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Environmental and Cost Advantages of Using Polyethylene Terephthalate Fibre Reinforced Concrete with Fly Ash as a Partial Cement Replacement

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Solid waste disposal is an alarming problem in most African countries. Plastic wastes like Polyethylene Terephthalate (PET) bottles and powdered wastes like fly ash are severely persisting environmental hazards. They are brutally polluting the water bodies, landfills, as well as the atmosphere. The construction industry has been working towards improving concrete quality by developing alternative methods like partial cement replacement with different pozzolanic elements as well as using waste fibrous materials. Fly ash and PET bottle fibres are two common waste materials that can be used. This article is a part of a research that studied the combined effects of the addition of PET bottle fibres and fly ash (as a partial cement replacement) on the structural performance of concrete. From a purely engineering point of view, the research results indicate that the utilization and incorporation of PET and fly ash wastes in the construction industry are a viable solution to make concrete quality better. This article presents, beyond the engineering properties and experimental works, the economic and environmental advantages of the addition of these waste materials to the conventional concrete mixture. The addition of PET bottle fibres and fly ash resulted in positive cost implications providing a production cost reduction of 19% over the conventional concrete mixture. The removal of these materials from the environment also showed reduction of the emission of toxic elements to landfills and water bodies that put human, animal and plant lives in danger.
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Open Journal of Civil Engineering, 2019, 9, 281-290
https://www.scirp.org/journal/ojce
ISSN Online: 2164-3172
ISSN Print: 2164-3164
DOI:
10.4236/ojce.2019.94020 Oct. 29, 2019 281
Open Journal of Civil Engineering
Environmental and Cost Advantages of Using
Polyethylene Terephthalate Fibre Reinforced
Concrete with Fly Ash as a Partial Cement
Replacement
Rebecca Belay Kassa1*, Christopher Kanali2, Nathaniel Ambassah3
1Department of Civil Engineering, Pan African University Institute for Basic Sciences, Technology and Innovation (PAUSTI),
Nairobi, Kenya
2Department of Agricultural and Biosystems Engineering, Jomo Kenyatta University of Agriculture & Technology (JKUAT),
Nairobi, Kenya
3Department of Civil Engineering, Jomo Kenyatta University of Agriculture & Technology (JKUAT), Nairobi, Kenya
Abstract
Solid waste disposal is an alarming problem in most African countries. Plastic
wastes like Polyethylene Terephthalate (PET) bottles and
powdered wastes
like fly ash are severely persisting environmental hazards. They are brutally
polluting the water bodies, landfills, as well as the atmosphere. The construc-
tion industry has been working towards improving concrete quality by de-
veloping alte
rnative methods like partial cement replacement with different
pozzolanic elements as well as using waste fibrous materials. Fly ash and PET
bottle fibres
are two common waste materials that can be used. This article is
a part of a research that studied th
e combined effects of the addition of PET
bottle fibres and fly
ash (as a partial cement replacement) on the structural
performance of concrete. From a purely engineering point of view, the re-
search results indicate that th
e utilization and incorporation of PET and fly
ash wastes in the construction industry are a viable solution to make concrete
quality better. This article presents,
beyond the engineering properties and
experimental works, the economic and environmental advantages of the ad-
dition of these waste materials to the conventional concrete mixture. The ad-
dition of PET bottle fibres
and fly ash resulted in positive cost implications
providing a production cost reduction of 19% over the conventional concrete
mixture
. The removal of these materials from the environment also showed
reduction of the emission of toxic elements to landfills
and water bodies that
put human, animal and plant lives in danger.
How to cite this paper:
Kassa, R.B., Kana-
li,
C. and Ambassah, N. (2019) Environ-
mental and Cost
Advantages of Using Po-
lyethylene Terephthalate Fibre Reinforced
Concrete with Fly Ash as a Partial Cement
Replacement
.
Open Journal of Civil Eng
i-
neering
,
9
, 281-290.
https://doi.org/10.4236/ojce.2019.94
020
Received:
September 25, 2019
Accepted:
October 26, 2019
Published:
October 29, 2019
Copyright © 201
9 by author(s) and
Scientific
Research Publishing Inc.
