Transcript Slide 1

Greening Mineral Binders
The technology
paradigm defines
what is or is not a
resource - Pillzer
Presentation by John
Harrison, managing director
of TecEco and inventor of
Tec and Eco-Cements and
the CarbonSafe process.
Our slides are deliberately verbose as most people download
and view them from the net. Because of time constraints I will
have to race over some slides
John Harrison B.Sc. B.Ec. FCPA.
Presentation downloadable from www.tececo.com
1
Under Materials Flows in the Techno-Processes are Molecular Flows
Take → Manipulate → Make → Use → Waste
[
[
←Materials→
]
← Underlying molecular flow → ]
If the underlying molecular flows are “out of tune” with
nature there is damage to the environment
e.g. heavy metals, cfc’s, c=halogen compounds and CO2
Moleconomics
Is the study of the form of atoms in molecules, their flow, interactions,
balances, stocks and positions. What we take from the environment
around us, how we manipulate and make materials out of what we take
and what we waste result in underlying molecular flows that affect earth
systems. These flows should mimic or minimally interfere with natural
flows.
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Abatement and Sequestration
 To solve sustainability problems our approach
should be holistically balanced and involve
– Everybody, every day New technical
– Be easy
paradigms are
– Make money
required
Sequestration
Abatement
and
+
Abatement = Efficiency
and conversion to non
fossil fuels
CarbonSafe =
Sequestration and
waste utilisation.
TecEco’s Contribution
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The TecEco CarbonSafe Geo-Photosynthethic Process
Inputs:
Atmospheric or smokestack CO2, brines,
waste acid, other wastes
Outputs:
The CarbonSafe Geo-Photosynthetic
Process is TecEco’s evolving technoprocess that delivers profitable
outcomes whilst reversing underlying
undesirable moleconomic flows from
other less sustainable processes.
Potable water, gypsum, sodium bicarbonate, salts, building
materials, bottled concentrated CO2 (for geo-sequestration
and other uses).
Solar or solar
derived energy
CO2
CO2
CO2
MgO
TecEco
MgCO2
Cycle
TecEco
Kiln
MgCO3
Coal
Carbon or carbon compounds
Magnesium oxide
Fossil fuels
CO
Oil
Presentation downloadable from www.tececo.com 2
CO2
Greensols
Process
1.29 gm/l
Mg
4
The TecEco CarbonSafe Industrial Ecology
Inputs
Brines
Waste Acid
CO2
Outputs
Gypsum, Sodium
bicarbonate, Salts,
Building materials,
Potable water
We must design whole new technical
paradigms that reverse many of our
problem molecular flows
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The CarbonSafe Geo-Photosynthetic Process
Waste
Acid
Seawater
Carbonatio
n Process
CO2 from power
generation or industry
Other salts
Na+,K+,
Ca2+,Cl-
Magnesite (MgCO3)
Solar Process to Produce
Magnesium Metal
Simplified TecEco Reactions
Tec-Kiln MgCO3 → MgO + CO2 - 118 kJ/mole
Reactor Process MgO + CO2 → MgCO3 + 118
kJ/mole (usually more complex hydrates)
CO
2
Other Wastes
1.354 x 109 km3 Seawater containing 1.728 10 17
tonne Mg or suitable brines from other sources
Magnesia
(MgO)
Eco-Cement
Tec-Cement
Gypsum +
carbon waste
(e.g.
sewerage) =
fertilizers
Bicarbonate
of Soda
(NaHCO3)
Gypsum
(CaSO4)
Sewerage compost
CO2 as a biological or
industrial input or if no
other use geological
sequestration
Magnesium
Thermodynamic
Magnesite
Cycle
(MgCO3)
Hydroxid
e
Reactor
Process
CO2 from power
generation, industry
or out of the air
Sequestration Table – Mg from Seawater
Tonnes CO2 sequestered per tonne magnesium with various cycles
through the TecEco Tec-Kiln process. Assuming no leakage MgO to built
environment (i.e. complete cycles).
Billion
Tonnes
Tonnes CO2 sequestered by 1 billion tonnes of Mg in seawater
1.81034
Tonnes CO2 captured during calcining (same as above)
1.81034
Tonnes CO2 captured by eco-cement
1.81034
Total tonnes CO2 sequestered or abated per tonne Mg in seawater
(Single calcination cycle).
3.62068
Total tonnes CO2 sequestered or abated (Five calcination cycles.)
18.1034
Total tonnes CO2 sequestered or abated (Ten calcination cycles).
36.20
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TecEco CO2 Capture Kiln Technology
 Can run at low temperatures.
 Can be powered by various
non fossil fuels.
