Recycled Plastic in Concrete: A Review

Review
Use of recycled plastic in concrete: A review
Rafat Siddique
a,*
, Jamal Khatib
b
, Inderpreet Kaur
a
a
Thapar Institute of Engineering and Technology, Deemed University, Patiala – 147 004, India
b
School of Engineering and the Built Environment, University of Wolverhampton, City Campus, Wolverhampton, West Midlands WV1 1SB, United Kingdom
Accepted 15 September 2007
Available online 5 November 2007
Abstract
Numerous waste materials are generated from manufacturing processes, service industries and municipal solid wastes. The increas-
ing awareness about the environment has tremendously contributed to the concerns related with disposal of the generated wastes.
Solid waste management is one of the major environmental concerns in the world. With the scarcity of space for landfilling and
due to its ever increasing cost, waste utilization has become an attractive alternative to disposal. Research is being carried out on
the utilization of waste products in concrete. Such waste products include discarded tires, plastic, glass, steel, burnt foundry sand,
and coal combustion by-products (CCBs). Each of these waste products has provided a specific effect on the properties of fresh
and hardened concrete. The use of waste products in concrete not only makes it economical, but also helps in reducing disposal prob-
lems. Reuse of bulky wastes is considered the best environmental alternative for solving the problem of disposal. One such waste is
plastic, which could be used in various applications. However, efforts have also been made to explore its use in concrete/asphalt con-
crete. The development of new construction materials using recycled plastics is important to both the construction and the plastic
recycling industries.
This paper presents a detailed review about waste and recycled plastics, waste management options, and research published on the
effect of recycled plastic on the fresh and hardened properties of concrete. The effect of recycled and waste plastic on bulk density, air
content, workability, compressive strength, splitting tensile strength, modulus of elasticity, impact resistance, permeability, and abrasion
resistance is discussed in this paper.
2007 Elsevier Ltd. All rights reserved.
1. Introduction
Plastics have become an inseparable and integral part of
our lives. The amount of plastics consumed annually has
been growing steadily. Its low density, strength, user-
friendly designs, fabrication capabilities, long life, light
weight, and low cost are the factors behind such phenom-
enal growth. Plastics have been used in packaging, automo-
tive and industrial applications, medical delivery systems,
artificial implants, other healthcare applications, water
desalination, land/soil conservation, flood prevention,
preservation and distribution of food, housing, communi-
cation materials, security systems, and other uses. With
such large and varying applications, plastics contribute to
an ever increasing volume in the solid waste stream. In
the year 1996, plastics amounted to about 12% of MSW,
by weight, in United States (Franklin Associates Ltd.,
1998). The waste plastics collected from the solid wastes
stream is a contaminated, assorted mixture of plastics. This
makes the identification, segregation, and purification of
the various types of plastics very challenging. In the plastics
waste stream, polyethylene forms the largest fraction,
which is followed by PET. Lesser amounts of other plastics
can also be found in the plastics waste stream, as given in
Table 1 (Subramanian, 2000).
The world’s annual consumption of plastic materials has
increased from around 5 million tons in the 1950s to nearly
100 million tons in 2001 (http://www.wasteonline.org.uk).
0956-053X/$ - see front matter 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.wasman.2007.09.011
*
Corresponding author. Tel.: [phone]; fax: [phone]/
2364498.
E-mail address: [email protected] (R. Siddique).
www.elsevier.com/locate/wasman
Available online at www.sciencedirect.com
Waste Management 28 (2008) 1835–1852

Table 2 presents the details about the amount of plastic
consumption and plastic waste generated in the UK,
USA and Western Europe. In the UK, a total of approxi-
mately 4.7 million tons of plastic products were used in var-
ious economic sectors in 2001. The amount of plastic waste
generated annually in the UK is estimated to be nearly 3
million tons. An estimated 56% of all plastics waste is used
packaging, three-quarters of which is from households. It is
estimated that only 7% of total plastic waste arising is cur-
rently being recycled. According to a 2003 Environment
Agency report, 80% of post-consumer plastic waste is sent
to landfill, 8% is incinerated and only 7% is recycled. In
addition to reducing the amount of plastics waste requiring
disposal, recycling plastic can have several other advanta-
ges. In the United States, approximately 11 million tons
of plastic wastes are produced each year, which represents
about 11.1% of total MSW generation (EPA, 2003). Plastic
wastes are very visible as they contribute to a large volume
of the total solid wastes. Precisely because of their large
visibility, plastic wastes (and particularly non-sustainable
plastic products) have been viewed as a serious solid waste
problem.
