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In the format provided by the authors and unedited.
1
Supplementary
Information
for
Quantification of the global carbon uptake by
cement carbonation
Fengming Xi et al.
This PDF file includes:
Supplementary Methods
Supplementary Figures
1-4
Supplementary Tables 1
-12
Supplementary Acknowledgments
Supplementary References
Other Supplementary Materials for this manuscript includes the following:
Supplementary D
ata 1 to Supplementary
Data
24 as zipped archives:
Supplementary Data 1
Cement production by region, 1930 to 2013
Supplementary Data 2 Estimates
of cement used for concrete and mortar by region
Supplementary Data 3 Differences in cement produced
and consumed
by region
Supplementary Data 4 Estimates of cement kiln dust (CKD)
production by region
Supplementary Data 5 Categories of cement use and their proportions
by region
Supplementary Data 6 Distribution of concrete by strength class and region
Supplementary Data 7 Cement content of concrete by region
Supplementary Data 8
Concrete carbonation rate coefficients by region
Supplementary Data 9 Exposure times of cement materials in service life by region
Supplementary Data 10 Exposure times of cement materials in demolition stage by region
Supplementary Data 11 Concrete st
ructure thickness by region
Supplementary Data 12 Waste concrete treatment methods and particle size distribution by region
Supplementary Data 13 Categories of mortar use and their proportions as
surveyed in China
Supplementary Data 14 Distribution of
mortar uses and
related parameters
Supplementary Data 15 Mortar carbonation rate coefficients measured in China
Substantial global carbon uptake by cement
carbonation
©
2016 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
SUPPLEMENTARY INFORMATION
DOI:
10.1038/NGEO2840
NATURE GEOSCIENCE
|
www.nature.com/naturegeoscience
1
2
Supplementary Data 16 Measurements of CaO converted to CaCO
3
in
Chinese mortars
Supplementary Data 17 Chinese survey statistics for walls
with
various extents of mortar
rendering
Supplementary Data 18 U.S. survey results of proportion of
cement kiln dust (CKD) diverted to
landfill
Supplementary Data 19 Annual carbon uptake by cement material and region
Supplementary Data 20 Global
carbon uptake by cement material and use
Supplementary Data 21 Global carbon uptake by cement materials and region
Supplementary Data 22 Annual carbon uptake by
cement material and relevant lag time, 1930 to
2013
Supplementary Data 23 Global
process C
O
2
emissions from cement production and carbon uptake
by carbonating cement materials from 1930 to 2013
Supplementary Data 24 Cumulative
process CO
2
emissions from cement production by region and
category, 1930 to 2013
1
Supplementary
Methods
1
Cement chemistry
1.1
Cement constituents and hydration reactions
The primary constituents of cement are calcium oxide (CaO), tricalcium silicate (C
3
S),
dicalcium silicate (C
2
S), tricalcium
aluminate (C
3
A), tetracalcium
aluminoferrite (C
4
AF), gypsum
(C
S
H
2
), as well as other, lesser constituents such as alkali, MgO, Na
2
O, Ka
2
O, heavy metal, etc.
1,2
as well as additions of limestone, fly
-
ash, silica
-
fume, and Ground
G
ranulated
B
last
-
F
urnace slag
(
GGBF
-
slag
)
depending on pro
prietary recipes and use
3
.
Following conventions in the cement, we
abbreviate these ingredients: CaO = C; SiO
2
= S; Al
2
O
3
= A; Fe
2
O
3
= F; H
2
O = H; SO
3
=
S
.
Cement hydration
reactions form calcium hydroxide
, calcium silicate hydrates, and other
hydration products as follows
4
:
2
2
CaO H O
Ca OH

