1-s2.0-S0378778820333983-main.pdf

Embodied energy and embodied carbon of structural building materials:
Worldwide progress and barriers through literature map analysis
Luisa F. Cabeza a,⇑
, Laura Boquera a,b
, Marta Chàfer a,b
, David Vérez a
a
GREiA Research Group, Universitat de Lleida, Pere de Cabrera s/n, 25001 Lleida, Spain
b
CIRIAF-Interuniversity Research Centre on Pollution and Environment Mauro Felli, Via G. Duranti 63, 06125 Perugia, Italy
a r t i c l e i n f o
Article history:
Received 8 August 2020
Revised 30 October 2020
Accepted 4 November 2020
Available online 7 November 2020
Keywords:
Climate change mitigation
Embodied energy
Embodied carbon
Range of values
Structural building materials
Literature map
Bibliometric analysis
a b s t r a c t
Climate change mitigation is a recurrent consciousness topic among society and policymakers. Actions
are being adopted to face this crucial environmental challenge, with a rising concern with a big impact
on the building sector. Construction materials have a high carbon footprint as well as an energy-
intensive activity. To measure the environmental damage and effects, life cycle assessment (LCA) is the
methodology most widespread. However, the LCA methodology itself and the assumptions done to carry
it out leads to a generalized burden to compare the case studies outcomes. LCA method and for instance
geographical location are incompatibilities also revealed in embodied energy and embodied carbon
assessments. Urgent actions are needed to clarify the confusions arisen in the research, considering a
detailed study on the embodied energy and embodied carbon values. From a material level point of view,
this paper aims to illustrate the chronological overview of embodied energy and embodied carbon
through keywords analysis. Moreover, to support and corroborate the analysis, an organized summary
of the literature data is presented, reporting the range of embodied energy and embodied carbon values
up to now. This systematic analysis evidences the lack of standardization and disagreement regarding the
assessment of coefficients, database source, and boundary system used in the methodology assessment.
Ó 2020 Elsevier B.V. All rights reserved.
1. Introduction
Climate change is the most serious global sustainability issue
our planet faces today and the energy required to operate buildings
is a major component of global emissions [1]. According to the IPCC
AR5 [2], buildings accounted for 32% of the total global final energy
use in 2010, which may potentially double or even triple by 2050.
More and more, awareness of embodied energy and greenhouse
gas (GHG) emissions has increased among environmental profes-
sionals, companies or other stakeholders, and are considered tools
to evaluate the environmental impact from building construction
activities since 1990s [3]. Thus, reducing the energy demand and
consequential carbon emissions attributed to buildings is clearly
an important goal for government climate policy [4,5].
There is a clear dichotomy between operational and embodied
impacts [6], and usually this is directly related to the use of the life
cycle assessment (LCA) methodology in the evaluation of the envi-
ronmental impact of buildings and their operation [7–9]. In the
past, environmental impacts from building operation were the
only issue to evaluate the environmental performance of those
buildings [10]. Moreover, some authors also show that reducing
the building operational use can lead to an increase in the total
building life cycle energy use coming from an increase of embodied
energy from the buildings components [10,11]. Therefore, embod-
ied energy has increased the attention of researchers in recent
years [12,13]. Nevertheless, it should be highlighted that it is
important that the overall building impact decreases, meaning that
both operational and embodied impacts should be considered
together [14,15].
Literature shows that embodied impacts are significant contrib-
utors to global emissions coming from buildings [6]. Embodied
impacts can account for 50% to 70% of the total ones. But the liter-
ature also shows that the contribution of each impact depends a lot
on the type of building [12]. In conventional buildings, operational
energy is closer to total energy and the embodied energy is com-
paratively really low; low-energy buildings have a higher contribu-
tion of embodied energy to the total energy; passive house
buildings have equal operational and embodied energy; and,
finally, those called self-sufficient buildings or energy plus-
buildings have no operational energy and the total energy consid-
ered in the LCA is embodied energy (the total energy is higher than
in passive houses). The embodied energy and embodied carbon of
buildings are commonly measured using an adapted form of LCA, a
https://doi.org/10.1016/j.enbuild.2020.110612
0378-7788/Ó 2020 Elsevier B.V. All rights reserved.
⇑ Corresponding author.
E-mail address: luisaf.cabeza@udl.cat (L.F. Cabeza).
Energy & Buildings 231 (2021) 110612
Contents lists available at ScienceDirect
Energy & Buildings
journal homepage: www.elsevier.com/locate/enb

method of analysing the environmental impacts of the whole life of
a product [16].
The serious concern on climate change current situation is lead-
ing to a global modification of building standards. The reduction of
building consumption not only should be considered from the
active systems used in the buildings, passive strategies represent
are becoming a key element during the building design process
[10,11]. In extreme climates, is required a rigorous construction
configuration where high insulation is added or massive materials
are used to preserve the thermal comfort. Consequently, influence
in the increase of embodied energy and carbon in the buildings, in
particular passive houses and nearly zero energy buildings [12].
Embodied energy is studied in the literature at different levels,
going from a particular to a general part of the building: at mate-
rials level, at building component level, and at building level. Sev-
eral researchers [10,15,17] reported that, operational energy,
embodied energy and embodied carbon are highly related to the
geographical location during the life cycle considered in the study.
A lot of effort has been done to show this variation of results
between countries, but this also means that the comparison of
ratios is extremely difficult. This absence of homogenous data
and methodology was already mentioned by Cabeza et al. [15].
Moreover, a needed consensus on the assessment methods is being
claimed in order to have an objective and realistic knowledge
about embodied energy and carbon data [10,18].
Embodied carbon has raised attention much more recently than
embodied energy and the literature on the topic is more scarce [6].
Moreover, its interest grew also related to CO2 emissions and the
impact factor carbon footprint.
The vast majority of literature studies evidence the insufficient
consensus in the methodologies selected and the incomparable
results. Further attention should be paid to embodied energy and
embodied carbon numerical values that are considered in the dif-
ferent research publications. Pomponi et al. [11] presented a sys-
tematic review of embodied carbon in buildings, considering
their main structural materials. This paper goes beyond that study
and has a deep approach collecting and organizing quantitatively
data of the embodied energy and embodied carbon in building
materials. Due to the complexity of buildings and the amount of
different materials used in each one, this papers is focused on
the materials used as structure frame materials, which have been
identified as those being major components in terms of mass and
embodied impacts, and thus, being the ones to achieve reduction
of environmental impacts [17].
2. Taxonomy
There is no agreement in how to define embodied energy (EE).
For example, Hu 2020 [3] and De Wolf et al. 2017 [14] concluded
that ‘‘EE can be defined as the energy consumed during a building
whole life cycle; this excludes the operating energy, but includes
raw material extraction, product production, manufacturing,
installation, on-site construction, maintenance, repair and replace-
ment, and finally the demolition and disposal of a building” [3,14].
However, Dixit et al. [19] stated that ‘‘the term embodied energy is
subject to numerous interpretations rendered by different authors
and its published measurements are found to be quite unclear”. On
the other hand, according to the literature embodied carbon (EC)
can be defined as ‘‘the sum of fuel related carbon emissions and
process related carbon emissions; this can be measured from cra-
dle to gate, or cradle to grave [1]”. Embodied energy and embodied
carbon is now equally viewed as being important in the context
of buildings and construction materials [20]. Thus, the authors of
this paper tried to summarize the definitions of EE in Fig. 1.
Fig. 1 presents the stages and boundaries of LCA. Following the
standard EN-15804:2012 + A1:2014 [21], the LCA stages go from
A1-A5, B1-B7, C1-C4 to D. The boundaries used when performing
a LCA are cradle to gate, cradle to site, cradle to handover, cradle
to end of use, cradle to grave, and cradle to cradle. The boundaries
mostly used in the definition of EE are cradle to gate [22–24] and
cradle to handover [25–28], although definitions with the other
boundaries considered can also be found; Meanwhile, definitions
for EC were found considering cradle to gate [29] and cradle to
handover [30].
As discussed before, EE and EC are commonly measured within
the LCA context. The LCA method traces a range of environmental
impacts of all materials, components and processes conforming the
Fig. 1. Embodied energy [22–28,31–37] and embodied carbon [29,30,38] definitions/concepts in a life cycle stage frame.
L.F. Cabeza, L. Boquera, M. Chàfer et al. Energy & Buildings 231 (2021) 110612
2

