29-09-2012, 11:17 AM
Properties and durability of concrete containing polymeric wastes (tyre rubber and polyethylene terephthalate bottles): An overview
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ABSTRACT
The volume of polymeric wastes like tyre rubber and polyethylene terephthalate bottles (PET) is increasing
at a fast rate. An estimated 1000 million tyres reach the end of their useful lives every year and 5000
millions more are expected to be discarded in a regular basis by the year 2030. Up to now a small part is
recycled and millions of tyres are just stockpiled, landfilled or buried. As for PET bottles annual consumption
represent more than 300,000 million units. The majority is just landfilled. This paper reviews
research published on the performance of concrete containing tyre rubber and PET wastes. Furthermore
it discusses the effect of waste treatments, the size of waste particles and the waste replacement volume
on the fresh and hardened properties of concrete.
Introduction
Polymeric wastes namely tyre rubber and PET represents a major
environmental problem of increasing relevance. An estimated
1000 million tyres reach the end of their useful lives every year
[1]. At present enormous quantities of tyres are already stockpiled
(whole tyre) or landfilled (shredded tyre), 3000 millions inside EU
and 1000 millions in the US [2]. By the year 2030 the number of
tyres from motor vehicles is expect to reach 1200 million representing
almost 5000 millions tyres to be discarded in a regular basis.
Tyre landfilling is responsible for a serious ecological threat.
Mainly waste tyres disposal areas contribute to the reduction of
biodiversity also the tyres hold toxic and soluble components [3].
Secondly although waste tyres are difficult to ignite this risk is always
present. Once tyres start to burn down due to accidental
causes high temperature take place and toxic fumes are generated
[4] besides the high temperature causes tyres to melt, thus producing
an oil that will contaminate soil and water. In Wales a tyre
dump with 10 million tyres has been burning continuously for
9 years [5]. The implementation of the Lanfill Directive 1999/31/
EC [6] and the End of Life Vehicle Directive 2000/53/EC [7] banned
the landfill disposal of waste tyres creating the driving force behind
the recycling of these wastes. Still millions of tyres are just
being buried all over the world [8].
Concrete with scrap-tyre wastes
Fresh concrete properties
Workability
Cairns et al. [5] used long and angular coarse rubber aggregates
with a maximum size of 20 mm obtaining concretes with an
acceptable workability for low rubber content. These authors reported
a reduction in the workability for higher rubber content,
being that a rubber content of 50% lead to a zero slump value.
Other authors [18] studied concretes containing silica fume, crumb
rubber and tyre chips reporting a decrease in slump with increasing
rubber content, being that a 50% rubber content leads to mixtures
without any workability. The results obtained by those
authors show that reducing W/C is associated to a decrease in
the slump values and that the silica fume worsens the workability
performance. Albano et al. [19] replace fine aggregates by 5% and
10% of scrap rubber waste (particle sizes of 0.29 mm and
0.59 mm) reporting a decreased of 88% in concrete slump. Bignozzi
and Sandrolini [20] used scrap-tyre (0.5–2 mm) and crumb-tyre
(0.05–0.7 mm) to replace 22.2% and 33.3% of fine aggregates in
self-compacting concretes referring that the introduction of the
rubber particles does not influence the workability in a significant
way if the superplasticizer also increases. Skripkiunas et al. [21]
used crumbed rubber to replace 23 kg of fine aggregates in concretes
with 0.6% of a policarboxile superplasticizer by cement mass
obtaining the same workability of the reference concrete. Other
authors [22] used crumb rubber tyres (0.075–4.75 mm) in the concrete
to replace sand in various percentages (20%, 40%, 60% and
100%). These authors stated that increasing rubber waste content
decreases the concrete slump (Table 1).
Shrinkage
Kim et al. [62] studied the influence of three types of PET based
fibres (Fig. 8) on the control of plastic shrinkage. These fibres are
obtained from melted PET waste to form a roll-type sheet. Then
the sheet is cut into 0.5 mm long fibres and a deforming machine
is used to change the fibre surface geometry. They mentioned that
the use of a volume of just 0.25% PET fibres can reduce the plastic
shrinkage, increasing PET fibres volume beyond 0.25% does very
little to the shrinkage reduction. The results confirmed that the
embossed type fibre, the one that has the best mechanical resistance
leads to the best shrinkage performance. Kim et al. [63] confirm
the concrete crack control ability of PET fibre composites.
These authors compared the shrinkage performance of embossed
type PET fibre previously submitted to a surface treatment to improve
dispersion and bonding strength [64] to the shrinkage performance
of crimped polypropylene commercial fibres (PP)
reporting a slightly better behaviour for composites containing
0.5% of PP fibres. Nevertheless, composites containing 1% of PET fibres
have a quite similar performance. Since investigations on concrete
shrinkage performance used treated PET fibres investigations
should study which treatment is the one with the lowest environmental
impact
Other polymeric wastes
Several other polymeric wastes have been investigated about
their potential to be used as aggregate replacement in cementitious
composites. Laukaitis et al. [88] studied the development of lightweight
thermo-insulating cementitious composites containing
crumbled polystyrene waste and spherical blown polystyrene
waste. The authors report the need to use a 0.2% sulfonyl and
0.03% glue hydro solution to increase the adhesion between the
polystyrene granules and the cement paste. The results show that
it is possible to produce a composite with 150–170 kg/m3 and a
thermal conductivity of coefficient between 0.06 and 0.0.64 W/
m K. Ismail et al. [89] mentioned that the use of polymeric wastes
composed by 80% of polyethylene and 20% polystyrene as fine
aggregate replacement increases the toughness of concrete with
minor compressive and tensile strength decrease. However, the
same authors report workability issues that need to be addressed.
For instance mixtures with a 15% replacement volume have an almost
null slump. Other authors [90] studied concretes with ground
thermosetting polymer (melamine) waste reporting a reduction in
compressive strength with waste content increase related to the
poor adhesion between waste plastic and cement paste. Yadav
[91] also confirms the strength reduction associated with concrete
polymeric waste composites.
Conclusions
Tyre rubber and PET wastes represent a serious environmental
issue that needs to be addressed with urgency by the scientific
community. Investigations carried out so far reveal that tyre waste
concrete is specially recommended for concrete structures located
in areas of severe earthquake risk and also for applications submitted
to severe dynamic actions like railway sleepers. This material
can also be used for non-load-bearing purposes such as noise
reduction barriers. Investigations about rubber waste concrete
show that concrete performance is very dependent on the waste
aggregates. Further investigations are needed to clarify for instance
which are the characteristics that maximize concrete performance.
As to PET based concrete the investigations show that this material
is very dependent on the treatment of these wastes. At present PET
fibres are already used to replace steel fibres and some authors
even report the use of PET concrete mixtures for repairing concrete
structures submitted to high underwater erosion. Nevertheless, future
investigations should clarify which treatments can maximize
concrete performance being responsible for the lowest environmental
impact. Further investigations should also be carried on
about the use of other polymeric wastes in concrete.