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CHAPTER ONE

INTRODUCTION

1.1 BACKGROUND TO THE STUDY

In the world today, industrialization is on the increase. This single fact translates into great increase

in construction of industrial structures and corresponding increase in environmental pollution from

emission of industrial wastes. Industrial wastes may include chemical solvents, paints, sand paper,

paper products, industrial by-products, metals and radioactive wastes.

Following the onset of industrialization and the sustained urban growth of large population centers

in England, the buildup waste in the cities caused a rapid deterioration in levels of sanitation and

the general quality of urban life. The streets became choked with filth due to the lack of waste

clearance regulations. Calls for the establishment of a municipal authority with waste removal

powers were mooted as early as 1751 by Corbyn Morris in London, who proposed that as the

preservation of the health of the people is of great importance, it is proposed that the cleaning of

this city, should be put under one uniform public management, and all the filth be conveyed by the

Thames to proper distances in the country (Herbert, Lewis, 2007). However, According to

Davidson, G. (2011), Waste management practices are not uniform among countries (developed

and developing nations), regions (urban and rural area), and sectors (residential and industrial). In

the light of these, researchers have taken different approaches to finding alternative methods to

minimize the effects of the chemical wastes on the environment.

Cement concrete is the most widely used building material due to its satisfying performance in

strength requirement but when one deal with the durability aspects of concrete, the chemical attack,

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which results in volume change, cracking of concrete and consequent deterioration of concrete,

becomes an important part of discussion (Prasad, Jain and Ahuja, 2006, p.256).

The high cost of construction led some countries in Europe and America to manufacture pozzolana

cements so as to reduce the demand in Portland cement. Some industrial wastes have been used

for a number of years as cement and concrete components; examples include fly ash (Bilodeau and

Malhotra 1998; Bouzoubaa et al., 1999), silica fume (Khedr and Abou-Zeid 1994), Slag

(Olorunsogo and Wainwright 1998), and a host of others.

Concrete structures may be exposed to sulphate resulting from environmental pollution especially

in industrial areas. Deterioration of concretes by sulphate is a serious problem affecting concrete

durability. Sulphate in soils, groundwater, and sea water reacts with various phases of hydrated

cement paste such C3A and Ca(OH)2 leading to expansion, cracking, and strength reduction. Using

pozzolans such as fly ash, silica fume, and natural pozzolans is one method used to improve the

sulphate resistance of concrete. Prasad, et al., (2006), noted that most soil contains some sulphate

in form of calcium, magnesium, sodium and potassium. Ammonium sulphate is frequently present

in agricultural soil and water. Decay of organic matter in the matter in the marshes, shallow lakes,

mining pit and sewer pipes often lead to the formation of H2S.

In this experimental study, an attempt will be made to test the performance of shredded polythene

waste concrete in sulphate environment with respect to durability of concrete. The polythene waste

to be used in this research is pure water sachets. The above polythene waste will be shredded and

then mixed with cement concrete in various proportions (0.5% and 1%) and test specimens (100 x

100 x 100mm cubes) will be cast to study the behavior of the shredded polythene waste subject to

varying amount of magnesium sulphate solution in curing water.

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1.2 STATEMENT OF RESEARCH PROBLEM

Blending of mineral admixtures like Ground Granulated Blast Furnace Slag (GGBFS), Fly Ash

(FA), Silica Fume (SF) etc in cement increase resistance of concrete to Sulphate attack. The

superior performance of blended cement over plain cement concrete is attributed to the pozzolanic

reaction that consumes the Calcium Hydroxide and to the dilution of Calcium Aluminate Hydrate

phase due to a reduction in the quantity of plain cement in total binder (Prasad, et al., 2006, p.263)

In the light of the above, this work will test the performance of shredded polythene concrete in

sulphate environment with a view to ascertain it's durability.

Lasisi et al., (1990) as cited by Ajala (2010) opined that there is an increased failure in the

durability of concrete especially in riverine and swampy areas of Nigeria due to the presence of

sulphates.

According to Prasad et al., (2006), there are three modes of concrete deterioration usually

associated with sulphate attack. The first mode of deterioration is due to eating away of the

hydrated cement paste and leaving cohesion less granular mass. This mode of deterioration is

known as acidic type and attributed mainly to the formation of gypsum. The second mode of

deterioration is due to the reaction of sulphate of hydrated Aluminates phase, forming Tricalcium

Sulpho Aluminate Hydrate, also called Etrrigite. This mode is expansion type and attributed

mainly to the formation of Ettringite in the presence of high concentration of Calcium Hydroxide

(Portlandite). The third type of deterioration is the onion-peeling type, which is characterized by

scaling of concrete surface in successive layers.

It has been established that Sulphate Resisting Portland Cement (SRPC) is good under sulphate

attack due to less content of C3A. Therefore, any cement with low C3A will perform well under

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sulphate attack. According to Prasad et al., Modern cement is made for rapid development of

strength resulting in an increase in Tri-Calcium Silicate (C3S) content in the Cement. This increase

in the C3S results in an increased Calcium Hydroxide content in the hardened cement; thereby

enhancing the susceptibility to sulphate attack. Rasheeduzzafar et al., reported that, in addition to

the C3A content, the C3S/C2S ratio of cement has a significant effect on the sulphate resistance of

cement mixes.

BS 8110 (1997) indicated that concrete made from materials or techniques not covered by British

Standards may exhibit different properties from those made with conventional materials, hence,

their performance and suitability should be established by appropriate tests before recommending

them for use.

Therefore, this research will attempt to answer the following questions:

1. What effect will varying percentage content of shredded polythene waste (SPW) have on

compressive strength of concrete exposed to SO42- environment?

2. What effect will change in concentration of MgSO4 have on shredded polythene waste

(SPW) concrete exposed to SO42- environment?

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1.3 AIM AND OBJECTIVES OF STUDY

1.3.1 Aim of study

The aim of this study is to investigate the effect of shredded polythene in concrete exposed to

sulphate environment with a view to ascertain it's durability.

1.3.2 Objectives of the Research

The Objectives of this study are to

1. determine the effect of varying percentage content of shredded polythene on compressive

strength of concrete exposed to MgSO4 solution.

2. investigate the effect of varying concentration of MgSO4 on compressive strength of

shredded polythene concrete exposed to MgSO4 solution.

1.4 JUSTIFICATION OF STUDY

Blending of mineral admixtures like Ground Granulated Blast Furnace Slag (GGBFS),

Fly Ash (FA), Silica Fume (SF), in cement increases resistance of concrete to Sulphate attack.

The choice of this study is as a result of the drive to find alternate sulphate resistant materials

locally available.

1.5 SCOPE OF THE STUDY

This research will focus on the resistant level and compressive strength of concrete cubes

incorporated with shredded polythene waste.

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1.6 LIMITATION OF THE STUDY

This practical experiment will be limited to manual method of compaction, wooden moulds of

100mm2 size, hand mixing method, immersion method of curing and curing age of 7, 14, and

28 days.

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CHAPTER TWO

LITERATURE REVIEW

2.1 PREAMBLE

Sulphates are salts in which the negatively charged ion (anion) SO42- forms a compound

with a metal positively charged ion (cation) such as Ca2+. Sulphates include gypsum (calcium

sulphate, CaSO4), epsomite (magnesium sulphate, MgSO4), and Glaubers salt (sodium sulphate,

Na2SO4) (Ian Langworth, 2008). These are readily soluble sulphates which are easily transported

to react with concrete.

According to Ditao et al, (2013) and Oymael et al, (2008), of all the solutions of sulphate

compound, MgSO4 solution has the most detrimental effect. In their different experiments on

deterioration of concrete and mortar exposed to sulphate attack, they both realised that specimens

in MgSO4 solution had relatively lower compressive strength compared to those in Na2SO4

solution. The end result of sulphate attack can be excessive expansion, delamination, cracking, and

loss of strength. The degree to which this attack can occur depends on water penetration (as

referred to above), the sulphate salt and its concentration and type (e.g. sodium or magnesium)

(QCL Group Technical Note, 1999).

The American Concrete Institute (ACI) divides sulphate attack into two general categories:

(1) a sulphate reaction with calcium hydroxide to form gypsum (sometimes called gypsum attack,

gypsum corrosion, and acid type of sulphate attack), and (2) a sulphate reaction with calcium

aluminate hydrate to form ettringite (sometimes called sulphoaluminates attack or corrosion)

(American Concrete Institute, 2001). According to Ian Longworth, (2008) two mechanisms of

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sulphate attack have been identified. These are the ettringite form of sulphate attack and the

thaumasite form of sulphate attack.

