Scholarly article on topic 'Sustainable concrete with high volume GGBFS to build Masdar City in the UAE'

Sustainable concrete with high volume GGBFS to build Masdar City in the UAE Academic research paper on "Civil engineering"

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Abstract of research paper on Civil engineering, author of scientific article — Mohamed Elchalakani, Tarek Aly, Emad Abu-Aisheh

Abstract Masdar City (MC) is leading the Middle East in the development of energy and resource efficient low-carbon construction in the United Arab Emirates (UAE). One of its major goals is to develop and specify materials and processes that will help reducing its environmental footprint through resource and energy conservation, as well as renewable energy generation. In 2010 MC announced on its website a prized-competition for the best proposal of “Sustainable Concrete” and “Lowest Carbon Footprint” to build MC with a total of two million cubic meter of concrete on 4 years period. This paper presents the experimental test results of 13 types of concrete mixes made with high volume of ground granulated blast furnace slag (GGBFS) cement with 50%, 60%, 70% and 80% replacement of ordinary Portland cement (OPC) to reduce the carbon emissions. A fly ash-blended mix made with 30% fly ash was also tested. The paper provides more information on the mix design parameter, full justification of CO2 footprint, and cost reduction for each concrete type. The hardened and plastic properties and durability test parameters for each mix are presented. The results show that the slag concrete mixes significantly reduce the carbon footprint and meet the requirements of MC. An economical mix with 80% GGBFS and 20% OPC was nominated for use in the future construction of MC with 154kg/m3 carbon foot print.

Academic research paper on topic "Sustainable concrete with high volume GGBFS to build Masdar City in the UAE"

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Case Studies in Construction Materials

journal homepage: www.elsevier.com/locate/cscm

Case Study

Sustainable concrete with high volume GGBFS to build Masdar City in the UAE§

Mohamed Elchalakania'*, Tarek Alyb, Emad Abu-Aishehc

a Civil Engineering Department, Higher Colleges of Technology, Dubai Men's College, PO Box 15825, Dubai, United Arab Emirates b WorelyParsons Services, Perth, WA 6000, Australia

c Consulting Services Department, Civil Engineering Unit, Saudi Aramco, Dhahran, Saudi Arabia

ARTICLE INFO

ABSTRACT

Article history:

Received 14 October 2013

Received in revised form 19 November 2013

Accepted 28 November 2013

Keywords: Concrete Sustainability GGBFS Fly ash

Masdar City (MC) is leading the Middle East in the development of energy and resource efficient low-carbon construction in the United Arab Emirates (UAE). One of its major goals is to develop and specify materials and processes that will help reducing its environmental footprint through resource and energy conservation, as well as renewable energy generation. In 2010 MC announced on its website a prized-competition for the best proposal of''Sustainable Concrete'' and ''Lowest Carbon Footprint'' to build MC with a total of two million cubic meter of concrete on 4 years period. This paper presents the experimental test results of 13 types of concrete mixes made with high volume of ground granulated blast furnace slag (GGBFS) cement with 50%, 60%, 70% and 80% replacement of ordinary Portland cement (OPC) to reduce the carbon emissions. A fly ash-blended mix made with 30% fly ash was also tested. The paper provides more information on the mix design parameter, full justification of CO2 footprint, and cost reduction for each concrete type. The hardened and plastic properties and durability test parameters for each mix are presented. The results show that the slag concrete mixes significantly reduce the carbon footprint and meet the requirements of MC. An economical mix with 80% GGBFS and 20% OPC was nominated for use in the future construction of MC with 154 kg/m3 carbon foot print.

© 2013 The Authors. Published by Elsevier Ltd. All rights reserved.

1. Introduction

1.1. General

The production of 1 tonne of Portland cement requires 1.5 tonnes of raw material. The production of Portland cement is highly energy intensive, consuming 4-7 MJ of fossil fuel energy per kg (Malhotra, 1988; Swamy, 1998), and releases approximately 1 tonne of carbon dioxide for manufacture of each tonne of Portland cement. The production of cement contributes 5% of the global greenhouse gas emissions (Collins and Sanjayan, 2002). The use of slag (GGBFS), an industrial byproduct which otherwise would contribute to land pollution, as a replacement for Portland cement in concrete will result in less energy for the manufacture of cement and reduce the green gas emissions due to concrete construction (Flower et al., 2005).