– E.g. solar
 Theoretically capable of producing much more reactive
MgO
– Even with ores of high Fe content.
 Captures CO2 for bottling and sale to the oil industry
(geological sequestration).
 Grinds and calcines at the same time.
– Runs 25% to 30% more efficiently as use waste heat from
grinding
 Will result in new markets for ultra reactive low lattice
energy MgO (e.g. cement, paper and environment
industries)
Presentation downloadable from www.tececo.com
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Re - Engineering Materials – What we Build With
Environmental
problems are
the result of
inherently
flawed
materials,
materials flows
and energy
systems
 To solve environmental problems
we need to understand more
about materials in relation to the
environment.
– the way their precursors are derived and
their degradation products re assimilated
• and how we can reduce the impact of
these processes
– what energies drive the evolution,
devolution and flow of materials
• and how we can reduce these energies
– how materials impact on lifetime energies
 With the knowledge gained redesign materials to not only be
more sustainable but more
sustainable in use
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Huge Potential for Sustainable Materials
Reducing the impact of the take and
waste phases of the techno-process.
– including carbon in materials
Many wastes can
they are potentially carbon sinks. contribute to
physical
– including wastes for
properties
reducing lifetime
physical properties as
energies
well as chemical composition
CO
they become resources.
– re – engineering
CO
Waste
materials to
reduce the lifetime
energy of buildings CO
2
2
2
C
Waste
CO2
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Utilizing Carbon and Wastes (Biomimicry)
 During earth's geological history large tonnages of
carbon were put away as limestone and other
carbonates and as coal and petroleum by the activity of
plants and animals.
 Sequestering carbon in magnesium binders and
aggregates in the built environment mimics nature in that
carbon is used in the homes or skeletal structures of
most plants and animals.
We all use carbon and wastes to
make our homes! “Biomimicry”
In eco-cement blocks
and mortars the
binder is carbonate
and the aggregates
are preferably wastes
Presentation downloadable from www.tececo.com
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Impact of the Largest Material Flow - Cement and Concrete
 Concrete made with cement is the most widely
used material on Earth accounting for some
30% of all materials flows on the planet and 70%
of all materials flows in the built environment.
– Global Portland cement production is currently in the
order of 2.2 billion tonnes per annum.
– Globally over 15 billion tonnes of concrete are poured
per year.
– Over 2 tonnes per person per annum
– Much more concrete is used than any other building
material.
TecEco Pty. Ltd. have benchmark technologies for
improvement in sustainability and properties
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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)
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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/indserv/brochures/embodied/embodied.htm (last accessed 07 March 2000)
Presentation downloadable from www.tececo.com
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Emissions from Cement Production
 Chemical Release
– The process of calcination involves driving off chemically bound
CO2 with heat.
CaCO3 →CaO + ↑CO2
CO2
 Process Energy
– Most energy is derived from fossil fuels.
CO2
– 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).
Arguments that we should reduce cement production relative to other
building materials are nonsense because concrete is the most sustainable
building material there is. The challenge is to make it more sustainable.
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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
Between Tec, Eco and Enviro-Cements TecEco can provide
a viable much more sustainable alternative.
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The TecEco Dream – A More Sustainable Built Environment
CO2
CO2 FOR
GEOLOGICAL
SEQUESTRATION
CO2
MINING
MAGNESITE
+ OTHER
INPUTS
“There is a way to
make our city streets
as green as the
Amazon rainforest”.
Fred Pearce, New
Scientist Magazine
TECECO
KILN
MgO
OTHER
WASTES
PERMANENT
SEQUESTRATION &
WASTE
UTILISATION (Man
made carbonate
rock incorporating
wastes as a
TECECO CONCRETES building material)
RECYCLED
BUILDING
MATERIALS
SUSTAINABLE CITIES
We need materials that
require less energy to
make them, that last
much longer and that
contribute properties
that reduce lifetime
energies
Presentation downloadable from www.tececo.com
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A Low Energy Post – Carbon & Waste Age?
The construction
industry can be
uniquely responsible
for helping achieve this
transition
Maybe then we can move
confidently into a more
sustainable future.
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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
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Greening the Largest Material Flow Concrete
1. Scale down Production.
– Untenable nonsense, especially to developing
nations
2. Use waste for fuels
– Not my area of expertise but questioned by many.
3. Reduce net emissions from manufacture
– Increase manufacturing efficiency
– Increase fuel efficiency
– Waste stream sequestration using MgO and CaO
•
Not
discussed
E.g. Carbonating the Portlandite in waste concrete
– Given the current price of carbon in Europe this could be
viable
•
TecEco have a mineral sequestration process that is
non fossil fuel driven using MgO and the TecEco kiln
Presentation downloadable from www.tececo.com
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Greening Concrete
4. 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.
