Elaborating the History of Our Cementing Societies: An in-Use Stock

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Elaborating the history of our cementing societies: an in-use stock perspective Zhi Cao, Lei Shen, Amund N. Løvik, Daniel B. Müller, and Gang Liu Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b03077 • Publication Date (Web): 24 Aug 2017 Downloaded from http://pubs.acs.org on August 27, 2017

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Environmental Science & Technology

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Elaborating the history of our cementing societies: an in-use stock

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perspective

3 4

Zhi Cao †,‡,§, Lei Shen †,‡, Amund N. Løvik ∥, Daniel B. Müller ⊥, and Gang Liu *,§

5 6

† Institute of Geographic Sciences and Nature Resources Research (IGSNRR),

7

CAS,11A Datun Road, Chaoyang District, Beijing 100101, China

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‡ University of Chinese Academy of Sciences, Beijing 100049, China

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§ SDU Life Cycle Engineering, Department of Chemical Engineering, Biotechnology,

10

and Environmental Technology, University of Southern Denmark, 5230 Odense,

11

Denmark

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∥ Empa, Swiss Federal Laboratories for Materials Science and Technology, CH-9014,

13

St. Gallen, Switzerland

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⊥ Industrial Ecology Programme, Norwegian University of Science and Technology

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(NTNU), 7191 Trondheim, Norway

16 17 18 19 20 21 1

ACS Paragon Plus Environment


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ABSTRACT

23

Modern cities and societies are built fundamentally based on cement and concrete.

24

The global cement production has risen sharply in the past decades due largely to

25

urbanization and construction. Here we deployed a top-down dynamic material flow

26

analysis (MFA) model to quantify the historical development of cement in-use stocks

27

in residential, non-residential, and civil engineering sectors of all world countries. We

28

found that global cement production spreads unevenly among 184 countries, with

29

China dominating the global production and consumption after the 1990s. Nearly all

30

countries have shown an increasing trend of per capita cement in-use stock in the past

31

century. The present per capita cement in-use stocks vary from 10 to 40 tonnes in

32

major industrialized and transiting countries and are below 10 tonnes in developing

33

countries. Evolutionary modes identified from historical patterns suggest that per

34

capita in-use cement stock growth generally complies with an S-shape curve and

35

relates closely to affluence and urbanization of a country, but more in-depth and

36

bottom-up investigations are needed to better understand socioeconomic drivers

37

behind stock growth. These identified in-use stock patterns can help us better estimate

38

future demand of cement, explore strategies for emissions reduction in the cement

39

industry, and inform CO2 uptake potentials of cement based products and

40

infrastructure in service.

2


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41

Table of Contents

Progressive Stages t/cap

time I

II

III

IV

42 43 44

1. INTRODUCTION

45

Concrete is one of the most fundamental materials used in the built environment and

46

the most widely used man-made materials on earth1. Concrete is produced via a

47

mixture of chemically inert mineral aggregates (e.g., sand and gravel) and additives,

48

water, and cement (a binder that sets and hardens when mixed with water)2. Due to its

49

irreplaceable role in the construction industry, cement is seen as the foundation of

50

modern human civilization3. The second half of the 20th century has witnessed a fast

51

growth in the global cement consumption4. It is foreseen that the ongoing

52

urbanization and industrialization, especially in emerging countries, will still lead to a

53

massive production of cement to satisfy the growing demand in dwellings and

54

infrastructure facilities5.

55 56

Cement production has been recognized as one of the major contributors to

57

anthropogenic greenhouse gas emissions, accounting for roughly 5-8% of global CO2

58

emissions6. Facing the growing pressure of energy saving and emission reduction, 3



59

CO2 emissions reduction roadmaps have been proposed by the International Energy

60

Agency (IEA) and the World Business Council for Sustainable Development

61

(WBCSD)7,8. Complying with these roadmaps, the cement industry has already made

62

significant improvements in energy efficiency9. Hence, cement demand reduction and

63

material efficiency options must also be explored to further reduce CO2 emissions

64

from cement production, as recommended in the Fifth Assessment Report of the

65

Intergovernmental Panel on Climate Change (IPCC)10.

