Greening Concrete
 Why Green Concrete?
– Huge impact on
sustainability
– Most widely used material
on Earth
• 30% of all materials flows on
the planet
– 70% of all materials flows in
the built environment.
• > 2.1 billion tonnes per annum.
• >15 billion tonnes poured each
year.
• Over 2 tonnes per person per
annum
The fine print which is there for people to read if
they download the presentation from the web site
Presentation downloadable from www.tececo.com
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Roadmap to Greening Concrete
A. Background
– Emissions, contribution and production
B. Options for Greening Concrete
1. Scale down production.
•
Untenable, especially to developing nations unless population
growth also attenuated
2. Use waste for fuels
•
OK in some circumstances, others questionable.
3. Capture and convert CO2 emissions to fuel and other materials
•
Very promising technology.
4. Reduce net emissions from manufacture
•
•
Increase manufacturing efficiency
Waste stream sequestration using MgO and CaO
– E.g. Carbonating the Portlandite in waste concrete
» Given the current price of carbon in Europe this could be viable
Presentation downloadable from www.tececo.com
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Greening Concrete
5. Increase the proportion of waste materials that
are pozzolanic
•
Using waste pozzolanic materials such as fly ash and
slags has the advantage of not only extending cement
reducing the embodied energy and net emissions but
also of utilizing waste.
– We could run out of fly ash as coal is phasing out. (e.g.
Canada)
– TecEco technology will encourage the use of pozzolans
6. Improve particle packing for binder minimisation
and carbonation
•
Probably the lowest cost alternative for making a big difference.
Presentation downloadable from www.tececo.com
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Greening Concrete
7. Innovative New Concrete Products
–
Including aggregates that improve or introduce new properties reducing
lifetime energies
•
•
–
E.g. Including wood fibre or Hemp hurd reduces weight and conductance
Phase change minerals to improve specific heat capacity
Use aggregates with lower embodied energy and that result in less
emissions or are themselves carbon sinks
•
materials that be used to make concrete have lower embodied energies.
–
–
–
–
•
Materials that are non fossil carbon are carbon sinks in concrete
–
–
Plastics, wood etc.
Using aggregates that extend concrete
•
•
Aluminium use questionable
Foamed Concretes
–
–
Local low impact waste aggregates
Local “dirt”
Recycled aggregates from building rubble
Glass cullet
Use for slabs to improve insulation
Innovative products the reduce emissions and other impacts
•
TecEco Eco-Cement Porous Pavement
Presentation downloadable from www.tececo.com
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Greening Concrete
8. Replace or partially replace Portland cement with
viable alternatives
•
There are a number of products with similar properties to
Portland cement
– Carbonating Binders
» Lime mixes, Eco-Cements.
– Non-carbonating binders
» Tec-Cements, geopolymers etc.
•
The research and development of these binders needs to be
accelerated
C. Conclusion
•
There is plenty of scope!
Presentation downloadable from www.tececo.com
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Portland Cement & Global Warming
Hansen, J
et. al.
Climate
Change
and Trace
Gases
 Third largest contributor to CO2 emissions after the
energy and transportation sectors.
 Portland cement production will reach 3.5 billion tonnes
by 2020 - a three fold increase on 1990 levels.
 To achieve Kyoto targets the industry will have to emit
less than 1/3 of current emissions per tonne of concrete.
 Carbon taxes and other legislative changes will provide
legislative incentive to change.
 There is already strong evidence of market incentive to
change
Presentation downloadable from www.tececo.com
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Emissions from Cement Production
 Chemical Release (approx 50%)
– The process of calcination involves driving off
chemically bound CO2 with heat.
CO2
CaCO3 →CaO + ↑CO2
 Process Energy (approx 50%)
– Most energy is derived from fossil fuels.
– Fuel oil, coal and natural gas are directly or indirectly burned to
produce the energy required releasing CO2.
 The production of cement for concretes accounts
for around 10% of global anthropogenic CO2.
– Pearce, F., "The Concrete Jungle Overheats", New Scientist, 19
July, No 2097, 1997 (page 14).
Presentation downloadable from www.tececo.com
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The Carbon Cycle and Emissions
Emissions
from fossil
fuels and
cement
production
are the
cause of the
global
warming
problem
Source: David Schimel and Lisa Dilling, National Centre for Atmospheric Research 2003
Presentation downloadable from www.tececo.com
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Cement Production ~= Carbon Dioxide Emissions
Metric Tonnes
2,500,000,000
2,000,000,000
1,500,000,000
1,000,000,000
500,000,000
2001
1996
1991
1986
1981
1976
1971
1966
1961
1956
1951
1946
1941
1936
1931
1926
0
Year
Presentation downloadable from www.tececo.com
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Embodied Energy of Building Materials
Concrete is
relatively
environmentally
friendly and has a
relatively low
embodied energy
Downloaded from www.dbce.csiro.au/indserv/brochures/embodied/embodied.htm (last accessed 07 March 2000)
Presentation downloadable from www.tececo.com
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Average Embodied Energy in Buildings
Most of the embodied energy in the
built environment is in concrete.