This work is licensed under the Creative
Commons Attribution International
License (CC BY
4.0).
http://creativecommons.org/licenses/by/4.0/
Open Access
R. B. Kassa et al.
DOI:
10.4236/ojce.2019.94020 282
Open Journal of Civil Engineering
Keywords
Concrete, PET, Fly Ash, Cost, Environment, Pollution, Landfill
1. Introduction
Solid waste disposal is an alarming environmental problem in most African
countries. Plastic wastes like Polyethylene Terephthalate (PET) bottles and pow-
dered wastes like fly ash are severely persisting environmental challenges. They
are obnoxiously polluting the water bodies, landfills, as well as the atmosphere.
This in turn destroys human, animal and plant lives. Recently studies are being
done regarding using waste materials in concrete mixes both to improve its
quality as well as to benefit the environment. The construction industry has been
working towards minimizing the cement usage and improving concrete quality
by developing alternative methods like partial cement replacement with different
pozzolanic elements as well as using waste fibrous materials. Fly ash and PET
bottle fibres are two of the common waste materials that are currently polluting
the environment. This article is a part of a research that studied the combined
effects of the addition of PET bottle fibres and fly ash (as a partial cement re-
placement) on the structural performance of concrete. The study investigated
the effects of the addition of PET bottles and fly ash on the engineering proper-
ties and flexural performance of concrete. PET bottles with an aspect ratio of 50
(100 mm length and 2 mm width) and fly ash were added to the concrete mix at
different percentages and optimized as per the experimental work results. The
optimized percentages of PET bottle fibres and fly ash are 1.5% and 27.5% by
weight of concrete respectively [1] and [2]. From a purely engineering point of
view, these results indicate that the utilization and incorporation of PET and fly
ash wastes for the improvement of concrete quality are a move in the right direc-
tion and are highly recommended. However, other considerations like cost and
environmental advantages should be assessed before the materials are used
widely.
The environmental and economic advantages of waste minimization and re-
cycling are undeniable as both the environment and the construction industry
benefit in terms of pollution and cost reduction respectively. A study by [3]
looked into the effects of recycling waste materials (glass, plastic and demo-
lished concrete) and using them in a concrete mix. Alongside the engineering
properties, the results of the study showed that there was a significant reduc-
tion in cost of waste disposal and construction expenses. Another study by [4]
also studied the early age strength development of concrete with the addition
of Activator Blast Furnace Slag. The results of this study revealed that the de-
velopment of early age strength of concrete contributed to the reduction of
construction period. This in turn had an economic advantage. The experi-
mental results of compressive strength and sorptivity of PET fibre reinforced
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concrete were given by [5]. Fibres used were made from plastic bottle wastes
which are non-biodegradable. The study presented that the addition of waste
materials reduced the cost of the plastic fibre reinforced concrete while at the
same time resolving the problem of solid waste disposal. It was reported by [6]
that the partial cement replacement of concrete using fly ash as a replacing ma-
terial reduced construction and production costs. The study also underscored
that concrete modified with fly ash was more cost effective compared to the
conventional ordinary Portland cement concrete.
The other significant benefit of modifying concrete with waste materials is
reducing the risks the environment is facing. PET bottles are one of the major
non-biodegradable plastic wastes that are considered to be dangerous for the en-
vironment. Fly ash again is a by-product of burning coal for energy generation.
Because of the chemical it consists, it negatively affects soil, plants, atmosphere
and the environment in general if not disposed properly. As this study is pro-
posing to use these products for construction, it is definitely contributing to the
benefit of saving the environment from the undesirable effects it is facing.
This article presents, beyond the engineering properties and experimental
works, the combined economic and environmental advantages of the addition of
PET bottle fibres and fly ash to the conventional concrete mixture. By doing so,
it presents the necessary information for further researchers as well as individu-
als or companies that might want to use these materials in concrete production.