66 67

Dynamic material flow analysis (MFA) is a widely used method to quantify the

68

socioeconomic metabolism and long term demand and supply of long-lived

69

materials11. Within the dynamic MFA framework, the future material cycles are often

70

simulated by assumed future patterns of material in-use stocks12. Characterizing the

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historical patterns of in-use material stock has thus been acknowledged as a

72

fundamental step to extrapolate future material metabolism in such a stock-driven

73

approach11,13,14,15,16,17,18.

74 75

There have been efforts to estimate, from a bottom-up or data driven approach (i.e.,

76

adding up the amount of material contained in all relevant products), the in-use

77

cement stock (or more precisely, cement equivalent embodied in the concrete stock)

78

existing in the building or infrastructure sectors19,20,21,22,23. Using a top-down or mass

79

balance driven approach (i.e., based on apparent consumption of a material and the 4


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80

life span of its end-use products), previous studies have also quantified the in-use

81

cement stock on a country level (e.g., China5 and USA24). On the global level, Müller

82

et al.25 have made a rough estimation on the in-use cement stock of all countries;

83

however, they didn’t consider the discrepancies of product lifetimes in various sectors

84

and countries, the international trade of cement and cement products, and the

85

evolutionary modes of in-use cement stock growth across countries. These gaps

86

should be addressed to provide a more robust understanding of the historical patterns

87

of cement in-use stocks.

88 89

In addition to benchmarking future development and informing demand forecasting, a

90

retrospect of the historical patterns of in-use cement stock can also lay the foundation

91

for capturing the future trend of demolition waste generation once those relevant

92

buildings and infrastructure reach their end of life. This is of great significance for

93

waste management, considering the continuing urbanization globally26. Further,

94

estimating in-use cement stock could help quantify the CO2 uptake by carbonation of

95

cement materials over their entire life cycle27,28.

96 97

In this paper, we developed a top-down dynamic MFA model to estimate the historical

98

in-use cement stocks for all the world countries during 1931-2014. We aim to answer

99

three questions: (i) What are the historical production, trade, and consumption

100

patterns of cement by country? (ii) What is the evolutionary mode of cement in-use 5



101

stocks across countries all over the world? (iii) How will the identified patterns and

102

evolutionary mode inform us the long-term dynamics of cement flows in the future?

103 104

2. MATERIALS AND METHODS

105

2.1. System definition and model framework

106

The cement cycle is simplified as shown in Figure 1. Our model covers 184 countries

107

or regions and the time period from 1931 to 2014, in which period historical data are

108

available. The 184 countries have been aggregated into 10 world regions (see

109

definition Table S1 in the Supporting Information). A time-cohort-type (TCT)

110

top-down stock estimation method was used 11,27, i.e., the cement in-use stock was

111

derived from the sum of apparent consumption survived in each year (see Figure 1).

112

The detailed quantification method for the apparent cement consumption can be found

113

in the Supporting Information. Three overarching end-use sectors are differentiated in

114

our model, i.e., residential building, non-residential building, and civil engineering.

6


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Other Countries Import (CI)

Export (CE)

Import (CPI)

Export (CPE)

In-Use Stock (S) Cement Manufacturing (CP)

Apparent Consumption (AC)

Cement Product Manufacturing

Sector Ratio

Inflow (IN)

RES

Inflow (IN)

NRES

Inflow (IN)

CE

Waste Management

(SR)

Recycling (as aggregate)