Internal sulphate attack refers to situations where the source of sulphate is internal to

concrete. The source of sulphate can be the cement, supplementary materials such as fly ash or

slag, the aggregate, the chemical admixtures or the water. Two examples of such internal sulphate

attack are the classical attack excess (with respect to the clinker aluminate phase) of cement

sulphate and the so-called delayed ettringite formation (DEF). External sulphate attack on the other

hand is caused by a source external to concrete. Such sources include sulphates from ground water,

soil, solid industrial waste, and fertilizers, or from atmospheric SO3 or from liquid industrial wastes

(Ata, 2012).

Several researches had been carried out in the past directed towards mitigating the effect

of chemical attack on concrete. Materials such as fly ash, ground granulated blag furnace slag

(GGBFS), corncob ash, rice husk ash, silica fume, periwinkle shell ash and palm kernel shell.

However, this research is looking into ascertaining the resistivity of polythene as an alternative yet

economical admixture to concrete exposed to MgSO4 environment.

Sulphate attack is one of the most aggressive environmental deteriorations that affect the

long-term durability of cement-based structures and can cause huge economic loss (Ata, 2014). In

the light of the above, it is imperative to continue research on the durability of concrete since

concrete is widely used and lacks a viable alternative at the moment.

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2.2 DURABILITY OF CONCRETE

It is essential that every concrete structure should continue to perform its intended functions, that

is, maintain its required strength and serviceability, during the specified or traditionally expected

service life. It follows that concrete must be able to withstand the processes of deterioration to

which it can be expected to be exposed. Such concrete is said to be durable. Durability

requirements for a service life of 50 and 100 years are given in BS 8500-1: 2006.

2.2.1 CAUSES OF INADEQUATE DURABILITY

Inadequate durability manifests itself by deterioration which can be due either to external factors

or to internal causes within the concrete itself. The various actions can be physical, chemical, or

mechanical. External chemical attack occurs mainly through the action of aggressive ions, such as

chlorides, sulphates, or of carbon dioxide, as well as many natural or industrial liquids and gases.

The damaging action can be of various kinds and can be direct or indirect. With the exception of

mechanical damage, all the adverse influences on durability involve the transport of fluids through

the concrete.

2.2.2 TRANSPORTATION OF FLUIDS IN CONCRETE

Whenever transportation of fluid in concrete is discussed, the major concern is about the

penetrability of concrete. According to Neville, (There are three fluids principally relevant to

durability which can enter concrete: water, pure or carrying aggressive ions, carbon dioxide and

oxygen. Durability of concrete largely depends on the ease with which fluids, both liquids and

gases, can enter into, and move through, the concrete; this is commonly referred to as permeability

of concrete. Porosity is a measure of the proportion of the total volume of concrete occupied by

pores, and is usually expressed in per cent. If the porosity is high and the pores are interconnected,

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they contribute to the transport of fluids through concrete so that its permeability is also high. On

the other hand, if the pores are discontinuous or otherwise ineffective with respect to transport,

then the permeability of the concrete is low, even if its porosity is high.

Absorption of concrete is a measure of the volume of pore spaces in concrete and the ease with

which fluid can penetrate it. An absorption test on several small portions of concrete is prescribed

by ASTM C 642-06; drying at 100 to 110 C (212 to 230 F) and immersion in water at 21 C (70

F) for at least 48 hours are used. The requirements of BS 1881-122: 1983 are similar except that

the test is performed on whole core specimens.

Since chemical attack do occur externally, it is important to talk about surface absorption. Neville

(1995) mentioned that it is the absorption characteristic of the outer zone of concrete (concrete

cover) that is of greatest interest. A test to determine the initial surface absorption is prescribed in

BS 1881-5: 1984. A shortcoming of the initial surface absorption test is that the flow of water

through the concrete is not unidirectional. To remedy this, several modified tests have been

proposed but none has gained general acceptance.

Bearing the above limitation in mind, the initial surface absorption test can be used to compare the

effectiveness of curing of the outer zone of concrete.

2.2.3 PERMEABILITY OF CEMENT PASTE

The permeability of cement paste varies with the progress of hydration. Permeability of concrete

is not a simple function of its porosity, but depends also on the size, distribution, shape, tortuosity

and continuity of the pores. The cement gel has a porosity of 28%, its permeability is only about

7 x 10-6m/s.

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2.2.4 ACID ATTACK ON CONCRETE

Concrete is generally well resistant to chemical attack, provided an appropriate mix is used and

the concrete is properly compacted. There are, however, some exceptions.

Portland cement concrete which is highly alkaline is not resistant to attack of concrete occurs by

way of decomposition of products of hydration and formation of new compound which if soluble

maybe leached out but if not soluble may be disruptive in situ. The attacking compounds must be

in solution. Ca(OH)2 and C-H-S are the most vulnerable cement hydrate.

A liquid of PH value below 6.5 is dangerous to concrete but a liquid with PH value of 5.5 poses

more attack while one with 4.5 PH attacks most severely. The ability of aggressive ions to be

transported and the PH of such solution influence the progress of the attack.

Sulphate acid is particularly aggressive because, in addition to the sulphate attack of the aluminate

phase, acid attack on Ca(OH)2 and C-S-H takes place. Reduction in the cement content of the

concrete is therefore beneficial, provided, of course, that the density of the concrete is unimpaired.

2.2.5 SULPHATE ATTACK ON CONCRETE

Common solid salts which when in solution attack concrete are sulphates of sodium, potassium,

magnesium and calcium which occur in soil or in groundwater. Sulphate in groundwater are

usually of natural origin but can also come from fertilizers or from industrial effluents.

Types of sulphate and their rates of aggressiveness

1. Calcium Sulphate (CaSO4) also known as Gypsum.

2. Sodium Sulphate (Na2SO4) also called Salt cake or Glaubers salt.

3. Magnesium Sulphate (MgSO4) also called Epsum salt.

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Generally, solubility is key when it comes to chemical attack on concrete. Calcium Sulphate is the

least soluble type of sulphate hence the least aggressive to concrete. Rebel et al. (2005) is of the

opinion that this low solubility limits its concentration in groundwater and this subsequently limits

its effect on concrete. Hansen and Pressler, (1947) on the other hand said; once calcium sulphate

enters concrete, its solubility increases as it encounters high alkaline pore solutions within the

concrete and the higher sulphate concentrations can then more aggressively attack the hydrated

cement paste.

Sodium sulphate attack occurs in two ways. The first is sodium sulphate reacts with calcium

hydroxide to form gypsum;

Ca(OH)2 + Na2SO4.10H2O CaSO4.2H2O + 2NaOH + 8H2O Eq. 1

The second form of attack involves sodium sulphate reacting with tri-calcium aluminate to form

ettringite;

2(3CaO.Al2O3.12H2O) + 3(NaSO4.10H2O) 3CaoAl2O3.3CaSO4.32H2O +

2Al(OH)3 + 6NaOH + 17H2O Eq. 2

Magnesium Sulphate attacks calcium silicate hydrate as well as Ca(OH)2 and calcium aluminate

hydrate;

3CaO.2SiO2aq + 3MgSO4.7H2O 3CaSO4.2H2O + 3Mg(OH)2 + 2SiO2aq + xH2O Eq. 3

However, MgSO4 has the most severe attack on concrete due to its very low solubility. The critical

consequence of attack by MgSO4 is destruction of C-S-H.

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2.2.5.1 THAUMASITE FORM OF SULPHATE ATTACK

This type of attack occurs in concrete buried in the ground. At temperatures below about 15 C

(59 F) in the presence of sulphate, carbonate and water, C-S-H can convert to thaumasite, which

is a non-binder, with a composition of CaSiO3.CaCO3.CaSO4.15H2O. The carbonate may be

present in the aggregate (limestone or dolomite) or as bicarbonate in the groundwater. Mixes

containing GGBFS offer resistance to thaumasite attack.

2.2.5.2 DELAYED ETTRINGITE FORMATION

This is an early-age controlled expansion. However, the formation of ettringite in mature concrete

tends to be disruptive and harmful, and is a form of sulphate attack, resulting in the compound

3CaO.Al2O3.3CaSO4.32H2O Eq. 4

High temperature during hydration can be the result of applied heat or be due to heat generation in

a large pour when natural loss of heat is inadequate. If the temperature in the interior of concrete

reaches 70 to 80 C, a slow formation of ettringite can lead to expansion and cracking. For the

harmful effects to take place after return to room temperature, the concrete has to be wet or moist

either permanently or intermittently. These harmful effects are a loss of strength, a decrease in the

modulus of elasticity, and sometimes cracking. Occasionally, there is a problem of distinguishing

(DEF) from alkali-silica reaction. One reason for confusion is that ettringite may be so fine as to

look like alkali-silica gel.

Delayed ettringite formation (DEF) is often avoidable by a selection of appropriate blended cement

that does not lead to an excessive temperature rise.