The largest component of the plastic waste is low density
polyethylene/linear low density polyethylene (LDPE) at
about 23%, followed by 17.3% of high density polyethyl-
ene, 18.5% of polypropylene, 12.3% of polystyrene (PS/
extended PS), 10.7% polyvinyl chloride, 8.5% polyethylene
terephthalate and 9.7% of other types (Association of Plas-
tics Manufactures in Europe, 2004).
2. Types of plastic and plastic waste
The quantity of plastics consumed annually all over the
world has been growing phenomenally. Its exceptionally
user-friendly characteristics/features, unique flexibility,
fabricatability and processability coupled with immense
cost-effectiveness and longevity are the main reasons for
such astronomical growth. Besides its wide use in packag-
ing, automotive and industrial applications, plastics are
also extensively used in medical delivery systems, artificial
implants and other healthcare applications, water desalina-
tion and bacteria removal, preservation and distribution of
food, housing appliances, communication and the electron-
ics industry, etc. Table 3 details the uses of plastics and
recycled plastics (Recycling and Resource Recovery Coun-
cil, 1994).
2.1. Benefits/advantages of plastics
The growth in the use of plastic is due to its beneficial
properties, which include:
Extreme versatility and ability to be tailored to meet
specific technical needs.
Lighter weight than competing materials reducing fuel
consumption during transportation.
Good safety and hygiene properties for food packaging.
Durability and longevity.
Resistance to chemicals, water and impact.
Excellent thermal and electrical insulation properties.
Comparatively lesser production cost.
Unique ability to combine with other materials like alu-
minum foil, paper, adhesives.
Far superior aesthetic appeal.
Material of choice – human life style and plastic are
inseparable.
Intelligent features, smart materials and smart
systems.
2.2. Disadvantages of plastics
Plastics production also involves the use of potentially
harmful chemicals, which are added as stabilizers or colo-
rants. Many of these have not undergone an environmental
risk assessment and their impact on human health and the
environment is currently uncertain. Such an example is
phthalates, which are used in the manufacture of PVC.
PVC has in the past been used in toys for young children
and there has been concern that phthalates may be released
when these toys are sucked (come into contact with saliva).
Risk assessments of the effects of phthalates on the envi-
ronment are currently being carried out. The disposal of
plastics products also contributes significantly to their envi-
ronmental impact. Because most plastics are non-degrad-
able, they take a long time to break down, possibly up to
Table 1
Types and quantities of plastics in municipal solid waste in the USA
(Subramanian, 2000)
Type of plastic Quantity (1000 tons)
Polyethylene terephthalate (PET) 1700
High density polyethylene (HDPE) 4120
Low density polyethylene (LDPE) 5010
Polypropylene (PP) 2580
Polystyrene (PS) 1990
Other 3130
Table 2
Plastic consumption and plastic waste data
Quantity
(million tons)
Reference
Plastic consumption in UK
in 2001
4.7 www.wasteonline.org.uk
(2001)
Plastic waste in UK in
2001
3.0 www.wasteonline.org.uk
(2001)
Plastic consumption in
Western Europe in 2004
43.5 APME (2004)
Plastic consumption in
USA in 2003
26.7 EPA (2003)
Plastic waste in USA in
2003
11.0 EPA (2003)
1836 R. Siddique et al. / Waste Management 28 (2008) 1835–1852

hundreds of years – although no-one knows for certain as
plastics have not existed for long enough – when they are
landfilled. With more and more plastics products, particu-
larly plastics packaging, being disposed of soon after their
purchase, the landfill space required by plastics waste is a
growing concern.
