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Readily implementable techniques can cut annual CO2 emissions from the production of
concrete by over 20%
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2016 Environ. Res. Lett. 11 074029
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Environ. Res. Lett. 11 (2016) 074029
doi:10.1088/1748-9326/11/7/074029
LETTER
OPEN ACCESS
Readily implementable techniques can cut annual CO2 emissions
from the production of concrete by over 20%
RECEIVED
25 March 2016
REVISED
21 June 2016
ACCEPTED FOR PUBLICATION
Sabbie A Miller1, Arpad Horvath2 and Paulo J M Monteiro2
1
2
Department of Civil and Environmental Engineering, University of California, Davis, USA
Department of Civil and Environmental Engineering, University of California, Berkeley, USA
6 July 2016
E-mail: sabmil@ucdavis.edu
PUBLISHED
Keywords: concrete, supplementary cementitious materials (SCMs), life-cycle assessment (LCA), greenhouse gas (GHG) emissions
25 July 2016
Supplementary material for this article is available online
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Abstract
Due to its prevalence in modern infrastructure, concrete is experiencing the most rapid increase in
consumption among globally common structural materials; however, the production of concrete
results in approximately 8.6% of all anthropogenic CO2 emissions. Many methods have been
developed to reduce the greenhouse gas emissions associated with the production of concrete. These
methods range from the replacement of inefficient manufacturing equipment to alternative binders
and the use of breakthrough technologies; nevertheless, many of these methods have barriers to
implementation. In this research, we examine the extent to which the increased use of several currently
implemented methods can reduce the greenhouse gas emissions in concrete material production
without requiring new technologies, changes in production, or novel material use. This research
shows that, through increased use of common supplementary cementitious materials, appropriate
selection of proportions for cement replacement, and increased concrete design age, 24% of
greenhouse gas emissions from global concrete production or 650 million tonnes (Mt) CO2-eq can be
eliminated annually.
Resource consumption
Population growth and changes in the world economy
combined with technological and political change over
the last 65 years have led to an increase in the percentage
of the world’s population living in urban areas, which
rose from 30% to 54% [1]. In the next 35 years, 66% of
the world’s population is expected to reside in urban
areas, which is an increase of 2.5 billion people [1]. These
population shifts have led to a dramatic increase in both
the quantity and scale of infrastructure [2, 3]. Internationally, the resultant rise in construction material
demand has been driven by different factors: some
countries are experiencing infrastructure that has lost
functionality, whereas other countries are seeking to
expand infrastructure [2]. In countries with developing
economies, the consumption associated with expansion
is exacerbated by the potential need to replace structures
before they reach the end of their design life [3].
Of the most common globally used construction
materials, concrete has experienced the most rapid
© 2016 IOP Publishing Ltd
growth in consumption over the past 50 years; its consumption has increased 2-fold relative to that of steel
and is approximately 6 times higher than that of wood
and wood-based products on a per capita basis [4–7].
Concrete, which is composed of several materials,
including cement, water, granular rocks (aggregates),
and, depending on the application, chemical admixtures and/or reinforcing fibers, is highly desirable
because of its ease of production and low cost. Consequently, the world consumed approximately 3.8 Gt of
cement, over 2 Gt of water used in concrete mixtures,
and 17.5 Gt of aggregate in 2012, which total approximately 10 billion m3 of concrete (table 1).
Cement production and greenhouse gas (GHG)
emissions
Although there are many local, regional, and global
impacts from the production of cement and concrete
materials, the focus of this analysis is on greenhouse
gas (GHG) emissions because of the typically high
Environ. Res. Lett. 11 (2016) 074029
Figure 1. Greenhouse gas emissions from the production of concrete by cubic meter. Contributions from the two highest emitting
components of concrete production (i.e., CO2 emissions from calcination and CO2-eq emissions from thermal energy use in cement
production) are shown relative to the remaining emissions from cement production and the remaining greenhouse gas emissions
from concrete production. (The calculation of values can be found in supplementary material sections 5 and 6). Note: C.I.S. is used as
an abbreviation for the Commonwealth of Independent States.
associated GHG emissions from the production of
cement. Cement can contain a variety of constituents,
including clinker (a kilned and quenched cementitious
product), gypsum, and supplementary cementitious
materials (SCMs) (the most commonly reported are
fly ash, a byproduct from coal combustion, slag, a
byproduct from steel refining, and naturally occurring
materials, such as limestone or natural pozzolans [8]).
