CHALLENGES IN HIGH

STRENGTH CONCRETE

PRODUCTION IN ETHIOPIA AND

THE WAY FORWARD

Abebe Dinku Prof. (Dr.-Ing.)

Chair, Construction Materials and Management

AAiT, AAU

April 20, 2017

1

Acknowledgement

I would like to thank the organizers

of this event for inviting me to

present my work on this important

occasion.

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Presentation outline

Definitions and historical timelines

Classifications of concrete

Concrete making materials

HSC uses and application

Concrete specifications in Ethiopia

Discussions and conclusions

3

Concrete is ….

The word Concrete comes from the Latin verb “Concretus” which means to grow together.

Concrete is a composite material that literally forms the basis of our modern society.

When did we have the first “concrete” in history? Some says Roman concrete (Neville) Others say in the Middle East (eg. Galilee, Israel around 7,000

years ago), In Cyprus, Greece, … by the fact that lime mortar was used by

calcining limestone as early as 6,000-12,000 BC. There is no consensus on the exact timeline, and research

continues

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Major concrete historical background: 3000BC to present

~3000 BC: Egyptians used mud mixed with straw to bind bricks. They used gypsum and lime mortar in the pyramid.

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Yeha temple, Abyssinia/Ethiopia (~ 3000 years)

Major concrete historical background: 3000BC to present

Greeks (~1000Bc – 100BC)

Romans (~300 BC –

400AD) built baths, the Coliseum and Pantheon using pozzolana cement. It was reported that animal fat, milk and blood were used as admixtures.

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Roman concrete samples 10

Major concrete historical background: 3000BC to present

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The middle ages (~500 - 1500 AD) brought no significant development in cement production and application.

After European Industrial revolution (~16th cent.) that innovative ideas surfaced.

Major concrete historical background: 3000BC to present (contd.)

1793: John Smeaton used hydraulic lime to rebuilt

Eddystone lighthouse in Cornwall, England.

1824: Joseph Aspdin of England invented/patented

Portland cement.

1836: The first systematic test of tensile and

compressive strength took place in Germany.

1867: Joseph Monier of France wire ushering in the

idea of iron reinforcing bars.

1886: Rotary kiln was introduced in England,

which allowed continuous production of cement.

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Major concrete historical background: 3000BC to present (contd.)

1889: First concrete reinforced bridge was built.

1891: First concrete street in USA was placed in Bellefontaine, Ohio.

1906: First major concrete dam, Hoover dam and Grand Cooley Dam built.

1967: First concrete dome sport structure, University of Illinois, USA.

1992: Tallest reinforced building, Chicago, USA.

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Concrete is young in Ethiopia

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Menelik’s palace

fence, Ankober

Ethiopia,19th cent.

17th century Gondar castle and bridge

Major concrete historical background: 3000BC to present (contd.)

Some 20th century world achievements of concrete and composite structures

to date include:

417m Freedom tower, New York; USA;

437m tall building in Doha;

484m tall building in Hong Kong;

632m tall building in Shanghai, China;

828m tall tower in Burj Khalifa, Dubai, UAE

In 2020 China will have much of the tallest buildings in the world.

China was about to start building the tallest building in the tower but

stopped after the Saudi’s attempt.

Buildings 400-600 m tall are not any more listed in world record.

1000m, Kingdom tower, Jeddah, Saudi Arabia, under construction.

~250m, CBE New HQ building, Addis Ababa, Ethiopia, under construction.

All of the above were made possible using cement and HSC !!

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Classification of concrete

General classifications of concrete based on

mechanical properties (compressive strength) :

lean concrete, 5-10MPa

Light weight concrete, 10-20 MPa

Normal weight concrete, 20-40 MPa

High strength concrete (HSC), > 40/50 MPa

High Performance Concrete (HPC), >100 MPa

Ultra High Performance Concrete (UHPC), 150-200 MPa

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High strength concrete

The use of HSC is becoming popular since early 1970’s.

It has now become normal to use concrete having high compressive strength practically in all continents but mainly in Europe, USA, Asia (China, Hong Kong, …)

Advantages: improved quality, strength & durability, saves time, reduce cost

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China

Kuwait

New york

The construction of these skyscrapers were made possible using modern concrete technology and HSC.