2. Materials and Methods
The purpose of this article is to meticulously analyze the actual utilization and
management of PET and fly ash wastes by incorporating them in the construc-
tion industry and finding out whether or not costs can be saved by adopting a
more sustainable and judicious use. It also addresses how much plastic and
powdered waste can be collected from the environment reducing a long term
risk of pollution. The study was carried out at the Pan African University Insti-
tute for Basic Sciences, Technology and Innovation which is hosted at the Jomo
Kenyatta University of Agriculture and Technology in Nairobi, Kenya.
2.1. Cost Implication
The analysis crystallises into a statement of costs and returns and shows the
gains or losses of a relative change in the pattern of use and management of
these waste materials in concrete production. This will provide expected change
in cost. The analysis takes into account only those changes in costs and returns
that result directly from the proposed new practices (s). More precisely, this
analysis is concerned with the costs that can be changed by partially replacing
cement with fly ash and addition of PET bottle fibers. The major costs in con-
sideration are material costs, transportation costs and labor costs.
The comparison includes the production cost of one cubic metre of conven-
tional concrete to the production cost of the same quantity of concrete modified
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with waste materials (fly ash and PET bottle fibres). Evaluation on cost of con-
crete production using both methods will be done through preparing the ma-
terial breakdown for one cubic metre concrete and identifying the unit prices of
the materials needed including labour and transportation cost. The comparison
will then be based on the cost saving of both types of concrete.
A mix design ratio of 1:1.63:3.13 was used for cement, coarse and fine aggre-
gates respectively in order to carry out the experimental research study. The wa-
ter to binder ratio used was 0.6. Cement, fly ash, coarse aggregates and fine ag-
gregates were purchased from local distributors. The unit cost for each of these
materials including transportation and labour cost was collected from the avail-
able price range in the Kenyan market.
PET bottles were collected from the surrounding environment. They were
washed, dried and cut into rectangular fibre strips (Figure 1). Only the mid-section
of the bottles was used in the process of preparation of the fibres as it is a uniform
section. Therefore, the top and bottom sections of the bottles were superfluous
(Figure 2). Following this, the amount of fibres acquired from one bottle was
five (5) grams. As one bottle on average weighs 18 grams, this leaves 13 grams of
cleaned part of the bottle. The cost involved with the PET fibres includes labor
cost for collection and cleaning as well as cost for cutting. After extracting the
fibres from each bottle, the remaining part was sold to plastic recycling compa-
nies. This was considered as an income and was deducted from the cost of PET
fibre preparation.
The total cost calculation of each item or service includes the collection of re-
spective unit prices from the available market and multiplying it by the quantity
needed to produce one cubic meter of concrete. Equation (1) summarizes the
cost calculation for each item or service. In the equation, UP represents unit
price, TP represents total price and Q represents quantity of the items.
2.2. Environmental Implication
Waste PET bottles used for packaging of water, soft drinks and other beverages
Figure 1. PET fibre preparation.
Collecting Cleaning Fibres
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Figure 2. A representation of the parts of the PET bottle
that were disposed and used for fibre preparation.
are seen covering the surrounding environment in most African countries.
Landfills, sewerage systems as well as water bodies are infested by the abundance
of litter from the improperly disposed bottles blocking and clogging sewerage
systems, killing animals and destroying marine life once they are ingested [7].
Beyond its physical harm, the improper disposal of PET bottles has a serious
chemical impact. Although they can be degraded (broken into smaller portions)
due to different environmental factors like the sun and the rain, PET bottles are
non-biodegradable (consumed by living organisms). The photo degradation of
these bottles releases toxic chemicals in small portions for a very long time. Cur-
rently waste plastic bottles are covering and releasing these toxins into water bo-
dies, landfills and the atmosphere in general. This again upsets the environment
killing human beings, animals and plants slowly [8].