Of these constituents, clinker is responsible for 65%–
85% of the global cement mass (table 1) and 90%–98%
of cement GHG emissions (figure 1). These high
relative emissions are a function of two main components: (1) during the manufacturing of clinker,
through a process called calcination, commonly available calcium carbonate (CaCO3) undergoes a reaction
to produce calcium oxide (CaO) and emits carbon
dioxide (CO2); and (2) during the formation of
calcium silicates, the materials used to form clinker are
heated to temperatures of approximately 1400 °C
[3, 9], which requires large energy inputs and results in
additional GHG emissions. Depending on the equipment efficiency, the kiln fuel and the energy mixes, as
well as the other materials used in the production of
cement, the GHG emissions associated with calcination can range from 45% to 60% of the total cement
GHG emissions (supplementary material section 6).
Depending on a regions’ manufacturing technology, energy mix, SCM use, and concrete strength
requirements, the production of 1 m3 of concrete produces varying amounts of GHG emissions. However,
based on regional averages for production and
demand, the arithmetic mean GHG emissions for the
production of 1 m3 of concrete fall in a relatively tight
range: from 240 to 320 kg CO2-eq/m3 (figure 1), with
90%–95% attributed to the production of cement.
Although the emissions associated with the
2
production of concrete and its constituents play a large
role in the global warming potential per cubic meter of
concrete in any given region, the overall consumption
of concrete is the largest factor contributing to GHG
emissions (figure 2). For example, using the assessment method presented in the supplementary material, despite the near average emissions per m3 of
concrete produced (270 kg CO2-eq/m3), high levels of
concrete consumption in China resulted in approximately 1.5 Gt of GHG emissions from concrete production in 2012. This value is over 84% greater than
concrete-related GHG emissions in any other country
or region in the world.
Opportunities for improvement
Because of the GHG emissions associated with concrete production, many methods have been investigated to reduce these impacts. Among the most
common methods discussed for reducing GHG emissions are : (1) substitute raw materials in cement; (2)
use alternative fuels in manufacturing; (3) improve
kiln efficiency and electricity usage; and (4) develop
carbon capture and storage [3, 10, 11]. In this vein,
researchers have examined the role of mitigation
strategies, such as alternative fuel sources or improved
equipment efficiency, on CO2 emissions in cement
production as well as inherent uncertainties or barriers
to use (e.g., [12]). Similarly, Neuhoff et al [13]
discussed several modes for CO2 emission mitigation
in cement production, but coupled the discussion with
a detailed analysis of financial and policy roles in
implementation. Additionally, more detailed and
localized assessments have been conducted on the role
of different production methods on the CO2 emissions
from cement production (e.g., [14]). While several
researchers have examined mitigation methods for
Environ. Res. Lett. 11 (2016) 074029
Figure 2. Cumulative greenhouse gas emissions from concrete manufacturing by region. Based on regional cement production
technology, cement constituents, energy mixes, strength requirements, and consumption values, cumulative greenhouse gas
emissions associated with manufacturing concrete by region is shown. (The calculation of values can be found in supplementary
material sections 5 and 6). Note: C.I.S. is used as an abbreviation for the Commonwealth of Independent States.
GHG emissions for the production of concrete (e.g.,
[15, 16]), to the best of the authors’ knowledge, such
studies have not been conducted at a global scale.
Although there are many approaches for potentially reducing the GHG emissions from concrete production, many of these methods have roadblocks to
their implementation. Among these inhibitors to
implementation are the following: the required monetary investment [17]; the future price of fuels and the
ability to use certain fuels [3, 10]; the level of maturation of technologies [3, 10]; the viability and regional
availability of SCMs; and the role of stakeholder participation beyond manufacturers [3].
Although barriers to implementation are inherent
in most approaches to reduce the GHG emissions
from the cement and concrete industries, it is possible
to reduce the GHG emissions from concrete production in ways that would not require new production
equipment, significant changes in design codes, further academic research or validation, or specialized
training. In this research, three such methods are
examined for their GHG emission mitigation potential. Through this study, abatement strategies for concrete are examined at a global scale, rather than local
assessments or solely cement based approximations.