•
TecEco technology will allow the use of marginal pozzolans
– Slow rate of strength development increased in first few hours and days
– Potential long term (50 year plus) durability issues overcome using teccement technology
– Finishing problems overcome
•
We could run out of fly ash as coal is phasing out. (e.g. Canada)
5. Replace Portland cement with viable alternatives
– There are a number of products with similar properties to Portland
cement
a) Carbonating Binders
b) Non-carbonating binders
– The research and development of these binders needs to be
accelerated
Presentation downloadable from www.tececo.com
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Greening Concrete
6. Use aggregates that extend cement
–
Use air as an aggregate making cement go further
•
•
Foamed Concretes work well with TecEco cements
Use for slabs to improve insulation
•
Aluminium use questionable
7. Use aggregates with lower embodied energy and that result in
less emissions or are themselves carbon sinks
–
Other materials that be used to make concrete have lower embodied energies.
•
•
•
•
–
Local low impact aggregates
Waste materials
Recycled aggregates from building rubble
Glass cullet
Materials that non fossil carbon are carbon sinks in concrete
•
Plastics, wood etc.
8. Improve the performance of concrete by including aggregates that
improve or introduce new properties reducing lifetime energies
–
Wood fibre reduces weight and conductance.
Presentation downloadable from www.tececo.com
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4. Increasing the Proportion of Waste
Materials that are Pozzolanic
 Advantages
– Lower costs
– More durable greener concrete
 Disadvantages
– Rate of strength development retarded
– Potential long term durability issue due to leaching of Ca from
CSH.
• Resolved by presence of brucite in tec-cements
– 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 in the first 3-4 days.
• Internal consumption of water by MgO as it hydrates reducing
impact of fineness demand
• More pozzolanic reactions
• Mg Al hydrates?
– Followed by straight line development
– Improved durability as brucite is much less soluble or reactive
• Potential long term durability issue due to leaching of Ca from CSH
resolved.
– Influence of kosmotopic Mg++
• Concretes easier to finish with a strong shear thinning property
• Gel up more quickly – so finishers can go home earlier even with
added pozzolan
• Early strength development in the first few days – previously a
problem with added pozzolan
• Less shrinkage and cracking
Presentation downloadable from www.tececo.com
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Portlandite Compared to Brucite
Property
Portlandite (Lime)
Brucite
Density
2.23
2.9
Hardness
2.5 – 3
2.5 – 3
Solubility (cold)
1.85 g L-1 in H2O at 0 oC
0.009 g L-1 in H2O at 18
oC.
Solubility (hot)
.77 g L-1 in H2O at 100 oC .004 g L-1 H2O at 100 oC
Solubility (moles, cold)
0.000154321 M L-1
0.024969632 M L-1
Solubility (moles, hot)
0.000685871 M L-1
0.010392766 M L-1
Solubility Product (Ksp)
5.5 X 10-6
1.8 X 10-11
Reactivity
High
Low
Form
Massive, sometime
fibrous
Usually fibrous
Free Energy of
Formation of
Carbonate Gof
- 64.62 kJ.mol-1
-19.55 kJ.mol-1
-119.55 kJ.mol-1(via
hydrate)
Cement chemists in the industry should be
getting their heads around the differences
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Tec-Cement Concrete Strength Gain Curve
HYPOTHETICAL STRENGTH
GAIN CURVE OVER TIME
(Pozzolans added)
MPa
We have
observed
this kind of
curve with
over 300
cubic
meters of
concrete
Tec – Cement Concrete with
10% reactive magnesia
OPC Concrete
3
Plastic
Stage
7
14
28
Log Days
The possibility of high early strength gain
with added pozzolans is of great economic
and environmental importance.
Presentation downloadable from www.tececo.com
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5.a Replacement of PC by Carbonating Binders
Lime
– The most used material next to Portland cement in
binders.
– Generally used on a 1:3 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.
Presentation downloadable from www.tececo.com
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5.a Replacement of PC Carbonating Binders
 Eco-Cement (TecEco)
– Have high proportions of reactive magnesium oxide
– Carbonate like lime
– Generally used in a 1:5-1:12 paste basis because much more
carbonate “binder” is produced than with lime
MgO + H2O <=> Mg(OH)2
Mostly CO2
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)
– Carbonates tend to be fibrous adding significant micro structural
strength compared to lime
Presentation downloadable from www.tececo.com
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5.b 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
– Geopolymers
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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
– 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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TecEco Cements
SUSTAINABILITY
PORTLAND
+ or - POZZOLAN
Hydration of the
various components
of Portland cement
for strength.
