Metakaolin as an alternative Ordinary Portland

cement extender

Zonke Dumani & Joe Mapiravana

CSIR Built Environment

OUT-OF-THE-BOX Human Settlements Conference 24-25 October 2018

2

Background

Ordinary Portland cement

❑ Production of Ordinary Portland cement (OPC) is an energy intensive process

❑ Releases large amount of greenhouse gas emissions, mainly CO2 into the

atmosphere

Source: Zyga, 2012

3

Background

60%

11%

7%

1%

7% 6%5%

3% 0%Power (coal)

Power (gas)

Power (oil)

Power (other)

Cement

Refining

Iron and steel

Petrochemicals

Other

Percent of global greenhouse gas emissions (GHGs)

adapted from: http://www.ipcc.ch/pdf/special-reports/srccs/srccs_wholereport.pdf.

❑ Globally, cement sector accounts for 5-7% of total CO2 emissions

❑ Interest has shifted towards cement blends whereby OPC is partially replaced by

cement extenders

4

Cement extenders

Fly ash SlagSilica fume

❑ Suitable cement extenders reduce energy consumption of cement production

and CO2 emissions

❑ However, use of these materials is constrained by geographical availability

❑ There is need to find alternative cement extenders from local sources that are

abundantly available

5

Metakaolin

Kaolinitic claysMetakaolin

❑ Use of metakaolin (MK) as an alternative cement extender has received interest

❑ Kaolinitic clays used to produce MK are ubiquitously and abundantly available

Al2O3.2SiO2.2H2O (Kaolinite) → Al2O3.2SiO2 (Metakaolinite) + 2H2O

6

Metakaolin advantages

❑ Lower carbon footprint (CO2 emissions)

❑ Improved strength

❑ Higher durability

Use of MK has failed to achieve industry-wide use globally due to its relatively high

market price

7

Method of calcination

Flash calciner Multiple-hearth furnace Rotary kiln

❑ These processes are capital intensive and complex thereby increasing the price of

metakaolin

8

Vertical shaft kiln process

❑ CSIR has successfully developed a low cost process for the production of MK

using a coal-fired vertical shaft kiln (VSK)

3.2 ton per day pilot VSK 12 ton per day semi-industrial VSK

9

Vertical shaft kiln process

❑ VSK process is simpler in design, operation and has a lower capital cost than

other processes

❑ VSK process development was motivated by need to produce MK economically

❑ Ultimately reducing its market price

3.2 ton per day VSK metakaolin 12 ton per day VSK metakaolin

Metakaolin with different amorphous content successfully produced from kaolinitic

clays using VSKs

10

Research objectives

❑ Primary objective of the study was to compare the carbon footprint (CO2

emissions) of Ordinary Portland cement (OPC) and OPC/MK cement blends

❑ Secondary objective is to evaluate the compressive strength of OPC/MK blends

produced using the 3.2 ton per day VSK and 12.5 ton per day VSK

11

Research methodology

Research design and approach

❑ Life cycle assessment (LCA) methodology used in this study follows the four steps

outlined by ISO 14040:2006 and ISO 14044: 2006:

Source: ISO/SANS 14040:2006

12

Goal and scope definition

Goal

The LCA study compares 100% OPC with metakaolin cement blends, namely:

❑ 90% OPC/ 10% MK blend

❑ 80% OPC/ 20% MK blend

❑ 70% OPC/ 30% MK blend

13

Goal and scope definition

Scope

4.

Use and

maintenance

stage

5.

End-of-life

stage

2.

Building

material

production

stage

3.

On-site

construction

stage

1.

Raw material

acquisition

stage

Cradle-to-gate analysis

Cradle-to-grave analysis

Energy resources Water Land

Solid wasteEmissions to air Emissions to water

❑ Scope of the study limited to a cradle-to-gate analysis

❑ The functional unit is the comparison of 1 kg 100% OPC with 1 kg of the OPC/MK

blends

14

Life cycle inventory

❑ LCA software tool SimaPro 8.1 with Ecoinvent Database version 3 was used to

compile the LCI dataset

Unit process Sub-process Assumptions Source

Ordinary Portland cement

ManufacturingSwiss average data for CEM I (class Z

52.5) used as proxyEcoinvent 3 database

Transporting

Road distance, PPC Jupiter to CSIR

Pretoria = 74 km

Transport = lorry, 16-32t

Charging rate = 50%

Ecoinvent 3 database

Ordinary Portland cement production assumptions

15

Life cycle inventory

Unit process Sub-process Assumptions Source

Metakaolin

Mining and

extraction

European average data for kaolin mining and extraction used as a proxy

dataset

Ecoinvent 3

database

Crushing Swiss average data for crushing of limestone used as proxyEcoinvent 3

database

Transporting

Road distance, Hammanskraal to Pretoria (site) = 62 km

Transport = lorry, > 16-32t

Charging rate = 50%

Ecoinvent 3

database

Calcining

Coal calorific value is 19.57 MJ/kg

Fuel efficiency of the vertical shaft kiln is 23%

Eskom integrated

report 2016

Transporting

Road distance, Pretoria (site) to Johannesburg = 94 km

Transport = lorry, > 16-32t

Charging rate = 50%

Ecoinvent 3

database

Milling Swiss average data for quicklime, milled, loose, at plant, used as proxyEcoinvent 3

database

Transporting

Road distance, Johannesburg to CSIR Pretoria = 79 km

Transport = lorry, > 16-32t

Charging rate = 50%

Ecoinvent 3

database

Metakaolin production assumptions

16

Life cycle impact assessment

❑ Climate change (global warming) was the only impact category considered

❑ ReCiPe midpoint (H) methodology was used to generate the results in CO2

equivalents.