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2.2.6 MECHANISMS OF ATTACK

The mechanism of the delayed ettringite expansion is still debated, there being two principal

schools of thought. Mather et al. are of the opinion that the reaction between calcium sulphate and

C3A is topochemical. Ping and Beaudoin (1992) describe the topochemical or solid-solid reaction

as a process in which atoms or ions create new crystal directly on the surface of one of the reaction

substrates. If the product of the topochemical reaction occupies a larger volume than the volume

of the two original compounds, then expansive and disruptive forces are created. In the case of the

reaction between calcium sulphate and Ca(OH)2, there is no overall increase in volume but,

because of the differences in the solubility of C3A and gypsum, oriented, acicular ettringite is

formed at the surface of the C3A. Thus, there is a low increase in volume and, at the same time,

an increase in porosity elsewhere.

Mehta on the other hand attributes the development of expansive forces to the swelling pressure

induced by the adsorption of water by the originally colloidal ettringite which precipitated in the

solution in the presence of lime. Thus, the formation of ettringite per se is thought to be the cause

of expansion. However, Odler and Glasser point out that an uptake of water from the environment

is not a necessary condition for expansion to take place. Nevertheless, expansion increases

significantly under wet conditions so that it is likely that both the mechanisms of expansion

discussed above are involved at different stages.

Skalny et al. (2002) are of the opinion that the following conditions must be reached if ettringite

crystallization is to lead to the expansion:

1. Volume of ettringite must exceed some threshold value which depends on the capillary

porosity of concrete.

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2. Only ettringite formed after the hydration of cement leads to the expansion. The

volumetric expansion of ettringite formed during the hydration of cement (primary

ettringite) can be accommodated by the elasticity of fresh cement paste hence no

expansion.

3. If sulphate attack leads to concrete expansion ettringite must be formed in a

topochemical reaction.

Ettringite can also form from the reaction between sulphate and C4AF, but this ettringite is nearly

amorphous and no damaging expansion has been reported. Nevertheless, ASTM C 150-09

prescribes a limit on the combined content of C3A and C4AF, when sulphate resistance is required.

The consequences of sulphate attack include not only disruptive expansion and cracking, but also

loss of strength of concrete due to the loss of cohesion in the hydrated cement paste and of adhesion

between it and the aggregate particles. Concrete attacked by sulphates has a characteristic whitish

appearance. The damage usually starts at edges and corners and is followed by progressive

cracking and spalling which reduce the concrete to a friable or even soft state.

The attack occurs only when the concentration of the sulphates exceeds a certain threshold. Above

that, the rate of sulphate attack increases with an increase in the strength of the solution, but beyond

a concentration of about 0.5 per cent of MgSO4 or 1 per cent of Na2SO4 the rate of increase in the

intensity of the attack becomes smaller. A saturated solution of MgSO4 leads to serious

deterioration of concrete, although with a low water/cement ratio this takes place only after 2 to 3

years. BS EN 206-1 : 2000 expresses sulphate as SO3 while ACI uses SO4; multiplying the former

by 1.2 converts it into the latter. Water-soluble sulphates, and not acid-soluble, are considered. The

classification of the severity of exposure recommended by ACI 318-0810.42 and BS EN 206-

1:2000 is given in Table below. Because extraction of sulphates from soil depends on the

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compaction of the soil, and on the water-soil extraction ratio, the measurement of sulphates in

groundwater is more reliable. The class boundaries are, in a sense, arbitrary because they have not

been calibrated by measurement of recorded incidence of damage to concrete caused by sulphate

attack. Moreover, the actual conditions of exposure may vary during the lifetime of a structure

owing to a variation in groundwater flow or the drainage pattern.

It should be noted that, under certain conditions, the sulphate concentration in water can be greatly

increased by evaporation. This is the case with sea water splash on horizontal surfaces and on the

surface of cooling towers.

In addition to the concentration of the sulphate, the speed with which concrete is attacked depends

also on the rate at which the sulphate removed by the reaction with cement can be replenished.

Thus, in estimating the danger of sulphate attack, the movement of groundwater has to be known.

When concrete is exposed to the pressure of sulphate-bearing water on one side, the rate of attack

will be highest. Likewise, alternating saturation and drying leads to rapid deterioration. On the

other hand, when the concrete is completely buried, without a channel for the groundwater,

conditions will be much less severe.

2.2.7 MITIGATING THE ATTACK

Two approaches can be used. The first one is to minimize the C3A content in the cement, that is,

to use sulphate-resisting cement. The second approach is to reduce the quantity of Ca(OH)2 in

hydrated cement paste by the use of blended cements containing blast furnace slag or pozzolana.

The effect of pozzolana is two-fold. First, it reacts with Ca(OH)2 so that Ca(OH)2 is no longer

available for reaction with sulphates. Second, compared with Portland cement only, the same

content of blended cement per cubic metre of concrete results in less Ca(OH)2. These measures

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are helpful, but even more important is the prevention of ingress of sulphates into the concrete:

this is achieved by making the concrete as dense as possible and with as low a permeability as

possible.

2.2.7.1 GROUND GRANULATED BLAST-FURNACE SLAG (GGBFS)

The use of Type II cement, or of blended cement with blast-furnace slag or pozzolana is

recommended, for severe exposure, sulphate-resisting cement is the preferred choice but for very

severe exposure, a blend of sulphate-resisting cement and pozzolana (between 25 and 40 per cent

by mass of total cementitious material) or blast furnace slag (not less than 70 per cent by mass)

proven to improve sulphate resistance, is required. The relevant property of the blast-furnace slag

is its alumina content, advice on this is given in ASTM C 989-09a. It should also be noted that not

all pozzolanas are beneficial: a low calcium oxide content is desirable. Specifically, Class C fly

ash decreases the sulphate resistance of concrete.

The reason why sulphate-resisting cement alone is inadequate under severe conditions is that not

only calcium sulphate but also other sulphates are present. Therefore, although sulphate-resisting

cement does not contain enough C3A for the formation of expansive ettringite, the Ca(OH)2 present

and possibly also C-S-H are vulnerable to the acid-type attack of the sulphates.

The recommendations of ACI 201.2R-9210.42 reflect the beneficial effect on sulphate resistance

of pozzolanas and ground granulated blastfurnace slag used with Portland cement. Pozzolanas

have also to be used with regulated-set cement, which alone shows a poor resistance to sulphates.

However, partial replacement (20 per cent) of this cement by pozzolanas reduces the early strength

of concrete, so that the practicality of use of regulated-set cement under conditions of sulphate

attack is questionable.

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2.2.7.2 SILICA FUME

Silica fume incorporated in concrete is beneficial with respect to permeability, but tests on

hardened cement paste indicate that the effect of silica fume in various sulphate environments is

not clear.

Super-sulphated cement offers very high resistance to sulphates, especially if its Portland cement

component is of the sulphate-resisting variety.

High-pressure steam curing improves the resistance of concrete to sulphate attack. This applies to

concretes made both with sulphate-resisting and ordinary Portland cements because the

improvement is due to the change of C3AH6 into a less reactive phase, and also to the removal of

Ca(OH)2 by the reaction with silica.

Since there are changes in solubility with temperature, expansion due to the formation of ettringite

is very low at temperatures above 30 C (86 F).

There is need to specify mix proportions since low permeability of concrete is the consequence of

an appropriate microstructure of the hardened cement paste. There are three possible approaches:

specifying a maximum water/cement ratio, specifying a minimum strength, and specifying a

minimum cement content.

The concept of ensuring protection from sulphate attack by specifying a minimum cement content

has no scientific basis. As Mather points out, for instance, with 356 kg of ordinary Portland cement

per cubic metre of concrete (600 lb/yd3) it is possible to obtain concretes ranging in cylinder

strength from 14 MPa (2000 psi) to 41 MPa (6000 psi) depending on the water/cement ratio and

on slump. The durability of these concretes will clearly vary enormously.

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The use of strength for specifying purposes is convenient but strength only reflects the

water/cement ratio; it is this that is relevant to density and permeability. However, specifying the

water/cement ratio regardless of the nature of the cement used is inadequate.

2.3 EFFECTS OF SEA WATER ON CONCRETE

Concrete exposed to sea water can be subjected to various chemical and physical actions. The pH

of sea water varies between 7.5 and 8.4, the average value in equilibrium with atmospheric CO2

being 8.2. Ingress of sea water into concrete per se does not significantly lower the pH of pore

water in the hardened cement paste: the lowest value reported is 12.0.

The presence of a large quantity of sulphates in sea water could lead to the expectation of sulphate

attack. Indeed, the reaction between sulphate ions and both C3A and C-S-H takes place, resulting

in the formation of ettringite, but this is not associated with deleterious expansion because

ettringite, as well as gypsum, are soluble in the presence of chlorides and can be leached out by

the sea water. However, the use of sulphate-resisting cement in concrete exposed to the sea is not

essential, but a limit on C3A of 8 per cent when the SO3 content is less than 3 per cent, is

recommended; cements with a C3A content up to 10 percent can be used, provided the SO3 content

does not exceed 2.5 percent. It seems that it is the excess of SO3 that leads to a delayed expansion

of concrete.

