quarry dust with PET

Figure 4.7 Compressive strength for variations of partial replacement of quarry dust with PET

Figure 4.8 Water absorption test for control pavement blocks

Figure: 4.9 Water absorption for complete replacement of cement with PET pavement

Figure 4.10 Water absorption test for control and complete replacement of cement with PET pavements

Figure 4.11 Water absorption test for partial replacement of quarry dust with PET

Figure 4.12 Water absorption for variation of quarry dust with PET

Figure 4:13 Effect of sulphuric acid on the weight of the control cement pavements

Figure 4:14 Effect of sulphuric acid on the weight of the complete replacement of cement with PET

Figure 4:15 Effect of sulphuric acid on the weight of the control and complete replacement of cement with PET pavements

Figure 4:16 Effect of sulphuric acid on the weight of the partial replacement of quarry dust with PET pavements

Figure 4.17 Effect of sulphuric acid on the variations of partial replacement of quarry dust with PET

CHAPTER ONE INTRODUCTION

1.1Background to the Study

Economic growth and changing consumption patterns are resulting in the rapid increasein theuse of plastics in the world. The consumption of plastic materials has increased from 5 million tons in the 1950s to 100 million tons in the 2000s (Wusu-Sekyere Ebenezer, 2013).

In Ghana, about 10 to 15% of our municipal solid wastes produced consist of plastics. The amount of plastic waste is ever increasing due to increase in human population, developmental activities, and changes in lifestyle and socio-economic conditions (Frederick, 2015). Plastic wasteis a significant portion of the total municipal solid waste.Therefore there should be the need for proper waste management system.

Solid waste management is one of the major environmental concerns in Ghana. Landfills are becoming scarce and the cost in building landfill sites are increasing.The only ones we have here is the dumping sites which is been managed by the MMDAs and some sanitation agencies.

During transportation of wastes from homes and industries by these sanitation agencies to the dumping sites some fallout from the trucks into gutters. Moreover plastics arebeing littered andmisused all over the country and nowcausing threat to the nation. Some of these problems associated with plastic waste in Ghana include:

1. Plastics block drains and gutters and causes floods.
2. Plastics release toxic gas into the atmosphere when burnt.
3. Plastic bottles and containers act as breeding ground for mosquitoes when filled with rainwater.

Fortunately, there are various ways in which waste plastics could be reuse or converted to other products (Welle, 2011).

Recycling technology has been the solution of choice in the developed countries, but in developing countries, like Ghana it may not be economically important since it involve a lot of capital (Asnani, 2006).

High density polyethylene (HDPE) waste is used in making bags and dustbins. These materials serve as an alternative for the metallic dust bins and leather bags.

Many developing countries including Ghana are currently experiencing rapid urbanization and industrialization and as a result a lot of infrastructure developments are going on in these countries.

Expanded polystyrene (EPS) based waste, high density polyethylene (HDPE), polyethylene terephthalate (PET) waste bottles, polypropylene fibers and polyethylene bags have all been used in different forms by researchers in concrete (Kodua, 2015a).

PET plastic is one major component of Municipal Solid Waste (MSW) which is becoming a major research issue for its possible use in pavement blocks. Polymer modified pavement blocks has applications in road construction and buildings.

Hence waste PET plastic can therefore, be mixed in concrete mass in some form, without significant effect on its other properties or slight compromise in strength (Polymer Modified Concrete).

In this study waste Voltic bottles found on KNUST campus were shredded into flakes and was used in the production of pavement blocks.

1.2 Problem Statement

In Ghana, solid waste management is among the primary essential services provided by municipal authorities in the country to keep urban centers clean. However, it is among the most poorly rendered services in Ghana. Systems applied are not scientific, outdated and inefficient, population coverage is low (Asnani, 2006).

These MMDAs have contracted sanitation companies such as Zoom lion Ghana, Asadu Royal, and other agencies to clean the environment of the various waste generated from human activities. Despite the efforts of these contracted sanitation companies, solid waste management problem is prevalent everywhere in Ghana.

Polymer wastes take years to degrade in the natural environment. The slow degradation properties of waste polymer materials cause environmental and ecological problems such as:

1. The burning of waste plastic release toxic gas into the atmosphere
2. Breeding sites for mosquitoes.
3. Causes floods

Therefore there is the need for an efficient and reliable method for solid waste management in Ghana.A developing country like Ghana is currently experiencing rapid urbanization and industrialization and as a result a lot of infrastructure developments are going on. These developments come with problems such as shortage of construction materials, high cost of building due to importation of cement and other building materials.