building. There is a growing body of literature on embodied energy
and carbon in the construction of houses. Studies typically use a
process based LCA methodology (bottom up) rather than an
input–output (top-down) methodology. Individual process based
studies have used different parameters, factors, datasets, and
boundaries. Shortcomings in process and input–output analysis
were found by the authors in the literature. In a process-based
method, detailed analysis is carried out for a specific process while
input–output analysis considers the national average statistics. To
overcome these limitations the method ‘‘process-based hybrid
method” and ‘‘input–output based hybrid method” were devel-
oped, taking advantage of the strength of each method [39–41].
Consequently, results from lifecycle studies are indicative and
should be interpreted with caution and careful attention to the
methods used, the system boundaries applied, and what has (or
has not) been included before any interpretation can be made or
conclusions drawn [38]. For instance, Yu et al. [42] calculated the
Australian-specific GHG emission intensities of several construc-
tion materials, reporting that process-based results were 3% to
59% lower compared to hybrid results, obtaining an average trun-
cation error of 20%.
Moreover, sometimes identifying the terms used in the assess-
ment or calculation of EE and EC is not clear, since their concepts
are mixed with others such as carbon footprint. To show this, a
search in Scopus was carried out where the terms ‘‘embodied
energy”, ‘‘embodied carbon”, ‘‘carbon footprint”, ‘‘embodied GHG”
can be found together with ‘‘building” or ‘‘material” (Fig. 2). The
term ‘‘carbon footprint” is the one most used both related to build-
ings and to materials, being a unit to evaluate the impact in
methodologies such as LCA; this finding agrees with the literature
[43]. On the other hand, when considering buildings, the global
warming potential is related to embodied carbon, while in materi-
als it is related to embodied energy. Again, this shows that there is
no consensus in the literature on how to consider these terms and
their relation with other concepts such as climate change.
3. Building structures definition
Since the present paper scope focuses on the mainstream struc-
tural materials used over the world, an outline description of them
is presented in this section. Engineering structures are composed
of materials. These materials are known as engineering materials
or building materials or materials of construction. A wide range
of building materials is available for the construction of buildings
and structures. The proper selection of materials to be used in a
particular building or structure can influence the cost, mainte-
nance, ease of cleaning, durability, appearance or aesthetics, and
climate impact [4]. The main building structures construction
materials can be classified as concrete, steel, masonry, rammed
earth, and wood.
Concrete, a composite man-made material, is the most widely
used building material in the construction industry [44]. It consists
of a rationally chosen mixture of binding material such as lime or
cement, well-graded fine and coarse aggregates, water, and admix-
tures (to produce concrete with special properties) [45]. For a con-
crete construction of any size, as concrete has a rather low tensile
strength, it is generally strengthened using steel rods or bars. This
strengthened concrete is then referred to as reinforced concrete
[44,46]. Concrete has been the predominant material in this mod-
ern age due to its longevity, formability, and ease of transport.
Moreover, concrete can be found in all climates worldwide [44].
An example of concrete structural material can be seen in Fig. 3,
for the Mediterranean climate and Fig. 4 for tropical climate.
Steel is one of the strongest building materials available with
excellent strength capacity in both tension and compression.
Because of its high strength-to-weight ratio, it is ideal for struc-
tural framework of tall buildings and large industrial facilities
(Fig. 5) [47,48]. The primary characteristics of structural steel
include mechanical and chemical properties, metallurgical struc-
tures and weldability [49]. However, one important property of
steel is that it quickly loses its strength in a fire. Therefore, steel
in buildings must be protected from fire or high temperature; this
is usually done by wrapping it with boards or spray-on material
called fire protection [50].
Masonry is a heterogeneous material that consists of units and
joints. Units are bricks, blocks, ashlars, adobes, irregular stones,
Fig. 2. Trends of keywords used (from Scopus database) to refer to embodied
energy or embodied carbon studies in (a) buildings and (b) materials. Fig. 3. Museum Can Framis, Barcelona, Spain. By BAAS architects.
3

and others. Mortar can be clay, bitumen, chalk, lime-/cement-
based mortar, glue, or others [51]. Over the last three decades,
the term ‘masonry’ has been widened from its traditional meaning
of structures built of natural stone to encompass all structures pro-
duced by stacking, piling, or bonding together discrete chunks of
rock, fired clay, concrete, etc. to form the whole. In contemporary
construction, most masonry is built from man-made materials
such as bricks and blocks (Fig. 6). Stone, because of its relatively
high cost and the environmental disadvantages of quarrying, is
mainly used as thin veneer cladding or in conservation work on
listed buildings and monuments. The basic principle of masonry
is of building stable bonded (interlocked) stacks of handleable
pieces [52].
On the other side, rammed earth construction is a structural
building method of compressing a sandy mixture into a hard
sandstone-like material (Fig. 7). Rammed earth has a long and con-
tinued history throughout many regions of the world. Rammed
earth, like most types of earthen construction, is relatively stronger
in compression than it is in bending and shear [53]. Moreover,
rammed earth buildings around the world are renowned for their
ability to provide comfortable living conditions for a range of cli-
mate types without the need for active HVAC control [54].
Rammed earth has been used successfully in mild to hot climates
as the thermal mass effectively moderates the daily temperature
swings, creating a comfortable living environment [55].
Finally, wood is a natural organic material that has been used
for many centuries for the construction of buildings, bridges, and
a variety of other structures. It remains an important construction
material today as research and improved technology have led to a
better knowledge of the material behavior construction. This has
helped designers to use timber more efficiently [56,57], an exam-
ple can be seen in Fig. 8. Wood is easily available and easy to trans-
port and handle, important thermal insulation, sound absorption,
and electrical resistance. It is the ideal material to be used in sea-
water. Wood is a good absorber of shocks and so is suitable for con-
struction work in hilly areas which are more prone to earthquakes.
Finally, since wood can be easily worked, repairs, and alterations to
wood work can also be done easily [58].
Fig. 4. School of Design and Environment, SD4, Singapore. Serie Architects.
Fig. 5. 20 Fenchurch Street, London, United Kingdom. By Rafael Viñoly Architect.
Fig. 6. Lolita Restaurant, Almunia de Doña Godina, Spain. By Langarita Navarro Architects.
Fig. 7. Visitors Centre, Eden Project, Cornwall. UK. Grimshaw Architects [53].
4

Inside the ‘‘wood group” of structural materials it can be found
bamboo. Bamboo is a traditional building material throughout the
worlds tropical and sub-tropical regions. Bamboo is a renewable
and versatile resource, with high strength and low weight. That
is why it is widely used in different forms of construction, particu-
larly for housing in rural areas [59]. However, bamboos have some
shortcomings that limit their application. The low durability of
bamboo is one of its most serious defects, along with its flammabil-
ity and tendency to split easily. Moreover, dry bamboo is extremely
susceptible to fire, but it can be covered or treated with fire-
retardant material. The strength properties of bamboo vary widely
with species, growing conditions, position within the culm, season-
ing, and moisture content. Generally, bamboo is as strong as timber
in compression and very much stronger in tension. However, bam-
boo is weak in shear, with only about 8% of compressive strength,
whereas timber normally has 20%–30%. It is used mainly in build-
ing construction, for wall poles, frames, roof construction, roofing,
and water pipes and, after splitting, to form flattened boards or
woven wall, floor, and ceiling panels (Fig. 9) [58].
4. Methodology
Fig. 10 presents the methodology of this study, which is divided
in two parts. The first one is an analysis of the literature on the
topic, developed through a bibliometric analysis and some litera-
ture maps based on a search in the Scopus database. The second
part is a quantitative analysis of the embodied energy and embod-
ied carbon values reported in the literature.
Regarding the bibliometric analysis, scholars have defined bib-
liometrics as the research field of library and information sciences
that studies bibliographic material with quantitative methods
[60,61]. This methodology has become very useful in providing a
historical and quantitative overview of a set of bibliographic data.
Scopus database was chosen due to it covers a wider range of engi-
neering documents than Web of Science [62]. The search process
was conducted in March 2020, what means that the documents
found range from 1981 to 2020. Moreover, the bibliographic mate-
rial was also mapped graphically to provide a visual representation
of key indicators. The visualization of similarities was done using
the software VOSviewer developed by van Eck and Waltman
[63,64] to facilitate bibliometric mapping with visual reports,
including bibliographic coupling relations, co-citation analysis,
and co-occurrence of keywords a visual representation of key
indicators.
In this study, several queries were used to identify and analyse
the literature on the topic. The queries were divided as shown in
Table 1; first, there was a general query (named Query 1) which
includes ‘‘embodied energy or embodied carbon” and all the mate-
rials selected for the study. The following queries 2, 3, 4 and 5 are
restrictive queries or subqueries classified by materials: concrete,
steel, masonry, and wood.
In the second part of the paper, a systematic review was carried
out searching for embodied energy and embodied carbon coeffi-
cients of the material, without considering the results of a building
component or the total building (see above definitions of the
queries used). From all papers found, only those giving a value
for embodied energy or embodied carbon of the material itself
were considered in this part of the study. The data found was listed
in an organised way to be able to compare it. It is important to
highlight that the boundaries of the LCA defined above were con-
sidered to carry out this organization.
The papers are presented in a chronological order. First the
boundary of the LCA is stated. Then, the table indicates if the value
presented comes from the literature or from a data base. Further-
more, the construction system is specified as it is mentioned in
the original paper, together with the location of the project (with-
out considering if the material database also considers this same
country in the assigned EE/EC). Another determinant factor that
was considered during the articles scrutiny was the EE or EC unit.
Hence, to narrow this research MJ/kg or MJ/m3
and kg CO2/kg or
kg/CO2m3
were considered to identify embodied energy and
embodied carbon coefficients.
5. Bibliometric and keyword analysis
The general query (Query 1) gave 1003 documents, which were
the references used in this section of the paper. The study was per-
formed considering no time limitation, therefore the results show
the publications until March 2020 (nevertheless, publications with
Fig. 8. Residential building of timber structure, located in Lleida, Spain. By Ramon Llobera Architect.
Fig. 9. Green Village in Bali, Indonesia. Ibuku Architects.
5

