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Comparison of embodied energy and carbon dioxide emissions of brick and concrete based on functional units

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Building materials have different consumption patterns of energy and emissions of carbon dioxide during their production. These differences result from the treatment of the raw materials and the techniques applied to production. Subsequently on an environmental classification one wonders what kind of constructive solution becomes more benevolent to the environment. Masonry building technique has made a comeback as an alternative to conventional reinforced concrete structures with ceramic blocks for closing the spans. The present study refers to the environmental comparison of these two systems. As the definition of functional unit has been introduced to facilitate the comparison of different existing alternatives, the walls are chosen as the functional units, for different building plans and conditions. The comparison considers the most important environmental parameters, i.e. the embodied energy and the carbon footprint. Results obtained indicate that masonry-building walls have a lower embodied energy and carbon footprint compared to those of conventional building. The differences vary with the length of the walls, but are over 22% and reach some 55%. It is hoped that the different wall types considered will enable the comparison of the two options for real application.
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Comparison of embodied energy and carbon dioxide emissions of brick and
concrete based on functional units
Soheyl Sazedj
University of Évora, Department of Rural Engineering, Évora, Portugal
sazedj@uevora.pt
António J. Morais
Architecture Faculty Technical University of Lisbon, Department of Technology, Lisbon, Portugal
ajmorais@fa.utl.pt
Said Jalali
University of Minho, School of Engineering, Guimarães, Portugal
said@civil.uminho.pt
Abstract
Building materials have different consumption patterns of energy and emissions of
carbon dioxide during their production. These differences result from the treatment of the raw
materials and the techniques applied to production. Subsequently on an environmental
classification one wonders what kind of constructive solution becomes more benevolent to the
environment.
Masonry building technique has made a comeback as an alternative to conventional
reinforced concrete structures with ceramic blocks for closing the spans. The present study
refers to the environmental comparison of these two systems. As the definition of functional
unit has been introduced to facilitate the comparison of different existing alternatives, the
walls are chosen as the functional units, for different building plans and conditions. The
comparison considers the most important environmental parameters, i.e. the embodied energy
and the carbon footprint.
Results obtained indicate that masonry-building walls have a lower embodied energy
and carbon footprint compared to those of conventional building. The differences vary with
the length of the walls, but are over 22% and reach some 55%. It is hoped that the different
wall types considered will enable the comparison of the two options for real application.
1. Introduction
In order to enable a decision on a structural solution to find the more environmental
friendly structure, specific information is needed. A tool recommended by ISO 14040, which
regulates international environmental assessment and life cycle of products, is the comparison
of functional units. Applying it to construction and having in mind the comparison of
structural solutions it seems most likely that the consideration of walls as functional units are
more suitable, as the architectural form remains untouched or is not predefined. In this case
the units must have the same function in stability, thermal and acoustic insulation. Hence,
structural walls, exterior and interior, with spans of 4, 6 and 7 and height of 2.7 meters are
regarded as functional units for the comparison of the materials already mentioned.
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1!
The model shown in Figure 1 with a building area of 167.6 m2 is structurally designedi
for both constructive solutions.
!
Figure 1, Plant of the ground floor
The comparison is meant between the functional units of the same span, one as
reticulated structure with reinforced concrete columns and ceramic blocks for closing the
spans and the other totally in masonry of ceramic blocks. The rendering and slabs are not
considered in the functional units, as they are the same for the two constructive solutions. So,
the assessment will highlight the differences in the two constructive options and compares the
structural core construction materials.
The Figures 2 and 3 show the functional units which can be used in any adequate
architectural design.
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!
!
!
!
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Figure 2. Brick wall as functional unity
In case of the masonry the unit consists of the height of 2,7 m and the span of the
stiffness walls considering the axis of the walls. The other case has the same height multiplied
by the span between the pillars, also considering the axis of the pillars, and additionally the
concrete beam at the floor level.
!
2.7!m!height!
Span!of!4,!6!or!7!m,!
between!the!interior!
walls!
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2!
!
!
!
!
!
!
!