PET plastics waste can be used as a complement of cement or aggregate in the manufacturing of concrete which can help solve the above problems (Chowdhury et al., 2013).

1.3 Main objective

The aim of this research is to determine the suitability of waste Voltic bottles (PET bottles) in the development of pavement blocks for construction.

1.4 Specific objectives

1. To prepare various proportions of polymer modified pavement blocks using recycled PET.
2. To determine water absorption content of polymer modified pavement blocks.
3. To determine the durability of cube specimens in acidic media
4. To determine the engineering property (compressive strength) of samples of prepared polymer modified pavement blocks.

1.5 Scope of the study

In this research work, waste PET plastics foundon KNUST campus were collected, washed and shredded into flakes, heated and then used to replace cement completely whiles some were shredded into pieces and were used to replace quarry dust partially. In order to complement this research and to gain a comprehensive perspective on the growing volume of research on polymer modified pavement blocks, established fundamental and empirical laboratory tests such as compressive strength, water absorption and effect of acids on the mechanical properties were employed to determine the suitability of the pavement blocks made with waste PET bottles in the construction work.

1.6 Justification

Despite the economic importance of plastics to Ghana’s economy, its contribution to waste generation and management problems in the country has resulted in threats by some Municipal Metropolitan and District Assemblies (MMDAs) and the central government to impose levies on its production or ban its production outright.

These threats if carried out will increase the cost of production of plastics and worsen the unemployment situation in Ghana.

Polyethylene, polypropylene, polyethylene terephthalates and polystyrene which are non-degradable polymers form a major composition of the plastic wastes in the environment. Therefore, there is the need for an economically recycling and value addition to the plastic waste generated in our communities.

Several studies have been carried out in countries like Egypt, India, Australia, and U.S.A where waste plastics have been converted to other products. Ghana is yet to document a work done on the reuse of plastics into pavement blocks.

This study defines the potentials and benefits in the addition of plastic waste in the concrete mixture to produce a more flexible and durable concrete pavement blocks and at the same time being an alternative way to recycle the plastic waste. The fundamental advantage of plastics replacing aggregates would be reducing the bulk density of the composite and hence improved cost (Kodua, 2015b).

CHAPTER TWO LITERATURE REVIEW

2.1 Concrete

Concrete consist of sand or stone, known as aggregate combined with cement paste to bind it. It consist of binding material called cement, composed of lime, silica, alumina and gypsum, that is mixed with sand, aggregate and water (Gibbons et al., 1999).

The aggregate can be of various sizes. It is broadly categorized as fine or commonly sand and coarse (typically crushed stone or gravel). In every concrete mixture, the greater proportionis theaggregate which is bulky and relatively cheaper than the cement.

Concrete is the most widely used construction material in the world due to its low cost, high availability, and simple constructability. However, the use of cement is a main contributor to high-energy usage, CO2 and dust emissions, natural resource depletion, air pollution, ozone layer destruction, global warming, and continuous environmental deterioration (Koo et al., 2014).

Concrete is relatively durable and robust building material, but it can be severely weakened by poor manufacture or a very aggressive environment. There are a number of historic concrete structures which exhibit problems that are related to their date of origin. Such problems are beingsolved by application of polymer in concrete construction (Hing, 2008).

2.2 Concrete pavement blocks

Concrete pavement blocks were first manufactured in the Netherlands in 1924. It was probably World War II that led to the growth of concrete pavement blocks. Large areas of the Netherlands were destroyed during the War and, because clay bricks were in short supply, concrete pavement blocks were introduced as an alternative (Concrete Manufacturers Association, 2009).

These blocks are rectangular in shape and have more or less the same size as the brick.

Common names for the concrete blocks include paving blocks, pavers, paving stones, interlocking paving blocks and road stones. Paver sizes are a nominal 4x8 inches (100 x 200mm). Block thickness is specified according to traffic and SABS 1200 MJ specifies standard thicknesses of 50, 60, 80, 100 and 120mm. It is not normally economical to manufacture the last two sizes (Cement & Concrete Institute, 2002).