DURABILITY
Reaction of alkali with
pozzolans (e.g. lime with fly
ash.) for sustainability,
durability and strength.
TECECO CEMENTS
STRENGTH
TecEco concretes are
a system of blending
MAGNESIA
reactive magnesia,
Hydration of magnesia => brucite for strength, workability, Portland cement and
dimensional stability and durability. In Eco-cements
usually a pozzolan
carbonation of brucite => nesquehonite, lansfordite and an with other materials
amorphous phase for sustainability.
and are a key factor
for sustainability.
Presentation downloadable from www.tececo.com
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The Magnesium Thermodynamic Cycle
Calcination
CO2 Capture
Non fossil fuel energy
We think this cycle is relatively
independent of other constituents
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TecEco Cement Technology Theory
Portlandite (Ca(OH)2) is too soluble, mobile
and reactive.
– It carbonates, reacts with Cl- and SO4- and being
soluble can act as an electrolyte.
TecEco generally (but not always) remove
Portlandite using the pozzolanic reaction
and
TecEco add reactive magnesia
– which hydrates, consuming water and
concentrating alkalis forming brucite which is
another alkali, but much less soluble, mobile or
reactive than Portlandite.
In Eco-cements brucite carbonates
Presentation downloadable from www.tececo.com
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TecEco Formulations
 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.
– Reactions with pozzolans are more affective. 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.
 Eco-cements (High MgO)
– contain more reactive magnesia than in tec-cements. Brucite in porous
materials carbonates forming stronger fibrous mineral carbonates and therefore
presenting huge opportunities for waste utilisation and sequestration.
 Enviro-cements (High MgO)
– contain similar ratios of MgO and OPC to eco-cements but in non porous
concretes brucite does not carbonate readily.
– Higher proportions of magnesia are most suited to toxic and hazardous waste
immobilisation and when durability is required. Strength is not developed
quickly nor to the same extent.
Presentation downloadable from www.tececo.com
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TecEco Cements – Impact on Sustainability
 The CO2 released by calcined carbonates used to
make binders can be captured using TecEco kiln
technology.
 MgO can be made using non fossil fuel energy
 Tec-Cements Develop Significant Early Strength
even with Added Supplementary Materials.
 Eco-Cements carbonate sequestering CO2
requiring 25-75% less binder in some mixes
Presentation downloadable from www.tececo.com
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Benefits to the Concrete Industry of
Adopting TecEco Technology
 Both Tec and Eco-Cements provide a benign low pH environment for
hosting large quantities of waste overcoming problems of delayed
reactions:
–
–
–
–
–
–
Using acids to etch plastics so they bond with concretes.
sulphates from plasterboard etc. ending up in recycled construction materials.
heavy metals and other contaminants.
delayed reactivity e.g. ASR with glass cullet
Resolving durability issues
Indian and Chinese quality control issues
 Concretes containing MgO
– shrink less
– are demonstrably more durable.
– can incorporate wastes that contribute to physical properties reducing
lifetime energies
The biggest business on the planet is going
to be the sustainability business
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6. Using Aggregates that Extend 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 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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7. Use Aggregates with Lower Embodied
Energy and that Result in less Emissions or
that are Themselves Carbon Sinks
 Use of aggregates that lower embodied energies
– wastes such as recycled building rubble Tec and EcoCements do not have problems associated with high
gypsum content
 Use of other aggregates that include non fossil carbon
– sawdust and other carbon based aggregates can make
eco-cement concretes a net carbon sink.
 Reduce transport embodied energies by using local
materials such as earth
– mud bricks and adobe.
– our research in the UK and with mud bricks in Australia
indicate that Eco-Cement formulations seem to work better
than PC for this
Presentation downloadable from www.tececo.com
37
Using Wastes and Non-Traditional Aggregates to Make
TecEco Cement Concretes
 As the price of fuel rises, the
use of local or on site low
embodied energy materials
rather than carted aggregates
will have to be considered.
No longer an option?
The use of on site and local wastes will be made possible by the use of low reactivity TecEco mixes
and a better understanding of particle packing. We hope with our new software to be able to
demonstrate how adding specific size ranges can make an unusable waste such as a tailing or sludge
suitable for making cementitious materials.
Recent natural disasters such as the recent tsunami and Pakistani earthquake
mean we urgently need to commercialize technologies like TecEco’s because they
provide benign environments allowing the use of many local materials and wastes
without delayed reactions
Presentation downloadable from www.tececo.com
38
8. Improve the Performance of Concrete
by Including Aggregates that
Improve or Introduce New Properties
Reducing Lifetime Energies
 Rather than be taken to landfill many wastes can
be used to improve properties of concrete that
reduce lifetime energies.