Mining

Lithosphere

Landfill

Repositories Time

115

1931

1931

1931

1931

1931

1931

1931

1932

1932

1932

1932

1932

1932

1932

1932

1933

1933

1933

1933

1933

1933

1933

1933

……

……

……

……

……

……

……

……

……

……

……

……

……

……

……

……

2012

2012

2012

2012

2012

2012

2012

2012

2013

2013

2013

2013

2013

2013

2013

2013

2014

2014

2014

2014

2014

2014

2014

2014

CE

+ CPI -

CPE

CP

+

CI

-

=

AC

×

SRi

=

IN 1931,1

IN 1931,2

……

……

IN IN IN 1931,81 1931,82 1931,83

IN 1932

IN 1932,1

……

……

IN IN IN 1932,80 1932,81 1932,82

IN 1933

……

……

IN IN IN 1933,79 1933,80 1933,81

……

……

……

……

……

……

……

……

IN 2012

IN 2012,1

IN 2012,2

IN 2013

IN 2013,1

Cohort

1931

IN 1931

Type

……

IN 2014

∑

INi

S 1931

S 1932

S 1933

……

……

S 2012

S 2013

S 2014

116

Figure 1. System definition and Time-Cohort-Type (TCT) method for the top-down

117

estimation on in-use cement stock. The TCT method is expressed as matrixes, of

118

which the diagonal cell is the cement inflow in every year and each cell is the

119

survived cement inflow after certain years. The sum of each column in a matrix is the

120

in-use cement stock of every year. Three categories of end-use sectors are

121

differentiated: residential building (RES), non-residential building (NRES), and civil

122

engineering (CE).

123 124

2.2. Data collection and parameters setting

125

Cement production data of each country were collected from United States Geological

126

Survey (USGS)29. Trade data were collected from the United Nations Comtrade

127

Database30. The physical values are missing in about 10% of trade records. Trade 7



128

flows are recorded twice in the United Nations Comtrade Database, once by the

129

importer and once by the exporter. These two records are often inconsistent. The mean

130

value of two records for a single trade flow is used as the initial input of export or

131

import in the TCT method. To resolve the physical data gaps and inconsistency in

132

trade data, the treatment method proposed by previous literatures was applied here11,31.

133

The physical data gaps are filled with the result of dividing monetary values by

134

“world average price”.

135 136

The split ratios of end-use sectors were collected from industrial statistics provided by

137

experts from the cement industry associations, e.g., U.S. Portland Cement Association

138

and European Cement Association (Cembureau). For the years of which data are not

139

available, we assumed that split ratios were held constant. This assumption will not

140

significantly affect estimation on in-use cement stocks in less-developed countries,

141

Cement stocks in less-developed countries are mainly formulated in the recent

142

decades, and they are short-lived as well. For developed countries, the assumption

143

that split ratios were held constant will influence estimation on in-use cement stocks

144

in those countries. Details of sector split are presented in Figure S1 in the Supporting

145

Information.

146 147

The survival function5 that determines the probability that the cement flow into use

148

survives after a certain time32 was used in the stock estimation. The survival function 8


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149

was set as a cumulative distribution function (CDF) of the Normal distribution. The

150

mean (average lifetime) of the CDF is obtained from a comprehensive literature

151

review (see Table S4 in the Supporting Information) and the standard deviation of the

152

CDF was set as 1/5 of the mean25.

153 154

2.3. Uncertainty Analysis

155

Since production, trade, and average lifetime exert significant impacts on in-use

156

cement stock estimation, we considered uncertainties in these data.

157

•

We adopted the assumptions recommended by the Intergovernmental Panel on

158

Climate Change (IPCC)33 and used a Normal distribution with coefficients of

159

variation (CVs) of 5% and 10%, respectively, for developed countries and

160

less-developed countries. Countries were categorized into developed and

161

less-developed according to their Human Development Index (HDI)34.

162

•

We used a Normal distribution to assess uncertainties in the trade data. The

163

mean of the Normal distribution is the average of the two records. The

164

standard deviation of the Normal distribution is the half of the absolute

165

difference between the two records. The details of uncertainties in trade data

166

can be found in the Supporting Information.