Slag-blended cement, a blend of ordinary Portland cement (OPC) and ground granulated blast furnace slag (''slag'') has had many years use worldwide in the construction industry. In recent years, many industrial waste by-products such as slag

§ This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-No Derivative Works License, which permits non-commercial use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Corresponding author. Tel.: +971 551219661; fax: +971 42888350. E-mail addresses: mohamed.elchalakani@hct.ac.ae, melchalakani@hct.ac.ae, melchalakani@hotmail.com (M. Elchalakani), tkamalali@hotmail.com (T. Aly), emad.abuaisheh@aramco.com (E. Abu-Aisheh).

2214-5095/$ - see front matter © 2013 The Authors. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.cscm.2013.11.001

and fly ash are rapidly becoming the main source of supplementary cementitious materials (SCM) for use in concrete manufacture. These SCMs are well known having a significant effect on reducing the concrete permeability, when properly cured, which is the main governing property for producing durable concrete (Mehta, 1984; Hooton, 2000) suitable for the Gulf environment where sever conditions prevail. SCMs can also be used to reduce the heat generation associated with cement hydration and reduce the potential for thermal cracking in massive structural elements. The SCMs modify the microstructure of the concrete and reduce its permeability thereby reducing the penetration of water and waterborne salts into concrete thus enhancing the service life of the structure.

The inappropriate selection of cementitious materials and admixtures in mixture proportioning could have an either significant impact on cost and/or may not achieve the properties required for producing a durable concrete (i.e. high chloride resistance).

Producing sustainable concrete with a low carbon foot print was among the aims of this research. It is well known that the production of OPC produces a carbon foot print of about 1000 kg/m3 (Malhotra and Mehta, 2008). One solution to reduce the high and unaccepted construction emissions is by replacing the cement in the concrete mix (Elchalakani and Elgaali, 2010). The ground granulated blast furnace slag (GGBFS) is widely used to replace the cement to enhance the durability (Mehta, 1984; Hooton, 2000). The GGBFS is a by-product of the steel production process (thus it is a green material), therefore, it is used here to enhance the durability and lower the carbon foot print. Thus except for the remaining small quantity of OPC used in the concrete mix, the concrete used in this project may be termed 'sustainable concrete'. To this end, this paper reports the findings of an experimental program to provide general guidelines on designing sustainable concrete mixtures suitable for use in the future construction of Masdar City in the Gulf which is a well known harsh environment.

Within such environment, the high ambient temperature, low humidity, drying winds and dust blown salts all present great challenge to the construction of high quality concrete in the Gulf. Accordingly, special precautions need to be instituted under these extreme ambient conditions to enhance the design life and durability of MC concrete structures in service. One approach to deal with such conditions is to use high volume GGBFS concrete to increase the setting times which is beneficial for the hot climate. The GGBFS cement particles are finer (>450 m2/kg) than the OPC ones (<350 m2/kg). This would reduce the amount and rate of bleeding of these concretes. The reduction in bleeding together with the increase in setting times of concrete can increase the risk of plastic shrinkage cracking and may warrant special precautions during placing and finishing operations. Plastic shrinkage usually occurs within 10-12 h after placement only when concrete is exposed to unsaturated air (RH < 95%) in the presence of high speed wind and hot temperature (Collepardi, 2006; ACI Manual, 2005).

1.2. Masdar City requirements

Masdar City (MC) is a relatively new origination based in the UAE and is leading the Middle East in the development of energy and resource efficient low-carbon construction. One of its major goals is to develop and specify materials and processes that will help reducing its environmental footprint through resource and energy conservation, as well as renewable energy generation. In 2010 MC announced on its website (http://www.masdar.ac.ae) a prized-competition for the best proposal of ''Sustainable Concrete'' and ''Lowest Carbon Footprint'' to build MC with the following requirements.