The most damaging effect of sea water on concrete structures arises from the action of chlorides

on the steel reinforcement.

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Concrete in water and wastewater environment are susceptible to different forms of attack. The

attack primarily comes in the form of sulphate and acid attack which when in contact with the

concrete changes the chemical structure of the cement matrix leading to degradation.

2.3.1 THE MECHANISMS OF ATTACK ON CONCRETE IN WASTE WATER

ENVIRONMENTS

i. Biologically Produced Sulphuric acid

1. Hydrogen Sulphide (H2S) formation:

In near anaerobic conditions sulphate reducing bacteria act on the sulphates in raw sewage

to form sulphides. The bacteria use the sulphates in the wastewater as their source of

essential oxygen and as part of this process sulphur ions are produced.

The sulphur ions in turn react with dissolved hydrogen in the wastewater to form hydrogen

sulphide (H2S). H2S alone is not corrosive to concrete. The H2S forms as gas above the

wastewater. It is this area of a concrete element of a wastewater system, above the water

line, that is most susceptible to corrosion

2. Absorption of H2S:

There exists a slightly moist layer of concrete above the wastewater level. This has a

relatively high pH level due to the alkalinity of the concrete. At these high pH levels the

H2S absorbs into the surface of the concrete and separates into HS- or S2- which attracts

more H2S into the moisture layer and in turn further H2S disassociation. As the

concentration of H2S increases the pH of the concrete decreases which may make it

susceptible to possible attack.

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3. Formation of Sulphuric Acid (H2SO4):

In the presence of oxygen the H2S reacts to form elemental sulphur. The bacteria can be

found in wastewater. These bacteria oxidise the sulphur to form sulphuric acid. These

bacteria only attach themselves to concrete when the pH of the concrete has reduced to

around 9 and there is sufficient moisture, oxygen and nutrients available.

4. Sulphuric acid attack of concrete:

Sulphuric acid reacts with calcium hydroxide (CH) to form calcium sulphate (Gypsum).

Gypsum in turn reacts with calcium aluminate hydrate (C3A) to form ettringite. This is an

expansive process which will degrade the cement matrix.

ii. Sulphates

Sulphuric acid reacts with the calcium hydroxide to produce gypsum. This is a white putty-

like deposit, moist and flaky. It acts as a barrier to further penetration but the rougher surface area

formed also provides for more places for attack to take hold. The formation of gypsum leads to an

eventual loss in cohesion as the cementitious calcium compounds are broken down.

The formation of gypsum may also be due to attack by sodium sulphate (Na2SO4) or magnesium

sulphate (MgSO4) or a combination of both. In sodium solutions the CH primarily undergoes

decomposition with the calcium being taken up by the formation of gypsum. Only when there is

no more CH available will the solution attack the CSH paste. Attack by magnesium solutions is

more severe than that of sodium in that it attacks both the CH and CSH simultaneously, but with

22

a preference to CH. The products from the magnesium sulphate reaction include magnesium

sulphate hydrate, which lacks cohesive properties, brucite and gypsum.

It has been proven that hydrated cements with high CH contents are more resistant to magnesium

sulphate attack.

2.4 POLYTHENE IN CONCRETE

One of the fastest growing industries is the polythene industry. From packaging of goods in stores

and malls to packaging of the nationwide popular pure water industries, polythene comes up in

our everyday use. Polythene is normally stable and non-biodegradable. So, there is disposal

problem. Research works are going on in making use of polythene wastes effectively as additives

in plain and reinforced concrete mixes for variety of purposes. Domestic polythene waste, most

especially Pure water sachets are causing considerable damage to the environment and hence an

attempt has been made to understand whether they can be successfully used in concrete to improve

its compressive strength. Different forms and types of polythene wastes are utilized to check the

feasibility of them in concrete. Literatures indicate that addition of SPW in concrete not only solves

the problem of their safe disposal but also improves the basic properties of concrete like,

permeability to water, flexural strength, and compressive strength with higher strength to weight

ratio of material, workability, thermal insulation and reduction in self weight. A few of previous

researches are highlighted as follows.

This study however attempts to ascertain the durability of concrete subjected to sulphate

attack by incorporating polythene in concrete. Plastic bags are popular with consumers and

retailers as they are a functional, lightweight, strong, cheap, and hygienic way to transport food

23

and other products. After they used plastic bags, most of these are become to waste and some are

recycled. Each year, plastic bags are consumed approximately 500 billion to 1 trillion in

worldwide. That is over one million bags are consumed per one minute. Particularly in China, the

total number of plastic bags used is 3 billion per day. According to the number of plastic bags

used, it can be affected to the environment. Plastic bags create visual pollution problems and can

have harmful effects on aquatic and physical animals. Also plastic bags are especially components

of the litter stream due to their size and it takes a long time to completely degradation.

Different curing conditions were used to note the effect of chemical attack and corresponding

changes in the compressive strength of concrete mix. In another study, Bhogayata et al. (2012)

used ordinary plastic bags having thickness less than 20 in the form of plastic fibres in the range

of 0% to 1.2% by volume of concrete and the compressive strength was compared for manually

cut and shredded plastic. They concluded that the plastic bags could be used preferably in shredded

form to avoid difficulty in workability of concrete. Rai et al. (2012) used plastic pallets as fine

aggregate and studied the workability, compressive strength and flexural strength of waste plastic-

mix concrete with and without using superplasticizer. Rebeiz (1996) investigated the strength

properties of unreinforced polymer concrete using an unsaturated polyester resin based on recycled

polythene terephthalate (PET).

Marzuok et al. (2006) studied the use of consumed plastic bottle waste as sand-substitution

aggregates within composite material for building application and showed the effects of PET waste

on the density and compressive strength of concrete. Torgal et al. (2012) investigated the durability

aspects of concrete added with rubber wastes and PET bottles fibre in different aspects ratio and

form of rubber wastes. They observed that such materials can be used for non-load bearing

24

structures. This study presents the workability and compressive strength of concrete made with

waste plastic in fibrous form at different doses (0.5%, 0.75% and 1.0%) and results are compared

with conventional concrete.

From the present study, following conclusions may be drawn:

I. On addition of waste polythene, workability of concrete is reduced and slump loss

increased with increase in dose of waste polythene.

II. Compressive strength of concrete made using waste polythene is increased by 4.03%,

4.55% and 17.11% at 7, 28 and 56 d respectively at 0.75% dose of waste polythene.

III. Compressive strength of concrete made using waste polythene is increased by 3.03%,

1.32% and 2.76% at 7, 28 and 56 days respectively at 0.5% dose of waste polythene.

IV. The increase in compressive strength of concrete on inclusion of waste polythene is

observed up to 0.75% and thereafter compressive strength is reduced however,

compressive strength at 1% waste polythene is more than the referral concrete.

V. The concept of mixing of plastic wastes in concrete could be a very environment friendly

method for disposal of solid waste in the country, this study has shown a potential towards

this concept.

25

Table 2.1 Chemical resistance of polyethylene

Chemical or Solvent

Concentration

LDPE & MDPE

HDPE Resins

70oF 140oF 70oF 140oF

Magnesium Nitrate Satd S S S S

Magnesium Sulfate Satd S S S S

Maleic Acid Satd S S

Mercuric Chloride Satd S S

Mercuric Cyanide Satd S S S S

Mercurous Nitrate Satd S S

Mercury S S S S

Methyl Alcohol 100% S S S S

Methyl Bromide O U O

Methyl Chloride O U

Methyl Ethyl Ketone 100% U U U U

Methylene Chloride 100% U U U U

Methylsufuric Acid S S S S

Milk S S

Mineral Oils O U S U

Molasses Comm. S S

Naphtha 100% S U

Naphtha 100% S U

Naphthalene U U

26

Nickel Chloride Satd S S S S

Nickel Nitrate Con. S S S S

Nickel Nitrate Conc. S S

Nickel Sulfate Satd S S S S

Nicotinic Acid 100% S S

Nitric Acid 0-30% S S S S

Nitric Acid 30-50% S O S O

Nitric Acid 70% S O S O

Nitric Acid 95-98% U U U U

Nitrobenzene 100% U U U U

Octyl Cresol O U

Oils and Fats O U

Oleic Acid Conc. O U

Oleum Conc. U U U U

Orange Extract Dilute S S

Oxalic Acid Dilute S S S S

S = satisfactory (no attack) O = slight attack U = unsatisfactory 70F = 21C, 140F = 60C

Source: Undated publication by Lyondell Chemical Company, United States.