Figure!3.!Wall!of!conventional!reticulated!reinforced!concrete!building!filled!with!ceramic!blocks!as!
functional!unit!
2. The Benchmarks
The data used for the ceramic blocks are supplied by the factory, Preceramii, a large-
scale producer of ceramic blocks, who applies advanced technology in the production, and
more two documents, "INVENTORY OF CARBON AND ENERGY" (ICE)iii, (UB), 2011
with data from UK, the publication "DADOS DE REFERÊNCIA PARA
BENCHMARKING"iv (CTCV) from 2004 with data from Portugal. The last document
confirms the data obtained from the manufacturer in Portugal.
Besides these current data the following sources have been also considered. A survey
of data in Spain, "GUIDE DE L'EDIFICACIÓN SOSTENIBLE"v (IC) and “Ecologia dos
Materiais de Construção’’vi (UM) with ecological data on building materials, collected at the
European level.
The Institutions and authors referred above present the data according to the type of
energy used for the production, electric and thermal energy, and depending on the size of the
factory, small, medium and large. Generally the statistics and the results are based more on
the use of thermal energy, electricity has only a contribution of 20%. The values used here are
average values to increase the likelihood of a fair comparison of the data.
Table 1, Comparison of embodied energy and carbon emission in the production of ceramic block
UB
PRECERAM
IC
EMBODIED ENERGY (MJ/kg)
3,0
1,02
4,5
CARBON DIOXIDE EMISSION
(kgCO22/kg)
0,22
0,100
-
Table 1 shows that the data of CTCV are significantly lower. The reason lies in the
statistical analysis of the period. The other institutions analyzed data from the plants over a
period of several years beginning in 1995 with some accuracy. However, these data, which
are averages, reflect also the years where the industry had not yet taken steps to reduce energy
and pollution in production. Unlike the survey, CTCV refers only to the year 2004 with the
latest industry data already applying the new manufacturing technologies with new measures
to reduce energy and pollution. The values of Portuguese plants already incorporate
technological advances. In the Kyoto Protocol industrialized countries agreed to a reduction
2.7!m!height!
!
Span!of!4,!6!or!7!m,!
between!the!columns!
!
3!
of 25 to 40% of emissions by 2020. Considering the plausibility of future developments in
most ceramic plants, this research, adopts the data of the Portuguese manufacturer indicating
the lowest embodied energy and carbon dioxide emission.
Regarding the data for cement, the same sources and data from a Portuguese cement
factory are presented in Table 2. Data for CIMPOR Company, the largest cement producer in
Portugal, is from the latest annual report "Sustainability Report '08"vii values related to the
production of cement in 2008.
Table 2, Comparison of embodied energy and carbon emission in the production of cement
UB
CIMPOR
IC
UM
EMBODIED ENERGY (MJ/kg)
4,6
3,591
7,02
4,00
CARBON EMISSION (kgCO22/kg)
0,83
0,676
-
-
In Table 2 the data of CIMPOR are more relevant for Portugal, as they represent the
real energy consumption and pollution from year 2008 and do not represent other sources
such as average values of several years and of other countries.
It is considered that the cement constitutes about 14% of concrete, water (with water /
cement ratio = 0.5) between 6 and 7% and the rest are almost 80% of aggregates, one can
conclude that proportionally the carbon emission in the manufacturing of concrete is 0,10
kgCO2/kg with 0.095 for cement (14%) and 0,005 (80%) for aggregates, whereas the
contribution of water is negligible. The carbon emission in the production of aggregates is
composed of grinding of aggregates using thermal energy and mixing them using electricity
when manufacturing concrete. The ICE document supplies the value of carbon emission in
the production of aggregates. Since the process is the same in Portugal or UK and there is no
technological development in this process and furthermore as the principal pollution is dust, it
is confirmed that the data of the United Kingdom should be equal for Portugal. Likewise the
values for the energy consumption in production of concrete can be determined. The assigned
value for concrete is 0.81 MJ/kg, with 0.504 for the cement and 0.307 for the aggregates and
water. These values appear according to author’s own survey (S) in the following table.