1. Total CO2 emission per cubic meter of concrete should be less than Masdar baseline mix which has a carbon footprint of 192 kg/m3.

2. Total cost of all constituent materials required per cubic meter of concrete comparable with Masdar baseline mix which has a cost of 211 AED/m3 (1.0 USD = 3.679 AED).

3. Production capacity is anticipated at 500,000 m3 per year for four years.

4. Concrete performance for proposed mix design, including but not limited to:

• Workability: slump and slump retention. A minimum slump of 150 mm is required.

• Compressive strength at 28 days not less than 40 MPa.

• Durability: rapid chloride penetration less than 1000 C at 28 days.

• Hot weather: maximum temperature of fresh concrete of 35 °C.

• Temperature rise: maximum concrete temperature of less than 70 °C.

This paper presents the recent research findings of 14 controlled laboratory trial mixes. It will be discussed how such mixes reduce the carbon footprint and could meet the requirements of MC. The paper provides more information on the mix design parameter, full justification of CO2 footprint, and cost involved. The hardened and plastic properties and durability test parameters for each mix are also presented and discussed.

2. Test program

2.1. Material properties

Table 1 shows the chemical composition of the General Portland cement type CEM I 42.5 N complying with BS EN 197-1 (2000) GP and the ground granulated blast furnace slag (GGBFS) complying to BS 6699 (1992) and fly ash to ASTM C618 Class F. The nominal target strength of concrete was 40 MPa at 28 days. Standard cubes 100 mm x 100 mm x 100 mm were

Table 1

Chemical composition of GP and GGBS.

Constituent/property (%)

SiO2 Al2O3 Fe2O3 CaO MgO Mn2O3 SO3 S Cl

PC-CEM 142.5 N BS EN 197 (2000) 21.29 4.89 3.42 64.16 1.41 - 2.53 - 0.010

GGBS-BS 6699 (1992) 33.22 16.12 0.72 42.42 5.53 0.30 0.32 1.30 0.009

FA-ASTM C618 Class F 70 (min) - - - 5.00 N/A -

prepared to BS 1881-116 (1983) and moist cured in a water tank at temperature of 25 °C. Several tests were performed to measure the durability parameters of the concrete namely rapid chloride penetration (RCP) test to ASTM C1202-97 (1997), chloride migration coefficient to NBuild 492 (1999), drying shrinkage to ASTM C157/C (2006), and water absorption (WA) test to BS 1881-122 (1983).

2.2. Concrete mix proportions

The MC control mix had 148 kg/m3 OPC, 222 kg/m3 GGBFS, 137 kg/m3 of DEWA fresh water, 720 kg/m3 of 20 mm crushed RAK rock, 350 kg/m3 of 10 mm crushed RAK rock, 580 kg/m3 of 5 mm crushed RAK rock, and 300 kg dune sand. A high range water reducer addition of 4500 g/m3 was used in the mix. The water/cement (w/c) ratio was 0.37 and the GGBFS amount represented 60% OPC replacement. The term cement refers to the binder including OPC, FA and GGBFS. Three approaches were adopted in this study to obtain better performance than that of the baseline mix. The use of high percentages of GGBFS with low water cement ratios and medium to low total cement content was the main factor used in the design mix for each group. The first approach (Group M) was to use medium cementitious material (CM) content with a total amount of 360 kg/ m3 with different w/c ratios in the range of 0.35-0.42. This approach was represented in Mixes #1, 2, 3, 4, 5, and 10. Table 2 shows the mix proportion and test results for these later mixes. The second approach (Group H) was to use a comparatively high content with a total amount in the range of400-440 kg/m3 with the same w/c of 0.38 and variable GGBFS content in the range of 70-80%. This approach was represented in Mixes no. 6, 7, 8, and 9. Table 3 shows the mix proportion and test results for these later mixes. The third approach (Group L) was to use very low binder content in the range of 300-340 kg/m3 with different w/c ratios. This approach was represented in Mixes 11, 12, 13, and 14. Table 2 shows the mix proportion and workability test results for all mixes. Table 4 shows the mix proportion and test results for these later mixes.