2
3
3
3
2
2
6
3
(
)
C S
H
C S H
Ca OH
 
2
2
3
3
2
4
(
)
C S
H
C S H
Ca OH
 
3
2
6
3
32
3
26
C A
CSH
H
C AS H
 
3
3
6
32
4
18
2
3
22
3
C A
C AS H
H
C ASH
 
3
4
2
3
2
3
3
6( , )
( , )
(
)
C AF
CSH
H
A F S
A F H
Ca OH
 
Upon wetting of cement materials such as mortar and concrete, the main constituents are
hydrated by the above reactions to produce CH [Ca(OH)
2
or unhydrated CaO•H
2
O], CSH
[2(CaO)•SiO
2
•0.9
-
1.25(H
2
O),
and/or;
CaO•SiO
2
•1.1(H
2
O),
and/or;
0.8
-
1.5(CaO)•SiO
2
•1.0
-
2.5(H
2
O)], CAH [more complex than C
-
S
-
H], AF
t
(C
3
AS
3
H
30
-
32
), AFm
(C
2
ASH
12
), C
3
AH
6
(3CaO•Al
2
O
3
•6 H
2
O), MgO•SiO
2
•x(H
2
O), and so on
1
. In turn, these alkaline
hydrated products are unstable and progressivel
y react with the carbon dioxide in the air
5
.
1.2
Carbon
uptake
by cement carbonation
C
arbonation
is
a complicated physicochemical reaction between CO
2
and hydrated cement
products in the presence of pore water, which ultimately sequesters
carbon in cement
6,7
,
8
.
Eventually, the carbonation process weakens structures and materials, as the carbonation
reactions dissolve cement from concrete and mortar and return it to the constituent ingredients of
calcium carbonate, and hydrated silica, alumina, and iron oxide
9
.
The main chemical reactions of
cement
carbonation
are showed in method.
2
Cement production and consumption
Cement production data for China,
the
U.S., Europe, and rest of world from 1930 to 2013 is
from the US Geological Survey
10
(
Supplementary Data
1)
. Concrete and mortar account for most
of the produced cement (roughly 70% and 30%, respectively;
Supplementary Data 2
),
with a
small fraction related to
c
ement
k
iln
d
ust (CKD) generated during clinker production.
On average, 69.7%
-
86.0% of cement is used for concrete, with little variation among world
regions (
Supplementary Data 2
). Based on
survey
statistics of 1144 samples of civil engineering
2
projects between 1980
and
2012, we estimate that 69.7% of cement produced in China is used for
concrete, 28.8% for mortar
,
and 1.5% loss in construction
waste. In the U.S., sources suggest that
86.0% of cement is used for concrete
11
. In Europe, the proportion falls in between Ch
ina and the
U.S.: we estimate that 71.1% of European cement is used for concrete based on European Ready
Mixed Concrete Organization (ERMCO) statistics
12
and research in Nordic countries in 2003
13
(
Supplementary
Table 1)
. Owing to a lack of data for other
regions, we assume the central
estimate of cement used for concrete (i.e. Europe’s) applies.
Of the produced concrete and mortar, roughly 1
-
3% is wasted during construction, but the
shel
f
life of cement is only 3 to 6 months on average, such that the actua
l cement consumed
in a
given year is 97%
-
99% of the total cement produced
(
Supplementary
Table 1)
.
Prior studies show
only minor variation in this utilization fraction across regions (<4.5%;
Supplementary Data
3)
.
C
ement
k
iln
d
ust (CKD)
related to
clinker
production
14,15
(
Supplementary Table 4
) will absorb
carbon dioxide during
landfill/waste treatment
16,17
, as will
cement waste generated in
construction.
3
Process model of cement carbonation
Using production data as described in section 2,
we adopt a life
cycle assessment (LCA)
method to estimate
carbon up
take
by cement materials over time
(
Supplementary
Figure1).
Total
carbon uptake of cement
is calculated
by
adding
carbon uptake by concrete cement
,
carbon
uptake by mortar cement
,
carbon uptake by
construction cement waste
, and
carbon uptake by
cement kiln dust (
see method
).
3.1
Carbon uptake by concrete cement
We divide the concrete life cycle into three phases: service life
(e.g., in buildings)
,
demolition, and secondary use
(including both disp
osal in a landfill and recycling)
18
.
I
n case, we
calculate
CO
2
uptake
of concrete
by adding
carbon uptake during the service life
,
carbon uptake
during
the demolition
and
carbon uptake during the secondary use stage.
3.1.1 Service life
Concrete categories
We further break down cement utilization for different categories of concrete
19
. For China,
our estimates are based on the average cement consumption from 1999 to 2002 in
China
Statistical Yearbook on
Construction
, with
concrete used for residential construction also
incorporating data on proportion of housing floor types completed areas from 1996 to 2012
published in the
China Statistical Yearbook on Construction
. The concrete utilization category in
THE U.S. is based on statistics of apparent cement consumption in the United States from 1975 to
2013
10
and a report by the Portland Cement Association
9
. Categories of concrete used in Europe