Table 3, Comparison of embodied energy and carbon emission in the production of concrete
UB
S
IC
UM
EMBODIED ENERGY (MJ/kg)
0,95
0,81
1,008
1,00
CARBON EMISSION (kgCO22/kg)
0,13
0,10
-
0,065
The collection of data on steel production, particularly the rebar used in concrete, and
the analysis and justification of data on the embodied energy and carbon emission is a
difficult and complex task. The steel industry is the largest producer of carbon among the
industries in general, in the world. The steel industry is conscious of this fact. In Europe
several projects are running to develop technologies for the reduction of carbon emission and
also for the storage of CO2 and its use for electricity production. The best-known project is
ULCOS (Ultra Light Steel manufacturing CO2). ULCOS is a consortium of industry
associations funded by the European Union. The project started in 2009 in the second phase
!
4!
(ULCOS II) with the aim of reducing CO2 emissions by half. There was also a significant
development in reducing pollution over the last 15 years by using electric oven. However, the
industry is still far from the goal.
Moreover, the issue is the complexity of the manufacture of steel and the different
methods of production. In addition to this fact some data refer to the raw steel and others to
treated steel, ready for use in construction. Furthermore attention should be paid if the data
refers to virgin or recycled steel.
As it is almost impossible to have the actual data, it has been decided to establish
average values, because every order of rebar can be treated differently by the industry and it is
almost impossible to define the embodied energy and the carbon emissions of steel shipped
accurately.
The data provided by the ICE document seems to be more accurate. The documents
"Energy Management"viii (SI), and "Insights from Steel - Benchmarks and Environment"ix
(TK), although not complete, confirm the mentioned data.
Table 4, Comparison of embodied energy and carbon emission in the production of steel
UB (ICE)
SI
TK
UM
virgin
recycled
average
raw
virgin
virgin
EMBODIED ENERGY (MJ/kg)
36,40
8,8
24,6
18,4
-
10
CARBON EMISSION (kgCO22/kg)
2,68
0,42
1,71
1,361
2,0
0,557
Considering the data of Table 4 and the facts mentioned above, the average values for
the rebar in the ICE document reflect better the reality and are more suitable for this analysis.
Thus the average value for energy consumption is considered 24.60 MJ/kg and
1.71 kgCO2/kg carbon pollution.
According to tables 1 - 4 the following quantifications of embodied energy and carbon
dioxide emission are chosen for the two construction solutions studied.
Carbon Emission
Ceramic block 0,100 kg CO2 / kg
Concrete 0,100 kg CO2 / kg
Steel 1,710 kg CO2 / kg
Mortar (5 to 10 MPa strength) 0,213 kg CO2 / kg
Embodied Energy
Ceramic block 1,02 MJ / kg
Concrete 0,81 MJ / kg
Steel 24,60 MJ / kg
Mortar (5 to 10 MPa strength) 1,40 MJ / kg
These figures relate to the manufacture of materials up to the preparation for transport at
the factory gate. Emissions and embodied energy for the transport of materials for the
functional units have not been considered.
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5!
3. Comparison of the Results
The functional units in masonry are considered for spans of 4, 6 or 7 m of two types, an
exterior wall with ceramic blocks of 290 mm thick, so called thermal blocks with the
minimum necessary resistance of 10 MPa, and interior wall using ceramic blocks of 110 mm,
with high density and resistance of 45 MPa. The higher resistance design of structural interior
walls sustains the stability of masonryx, on the other hand the higher density of the block is
environmentally not in favor of masonry.
In the case of conventional construction the same spans are considered, but the exterior
or interior units have side columns of 30x30 cm cross section. The width of 30 cm is a
common dimension, which can be found in most of the small 4 or 5 story buildings and is
structurally appropriate especially in earthquake zones. So the exterior walls will use the same
thermal block to guarantee similar thermal insulation quality and the spans of the inner walls
are filled with inferior quality of light ceramic blocks. This is in favor for the conventional
construction, but as structural inner walls are considered, their width may annul the benefit.