Table 2

Group M. Trial mixes with medium cement content of 360 kg/m3.

Total cement content: 360 kg

Trial mix Ref. mix 1 1227 2 1228 3 1229 4 1230 5 1231 10 1236

General details Grade (N) 40 40 40 40 40 40

Cement (kg) 360 360 360 360 360 360

GGBS % 0 70% 80% 80% 80% 50%

Fly ash % - - - - - 30%

w/c 0.38 0.38 0.38 0.35 0.42 0.38

Admixture (g/m3) 8800 8200 6800 9200 6000 5200

Slump (mm) Initial 195 235 200 220 235 210

30 min 185 240 80 230 175 185

60 min 150 245 45 230 75 140

Temperature (°C) Initial 29.5 28.0 28.0 26.5 27.0 26.5

30 min 27.5 27.0 27.0 26.0 25.5 25.5

60 min 27.0 26.5 26.5 24.5 24.5 25.0

Average-compressive strength (N/mm2) 1 day 26.0 9.3 9.3 11.3 9.5 7.0

3 days 57.0 35.5 32.8 36.5 28.0 28.5

7 days 63.0 55.5 50.3 54.8 41.0 37.3

28 days 74.3 68.0 66.0 68.3 54.0 51.3

Durability (28 days) RCP (C) 1971 465 397 383 402 331

1732 486 411 377 409 314

Water absorption % 1.62 1.49 1.35 1.24 1.68 1.05

1.67 1.45 1.46 1.09 1.71 1.16

Carbon Carbon (kg/m3) 386 183 153 154 153 147

Cost (AED) Cost (AED) 222 229 223 235 220 217

Table 3

Group H. Trial mixes with high volume cement content of 400-440 kg/m3.

High volume cement content: 400 kg and 440 kg

Trial mix Ref. mix 6 1232 7 1233 8 1234 9 1235

General details Grade (N) 40 40 40 40

Cement (kg) 400 400 440 440

GGBS % 70% 80% 70% 80%

Fly ash % - - - -

w/c 0.38 0.38 0.38 0.38

Admixture (g/m3) 5200 5600 5000 5200

Slump (mm) Initial 215 235 230 220

30 min 100 220 195 110

60 min 35 115 60 40

Temperature (°C) Initial 26.0 27.0 26.5 26.5

30 min 25.0 25.5 25.0 25.0

60 min 24.5 24.5 24.6 24.5

Average-compressive strength (N/mm2) 1 day 11.8 9.0 9.5 9.0

3 days 33.3 34.5 35.3 32.0

7 days 49.8 43.0 43.8 37.5

28 days 60.8 56.3 55.8 49.5

Durability (28 days) RCP (C) 551 329 525 479

553 364 513 491

Water absorption % 1.58 1.67 1.65 1.90

1.77 1.75 1.55 1.96

Carbon Carbon (kg/m3) 196 164 209 176

Cost (AED) Cost (AED) 223 227 231 234

Table 4

Group L. Trial mixes with very low cement content of 300-340 kg/m3.

Low cement content: 300 kg and 340 kg (60% GGBS)

Trial mix # Ref. mix 11 1237 13 1237 B 12 1238 14 1238 B

General details Grade (N) 40 40 40 40

Cement (kg) 340 340 300 300

GGBS % 60% 60% 60% 60%

Fly ash % - - - -

w/c 0.40 0.38 0.40 0.38

Admixture (g/m3) 7600 7500 9200 8590

Slump (mm) Initial 225 230 225 215

30 min 220 235 220 235

60 min 210 240 220 215

Temperature (°C) Initial 27.5 30.5 27.0 31.0

30 min 26.5 29.5 26.0 30.0

60 min 26.0 29.0 25.5 29.5

Average-compressive strength 1 day 12.8 - 18.0 -

3 days 41.0 - 36.3 -

7 days 52.5 61.8 48.0 56.8

28 days 67.5 78.5 65.5 72.5

Durability (28 days) RCP (C) 631 522 1421 504

595 549 1606 481

Water absorption % 1.40 1.36 1.17 0.96

1.39 1.34 1.19 0.93

Carbon Carbon (kg/m3) 202 202 184 184

Cost Cost (AED) 220 219 217 214

. 50.0

£ о и

20.0 10.0 0.0

Compressive Strength Cement Content: 360kg

-Mix 1 : 360 kg : 0% GGBS (W/C: 0.38) Mix 3 : 360 kg : 80% GGBS (W/C: 0.38) -Mix 5 : 360 kg : 80% GGBS (W/C: 0.42)