– For example 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
39
Biomimicry - Ultimate Recyclers
 As peak oil looms and the price of transport is
set to rise sharply
– We should not just be recycling based on chemical property
requiring sophisticated equipment and resources
– We should be including wastes based on physical properties
as well as chemical composition in composites whereby they
become local resources.
The Jackdaw recycles all sorts of things it finds nearby based on physical
property.
The bird is not concerned about chemical composition and the nest it
makes could be described as a composite material.
TecEco cements are benign binders
that can incorporate all sort of wastes
without reaction problems. We can
do the same as the Jackdoor
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40
TecEco Technologies Take Concrete into the Future
 More rapid strength gain even with added
pozzolans
– More supplementary materials can be used reducing
costs and take and waste impacts.
 Easier to finish even with added pozzolans
Tec Cements
– The stickiness concretes with added fly ash is
retarding use
 Higher strength/binder ratio
 Less cement can be used reducing costs and
take and waste impacts
 More durable concretes
Tec & EcoCements
– Reducing costs and take and waste impacts.
 Use of wastes
 Utilizing carbon dioxide
 Magnesia component can be made using non
fossil fuel energy and CO2 captured during
production.
Eco-Cements
Contact:
John Harrison, TecEco Pty. Ltd. www.tececo.com
Presentation downloadable from www.tececo.com
41
Eco-Cements
 Eco-cements are similar but potentially superior to lime mortars
because:
– The calcination phase of the magnesium thermodynamic cycle takes
place at a much lower temperature and is therefore more efficient.
– Magnesium minerals are generally more fibrous and acicular than calcium
minerals and hence add microstructural strength.
 Water forms part of the binder minerals that forming making the
cement component go further. In terms of binder produced for
starting material in cement, eco-cements are much more
efficient.
 Magnesium hydroxide in particular and to some extent the
carbonates are less reactive and mobile and thus much more
durable.
Presentation downloadable from www.tececo.com
42
Eco-Cement Strength Development
 Eco-cements gain early strength from the hydration of
PC.
 Later strength comes from the carbonation of brucite
forming an amorphous phase, lansfordite and
nesquehonite.
 Strength gain in eco-cements is mainly microstructural
because of
– More ideal particle packing (Brucite particles at 4-5 micron are
under half the size of cement grains.)
– The natural fibrous and acicular shape of magnesium carbonate
minerals which tend to lock together.
 More binder is formed than with calcium
– Total volumetric expansion from magnesium oxide to lansfordite
From air and water
is for example volume 811%.
Mg(OH)2 + CO2  MgCO3.5H2O
Presentation downloadable from www.tececo.com
43
Eco-Cement Strength Gain Curve
HYPOTHETICAL STRENGTH
GAIN CURVE OVER TIME
(Pozzolans added)
MPa
?
OPC Concrete
?
Eco – Cement Concrete with
50% reactive magnesia
?
?
3
Plastic
Stage
7
14
28
Log Days
Eco-cement bricks, blocks, pavers and mortars etc. take a
while to come to the same or greater strength than OPC
formulations but are stronger than lime based formulations.
Presentation downloadable from www.tececo.com
44
Chemistry of Eco-Cements
 There are a number of carbonates of magnesium. The main ones
appear to be an amorphous phase, lansfordite and nesquehonite.
 The carbonation of magnesium hydroxide does not proceed as readily
as that of calcium hydroxide.
– Gor Brucite to nesquehonite = - 38.73 kJ.mol-1
– Compare to Gor Portlandite to calcite = -64.62 kJ.mol-1
 The dehydration of nesquehonite to form magnesite is not favoured by
simple thermodynamics but may occur in the long term under the right
conditions.
 Gor nesquehonite to magnesite = 8.56 kJ.mol-1
– But kinetically driven by desiccation during drying.
 Reactive magnesia can carbonate in dry conditions – so keep bags
sealed!
 For a full discussion of the thermodynamics see our technical
documents.
TecEco technical documents on the web
cover the important aspects of carbonation.
Presentation downloadable from www.tececo.com
45
Eco-Cement Reactions
In Eco - Cements
Magnesia
Amorphous Lansfordite
Brucite
Nesquehonite
MgO + nH2O  Mg(OH)2.nH2O + CO2  MgCO3.nH2O + MgCO3.5H2O + MgCO3.3H2O
Form: Massive-Sometimes Fibrous Often Fibrous Acicular - Needle-like
crystals
Hardness:
2.5 - 3.0
2.5
Solubility (mol.L-1): .00015
.01
.013 (but less in acids)
Compare to the Carbonation of Portlandite
Portlandite
Calcite
Aragonite
Ca(OH)2 + CO2  CaCO3
Form: Massive
Massive or crystalline
Hardness:
Solubility (mol.L-1):
More acicular
2.5
.024
3.5
.00014
Presentation downloadable from www.tececo.com
46
Eco-Cement Micro-Structural Strength
Presentation downloadable from www.tececo.com
47
Carbonation
 Eco-cement is based on blending reactive magnesium oxide with
other hydraulic cements and then allowing the Brucite and
Portlandite components to carbonate in porous materials such as
concretes blocks and mortars.