2.5 PREVIOUS RESEARCHES ON SULPHATE ATTACK

Sulphate attack is mostly associated to the reaction of sulphate ions with calcium hydroxide

and calcium aluminate hydrate to form gypsum and ettringite. The gypsum and ettringite formed

as a result of sulphate attack is significantly more voluminous (1.2 to 2.2 times) than the initial

27

reactants (Hobbs and Taylor, 2000; Al-Alkhras, 2006). The formation of gypsum and ettringite

leads to expansion, cracking, deterioration and disruption of concrete structures. In addition to the

formation of ettringite and gypsum and its subsequent expansion, the deterioration due to sulphate

attack is partially caused by the degradation of calcium silicate hydrate (C-S-H) gel through

leaching of calcium compounds. This process leads to loss of C-S-H gel stiffness and overall

deterioration of the cement paste matrix (Mbessa and Pera, 2001, Santhanam et al., 2002;

Santhanam et al., 2003; Irassar, 2009).

Bates et al (1913) investigated sulphate attack on concrete in the early 20th century in

North America. Extensive studies however have been made since then to identify the cause and

develop methods to prevent sulphate attack in concrete. Skalny et al., (2002), Liu et al. (2012)

submitted that ready availability of sulphates to cause damage to concrete depends on their

concentration and solubility, transport of water, and environmental conditions. The increased

incidence of deterioration of the low C3A ASTM Type V cement. Though this was a well-

recognized and documented achievement towards good performance of this cement in the

experimental trials, both in laboratory and field exposures, there have been occurrence of sulphate

deterioration of concrete, particulary when structures were exposed to moderate to severe sulphate

environments (Al-Amoudi, 2002; Al-Alkhras, 2006; Bellmann et al., 2006; Al-Dulaijan).

2.6 BRIEF HISTORY OF PLASTIC

The development of plastics has come from the use of natural plastic materials (e.g., chewing gum,

shellac) to the use of chemically modified natural materials (e.g., rubber, nitrocellulose, collagen,

galalite) and finally to completely synthetic molecules (e.g., Bakelite, epoxy, polyvinyl chloride).

28

2.6.1 PARKESINE

The plastic material, Parkesine was made from cellulose (the major component of plant cell walls)

treated with nitric acid as a solvent. The output of the process (commonly known as cellulose

nitrate or pyroxilin) could be dissolved in alcohol and hardened into a transparent and elastic

material that could be molded when heated. By incorporating pigments into the product, it could

be made to resemble ivory.

2.6.2 BAKELITE

In 1907, Leo Hendrik Baekeland invented the first so called plastic based on a synthetic polymer

which was made from phenol and formaldehyde with the first viable and cheap synthesis.

Baekeland was looking for an insulating shellac to coat wires in electric motors and generators.

He found that combining phenol (C6H5OH) and formaldehyde (HCOH) formed a sticky mass and

later found that the material could be mixed with wood flour, asbestos, or slate dust to create strong

and fire resistant "composite" materials. The new material tended to foam during synthesis,

requiring that Baekeland build pressure vessels to force out the bubbles and provide a smooth,

uniform product, as he announced in 1909, in a meeting of the American Chemical Society

(Watson Peter, 2001). It was an early thermosetting plastic.

2.7 COMPOSITION

Plastics encompass a large and varied group of materials consisting of different combinations or

formulations of carbon, oxygen, hydrogen, nitrogen and other organic and inorganic elements.

Most plastics are a solid in finished form; however, at some stage of their existence, they are a

liquid and may be formed into various shapes. The forming is usually done through the application,

29

either singly or together, of heat and pressure. There are over fifty different, unique families of

plastics in commercial use today and each family may have dozens of variations.

The vast majority of these polymers are based on chains of carbon atoms alone or with oxygen,

sulfur, or nitrogen as well. The backbone is that part of the chain on the main "path" linking a large

number of repeat units together. To customize the properties of a plastic, different molecular

groups "hang" from the backbone (usually they are "hung" as part of the monomers before linking

monomers together to form the polymer chain). The structure of these side chains influences the

properties of the polymer. This fine tuning of the properties of the polymer by repeating unit's

molecular structure has allowed plastics to become an indispensable part of the twenty-first century

world.

2.7.1 ADDITIVES

Most plastics contain other organic or inorganic compounds blended in. The amount of additives

ranges from zero percentage for polymers used to wrap foods to more than 50% for certain

electronic applications. The average content of additives is 20% by weight of the polymer. Fillers

improve performance and/or reduce production costs. Stabilizing additives include fire retardants

to lower the flammability of the material. Many plastics contain fillers, relatively inert and

inexpensive materials that make the product cheaper by weight. Typically fillers are mineral in

origin, e.g., chalk. Some fillers are more chemically active and are called reinforcing agents. Since

many organic polymers are too rigid for particular applications, they are blended with plasticizers,

oily compounds that confer improved rheology. Colorants are common additives, although their

weight contribution is small. Many of the controversies associated with plastics are associated with

the additives (Hans-Georg Elias, 2005).

30

Polymers contain additives for a number of reasons. The following list outlines the purpose of the

main additives used in plastics:

Antistatic Agents: Most polymers, because they are poor conductors of current, build up a charge

of static electricity. Antistatic agents attract moisture from the air to the plastic surface, improving

its surface conductivity and reducing the likelihood of a spark or a discharge.

Coupling Agents: Coupling agents are added to improve the bonding of the plastic to inorganic

filler materials, such as glass fibres. A variety of silanes and titanates are used for this purpose.

Fillers: Some filler, such as short fibres or flakes of inorganic materials, improve the mechanical

properties of a plastic. Others, called extenders, permit a large volume of a plastic to be produced

with relatively little actual resin. Calcium carbonate, silica and clay are frequently used extenders.

Flame Retardants: Most polymers, because they are organic materials, are flammable. Additives

that contain chlorine, bromine, phosphorous or metallic salts reduce the likelihood that combustion

will occur or spread.

Lubricants: Lubricants such as wax or calcium stearate reduce the viscosity of the molten plastic

and improve forming characteristics.

Pigments: Pigments are used to produce colors in plastics.

Plasticizers: Plasticizers are low molecular weight materials which alter the properties and

forming characteristics of the plastic. An important example is the production of flexible grades

of polyvinyl chloride by the use of plasticizers.

Reinforcement: The strength and stiffness of polymers are improved by adding fibres of glass,

carbon, etc.

31

Stabilizers: Stabilizers prevent deterioration of the polymer due to environmental factors.

Antioxidants are added to ABS, polyethylene and polystyrene. Heat stabilizers are required in

processing polyvinyl chloride. Stabilizers also prevent deterioration due to ultra-violet radiation.

2.7.2 POLYMERIC MATERIALS

S7ynthetic large molecules are made by joining together thousands of small molecular units known

as monomers. The process of joining the molecules is called polymerization and the number of

these units in the long molecule is known as the degree of polymerization. The names of many

polymers consist of the name of the monomer with the suffix poly-. For example, the polymers

polypropylene and polystyrene are produced from propylene and styrene respectively.

It is an unfortunate fact that many students and indeed design engineers are reluctant to get

involved with plastics because they have an image of complicated materials with structures

described by complex chemical formulae. In fact it is not necessary to have a detailed knowledge

of the structure of plastics in order to make good use of them. Perfectly acceptable designs are

achieved provided one is familiar with their performance characteristics in relation to the proposed

service conditions. An awareness of the structure of plastics can assist in understanding why they

exhibit a time-dependent response to an applied force, why acrylic is transparent and stiff whereas

polyethylene is opaque and flexible, etc., but it is not necessary for one to be an expert in polymer

chemistry in order to use plastics. The words polymers and plastics are often taken as synonymous

but in fact there is a distinction. The polymer is the pure material which results from the process

of polymerization and is usually taken as the family name for materials which have long chain-

like molecules (and this includes rubbers). Pure polymers are seldom used on their own and it is

when additives are present that the term plastic is applied.

32

2.8 CLASSIFICATION

Plastics are usually classified by their chemical structure of the polymer's backbone and side

chains. Some important groups in these classifications are the acrylics, polyesters, silicones,

polyurethanes, and halogenated plastics. Plastics can also be classified by the chemical process

used in their synthesis, such as condensation, poly-addition, and cross-linking.

2.8.1 THERMOSET

A "Thermoset" is like concrete. You only get one chance to liquefy and shape it. These materials

can be "cured" or polymerized using heat and pressure or as with epoxies a chemical reaction

started by a chemical initiator. Curing (also referred to as vulcanizing) is an irreversible chemical

reaction in which permanent connections (known as cross-links) are made between the materias

molecular chains. These cross-links give the cured polymer a three-dimensional structure, as well

as a higher degree of rigidity than it possessed prior to curing.