-Mix 2 : 360 kg : 70% GGBS (W/C: 0.38) -Mix 4 : 360 kg : 80% GGBS (W/C: 0.35) Mix 10 : 360 kg : 50% GGBS + 30% FA (W/C: 0.38)

Fig. 1. Mechanical strengths for Group M (360 kg/m3

3. Test results

3.1. Group M (360 kg/m3)

Figs. 1 and 2 show the results of compressive strength development for Group M which includes Mixes #1, 2, 3, 3, 5, and 10 where the total binder content is constant at 360 kg/m3. As expected Mix 1 with 0% OPC replacement had the highest mechanical strength rate while Mix 10 had the lowest rate with 50% FA+ 30% GGBFS (80% OPC replacement). The 28-day compressive strength was 74.3 and 51.3 MPa, for Mix 1, and 10, respectively. Mix 4 with 80% GGBFS (w/c = 0.35) had relatively good compressive strength rate and achieved 68.3 MPa strength at 28-day of concrete age. Mix 5 with 80% GGBFS (w/c = 0.42) had relatively low compressive strength rate (54 MPa strength at 28-day). It is obvious from the results that Mix 4 had good compressive strength performance due to the lowest w/c ratio in the mix.

Fig. 2. Cube axial compressive strength results for Group M (360 kg/m3).

Fig. 3. RCP test results for Group M (360kg/m3).

Fig. 4. WA test results for Group M (360kg/m3).

Figs. 3 and 4 show the RCP and WA durability test results for all group of mixes of which Group M with 360kg/m3, respectively. It can be seen that the Mix 1 had the worst performance where it had 1971 (>1000) C and 1.67% water absorption. Mixes #2, 3, 4, 5, and 10 all can be classified as low (<1000 C) to ASTM C1202-97 (1997). Mix 10 had the best performance where it had 331 (<1000) C and 1.16% water absorption. Mix 4 had 383 (<1000) C and 1.24% water absorption. The effect of GGBFS on the resistance to chloride penetrability is clearly shown in the figure where the Mix 1 with 0% GGBFS had the worst performance. Fig. 5 shows the workability test results of the trial mixes for Group M. It is seen that Mixes 3, 5 and 10 failed to achieve the required slump of 150 mm at 60min. The amount of the admixture for Mix 3, 5 and 10 was insufficient and of the order of 6800, 6000, 5200 g/m3, respectively. Mixes 2 and 4 with 8200 and 9200 g/m3 of admixture achieved higher slumps than the required.

3.2. Group H (400-440 kg/m3)

Figs. 6 and 7 show the compressive strength test results for Group H which includes Mixes 6, 7, 8, and 9 where the total binder content is in the range of 400-440 kg/m3. It is seen that Mix 6 with 70% GGBFS had the highest compressive strength rate while Mix 9 had the lowest rate with 80% GGBFS. The 28 days strength was 60.8 and 49.5 MPa, for Mix 6 and 9, respectively. Figs. 8 and 9 show the RCP and WA durability test results for the Group H mixes with 400-440 kg/m3, respectively. It can be seen in Fig. 8 that all the mixes in Group H achieved below 600 C. In Fig. 9, Mix 9 had experienced the highest WA performance among all the Group H mixes with 1.93%. Table 3 also shows the workability test results of the trial mixes for Group H. It is seen although all the mixes achieved over than 150 mm initial slump, they all failed to achieve the required final slump at 60 min. Thus, none of these mixes could be recommended for the construction of MC (Fig. 10).

Fig. 5. Slump test results for Group M (360kg/m3).