Concrete pavement blocks(paver) have been used in pavements for more than 50 years in Europe.Pavers have being used in heavy industrial port and airfield pavement since 1970’s in Europe (Abate, 1993).This is why recently concrete block pavements have become an attractive engineering and economical alternative to both flexible and rigid pavements. The strength, durability and aesthetically pleasing surfaces have made paving blocks attractive for many commercial, municipal and industrial applications such as parking areas, pedestrian walks, traffic inter- sections, container yards and roads (Gencel et al., 2012).Water-retentive concrete block pavements, are also used in areas frequented by many people including sideways, parks, and plazas, and such applications are expected to grow in the future (Karasawa et al., 2006).

2:2:1 Properties of concrete pavement block

1. Blocks should meet structural requirements for paving (specified in terms of block compressive strength).
2. Blocks should be durable: they should be able to withstand abrasion, impact and chemical attack.
3. Blocks should be of uniform dimensions to facilitate correct and easy placing and ensure good readability.

2:2:2 Specification requirements of a good concrete pavement block

In some applications concrete blocks are required to be aesthetically attractive.The specification requires that the pavers comply with certain tolerances, and have a compressive strength of 25MPa, for lightly trafficked situations, or 35MPa, for more severe conditions or where a wheel load greater than 30kN is encountered (cement & concrete institute, 2002).

The average absorption of pavement blocks should not exceed 5%, with no individual unit greater than 7% according to American Society for Testing and Materials (ASTM)specification (936).

Abbildung in dieser Leseprobe nicht enthalten

Figure2.1A standardpavement block for construction

2:3 Polymers

The word polymer literally means many (poly) units (mer). A small, simple chemical unit appears to repeat itself a (very) large number of times in the structure of a polymer molecule or macromolecule. The so called repeat unit may consist of a single atom, or more commonly a small groups with the distinctive feature that the repeated units are successively linked to one another on each side by covalent bonds (Ghosh, 2006).

Polymers are substances whose molecules have high molar masses and are composed of a large number of repeating units. Polymers can be natural orsynthetic. Some naturally occurring polymers are proteins, starches, cellulose, and latex. Synthetic polymers are produced commercially on a very large scale and have a wide range of properties and uses. The materials commonly called plastics are all synthetic polymers.

Polymers are produced by chemical reactions in which a large number of molecules called monomers are joined sequentially, forming a chain. In many polymers, only one monomer is used. Others too consist of two or three different monomers combined. Polymers are also classified by the characteristics of the reactions by which they are formed. If all atoms in the monomers are incorporated into the polymer, the polymer is called an addition polymer. On the other hand, if some of the atoms of the monomers are released into small molecules, such as water, the polymer is called a condensation polymer.

Most addition polymers are made from monomers containing a double bond between carbon atoms. Such monomers are known as olefins, and most commercial addition polymers are polyolefin. Condensation polymers, are formed from monomers that have two different groups of atoms which can join together to form, for example, ester or amide links. Polyesters are an important class of commercial polymers, as are polyamides normally known as (nylon) (Shakhashiri, 1983).

The physical and chemical properties of polymers depend on the nature, arrangement of chemical groups of their composition and the magnitude of intra or intermolecular forces that is primary and secondary valence bonds present in the polymer. Degradation process occurs due to the influence of thermal, chemical, mechanical, radioactive and biochemical factors occurring over a period of time resulting in deterioration of mechanical properties and colour of polymers (Venkatachalam et al., 2012).

Polymers have a number of vital properties, which exploited alone or together, make a significant and expanding contribution to constructional needs (Tapkire et al., 2014).

1. Durable and corrosion resistant.
2. Good Insulation for cold, heat and sound saving energy.
3. It is economical and has a longer life.
4. Maintenance free (such as painting is minimized)
5. Hygienic and clean
6. Ease of processing / installation
7. Light weight

2:4 Polymer modified concrete

Polymers have been used in construction as long ago as the fourth millennium B.C., when the clay brick walls of Babylonia were built using the natural polymer asphalt in the mortar. The temple of Ur-Nina (King of Lagash), in the city of Kish, had masonry foundations built with mortar made from 25 to 35% bitumen (a natural polymer) until in the year 1950’s wheresynthetic polymers were incorporated in Portland cement mortars and concrete (Hirde & Dudhal, 2016).