Because so much concrete is used there is a
huge opportunity for sustainability by reducing
the embodied energy, reducing the carbon debt
(net emissions) and improving properties that
reduce lifetime energies.
Downloaded from www.dbce.csiro.au/ind-serv/brochures/embodied/embodied.htm
(last accessed 07 March 2000)
Presentation downloadable from www.tececo.com
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Concrete Industry Objectives
PCA (USA)
– Improved energy efficiency of fuels and raw
materials
– Formulation improvements that:
• Reduce the energy of production and minimize
the use of natural resources.
• Use of crushed limestone and industrial byproducts such as fly ash and blast furnace slag.
WBCSD
– Fuels and raw materials efficiencies
– Emissions reduction during manufacture
Presentation downloadable from www.tececo.com
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1. Scale Down Production?
 Currently growing at around 5% a year globally. Mainly
China and India.
 GDP growth = concrete poured
– Can the Asian economic boom continue?
– What is Africa and South America also catch up to the western
world?
 Zero population growth?
– Is really the amount of concrete we pour a measure of the
welfare or wellbeing of a society?
 Buildings and infrastructure are only being designed to
last 50 not hundreds of years.
– Will there be a shift to quality not quantity
– If so when?
Presentation downloadable from www.tececo.com
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2. Use Waste for Fuels
 Expanded use of alternative fuels is viewed by the
industry as the most significant opportunity to enhance
sustainability and reduce consumption of fossil fuels
 Cement kilns are being integrated into the recycling
hierarchy for some common wastes
– Biomass, tires, used oils and used solvents.
 Questionable emissions implications?
 Do some organics have more value than as fuel?
– Tyres?
– Solvents that can be recycled
– Oils that can be recycled
Presentation downloadable from www.tececo.com
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3. Capture and Convert CO2 Emissions to Fuel
Presentation downloadable from www.tececo.com
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ACC Emissions to Fuel Project
 ACC, formerly Associated Cement Companies and now part of
the Holcim group have initiated a project to
– Sequester CO2 generated by cement kilns
– Produce high energy algal biomass
• Reused as fuel in its cement kilns.
• Cellulose contents could be converted to alcohols
• Protein residue could be use for animal feed
 The project involves
–
–
–
–
The screening of appropriate high yielding algae cultures
The development of a bioreactor on a lab bench scale
Scaling up the technology to a pilot plant and then
Demonstrating the commercial viability.
 This will require
– A multi disciplinary approach and
– Involve microbiologists, algae experts, bio-technologists, engineers and
other professionals
– Cost around $ 3m over a period of 3 years.
Presentation downloadable from www.tececo.com
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4. Reduce Net Emissions from Manufacture
 Increase manufacturing efficiency
– Has the industry reached the point of diminishing returns?
• Wet to dry process, heat exchangers etc
– Combining calcination with size reduction using a new type of kiln
TecEco are developing may reduce energy consumption by 20-30%
• Reason - Only about 98% of the energy of grinding actually goes into
cleaving minerals
• Around 30% of the energy used to make cement is used for grinding
 CO2 capture
– Calcination in an oxygen atmosphere to capture pure CO2
• Suggested to me by a director of ACC a few weeks ago
• Would make capture of CO2 more worthwhile but cost money
– Use of CO2 for carbonation of concrete seems pointless
 Better to have use e.g. algal bioreactor on site (See 3)
Presentation downloadable from www.tececo.com
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5. Increasing the Proportion of Waste
Materials that are Pozzolanic
 Advantages
– Lower costs
– More durable greener concrete
 Disadvantages
– Rate of strength development retarded
• Resolved by TecEco technology
– Potential long term durability issue due to leaching of Ca from
CSH.
• Glasser and others have observed leaching of Ca from CSH and this will
eventually cause long term unpredictable behavior of CSH.
• Resolved by TecEco technology
– Higher water demand due to fineness.
– Finishing is not as easy
 Supported by WBCSD and virtually all industry
associations
 Driven by legislation and sentiment
Presentation downloadable from www.tececo.com
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Impact of TecEco Tec-Cement Technology
on the use of Pozzolans
 In TecEco tec-cements Portlandite is generally
consumed by the pozzolanic reaction and replaced
with brucite
– Increase in rate of strength development particularly in the first
3-4 days.