= Mix6 :400 kg : 70%GGBS (W/C: 0.38) -«-Mix7 :400 kg : 80%GGBS (W/C: 0.38) Mix8 :440 kg : 70%GGBS (W/C: 0.38) -*-Mix9 :440 kg : 80%GGBS (W/C: 0.38) Fig. 6. Mechanical strengths for Group H (400-440 kg/m3).

3.3. Group L (300-340 kg/m3)

Figs. 11 and 12 show the compressive strength test results for Group L which includes Mix 11,12,13 and 14 where the total binder content is in the range of 300-340 kg/m3. It is seen that Mix 13 with 60% GGBFS and w/c = 0.38 had the highest compressive strength rate while Mix 12 had the lowest rate with 60% GGBFS and w/c = 0.4. The amount of admixture used for these mixes was 9200 and 7500 g/m3 for Mix 12 and 13 respectively. The 28-day strengths were 60.5 and 78.55 MPa, for Mix

Fig. 7. Cube axial compressive strength results for Group H (400-440 kg/m3

80% 70%

Fig. 8. RCP test results for Group H (400-440 kg/m3).

Water Absorption % (High Volume Cement Content: 400kg & 440 kg)

1.50 1.45

70% 80% 70% 80%

Fig. 9. WA test results for Group H (400-440 kg/m3).

Fig. 10. Slump test results for Group H (400-440 kg/m3;

Fig. 11. Mechanical strengths for Group L (300-340 kg/m3

12 and #13, respectively. Figs. 13 and 14 show the RCPandWA durability test results for Group L mixes with 300-340 kg/m3, respectively. It can be seen in Fig. 13 that all the Group L mixes achieved below 700 C, except for Mix 12 where it had poor performance and achieved relatively high value of 1513 C. Mix 14 had the best RCP and WA performance among all Group L mixes with 493 C and 0.945%, respectively. Fig. 15 shows the workability test results of the trial mixes for Group L. It is seen though all the mixes achieved the 150 mm slump at initial and final stages.

4. Summary of results

Tables 2-4 show the initial, 30 min and 60 min setting times at temperatures below 35 °C for all the mixes. Fig. 16 shows the initial and final setting times for all the mixes except for Mix 3, 13, and 14 where their data was lost. It is seen that increasing the GGBFS from 0% (Mix 1) to 70% (Mix 2) the initial and final setting times increased by 10% and 29%, respectively. Also, Mix 12 (with low cement 300 kg, large admixture amount and 60% GGBFS) had the highest initial and final setting times of 15.3 and 21.5 h respectively. Mixes 9 (with high cement content of 440 kg, low admixture 5200 g/m3 and 80% GGBFS) had

Fig. 12. Cube axial compressive strength results for Group L (300-340 kg/m3

Fig. 13. RCP test results for Group L (300-340 kg/m3;

Water Absorption % (Low Cement Content: 300kg & 340 kg - 60% GGBS)

§ 0.80 <

S 0.60

® 0.40 0.20 0.00

0.40 0.38 0.40 0.38

Water Cement Ratio Fig. 14. WA test results for Group L (300-340 kg/m3).

Fig. 15. Slump test results for Group L (300-340 kg/m3).

Mix 1 Mix2 Mix4 Mix5 Mix6 Mix7 Mix8 Mix9 Mix 10Mix 11 Mix 12 Fig. 16. Setting time (initial and final) test results for all except for Mixes #3, 13, 14 (data not available).

Fig. 17. RCP test results for all mixes.

Fig. 18. WA test results for all mixes.

Mix 1 Mix2 Mix3 Mix4 Mix5 Mix6 Mix7 Mix8 Mix9 MixlOMixllMixl2Mixl3Mixl4 Fig. 19. Chloride migration coefficient test results for all mixes.

10 11 12 13 14 Fig. 20. Drying shrinkage test results for all mixes.

the lowest initial and final setting times of 5.3 and 8.3 h. Fig. 16 shows that the initial and final setting times for Mix 4 are 11.4 and 16 h.