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Cement: 513 kg/m3

w/c: 0.25

Silica fume: 43 kg/m3

Fine aggr.: 685 kg/m3

HRWR: 15.7 L/m3

28d strength: 119 MPa

91d strength: 145 MPa

Mix proportion for HSC: Two Union Square Seattle, 1988, USA

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Sample Mix Proportions and Properties of High-Strength Concrete (USA, 1994)

C + SF + FA C + SF

Cement, Type I, kg/m3 475 564

Silica fume, kg/m3 24 89

Fly ash, kg/m3 59 —

HRWR Type F, liters/m3 11.6 20.11

Retarder, Type D, liters/m3 1.05 1.46

Water to cementing materials ratio 0.29 0.22

Slump, mm 248 254

Compressive strength, 28d, MPa 92 117

Compressive strength, 91d, MPa 105 124

Modulus of elasticity, 91d, GPa 49.9 56.5

Drying shrinkage, 369d, millionths 677 527 20

High strength concrete (contd.)

High strength concrete is in use in the world since the last (at least) 40 years.

The use of high strength concrete in the world is expected to substantially increase for many good reasons.

Its use and application in Ethiopia is, however, extremely limited. Why?

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Concrete production in Ethiopia

Cement

Water

Fine Aggregate

Coarse Aggregate

Additives

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Concrete production in Ethiopia (contd.)

Concrete = cement + fine aggregate + coarse aggregate + water + additives

Aggregates take 65-75% of concrete making materials

Water takes 14-22% of concrete volume

Cement is usually the most expensive ingredients (9-15% of the concrete volume)

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Typical sand mining in Ethiopia 24

Sand mining and environment 25

Coarse aggregate production

Environment pollution/degradation, grading, standard, safety, cleanness, …. need to be observed.

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Cement production in Ethiopia Cement is said to be the second

most consumed material on the planet next to water.

World cement consumption in 2015 was over 4billion tons

Cement per capita consumption:

World average is 500kg/person/year

African average is ~175 - 200

China ~1500 (~60% of world cement is consumed in China)

Europe 700-1200

Ethiopian cement consumption varies between 60-90 kg/person/year

Still a long way to go to reach world average !!

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Cement production and use in Ethiopia

Cement production in Ethiopia Five (6-7) major

factories and 11 smaller ones

Current annual production ~12 million Ton/year

Production capacity and outputs are different

Cement cost in Ethiopia

On the high side

Highly profitable

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Current cement specification: ES 1177 - 1

The five main cement types: CEM I Portland cement

CEM II Portland Composite cement

CEM III Blast Furnace cement

CEM IV Pozzolanic cement

CEM V Composite cement

Are we all familiar with the designation? (OPC/PPC/PLC/…)

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The standard strength of cement

Remark

Designation 2 days early strength [MPa]

Standard strength [MPa]

32.5N -- ≥ 32.5 & ≤ 52.5 PLC/PPC/OPC?

32.5R ≥ 10

42.5N ≥10 ≥ 42.5 & ≤ 62.5 OPC

42.5R ≥20

52.5N ≥20 ≥52.5 OPC

52.5 R ≥30

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The 27 products in the family of common cements

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Cement bags should provide correct and simple information.

Do we really check cement designation when we buy?

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Cement need to be handled properly!

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Specification for concrete in Ethiopia

The specification of concrete in Ethiopia is limited to a

maximum of C40, although the majority of construction use

concrete specified to C25.

“ …. Use Ordinary Portland Cement for all structural

concrete ….”

“ ……Use a mix proportion of 1:2:3 ….”

Specifications are normally based on either “Performance” or

“Prescription”. Some times mixed.

Our existing practice will not confidently lead us to produce

the expected quality of concrete.

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Specification for concrete in Ethiopia (contd.)

Concrete specifications need to be scientific and

drafted by professional material engineers.

Who writes specifications for concrete in Ethiopia?

Architects? Structural engineers? Material

engineers? Consultants/Contractors …… !!

Usually cut and paste from past documents.

Due to limited research outputs and guidelines,

there exist lack of competence in writing

specification.