Concerning the comparison with masonry, it must be considered that masonry
buildings, as advised by the Eurocode 8, standard for seismic design, may not surpass 4
stores. Therefore the chosen width for the columns in conventional construction is an average
figure that serves for this study, equal for interior as exterior walls, as generally it is used for
the ground floor. All functional units have a height of 2,70 m. It has to be considered that on
upper floors the width or at least the reinforcement steel in columns can be reduced.
Therefore, the following results must be different for upper floors. It will be a matter of
another quantification to verify the data for each floor.
Regarding the equal thermal and acoustical insulation quality for the functional units,
especially for the exterior walls, which are of concern, as the thermal block is beneficial for
both solutions the fact remains that in case of the conventional construction the concrete
pillars are thermal bridges. This problem is be solved by considering an external 30 mm
thermal insulation for both cases. The thermal transmittance for the conventional solution is
0,456 and for masonry 0,422 W/m2K, which is a rather very small difference. Therefore, for
both solutions can be concluded that the functional units, hereby, fulfill similar thermal,
acoustical and structural criteria for the process of comparison.
3.1 Functional Unit: Exterior Wall
Data for exterior walls are estimated based on the sources indicated before and
presented in Table 5. For the exterior walls Table 5 clearly shows that in the case of structural
masonry increasing emissions are directly proportional to the increase of the span. Given the
values for the span of 4 m as the base value, the Factor shows the proportion of increase
according to the length of the wall. The increase is 50% when the length of the wall increases
from 4 m to 6 m and 75% from 4 m to 7 m. It is noticed that the same proportions exist for the
carbon dioxide emissions. Unlike the conventional construction an increase of 50% in length
shows an increase of 36% of the emission. An increase of 75% in the length shows an
increase of 55% of the emission. In conventional construction the larger spans are more
environmental friendly compared to smaller spans for the same construction. Comparing the
two construction techniques it is noticed that the masonry building has a lower CO2 emissions
!
6!
than the conventional construction. The difference decreases from 27% to 18% when the
length of the wall increases from 4 to 7 m.
Table 5, Carbon Emission (kg CO22 / Functional Unity)
Functional Unity
Conventional Construction
Masonry
Difference
Carbon
Factor
Carbon
Factor
4 m
748,34
1,00
545,18
1,00
27,15%
6 m
1020,93
1,36
817,78
1,50
19,90%
7 m
1157,23
1,55
954,07
1,75
17,56%
The embodied energy values change in a similar way to the carbon emission. The
embodied energy increases proportionally to the increasing span. In conventional construction
embodied energy increases 33% when the span increases from 4m to 6m and 49% when
increases from 4 m to 7 m. This behavior is similar to the changes in CO2 emission indicated
in Table 5.
Table 6, Embodied Energy (MJ) in Functional Unities
Functional Unity
Conventional Construction
Masonry
Difference
Energy
Factor
Energy
Factor
4 m
7675
1,00
5060
1,00
34,07%
6 m
10206
1,33
7591
1,50
25,62%
7 m
11471
1,49
8856
1,75
22,80%
The variation of embodied energy between the two constructive solutions is also similar
to variation observed for the carbon emission, albeit the values are larger for embodied
energy.
3.2. Functional Unit: Interior Wall
Values of carbon emission estimated for interior walls with 4m, 6m and 7m lengths are
presented in Table 7. The trend of the values for the interior walls is similar to those shown
for exterior walls. However, it has to be considered that while the volume of masonry material
is less, 110 mm thick, the concrete columns, 30x30 cm, have the same size as the exterior.
This explains the higher values of the differences observed between the two types of
construction technique for interior walls and exterior walls.
Table 7, Carbon Emission (kg CO2 / Functional Unity)
Functional Unity
Conventional Construction
Masonry
Difference
Carbon
Factor
Carbon
Factor
4 m
381,89
1,00
195,97
1,00
48,68%
6 m
438,92
1,15
293,95
1,50
33,03%
7 m
467,44
1,22
342,95
1,75
26,63%
!
7!