– Magnesium is a small lightweight atom and the carbonates that form contain
proportionally a lot of CO2 and water and are stronger because of superior
microstructure.
 The use of eco-cements for block manufacture, particularly in
conjunction with the kiln also invented by TecEco (The Tec-Kiln)
would result in sequestration on a massive scale.
 As Fred Pearce reported in New Scientist Magazine (Pearce, F.,
2002), “There is a way to make our city streets as green as the
Amazon rainforest”.
Ancient and modern carbonating lime
mortars are based on this principle
Presentation downloadable from www.tececo.com
48
Aggregate Requirements for Carbonation
 The requirements for totally hydraulic limes and all hydraulic
concretes is to minimise the amount of water for hydraulic
strength and maximise compaction and for this purpose
aggregates that require grading and relatively fine rounded
sands to minimise voids are required
 For carbonating eco-cements and lime mortars on the on the
hand the matrix must “breathe” i.e. they must be porous
– Requiring relative mono grading so that particle packing is imperfect
causing physical air voids and some vapour permeability.
Presentation downloadable from www.tececo.com
49
CO2 Abatement in Eco-Cements
For 85 wt%
Aggregates
15 wt%
Cement
Eco-cements in
porous products
absorb carbon
dioxide from the
atmosphere.
Brucite carbonates
forming lansfordite,
nesquehonite and
an amorphous
phase, completing
the thermodynamic
cycle.
Portland
Cements
15 mass%
Portland
cement, 85
mass%
aggregate
Emissions
.32 tonnes to
the tonne.
After
carbonation.
Approximately
.299 tonne to
the tonne.
No
Capture
11.25% mass%
reactive
magnesia, 3.75
mass% Portland
cement, 85
mass%
aggregate.
Emissions
.37 tonnes to
the tonne. After
carbonation.
approximately
.241 tonne to
the tonne.
Capture
CO2
11.25% mass%
reactive
magnesia, 3.75
mass% Portland
cement, 85
mass%
aggregate.
Emissions
.25 tonnes to the
tonne. After
carbonation.
approximately
.140 tonne to
the tonne.
Capture
CO2. Fly and
Bottom Ash
11.25% mass%
reactive magnesia,
3.75 mass%
Portland cement,
85 mass%
aggregate.
Emissions
.126 tonnes to the
tonne. After
carbonation.
Approximately .113
tonne to the tonne.
Greater Sustainability
.299 > .241 >.140 >.113
Bricks, blocks, pavers, mortars and pavement made using eco-cement, fly
and bottom ash (with capture of CO2 during manufacture of reactive
magnesia) have 2.65 times less emissions than if they were made with
Portland cement.
Presentation downloadable from www.tececo.com
50
TecEco Cement LCA
TecEco
Concretes
will have a
big role post
Kyoto as they
offer potential
sequestration
as well as
waste
utilisation
The TecEco LCA model is
available for download under
“tools” on the web site
Presentation downloadable from www.tececo.com
51
Tec-Cement Concretes - Lattice Energy Destroys a Myth
 Magnesia, provided it is reactive rather than “dead burned” (or
high density, crystalline periclase type), can be beneficially
added to cements in excess of the amount of 5 mass%
generally considered as the maximum allowable by standards
prevalent in concrete dogma.
– Reactive magnesia is essentially amorphous magnesia with low lattice
energy.
– It is produced at low temperatures and finely ground, and
– will completely hydrate in the same time order as the minerals contained
in most hydraulic cements.
 Dead burned magnesia and lime have high lattice energies
– Crystalline magnesium oxide or periclase has a calculated lattice energy
of 3795 Kj mol-1 which must be overcome for it to go into solution or for
reaction to occur.
– Dead burned magnesia is much less expansive than dead burned lime in
a hydraulic binder (Ramachandran V. S., Concrete Science, Heydon &
Son Ltd. 1981, p 358-360 )
Presentation downloadable from www.tececo.com
52
More Rapid Early Strength Development
 Concretes are more often than not made to strength.
 The use of tec-cement results in
– more rapid early strength development even with added
pozzolans.