The assessment of the environmental advantages of using polyethylene te-
rephthalate fibre reinforced concrete with fly ash as a partial cement replacement
focuses on the physical and chemical effects of waste PET bottles on the envi-
ronment and sheds light accordingly on the benefits of using these waste bottles
in the construction industry. The physical aspect deals with land and water bo-
dies covered with improperly disposed bottles as well as their ingestion by ani-
mals and underwater beings. The chemical aspect on the other hand reveals the
toxic chemicals that are released as PET bottles are carelessly disposed in differ-
ent parts of the environment. It then provides the advantage of recycling the
bottles to incorporate them in concrete production.
The rapid industrial development, environmental pollution from the bypro-
ducts is becoming a pressing issue. Fly ash generated from the combustion of
coal in thermal power plants is usually disposed in the open landfills. It has a
high surface concentration of a number of toxic elements. Following its light
weight and high atmospheric mobility, the particles of fly ash enter the terrestrial
and aquatic environment, making the dissipation of the toxic elements of fly ash
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even a worse [9]. This section also focuses on quantifying the risks of fly ash im-
properly disposed in the landfills and the advantages of recycling it to be used in
the construction industry.
3. Results and Discussions
3.1. Cost Implications
The cost implications were calculated by comparing the price of preparation of
one cubic meter of the conventional concrete with price of preparation of the
same volume of the modified concrete. The material breakdown according to the
mix design ratio used for this particular study was arranged. Table 1 shows the
material compositions needed to produce one cubic meter of both control and
modified mixes.
Depending on the material composition needed, the unit prices of each ma-
terial including labour and transportation were collected from the available
Kenyan market. The prices and amounts of coarse aggregate, fine aggregate
and water stay the same for both control and modified concrete. The amount
needed for purchasing and transporting of the coarse and fine aggregates was
taken as per the local distributors’ price. The cost of water on the other hand was
taken from the tariff set by Nairobi City Water and Sewerage Company. A rapid
market appraisal survey was done interviewing five local distributors within the
available market and it revealed that the average price of each of the materials
needed per kilogram. Accordingly, Table 2 and Table 3 give the summary of
costs related to each material for control and modified concrete mixes respec-
tively.
The cost of binder (cement and fly ash) needed to produce one cubic meter of
concrete decreased by 19.25% for the modified concrete as compared to the con-
trol concrete. This is due to partial (27.5%) cement replacement by fly ash. The
price of one (1) kilogram of cement including transportation and offloading
costs is 28 KSh while the price of the same amount of fly ash including transpor-
tation and offloading costs is 8.4 KSh. This shows that fly ash is a cost effective
alternative to cement.
Table 1. Material composition for the preparation of one cubic meter of conventional
concrete and one cubic meter of modified concrete.
Material Modified Mix (kg/m3) Control Mix (kg/m3)
Cement 266.15 367.11
Fly ash 100.95 -
Coarse aggregate 1150 1150
Fine aggregate 583 583
Water 221.26 221.26
PET fibres 5.51 -
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Table 2. Quantity and price of materials to prepare one cubic meter of control concrete.
Type and description of Material Unit price per Kg
(Kenyan Shillingsa)
Quantity
(Kg)
Total Price
(Kenyan Shillings)
Ordinary Portland Cement, delivered
and offloaded 28 367.11 10,279.08
Fly ash, delivered and offloaded - - -
Coarse aggregate, delivered and offloaded 3 1,150 3450
Fine aggregate, delivered and offloaded 2.5 583 1457.5
Water 0.053 221.26 11.73
PET fibres, collection, cleaning and cutting - - -
Total 15,198.31
a. The current official exchange rate is 1 USD = 100 Kenyan Shillings.
Table 3. Quantity and price of materials to prepare one cubic meter of modified concrete.