It is important to note that a cured, thermoset material will not re-melt or otherwise regain the

process-ability it had before being cured. Curing changes the material forever. Thermoset

polymers outperform other materials (such as thermoplastics) in a number of areas, including

mechanical properties, chemical resistance, thermal stability, and overall durability. For these

reasons, thermoset parts tend to make more effective seals.

2.8.2 THERMOPLASTIC

A "Thermoplastic" is like wax; that is, one can melt it and shape it several times. A thermoplastic

material softens (becomes pliable and plastic) when heated, but it does not cure or set. A

thermoplastic often begins in pellet form, and then becomes softer and more fluid as heat increases.

33

This fluidity allows it to be injected under pressure from a heated cavity into a cool mold. As it

cools, the thermoplastic will harden in the shape of the mold, but there is no chemical curing at

work. No cross-links are formed as with a thermoset material. The changes seen in the

thermoplastic are purely physical and, with the reapplication of heat, wholly reversible. A

thermoplastic material can therefore be reprocessed many times, though continual recycling will

eventually degrade the polymer.

2.8.2.1 CRYSTALLINE AND AMORPHOUS

An important subdivision within the thermoplastic group of materials is related to whether they

have a crystalline (ordered) or an amorphous (random) structure. Some plastics, such as

polyethylene and nylon, can achieve a high degree of crystallinity but they are probably more

accurately described as partially crystalline or semi-crystalline. Other plastics such as acrylic and

polystyrene are always amorphous. The presence of crystallinity in those plastics capable of

crystallizing is very dependent on their thermal history and hence on the processing conditions

used to produce the moulded article. In turn, the mechanical properties of the moulding are very

sensitive to whether or not the plastic possesses crystallinity.

In general, plastics have a higher density when they crystallize due to the closer packing of the

molecules.

34

Table 2.2 Typical characteristics of crystalline and amorphous plastics

AMORPHOUS CRYSTALLINE

Broad softening range - thermal agitation of the

molecules breaks down the weak secondary bonds.

The rate at which this occurs

Sharp melting point the regular close-packed

structure results in most of the secondary bonds being

broken down at the same time.

throughout the formless structure varies producing

broad temperature range for softening.

Usually transparent - the looser structure transmits

light so the material appears transparent.

Usually opaque the difference in refractive indices

between the two phases (amorphous and crystalline)

causes interference so the material appears

translucent or opaque.

Low chemical resistance the more open random

structure enables chemicals to penetrate deep into the

material and to destroy many of the secondary bonds.

High chemical resistance - the tightly packed

structure prevents chemical attack deep within the

material

35

Poor fatigue and wear resistance the random

structure contributes little to fatigue or wear

properties.

Good fatigue and wear resistance the Uniform

structure is responsible for good fatigue and wear

properties.

Source: Ted Pella, 2006

Table 2.3 Examples of amorphous and crystalline thermoplastics

AMORPHOUS CRYSTALLINE

Polyvinyl Chloride (PVC)

Polystyrene (PS) Polycarbonate (PC)

Acrylic (PMMA)

Polyethylene (PE)

Polypropylene (PP)

Polyamide (PA)

Acrylonitrile-butadiene-styrene (ABS)

Polyphenylene (PPO)

Acetal (POM)

Polyester (PETP, PBTP)

Fluorocarbons (PTFE, PFA, FEP and

ETFE)

Source: Ted Pella, 2006

Again, the advances in chemistry make it possible for a chemist to construct a material to be either

thermoset or thermoplastic. The main difference between the two classes of materials is whether

the polymer chains remain "LINEAR" and separate after molding (like spaghetti) or whether they

undergo a chemical change and form a three dimensional network (like a net) by

"CROSSLINKING." Generally a cross-linked material is thermoset and cannot be reshaped.

36

Due to recent advances in polymer chemistry, the exceptions to this rule are continually growing.

These materials are actually cross-linked thermoplastics with the crosslinking occurring either

during the processing or during the annealing cycle. The linear materials are thermoplastic and are

chemically unchanged during molding (except for possible degradation) and can be reshaped again

and again.

As previously discussed, crosslinking can be initiated by heat, chemical agents, irradiation, or a

combination of these. Theoretically, any linear plastic can be made into a cross-linked plastic with

some modification to the molecule so that the crosslinks form in orderly positions to maximize

properties. It is conceivable that, in time, all materials could be available in both linear and cross-

linked formulations.

Figure 2.1 Classification of polymers by property

37

The formulation of a material, cross-linked or linear, will determine the processes that can be used

to successfully shape the material. Generally, cross-linked materials (thermosets) demonstrate

better properties, such as improved resistance to heat, LESS CREEP, better chemical resistance,

etc. than their linear counterpart: however, they will generally require a more complex process to

produce a part, rod, sheet, or tube.

Some examples of the various types of materials:

Linear Thermoplastics

PVC, Nylon, Acrylic, Polycarbonate and Acrylonitrile-butadiene-styrene (ABS).

Thermoplastics Cross-linked after Processing

Polyether ketones (PEEK), Polyamide-imide and UHMWPE.

Thermosets

Phenolics, Epoxies and Melamines

2.9 OTHER CLASSIFICATIONS

Other classifications are based on qualities that are relevant for manufacturing or product design.

Examples of such classes are the thermoplastic and thermoset, elastomer, structural,

biodegradable, and electrically conductive. Plastics can also be classified by various physical

properties, such as density, tensile strength, glass transition temperature, and resistance to various

chemical products.

38

2.9.1 BIODEGRADABILITY

Biodegradable plastics break down (degrade) upon exposure to sunlight (e.g., ultra-violet

radiation), water or dampness, bacteria, enzymes, wind abrasion, and in some instances, rodent,

pest, or insect attack are also included as forms of biodegradation or environmental degradation.

Some modes of degradation require that the plastic be exposed at the surface, whereas other modes

will only be effective if certain conditions exist in landfill or composting systems. Starch powder

has been mixed with plastic as a filler to allow it to degrade more easily, but it still does not lead

to complete breakdown of the plastic. Some researchers have actually genetically engineered

bacteria that synthesize a completely biodegradable plastic, but this material, such as Biopol, is

expensive at present. The German chemical company BASF makes Ecoflex, a fully biodegradable

polyester for food packaging applications.

2.9.2 NATURAL AND SYNTHETIC

Most plastics are produced from petrochemicals. Motivated by the finiteness of petrochemical

reserves and possibility of global warming, bioplastics are being developed. Bioplastics are made

substantially from renewable plant materials such as cellulose and starch.

In comparison to the global consumption of all flexible packaging, estimated at 12.3 million

tonnes/year, estimates put global production capacity at 327,000 tonnes/year for related bioderived

materials (Plastics News, 2011).

39

2.10 REPRESENTATIVE POLYMERS

2.10.1 POLYSTYRENE

Plastic piping and fire stops being installed in Ontario. Certain plastic pipes can be used in some

non-combustible buildings, provided they are fire stopped properly and that the flame spread

ratings comply with the local building code.

Styrene polymerization

Polystyrene is a rigid, brittle, inexpensive plastic that has been used to make plastic model kits and

similar knick-knacks. It would also be the basis for one of the most popular "foamed" plastics,

under the name styrene foam or Styrofoam. Foam plastics can be synthesized in an "open cell"

form, in which the foam bubbles are interconnected, as in an absorbent sponge, and "closed cell",

in which all the bubbles are distinct, like tiny balloons, as in gas-filled foam insulation and flotation

devices. In the late 1950s, high impact styrene was introduced, which was not brittle. It finds much

current use as the substance of toy figurines and novelties.

2.10.2 POLYVINYL CHLORIDE

Polyvinyl chloride (PVC, commonly called "vinyl") incorporates chlorine atoms (Jezek Geno,

2011). The C-Cl bonds in the backbone are hydrophobic and resist oxidation (and burning). PVC

is stiff, strong, heat and weather resistant, properties that recommend its use in devices for

plumbing, gutters, house siding, enclosures for computers and other electronics gear. PVC can also

40

be softened with chemical processing, and in this form it is now used for shrinkwrap, food

packaging, and rain gear.

Vinylchloride polymerization

All PVC polymers are degraded by heat and light. When this happens, hydrogen chloride is

released into the atmosphere and oxidation of the compound occurs. Because hydrogen chloride

readily combines with water vapor in the air to form hydrochloric acid, polyvinyl chloride is not

recommended for long-term archival storage of silver, photographic film or paper (Mylar is

preferable).

2.10.3 NYLON

The plastics industry was revolutionized in the 1930s with the announcement of polyamide (PA),

far better known by its trade name nylon. Nylon was the first purely synthetic fiber, introduced by

DuPont Corporation at the 1939 World's Fair in New York City.

In 1927, DuPont had begun a secret development project designated Fiber66, under the direction

of Harvard chemist Wallace Carothers and chemistry department director Elmer Keiser Bolton.