This research takes into consideration world consumption of concrete, structural strength requirements, and availability of cementitious resources to
characterize the role that currently accepted greenhouse gas emissions mitigation methods could have if
they were implemented to a greater extent. To quantify the potential reduction in GHG emissions from
concrete manufacturing in this research, the approximations for global concrete demand were made based
on consumption statistics, strength requirements, and
3
the reported technologies and energy mixes used in
concrete manufacturing by region.
GHG emissions from concrete manufacturing
were determined by conducting life-cycle assessments
(LCAs), a method for evaluating the environmental
effects associated with a material or product over its
life cycle [18]. The LCAs were performed by incorporating relevant processes from raw material acquisition
through production based on one cubic meter of concrete. Because of the prevalence in reporting on the use
of fly ash, slag, and limestone as SCMs [8] and the
availability in production or reserves of these materials, these SCMs were considered to be possible binder
replacements at varying ratios. Potential mixture proportions in the analysis were determined based on the
strength requirements and the current use of SCMs.
Using the availability of resources such as aggregates,
SCMs, and cement combined with regional energy
mixes and the efficiency of manufacturing methods,
the GHG emissions associated with the production of
concrete were assessed globally based on 13 regions
(details on regions are given in supplementary material section 1). For this research, all hydraulic cement
was assumed to be used in the production of concrete
as 95% of cement is reported to be used in concrete
[3]. The impacts were weighted by regional use of different strength classes and scaled based on regional
material consumption. This assessment method
allowed for consideration of average regional production methods and demand as well as considerations for
the role of GHG emissions from concrete constituents,
transportation, and compressive strength. While this
method does not account for all possible concrete
mixtures, nor does it capture other material property
requirements, it provides an initial baseline to assess
GHG emissions and mitigation methods for global
Environ. Res. Lett. 11 (2016) 074029
concrete production (for more details, see supplementary material section 5).
Based on these data, three mechanisms were evaluated for their potential to lower the GHG emissions
from concrete production. The mechanisms considered are as follows: (1) the increased use of fly ash
and slag, as well as increased use of limestone filler (at
20% and 35% replacement), as components of cementitious materials; (2) the ideal allocation of SCMs,
knowing certain strength goals benefit from different
levels of particular SCM use; and (3) the use of higher
design ages, past the typical 28 d strength, to benefit
from concrete strength development when possible.
These methods for potential GHG emissions reduction were selected because they are based on currently
used strategies [19, 20] that have not been implemented to their full abilities in terms of mitigation
potential. Additionally, the methods selected do not
require changes in production equipment or fuel
sources, suggesting they could be rapidly implemented
if accepted by decision-makers.
The first of these three mechanisms is based on the
often-studied concept of reducing GHG emissions
from concrete by reducing the quantity of clinkerbased cement content. From assessments conducted
on fly ash and slag production as well as their consumption, respectively, the quantities produced globally exceed consumption (see supplementary material
section 4). Because these SCMs and limestone have
gained acceptance for use in the concrete industry, the
first improvement method considers the use of all produced fly ash and slag as potential cement replacement, which was modeled as each region using 8%
more fly ash and 28% more slag. Additionally, up to
35% limestone use as clinker replacement for concrete
mixtures not containing other SCMs was assessed.
Although different regions produce varying levels of
SCMs, this assessment assumed use of a uniform
increase in replacement average to avoid issues with
the regions that produce disproportionately high
levels of SCMs.
As the second potential improvement method, the
use of mixtures with an ideal distribution of SCM
replacement to provide the lowest GHG emissions
while maintaining each region’s average consumption
and strength requirements was examined. To conduct
this assessment, representative concrete mixtures with
varying SCM replacement levels were used. While
keeping within the bounds of each region’s average
SCM consumption, ideal percent SCM replacement
for each strength class was determined to meet design
strength demands with the lowest GHG emissions.
Finally, the third improvement considered was an
assessment of the influence of design age on potential
GHG emission reductions, which was examined at
three alternative design ages beyond the typical 28 d
design age (i.e., 56, 90, and 180 d). By using higher
design ages, the structural design methods do not have
to be altered, but by allowing concrete strength
4
development to occur with a higher concrete design
age, potentially less cement is necessary to meet the
concrete strength requirements in any given region
(for more details, see supplementary material section
7). With lower clinker-based cement demand, lower
GHG emissions per cubic meter of concrete production can potentially be achieved.