are based on ERMCO Statistics 2001
-
2013
12
and the studies of Pad
e and Guimaraes
13,18
. Again,
we assume the rest of world uses concrete as Europe does (
Supplementary Data
5).
Concrete strength classes
We estimate streng
th classes of Chinese concretes based on the
survey
statistics for U.S.
concrete
based on data from ERMCO Statistics 2001
-
2013
12
and stud
ies
by Low and Nisbet
20,21
,
and for European and rest of world concretes based on ERMCO Statistics 2001
-
2013
12
and
the
study
of
Pade and Guimaraes in Nordic countries
18
(
Supplementary Table 2 and Supplementary
Data
6).
3
Concrete cement content
The cement content for concrete
is the mass of cement used in one cubic meter of concrete
(kg/m
3
) (
Supplementary Data
7
). We use Ch
inese cement contents from the
Construction and
Installation Engineering Budget Manual
and
Concrete Mix Proportion Quick Manual
22,23
, U.S.
cement contents from the same ERMCO Statistics 2001
-
2013 as well a
s a study by Low
20
, and
European and rest of world cement contents
from EN 206
-
1:2000 and averages in ERMCO
Statistics 2001
-
2013
12,13,24
,
Exposure conditions, CO
2
concentrations, and additives
.
Following
the study of
Pade and Guimareas, we estimate
carbon
uptake
of cement materials
carbonation
under five different categories of exposure conditions: exposed, sheltered, indoors,
wet, and buried
18
. Specifically, relative humidity, ambient CO
2
concentration
35
,
36
, and
additives
have been shown to affect carbonation rate
coefficients
25
. The range of applicable conditions are
estimated based on the previously referenced, region
-
specific studies and survey
statistics
9,18
.
Because the
concrete
carbonation depth is proportional to
2
CO concentration
25,26
, we apply
the correction factors shown in
Supplementary T
able
3
. Similarly, additives to cement and
concrete may affect the carbonation rate
18
, and we take this into account by applying other
correction factors as shown in
Supplementary T
able
4
.
C
oating and coverings
Studies have shown that application of surface coating and coverings
such as paints can
reduce the rates of cement carbonation
by 10
-
30%
27
,
19
. However, some studies have also shown
that paint does not
substantially reduce the carbonation depth
28,29
.
Covering concrete with mortar
has also been shown to reduce the concrete carbonation rate, and previous studies have
applied
the carbonation rate
correction coefficient to calculate carbonation depth of conc
rete
8,27,30
.
Recent
study showed that paint coating can reduce 28
-
day carbonation depth of concrete by 46%
31
. The
accelerated carbonation test of prime impermeable anti
-
deteriorating coating in Republic of
Korea for 7days, 14days, 28 days, and 56 days show
ed that the carbonation correction
coefficients of coating ranged from 24% to 42%
32
.
The
paints and other coatings may protect
against carbonation for
1
-
2 years,
and
the
protection will diminish over time if these coverings are not reapplied
33
.
However,
t
h
ere are no
long
-
term studies of the extent to which carbonization is delayed over multiple years. Given this
uncertainty, we assess carbonation using carbonation correction coefficients meant to reflect the
potential effects of coatings, including decrease
s in carbonation rates of up to 50% over the life
cycle of concretes
(
Supplementary T
able
5
)
.
Concrete carbonation rates
Using our estimates of concrete category, cement content, exposure conditions, additives
and coatings, we use relevant concrete
carbonation rate coefficients from various region
-
specific
references
18
,
9
(Supplementary Table 6 and Supplementary Data
8
)
. We further revised concrete
carbonation rate coefficients in China and other countries considering
the impacts of
compressive
4
streng
th class and exposure conditions (
sec
c
)
34
, cement addition (
ad
)
19
, CO
2
concentration (
2
CO
)
25,26
, and coating and cover (
CC
)
29,35
.
Service life
duration
Based on the previous, region
-
specific references, we estimate concrete service life
(t
l
)
in
China is 35 years
(ranging from 4
-
73 years)
, the duration of the demolition stage
(t
d
)
is 0.4 years
(ranging from 0.1
-
0.8 years)
, and the duration of the secondar
y use stage
(t
s
)
is 64.6 years
36,37
. In
Europe, service life is estimated to be 70 years
(ranging from 50
-
90 years)
, demolition stage is
0.4 years
(ranging from 0.1
-
0.7 years)
, and secondary use stage is 29.6 years
18,24
. In the U.S.,
service life is estimated to be 65 years
(ranging from 56
-
84 years)
, the demolition stage is again
0.4
(0.1
-
0.7)
years, and the secondary use stage is 34.6 years
38
. In the rest of world region, we
estimate