– Straight line strength development for a long time
HYPOTHETICAL STRENGTH
GAIN CURVE OVER TIME
(Pozzolans added)
MPa
We have
observed
this sort of
curve in over
500 cubic
meters of
concrete
now
Tec – Cement Concrete with
10% reactive magnesia
OPC Concrete
3
Plastic
Stage
7
14
28
Log Days
Presentation downloadable from www.tececo.com
Early strength
gain with less
cement and
added
pozzolans is of
great
economic and
environmental
importance as
it will allow the
use of more
pozzolans.
53
Reasons for Compressive Strength Development in Tec-Cements.
 Kosmotropic nature of Mg++
 Reactive magnesia requires considerable water to hydrate resulting in:
– Denser, less permeable concrete. Self compaction?
– A significantly lower voids/paste ratio.
 Higher early pH initiating more effective silicification reactions?
– The Ca(OH)2 normally lost in bleed water is used internally for reaction with pozzolans.
– Super saturation of alkalis caused by the removal of water?
 Micro-structural strength due to particle packing (Magnesia particles at 45 micron are a little over ½ the size of cement grains.)
 Formation of MgAl hydrates? Similar to flash set in concrete but slower??
 Formation of MSH??
 Slow release of water from hydrated Mg(OH)2.nH2O supplying H2O for
more complete hydration of C2S and C3S?
Brucite gains weight in excess of the theoretical increase due to
MgO conversion to Mg(OH)2 in samples cured at 98% RH .
Dr Luc Vandepierre, Cambridge University, 20 September, 2005.
Presentation downloadable from www.tececo.com
54
+
+
+ +
+ Cement + +
MgO
+
+ + +
+
Mutual Repulsion
=>
+
Ph
12 ?
+ + +
Sand +
+
+
+ +
Mutual Repulsion
+ +
+ - +
+
Cement + MgO Sand
+
+
+
- + +
+
+
Mutual Attraction
STRENGTH (MPa)
Greater Tensile Strength
6
5
4
3
OPC(100%)
2
OPC(90%)+ MgO(10%)
1
0
0
2
4
6
8 10 12 14 16 18 20 22 24 26 28 30
CURING TIME (days)
MgO Changes Surface Charge as the Ph Rises.
This could be one of the reasons for rapid gelling and
greater tensile strength displayed during the early plastic
phase of tec-cement concretes. The affect of additives is
not yet known
Presentation downloadable from www.tececo.com
55
Non Newtonian Rheology – Rapid Gelling
It is not
known
how
deep
these +
layers
+
get
Etc.
+
O
+
+
O
-
+
O
O +
O - +
+
+
+
O
- Mg++
O
+
+
Etc.
-
-
O
+
+
+
The strongly
positively charged
small kosmotropic
Mg++ atoms attract
water (which is
polar) in deep layers
introduce a shear
thinning property
affecting the
rheological
properties and
making concretes
less “sticky” with
added pozzolan
Ca++ = 114, Mg++ = 86 picometres
Presentation downloadable from www.tececo.com
56
Durability
 Concretes are said to be less durable when they are physically or
chemically compromised.
 Physical factors can result in chemical reactions reducing
durability
– E.g. Cracking due to shrinkage can allow reactive gases and liquids to
enter the concrete
 Chemical factors can result in physical outcomes reducing
durability
– E.g. Alkali silica reaction opening up cracks allowing other agents such as
sulfate and chloride in seawater to enter.
 This presentation will describe benchmark improvements in
durability as a result of using the new TecEco magnesia cement
technologies
Presentation downloadable from www.tececo.com
57
Crack Collage
Thermal
Freeze Thaw
D Cracks
Alkali aggregate
Reaction
Evaporative
Crazing
Shrinkage
Settlement
Shrinkage
Structural
Plastic
Shrinkage
Corrosion Related
Drying
Shrinkage
Photos from PCA and
US Dept. Ag Websites
Autogenous or self-desiccation shrinkage
(usually related to stoichiometric or chemical shrinkage)
 TecEco technology can reduce if not solve problems of cracking:
–
–
–
–
Related to (shrinkage) through open system loss of water.
As a result of volume change caused by delayed reactions
As a result of corrosion.
Related to autogenous shrinkage
Presentation downloadable from www.tececo.com
58
Causes of Cracking in Concrete
 Cracking commonly occurs when the induced stress exceeds the
maximum tensile stress capacity of concrete and can be caused
by many factors including restraint, extrinsic loads, lack of
support, poor design, volume changes over time, temperature
dependent volume change, corrosion or delayed reactions.
 Causes of induced stresses include:
– Restrained thermal, plastic, drying and stoichiometric shrinkage, corrosion
and delayed reaction strains.
– Slab curling.
– Loading on concrete structures.
 Cracking is undesirable for many reasons
– Visible cracking is unsightly
– Cracking compromises durability because it allows entry of gases and ions
that react with Portlandite.