the date 2020 are not considered in the bibliometric analysis since
is not representative for the whole year).
The trends in the number of publications per type of material
are shown in Fig. 11. The analysis of embodied energy and embod-
ied carbon in materials was a topic of interest in research already
in the 1980s since two publications appeared in 1981 (not included
in the figure); and the interest has continued in the peer-reviewed
literature until today. From 2004 the publications started to grow
(from 1 document in 2003 to 137 in 2019), with a slight decrease
in 2009 (20 documents compared to 24 in 2008). The same trend
can be seen for each group of materials. It is interesting to see that
all groups of materials started to be published in the same decade,
but concrete has grabbed the largest number of publications in the
last 8 years. It is also interesting to see that the number of publica-
tions on masonry and earth stagnated in the last few years to a
constant number of 35 documents per year, while the number of
publications on wood is recently growing at a somehow higher
rate.
Fig. 12 shows the regional distribution by country and material
groups, showing a heterogeneous distribution worldwide. The first
thing to highlight is that all continents have publications on the
topic studied in this paper; moreover, Asia is very well represented
in number of countries with documents, and South America and
Africa also list a few countries.
Fig. 10. Methodology for the bibliometric and the quantitative analysis of embodied energy and embodied carbon data.
Table 1
Queries used in this study.
Number Documents Query
1 1003 (‘‘metal*” OR ‘‘iron” OR ‘‘steel*” OR ‘‘wood” OR
‘‘timber” OR ‘‘bamboo” OR ‘‘concrete*” OR
‘‘reinforced concrete*” OR ‘‘geopolymer” OR
masonry OR ‘‘stone*” OR ‘‘rock*” or ‘‘rammed earth”
OR ‘‘earth block*” OR ‘‘earth brick*” OR ‘‘mud” OR
‘‘soil” OR ‘‘cob”) AND (‘‘embodied energy” OR
‘‘embodied carbon”)
2 546 (‘‘concrete*” OR ‘‘reinforced concrete*” OR
‘‘geopolymer”) AND (‘‘embodied energy” OR
3 384 (‘‘metal*” OR ‘‘iron” OR ‘‘steel*”) AND (”embodied
energy‘‘ OR ”embodied carbon‘‘)
4 285 (masonry OR ‘‘stone*” OR ‘‘rock*” or ‘‘rammed earth”
OR ‘‘earth block*” OR ‘‘earth brick*” OR ‘‘mud” OR
‘‘soil” OR ‘‘cob”) AND (‘‘embodied energy” OR
5 216 (‘‘wood” OR ‘‘timber” OR ‘‘bamboo) AND (”embodied
energy‘‘ OR ”embodied carbon‘‘)
Fig. 11. Trends in number of publications per type of material.
6

United States of America, the United Kingdom, Israel, and Aus-
tralia show a greater number of publications on concrete. More-
over, a higher number of publications in masonry and earth
materials can be found in India, Vietnam, and France; and more
publications on steel in China, probably due to the construction
of steel framed high-rise buildings in cities such as Shanghai and
Beijing. The countries with raising interest in wood are Slovenia,
Estonia, Norway, Austria, and Denmark.
Next, author keywords were evaluated to understand the rela-
tion between the materials studied and the topic of study, using
the general query (Query 1) (Fig. 13). As expected, Fig. 14 details
that the research on embodied energy (251 occurrences) and
embodied carbon (76 occurrences) in building materials is highly
related to the development of life cycle assessment (LCA) studies
(155 occurrences) [65–73]. The co-occurrence network (Fig. 13)
shows the keywords grouped in five clusters. The first cluster, in
blue, groups ‘‘embodied carbon” with ‘‘environmental impact”,
‘‘high rise building”, ‘‘building material”, and ‘‘global warming
potential”. It also links ‘‘carbon footprint” with ‘‘reinforced con-
crete”, ‘‘glulam” (Glued laminated timber), and ‘‘prefabrication”.
The second cluster, in purple, groups ‘‘greenhouse gases emissions”
with ‘‘environment”, and ‘‘clay”, ‘‘brick”, and ‘‘bamboo” with ‘‘ther-
mal performance”. The third cluster, in red, groups ‘‘sustainability”
with ‘‘green building”, ‘‘fly ash”, ‘‘geopolymer”, ‘‘silica fume” and
‘‘natural fibers”, and ‘‘concrete” with ‘‘durability”, ‘‘strength”, and
‘‘slag” and ‘‘cost”, also links ‘‘rammed earth”, and ‘‘sustainable
development”, ‘‘durability”, and ‘‘adobe”. The fourth cluster, in
green, links ‘‘embodied energy” with ‘‘carbon dioxide emissions”,
and ‘‘energy efficiency”, and ‘‘recycling” with ‘‘cement”, ‘‘alu-
minium”, ‘‘biomass” and ‘‘circular economy”. Finally, the fifth clus-
ter in yellow groups ‘‘LCA” with ‘‘climate change”, ‘‘low embodied
energy”, and ‘‘sustainable construction”.
When analysing in detail the material groups considered in
the paper (concrete, masonry and earth materials, wood, and steel)
(Fig. 15), it can be seen that the first two materials are consid-
ered almost three times more than the other ones (with 41
occurrences for concrete, 44 occurrences for masonry and earth
materials, 16 for wood, and 14 for steel). But more interesting
in this figure is the fact that composite materials can be identi-
fied, showing overlaps between the materials studied and also
showing how these materials are used. For example, ‘‘reinforced
concrete” [74–76], ‘‘timber-concrete” composite[77], ‘‘concrete-
glulam” prefabricated composite[78], and bamboo and com-
pressed earth walls [79].
(a)
(b) (c)
Fig. 12. Regional distribution of located documented per country and groups of materials, (a) worldwide, (b) Europe, (c) Australia, (d) North America, (e) South America, (f)
Africa and Middle East, (g) Asia.
7

The co-occurrence network for concrete materials (Query 2)
groups five different clusters (Fig. 16). The first cluster, in yellow,
groups ‘‘concrete” with ‘‘sustainability”, ‘‘durability”, and ‘‘steel”,
also links ‘‘concrete” with ‘‘recycling”, and ‘‘recycled aggregates”.
The second cluster, in blue, groups ‘‘LCA”, with ‘‘carbon footprint”,
‘‘building material”, ‘‘building envelope”, and ‘‘green building”
with ‘‘glulam” and ‘‘wood products”. The third cluster, in green
groups ‘‘embodied energy” with ‘‘embodied carbon”, ‘‘environmen-
tal impact”, ‘‘carbon dioxide emissions”, and ‘‘thermal mass” with
‘‘input output analysis”, and ‘‘optimization”. The fourth cluster, in
purple brings together ‘‘compressive strength”, ‘‘rammed earth”,
‘‘cement combination”, and ‘‘limestone”. And the five cluster, in
red groups ‘‘climate change”, ‘‘cement”, ‘‘geopolymer”, ‘‘fly ash”,
and ‘‘composite material”.
The co-occurrence network for wood materials also brings five
different clusters Fig. 17. The first cluster, in red, groups ‘‘carbon
dioxide emissions” with ‘‘climate change”, ‘‘energy”, and ‘‘steel”,
‘‘bamboo”, and ‘‘global warming potential”, with ‘‘sustainable
building”. The second cluster, in blue, groups ‘‘LCA”, with ‘‘embod-
ied energy”, ‘‘embodied carbon”, and ‘‘bio-based materials”. The
third cluster, in green groups ‘‘timber” with ‘‘sustainability”, ‘‘com-
posite materials”, ‘‘cross laminated timber”, and ‘‘silica fume”. The
fourth cluster, in yellow groups ‘‘environmental impact”, ‘‘prefabri-
cation”, ‘‘reinforced concrete”, and ‘‘glulam”. And the five cluster, in
purple link ‘‘carbon footprint”, with ‘‘wood products”, and ‘‘life-
cycle inventory”.
The co-occurrence network for steel materials shows five clus-
ters in Fig. 18. The first cluster, in red, groups ‘‘embodied energy”
with ‘‘LCA”, ‘‘optimization”, and ‘‘raw material”, and ‘‘cross lami-
nated timber”, with ‘‘prefabrication”. The second cluster, in green,
groups ‘‘carbon dioxide emissions”, with ‘‘greenhouse gases emis-
sions”, ‘‘energy consumption”, and ‘‘sustainable construction” with
‘‘input output analysis”. The third cluster, in blue groups ‘‘carbon
footprint” with ‘‘sustainability”, and ‘‘thermal performance” with
‘‘geopolymer”. The fourth cluster, in yellow groups ‘‘steel”, ‘‘con-
crete”, ‘‘recycling” and ‘‘energy efficiency” with ‘‘operational
energy”. The five cluster, in purple link ‘‘embodied carbon”, with
‘‘building material”, and ‘‘environmental impact” with ‘‘high rise
building”, and ‘‘structure frame”.
The co-occurrence network for masonry and earth materials
group four clusters Fig. 19. The first cluster, in blue, groups
‘‘rammed earth” with ‘‘geopolymer”, and ‘‘thermal performance”,
and links ‘‘sustainable building” with ‘‘environmental impact”,
‘‘brick”, and ‘‘bamboo”. The second cluster, in red, groups ‘‘LCA”,
with ‘‘embodied carbon”, ‘‘sustainability”, ‘‘carbon footprint”, ‘‘glo-
bal warming potential”, and ‘‘recycling”. The third cluster, in green
groups ‘‘embodied energy” with ‘‘energy efficiency”, ‘‘building
material”, ‘‘sustainable development”, and ‘‘greenhouse gases
emissions”. The fourth cluster, in yellow groups ‘‘concrete”, ‘‘dura-
bility”, ‘‘steel”, ‘‘recycling” and ‘‘recycled aggregates”.
When comparing the main author keywords for the different
queries (Figs. 15–19) it can be seen that ‘‘prefabrication” can be
Fig. 12 (continued)
8