The use of polymers in construction works is becoming common in the world. It physical properties and relatively low cost makes it the most widely used construction material than conventional Portland cement concrete. Conventional Portland cement concrete has a number of limitations, such as low flexural strength, low failure strain, susceptibility to frost damage and low resistance to chemicals. These limitations are well recognized by the engineer and can usually be allowed for in most applications.Polymer modified binders also show improved adhesion and cohesion properties (Sulyman et al., 2016).

In some situations, these problems can be solved by using materials which contain an organic polymer or resin (commercial polymer) instead of or in conjunction with Portland cement. These relatively new materials offer the advantages of higher strength, improved durability, good resistance to corrosion and reduced water permeability.There are three principal classes of composite materials containing polymers (Hing, 2008). These are:

2:4:1 Polymer impregnated concrete

The first type which is the polymer impregnated concrete is made by impregnation of pre-cast hardened Portland cement concrete with low viscosity monomers (in either liquid or gaseous form) that are converted to solid polymer under the influence of physical agents (ultraviolet radiation or heat) or chemical agents (catalysts).

The monomers which are widely used in the impregnation of concrete are the vinyl type, such as methyl methacrylate (MMA), styrene, acrylonitrile, t-butyl styrene and vinyl acetate. The preferred impregnated materials are acrylic monomer systems such as methyl methacrylate or its mixtures with acrylonitrile, because they have low viscosity, good wetting properties, high reactivity, relatively low cost and result in products with superior properties. The applications of concrete impregnated in depth in building and construction include structural floors, high performance structures, food processing buildings, sewer pipes, and storage tanks for seawater, desalination plants and distilled water plants, marine structures, wall panels, tunnel liners, prefabricated tunnel sections and swimming pools (Hing, 2008).

2:4:2 Polymer cement concrete

The polymer cement concrete is a modified concrete in which part (10 to 15% by weight) of the cement binder is replaced by a synthetic organic polymer. It is produced by incorporating a monomer, pre-polymer-monomer mixture, or a dispersed polymer (latex) into a cement-concrete mix. To affect the polymerization process of the monomer or pre- polymer-monomer, a catalyst is added to the mixture.

Generally, polymer cement concrete made with polymer latex exhibits excellent bonding to steel reinforcement and to old concrete. Its compressive, flexural strength and toughness are usually higher than those of unmodified concrete and also the modulus of elasticity may or may not be higher than that of unmodified concrete, depending on the polymer latex used. Generally, as the polymer forms a low modulus phase with the polymer cement concrete, its creep is higher than that of plain concrete and decreases with the type of polymer latex used in the following order: polyacrylate, styrene-butadiene copolymer, polyvinylidene chloride, unmodified cement

The major application of latex-containing polymer cement concrete is in floor surfacing, as it is non-dusting and relatively cheap and also because ofits lower shrinkage, good resistance to permeation by various liquids such as water and salt solutions, and good bonding properties to old concrete, it is particularly suitable for thin (25 mm) floor toppings, concrete bridge deck overlays, anti-corrosive overlays, concrete repairs and patching (Hing, 2008).

2:4:3 Polymer concrete

Polymer concrete (PC) is a composite material in which the binder consists mainly of a synthetic organic polymer. It is variously known as synthetic resin concrete, plastic resin concrete or simply resin concrete.

The use of a polymer instead of Portland cement represents a substantial increase in cost; polymers should be used only in applications in which the higher cost can be justified by superior properties, low labor cost or low energy requirements during processing and handling (Hing, 2008).

2:5 Interactions between polymer and cement

Polymer modified concrete or mortar is a composite material consisting of two solid phases. These phases are: the aggregates which are discontinuously dispersed through the material and the binder which itself consists of a cementations phase and a polymer phase. According to the volume fraction of the polymer in the binder phase the material shifts from PCC, i.e. polymer cement concrete, to PC, i.e. polymer concrete (Gemert et al., 2004).

In the case of PCC, the binder consists of a polymer-cement co-matrix. The polymer is added to the fresh mixture as an emulsion or as redispersible polymer powders. During hardening and curing, cement hydration and polymer film formation take place resulting in a co-matrix in which polymer film is intermingled with cement hydrates.