3. Utilization of waste/recycled plastics
Applications of plastic usage are wide-ranging. Some
plastic items such as food packaging become waste only a
short time after purchase. Other plastic items lend them-
selves to be reused many times over. Reusing plastic is pref-
erable to recycling as it consumes lesser amounts of energy
and resources. Long life, multi-trip plastics packaging has
become more widespread in recent years, replacing less
durable and single-trip alternatives, thereby reducing
waste. In the United States, 80% of post-consumer plastic
waste is sent to landfill, 8% is incinerated and only 7% is
recycled (EPA, 2003). In addition to reducing the amount
of plastic waste requiring disposal, recycling plastic can
have several other advantages:
Conservation of non-renewable fossil fuels – plastic pro-
duction uses 8% of the world’s oil production, 4% as
feedstock and 4% during manufacture.
Reduced consumption of energy.
Reduced amounts of solid waste going to landfill.
Reduced emissions of carbon-dioxide (CO
2
), nitrogen-
oxide (NO) and sulphur-dioxide (SO
2
).
3.1. Advantages of waste/recycled plastic
Advantages of using waste/recycled plastics are: (i)
reduction of municipal solid wastes being landfilled; and
(ii) an alternative to pressure-treated lumber that leaches
toxic chemicals into water.
3.2. Classification of recycled plastic in concrete
3.2.1. Virgin polypropylene
The virgin polypropylene fibers are 19 mm (3/4 in.) long
fibrillated fibers. These are in slender fiber-form.
3.2.2. Recycled plastic (melted processed)
The recycled plastic (melted processed) is produced by
drawing molten automobile bumpers into long strands,
which are cut to 28 mm (1.1 in.) length. It is in slender
fiber-form.
3.2.3. Recycled plastic (automobile shredded residue)
Automobile shredded residue comprised mainly mixed
plastics and some rubber, with a maximum particle dimen-
sion of 19 mm (3/4 in.). It is in flake form.
Table 3
Uses of plastics and recycled plastics (Recycling and Resource Recovery Council, 1994)
Name of plastic Description Some uses for virgin plastic Some uses for plastic made from recycled waste
plastic
Polyethylene
terephthalate
(PET)
Clear tough plastic, may
be used as a fiber
Soft drink and mineral water bottles, filling for
sleeping bags and pillows, textile fibers
Soft drink bottles, (multi-layer) detergent bottles,
clear film for packaging, carpet fibers, fleecy jackets
High density
polyethylene
(DPE)
Very common plastic,
usually white or coloured
Crinkly shopping bags, freezer bags, milk and
cream bottles, bottles for shampoo and cleaners,
milk crates
Compost bins, detergent bottles, crates, mobile
rubbish bins, agricultural pipes, pallets, kerbside
recycling crates
Unplasticised
polyvinyl
chloride
(UPVC)
Hard rigid plastic, may be
clear
Clear cordial and juice bottles, blister packs,
plumbing pipes and fittings
Detergent bottles, tiles, plumbing pipe fittings
Plasticized
polyvinyl
chloride
(PPVC)
Flexible, clear, elastic
plastic
Garden hose, shoe soles, blood bags and tubing Hose inner core, industrial flooring
Low density
polyethylene
(LDPE)
Soft, flexible plastic Lids of ice-cream containers, garbage bags,
garbage bins, black plastic sheet
Film for builders, industry, packaging and plant
nurseries, bags
Polypropylene
(PP)
Hard, but flexible plastic –
many uses
Ice-cream containers, potato crisp bags, drinking
straws, hinged lunch boxes
Compost bins, kerbside recycling crates, worm
factories
Polystyrene (PS) Rigid, brittle plastic. May
be clear, glassy
Yoghurt containers, plastic cutlery, imitation
crystal ‘‘glassware’’
Clothes pegs, coat hangers, office accessories,
spools, rulers, video/CD boxes
Expanded
polystyrene
(EPS)
Foamed, lightweight,
energy absorbing, thermal
insulation
Hot drink cups, takeaway food containers, meat
trays, packaging
R. Siddique et al. / Waste Management 28 (2008) 1835–1852 1837

3.2.4. Recycled plastic (shredded)
The recycled plastic (shredded) is produced by shredding
plastics obtained from a mixed plastic stream; the process
yielded plastic flakes with a maximum planar dimension
of 25 mm (1 in.). It is in flake form.