found in wood and steel, but not in concrete as it would be
expected; steel also lists ‘‘high rise building”. On the other hand,
concrete lists properties and tests as important keywords. Recycla-
bility is a key topic in several material groups; for example, ‘‘recy-
cling” appears in steel and masonry and ‘‘recycled aggregate” in
concrete. On the other hand, wood lists ‘‘bio-based material” and
‘‘composite” as keywords. The topic of energy efficiency is also
important in the research related to EE/EC; for example, steel lists
‘‘energy consumption” and ‘‘thermal performance”, concrete ‘‘ther-
mal mass”, masonry ‘‘energy efficiency”, and the general query ‘‘en-
ergy savings”. Finally, contrary to what could be expected, ‘‘climate
change” only appears as a key author keyword in wood materials.
The analysis of the overlay of the keywords network (Fig. 20)
shows that most publications can be found from 2012 to 2018. In
2012 the studies were focused on the analysis of the environmen-
tal impact, embodied energy, and carbon of materials such as con-
crete, steel, masonry, and mostly wood products [80–84]. In recent
years, studies have focused on the fight against climate change,
with research on topics such as circular economy and recycling
of materials [85–88]. At the building level, the emphasis has been
placed on the building envelope [8,89–92], and building structural
optimization [93–97], to increase embodied energy, and embodied
carbon, decrease the overall cost and operational energy, while
maintaining comfort levels. When analysing materials, concrete is
the most recent topic with studies on geopolymer [98–107], recy-
cled aggregates [65,108,109], and fly ash [110,111].
6. Embodied energy and embodied carbon in building materials
Tables 2–6 present a summary of the quantified values for EE
and EC from 70 research documents found in the literature. Several
articles present data for the different materials categories studied.
In the tables are found the following publications per group: con-
crete 47, steel 26, masonry 32, earth material 22, and timber 17.
In general, Tables 2–6 highlight the fact that concrete is the
most assessed material by authors. Also, it is worth noting that
the LCA boundary system used more is within the product stage,
Fig. 13. Co-occurrence keywords network (Query 1 - general).
Fig. 14. Keywords network (LCA) (Query 1 - general).
9

from ‘‘cradle to gate”. This fact facilitates the data comparison of
the materials studied.
On the other hand, it can be observed that in some papers the
value is reported without notifying the source or the life cycle
stages considered in the analysis. The study of the data source
shows that usually databases, such as Ecoinvent, are the preferred
ones. Here, it should also be highlighted that sometimes the paper
states that the data is provided from a country different from
where the project is located. Often the results collected from liter-
ature are subjected to a slight change adopted to reach each pub-
lication target.
The first publications related to EE/EC that date from years 2002
to 2011, are based on the same databases. Whereas, from 2012
software programs started to be used for the assessments.
Table 2 shows that concrete is the material with more research;
therefore it is considered a benchmark to study and compare with
the other materials. The table also shows that concrete can be
found used as composite mixed with many other materials and
that concrete can be produced in different formats (e.g. prefabri-
cated, blocks). Concrete is a heterogeneous material that allows
to vary its components in relation the final application properties
demand. In some cases, to reduce the carbon emissions from
cement, supplementary cementitious materials, like fly ash or sil-
ica fume, are added. This partial replacement of cement was
noticed by Sabapathy et al. [112] in 2013 and its interest increased
since 2017. Looking at the countries with EE/EC values, Australia
have the highest number of publications related to concrete mate-
rials, followed by New Zealand, India, and UK. Like in the other
materials, ‘‘cradle to gate” is the system boundary most selected
by the authors to asses embodied energy and embodied carbon
in concrete.
Table 3 shows the main steel materials used for structural pro-
poses, iron, and steel. Several types of steel format are presented,
for instance, the steel welded sections, rebars used in concrete,
or the steel-frame profiles. Also, stand out that some authors take
into consideration the recycled steel which will represent a
decrease in embodied energy and carbon above all.
For the group masonry and earth materials, the valued found in
the literature for EE and EC could be split in two tables, one for
masonry (Table 4) and one for rammed earth (Table 5).
Table 4 embraces masonry materials, mainly brunt clay bricks
and stone. Despite the fact that adobe, compressed earth blocks,
and concrete can be used in a masonry format, they were grouped
in the other tables that have similar material components and
treatments. This category prevails de traditional ceramic brick
and India is the country that has done the most research on it, fol-
lowed by UK and China.
Table 5 presents the different types of earthen construction
material systems. The commonly assessed are rammed earth and
adobe. Like in wooden materials the first coefficients provided
are from New Zealand. However, the leading countries in this cat-
egory are India and Cyprus. Earthen material used is the one locally
Fig. 15. Co-occurrence keywords network (Query 1 - general), highlighting materials relations.
10

available, usually with fibre or cement addition. Since the trend is
to use the material from the construction site, in this category the
boundary system observed is divided into ‘‘cradle to gate” and
‘‘cradle to site”.
Table 6 shows naturally grown materials, diversity types of tim-
ber and along to this group, bamboo was added which is recently
in the spotlight, considered as an environmentally friendly mate-
rial. Even though, nearly all references from this category selected
a ‘‘cradle to gate” boundary system, the embodied energy presents
a wide range of coefficients concerning the wood type and its treat-
ment. New Zealand rules the timber category followed by the UK,
Australia and the USA. Lately, Asiatic countries are drawing more
attention in further research of wooden materials. Embodied car-
bon in wood only considered in seven publications out of 17.
Fig. 16. Co-occurrence keywords network (Query 2 - concrete materials).
Fig. 17. Co-occurrence keywords network (Query 3 - wood materials).
11

Embodied carbon coefficients are similar, only Alcorn et al. [113]
reported negative values. These results are related to the carbon
dioxide stored by trees during their life growth. This concept is
referred as carbon sequestration.
Analysing the general boundary system determined in each
group of materials, Fig. 21 shows that despite the fact that cradle
to gate is the most selected in the studied literature, there is high
percentage in all categories in which the boundary system is not
defined. In particular, in steel and masonry categories the boundary
system in half of the literature is not defined. This figure also high-
lights that cradle to handover is only present in the group steel and
that in earth materials the boundary system is adapted by the
authors to each life cycle stage.
In addition, the database sources in the publications studied in
Tables 2–6 are shown in Fig. 21b. Like in Fig. 21a, there is an impor-
tant number of publications that do not define the database source
Fig. 18. Co-occurrence keywords network (Query 4 - steel materials).
Fig. 19. Co-occurrence keywords network (Query 5 - masonry and earth material).
12

