Greening Concrete

1
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.
• gt 2.1 billion tonnes per annum.
• gt15 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
2
Roadmap to Greening Concrete

• Background
• Emissions, contribution and production
• Options for Greening Concrete
• Scale down production.
• Untenable, especially to developing nations
  unless population growth also attenuated
• Use waste for fuels
• OK in some circumstances, others questionable.
• Capture and convert CO2 emissions to fuel and
  other materials
• Very promising technology.
• 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

3
Greening Concrete

• 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
• Improve particle packing for binder minimisation
  and carbonation
• Probably the lowest cost alternative for making a
  big difference.

4
Greening Concrete

• 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.
• Local low impact waste aggregates
• Local dirt
• Recycled aggregates from building rubble
• Glass cullet
• Materials that are non fossil carbon are carbon
  sinks in concrete
• Plastics, wood etc.
• Using aggregates that extend concrete
• Aluminium use questionable
• Foamed Concretes
• Use for slabs to improve insulation
• Innovative products the reduce emissions and
  other impacts
• TecEco Eco-Cement Porous Pavement

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Greening Concrete

• 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
• Conclusion
• There is plenty of scope!

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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

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Emissions from Cement Production

• Chemical Release (approx 50)
• The process of calcination involves driving off
  chemically bound CO2 with heat.
• 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).

CO2
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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
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Cement Production Carbon Dioxide Emissions
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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/ind-serv/brochur
es/embodied/embodied.htm (last accessed 07 March
2000)
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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/brochur
es/embodied/embodied.htm (last accessed 07 March
2000)
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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
  by-products such as fly ash and blast furnace
  slag.
• WBCSD
• Fuels and raw materials efficiencies
• Emissions reduction during manufacture

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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?

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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

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3. Capture and Convert CO2 Emissions to Fuel
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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.

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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)

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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

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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

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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 worlds 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)
• Dramatically reduce the number of experiment
  needed to design a concrete for a special
  application

Satterfield, S. G. (2001). Visualization
aggregate in high performance concrete, National
institute of standard and technology.(NIST)
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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

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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

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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

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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

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Lower Net Emissions

• Making Concretes that are carbon sinks
• Eco-Cements - Addition of magnesium oxide which
  re-carbonates 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

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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?

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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

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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

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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 13 (PCSand) paste basis
  since Roman times
• Non-hydraulic limes set by carbonation and are
  therefore close to carbon neutral once set.
• CaO H2O gt Ca(OH)2
• Ca(OH)2 CO2 gt 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

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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 1218 (PCMgOSand) 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
• MgO H2O ltgt Mg(OH)2 Mg(OH)2 CO2 H2O ltgt
  MgCO3.3H2O
• 58.31 44.01 ltgt 138.32 molar mass (at least!)
• 24.29 gas ltgt 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

Mostly CO2 and water
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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
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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

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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 voidspaste
  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 its
  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.