ANALYSIS OF REPLACEMENT OF PORTLAND CEMENT BY OF CONCRETE

ANALYSIS OF REPLACEMENT OF PORTLAND CEMENT BY
MICRONIZED POLYETHYLENE TEREPHTHALATE IN THE PRODUCTION
OF CONCRETE
Mauro Henrique Alves Nascimento¹,a; Ana Maria Gonçalves Duarte Mendonça²,b; John Kennedy
Guedes Rodrigues³,c, Taíssa Guedes Rodrigues4,d
1
Civil Engineering Master Student; Universidade Federal de Campina Grande- UFCG, Paraíba, Brazil
2
Researcher Professor, Universidade Federal de Campina Grande- UFCG, Paraíba, Brazil
3
4
a
Associate Professor, Universidade Federal de Campina Grande- UFCG, Paraíba, Brazil
Civil Engineering student, Universidade Federal de Campina Grande- UFCG, Paraíba, Brazil
b
c
[email protected], ana.duartemendonç[email protected], [email protected]
d
[email protected]
KEYWORDS: Concrete, Portland cement, Polyethylene Terephthalate (PET), Recycling,
Chemical, Mineralogical and Thermal Properties.
ABSTRACT
Tied to the industrial and population growing is the search for new technologies and materials that
meet the sustainable development concept. In the disposable packaging production industry, it is
highly used Polyethylene Terephthalate – PET, a low density, transparent, easy to mold product that
also provides high mechanic and chemical resistance. However, this product, derived from
petroleum, a non-renewable substance, can take centuries to naturally decompose and when
incorrectly disposed generates a huge environmental impact, being necessary its reuse. In turn, the
great demand for concrete around the world propelled the construction sector to search for new
materials that introduce the necessity of reduction, reuse and recycling. Faced with this scenery, the
present work presents a comparative study between chemical, mineralogical and thermal properties
of micronized polyethylene terephthalate and Portland cement, aiming to reduce the proportion of
cement by cubic meter of concrete produced. This can provide a reduction of costs and offer a
noble destination for PET after consumption through a possible replacement, in mass, of cement by
micronized PET in the concrete production process. For the determination and subsequent
comparison between the properties of PET and Portland cement, it was adopted in the methodology
differential thermal analysis (DTA) and thermal gravimetric analysis (TGA) as well as
determination of chemical properties using X-Ray Fluorescence (XRF). Through the results
obtained, it is possible to conclude that micronized PET presents similar properties to Portland
cement, providing a possible recycling of PET in concrete production.
1. INTRODUCTION
The solid urban residues issue is linked to evolution processes and men development. This
residue generation due to the diverse human activities is a great challenge to be faced by the current
generation. Another issue related to such residues resides in the fact that the production speed
surpass the degradation capacity of the compounds in the environment, compromising natural
resources and life quality of current and future generations.
Two sectors of the Brazilian industry that fit into this issue are the PET industry and the
construction industry, because they cause huge environment impacts, whether by natural resources
consumption, landscape modification or residues generation.
In contrast, according to [1] the growing awareness about the environment has contributed
to concerns about the elimination and reuse of generated residues. The solid waste management is
one of the main environmental concerns in the world. With the shortage of deposition space in
landfills and due to the higher cost, the use of residues has become an alternative to avoid their
deposition.
The Polyethylene Terephthalate (PET) is used in products with short lifetime, such as
packages. Due to the high amount and variety of applications of PET packages and its long-term
degradation, they are considered one of the environment villains, once they occupy a good volume
in landfills and mainly because they are discharged directly in nature, causing visual pollution in
urban centers. However, environmental problems are not caused by the production of PET but by
its inadequate discharge. In this way, systematic recycling is the solution to minimize this
environmental impact.
Even discharged in landfills, PET packages represent a problem to the public power, once
that because of its long-term decomposition (more than 100 years) and the high volume occupied,
when discharged in large amounts, they diminish the storage capacity of landfills and provoke a
superficial sealing of soil, forming an impermeable layer that impedes circulation of gases and
liquids, affecting the organic matter decomposition process [2].
According to the Brazilian Association of PET Industry (ABIPET) [3] the Brazilian
production in 2012 was of 562 thousands of tons, 59% of which were recycled (331thousands of
tons). This is superior to the average in USA and similar to European countries, where recycling
activity is more professionalized. However, from the 562 thousand tons of PET consumed in 2012
in Brazil, approximately 40% were not reused, occasioning a discharge in nature of 231 Ktons of
this material, causing serious environmental problems. The main consumer of recycled PET in
Brazil is the textile industry with 38.2%, industries of unsaturated and alkyd resins with 23.9% and
packaging industries with 18.3%.
New alternatives to reuse these packages after consumption must be investigated, in a way
to avoid discharge in landfills and in the environment. The awareness of technological
characteristics of residues increases the possibility of products produced with such materials,
besides the reduction in the generation of harmful residue, once that every processing activity
generates residues [4].
Along with the need for PET recycling, there is the search, in the construction sector, for
constructive techniques that take advantage on the diverse available resources, preserving the nonrenewable natural resources and avoiding the use of materials and technologies harmful to the
environment.