Carothers had been hired to perform pure research, and he worked to understand the new materials'

molecular structure and physical properties. He took some of the first steps in the molecular design

of the materials.

His work led to the discovery of synthetic nylon fiber, which was very strong but also very flexible.

The first application was for bristles for toothbrushes. However, Du Pont's real target was silk,

41

particularly silk stockings. Carothers and his team synthesized a number of different polyamides

including polyamide 6.6 and 4.6, as well as polyesters (Kinnane Adrian, 2002).

Eq. 5

General condensation polymerization reaction for nylon

It took DuPont twelve years and US$27 million to refine nylon, and to synthesize and develop the

industrial processes for bulk manufacture. With such a major investment, it was no surprise that

Du Pont spared little expense to promote nylon after its introduction, creating a public sensation,

or "nylon mania".

Nylon mania came to an abrupt stop at the end of 1941 when the USA entered World War II.

The production capacity that had been built up to produce nylon stockings, or just nylons, for

American women was taken over to manufacture vast numbers of parachutes for fliers and

paratroopers. After the war ended, DuPont went back to selling nylon to the public, engaging in

another promotional campaign in 1946 that resulted in an even bigger craze, triggering the so

called nylon riots.

Subsequently polyamides 6, 10, 11, and 12 have been developed based on monomers which are

ring compounds; e.g. caprolactam. Nylon 66 is a material manufactured by condensation

polymerization.

42

Nylons still remain important plastics, and not just for use in fabrics. In its bulk form it is very

wear resistant, particularly if oil-impregnated, and so is used to build gears, plain bearings, valve

seats, seals and because of good heat-resistance, increasingly for under-the-hood applications in

cars, and other mechanical parts.

2.10.4 NATURAL RUBBER

Natural rubber is an elastomer (an elastic hydrocarbon polymer) that was originally derived from

latex, a milky colloidal suspension found in the sap of some plants. It is useful directly in this form

(indeed, the first appearance of rubber in Europe was cloth waterproofed with unvulcanized latex

from Brazil). However, in 1839, Charles Goodyear invented vulcanized rubber; a form of natural

rubber heated with sulfur (and a few other chemicals), forming cross-links between polymer chains

(vulcanization), improving elasticity and durability.

2.10.5 SYNTHETIC RUBBER

The first fully synthetic rubber was synthesized by Sergei Lebedev in 1910. In World War II,

supply blockades of natural rubber from South East Asia caused a boom in development of

synthetic rubber, notably styrene-butadiene rubber. In 1941, annual production of synthetic rubber

in the U.S. was only 231 tonnes which increased to 840,000 tonnes in 1945. In the space race and

nuclear arms race, Caltech researchers experimented with using synthetic rubbers for solid fuel for

rockets. Ultimately, all large military rockets and missiles would use synthetic rubber based solid

fuels, and they would also play a significant part in the civilian space effort.

43

2.11 PROPERTIES OF PLASTICS

The properties of plastics are defined chiefly by the organic chemistry of the polymer such as

hardness, density, and resistance to heat, organic solvents, oxidation, and ionizing radiation. In

particular, most plastics will melt upon heating to a few hundred degrees Celsius while plastics

can be made electrically conductive, with the conductivity of up to 80 KS/cm in stretch-oriented

polyacetylene (Heeger, A. J. et al., 1988). They are still no match for most metals like copper

which have conductivities of several hundred KS/cm.

Table 2.4 Properties of plastics

Polystyrene Polypropyle ne Polyethylene

Polycarbona

te

Abbreviation PS PP

HD-PE High

Density

LD-PE Low

Density

PC

Optical

Features

transparent, bright

surface 90 % light

permeability

(with 400-

800nm)

translucent, bright

surface

translucent to

opaque, waxlike

surface

transparent, 88%

light transmission

(at 400 -

800nm)

44

General

Mechanical

Properties

low elongation at

break and heat

resistance,

excellent electrical

insulating features,

not suitable for

high centrifugal

forces

high tensile

strength at break,

insensitive to

tension cracks,

high rigidity

relatively low

tensile strength at

yield and surface

hardness, high

viscosity, soft to

rigid, sensitive to

tension cracks,

water repellent

displays high

levels of

mechanical optical,

electrical, and

thermal properties,

autoclavable and

gamma capable

Autoclavin

g

not suitable

Products made

from PP can be

autoclaved up to

121C without

significantly

impairing their

mechanical

properties. Users

are to test for

themselves if

autoclaving may

have any effect on

other characteristic

product

not suitable

Products made

from PC can be

autoclaved up to

121C without

significantly

impairing their

mechanical

properties. Users

are to test for

themselves if

autoclaving may

have any effect on

other characteristic

product

45

features so as to

influence the

individual

application

concerned.

features so as to

influence the

individual

application

concerned.

Max usage

temperatur

e1

60 - 70C 100 - 110C

HD-PE 70 -

80C

LD-PE 60 -

75C

115 - 125C

Short term

max usage

temperatur

e2

75 - 80C 120 - 140C

HD-PE 90 -

120C

LD-PE 80 -

90C

125 - 140C

Suitable for

application in

temperatur e

ranges below

zero2

not suitable

suitable for

limited

applications1

suitable for

limited

applications1

down to 80C

Density g/cm 1.05 0.90

HD-PE 0.95

LD-PE 0.92

1.19

46

Flammabili

ty

inflammable inflammable inflammable inflammable

Ignition

temperatur

e1

300 - 400C 300 - 360C 350 - 360C 380 - 450C

Humidity

absorption

47

aromatic

substances lead

to the formation

of cracks in PS.

Aromatic and

halogenised

carbon dioxides,

oxididising

substances such

as concentrated

nitric acid and

with higher

temperature fat,

oil and

wax make PP

swell.

alcohol, oil as

well as water

and salt

solutions do not

'attack' PE.

Concentrated,

oxidising acids

such as nitric

acid and

halogens have a

decomposing

effect.

agents, neutral

and acidic saline

solutions, a

number of

fats and oils,

saturated

aliphatic and

cycloaliphatic

hydrocarbons

and alcohols,

except for

methanol. PC is

destroyed by

lyes, ammonia

gas, its solution

and amines. PC

is soluable in a

number of

industrial

solvents, Other

organic

compounds such

as benzene,

acetone and

48

carbon

tetrachloride

tend to make it

expand or swell.

49

Disposal

PS is a pure

hydrocarbon

compound and

thus

environmenta

lly neutral

during disposal.

Incineration

does not yield

any harmful

substances.

PP is a pure

hydrocarbon

compound and

thus

environmenta

lly neutral

during disposal.

Incineration

does not yield

any harmful

substances.

PE is a pure

hydrocarbon

compound and

thus

environmenta

lly neutral

during disposal.

Incineration

does not yield

any harmful

substances.

PC is a pure

hydrocarbon

compound and

thus

environmenta

lly neutral

during disposal.

Incineration

does not yield

any harmful

substances.

Source: Ted Pella, 2006

1 - Suitability depending on the plastic material and the nature of load applied.

Plastics start to become brittle at temperatures below zero. The suitability of products intended for

use in these temperature ranges

2 - Caution: should be tested prior to application. These notes serve as a guideline only and do not

constitute any confirmation of warranted quality.

2.12 ENVIRONMENTAL IMPACT

Plastics are durable and degrade very slowly; the chemical bonds that make plastic so durable

make it equally resistant to natural processes of degradation. Since the 1950s, one billion tons of

plastic have been discarded and may persist for hundreds or even thousands of years (Alan

50

Weisman, 2010). Perhaps the biggest environmental threat from plastic comes from nurdles, which

are the raw material from which all plastics are made. They are tiny pre-plastic pellets that kill

large numbers of fish and birds that mistake them for food.

Prior to the ban on the use of CFCs in extrusion of polystyrene (and general use, except in life-

critical fire suppression systems; see Montreal Protocol), the production of polystyrene contributed

to the depletion of the ozone layer; however, non-CFCs are currently used in the extrusion process.

2.12.1 COMMON PLASTICS AND USES

Due to their relatively low cost, ease of manufacture, versatility, and imperviousness to water,

plastics are used in an enormous and expanding range of products, from paper clips to spaceships.

They have already displaced many traditional materials, such as wood, stone, horn and bone,

leather, paper, metal, glass, and ceramic, in most of their former uses.

Polyester (PES) Fibers, textiles.

Polyethylene terephthalate (PET) Carbonated drinks bottles, peanut butter jars, Plastic film,

microwavable packaging.

Polyethylene (PE) Wide range of inexpensive uses including supermarket bags, plastic

bottles.

High-density polyethylene (HDPE) Detergent bottles, milk jugs, and molded plastic cases.

Polyvinyl chloride (PVC) Plumbing pipes and guttering, shower curtains, window frames,

flooring.