the duration of concrete
service life is 40
(10
-
90)
years, demolition stage is 0.4
(0.1
-
1.0)
years, and
secondary use
stage is 59.6 years
39
(
Supplementary T
able
7
,
Supplementary Data9 and
Supplementary Data
10).
Carbonation depth
We use the applicable carbonation rate
coefficients and exposure times to calculate the
carbonation depth of concrete in each strength class and set of exposure conditions using Fick’s
diffusion law
18
.
Exposed surface area
We estimate the expose
d surface area of concrete in the U.S., China, Europe, and
rest of
world
based on average
typical
thickness of concrete structures in the literature
9,18,24
(
Supplementary Data 11
)
.
Volume of carbonated concrete and carbonated cement
We
calculate the carbonated concrete volume
by
exposed surface area
and
carbonation
depth
.
The carbonated cement in service life
can then be calculated
by
the cement content of
c
oncrete in different strength classes (kg cement/m³)
,
clinker to cement ratio
,
average CaO
content of clinker in cement
40
,
the proportion of CaO within fully carbonated cement that
converts to CaCO
3
9,18,34,41
-
43
, and
the ratio of C element to CaO
(see method)
.
Annual carbon uptake
by concrete in service
Finally, we combine the results of the above calculations to calculate the annual carbon
uptake in year
t
l
as the cumulative carbon uptake in year
t
l
minus the cumulative carbon uptake in
year
t
l
-
1
.
3.1.2 Demolition stage
During demolition
stage
,
t
he size of waste concrete pieces is determined according to the
intended secondary use (e.g., disposal in a landfill, stacking, or recycling). If the waste concrete
will be diverted to a landfill or dump, it will be transported to the landfill and dump sit
es after
demolition, where it may be further crushed for steel recycling, and probably stockpiled for a
short time period. Even so, some relatively large pieces of concrete (e.g., with diameters of 0.5 m)
5
may be
buried in a landfill. If the concrete is rec
ycled as new cement or asphalt concrete
aggregates, road base, backfills (e.g., in highway embankments), pieces will be transported to
recycling plants and crushed into different particle sizes according to the intended secondary use
(
Supplementary Figure
2
)
. The surface area of exposed concrete, duration of exposure,
and
exposure conditions
of demolished concretes will therefore vary substantially.
The fate of
demolition waste in different regions is taken from different
literature
sources
18,24
,
38
,
39,
44
-
46
(
Supplementary Table8
)
.
Size and surface area of concrete pieces
The
range and particle size distribution of different types of demolished concrete in each
region
is
estimated
in
Supplementary Table9
. In China, surveys of 179 demolition projects in 35
large cities
were
summarized
. According to the China National and Industrial Standard, the
maximum particle size of concrete recycled into new cement, asphalt concrete aggregates, or
highway base is 32.5
mm, and the maximum particle size recycled for second
-
level road
aggregates is 53
mm
47
. We use published particle size distributions for Nordic countries to
estimate distributions in Europe
18,48
, and a combination of European and Chinese distribution to
e
stimate values applicable to the U.S.. Finally, we adopt particle size distributions in Japan and
South Korea in estimating carbon uptake for demolished concretes in the rest of world
39,46
(
Supplementary Data 12
)
.
Exposure time
T
he average exposure time of concrete during the demolition stage is
estimated
about
0.4
years
in whole world
(
Supplementary Table7
)
. In China, this average exposure time is derived
from our field survey data
(
Supplementary Data 10
)
, which showed 1
-
4 weeks
for building
demolition and crushing processes related to steel recycling, 1
-
24 weeks for stockpiling before
transporting to landfill sites or recycling plants, and an additional 4
-
16 weeks for recycled
concrete products stockpiled before secondary use. Ac
cording to literature sources, the durations
are similar in
Japan, Korea, and
Europe
34,4
6
,4
8
.
Carbonation of
demolished concrete
The
carbonation fraction
of demolished concrete
is
calculated according to particle size
distributions and carbonation depths
using
the Fick’s diffusion law
24
,
49
. Using the fraction of
concrete that will undergo carbonation, we next calculate the mass of concrete cement
carbonated
d
uring
the demolition stage
by
the concrete cement carbonated during demolition for each
concrete strength class
i
,
the cement consumed for each strength class
i
of concrete, the concrete
cement carbonated during service life for each strength class
i
,
the
fraction of carbonated cement