• concrete gells more quickly and finishers can go home!
– Kosmotrophic property of the magnesium ion
– Change in surface charge on MgO
– Improved durability as brucite is much less soluble or reactive
• Potential long term durability issue due to leaching of Ca from CSH
resolved.
– Easier to finish fly ash concretes - Mg++ contributes a strong
shear thinning property
Presentation downloadable from www.tececo.com
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6. Improve Particle Packing for Binder
Minimisation and Carbonation
 In the past, concrete proportioning was based on experience and
estimates only.
 TecSoft Pty. Ltd. are developing batching software, using theory
from the world’s best experts (F. de Larrard and Ken Day), to
optimize mix design and particularly particle packing.
 Scientific knowledge of the concrete
behaviour coupled with the use of
optimization software will allow concrete
technologists to:
- Design more sustainable concrete
- Less cement of same strength
- More durable
- Use secondary aggregate and mining
wastes (poor size distribution)
Satterfield, S. G. (2001). Visualization
aggregate in high performance concrete,
National institute of standard and
technology.(NIST)
- Dramatically reduce the number of
experiment needed to design a concrete
for a special application
Presentation downloadable from www.tececo.com
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Scientific Approach to Concrete Design
 Optimization of particle packing will improve
– The strength/cost ratio and
– Concrete sustainability
• Less cement for the same strength
 Improving packing (other parameters being equal) leads to
an increase of:
– The compressive and tensile strength
– The workability
– The durability
And a decrease of:
– The porosity
– The risk of segregation
– The yield stresses (easier to compact)
 Could help improve the skill level in the industry
– An expert in the box
Presentation downloadable from www.tececo.com
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7. Innovative New Concrete Products
 Room for innovation in the concrete industry
– Demand for more sustainable materials
 Need to take a more holistic view
– Cementitious composites not cement
 Barriers to innovation are
– Low skill level
• For innovation to occur the skill level will have to improve
dramatically
• This could be a government initiative – i.e require people in the
industry to do an apprenticeship (as for other industries)
• As part of the course work alternatives would be examined.
– Formula rather than performance based standards entrench
mediocrity and dogma
– Better connections between market demand and production and
supply
Presentation downloadable from www.tececo.com
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Technologies that Introduce New Properties
 Introduce new components that improve
performance.
– Reducing lifetime energies in use e.g.
• That reduce conductance (e.g. wood fibre or hemp hurd )
• That increase specific heat capacity (e.g. phase change
materials)
– Reduce weight/strength ratio
• Organic fibres and fillers
– Many of the above components can be wastes
– Improve durability
• Remove lime by adding pozzolans or as in Tec-Cement
concretes
Presentation downloadable from www.tececo.com
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Reduce Embodied Energy
 Local low impact waste aggregates
– Local “dirt”
– On site excavation materials
 Recycled aggregates from building rubble
– Tec and Eco-Cements do not have problems associated with
high gypsum content
 Glass cullet fly ash, ggbfs and other industrial
wastes
 Reduce transport embodied energies by using
local materials such as low impact wastes and
earth
– Mud bricks and adobe.
– TecEco research in the UK and with mud bricks in Australia
indicate that eco-cement formulations seem to work much better
than PC for this
Presentation downloadable from www.tececo.com
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Lower Net Emissions
 Making Concretes that are carbon sinks
– Eco-Cements - Addition of magnesium oxide which recarbonates with carbon capture technology
– Materials that are non fossil carbon are carbon sinks in concrete
• Plastics, wood etc.
• Eco-Cements bond well to sawdust and other carbon based
aggregates.
– Many of the above components can be wastes
• paper and plastic have in common reasonable tensile strength, low
mass and low conductance and can be used to make cementitious
composites that assume these properties
Presentation downloadable from www.tececo.com
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Extending Cement
 Air used in foamed concrete is a cheap low embodied
energy aggregate and has the advantage of reducing
the conductance of concrete.
– Concrete, depending on aggregates weighs in the order of
2350 Kg/m3
– Concretes of over 10 mp as light as 1000 Kg/m3 can be
achieved.
– At 1500 Kg/m3 25 mpa easily achieved.
 From our experiments so far with Build-lite Cellular
Concrete PL Tec-Cement formulations increase
strength performance by around 5-10% for the same
mass.
 Claimed use of aluminium and autoclaving to make
more sustainable blocks questionable?
Presentation downloadable from www.tececo.com
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Concrete Porous Pavements?