Cement hydration in polymer modified material is influenced by the presence of the polymer particles and polymer film in the fresh state, during hydration as well as in the hardened state. The properties such as strength of the fresh mixture are influenced to a large extent by the surfactants present at the surface of the polymer particles. The cement particles are better dispersed in the mixture and a more uniform material is formed. The hydration of the cement is reflected in the strength evolution of the material (Kodua, 2015b).

The influence of the polymer modification is in two fold; firstly, due to the polymer and the surfactants, a retardation process of the cement hydration can be observed. This is especially visible in the compressive strength of the mortar beams. On the other hand, due to the film formation or due to the interaction between the cement hydrates and the polymer particles, the tensile strength of the binder matrix as well as the adhesion strength between the aggregate and the binder increase.

The mutual influences between the cement hydrates and the polymer particles and film are incorporated in an integrated model of structure formation.

Immediately after mixing, the cement particles and polymer particles are dispersed in the water. The first hydration of the cement takes place, which results in an alkaline pore solution. This is indicated as the first stage.

In the second step, a portion of the polymer particles is deposed on the surface of the cement grain and the aggregate. The polymer-cement ratio determines the amount of polymers present in the pore solution and present at the aggregate surface. Part of the polymer particles may coalesce into a continuous film. This preferably takes place at the surface of the cement hydrates where extra forces are exerted on the polymer particles due to the extraction of water for cement hydration. The polymer film can partly or completely envelop a cement grain, which results in a retardation or even a complete stop of the hydration of the cement grain The final step includes further hydration and final film formation. Through the cement hydrates, a continuous polymer film forms as water is further removed from the pore solution. The part of the polymer particles, that is still present in the dispersion, is restricted to the capillary pores and at the interface of the aggregates and the bulk polymer-cement phase. It is this part which contributes the most to the elastic and final strength properties. The continuity of the polymer phase through the binder matrix is more pronounced in the case of a higher polymer- cement ratio. If the polymer dispersion is much more elevated than the curing temperature, the polymer particles may not coalesce into a continuous film, but remain as closely packed polymer particles (Gemert et al., 2004).

2:6 Polyethylene terephthalate(PET)

Polyethylene terephthalate (PET) is thermoplastic in nature, meaning it can be recycled after use. It’s also known as “polyester, which often causes confusion, because polyester resins are thermosetting materials (Mishra, 2016).

PET is generally produced via two different routes or mechanisms; transesterification of dimethyl terephthalate (DMT) with ethylene glycol (EG) and direct esterification of purified terephthalicacid (TPA) with EG. The first stage of the two routes, known respectively as transesterification (ester interchange) and direct esterification, both produce a mixture of ethylene glycol ester of terephthalic acid. This mixture of linear oligomers (mainly bis-hydroxyethyl terephthalate) is subjected to a further stage known as polycondensation thatproduces polyethylene terephthalate of fiber-forming molecular weight. Solid statepolymerization is required only for the production of bottles (El-Rub, 2001).Poly (ethylene terephthalate) known by the trade names Mylar, Dacron , ethylene, recron has high crystalline melting temperature (260°C), and the stiff polymer chains possess in the PET polymer imparts high mechanical strength, toughness and fatigue resistance of150- 175°C as well as good chemical, hydrolytic and solvent resistance. Poly (ethylene terephthalate) fiber has a very good crease resistance, good abrasion resistance and can be treated with cross-linking resin to impart permanent wash and wear properties. The fiber can be blended with cotton and other cellulosic fibers to give better feel and moisture permeation. Thus PET fiber is used for applications such as wearing apparel, curtain, upholstery, thread, tire cord filaments, industrial fibers and fabric for industrial filtration (Venkatachalam et al., 2012) .

Abbildung in dieser Leseprobe nicht enthalten

Figure 2.2 Production of polyethylene terephthalate.

2:6:1 Properties of polyethylene terephthalate (PET)

PET is hygroscopic, which means that it absorbs water from its surroundings. However, when this "damp" PET is then heated, the water hydrolyzes the PET, decreasing its resilience. Thus, before the resin can be processed in a molding machine, it must be dried. Drying is achieved through the use of a desiccant or dryers before the PET is fed into the processing equipment.The polymer is composed of repeating unitseach unit having a physical length of about 1.09 nm and a molecular weight of ~200.The aromatic ring coupled with short aliphatic chain makes thepolymer a stiff molecule as compared to other aliphatic polymers such as polyolefin or polyamide. The lack of segmental mobility in the polymer chains results in relatively high thermal stability (Venkatachalam et al., 2012)

Table 2.1 Properties of PET (Mishra, 2016)

Abbildung in dieser Leseprobe nicht enthalten

2:6:2Polyethylene terephthalate (PET) in concrete work.