The construction sector is a great consumer of natural resources. Water, sand, granitic
crushed stone and mainly cement are the more traditional resources employed in concrete
production. Besides, main suppliers of civil construction are among the biggest polluters in the
world, especially the cement industry that daily discharge tons of industrial waste in the
environment, mainly gases and dust formed in the productive process and in the burn of fuels in the
rotatory ovens.
According to National Union of Cement Industry [6] – the production of cement in Brazil in
the first eleven months of 2014 reached approximately 70 thousand tons of cement.
One of the great villains in the productive chain of civil construction is the cement, the most
used input of the sector. Cement, according to [7], is a binder (pulverulent material that hydrates in
the presence of water, forming a strong paste able to bind aggregates) known worldwide as Portland
cement. The production of Portland cement occurs through the milling of a product called clinker,
obtained by the calcination (oxidation by heat) of a raw mixture of limestone and clay, dosed and
homogenized. This process occurs by the intense burning of fuels, in rotating ovens, delivering a
final product in the form of dark nodes that, after cooled, are milled and receive the addition of
gypsum, whose action is to stop hydration reactions between cement and water that instantly occur
[7]. The cement manufacturing process consumes huge amounts of energy, in the form of heat (in
rotating ovens) or electric energy in the industrial process.
Based on this, cement has an important function on the construction sector, having a
generalized use in great volumes. Thus, the search for materials that can replace it, even partially, in
the production of concrete is the first step to minimize its impact in the environment [5].
In this context, as the PET Recycling Industry is one of the most developed in the world and
has high recycling index and a variety of application for the recycled material, it creates a constant
and assured demand, favoring the possible replacement, in percentages, of Portland cement by
Polyethylene Terephthalate, after consumption, in the production of concrete.
As the search for alternatives to the reuse of PET, this research aims to evaluate the
technical viability, using chemical-mineralogical analysis, of recycling Polyethylene Terephthalate
in the production of concrete, replacing, in percentages, Portland cement.
2. MATERIALS AND METHODOLOGY
2.1. Materials
In the development of the present research, the following materials were used:
 Cement: High Early Strength Portland Cement, type V [Figure 1];
Figure 1 – HES Portland Cement.

Polyethylene terephthalate: micronized PET from ‘PET Reciclagem’ industry, located at
Campina Grande – PB, Brazil [Figure 2];
Figure 2 – Micronized PET.
2.2. Methodology
The present study aims to perform a comparative analysis between chemical, mineralogical
and thermal properties of micronized polyethylene terephthalate and HES V Portland Cement.
In order to reach this goal, the methodology exposed in Figure 3 was adopted.
Materials Characterization
1st Step
2nd Step


HES V Portland cement
Characterization
Polyethylene
terephthalate
Characterization
3rd Step




X-Ray Fluorescence (XRF);
Differential Thermal Analysis
(DTA);
Thermal Gravimetric Analysis
(TGA).
X-Ray Fluorescence (XRF);
Differential Thermal Analysis
(DTA);
Thermal Gravimetric Analysis
(TGA).
Results Analysis and Research Conclusion
Figure 3 – Flowchart of research steps.
The present research was divided into three steps. The first and second steps corresponded to
Portland cement and Polyethylene terephthalate characterization, enabling the analysis of results
and research conclusions, which was the third step.
Chemical, Mineralogical and Thermal analysis were performed according to procedures
used in Materials Characterization Laboratory at Science and Technology Centre of Federal
University of Campina Grande – PB, Brazil.
The methodology adopted to chemical, mineralogical and thermal analysis of materials is
described below.
2.2.1. X-Ray Fluorescence (XRF) Analysis
It is a chemical analysis technique used to determine qualitative and quantitative
composition of components of a given material through x-ray emission.
The principle of this method consists in the use of a radiation source to ionize inner levels of
constituent atoms in the sample, by photoelectric effect. In the atom reorganization and regress to
its fundamental state, it liberates the excess of energy through the emission of an X photon, whose
energy is equal to the binding energy difference of the two orbitals involved. Such radiation has the
characteristic energy of the element. The detection and analysis of the spectrum allows the
identification and quantification of constituent elements in the sample.
The chemical analysis by X – Ray Fluorescence were determined by wet method and by
Energy Dispersive X-Ray Analysis (EDX), using a SHIMADZU spectrometer, EDX-720 model. It
was determined loss on fire, insoluble residue and present oxides (SiO2, Al2O3, CaO, MgO, Na2O,
K2O and Fe2O3).
2.2.2. Differential Thermal and Thermal Gravimetric Analysis
An equipment produced by BP Engenharia, RB 3020 model, was used to the thermal
analysis and the samples were heated until 220ºC for PET and 1000ºC for Portland cement, with
heating ratio of 12.5ºC/min. Thermal Gravimetric (TGA) and Differential Thermal (DTA) Analysis
were performed using calcined alumina (Al2O3) as reference material.
