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TRANSCRIPT
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.
2
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
4
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.
5
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
17
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?
21
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).
42
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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