In conventional construction the change of 50% in the length increases only 12% in
CO2 emission and a 75% increase in length results in an increase of 18% in CO2 emission.
Table 8, Embodied Energy (MJ) in Functional Unity
Functional Unity
Conventional Construction
Masonry
Difference
Energy
Factor
Energy
Factor
4 m
4257
1,00
1874
1,00
55,98%
6 m
4776
1,12
2810
1,50
41,16%
7 m
5035
1,18
3279
1,75
34,88%
Table 8 presents data obtained for embodied energy for the two types of construction
technique and three spans considered. Comparing the embodied energy of the two
constructive solutions the trend is the same as the CO2 emissions. In conventional
construction the difference between the spans for embodied energy are 12% to 18%, but as
already noted, between the two solutions the differences are higher, varying from 35% to 56%
(Table 8) compared to 27% to 49% (Table 7).
4. Conclusion
The present study compares the CO2 emission and embodied energy for interior and
exterior walls of conventional construction with reinforced concrete columns and ceramic
bricks and the masonry building (using only ceramic bricks). The functional units considered
have the same structural and physical properties. The comparison shows that under the same
conditions the carbon dioxide emission of an exterior masonry wall is 27% to 17% less than
that of the conventional construction depending on the wall span. The smaller the span the
higher the differences obtained. In the case of interior walls the carbon dioxide emission is
49% to 27% less for the masonry building when compared to conventional building
technique. The embodied energy, for the exterior masonry walls are 34% to 23% less than
conventional building technique, while for interior walls they are 56% to 45% lower.
It is relevant to note that these differences are mainly due to the absence of reinforced
concrete columns in the masonry walls. Buildings in seismic areas can be built with ceramic
blocks up to 2 or 4 stories, depending on the seismic classification of the area. In non-seismic
areas this contribution can be multiplied as the boundaries only depend on the dimension of
the structure. Moreover, this study shows planers how to conduct a more environmental
friendly design and construction.
January 2014
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8!
References
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
i!! Sazedj, Soheyl, Análise de Sustentabilidade de Alvenaria Estrutural, PhD theses, Faculty
of Architecture, University of Lisbon, (2012)!
ii Grupo Preceram, Travasso, 3101-901, Pombal, Portugal, 2010
iii! Hammond, Geoff; Jones, Craig, Sustainable Energy Research Team, Department of
Mechanical Engineering, University of Bath (UB), United Kongdom, INVENTORY OF
CARBON AND ENERGY (ICE), 2008
iv Centro Tecnológico da Cerâmica e do Vidro (CTCV), , Portugal, "REFERENCE DATA
FOR BENCHMARKING", 2004
v Rovira Fontanals, Josep Lluis, Casado Martinez, de Institut Cerdá (IC), GUÍA DE
L’EDIFICACIÓN SOSTENIBLE, Spain, 1999
vi Said Jalali, F. da Eira Marcelo e J.A Nelson, ECOLOGIA DOS MATERIAIS DE
CONSTRUÇÃO, “ECOLOGY OF CONSTRUCTION MATERIALS” of Bjorn Berge,
1999, translated and adapted for Portuguese, Universidade Minho (UM), Portugal, 2007
vii CIMPOR Cimentos de Portugal, SGPS, SA., RELATÓRIO DE SUSTENTABILIDADE
’08, Portugal, 2008
viii Stahlinstitut VDEh und Wirtschaftsvereinigung Stahl im Stahl-Zentrum,
ENERGIEWIRTSCHAFT, "ENERGY MANAGEMENTE”, http://www.stahl-
online.de/Deutsch/Linke_Navigation/Technik_Forschung/Energie_und_Umwelttechnik/En
ergiewirtschaft.php?highmain=2&highsub=3&highsubsub=1, Germany, 2010, last
consulted May 2011
ix Weddige, Hans-Joern, Thyssen Krupp Steel, INSIGHTS FROM STEEL –
BENCHMARKS AND THE ENVIRONMENTE, Germany, 2009
x!! Sazedj, Soheyl, Análise de Sustentabilidade de Alvenaria Estrutural, PhD theses, Faculty
of Architecture, University of Lisbon, (2012)
... Peng, Zhao, Jiao, Zheng and Zeng [5] have calculated the CO2 emission and also suggest the options to reduce the emission in a ceramic tile manufacturer. For construction purpose, Sazedj, Morais and Jalali had compared the CO 2 emission from two types of materials, bricks and concrete block [6]. Bribian, Capilla and Uson [7] also studied the energy demand and CO 2 emission among different construction materials which are ceramic, steel, PVC, wood, mortar, cement, aluminium and lime. ...