PET is a transparent polymer, which has good mechanical properties and good dimensional stability under variable load (Sulyman et al., 2016).

To date, there are only three major ways which have been identified to recycle waste PET bottles into construction materials. Firstly, waste PET bottles can be depolymerized into unsaturated polyester resin to produce polymer mortar and polymer concrete. It benefits include that, the polymer concrete has higher compressive and flexural strength than conventional Portland cement concrete , and that polymer concrete achieves over 80% of its ultimate strength within 1 day. However, the properties of polymer concrete are sensitive and subjected to temperature and the cost of producing polymer concrete from waste plastic is high (Zhang, 2016).

The second method employs the use PET fiber to reinforce concrete. Theuse of PET fiber can enhance the ductility of quasi-brittle concrete and, therefore, reduce the cracking caused by plastic shrinkage. However, the water-resistance and low surface energy of plastic materials result in a weak mechanical bond between the fiber and the cement matrix. Poor mechanical bond strength may cause internal micro-cracks in the interfacial mechanical bond area between the fiber and the cement matrix

The last recycling method is to substitute PET waste for aportion of the aggregate used in the production of lightweight concrete or asphalt concrete. This method provides the most economical way to accomplish two important goals: to dispose of waste plastic and to produce lightweight concrete. However, the addition of PET waste negatively affects the quality of the concrete by decreasing its compressive strength, splitting tensile strength, and modulus of elasticity Recently, a fourth method has been attempted whereby a recycled PET bottle flakes are directly used as binder. The PET plastics are heated andwith two types of soil, clay and sand, to attain a uniform fused mix named plastic-soil. Recycled PET bottles used to produce mortar, have a promising results (Zhang, 2016).

In short, blocks with PET replacement have the following features as compared to conventional blocks:

1. Greater weather resistant due to chemically inert PET and HDPE;
2. Less stress or load on foundation (due to lighter blocks);
3. Economical foundation (since the stress on foundation is less)
4. Less manual labour in making blocks (mixture is lighter);
5. Less cost of transportation (due to lighter blocks)
6. Good sound insulation;
7. Variable strengths (dependent on size and nature of plastic aggregate);
8. Better shock absorption
9. Deduction in the dead load of concrete structure which allows the contractor to reduce the dimension of columns, footingsand other load bearing elements(precast strips with circular gaps) or by executing frames which have led to easy forms (caissons, - shaped roof elements etc.).

2:7 Solid waste management in Ghana.

The estimated quantity of Municipal Solid Waste (MSW) generated worldwide is 1.7 – 1.9 billion metric ton (Modak, 2010). With rapid urbanization, the situation is becoming critical. The urban population has grown fivefold in the last six decades with 285.35 million people living in urban areas worldwide as per the 2001 Census (Asnani, 2006).Solid waste management is one of the basic essential services provided by municipal authorities in the country to keep urban centers clean. However, it is among the most poorly rendered services in Ghana .The systems applied are unscientific, outdated and inefficient; population coverage is low; and the poor are marginalized. Solid Waste is littered all over leading to insanitary living conditions in our communities. Municipal laws governing the urban local bodies do not have adequate provisions to deal effectively with the ever- growing problem of solid waste management.

Municipal solid waste” (MSW) is a term usually applied to a heterogeneous collection of wastes produced in urban areas, the nature of which varies from region to region. The characteristics and quantity of the solid waste generated in a region is not only a function of the living standard and lifestyle of the region's inhabitants, but also of the abundance and type of the region's natural resources. Urban wastes can be subdivided into two major components -- organic and inorganic. In general, the organic components of urban solid waste can be classified into three broad categories: putrescible, fermentable, and non-fermentable. Putrescible wastes tend to decompose rapidly and unless carefully controlled, decompose with the production of objectionable odors and visual unpleasantness. Fermentable wastes tend to decompose rapidly, but without theunpleasant accompaniments of putrefaction.

[...]