17

Compressive strength

Mineralogical

composition MK1 MK2 MK3 MK4

Amorphous phase 76.5 82.6 90.7 81.0

Quartz 4.00 4.00 4.00 4.00

Anatase 0.71 1.04 1.58 1.10

Mullite 6.35 3.65 1.40 3.80

Cristobalite 11.53 6.96 1.49 6.50

Rutile 0.94 0.70 0.84 0.80

Four metakaolins were investigated in this study:

❑ MK1 – produced using 3.2 ton per day VSK with clay:coal = 4:1

❑ MK2 – produced using 3.2 ton per day VSK with clay:coal = 6.75:1

❑ MK3 – produced using 3.2 ton per day VSK with clay:coal = 8.5:1

❑ MK4 – produced using 12.5 ton per day VSK

18

Compressive strength

❑ Ordinary Portland cement 52.5 N was used

❑ Normal OPC paste with no MK was prepared as control

❑ OPC/MK blended pastes prepared had MK contents of 10%, 20% and 30%

❑ Compressive strengths of the pastes were determined at the ages of 2, 7, 14 and

28 day

19

Results and discussion

Life cycle assessment

Material Metakaolin comparison studies kg CO2eq/kg

Metakaolin

This study (VSK process) 0.313

Heath et al. 2014 0.423

Jones el al. 2011 0.330

Moropoulou, 2011 0.401

NLK, 2002 (flash calciner process) 0.370

Ordinary Portland cement - 0.973

VSK efficiency only 23%

20

0

50

100

150

200

250

300

350

400

0 10 20 30 40 50 60 70 80

CO

2e

qu

iva

len

ce/k

g

VSK efficiency

Results and discussion

Life cycle assessment

❑ Significant reductions of CO2 emissions can be achieved by increasing VSK fuel

efficiency

21

10

20

30

40

50

60

70

80

90

100

Climate change

%

100%OPC

10%MK/90%OPC cement blend

20%MK/80%OPC cement blend

30%MK/70%OPC cement blend

Results and discussion

Life cycle assessment

❑ Partial replacement of OPC with MK can significantly reduce CO2 emissions of

cement

22

Compressive strength

0

20

40

60

80

100

120

2 7 14 28

Str

en

gth

(M

Pa

)

Age (days)

10% replacement level Control

MK1

MK2

MK3

MK4

Results and discussion

❑ After 7 days the strength was influenced in positive manner by the addition of MK

❑ OPC/MK blends had higher compressive strength than the control (OPC) specimen

23

0

20

40

60

80

100

120

2 7 14 28

Str

en

gth

(M

Pa

)

Age (days)

20% MK replacement level Control

MK1

MK2

MK3

MK4

Results and discussion

Compressive strength

❑ Strength significantly increased in comparison to the OPC alone between 7 and

28 days

24

0

20

40

60

80

100

120

2 7 14 28

Str

en

gth

(M

Pa

)

Age (days)

30% MK replacement level Control

MK1

MK2

MK3

MK4

Results and discussion

Compressive strength

❑ MK2 and MK3 with highest amorphous (metakaolinite) contents exhibited the

highest strengths in comparison to OPC and other metakaolins

25

Conclusions and further research

❑ Use of MK to partial replace OPC can significantly reduce CO2 emissions

❑ Partial replacement of OPC with MK can increase compressive strength

❑ Positive influence of metakaolin was more apparent between 7 and 28 days

❑ Development of MK using VSK will contribute to economic growth, job creation and

building sustainable and affordable housing

❑ Next development is to demonstrate the production of MK using a 100 ton per day

industrial VSK kiln for commercialisation

Thank you

27

References

❑ Zyga, L., 2012, Solar thermal process produces cement with no carbon dioxide emissions. Phys.Org. [Online] available from

https://phys.org/news/2012-04-solar-thermal-cement-carbon-dioxide.html

❑ Heath, A., Paine, K., and McManus, M., 2014, Minimising the global warming potential of clay based geopolymers. Journal of

Cleaner Production 78, 75-83

❑ Jones, R., McCarthy, M., Newlands, M., 2011. Fly ash route to low embodied CO2 and implications for concrete construction.

In: World of Coal Ash (WOCA) Conference, Denver, Co, USA

❑ Krajči, L., Mojumdar,S.C., Janotka, I., Puertas, F., Palacios, M. and Kuliffayová , M., 2015, Performance of composites with

metakaolin-blended cements. Journal of Thermal Analysis and Calorimetry 119, 851-863

❑ IPCC, 2005, IPCC Special Report on Carbon Dioxide Capture and Storage. Prepared by Working Group III of the

Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY,

USA, http://www.ipcc.ch/pdf/special-reports/srccs/srccs_wholereport.pdf

❑ Moropoulou, A., Koroneos, C., Karoglou, M., Aggelakopoulou, E., Bakolas, A., Dompros, A., 2011, Life cycle analysis of

mortars and its environmental impact. National Technical University of Athenes, Greece

❑ NLK, 2002, Ecosmart Concrete Project: Metakaolin Pre-feasibility Study. NLK Consultants Inc., Vancouver, Canada.