Polyvinylidene chloride (PVDC) (Saran) Food packaging.

51

Low-density polyethylene (LDPE) Outdoor furniture, siding, floor tiles, shower curtains,

clamshell packaging.

Polypropylene (PP) Bottle caps, drinking straws, yogurt containers, appliances, car fenders

(bumpers), plastic pressure pipe systems.

Polystyrene (PS) Packaging foam/"peanuts", food containers, plastic tableware, disposable

cups, plates, cutlery, CD and cassette boxes.

High impact polystyrene (HIPS) -: Refrigerator liners, food packaging, vending cups.

Polyamides (PA) (Nylons) Fibers, toothbrush bristles, fishing line, under-the-hood car engine

moldings, tubings.

Acrylonitrile butadiene styrene (ABS) Electronic equipment cases (e.g., computer monitors,

printers, keyboards), drainage pipe.

Polycarbonate (PC) Compact discs, eyeglasses, riot shields, security windows, traffic

lights, lenses.

Polycarbonate/Acrylonitrile Butadiene Styrene (PC/ABS) A blend of PC and ABS that

creates a stronger plastic. Used in car interior and exterior parts and mobile phone bodies.

Polyurethanes (PU) Cushioning foams, thermal insulation foams, surface coatings, printing

rollers (Currently 6th or 7th most commonly used plastic material, for instance the most commonly

used plastic in cars).

52

2.12.2 PLASTIC WASTES

The plastic is one of the recent engineering materials which have appeared in the market all over

the world. Some varieties of naturally occurring thermoplastics were known to Egyptians and

Romans who extracted and used these plastics for various purposes. Plastics were used in bath and

sink units, corrugated and plain sheets, floor tiles, joint less flooring, paints and varnishes and wall

tiles. Other than these, domestically plastics were used in various forms as nylon bags, bottles,

packing strip, cans and also in various medical utilities. There has been a steep rise in the

production of plastics from a mere 30 million KN in 1955; it has touched 1000 million KN at

present. It is estimated that on an average 25% of the total plastic production in the world is used

by the building industry. The per capita consumption of plastics in the developed countries ranges

from 500 to 1000N (Gowri et al., 2005). There is however now increase in awareness regarding

the utilization of plastic as a useful building material in our country. These types of usages

normally generate more amounts of wastes which are to be disposed off properly.

Environmentally sensitive aware people condemn the use of plastics for amount of pollution

caused by them in disposal. However this is not a serious problem in comparison to the waste and

pollution generated by a host of other industries. The non-biodegradable plastic products used for

soft drink bottles, milk and juice bottles, bread bags, syrup bottles, coffee cups, plastics utensils

etc., can be conveniently recycled into carpets, detergent bottle, drainage pipes, fencing, handrails,

grocery bags, car battery cases, pencil holders, benches, picnic tables, road side posts etc., The

developing construction field consumes a huge amount of concrete and it leads to the depletion of

natural products and causes environmental pollution.

53

Plastics are normally stable and not biodegradable. So, their disposal poses problems. Research

works are going on in making use of plastics wastes effectively as additives in bitumen mixes for

the road pavements. Reengineered plastics are used for solving the solid waste management

problems to great extent.

2.12.3 RECYCLING

Thermoplastics can be remelted and reused, and thermoset plastics can be ground up and used as

filler, although the purity of the material tends to degrade with each reuse cycle. There are methods

by which plastics can be broken back down to a feedstock state.

The greatest challenge to the recycling of plastics is the difficulty of automating the sorting of

plastic wastes, making it labor intensive. Typically, workers sort the plastic by looking at the resin

identification code, although common containers like soda bottles can be sorted from memory.

Typically, the caps for PETE bottles are made from a different kind of plastic which is not

recyclable, which presents additional problems to the automated sorting process. Other recyclable

materials such as metals are easier to process mechanically. However, new processes of

mechanical sorting are being developed to increase capacity and efficiency of plastic recycling.

While containers are usually made from a single type and color of plastic, making them relatively

easy to be sorted, a consumer product like a cellular phone may have many small parts consisting

of over a dozen different types and colors of plastics. In such cases, the resources it would take to

separate the plastics far exceed their value and the item is discarded.

However, developments are taking place in the field of active disassembly, which may result in

more consumer product components being re-used or recycled. Recycling certain types of plastics

can be unprofitable, as well. For example, polystyrene is rarely recycled because it is usually not

54

cost effective. These unrecycled wastes are typically disposed of in landfills, incinerated or used

to produce electricity at waste-to-energy plants.

A first success in recycling of plastics is Vinyloop, a recycling process and an approach of the

industry to separate PVC from other materials through a process of dissolution, filtration and

separation of contaminations. A solvent is used in a closed loop to elute PVC from the waste. This

makes it possible to recycle composite structure PVC waste which normally is being incinerated

or put in a landfill. Vinyloop-based recycled PVC's primary energy demand is 46 percent lower

than conventional produced PVC. The global warming potential is 39 percent lower. This is why

the use of recycled material leads to a significant better ecological footprint (Life cycle of a plastic

product, 2011).

In 1988, to assist recycling of disposable items, the Plastic Bottle Institute of the Society of the

Plastics Industry devised a now-familiar scheme to mark plastic bottles by plastic type. A plastic

container using this scheme is marked with a triangle of three "chasing arrows", which encloses a

number giving the plastic type:

Plastics type marks: the resin identification code

PET (PETE), polyethylene terephthalate

HDPE, high-density polyethylene

PVC, polyvinyl chloride

55

LDPE, low-density polyethylene,

PP, polypropylene

PS, polystyrene

Other types of plastics

2.13 PAST RESEARCH WORKS ON PLASTIC CONCRETE

Agarwal F. (2004) has conducted pilot level studies using industrial PVC scrap to develop PVC

board. Efforts have been made in developing innovative number of such alternative building

materials. These would be helpful in saving our precious forest and environment efficiently and

economically on commercial exploitation. Developed materials are mostly wood alternatives used

in the construction of door shutters, frames, false ceiling, thermal insulation and alike applications.

Developed sustainable alternative building materials are good economic replacement of wood and

other reconstituted wood products commercially available and would be helpful in cost effective

constructions.

Vasudevan (2004), in his report has given most useful ways of disposing waste plastics and laying

roads have come to light in a research carried out by the Chemistry Department of Thiyagarajar

College of Engineering. They have reported that the waste plastics may be used in block making

modified light roofing, mastic flooring and polymer reinforced concrete. The novel composition

of waste polymer-aggregate blend has been patented. They have suggested that utilization of waste

plastics to enhance the binding property is better option than disposing or enforcing a blanket ban

on the use of plastics. It has been reported that the per capita use of plastics in India is 3.5 kg, with

virgin plastics accounting for 3.1 million tonnes and recycled plastics, one million. The use in

56

Tamilnadu, with over 7000 units manufacturing material is put at 2.4 lakh tonnes per year. The

Garbage Culture has made disposal of waste plastic a major problem for civic bodies.

Disposal of used plastics by land filling may be temporary solution and also affects ground water

recharging and soil microbe activities. Incineration of plastic material will cause air pollution,

global warming and monsoon failure. Investigations done so far have shown that waste plastics

can be utilized for making polymer aggregate blocks with ceramics and granite, which can be used

in laying footpaths. The blocks can take 350 tonnes of load and prevents water penetration. They

can also be used in lining of canals. A bitumen blend can be used as a coat over reinforced

cardboard for roofing. Besides enhancing the strength and life of roofing, used by the poor, the

blend will provide better moisture resistant. A blend of waste plastics with mastic components and

flooring materials provides floors of more strength, especially in industrial units. Waste polymers

also infuse greater strength when mixed with cement as a reinforced concrete. The author

suggested the residents and the users to segregate the plastics in their area and to pool the

segregated plastics for laying road with assistance of the civic body. Non-Governmental

organizations can be involved in the collection of plastic waste and its segregation, taking in to

account the money it can fetch.

Lakshmipathy et al. (2003) have done experimental investigations to study the suitability of the

use of Re-engineered plastics as fibers for road pavements. The properties studied include

compressive strength, tensile strength, flexural strength under reversed cyclic loading, impact

resistance, plastic shrinkage and abrasion resistance etc., Efforts have been made to compare it

steel fibers. The results have shown that the improvement of concrete properties at lower cost is

obtained with Re-engineered plastic shred reinforced concrete.

57

Prabir Das (2004) has suggested that plastics can be used in construction industry at various places.

Proper selection of material grade and suitable design considerations can help to replace many

more applications. Lighter weight, design flexibility, part integration, low system cost, very high

productivity and improved product appearance are the main features for use of engineering

plastics. The engineering thermoplastics and introduction of application specific grades has thrown

challenges to conventional materials in the industries. This paper provides all the supports in