167 168

•

To investigate the effect of the average lifetime, uncertainties in the average lifetime is captured by a Normal distribution with a 10% CV35.

169 9



170

A pure Monte Carlo simulation algorithm is developed to integrate uncertainties from

171

different sources. To guarantee the robustness of uncertainty analysis, 10,000 trials are

172

performed.

173 174

2.4. Evolutionary Mode Identification

175

The ARIMA (Autoregressive Integrated Moving Average) approach36 is employed to

176

investigate the growth patterns of historical in-use cement stock from 1931 to 2014.

177

According to the criterion of this time-series analysis approach, the evolutionary

178

modes of historical in-use cement stock in 184 countries are identified and

179

categorized into 5 types:

180

•

Type A: The acceleration (2nd order difference) of cement in-use stock is

181

stationary around zero; the speed (1st order difference) of cement in-use stock is

182

positive.

183

•

184 185

Type B: The acceleration of cement in-use stock is stationary with a positive value; the speed of cement in-use stock is positive.

•

Type C: The acceleration of cement in-use stock is nonstationary, and the

186

acceleration shows a general increasing trend throughout time; the speed of

187

cement in-use stock is positive.

188

•

Type D: The acceleration of in-use cement stock is nonstationary, and the trend

189

of acceleration partly exhibits deceleration phases; the speed of cement in-use

190

stock is positive. 10


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191 192

•

Type E: The acceleration of cement in-use stock is stationary around zero; the speed of cement in-use stock is negative or maintaining at zero.

193 194

3. RESULTS AND DISCUSSION

195

3.1. Apparent consumption and trade.

196

Figure 2 demonstrates the trends of apparent cement consumption by region during

197

the period of 1931-2014. Except that the North America is picking up in the last years,

198

apparent cement consumption in industrialized regions (e.g., North America and

199

Europe) shows a fluctuating but descending trend, while industrializing countries or

200

regions have maintained a staggering growth in apparent cement consumptions in the

201

past decade. Global cement apparent consumption is clearly dominated by China after

202

1990s. From 2011, China’s apparent cement consumption had surpassed the level of

203

2.0 billion metric tons (Gt) and further reached a stunning amount of 2.5 Gt in 2014,

204

accounting for about one-third of the global total (8.4 Gt). China’s apparent cement

205

consumption in the past ten years (2005-2014) is more than threefold to the United

206

States’ apparent cement consumption in the past eight decades. The apparent cement

207

consumption of the former Soviet Union region has plunged to 38.7 million metric

208

tons (Mt) in 1998 since the collapse of the Soviet Union, and rose up to 117.9 Mt in

209

2014.

11



450

3000 3000

400

Apparent consumption [Mt]

2500

2500

2000 350 300

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1500 1000

2000

500

250

0 1931

1961

1991

1500

200 150

1000

100 500 50 0

1931

210

0

1941

1951

1961

1971

1981

1991

2001

2011

North America

Latin America & Caribbean

Europe

Former Soviet Union

Africa

Middle East

India

Oceania

Other Asia

China (right axis)

211

Figure 2. Apparent cement consumptions in the 10 world regions (1931-2014). Values

212

for China are displayed on the right axis, all other countries and regions on the left

213

axis.

214 215

Cement is largely consumed locally, because cement is heavy and the transportation

216

cost is high. Figure 3 presents the 30 largest countries for cumulative net imports or

217

exports of cement and their foreign trade dependence (measured as cumulative net

218

import in cumulative cement consumption). It is demonstrated that Japan (335.4 Mt),

219

China (300.1 Mt), Thailand (216.8 Mt), and South Korea (116.6 Mt) are leading

220

exporters in Asia. Canada (126.5 Mt), Turkey (207.1 Mt), Greece (190.0 Mt),

221

Columbia (45.3 Mt), and Belgium-Luxembourg Economic Union (105.8 Mt), 12


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222

respectively, are the major exporters in North America, Middle East, South Europe,