nor the boundary system used. Regarding the database source, ma-
sonry, earth materials, and timber have a higher percentage of not
defined database source. In contrast, steel has more than fifty per-
cent of its database source is from literature data.
7. Discussion
A summary of the embodied energy and embodied carbon coef-
ficients of the four structural materials is presented in Fig. 22 only
considering those at the product stage (‘‘cradle to gate” or A1-A3)
for comparison purposes. To have an easier visual interpretation
and comparison of the materials, gradient colour bars present the
ranges between the lowest and highest value reported in the liter-
ature of each material and standing out the literature commonly
used coefficient in the darkest shade. From each material category,
the main sub-system materials used in the literature are presented.
As other researchers stated [11,17,168], there is a wide variety of
numerical results in both EE and EC, evidencing the confrontation
associated with data source and defined boundaries.
In Fig. 21a, it can be appreciated that earth materials have the
lowest embodied energy, around 0.60 MJ/kg, while general steel
has the highest, with a commonly considered value of 32–35 MJ/
kg [115,116,121,122,124]. The timber group shows a wide range
of results, having general timber a frequently used embodied
energy of 3 MJ/kg, while bamboo is 2.58 MJ/kg [125]. Going into
detail with the type of timber, glulam and cross laminated timber
present greater embodied energy than general timber. High
embodied energy values are associated to manufacture process
mostly in the kiln dried treatment [169]. The embodied energy in
earth materials is very similar among construction system types
(adobe, rammed earth, and compressed earth block), 0.45 MJ/kg
[1,116,121,122,124] is typically used. Sometimes cement can be
added to the earth as a stabilizer material, for this reason, embod-
ied energy can grow. For instance, in rammed earth is a bit higher
(0.83 MJ/kg [1]) than the other earth techniques. Since the earth is
a raw material that is available at all locations, this allows to use
the building site earth, shifting the transport stage and hence
reducing the embodied energy. Also, on concrete, the major part
of its components (aggregates and water) are worldwide available.
However, for cement production and concrete preparation high
energy is required, increasing the embodied energy in reinforced
concrete up to a frequently used 2–2.5 MJ/kg [120–122,152] and
for concrete 0.78–1 MJ/kg. Similar coefficients are found in the
masonry group, having stone a most widely used embodied energy
of 0.97 MJ/kg [115,116,121,122], while brick presents higher dis-
persion of values with a most repeated embodied energy of 2.5–
3 MJ/kg [1,113,115,116,124,129,152]. In the steel category, recy-
cled steel has a considerably lower embodied energy, for instance
100% recycled steel can have an embodied energy of 10 MJ/kg
[144].
On the other hand, Fig. 22b shows that traditional materials
used in vernacular architecture, such as rammed earth, stone,
and timber, have the lowest greenhouse gas emissions. While, steel
is the highest carbon intensive material, with an average of 2.53–
2.71 kg CO2/kg [1,114,125,155]. When comparing timber types, a
high variation of embodied carbon coefficients can be seen. How-
ever, in general for timber the value 0.30 – 0.40 kg CO2/kg
[1,125,150] is often used. Other than adobe, which does not have
reported embodied carbon values in the literature, similar coeffi-
cients are detected among the other earth materials techniques,
being 0.023–0.025 kg CO2/kg [1,167]. In reinforced concrete,
embodied carbon is between 0.19 and 0.24 kg CO2/kg [1,152],
while in common concrete 0.10 to 0.16 kg CO2/kg is reported
Fig. 20. Keywords network trends (Query 1 - general).
13

Table 2
Concrete based (precast concrete, concrete block, reinforced concrete) structure -frame material type.
LCA method/
system
boundaries
Software or data base used Construction system Project
location
Total Embodied
energy
Total Embodied
carbon
Reference
[MJ/m3
] [MJ/
kg]
[kg
CO2/
kg]
[kg
CO2/
m3
]
– – Reinforced concrete (2400) New
Zealand
7300 3.1 0.076 – Buchanan
(1994) [114]
Precast concrete 4780 – 168 kg/
m3
–
Concrete in-situ 3840 – 138 –
– – Concrete block New
Zealand
– 0.86 – Alcorn (1996)
[115]
Concrete glass reinforced – 3.40 – –
Concrete, 30 MPa – 1.40 – –
Concrete precast – 2.00 – –
Cradle to gate Literature Concrete block New
Zealand
– 0.94 – – Alcorn (1998)
[116]
Concrete mix 30 MPa – 1.3 – –
Precast concrete – 2 – –
– – Concrete UK 800 – – – Harris (1999)
[117]
– – Concrete Australia – 1.2 – – Lenzen (2002)
[118]
– – Concrete block New
Zealand
– 1.2 0.156 – Alcorn (2003)
[113]
concrete mix 30 MPa 2762 1.2 0.159 –
Precast concrete 4546 1.9 0.214 –
– – Hollow concrete block
7% cement
India 646 – – – Reddy (2003)
[119]
Hollow concrete block
10% cement
810 – – –
Cradle to gate – Concrete USA – 1.4 – – Ashley (2008)
[120]
Reinforced concrete – 2.5 – –
– Literature data Concrete Israel 2852 1.15 – – Pearmutter
(2007)
Huberman
(2008)
[121,122]
Reinforced concrete 6230 2.60 – –
Hollow concrete block 1216 1.08 – –
Autoclaved Aerated concrete block 1536 3.27 – –
– – 25 MPA concrete Australia 5010 – – Crawford
(2010) [123]
Concrete block 805 – –
Cradle to gate – Concrete UK – 0.75 0.1 – Hammond
(2011) [1]
25/30 MPa – 0.78 0.106 –
Reinforced concrete RC 25/30 MPa – 1.92 0.185 –
Concrete block 13 MPa – 0.83 0.1 –
Autoclaved Aerated blocks – 3.5 0.24–
0.375
–
– Literature data Concrete Bangladesh – 1.3 0.1311 – Shams (2011)
[124]
Cradle to gate – Concrete C40 MPa China – 1.12 0.20 – Yu (2011)
[125]
– Literature data Concrete 30 MPa Australia 5480 – – – Aye (2012)
[32]
Concrete 50 MPa 8550 – – –
Cradle to gate Ecoinvent database Concrete Czech
republic
– 0.57 – – Ruzicka (2013)
[126]
Cradle to site Company data Fly ash concrete blocks India – – 0.099 – Sabapathy
(2013)
Pomponi
(2018)
[11,112]
Fly ash concrete blocks_RTB – – 0.101 –
Cement Stabilized Soil Blocks (CSSB) – – 0.103 –
Solid concrete block – – 0.184 –
Hollow concrete block – – 0.223 –
AAC blocks 0.367
– Literature data Hollow concrete block Slovakia 971 – 26 kg/
m2
– Stone (2013)
[127]
– Literature data @Risk
software for simulation
Ready-mix concrete, reinforced Taiwan 0.0033 Chou (2015)
Pomponi
(2018)
[9,11]
Cradle to gate IBO database[11] Aerated concrete block Slovakia – 3.38 – – Estokova
(2015) [128]
Cradle to gate*
product
stage at
plant
Ecoinvent database Concrete Spain 1447.23 – – – Galan-Marin
(2015) [129]
Concrete block – 1.25 – –
Cradle to gate Literature data and
industrial sources
Concrete Australia – 1.01 – – Jamieson
(2015)
[105]
Geopolymer – 0.33 – –
Cradle to gate Literature data Concrete Australia – 0.78 0.113* – Nadoushani
(2015)
[130,131]
14

Table 2 (continued)
LCA method/
system
boundaries
location
Total Embodied
energy
Total Embodied
carbon
Reference
[MJ/m3
] [MJ/
kg]
[kg
CO2/
kg]
[kg
CO2/
m3
]
Pomponi
(2018) [11]
– Literature data Concrete 24 MPa South
Korea
– – – 304.8 Choi (2016)
[132]
Concrete 27 MPa – – – 324.8
Cradle to gate Literature data Concrete 25/30 Italy – 0.78 – – Copiello
(2016) [133]
Concrete 28/35 Italy – 0.82 – –
Concrete 32/40 Italy – 0.88 – –
– – A-10–10 (10 mm aggregates with a
porosity of 10%)
United
Arab
Emirates
1519.5 – – 188.7 El-Hassan
(2016) [134]
A-10-10f (10 mm aggregates with a
porosity of 10% with polypropylene
fibres)
1579 – – 188.7
A-10–15 (10 mm aggregates with a
porosity of 15%)
1467.2 – – 181.5
fibres)
1526.7 – – 181.5
porosity of 20%)
1415.7 – – 174.4
fibres)
1475.2 – – 174.4
porosity of 10%)
1572.7 – – 196.1
fibres)
1632.2 – – 196.1
A-10/20–15 (10 and 20 mm aggregates
in equal proportions, with a porosity of
15%)
1487.7 – – 184.4
A-10/20–20 (10 and 20 mm aggregates
in equal proportions, with a porosity of
20%)
1426 – – 175.8
Ref-OPC (Ordinary Portland cement,
10% porosity, 10 mm aggregates)
2310.6 – – 383.6
Cradle to gate Ecoinvent Concrete Spain 1447.23 – – – Galán-Marín
(2016) [135]
Cradle to gate Literature data Concrete China – 0.764 – – Liu (2016)
[136]
– – Slag-bond concrete block Canada – 1.332/
unit
0.20 – Mahoutian
(2016) [137]
Cement block – 1.26 –
Cradle to gate Literature/company data
Ecoinvent database
(Quantis version Q2.21)
Concrete block United
States
12.7 block
unit
0.85 – – Dahmen
(2017) [138]
Architectural concrete block 14 0.94 – –
Cradle to grate – C30 MPa 25% cement + 75%GGBS Hong Kong – – 0.072* 108* Gan (2017)
[29]Pomponi
(2018) [11]
C40 MPa 25% cement + 75%GGBS – – 0.080* 120*
C50 MPa 25% cement + 75%GGBS – – 0.086* 130*
C60 MPa 25% cement + 75%GGBS – – 0.094* 141*
C70 MPa 25% cement + 75%GGBS – – 0.101* 152*
C80 MPa 25% cement + 75%GGBS – – 0.108* 163*
C30 MPa 65% cement + 35%FA 0.113* 200*
C40 MPa 65% cement + 35%FA – – 0.151* 227*
C50 MPa 65% cement + 35%FA – – 0.176* 265*
C60 MPa 65% cement + 35%FA – – 0.180* 271*
C70 MPa 65% cement + 35%FA – – 0.195* 293*
C80 MPa 65% cement + 35%FA – – 0.210* 316*
– Literature data Non-fly ash mix 500 kg/m3
plastic
density
UK – – – 300 Jones (2017)
[139]
Non-fly ash mix 300 kg/m3
plastic
density
– – – 180
plastic
density
– – – 130
plastic
density
– – – 80
50 Portland cement /10 calcium
sulfoaluminate /40 fly ash
500 kg/m3
plastic density
– – – 180
(continued on next page)
15