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Energy use in the building is responsible for one-third of total carbon dioxide (CO2) emissions globally. Nearly half of the energy loss occurs through the building envelope due to heat transfer to/for the surroundings. Therefore, there is a need to design an optimum building envelope to reduce energy use in buildings that depend on several parameters. This study aims to review different building parameters and provide a conceptual framework to optimize the building envelope. In total, 260 papers were reviewed, and the building envelope design consideration was categorized into: 1) Design Parameters (design and geometry), 2) environmental conditions (indoor and outdoor) and 3) performance criteria (energy, environment, economic, comfort). Energy use and CO2-emission in buildings increase with high thermal conductivity, low thermal mass, and low solar absorption of its envelope. Geometrically, building orientation impacts energy use more than the building shape factor. Changing set point temperature according to surrounding conditions has reduced energy use and CO2-emission by 30% and 56%, respectively. However, indoor air quality, velocity, and occupancy have meagerly affected building energy use. Energy and emission optimization criteria are directly related, but the emission-based optimized envelope is thicker than the energy one. Other criteria such as economy and comfort (thermal and visual) are inversely proportional to the energy-efficient building envelope. Based on the comprehensive review, this study proposed a conceptual framework to design a sustainable building envelope that includes life cycle assessment, occupant's satisfaction, and social benefits. Several future research recommendations were made, including 1) the use of switchable reflective materials to minimize heat transfer, 2) dynamic insulation material to control insulation value as needed, and 3) smart windows with tunable optical properties.
Chapter
This chapter provides the reader with a better understanding of the life cycle environmental impacts, with a focus on the embodied impact of existing building stock. A systematic literature review is conducted to paint a clear picture of the current research activities and findings. The major components of embodied impact and parameters influencing the embodied impact are outlined and explained. Lastly, this chapter discusses the major barriers for the embodied impact assessment, and a potential analysis framework is proposed at the end.
Análise de Sustentabilidade de Alvenaria Estrutural, PhD theses, Faculty of Architecture
  • Sazedj
  • Soheyl
i Sazedj, Soheyl, Análise de Sustentabilidade de Alvenaria Estrutural, PhD theses, Faculty of Architecture, University of Lisbon, (2012)
  • F Vi Said Jalali
  • J Da Eira Marcelo E
  • Ecologia Nelson
  • Dos
  • De
  • Construção
vi Said Jalali, F. da Eira Marcelo e J.A Nelson, ECOLOGIA DOS MATERIAIS DE CONSTRUÇÃO, " ECOLOGY OF CONSTRUCTION MATERIALS " of Bjorn Berge, 1999, translated and adapted for Portuguese, Universidade Minho (UM), Portugal, 2007 vii CIMPOR Cimentos de Portugal, SGPS, SA., RELATÓRIO DE SUSTENTABILIDADE '08, " Portugal, 2008
ECOLOGY OF CONSTRUCTION MATERIALS" of Bjorn Berge, 1999, translated and adapted for Portuguese
  • Vi Said
  • F Jalali
  • J Da Eira Marcelo E
  • Ecologia Nelson
  • Dos
  • De
  • Construção
vi Said Jalali, F. da Eira Marcelo e J.A Nelson, ECOLOGIA DOS MATERIAIS DE CONSTRUÇÃO, "ECOLOGY OF CONSTRUCTION MATERIALS" of Bjorn Berge, 1999, translated and adapted for Portuguese, Universidade Minho (UM), Portugal, 2007