in concrete strength class
i
in the demolition stage
, and
the total
mass of concrete cement
carbonated in the demolition stage
(see method)
.
Total carbon uptake
during demolition stage
Finally,
we estimate total carbon
uptake
during the demolition
stage
based on cement
carbonated in demolition stage
and carbonation fraction of differently
treated concretes
18,34,42
.
3.1.3
Secondary use stage
6
It is estimated that
more than 91% of crushed concrete particles
worldwide are
buried, either
in landfills
or as part of their recycled use such as for road base or backfill aggregates
(
Supplementary Table
9).
The proportion diverted to landfills and dumps tends to be higher
instill
-
developing countries like China. Burial ensures
that little of this concrete is exposed to
air
42
, and concrete recycled as aggregate for new cement or asphalt concrete are bound in
concrete (making it difficult to evaluate its susceptibility to continued carbonation). Thus, we
assume
that concretes dive
rted to landfills or these secondary uses cannot be further carbonated.
C
arbonation depth in secondary use stages
The
total carbonation depth in
demolition stage and secondary use stage can be estimated by
carbonated depth in demolition stage
plus
new car
bonation depth during the secondary use stage
(
Supplementary
Fig
ure 3
a
and Supplementary
Fig
ure 3b
)
. There is the time
lag
(
i
t
)
for the
same carbonation depth from air exposure condition to buried condition
(
Supplementary
Fig
ure
3c
)
using the
Fick’s diffusion law
.
Fraction carbonized
The estimations details are showed in method.
Cumulative and annual carbon uptake during the secondary use stage
The estimations details are showed in method
.
3.2
Carbon uptake by mortar
cement
3.2.1 Cement utilization for mortars
The cement utilization for mortars is showed in
Supplementary T
able 1
0
50
.
Most mortar is
used for rendering, plastering and decorating (e.g., covering the exterior surfaces of concrete
structures
and walls
)
51
,
52
. The proportion of mortar cement for repairing in different building
types to total cement consumption ranges from 0.21% to 3.37%
9
.
Our
Chinese survey data
(
Supplementary
Data13
)
indicates that about 70% of mortar cement used for rendering, plastering
a
nd decorating, 18% of mortar cement used for masonry, 12% for maintenance and repairing, and
very small quantities for all other uses.
In the U.S., USGS end
-
use statistics show similar
proportions of cement used for different types of mortar
11
.
Because we
do not have other
region
-
specific data, we assume Chinese utilization rates
apply
Europe and rest of world
(
Supplementary Data14
)
.
3.2.2 The typical thickness of cement mortar utilization
The typical thickness of cement mortar utilization
is
showed in
(
Supplementary T
able
1
0)
27,
50
-
5
2
.
3.2.3 Carbonation rate coefficients of cement mortar
7
Cement mortars have been shown to undergo carbonation at a faster rate than concrete
because they have a
lower cement content, higher water/cement ratios,
and aggregates of finer
grain size (maximum grain size of 2
4 mm)
53,54
. However, there are relatively few studies of
mortar carbonation rates and depth.
Because mortar is essentially concrete with fine
-
grain
aggregate, the carbonation principles of mortar should be similar to those of low strength class
concrete (<C15), which on average have carbonation rate coefficients of between 6.1 mm/
year
and 36.8 mm/
year
in outdoor and indoor exposure conditions, respectively (in temperate
climate conditions and according to our field survey and experiment data using the 1% alcohol
phenolphthalein solution; see Supplementary
Data15). Carbonation depth will increase if
the
cement
contains
more additives
30
.
3.2.4 Carbon uptake
by mortar cements
The large exposure area and thin layers of mortar cement translates into rapid carbonation.
We calculate annual carbon uptake based on the proportion of annual carbonation depth
55,56
, and
estimate carbon uptake as the sum of uptake by
adding the
carbon uptake
of
rendering and
plastering mortar,
carbon uptake
of masonry mortar, and
carbon uptake
of maintain and repairing
mortar
(see method)
.
T
he proportion of
CaO
within fully carbonated mortar cement that converts
to CaCO
3
is
showed in
Supplementary Data 16
,
The
survey data
for
masonry walls are covered
by rendering mortar on both s
ides
,
only inside, and no rendering cover
is showed in
Supplementary
Data
1
7
.
The carbon uptake
calculation methods for both
rendering and plastering
mortar
and
maintain and repairing mortar
are showed in method.
The carbon uptake by masonry cement mortar
can is calculated as
r mat
mbt
mot
mnt
C
C
C
C
  