It must be noted that there are limitations to the
assessments conducted. The increased use of SCMs
investigated in this study was limited to fly ash, slag,
and limestone because of the established acceptance of
their use in hydraulic cement and readily available
data. However, the baseline models used for current
concrete production accounted for the use of other
SCMs. While not assessed here, the methods in this
research could be applied to increased use of SCMs
such as natural pozzolans and calcined clays, as well as
the potential to achieve better properties through ternary or quaternary blends (i.e., by using three or four
types of cementitious materials in the concrete binder)
[21]. Additionally, due to availability of data, only a
fraction of all possible SCM replacement levels were
considered. Also, the role of aging on changes in concrete strength were limited to the models based on the
literature cited and could vary with different properties of concrete constituents. For greater details and a
discussion of the uncertainty considerations for this
research, see the supplementary material.
Potential benefits of changes considered
The assessment method presented of concrete production in 2012 indicates that direct emissions from
concrete manufacturing represent 7.3% of all anthropogenic GHG emissions from energy and processes,
8.6% of all anthropogenic CO2 emissions, and 23% of
industrial process and energy CO2 emissions (supplementary material section 9 and [22, 23]); when
considering supply-chain inclusive emissions, this
percentage will be higher [24]. These results were used
as a baseline to perform an assessment of potential
mitigation through implementing the mechanisms
discussed. It must be noted that these results are
dependent on the methods used for calculation, the
mixtures used to calculate necessary rations of constituents to meet desired compressive strength, limitations in representative mixtures used, and available
data (for more detail, see discussion in supplementary
material section 8).
Implementing the three mechanisms to reduce global GHG emissions from concrete production resulted in
different degrees of potential reduction (figure 3). The
currently high use of fly ash has resulted in low excess
annual production of this SCM, so a negligible reduction
in GHG emissions was noted. With greater predicted
unused production streams of slag in concrete, the use of
all produced slag resulted in a reduction of 74 Mt of CO2eq emissions (i.e., a little over 1% reduction). The
increased use of limestone filler resulted in a decrease of
Environ. Res. Lett. 11 (2016) 074029
Figure 3. The influence of design alterations on the regional global warming potential associated with concrete production. The
original emissions that are associated with concrete production for 2012 are shown, along with the three proposed methods for
reducing emissions and the reduction in emissions using all three methods concurrently. The combination of all three methods
assumes a design age of 180 d as well as use of fly ash, slag, and 35% limestone replacement. In the combination of methods, a lower
relative reduction is found from using increased time and the ideal mixture proportions because of a greater quantity of the increased
use of limestone, which influences the strength development of concrete. The percentage reductions from each method are shown
(the calculation of the values can be found in supplementary material sections 7 and 9).
70 Mt at 20% replacement and 312 Mt of GHG emissions at 35% replacement. Considering the nonlinear
additive properties of using each of the SCMs, the cumulative reductions can be 111 Mt of CO2-eq emissions or
326 CO2-eq emissions with 20% or 35% limestone replacement, respectively. The use of ideal mixture proportions, which maintain the required strength and meet
regional consumption averages, resulted in a reduction
of 119 Mt of GHG emissions. Higher design ages, which
capitalize on concrete strength development as a function of time, typically allow for lower levels of cement to
be used leading to potential reductions in GHG emissions. At a 56 d design age, a decrease in emissions by
119 Mt can be expected. At 90 and 180 d, reductions of
165 and 281 Mt have been projected, respectively.
Although some designers may be disinclined to increase
the time for concrete to reach the desired strength, this
method may be applicable depending on the design scenario. For the analyzed regions, the greatest reduction
contributions were typically achieved through the implementation of improvements in China, followed by the
remaining Asia and Oceania region and India. If all of
these measures were implemented, again accounting for
the nonlinear additive properties of the considered measures, then the GHG emissions from concrete can be
decreased by 24% based on 2012 consumption values.
This reduction is equivalent to over 650 Mt of GHG
emissions.
Opportunities for implementation
According to the findings, reduction in emissions from
concrete production can be achieved with no changes in
either technology or manufacturing methods or the use
of novel concrete constituents. These methods can better
inform policy decisions that surround cement and
concrete use. The policies in the regions that are
5
expanding their infrastructure have raised concern
because of notably high concrete consumption [3, 25].