 Perhaps the greenest concrete product in the world is a new
porous low fines concrete that is being made using recycled
aggregate and with Eco-Cements that set by absorbing CO2
Presentation downloadable from www.tececo.com
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8. Replace Portland Cement with Viable Alternatives
 The concrete industry are in the business of selling
binders
– Need to get away from the “all that is grey is great, all we make
goes out the gate” philosophy
 The industry can also make money learning about
and selling alternatives
– Sell knowledge as well as product
• Many alternatives just as suitable
– The problem is in implementation
• Could be difficult given the low level of skill in the industry
 We will consider two main groups of alternative cements
• Carbonating alternatives
– Potentially carbon neutral of carbon sinks
• Non carbonating alternatives
– Some have much lower embodied energies
Presentation downloadable from www.tececo.com
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Replacement of PC by Calcium Based Carbonating Binders
 Lime
– The most used material next to Portland cement in binders.
– Generally used on a 1:3 (PC:Sand) paste basis since Roman
times
– Non-hydraulic limes set by carbonation and are therefore close
to carbon neutral once set.
CaO + H2O => Ca(OH)2
Ca(OH)2 + CO2 => CaCO3
33.22 + gas ↔ 36.93 molar volumes
– Very slight expansion, but shrinkage from loss of water.
– Carbonates not generally fibrous so do not add as much
microstructural strength as Mg cements
– Do not stick to other materials as well as Mg cements.
– Low long term pH = low reactivity with wastes included
Presentation downloadable from www.tececo.com
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Replacement of PC with Magnesium Based Carbonating Binders
 Eco-Cement (TecEco)
– Have high proportions of reactive magnesium oxide
– Carbonate like lime
– Generally used in a 1:2:18 (PC:MgO:Sand) paste basis because much
more carbonate “binder” is produced than with lime.
– Like lime are carbon neutral but take up more weight of CO2 due to low
weight of Mg
Mostly CO2
MgO + H2O <=> Mg(OH)2
and water
Mg(OH)2 + CO2 + H2O <=> MgCO3.3H2O
58.31 + 44.01 <=> 138.32 molar mass (at least!)
24.29 + gas <=> 74.77 molar volumes (at least!)
– 307 % expansion (less water volume reduction) producing much more
binder per mole of MgO than lime (around 8 times) and les shrinkage
– Carbonates tend to be fibrous adding significant micro structural strength
compared to lime
– Can include a wider range of wastes
• Stick well due to hydrogen bonding
• Low long term pH = low reactivity
Presentation downloadable from www.tececo.com
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Replacement with Non Carbonating Binders
 There are a number of other novel cements with
intrinsically lower energy requirements and CO2 emissions
than conventional Portland cements that have been
developed
– High belite cements
• Being research by Aberdeen and other universities
– Calcium sulfoaluminate cements
• Used by the Chinese for some time
– Magnesium phosphate cements
• Proponents argue that a lot stronger than Portland cement therefore
much less is required.
• Main disadvantage is that phosphate is a limited resource
– Sorel Type Cements
• Stronger and more convenient to place and use (with the appropriate
know how.
• Tend to break down in water
– PC – Magnesia blends (Tec-Cements)
– Geopolymers
More research needed. I will only have time to mention
geopolymers and Tec-Cements
Presentation downloadable from www.tececo.com
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Geopolymers
 “Geopolymers” consists of SiO4 and AlO4 tetrahedra linked
alternately by sharing all the oxygens.
– Positive ions (Na+, K+, Li+, Ca++, Ba++, NH4+, H3O+) must be present
in the framework cavities to balance the negative charge of Al3+ in
IV fold coordination.
 Theoretically very sustainable
 Unlikely to be used for pre-mix concrete or waste in the
near future because of.
– process problems
• Requiring a degree of skill for implementation
– Skill level problem in the industry needs to be addressed
– nano porosity
• Causing problems with aggregates in aggressive environments
– no pH control strategy for heavy metals in waste streams
Presentation downloadable from www.tececo.com
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Tec - Cements
 Tec-Cements (Low MgO)
– contain more Portland cement than reactive magnesia.
Reactive magnesia hydrates in the same rate order as Portland
cement forming Brucite which uses up water reducing the
voids:paste ratio, increasing density and possibly raising the
short term pH.
– More pozzolans can be used. After all the Portlandite has been
consumed Brucite controls the long term pH which is lower and
due to it’s low solubility, mobility and reactivity results in greater
durability.
– Other benefits include improvements in density, strength and
rheology, reduced permeability and shrinkage and the use of a
wider range of aggregates many of which are potentially
wastes without reaction problems.
Presentation downloadable from www.tececo.com
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