Zoorob and Suparma (2000) reported the physical
properties of recycled plastic (low density polyethylene,
LDPE), which are given in Table 4. Details of the proper-
ties of a virgin and recycled discrete reinforcement system
used in concrete by Soroushian et al. (2003) are given in
Table 5.
4. Management option/recycling methods
An integrated approach is required in an attempt to
manage such large quantities of a diverse, contaminated
mixture of plastics in an energy efficient and environmen-
tally benign manner. This would require examining
critically various steps in the life of the plastics such as
the raw materials for their manufacture, the manufactur-
ing processes, design and fabrication of the finished
products, possible reuse of those items, and the proper
disposal of the wastes, in totality. Such an integrated waste
management concept comprises: (i) source reduction;
(ii) reuse; (iii) recycling; (iv) landfill and (v) waste-to-
energy conversion.
4.1. Framework for plastic waste management
The flow chart of a plastic waste management operation
system is schematically shown in Fig. 1. The major opera-
tions involved in a waste management process include the
collection of the plastic waste outside or inside the munici-
pal waste stream, its disposal in landfills, its energy recov-
ery, recycling into useful products, and the establishment
of markets for the recycled products (Rebeiz and Craft,
1995).
4.1.1. Collection
Plastic wastes could be retrieved in two ways: the first
method consists of collecting plastics after they enter the
municipal waste stream, and the second method involves
Table 4
Physical properties of waste plastics (low density polyethylene, LDPE)
(Zoorob and Suparma, 2000)
Properties Low density polyethylene
(LDPE)
Granulate shape Pellet
Size (mm) 5.00–2.36
Specific gravity 0.92
Softening point (C) 120
Melting point (C) 140
Table 5
Properties of virgin and recycled discrete reinforcement system (Soroushian et al., 2003)
Mixture identification Discrete reinforcement Aspect ratio Specific gravity Dosage in concrete (kg/m
3
) Volume (%)
poly1.5 & poly3.0 Virgin polypropylene
a
150 1.2 0.9 0.075
1.8 0.15
plmp1.5 & plmp2.5 Recycled plastic (melt processed) 11.1 0.8 0.9 0.1
1.5 0.19
plasr34 Recycled plastic (automotive shredded residue) 1.65 1.0 20 2.0
plsh17 & plsh34 Recycled plastic (shredded) 3.70 1.0 10 1
20 2
a
Polypropylene fibers is not a waste plastic.
Plastic Wastes
Collection
Outside the
Municipal Waste
Stream
Inside the
Municipal Waste
Stream
Landfill Incineration
Energy
Separation/Purification
Recycling
Chemical
Modification
Thermal
Reprocessing Fillers
Plastic/Non-Plastic Products
Market
Non-Plastic
Wastes
Management
Fig. 1. Plastic waste management process (Rebeiz and Craft, 1995).
1838 R. Siddique et al. / Waste Management 28 (2008) 1835–1852

collection of plastics before they enter the municipal waste
stream. Most post-consumer wastes end up in the munici-
pal waste stream. Curlee (1986) reported that these plastic
wastes are usually very contaminated and are difficult to
recycle economically. Therefore, the wastes are either dis-
posed in landfills or incinerated to reduce their volume
and to recover their energy content. Conversely, plastic
wastes collected outside the municipal waste stream are rel-
atively clean and can be recycled after undergoing some
separation and purification processes.
4.1.2. Landfilling plastics
The disposal of plastics in landfills raises some concerns
since the material degrades very slowly. Wastes such as
paper and food wastes are equally very slow to degrade
in landfills. Therefore, the degradation of plastics and
other wastes should not be made an issue since it has little
effect on landfill capacity. Plastic wastes do not create dif-
ficulties in landfill operations and also do not contribute
to the toxicity of leachate from the landfills (EPA, 1991;
Office of Solid Waste and Office of Water, 1990). Biodeg-
radation (such as incorporating starch additives to the
plastic) and photo degradation (such as incorporating
photo-sensitive additives to the plastic) are the two tech-
nologies that are being explored for commercial applica-
tions. Light and air must be present for these materials
to decompose, along with sufficient moisture and nutrients
to sustain microbial action (Alter, 1993; Boettcher, 1992).