These regions can benefit from changes to typical
practices that will accommodate future demands and
offset high emissions [2]. The ability to implement
different improvements is highly dependent on many
factors, such as institutional systems, resource availability, geography and climate, as well as social and economic
factors [17]. However, the simplicity of the methods
proposed here can overcome many of the challenges
faced by commonly proposed GHG emissions reduction
methods because the classic production chains would
not need to be altered. However, similar to many
emissions reduction policies for cement and concrete,
the cooperation among different stakeholders and consumer education can play a critical role in implementation [3, 20, 26, 27]. For example, a potential avenue to
encourage some of the methods presented in this
research is the role of carbon markets. In 2014, the
average price of CO2 was $7/tonnes [22] and the
emissions-to-cost ratio of cement in 2012 was approximately 8950 g CO2/$ cost [4] based on US data. When
considering the carbon intensity of large markets such as
China (671 g CO2/$ GDP in 2013 [28]) and the US
(356 g CO2/$ GDP in 2013 [28]) and acknowledging the
global emission caps required to limit the global temperature rise to 2 °C (33–73 g CO2/$ GDP [28] for new
production cumulatively across industries), adjustments
to the constituents and processing of concrete are
excellent targets for increased mitigation. While some
barriers to pass-through of carbon prices have been
noted in some markets [13], the changes to cement and
concrete production discussed in this research can be
valuable methods to reach goals in this financially driven
market in the future.
Cementitious constituent consumption by type
Region
6
Africa
Australia and New
Zealand
Brazil
Canada
China
CIS
Europe
India
Japan
Middle East
Rest of Americas
Rest of Asia and Oceania
United States
Total
Hydraulic cement
consumption (Mt)
Clinker (Mt)
177
12
136
10
9
1
21
1
3
0
2
1
5
0
93
7
786
58
451.7
33.3
72
10
2203
103
234
268
46
191
108
321
80
3826
49
8
1605
83
175
192
34
156
76
256
67
2846
3
0
102
5
9
12
2
9
4
13
3
171
5
0
176
1
15
1
0
11
10
25
2
270
2
0
100
0
7
48
0
2
1
6
2
171
10
1
186
12
21
14
10
7
8
10
3
284
3
0
35
2
8
2
0
7
9
10
2
84
37
6
1189
60
127
157
26
106
55
178
52
2093
307
50
9915
516
1063
1274
224
907
456
1510
452
17 518
177.4
28.3
5704.7
292.0
610.4
737.8
126.3
516.7
264.1
861.5
253.9
100 58.0
Gypsum (Mt)
Limestone (Mt)
Ash (Mt)
Slag
(Mt)
Other (Mt)
Design batch
water (Mt)
Aggregates (Mt)
Concrete
(106 m3)
Environ. Res. Lett. 11 (2016) 074029
Table 1. Global concrete and concrete constituent consumption Calculations of the presented values can be found in supplementary material section 4. Note: the totals reflect rounding and estimates associated with the import/export of
cement and its constituents.
Environ. Res. Lett. 11 (2016) 074029
This research identifies three methods to reduce the
emissions associated with concrete production globally.
Because of the nature of the proposed methods, they can
be executed globally with minimal barriers to implementation. Although the proposed methods are simple,
if employed, their use can result in significant emission
reductions from the concrete sector. To gain a sense of
the role these mitigation strategies can have, one can
examine emissions reductions for a grater period of time.
Here we calculate such reductions using the projections
of cement consumption [29, 30], a linear trend in annual
global consumption, assuming the same ratios of materials are available annually, and no other improvements
are considered. Based on this simplified assessment, the
cumulative emissions that could be offset if all three
methods were globally implemented in 2016 would be
23–28 Gt CO2-eq by 2051, which is equivalent to 60%–
75% of all the processing and energy-related emissions
from 2013 [22]. It is interesting to note that these
improvements are not highly dependent on increasing
use of fly ash and slag, both of which are byproducts of
processes that may diminish under the pressure of emissions reduction measures; over 95% of the emissions
reductions reported in this study could be achieved
through increased limestone use, increased design age,
and ideal mixture proportion selection.
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
Acknowledgments
SM gratefully acknowledges the support of the University of California President’s Postdoctoral Fellowship Program. This work represents the views of the
authors, not necessarily the view of the sponsor.
[21]
[22]
[23]
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