[
Supplementary
eq.
1
]
where
mbt
C
is carbon uptake by masonry mortar of walls with both sides rendered,
mot
C
is
carbon uptake by
masonry mortar of walls with one side rendered, and
mnt
C
is carbon uptake by
masonry mortar of walls with no rendering.
The carbon uptake calculation method of
mbt
C
,
mot
C
, and
mnt
C
is similar as that of
rendering and plastering mortar
by considering wall
thickness and demolition effects.
We calculate carbonation of masonry mortar for walls with both sides rendered
(
mbt
C
)
by
r
0
(
)
2
(
)
r
mb
m
Trp
tt
d
K
t d
t t
 
[
Supplementary
eq.
2
]
r
1
0
(
)
/
100% (
)
100%
2
/
100% (
1)
 
 
l
r
mbt
mbt
w
sl
mb t
mbt
Trp
w
sl
tt
f
d
d
d
t
t
t
d
d
d
t
t
[
Supplementary
eq.
3
]
ker
1
mbt
m
rm
b
mbt
clin
CaO
r
C
W
r
r
f
C
f
M
    
  
[
Supplementary
eq.
4
]
where
mb
d
is the total carbonation depth of masonry mortar of wall with both sides rendered,
m
K
is the carbonation rate coefficient of mortar,
t
is the exposure time of masonry mortar after
8
construction, and
r
t
is the time of full carbonation of render mortar in
Trp
d
thickness
,
Trp
d
is
the thickness of render mortar on masonry wall
,
mbt
f
is the annual carbonation percent of
cement used for ma
sonry mortar with both sides rendered on year t
,
mbt
d
and
1
mb t
d
are
carbonation depth of masonry mortar with both sides rendered at t and t
-
1 times, respectively
;
w
d
is the thickness of masonry wall,
l
mbt
d
is the carbonation depth of a masonry mortar with
both sides render in service life years (
l
t
)
,
mbt
C
is the annual carbon uptake of cement for
mason
ry mortar with both sides render in year t
,
m
W
is the cement for mortar
, and
rm
r
is the
percentage of masonry mortar cement in total mortar cement.
We then calculate carbonation of masonry mortar for walls
with one side rendered
(
mot
C
) by
r
(
)
+
(
)

 
 
mr
mo
m
m
Trp
sl
K
t
t t
d
K
t
K
t d
t
t t
[
Supplementary
eq.
5
]
wr
1
w
/d
100% (
)
100%
2
/d
100% (
+1)
 
l
mot
sl
mo t
mot
mot
Trp
sl
d
d
t
t t
f
d
d
t
t
[
Supplementary
eq.
6
]
ker
1
mot
m
rm
o
mot
clin
CaO
r
C
W
r
r
f
C
f
M
    