223

Latin America & Caribbean, and West Europe. The U.S. stands out as the largest

224

cumulative cement importer in the world, but the share of accumulative net import in

225

cumulative consumption is merely 9.5%. Of the 30 largest net importers or exporters,

226

4 countries or regions (i.e., Hong Kong, Singapore, Kuwait, and Siri Lanka) import

227

over half of their cement consumption from abroad. 1000

a) Cumulative Net Import [Mt]

500 0 -500 -1000 80% 60%

b) Cumulative Net Import/Cumulative Consumption

40% 20% 0% -20% -60%

228

Algeria Canada China Colombia Germany Ghana Greece Hong Kong India Indonesia Iraq Japan South Korea Kuwait Libya Mexico Netherlands Nigeria Romania Saudi Arabia Singapore Spain Sri Lanka Thailand Turkey United States Venezuela Czechoslovakia East and West Pakistan Belgium-Luxembourg

-40%

229

Figure 3. Absolute amounts of cumulative net import of cement (a) and foreign trade

230

dependence (b). Countries whose total in-use cement stocks rank the top 30 are

231

selected out of 184 countries. The time coverage of cumulative net cement import is

232

1931-2014. The foreign trade dependence refers to the proportion of cumulative net

233

import in cumulative apparent consumption. 13



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234 235

3.2 Historical patterns of total and per capita cement stock.

236

The total in-use cement stocks in almost all regions show a steady growth in the past

237

decades (Figure 4(a)). China’s cement stock shows an exponential growth, reaching

238

26 Gt in 2014 with a 3-fold increase during the recent decade. In 2014, the in-use

239

cement stock in Asia takes up half of the global total (74.4 Gt). 30000

1 North America

a) Total in-use cement stock [Mt]

25000 9 20000 8

10

1

2 Latin America & Caribbean 3 Europe

2 3

Year 2014 4

15000 7 6

5

10000

4 Former Soviet Union 5 Africa 6 Middle East 7 India 8 China

5000

9 Oceania

240

0 1931 1941 1951 1961 1971 1981 1991 2001 2011

14


10 Other Asia

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b) Composition of in-use cement stocks 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%

Residential building

Non-residential building

Civil Engineering

241 242

Figure 4. Total in-use cement stocks in the 10 world regions (a) and composition of

243

in-use cement stocks for the 15 largest countries (b).

244 245

Figure 4 (lower panel) shows the composition of in-use cement stocks in 2014 for the

246

15 largest countries, amounting to 56.0 Gt in total. The distribution of in-use cement

247

stocks is almost in line with the split ratio of end-use sectors in different countries

248

(see the Supporting Information), according to the system definition of the TCT

249

method. One exception is the UK: its proportion of stock in the residential sector is 36%

250

while the corresponding split ratio of residential sector is 32% for the period of

251

1931-2000 and even less than 30% for the period of 2006-2014. This can be explained

252

by the fact that lifetime of UK’s residential sector is longer than that in other sectors,

253

meaning that cement in the residential sector demolishes at a slower pace. The 15



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254

varying compositions have significant implications for construction and demolition

255

waste management for different sectors and countries.

256 257

The historical patterns of in-use cement stock, on a per capita basis, present an

258

upward trend in all regions (Figure 5(a)). Per capita cement in-use stock of the world

259

is estimated to be 10.3 metric tons in 2014. The present per capita level of in-use

260

cement stocks vary from 10 to 40 tonnes in major industrialized and transiting

261

countries (especially the five regions Europe, China, Former Soviet Union, North

262

America, and Middle East) and are below 10 tonnes in developing countries. For

263

example, Europe has reached a level of above 20 t/cap while India and Africa have

264

just climbed up to a level of 2.5-3 t/cap. 35

35 30 25 20

a) In-use cement stock [t/cap] NA EU AF IN OC WA

30

LAC FSU ME CN OA

b) In-use cement stock G8 + BRICs [t/cap]