Table 2 (continued)
LCA method/
system
boundaries
location
Total Embodied
energy
Total Embodied
carbon
Reference
[MJ/m3
] [MJ/
kg]
[kg
CO2/
kg]
[kg
CO2/
m3
]
300 kg/m3
plastic density
– – – 100
200 kg/m3
plastic density
– – – 80
150 kg/m3
plastic density
– – – 50
Cradle to gate SimaPro Ecoinvent Concrete block Ecuador – 1.24 – – Macias (2017)
[140]
Cradle to gate Literature data [3] Precast concrete Portugal – 0.95 0.13 – Sazedj (2017)
[141]
Cradle to site – Concrete with fly ash 30%, 10% silica
fume
India 1872 – – – Sharma (2017)
[142]
Concrete with fly ash 30%, 10% silica
fume, 20% copper slag as fine aggregate
1855 – – –
Concrete with fly ash 30%, 10% silica
fume, 100% copper slag as fine
aggregate
1757 – – –
Manufacturing – Common concrete China 2757 – – – Yu (2017)
[143]
Concrete with fly ash 2072 – – –
Green concrete with fly ash class c 765 – – –
Cradle to gate Concrete Australia – 0.78 – – Chiniforush
(2018) [144]
Precast concrete – 1.50 – –
Cradle to gate SimaPro Concrete with recycled aggregates Portugal 1150 – – – Kurda (2018)
[145]
Concrete with recycled aggregates and
30% fly ash
1160 – – –
Cradle to gate Literature data Concrete with high volume of fly ash
and pva(polyvinyl alcohol) fibres
USA 4540 – – – Ohno (2018)
[146]
Engineered geopolymer composite
with fly ash and NaOH pellet and
Na2Si03 (without cement)
5120 – – –
Cradle to site – Concrete India 2400.82 m2 – – – Prem (2018)
[147]
Concrete with copper slag 11013.07 m2 – – –
Cradle to gate Literature data Concrete UK – – 0.198* Moncaster
(2018) [17]
Cradle to gate Literature data Ecoivent Natural aggregate ordinary Portland
cement concrete
Australia – – – 515* Teh (2018)
[148]
Recycled concrete aggregate ordinary
Portland cement concrete
– – – 510*
Natural aggregate geopolymer
concrete
– – – 375*
Recycled concrete aggregate
geopolymer concrete
– – – 370*
Cradle to gate Literature data Green
concrete LCA tool
Concrete with silica fume Singapore 720 – – – Gursel 2019)
[149]
Concrete with silica fume and 20%
copper slag replacing fine aggregate
650 – – –
600 – – –
550 – – –
490 – – –
420 – – –
– – Concrete Taiwan – – 0.961* – Huang (2019)
[150]
Ready mixed concrete – – 0.150* 346.01*
– – Concrete with 50% cement
replacement by fly ash
Indonesia 9000 – – – Kristiawan
(2019) [151]
Concrete with 55% cement
8000 – – –
7500 – – –
6000 – – –
5500 – – –
Cradle to gate Literature data Reinforced concrete Cyprus – 2.12 0.24 – Kyriakidis
(2019) [152]
Ecobrick mixture – 0.75 0.11 –
Cradle to gate BDEC ITEC Concrete HP-50 Spain 2575 – – – Penadés-Plà
16

Table 2 (continued)
LCA method/
system
boundaries
location
Total Embodied
energy
Total Embodied
carbon
Reference
[MJ/m3
] [MJ/
kg]
[kg
CO2/
kg]
[kg
CO2/
m3
]
(2019) [94]
Cradle to site – Concrete with common fine aggregate India 2044 – – – Siddique
(2019) [153]
Concrete with 20% ceramic as fine
aggregate
2053 – – –
aggregate
2040 – – –
aggregate
2026 – – –
Table 3
Steel and iron structure-frame material type.
LCA method/system
boundaries
Software or data
base used
Construction system Project
location
Total Embodied
energy
Total Embodied
carbon
Reference
[MJ/m3
] [MJ/
kg]
[kg CO2/
kg]
[kg CO2/
m3
]
– Literature data Structural steel (7600 kg/m3) New
Zealand
448,000 59.00 2.53 – Buchanan (1994)
[114]
– Literature data Steel general New
Zealand
– 32.00 – Alcorn (1996) [115]
Steel recycled sections – 8.90 – –
– Literature data Steel general New
Zealand
– 32.00 – – Alcorn (1998) [116]
Steel: galvanized – 34.80 – –
Steel: structural imported – 35.00 – –
– Literature data Steel UK 103,000 – – Harris (1999) [117]
– Literature data Iron structure Australia – 11.7 – – Lenzen (2002) [118]
– – Steel virgin structural New
Zealand
884,725 31.3 1.242 – Alcorn (2003) [113]
Stainless steel 2,208,726 74.8 5.457 –
– Literature data Reinforcing steel Israel 273,180 35 – – Pearmutter (2007)
Huberman (2008)
[121,122]
Cradle to gate – Iron UK – 25 1.91 – Hammond (2011) [1]
Steel – 35.4 2.71 –
Recycled steel 9.40 0.44
Stainless steel – 56.7 6.15 –
– Literature data Steel Bangladesh – 32 2.95 – Shams (2011) [124]
– – Steel (10% recycled content) China – 28.65 2.21 – Yu (2011) [125]
– – Structural steel Australia – 85.46 – Aye (2012) [32]
Cradle to gate Literature data Steel sections Australia – 25.30 1.950 – Akbarnezhad (2014)
[154]
Pomponi (2018) [11]
Steel rebar – 21.60 1.86 –
– – Steel USA – 35.3–
48.4
2.68–
3.19
– Trussoni (2014)
[155]
Rebar steel – 36.40 2.68 –
Cradle to handover Literature data Standard China – – 2.015 – Fu (2014) [156]
Pomponi (2018) [11]
Lean – – 1.950 –
Cradle to gate Literature data Steel Australia – 21.50 1.53 – Nadoushani (2015)
[130,131]
Pomponi (2018) [11]
– Literature data H-shape South
Korea
– – 0.4188 – Choi (2016) [132]
Rebar – – 0.3405 –
Cradle to gate Literature data Steel pillars and beams, welded
steel profiles
Italy – 21.50 – – Copiello (2016) [133]
Steel bars for reinforced concrete – 17.40 – –
Cradle to gate Literature data Steel China – 19.52 – – Liu (2016) [136]
Cradle to gate Literature data Steel – crude DRI Hong Kong – – 1.540 – Gan (2017) [29]
Pomponi (2018) [11]
Steel – crude pig iron – – 2.090 –
Recycled steel – plate – – 0.160 –
Recycled steel - rebar – – 0.160 –
Recycled steel - section – – 0.210 –
Recycled steel – tube – – 0.250 –
Recycled steel - wire – – 0.270 –
Recycled steel – crude (100%
scrap)
– – 0.390 –
Recycled steel – crude (30%
scrap)
– – 1.670 –
Cradle to gate SimaPro Ecoinvent Reinforcing steel Ecuador – 24.84 – – Macias (2017) [140]
Cradle to site Literature data Steel bars (59% recycled) Australia – 17.40 – – Chiniforush (2018)
17