  
[
Supplementary
eq.
7
]
where
mo
d
i
s total carbonation depth of masonry mortar of wall with one side rendered,
r
t
is
the full carbonation time of render mortar outside of the masonry wall
,
mot
f
is the annual
carbonatio
n percent of cement used for masonry mortar with one side rendered
,
mot
d
and
1
mo t
d
are total carbonation depth of masonry mortar with one side rendered at t and t
-
1 times,
respectively
;
l
mot
d
is the carbonation depth of masonry mortar with one side rendered during
the service life years (
l
t
)
,
Trp
d
is the thickness of render mortar of the masonry wall
,
mot
C
is
the annual carbon
uptake of cement for masonry mortar with one side render on year t.
Finally, we calculate carbonation of masonry mortar without rendering
(
mnt
C
) by
2
mn
m
d
K
t

[
Supplementary
eq.
8
]
w
1
w
2
/d
100% (
)
100% 2
/d
100% (
+1)
l
mnt
sl
mn t
mnt
mnt
sl
d
d
t t
f
d
t
t
[
Supplementary
eq.
9
]
ker
1
mnt
m
rm
n
mnt
clin
CaO
r
C
W
r
r
f
C
f
M
    
  
[
Supplementary
eq.
10
]
where
mn
d
is the total carbonation depth of masonry mortar of wall without wall render,
mnt
f
is the annual carbonation percent of cement used for masonry mortar without wall render in year
t.
mnt
d
and
1
mn t
d
are carbonation depth of masonry mortar with no wall render
at t and t
-
1
times, respectively
;
l
mnt
d
is the total carbonation depth of masonry mortar with no wall render
9
during the service life years (
l
t
)
,
mnt
C
is the annual carbon uptake of cement for masonry
mortar with no wall render in year t.
3.3
Carbon uptake by cement in construction wastes
Cement waste
d during construction
accounts for 1% to 3% (average 1.5%) of total cement
consumption according to c
onstruction budget standards
22
and survey data
58
. Most of this waste is
in small pieces and will be recycled as backfill or landfilled after the completion of building
projects. Of these wastes, about 45% is concrete and 55% is mortar
37,59
.
Given the small
sizes of
pieces, the waste mortar is assumed to completely
carbonate in the first year, and concrete wastes
are assumed to completely carbonate over the following 5 years (
ranging from 1 to 10 years
). We
estimate carbon uptake of construction waste by
add
ing
carbon uptake by construction waste
concrete and construction waste mortar
(see method)
.
3.4
Carbon uptake by cement kiln dust
Previous studies have shown that about 80%
(52% to 90%)
of the cement kiln dust removed
from cement
-
producing kilns is di
verted to landfills and 20% is beneficially re
-
used
14,60
(
Supplementary Data
1
8
)
. Given the very small particle size, substantial carbonation occurs
within the first 2 days of reaction in a landfill
and complete carbonation is achieved within one
year
16,17
. We estimate carbon uptake by CKD in different regions of the world based on the
cement production, CKD generation rate, proportion of CKD treatment in landfill
(
Supplementary
Data
4)
,
CaO proportion
in CKD
14
, and
the fraction of CaO within fully carbonated CKD that
has
been converted
to CaCO
3
(see method)
.
4
Annual and cumulative carbon uptake of cement materials
4.1 Annual carbon uptake of different cement materials
Annual carbon
uptake
of cement concrete
in different regions
The annual carbon uptake of cement concrete in historic years is larger than that in recent
years because carbon uptake of concrete occurs over many years and life cycle stages. We
estimate that the annual carbon up
take of cement concrete materials in China, Europe, the U.S.,
and the rest of world have increasing from
0.002
million ton to 27.57million ton, 0.14 million ton
to 9.61 million ton, 0.10 million ton to 4.08 million ton, and 0.01 million ton to 27.10 millio
n ton
from 1930 to 2013
, respectively (
Supplementary Data 19
)
. Cumulative carbon uptake of by
cement in concretes worldwide has increased from 0.25 million ton to 68.35 million ton
.
Annual carbon
uptake
o
f cement mortar
in different regions
The annual carbon uptake of cement mortar in rece
nt
years is greater than in historic years
because the cement mortar is used in thin layers
. The annual carbon uptake of cement mortar