Italy

Germany 25 Russia 20

15

15

10

10

5

France

USA UK Canada

Japan China

South Africa

Brazil

5 India

0 1950 1960 1970 1980 1990 2000 2010

0

1950 1960 1970 1980 1990 2000 2010

265 266

Figure 5. Per capita in-use cement stocks in the 10 world regions (a) and in 12

267

selected counties (b). Ten regions include North America (NA), Latin America & 16


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268

Caribbean (LAC), Europe (EU), Former Soviet Union (FSU), Africa (AF), Middle

269

East (ME), India (IN), China (CN), Oceania (OC) and other Asia (OA). WA

270

represents the world average level. These 12 countries include G8 and BRICs

271

countries. Russia is represented by aggregation of the former Soviet Union countries.

272 273

Figure 5(a) shows the per capita cement in-use stock growth of the 12 selected

274

countries during the period of 1950-2014. Still, the level of per capita cement in-use

275

stock in China has shown a sharp increase, and its value in 2014 (19.2 t/cap) has

276

surpassed that of several industrialized countries during the past decade, approaching

277

to Japan (20.0 t/cap) or France (20.7 t/cap). The former Soviet Union region has

278

increased at a stable growth rate in per capita in-use cement stock and reached at a

279

level of 17.3 t/cap in 2014. Per capita in-use cement stocks of Brazil and India are still

280

at a low level of 7.5 and 2.7 t/cap, respectively. It is revealed that per capita in-use

281

cement stocks of the UK and Japan have peaked at around 2008; however, this

282

phenomenon might be attributed to the 2008’s economic crisis and thus may not be

283

associated with saturation in the in-use cement stock. For other G8 countries, the

284

annual growth rate of per capita stock has slowed down. The per capita stock levels of

285

three G8 countries in Europe (i.e., Italy, Germany, and France) have reached up to

286

above 20 t/cap while the values of U.S. and Canada, are lower.

287 288

To illustrate the uncertainties in estimated in-use cement stock, simulation results for 17



289

year 2014 are plotted in Figure 6. Uncertainties in production data, especially for

290

countries which are self-sufficient in cement consumption, largely determine the

291

uncertainties in estimated in-use cement stock. The CVs of production for developed

292

and less-developed countries are 5% and 10%, which lead to 95% confidence levels

293

of [-9.8%, +9.8%] and [-19.6%, +19.6%]5, respectively. A 10% CV in lifetimes lead

294

to 95% confidence levels of [-19.6%, +19.6%] as well. Almost all of less-developed

295

countries fall in the range of [-19.6%, +19.6%] (except for North Korea), while 10

296

developed countries fall out of the range of [-9.8%, +9.8%]. Typically, cement

297

end-users in industrialized countries have a longer lifetime. When in-use cement

298

stocks consist of older buildings and infrastructures, uncertainties in lifetimes tend to

299

have greater impact on stock estimates. Another possible reason is that uncertainties

300

in each year’s production data are accumulated and propagated into in-use cement

301

stocks. Time scope of cement production in developed countries is longer, since

302

cement was popularized earlier in developed countries.

18


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303 304

Figure 6. Upper and lower quantiles of 95% confidence intervals of in-use cement

305

stock (year 2014) for all countries. Red points represent developed countries and blue

306

points represent less-developed countries.

307 308

3.3 Evolutionary modes of cement in-use stock growth.

309

The evolutionary modes of cement in-use stocks of the 184 world countries on the per

310

capita basis are demonstrated in Figure 7. The result for total cement in-use stock is

311

demonstrated in the Figure S2 in the Supporting Information. Most countries present a

312

positive growth trend (speed) in the in-use cement stock, both on a total and per capita

313

basis.