Type and description of Material Unit price per Kg
(Kenyan Shillings)
Quantity
(Kg)
Total Price
(Kenyan Shillings)
Ordinary Portland Cement, delivered and
offloaded 28 266.15 7452.2
Fly ash, delivered and offloaded 8.4 100.95 847.98
Coarse aggregate, delivered and offloaded 3 1150 3450
Fine aggregate, delivered and offloaded 2.5 583 1457.5
Water 0.053 221.26 11.73
PET fibres, collection, cleaning and cutting 100 5.51 551
Extra PET bottle to be sold 70 14.326 1002.82
Total 12,767.59
PET bottles that were collected from the surrounding environment had costs
of collection, cleaning and cutting into rectangular fibres. This particular re-
search used manual method of cutting the bottles into fibres therefore, machine
cutting costs are not included. The labor cost was 100 Kenyan Shillings per one
(1) kilogram of PET fibres. Only the mid-section of the bottle was used for ex-
tracting the fibres. The remaining top and bottom sections were sold to recycling
companies instead of disposing them back into the environment. This was also
considered as money returned and deducted from the labor cost for collection
and processing of PET bottles.
Generally, the total cost of production of one cubic meter of conventional
concrete mix as per the mix design used was 15,198.31 KSh while the modified
concrete mix would require 12,767.59 KSh for production. Thus, by using po-
lyethylene terephthalate fibre reinforced concrete with fly ash as a partial cement
replacement to produce one cubic meter of modified conrete 2430.72 KSh was
saved. Therefore, beyond the improvement in performance of concrete, the ad-
dition of PET bottle fibres and fly ash has positive cost implications providing a
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production cost reduction of 19%. This goes in line with conclusions drawn by
[3] [4] [5] [6].
3.2. Environmental Implications
3.2.1. PET Bottle Fibres
The material composition for the production of one (1) cubic meter of the con-
crete modified with PET fibres and fly ash as per the mix design ratio of this
study requires 5.51 Kg of PET fibres. Five (5) grams of fibres can be extracted
from one bottle. This makes the total number of bottles collected from the envi-
ronment to produce one (1) cubic meter of concrete 1,102 which is about 20 kilo-
grams (including the sections of the bottles that are not used to cut fibres from).
In December 2018 [10] published Kenya PET Recycling company’s statement
testifying the annual production of PET in Kenya is 20,000 tons and only 1000
tons (5%) is recycled. The remaining waste bottles end up layering landfills,
clogging sewerage systems and covering water bodies. Instead of being used for a
valuable purpose, the land covered by the excessive waste PET bottles is left to be
polluted by the toxic chemicals emitted during the photo degradation of the bot-
tles. When dumped to landfill, they disrupt the natural production of enzymes in
the soil. This interrupts the fertility of the soil causing a serious issue in the
agricultural sector. The polluting chemicals that are released include heavy met-
als like Cadium and Lead as well as chemicals as Benzene and Dioxin. Beyond
this leachate is produced in landfills leaking into surface and ground water. This
in turn risks human and animal health [8]. Animals and marine life exposed to
these waste bottles on the other hand ingest them and end up choking or failing
to digest or even get entangled.
Different ways of disposing PET bottles and their life cycle sustainability as-
sessment were looked up by [11]. One of these practiced disposal ways of PET
bottles in the study was landfills. It was based on the disposal of 1 tonne of PET
bottles as a functional unit. It showed the landfilling scenario was the only sce-
nario to negatively affect human health, ecosystem quality and resources. This
made disposal of PET bottles to the landfill the worst scenario at hand. Based on
this information alongside other studies, this study used an approach to reduce
the impact in the environment. The collection of 20 kilograms of PET bottles
from the surrounding just to produce one (1) cubic meter of concrete is an es-
sential move towards the recycling of these bottles as well as improving concrete
behavior. The incorporation of these bottles in the construction industry gives
room for the landfill reducing the possibility of pollution.
3.2.2. Fly Ash
The production of one (1) cubic meter of modified concrete as per this study
requires 100.95 kilograms of fly ash. This removes a great deal of fly ash from the
landfills. It is a critical solution to prevent the environment from excessive pol-
lution by improperly disposed fly ash. Fly ash is composed of harmful heavy
metals like arsenic, lead, nickel, cobalt, chromium, boron and antimony. The
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Table 4. Concentration of heavy metals in fly ash.