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Challenges and opportunities in HSC production in Ethiopia

Challenges in producing HSC in Ethiopia Nonstandard fine and coarse aggregates

Understanding of cement type/quality is low (?).

Labor intensive and old concrete production technology.

The use of HSC is not appreciated by many (why?)

Prospects Tall buildings are increasing in major cities.

The way forward We should overcome the challenge and exploit the

opportunity.

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Selected research reports on HSC production at AAiT, AAU

Cement type

w/c Cement amount (kg/m3)

28th day comp. strength (MPa)

Year and researcher

OPC-Mugher 0.35 400 80.3 2002, Tigist & AD

450 86.3

500 91

550 82

OPC-Mugher 0.38 400 78.2

450 81.7

500 84.9

550 70.9

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Selected research reports on HSC production at AAiT (contd.)

Cement type w/c Cement amount (kg/m3)

28th day comp. strength (MPa)

Year and researcher

OPC - Derba 0.65 290 32.7 2014, Addisu & AD

0.56 340 48.4

0.47 360 61.5

0.42 405 64.6

0.35 485 75.2

0.25 545 91.7

0.24 585 101.5

PPC-Derba 0.51 330 37.1

0.37 400 56.4

0.24 585 80.5

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Selected research reports on HSC production at AAiT (contd.)

CBE New Head quarter building (4B+G+M+46)

specification for C60 concrete, 2016/17,

Addis Ababa:

Cement = 520 kg/m3; OPC 42.5

w/c = 0.3

Water = 155 kg/m3

28th strength: 71.6MPa

Good attempt, will report details at later date!

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Discussion

The above sample results are obtained in the laboratory condition with standard materials and additives.

If we can produce C60 using 400kg cement per cubic meter of concrete in the laboratory condition, we should be able to produce at least C40-50 in the field using the same mix proportion.

Then why do we prefer to produce expensive but poor quality concrete? A question which need to be answered by all involved in the sector.

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Discussion

So far there is no clear and detailed guideline in HSC

production in Ethiopia.

Design consultants are shy to specify HSC.

Though some are catching up lately, contractors do not have

confidence to produce HSC.

Confusion/misunderstanding in the selection and use of

international standards: ASTM, BS, EBCS, ES, Euro,

Chinese? …. (we cannot use them directly as they are

designed for their own specific conditions).

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Discussion

Cement producers do not have sufficient

knowledge in concrete production except

producing cement.

Encouraging efforts are being made at the AAiT

and regional universities to study and understand

concrete properties and many research outputs

are made available for reference.

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Discussion (contd.)

A paradigm shift from the conventional cast in-situ

concrete production to modern concrete

construction practice is necessary to improve

quality, reduce cost and complete projects on time.

Such majors include: Introduction of new and modern methods of concrete mixing,

transporting, placing and compaction (eg. ready mix concrete,

pumping concrete, ..)

Use of chemical admixtures

Use of good formwork

Promoting prefabrication as alternative methods

…..

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Are we significantly better in

technique than 100 years ago?

Menelik and Alfred Ilg Late 19th century in Ethiopia

2015 in Addis 45

We have a lot to change in

this country.

Improvement in concrete

technology is a key for all.

Transition from the

traditional NSC to HSC is

essential for high raised

building constructions in

Ethiopia for many good

reasons.

CMC apartments (1980’s)

Condo’s , 2010

Rural accommodation (2017, >70% Eth.)

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Let us think big and use concrete correctly and efficiently!

• Advancement in concrete technology will surely change the life style of our society. If done correctly, everything is possible in concrete. Let us exploit the advantages of HSC !

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Conclusion

Provided we have standardized concrete making material we can produce HSC.

HSC, among others, reduce cost, improve quality and durability, saves time, …

Modern concrete production methods need to be encouraged: Ready mixed concrete, prefabrication techniques, use of additives,

modern/appropriate technology (in mixing, transporting, placing, …)

Use of alternative cement types need to be further exploited (eg. PLC, SLAG, PFA)

Continuous research and development (R&D): University and Industry linkage.

Encouraging Government Policy need to be formulated to popularize the use of cement for the rural community.

HSC is the better alternative and inevitable in the near future. We (academics, consultants, contractors, suppliers, …..) should make our selves prepared for it.

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Thank you!!

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