[1,113]. Comparable embodied carbon is observed in bricks, with
an embodied carbon of 0.14–0.23 kg CO2/kg [1,114,124,125].
Significant differences are identified in wood and concrete, with
a wide range of variation between data. Timber deserves a special
attention in the interpretation of embodied carbon data. European
standard EN-ISO 14067:2018 [170], reports that the carbon stored
within a biomass product life can be taken into consideration in a
study, for instance in case of wood during the tree growth. This car-
bon is known as ‘‘sequestered carbon”, being a variable that leads
to different research visions. Depending on the selected study
approach and frame defined, the embodied carbon can be even
considered negative [43]. In case a ‘‘cradle to gate” approach, it is
considered according to Jones [171], the ‘‘biogenic carbon stored”
should not be included since the disposal stage it is not contem-
plated. On the contrary, EN-ISO 14067:2018 mentions that it
would be meaningful to include ‘‘sequestered carbon” in case the
data is directly related to the considered value chain of the study.
This dichotomy results in a wide data variation in timber or bio-
based product, as it is observed in Fig. 21b.
In the literature, a comparison of three biogenic CO2 approaches
in glulam and CLT was carried out by Skullestad et al. [172]. The
first and second approaches are cradle to gate, while the third
one adds the ‘‘end of life stage”. In the second and third approaches
a GWPbio factor is considered. The study shows negative CO2eq
emissions, when natural gas is replaced by incineration residues
from felling, logging, and manufacturing and at EOL of the timber
materials.
Despite the fact that ‘‘cradle to gate” boundary system was
selected to frame this section; further attention should be paid to
assessments that are considering other LCA methods. However,
in particular cases, such as in cement stabilized soil blocks (CSSB)
or adobe bricks, the use of soil excavated at the construction site
reduces the transportation of one component of the final product.
Christoforou et al. [166], calculated the embodied energy of an
adobe brick with wheat straw considering a cradle to site boundary
system. The authors analysed the influence of production off site or
on site and the transportation of soil and straw. On site production
and the use of on-site materials represents 0.033 MJ/kg while
transporting all materials and carrying out an off-site production
entails five time more energy, 0.17 MJ/kg. Nevertheless, cradle to
site studies are highly dependent on the availability of the material
in a particular location and it becomes more difficult to homoge-
nize or to determine an average distance value.
Concerning the other boundary systems, the previous revised
literature shows that the embodied energy and embodied carbon
of a material analysis do not go beyond the cradle to site. These cir-
cumstances influence the comparison among life cycles stages.
8. Conclusions
This literature study shows that there is a worldwide fast-
growing interest on the energy and carbon emissions in building
materials. However, the publications given by query 1 ‘‘(‘‘metal*”
OR ‘‘iron” OR ‘‘steel*” OR ‘‘wood” OR ‘‘timber” OR ‘‘bamboo” OR
‘‘concrete*” OR ‘‘reinforced concrete*” OR ‘‘geopolymer” OR
masonry OR ‘‘stone*” OR ‘‘rock*” or ‘‘rammed earth” OR ‘‘earth
block*” OR ‘‘earth brick*” OR ‘‘mud” OR ‘‘soil” OR ‘‘cob”) AND (‘‘em-
bodied energy” OR ‘‘embodied carbon”)”, only 70 papers out of
1003 present values of embodied energy and/or embodied carbon
of a building material. Despite the fact that there is a lot of effort
invested on comparing case studies of environmental impacts in
the whole building or in particular building components, there is
a gap regarding the material coefficients.
The early steep development of the topic took place in 2009
with a general continuous increase until today. Concrete has been
the most researched material, followed closely by steel, which is
the second key element in reinforced concrete. On the other hand,
the research concerning masonry and earth materials stagnated
recently, while wood raised interest, even though it is the least
researched material.
As a part of the keyword analysis, highlight that ‘‘climate
change” it is not commonly mentioned or linked to the literature,
only in recent publications related to wood. Terms such as recycla-
bility were found in steel, masonry and concrete, indicating that it
exists a general concern on their environmental impact. Moreover,
‘‘prefabrication” stands out as an interesting keyword in wood and
steel. The trend literature map, shows that great amount of recent
developing research is driving attention to circular economy,
embodied energy and embodied carbon as well as the geopolymer
concrete as a cutting edge material to reduce carbon emissions.
Most part of the literature shows that cradle to gate is the bound-
ary system used; nevertheless, there is still literature that does not
specify this crucial parameter in their study. Likewise, the data
source used in the studies is rarely mentioned, most time comment-
ing that comes from ‘‘literature data” without a reference. Concern-
ing the origin of the publications, developing countries and India are
the ones researching on the earth materials and masonry, while con-
crete and steel publications are prevailing in China, who are the main
cement producers. On the other hand, wood is prevailing in some
European countries such as Norway, Slovenia and Estonia.
Table 3 (continued)
LCA method/system
boundaries
Software or data
base used
Construction system Project
location
Total Embodied
energy
Total Embodied
carbon
Reference
[MJ/m3
] [MJ/
kg]
[kg CO2/
kg]
[kg CO2/
m3
]
[144]
Steel bars (100% recycled) – 8.80 – –
Steel (59% recycled) – 21.50 – –
Steel (100% recycled) – 10 – –
Steel frame UK – 1.46 Moncaster (2018)
[17]
Cradle to gate Literature data
Ecoivent
BOF steel Australia – – – 1.50* Teh (2018) [148]
EAF steel – – – 0.85*
– – Reinforced Taiwan – – 1.21* Huang (2019) [150]
Steel – – 1.20*
Cradle to gate BDEC ITEC Steel B-500-S Spain – 10.44 – – Penadés-Plà (2019)
[94]
Cradle to gate Literature data Framework steel Cyprus – 45.68 6.10 – Kyriakidis (2019)
[152]
Cradle to site Literature data Steel Portugal – 25.30 – – Tavares (2019) [72]
18

Table 4
Masonry (stone and clay brick) structure -frame material type.
LCA method/system
boundaries
location
Total Embodied
energy
Total Embodied
carbon
Reference
[MJ/
m3
]
[MJ/kg] [kg
CO2/kg]
[kg CO2/
m3
]
– – Masonry stone New
Zealand
– 0.29 8.56 kg/
t
– Buchanan (1994)
[114]
Structural clay – 6.90 0.16 –
– – Stone New
Zealand
– 0.79 – – Alcorn (1996) [115]
Ceramic brick – 2.50 – –
Cradle to gate – Local stone New
Zealand
– 0.79 – – Alcorn (1998) [116]
Imported stone – 6.8 – –
Ceramic brick – 2.5 – –
– – Brick general common
brick (fletton)
– 300 – – – Harris (1999) [117]
– – Brick (ceramic products) Australia 880 m2
– – – Treloar (2001) [157]
– – Rock New
Zealand
83.3 0.06 3.1 g – Alcorn (2003) [113]
Ceramic brick new tech. 5310 2.7 272 –
Brick old tech av. 13,199 7.6 1021 –
Brick old tech, coal 14,885 5.8 1348 –
Brick old tech, gas 11,491 695 –
– – Burnt clay brick India – 4.25–4.75
unit
– – Reddy (2003) [119]
– Literature data Stone Israel 1890 0.79 – – Pearlmutter (2007)
Huberman (2008)
[121,122]
– Literature data Fired brick Israel 5185 – – – Pearlmutter (2007)
[121]
Cradle to gate Brick USA 2 – – Ashley (2008) [120]
– – Brick India 5 – – Chel (2009) [158]
– – Burnt clay brick India 2000–
3400
– – – Reddy (2009) [159]
– – Burnt brick India 1.8 – – Shukla (2009) [22]
– – Clay bricks Australia 560 – – – Crawford (2010)
[123]
Cradle to gate – Brick general common
brick
UK – 3.00 0.23 – Hammond (2011) [1]
Limestone – 1.50 0.087 –
General stone – 1.26 0.073 –
Granite – 11 0.64 –
– Literature data Brick Bangladesh – 2.50 0.189 – Shams (2011) [124]
Cradle to site Literature data, survey and
statistical data
Brick China – 1.75 0.14 – Yu (2011) [125]
Pomponi (2018) [11]
Cradle to gate – Sandstone UK – – 0.064 – Crishna (2011) [160]
Cradle to site – – 0.077 –
Cradle to gate Granite – – 0.093 –
Cradle to site – – 0.107
At plant Ecoinvent database Brick Czech
republic
– – 2.57 – Ruzicka (2013) [126]
Cradle to site Company database Clay bricks India – – 0.221 Sabapathy (2013)
[112]
Clay bricks_RTB – – 0.220
FaL-G bricks – – 0.259
FaL-G bricks_RTB – – 0.252
Fly ash clay bricks – – 0.266
Fly ash clay bricks_RTB – – 0.258
– Literature data Fired brick Slovakia 646 – 126 kg/
m2
– Stone (2013) [127]
– – Fired clay brick Uganda – – – – Esteban (2012)
Abanda (2015)
[161,162]
At plant Ecoinvent database Brick Spain – 2.84 – – Galan-Marin (2015)
[129]
Cradle to gate Literature data General brick Italy – 3 – – Copiello (2016) [133]
Cradle to gate Ecoinvent Brick Spain (4.25/
unit)
14.95 – – Galán-Marín (2016)
[135]
Cradle to gate Literature data Brick China – 0.218 – – Liu (2016) [136]
Cradle to gate Literature data Fired clay brick Cyprus – 3.00 – – Kyriakidis (2018–19)
[152,163]
Cradle to gate Literature data Load bearing masonry UK – – 0.065 Moncaster (2018)
[17]
– – Brick Taiwan – – 0.0.230* – Huang (2019) [150]
19