materials in China has increased fr
om
0.01
million tons in 1930 to 90.95 million tons in 2013.
The annual carbon uptake of cement mortar materials in Europe has meanwhile increased from
0.74 million ton in 1945 to 14.69 million tons in 1980, increasing little between 1980 and
1989,
10
and then
decreasing somewhat to between 14.62
million tons
and
12.13 million tons
from
1989 to
2013. The annual carbon uptake of cement mortar materials in the U.S.
increased from 0.18
million tons in 1933 to a peak of 1.76 million tons in 2006,
and then decreased
to 1.43 million
tons in 2013
(
Supplementary Data 19
)
. The annual carbon uptake of cement mortar materials in
the rest of the
world has increased from
1
.
70
million tons
in 1930 to
1
4
8
.
9
6 million tons
in 2013.
Annual carbon
uptake
of construction cement was
te
in different regions
The annual carbon uptake of cement mortar in recent years is larger than in historic years
because most of the construction cement waste are small particles and finish carbonation in short
time periods. The annual carbon uptake of c
onstruction cement waste materials in China, Europe,
T
he
U.S., and rest of world have increased from 479.37 tons to 5.87 million tons, 0.08 million
tons to 1.02 million tons, 56.03 thousand tons to 0.19 million tons, and 4.73 thousand tons to 3.01
million
tons
between 1930 and 2013
(
Supplementary Data 19
)
. Over the same period, annual
carbon uptake by cement in construction wastes worldwide
has increased from 0.15 million tons
to 9.85 million tons.
Annual carbon
uptake
of cement kiln dust
in different regions
The annual carbon uptake of cement kiln dust in China has increasing from 1817.64 tons to
10.85 million tons
between 1930 and 2013. The annual carbon uptake of cement kiln dust in
Europe was 187.63 thousand tons in 1930, 1.82 million
tons in 1980, and 1.38 million tons in
2013. The annual carbon uptake of cement kiln dust in the U.S. was 125.15 thousand tons in 1930
and increased to peak 0.45 million tons in 2005, before decreasing to 0.35 million tons in 2013.
The annual carbon uptake
of cement kiln dust in rest of world was 11.04 thousand tons in 1930,
and increased to 5.56 million tons in 2011 before decreasing to 5.42 million tons in 2013
(
Supplementary Data 19
)
. The annual carbon uptake of cement kiln dust worldwide
has increased
from 0.32 million tons to 18.00 million tons
between 1930 and 2013.
4.2 Annual carbon uptake of different cement material types
in different regions
On an annual basis, carbon uptake by mortars
is larger than that of concrete
;
uptake by
concrete is greate
r than that of
cement kiln dust
; and
cement kiln dust greater than that of
construction wastes
.
The annual carbon uptake of cement materials in China has increased from
18.13 thousand tons in 1930 to 135.23 million tons in 2013. The annual carbon uptake of
cement
materials in Europe has increased from 1.72 million tons in 1930 to a peak of 24.20 million tons
in 1989, before decreasing from 24.00 million tons in 1990 to 18.64 million tons in 1996, then
back up to24.66 million tons in 2008, and finally down t
o 23.89 million tons in 2013. The annual
carbon uptake of cement materials in the U.S. was increasing from 0.58 million tons in 1930 to
the peak 6.30 million tons in 2006 with some fluctuations
,
decreasing to 5.03 million tons in 2009
,
and increasing to 6.
05 million tons in 2013. The annual carbon uptake of cement materials in the
rest of the world
h
as
increased from 0.10 million tons in 1930 to 79.99 million tons in 2013.
Cumulative carbon uptake by cement materials in worldwide
has increased from 2.42 mil
lion tons
in 1930 to 245.15 million tons in 2013, dominated by carbon uptake of mortar
. On average,
more than 60% of carbon uptake was related to cement in mortar
(Supplementary Data 20).
T
he
majority of sequestration occurred in Europe and the
U.S.
p
rior
to 1982, but cement materials
used in China have absorbed more CO
2
than the other regions
s
ince 1994
(Supplementary Data
21)
.
The annual carbon uptake of global cement material from 1930 to 2013 is shown in