Figs. 17 and 18 summarize the RCP and WA results for all the mixes, respectively. It is seen that the worst RCP performance was for Mix 1 where 0% GGBFS was used. Mix 9 had the worst WA performance with 1.93%, whereas Mix 10 (50% GGBFS and 30% FA) had the best RCP performance with just 322 C and 1.11% WA. Mix 14 had a good RCP performance with 493 C and the best water absorption performance of 0.95%. Fig. 19 summarizes the chloride migration coefficient (CMC) test results for all the mixes. It is seen that the trends as similar to the RCP ones where Mix 4 achieved the lowest chloride ion migration resistance where CMC = 1.05 x 10~12 m2/s. Fig. 20 shows the 56-day drying shrinkage test results for all the mixes. Mix 10 (50% GGBFS and 30% FA) had the lowest shrinkage with just 110 microstrain. It is also seen that the trends is consistent with that of WA ones where Mix 4 and 14 achieved very low drying shrinkage at 160 and 140 microstrain. This attributed to the reduced water absorption and less paste volume which is the main source of drying shrinkage. Lower drying shrinkages will reduce the risk of cracking of concrete at the early age (Aly and Sanjayan, 2006, 2007).

Fig. 21 shows that the estimated CO2 emission due to the production of Mix 1 with 100% OPC is 386 kg/m3 whereas the emissions for Mix 4 and 14 are 154 and 184kg/m3, respectively.

Fig. 22 shows the values of the CO2 intensity indicator (ci = c/p) that is proposed by Damineli et al. (2010) for all the 14 mixes. Where c is the total CO2 (kgm~3) emitted to produce the concrete raw material, and p is the average compressive strength at 28 days (MPa). It is seen that all the mixes achieved a value less than the international future benchmark of

Fig. 21. CO2 emissions for all mixes.

Co2 Intensity indicator (c i =c/p)

Mix 1 Mix 2 Mix 3 Mix 4 Mix 5 Mix 6 Mix 7 Mix 8 Mix 9 Mix 10 Mix 11 Mix 12 Mix 13 Mix 14 Fig. 22. CO intensity indicator for all mixes (ci = c/p).

^ 4.0 CL

m 3.0 £ tw

♦ ♦

♦ ♦ ♦

♦ «*

8.0 9.0

3 0 4 0 5 0 6 0

bi = b/p (kg.m"3.MPa_1)

Fig. 23. CO2 intensity indicator (ci = c/p) versus binder intensity (bi = b/p) for all mixes.

Cost (AED)

Fig. 24. Cost (in AED) for all mixes.

ci = 5.0 kg m-3 MP-1, except for the control mix (Mix #1). Fig. 23 shows the CO2 intensity indicator plotted against the binder intensity (bi = b/p). Where b is the total consumption of the binder material including OPC, fly ash and GGBS (kg m-3). Except for the control mix, the binder intensity was in the middle range of bi = 4.0-9.0 kg m-3 MP-1 to produce a sustainable concrete with a favorably low CO2 intensity below 5.0 kg m-3 MP-1.

Fig. 24 shows that the estimated cost due to the production of one cubic meter of Mix 1 with 0% OPC replacement is 222 kg/m3 whereas the cost for Mix 4 and 14 is 235 and 214 AED, respectively. Although the costs of these mixes are slightly more than MC baseline mix (<12%) they are still economical.

5. Conclusions

Based on the plastic and hardened test results on of 14 types of concrete mixes, Mix 4 from Group M (360 kg total binder with, 80% GGBFS, 0.35 w/c) and Mix 14 from Group L (300 kg, 60% GGBFS, 0.38 w/c) are proposed for use in the construction of Masdar City in the UAE. These mixes meet the strength, durability, setting times, and workability requirements of Masdar

City as well as they are cost effective compared to MC baseline mix. Although Mix 10 with 50% GGBFS and 30% FA achieved good durability and shrinkage performance as well as low carbon emissions it could not meet the workability requirements of Masdar City.

Acknowledgments

The authors would like to thank Mr. Abdulazis Al Ali who is a former student of Dubai Mens College for supervising the experiments. Also thanks are given to Ready Mix Abu Dhabi's engineers and technicians for performing the trial mixes and BASF for providing the necessary admixtures.

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