Element Concentration per Kg of Fly ash (mg/kg)
Chromium (Cr) 87 - 103
Manganese (Mn) 47 - 139
Lead (Pb) 20 - 56
Zinc (Zn) 60 - 124
Copper (Cu) 56 - 83
Nickel (Ni) 28 - 63
Cobalt (Co) 8 - 18
emission of these elements to soil, surface and ground water by the leaching
process has a massive impact on human, animal and plant lives [12]. The ash
content of fly ash and the constituent elements were delivered by. [13]. It re-
vealed the concentration of toxic heavy metals per kilogram of fly ash. Table 4
shows this concentration as presented by [13].
The study further discussed the release of these metals to the environment
would mean plant and animals are exposed to them and through time it gets
through the food chain, which disrupts the whole ecosystem.
Therefore, this study has a potential to contribute to the environment by re-
moving 100.95 kilograms of fly ash and in turn preventing the heavy metals
from being emitted.
4. Conclusion
This paper looked at the cost and environmental advantages of incorporating
PET bottle fibres and fly ash to a conventional concrete mix. From the results,
the addition of PET bottle fibres and fly ash as a partial replacement of cement
showed positive cost implications, reducing the production cost for one cubic
meter of concrete by 19%. Similarly, the collection of improperly disposed PET
bottles and fly ash from the surrounding environment to be used in the con-
struction industry safeguards animals, plants and human beings. It reduces the
emission of toxic elements to landfill and water bodies. Therefore, beyond the
improvements on the structural performance of the concrete, PET bottle fibres
and fly ash have positive cost and environmental advantages if used as concrete
constituent materials. It can safely be concluded that the combination of the two
materials can be a way forward in the production of concrete.
Conflicts of Interest
The authors declare no conflicts of interest regarding the publication of this
paper.
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... Even replacing all virgin aggregates with recycled aggregates will reduce CO2 emissions by only 1%. But the use of recycled aggregates is important as it can reduce landfills and support sustainable development (Kassa;Kanali;Ambassah, 2019). So, there is a need to incentivize its use (Obla, 2009). ...
... Even replacing all virgin aggregates with recycled aggregates will reduce CO2 emissions by only 1%. But the use of recycled aggregates is important as it can reduce landfills and support sustainable development (Kassa;Kanali;Ambassah, 2019). So, there is a need to incentivize its use (Obla, 2009). ...
... Even replacing all virgin aggregates with recycled aggregates will reduce CO2 emissions by only 1%. But the use of recycled aggregates is important as it can reduce landfills and support sustainable development (Kassa;Kanali;Ambassah, 2019). So, there is a need to incentivize its use (Obla, 2009). ...
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Fly ash, generated during the combustion of coal for energy production, is an industrial by-product which is recognized as an environmental pollutant. Because of the environmental problems presented by the fly ash, considerable research has been undertaken on the subject worldwide. In this paper, the utilization of fly ash in construction, as a low-cost adsorbent for the removal of organic compounds, flue gas and metals, light weight aggregate, mine back fill, road sub-base, and zeolite synthesis is discussed. A considerable amount of research has been conducted using fly ash for adsorption of NOx, SOx, organic compounds, and mercury in air, dyes and other organic compounds in waters. It is found that fly ash is a promising adsorbent for the removal of various pollutants. The adsorption capacity of fly ash may be increased after chemical and physical activation. It was also found that fly ash has good potential for use in the construction industry. The conversion of fly ash into zeolites has many applications such as ion exchange, molecular sieves, and adsorbents. Converting fly ash into zeolites not only alleviates the disposal problem but also converts a waste material into a marketable commodity. Investigations also revealed that the unburned carbon component in fly ash plays an important role in its adsorption capacity. Future research in these areas is also discussed.
Impact of Plastics on Environmental Pollution
  • P Pavani
  • R Rajeswari
Pavani, P. and Rajeswari, R. (2014) Impact of Plastics on Environmental Pollution. Journal of Chemical and Pharmaceutical Sciences, 2014, 2087-2093.