These requirements are not met for materials buried in
landfills. Accordingly, the EPA does not believe that the
use of degradable plastics will help solve landfill capacity
problems. Furthermore, the environmental impact of
degradable residues is still not well understood (EPA,
1991; Office of Solid Waste and Office of Water, 1990).
Moreover, making plastics degradable would lower the
quality and performance of the material and therefore
would mitigate some of its major desirable features in var-
ious applications.
4.1.3. Incineration of plastics
The heat content of plastic wastes can be recovered by
incineration. Plastic wastes are a good fuel source because
most resins have a heating value almost equivalent to that
of the coal. In addition to providing an attractive source of
alternative energy, preserving natural resources and mini-
mizing the impact of dependency on energy, incineration
also greatly reduces the volume of garbage by about
90–95%. But, there is always public resistance emerging
against incineration because of the emission of some toxic
fumes. However, current technology makes it possible to
operate incineration plants in a way that emissions would
not be a problem and, therefore, would conform to the
Clean Air Act Amendments of 1990 (Alter, 1993; Yako-
witz, 1990).
Two types of ash are produced by an incineration pro-
cess; fly ash (the very fine particles entrained in incinerator
exhaust gases) and bottom ash (the large and heavy parti-
cles removed from the bed of the incinerator), which
require disposal. Landfilling these ash residues may not
always be acceptable because of the potential for ground-
water and soil pollution due to leachate carrying heavy
metals such as lead and cadmium. Methods of protecting
groundwater and soil from leachate, such as lining the
landfill, can be expensive and are not always effective from
an environmental standpoint. Accordingly, some research
is being undertaken to effectively stabilize and recycle incin-
eration residues in construction applications (Goumans
et al., 1991).
4.1.4. Plastics recycling
Plastics recycling has to be taken into consideration in
any plastic waste management program. In addition to
reducing the amount of waste disposed in landfills, it can
also significantly contribute to the conservation of raw pet-
rochemical products, as well as energy savings (EPA, 1991;
Office of Solid Waste and Office of Water, 1990). Rebeiz
and Craft (1995) have reported that there are a few techno-
logical and economic constraints that currently limit the
full and efficient recycling of plastic wastes into useful
products, and these are: (i) contamination of plastic wastes
with other materials such as dirt and metals that can dam-
age the equipment used in the reprocessing of the waste; (ii)
plastics are not homogeneous materials like aluminum or
paper, but consist of a large number of grades with differ-
ent molecular structures and properties, and each plas-
tic component in a mixed waste has a different melting
behavior, rheology, and thermal stability; (iii) plastic mix-
tures are usually insoluble and form discrete phases within
a continuous phase; (iv) plastic waste feedstock is not usu-
ally uniform over time and (v) plastic wastes have a rela-
tively low density. Therefore, they are usually compacted
or ground-up before transportation to reduce shipping
costs.
4.2. Recycling methods and construction applications
4.2.1. Mechanical recycling
Mechanical recycling of plastics refers to processes
which involve melting, shredding or granulation of waste
plastics. Plastics must be sorted prior to mechanical recy-
cling. Technology is being introduced to sort plastics auto-
matically, using various techniques such as X-ray
fluorescence, infrared and near infrared spectroscopy, elec-
trostatics and flotation. Following sorting, the plastic is
either melted down directly and moulded into a new shape,
or melted down after being shredded into flakes and than
processed into granules called regranulate.
Zhang and Forssberg (1999) studied the liberation and
its impact on the separation of personal computer (PC)
scrap and printed circuit board (PCB) scrap. Special equip-
ment functioning as a shape separator and an aspirator was
R. Siddique et al. / Waste Management 28 (2008) 1835–1852 1839