Download - Harrison Greening Concrete 19 Feb 07

Slide 130% 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
Roadmap to Greening Concrete
Use waste for fuels
Capture and convert CO2 emissions to fuel and other materials
Very promising technology.
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
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.
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”
Glass cullet
Materials that are non fossil carbon are carbon sinks in concrete
Plastics, wood etc.
Aluminium use questionable
Innovative products the reduce emissions and other impacts
TecEco Eco-Cement Porous Pavement
Replace or partially replace Portland cement with viable alternatives
There are a number of products with similar properties to Portland cement
Carbonating Binders
Tec-Cements, geopolymers etc.
The research and development of these binders needs to be accelerated
Conclusion
Portland Cement & Global Warming
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
Hansen, J et. al. Climate Change and Trace Gases
Emissions from Cement Production
Chemical Release (approx 50%)
The process of calcination involves driving off chemically bound CO2 with heat.
CaCO3 →CaO + ↑CO2
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
The Carbon Cycle and Emissions
Source: David Schimel and Lisa Dilling, National Centre for Atmospheric Research 2003
Emissions from fossil fuels and cement production are the cause of the global warming problem
Downloaded from www.dbce.csiro.au/ind-serv/brochures/embodied/embodied.htm (last accessed 07 March 2000)
Concrete is relatively environmentally friendly and has a relatively low embodied energy
Downloaded from www.dbce.csiro.au/ind-serv/brochures/embodied/embodied.htm (last accessed 07 March 2000)
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.
Most of the embodied energy in the built environment is in concrete.
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
Emissions reduction during manufacture
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?
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?
Tyres?
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 development of a bioreactor on a lab bench scale
Scaling up the technology to a pilot plant and then
Demonstrating the commercial viability.
Involve microbiologists, algae experts, bio-technologists, engineers and other professionals
Cost around $ 3m over a period of 3 years.
Increase manufacturing efficiency
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)
5. Increasing the Proportion of Waste Materials that are Pozzolanic
Advantages
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
Finishing is not as easy
Supported by WBCSD and virtually all industry associations
Driven by legislation and sentiment
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
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.
Satterfield, S. G. (2001). Visualization aggregate in high performance concrete, National institute of standard and technology.(NIST)
Scientific knowledge of the concrete behaviour coupled with the use of optimization software will allow concrete technologists to:
Design more sustainable concrete
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
Optimization of particle packing will improve
The strength/cost ratio and
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
Could help improve the skill level in the industry
An expert in the box
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
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
Improve durability
Remove lime by adding pozzolans or as in Tec-Cement concretes
Local “dirt”
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
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
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?
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
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
Non carbonating alternatives
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
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
Eco-Cement (TecEco)
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
MgO + H2O <=> Mg(OH)2
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
Mostly CO2 and water
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
Calcium sulfoaluminate cements
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
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
Skill level problem in the industry needs to be addressed
nano porosity
no pH control strategy for heavy metals in waste streams
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.
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Download - Harrison Greening Concrete 19 Feb 07

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