314 315

On the per capita basis, it is observed that most less-developed countries or regions

316

are categorized as type A. Per capita in-use cement stocks in type A is presenting a

317

steady growth trend, of which the acceleration is stationary around zero. Some of type 19



318

A economies are identified as type B or type C on the total basis (see Figure S2 in the

319

Supporting Information). After eliminating the effect of population growth, most of

320

them, whose per capita cement in-use stocks are at a low level, are in a state of

321

stationary growth. This indicates that the growth of cement in-use stock could be

322

partly attributed to population growth, especially for African and South American

323

countries. Countries or regions identified as type B and type C are all emerging

324

economies, manifesting an exponential growth trend with a positive acceleration.

325

Most of industrialized economies are identified as type D. Although the speed of stock

326

growth in type D is positive, the acceleration is undergoing a downtrend which slows

327

down the stock growth. Only six highly developed economies (i.e., Iceland, Japan,

328

Kuwait, Singapore, Sweden, and the United Kingdom) are identified as type E. Type

329

E countries show a relatively stationary trend in acceleration, but have a negative

330

speed of the stock growth. This decrease in level of per capita cement in-use stock

331

reflects the material efficiency strategies (i.e., higher-strength concrete with less

332

cement use and reduced demand for cement by using cement end-users more intensely)

333

come to play a significant role in type E countries.

20


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Progressive Stages t/cap

time I

II

III

IV

Type A (YM)

Type B (IR)

Type C (CN)

Type D (FR)

Type E (SW)

Level

Level

Level

Level

Level

Speed

Speed

Speed

Speed

Speed

Acceleration

Acceleration

Acceleration

Acceleration

Acceleration

334 335

Figure 7. Evolutionary modes of historical patterns of per capita cement in-use stocks.

336

Yemen (YM), Iran (IR), China (CN), France (FR) and Sweden (SW) are used as the

337

representatives for type A, B, C, D and E, respectively.

338 339

Based on the observations above, we can easily find out that different types of

340

countries are in various stages. According to speed and acceleration of cement stocks

341

in different types of countries, we speculate that development of cement in-use stocks

342

in a country could be divided into 4 progressive stages (Figure 7): (i) Initial stage,

343

when per capita in-use stock maintains at a low level but grows at a linear rate; (ii)

344

Take-off stage, when per capita in-use stock starts to grow at an accelerated rate; (iii) 21



345

Slow-down stage, when the growth rate of per capita in-use stock slows down; (iv)

346

Shrinking stage, when the growth rate of per capita in-use stock further slows down,

347

saturates around zero, and eventually drops to a negative level. The four progressive

348

stages, by and large, comply with a logistic growth (S-shape) curve. Since most of

349

less-developed countries are still at the initial stage, per capita cement in-use stock of

350

these countries is likely to continue to grow and consequently result in more cement

351

use in the future.

352 353

3.4 Per capita in-use cement stock vs. socioeconomic indicators.

354

Figure 8(a) shows that, within an individual country, the growth of in-use cement

355

stock is correlated with economic growth. But per capita GDP is not the only driver

356

since the slopes of the patterns vary by country. The developed countries start to

357

diverge at almost the same levels of per capita cement in-use stock (5 t/cap) and per

358

capita GDP (15000, 2010 international dollars/cap). The slopes of patterns in

359

emerging countries, especially in China, tend to be steeper (i.e., these societies have

360

been concretizing at a higher speed) than that in developed countries.

361 362

More linear correlation between per capita in-use cement stock and urbanization rate

363

(measured as the share of urban population in total population) is observed in

364

emerging economies (Figure 8(b)). The urbanization rates in developed countries have

365

already reached a relatively high level of above 50% in 1950. During the growth stage 22


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366

of per capita in-use cement stock in developed countries, the urbanization has less

367

impact on the growth of in-use cement stock. Although a thorough understanding of

368

the drivers behind requires bottom-up analysis11, we speculate that patterns of urban

369

expansion, architectural specification, choice of construction material, geographical

370

variation, and development stage would be other influential factors behind the growth

371

of cement in-use stock, which deserve more in-depth and bottom-up investigation. For

372

example, the cement stock of Brazil is still low at a high urbanization rate, indicating