3. RESULTS AND DISCUSSIONS
The determination of qualitative and quantitative composition of PET and cement oxides
was made by x-ray fluorescence experimental procedure (EDX).
Tables 1 and 2 present the chemical composition of Polyethylene terephthalate and Portland
cement, respectively.
Table 1 – Chemical composition of PET.
Determination of PET chemical components in percentage
Loss on Fire
SiO2
Al2O3
Fe2O3
CaO
Micronized PET
0.24
38.70 31.21
14.31
6.76
TiO2
5.77
Table 2 – Chemical composition of HES V Portland cement.
Determination of cement chemical components in percentage
HES V
Portland
LF
SiO2
Al2O3
Fe2O3
CaO
TiO2
K2O
4.06
17.1
3.68
3.05
64.8
-
0.091
SO3
4.6
MgO
0.72
K2O
3.25
cement
LF: Loss on Fire
It is observed in Table 1 that the micronized Polyethylene terephthalate (PET) is basically
constituted by silica (38.70%), Al2O3 (aluminum oxide), Fe2O3 (iron oxide), CaO (calcium oxide),
TiO2 (titanium oxide) and K2O (potassium oxide). The higher proportion of components was
composed by silica and aluminium oxide, representing 38.70% and 31.21%, respectively. From
these proportions, PET can be classified as an aluminosilicate complex.
According to [8], the main components of cement chemical composition, whose quantity
directly influences the characteristics of the concrete produced, are: calcium oxide (CaO),silica
(SiO2), aluminum oxide (Al2O3), iron oxide (Fe2O3), magnesium oxide (MgO), alkalis (Na2O e
K2O) and sulphates (SO3). Among these components, calcium oxide, silica, aluminium oxide, iron
oxide and potassium oxide are also present in PET composition, as seen in Table 1
[9] determines that the specific conditions of loss on fire and magnesium oxide (MgO)
chemical requirements must have upper limit, in relation to cement mass percentage, of 4.5% and
6.5%, respectively. Such normative requirements are respected by PET, as seen in Table 1, once
that magnesium oxide is not present in its composition, and the loss on fire is 0.24%, which means
it is 99.66% inferior to the value required by test method [9]
On one hand, the percentage of lime (CaO) in PET is 6.76%, which is inferior to the value
found in cement composition, between 60% and 67%, according to [8]. This difference in the
percentage of lime impedes the replacement of cement by PET, once that lime is an essential
component of cements, responsible for strength characteristics.
On the other hand, PET has silica (SiO2), aluminium oxide (AlO3) and iron oxide (FeO3)
percentages superior to the ones defined by [8] as being the maximum values found in cement,
which are respectively 17%, 3,6% e 3,05%.
In this way, PET has potential to replace Portland cement in the production of concrete;
however, it is limited due to the low quantity of lime.
Figure 4 presents Differential Thermal and Thermal Gravimetric analysis of micronized
Polyethylene terephthalate.
Figure 4 – PET Differential Thermal and Thermal Gravimetric results.
Analyzing the results presented in Figure 4, it is observed the presence of an endothermic
peak at 82°C approximately, related to the change in physical state (solid to liquid), having a
significant loss in PET mass and the occurrence of an exothermic peak at 129°C indicating another
change in physical state (liquid to vapor). From the thermal gravimetric curve, it is observed a total
mass loss of 0.24%
The differential thermal and thermal gravimetric analysis of HES V Portland cement are
presented in Figure 5.
Temperature / °C
Figure 5 – DTA and TGA results for HES V Portland cement.
Source: MEDINA, 2011.
According to the results obtained by [10] and presented in Figure 5, it is observed three main
loss bands: the first between 30°C and 370°C, referring to gypsum, ettringite and syngenite
decomposition [11]. The second band, between 370°C and 525°C, referring to portlandite Ca(OH)2
decomposition and the third between 525°C and 1000°C , referring to calcium carbonate (CaCO3)
decomposition. Portlandite content was equal to 1.69% and calcium carbonate content at anhydrous
cement was equal to 6.17%.
It is observed that both cement and polyethylene terephthalate have loss bands beginning at a
temperature of 30°C. However, for PET, mass losses are referent to chance of physical state, while
for cement there is constituent’s decomposition. Cement presented a higher mass loss, equal to
2.72%.
4. CONCLUSION
From the results obtained, it is possible to conclude that Polyethylene terephthalate (PET)
presents similar composition to Portland cement, but in different proportions. Therefore, due to the
need for PET recycling allied to the search, in the construction sector, for sustainable techniques,
PET has potential to replace Portland cement in concrete production. However, the replacing
percentage must be limited to avoid damages to the concrete produced, once that, as seen in the
chemical analysis, PET presents low quantity of lime in its composition.
5. ACKNOWLEDGEMENTS
To Universidade Federal de Campina Grande – UFCG – PB. Brazil;
To the Civil Engineering Department – CTRN – UFCG;
To Ph.D. Professor Ana Maria Gonçalves Duarte Mendonça, for guidance in this research;
To brazilian society for enabling me to study in Federal de Campina Grande – UFCG – PB.
Brazil.
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