Table 5
Earthen structure -frame material types.
LCA method/system boundaries Software or data base used Construction system Project
location
Total Embodied
energy
Total Embodied
carbon
Reference
[MJ/
m3
]
[MJ/kg] [kg
CO2/kg]
[kg
CO2/
m3
]
– – Earthwork New
Zealand
100 – – 0.58 Buchanan
(1994) [114]
Cradle to gate Literature Adobe block New
Zealand
– 0.47 – – Alcorn
(1998) [116]
Adobe bitumen – 0.29 – –
Adobe cement stabilized – 0.42 – –
Rammed earth soil
cement
– 0.50 – –
Pressed block – 0.42 – –
Cradle to site – Soil cement block (6%
cement)
India 646 2.6 unit – – Reddy
(2003) [119]
Steam cured mud block 1396 6.7 unit – –
– Literature Stabilized soil block Israel 938 0.49 – – Pearlmutter
(2007)
Huberman
(2008)
[121,122]
Fly ash soil block Israel 179 0.21 – –
Cradle to site – Mud (soil from the
construction site)
India – 0.0016 – – Chel (2009)
[158]
– – Stabilized mud blocks
(SMB)
India 500–
600
– – – Reddy
(2009) [159]
Stabilized rammed earth
wall
450–
550
– – –
Un-stabilized rammed
earth wall
0–180 – – –
– – Hydraform brick
hydraulically compressed
soil–cement mixture
South
Africa
– 0.632 – – Roux (2009)
Abanda
(2015)
[162,164]
Fly ash brick cement-
based brick
– 0.632 –
Cradle to gate ICE databaseUniversity of
Bath
General (Rammed soil) UK – 0.45 0.023 – Hammond
(2011) [1]
Cement stabilised soil (5%
cement)
– 0.68 0.06 –
Cement stabilised soil (8%
cement)
– 0.83 0.082 –
GGBS stabilised soil – 0.65 0.045 –
Fly ash stabilised soil – 0.56 0.039 –
Cradle to gate Ecoinvent database Prefabricated rammed
earth
Czech
republic
– 0.196 – Ruzicka
(2013) [126]
– Literature data Cement stabilized
rammed earth (6%
cement)
Cyprus 646 – 16 kg/
m2
– Stone (2013)
[127]
Cradle to gate Local enterprise and
literature data
Straw-clay block Argentina – 5.7/block – – Gonzalez
(2015) [165]
Cradle to site, on site production,
locally available soil,
transported wheat straw
– Adobe brick with wheat
straw
Cyprus 51.03 0.033 – – Christoforou
(2016) [166]
transported soil and wheat
straw
straw
119.99 0.078 – –
Cradle to site, off site production,
transported wheat straw
straw
261.74 0.17 – –
transported sawdust
– Adobe brick with sawdust 51.88 0.033 – –
transported soil and sawdust
Cradle to site, off site production,
transported soil and sawdust
Cradle to gate Literature/company data
Ecoinvent database (Quantis
version Q2.21)
conventional hollow-
celled structural
stabilized soil block
United
States
– 0.50 – – Dahmen
(2017) [138]
conventional hollow-
celled structural alkali
activated block
– 1.20 – –
Cradle to gate Literature data stone Cyprus – 0.30 – – Kyriakidis
(2018) [163]
Adobe brick – 0.033 – –
Cradle to site SimaPro Cob wall United
States
– 0.11 – – Ben-Alon
(2019) [67]
– – Compressed stabilized
earth block
India 572.58 0.2936 0.02642 – Davis (2019)
[167]
Cradle to gate – Compressed stabilized
earth block
Portugal – 3.94 per unit – – Fernandes
(2019) [70]
20

Table 6
Timber and bamboo structure -frame material types. * Embodied carbon equivalent results.
LCA method/
system
boundaries
location
Total
Embodied
energy
Total Embodied
carbon
Reference
[MJ/
m3
]
[MJ/
kg]
[kg
CO2/kg]
[kg
CO2/
m3
]
– – Treated timber (500 kg/m3) New
Zealand
1200 2.40 0.044 – Buchanan
(1994) [114]
Glue laminated timber (500 kg/m3) 4500 9 0.164 –
Hardboard 20,600 – – –
softwood 15,470 – – –
Cradle to gate Statistical analysis input output
analysis process analysis
Timber kiln dried dressed New
Zealand
– 2.50 – – Alcorn (1996)
[115]
Timber softwood: glulam – 4.60 – –
Cradle to gate Literature data Timber softwood: air dried rough sawn New
Zealand
– 0.30 – – Alcorn (1998)
[116]
– –
Timber softwood: kiln dried rough
sawn
– 1.60 – –
Timber softwood: air dried dressed – 1.16 – –
Timber softwood: kiln dried dressed – 2.50 – –
Timber softwood: moulding – 3.10 – –
Timber softwood: hardboard – 24.20 – –
Timber softwood: MDF – 11.90 – –
Timber softwood: glulam – 4.60 – –
Timber softwood: particle bd – 8.00 – –
Timber softwood: plywood – 10.40 – –
Timber softwood: shingles – 9.00 – –
Timber hardwood: air dried roughsawn – 0.50 – –
Timber hardwood: kiln dried
roughsawn
– 2.00 – –
Wood: softwoods, conifer – 13.40 – –
Particleboard: sawn timber, woodchips
and other sawmill products
– 5.90 – –
– – Timber (imported softwood) UK 27,144 – – – Harris (1999)
[117]
Timber (local oak) 396 – – –
Cradle to gate – Timber softwood: MDF New
Zealand
8213 11.90 0.568 – Alcorn (2003)
[113]
Timber pine air dried rough sawn 1179 2.80 1.665 –
Timber pine air dried rough sawn
(imported)
– 0.60 – –
Timber pine air dried rough sawn, treat 1252 3.00 1.657 –
Timber pine air dried dressed 1273 3.00 1.662 –
Timber pine bio dried dressed 1732 4.10 1.644 –
Timber pine bio gas dressed 4060 9.70 1.342 –
Glulam 5727 13.60 1.141 –
Cradle to gate – Timber USA – 2.00 – – Ashley (2008)
[120]
– – Hardwood Australia 21,330 – – – Crawford
(2010) [123]
MDF 30,350 – – –
Softwood 10,930 – – –
Cradle to gate ICE database University of Bath General UK – 10.00 0.300 – Hammond
(2011) [1]
Glue laminated timber – 12.00 0.390 –
Hardboard – 16.00 0.540 –
Laminated veneer lumber – 9.50 0.310 –
MDF – 11.00 0.370 –
Oriented Strand Board (OSB) – 15.00 0.420 –
Particle board – 14.50 0.520 –
Plywood – 15.00 0.420 –
Sawn hardwood – 10.40 0.230 –
Sawn softwood – 7.40 0.190 –
– Literature data Timber Bangladesh – 3 0.003 – Shams (2011)
[124]
Cradle to site Bamboo China – 2.58 0.130 – Yu (2011)
[125]
Wood 7.22 0.410 –
– – Dimensional, rough sawn timber Uganda – 1.50 – – Esteban
(2012)
Abanda
(2015)
[161,162]
Timber with steel connections – 1.50
35.0
– –
Site felled timber – 0 – –
Cradle to gate National LCI DB
SimaPRO
Native hardwood Australia 358 – – – May (2012)
[84]
Plantation softwood 173 – – –
Cradle to gate Literature data General timber Italy – 10 – – Copiello
(2016) [133]
Cradle to gate Literature data Cross laminated timber (CLT) China – 0.545 – – Liu (2016)
[136]
Cradle to gate Literature data Cross laminated timber (CLT) UK 0.420 Moncaster
(2018) [17]
– – Wood model Taiwan – – 0.330* – Huang (2019)
21

Table 6 (continued)
LCA method/
system
boundaries
location
Total
Embodied
energy
Total Embodied
carbon
Reference
[MJ/
m3
]
[MJ/
kg]
[kg
CO2/kg]
[kg
CO2/
m3
]
[150]
Cradle to gate – Cross laminated timber USA – 7.11 – – Zeitz (2019)
[73]
(a)
(b)
50%
38%
8%
4%
38%
47%
9%
6%
concrete steel
50%
31%
13%
6%
masonry
earth
materials
32%
27%
27%
14%
mber
35%
59%
6%
concrete
65%
4%
4%
27%
steel masonry
34%
40%
11%
11%
4%
29%
6%
12%
53%
18%
9%
9%
59%
5%
earth
materials
25%
9%
60%
6%
mber
Not defined Literature data Software database National database Several sources
Fig. 21. (a) Boundary system used in each material group (b) Database source used in each material group.
L.F. Cabeza, L. Boquera, M. Chàfer et al. Energy Buildings 231 (2021) 110612
22

Regarding the peer-reviewed embodied energy and embodied
carbon values, by far, steel represents the material with greater
embodied energy, 32–35 MJ/kg. In masonry, embodied energy is
higher than concrete and earth materials. Surprisingly, wood has
higher embodied energy than the previous mentioned materials.
On the other hand, earth materials and wood show the lowest
embodied carbon coefficients, being less than 0.01 kg CO2/kg sum-
marise the EE and EC values.
Embodied energy and embodied carbon are concepts that will
become together with LCA as a primary decision-support tool for
a product framework. Finally, the authors want to point out the
scarce data about EE and EC in the main structural building mate-
rials which means that probably for other materials which were
not part of this study are not studied enough. Thus, further
research is needed in order to homogenize this concept worldwide.
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
Acknowledgements
This work was partially funded by the Ministerio de Ciencia,
Innovación y Universidades de España (RTI2018-093849-B-C31 -
MCIU/AEI/FEDER, UE) and by the Ministerio de Ciencia, Innovación
y Universidades - Agencia Estatal de Investigación (AEI) (RED2018-
102431-T). The authors would like to thank the Catalan Govern-
ment for the quality accreditation given to their research group
GREiA (2017 SGR 1537). GREiA is a certified agent TECNIO in the
category of technology developers from the Government of Catalo-
nia. This work is partially supported by ICREA under the ICREA Aca-
demia programme.
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