373

that large amount of people living in Brazilian cities still have a low level of building

374

and infrastructure service (e.g., in urban slums). On the contrary, China’s cement

375

stock is already very high at an urbanization rate of over 50%, which may be

376

explained by a combination of factors such as its recent years’ fast infrastructure

377

development37 (e.g., the nation-wide high speed train systems), construction bubble38

378

(e.g., the popping-up “ghost cities”), and potential overestimation of production data1. 35 a) Cement Stocks [t/cap]

30

Italy Germany

25 France

China Former Soviet Union

20 15

UK

Japan USA Canada

10

South Africa Brazil

5

India

GDP [2010 Intl$/cap]

0

379

0

10000

20000

30000

40000

23


50000

60000


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35 b) Cement Stocks [t/cap]

30

Italy Germany

25 France

Former Soviet Union

20

China

15

Japan

USA UK

10 South Africa

Brazil

5 India

Urbanization Rate [%]

0

380

0

20

40

60

80

100

381

Figure 8. Per capita in-use cement stocks relative to per capita GDP (a) and

382

urbanization rate (measured as the share of urban population in total population) (b).

383

The time scopes of per capita GDP data39 and urbanization rate data38 are 1950-2014

384

and 1960-2014, respectively, due to the data availability.

385 386

The identified in-use stock patterns can help better estimate future demand of cement

387

and explore effect of material efficiency and urbanization strategies, e.g., lifetime

388

extension and material efficiency strategy (same service with less material), on

389

emission reduction. It is proved that an S-shape curve can be observed in cement

390

stocks, as in steel stocks41. The observation of S-shape curve in cement stocks may be

391

served as a robust hypothesis for future projections on cement demands, especially in

392

emerging economies. For example, China owns a huge volume of cement stock and is

393

still in the take-off stage. A lower saturation level of per capita cement stock will

394

significantly reduce Chinese cement demands, consequentially mitigate the total

395

absolute amount of emissions from Chinese cement sector. To achieve a lower 24


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396

saturation level, buildings and infrastructure should be used more intensively. Besides,

397

extending lifetimes of buildings and infrastructure in China will also contribute to

398

emission reduction since buildings and infrastructure in China tend to have a much

399

shorter lifetime than in European countries.

400 401

The age-cohort information have been recorded in the in-use cement stock dataset,

402

which provides robust information for forecasting long-term generation of demolition

403

waste and informing CO2 uptake potentials of cement based products and

404

infrastructure in service. Cement based products and infrastructure have been

405

reckoned as a substantial carbon sink28. Once related carbonation parameters for

406

different cement end-users are available, the age-cohort information recorded in the

407

cement stock dataset can be easily applied to understand the net carbon emissions

408

from the cement stocks.

409 410

ASSOCIATED CONTENT

411

Supporting Information

412

Model details, additional figures and data sources. This information is available free

413

of charge via the Internet at http://pubs.acs.org/

414 415

AUTHOR INFORMATION

416

Corresponding Author 25



417

*E-mail: [email protected] and [email protected]; tel.: + 45 65509441.

418

Notes

419

The authors declare no competing financial interest.

420 421

ACKNOWLEDGEMENTS

422

We thank Hendrik van Oss from United States Geological Survey, Karen Arneson

423

from U.S. Portland Cement Association, and Alessandro Sciamarelli from Cembureau

424

for providing end-use data and helpful clarification, and Andres Tominaga Terukina

425

and Mita Broca for data collection and research assistance. This work is financially

426

supported by the Danish Council for Independent Research (CityWeight;

427

6111-00555B), the Danish Agency for Science, Technology and Innovation

428

(International Network Programme, 5132-00029B and 6144-00036), Chinese

429

Academy of Sciences (XDA05010400), Natural Science Foundation of China

430

(41728002), and Chinese Geological Survey (121201103000150015).

431 432

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Elaborating the History of Our Cementing Societies: An in-Use Stock

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