– Cracking can compromise structural integrity, particularly if it accelerates
corrosion.
Presentation downloadable from www.tececo.com
59
Graphic Illustration of Cracking
Combined Effect of Concrete Volume Change (Example Only)
200
150
Max Tensile Strain
Temperature effect
100
Drying Shrinkage
Autogenous Shrinkage
Total Srain Induced
50
Total Strain Less Creep
0
Tim e since Cast (Hrs)
120
108
96
84
72
60
48
36
24
12
-50
0
Shrinkage/(Expansion) Microstrain
250
Autogenous
shrinkage has
been used to refer
to hydration
shrinkage and is
thus stoichiometric
After Tony Thomas (Boral Ltd.) (Thomas 2005)
Presentation downloadable from www.tececo.com
60
Cracking due to Loss of Water
Brucite gains
weight in excess
of the theoretical
increase due to
MgO conversion
to Mg(OH)2 in
samples cured at
98% RH.
Dr Luc
Vandepierre,
Cambridge
University, 20
September,
2005.
Fool
Drying
Shrinkage
Plastic
Shrinkage
Bucket of Water
Evaporative
Crazing
Shrinkage
Settlement
Shrinkage
Picture from: http://www.pavement.com/techserv/ACI-GlobalWarming.PDF
We may not be able to prevent too much water being added to concrete by fools.
TecEco approach the problem in a different way by providing for the internal
removal/storage of water that can provide for more complete hydration of PC.
Presentation downloadable from www.tececo.com
61
Solving Cracking due to Shrinkage from Loss of Water
 In the system water plus Portland cement powder plus
aggregates shrinkage is in the order of .05 – 1.5 %.
 Shrinkage causes cracking
 There are two main causes of Portland cements
shrinking over time.
– Stoichiometric (chemical) shrinkage and
– Shrinkage through loss
of water.
 The solution is to:
– Add minerals that compensate by stoichiometrically expanding
and/or to
– Use less water, internally hold water or prevent water loss.
 TecEco tec-cements internally hold water and prevent
water loss.
 The kosmotropic nature of Mg++ makes water more
viscous without shear.
MgO (s) + H2O (l) ↔ Mg(OH)2.nH2O (s)
Presentation downloadable from www.tececo.com
62
Preventing Shrinkage through Loss of Water
 When magnesia hydrates it consumes 18 litres of water per mole of
magnesia probably more depending on the value of n in the reaction below:
MgO (s) + H2O (l) ↔ Mg(OH)2.nH2O (s)
 The dimensional change in the system MgO + PC depends on:
–
–
–
The ratio of MgO to PC
Whether water required for hydration of PC and MgO is coming from stoichiometric mix
water (i.e. the amount calculated as required), excess water (bleed or evaporative) or
from outside the system.
In practice tec-cement systems are more closed and thus dimensional change is more a
function of the ratio of MgO to PC
 As a result of preventing the loss of water by closing the system together
with expansive stoichiometry of MgO reactions (see below).
MgO (s) + H2O (l) ↔ Mg(OH)2.nH2O (s)
40.31 + 18.0 ↔ 58.3 molar mass (at least!)
11.2 + liquid ↔ 24.3 molar volumes (at least!)
 It is possible to significantly reduce if not prevent (drying, plastic,
evaporative and some settlement) shrinkage as a result of water losses
from the system.
The molar volume (L.mol-1)is equal to the molar
mass (g.mol-1) divided by the density (g.L-1).
Presentation downloadable from www.tececo.com
63
Preventing Shrinkage through Loss of Water
 Portland cements stoichiometrically require around 23 -27% water
for hydration yet we add approximately 45 to 60% at cement
batching plants to fluidise the mix sufficiently for placement.
 If it were not for the enormous consumption of water by tri calcium
aluminate as it hydrates forming ettringite in the presence of
gypsum, concrete would remain as a weak mush and probably
never set.
– 26 moles of water are consumed per mole of tri calcium aluminate to from a
mole of solid ettringite. When the ettringite later reacts with remaining tri
calcium aluminate to form monosulfoaluminate hydrate a further 4 moles of
water are consumed.
 The addition of reactive MgO achieves water removal internally in
a closed system in a similar way.
MgO (s) + H2O (l) ↔ Mg(OH)2.nH2O (s)
Presentation downloadable from www.tececo.com
64
Other Benefits of Preventing Shrinkage through Loss of
Water
 Internal water consumption and prevention of loss
also results in:
– Greater strength
• More complete hydration of PC .
• Reduced in situ voids:paste ratio
– Greater density
• Increased durability
• Higher short term alkalinity
• More effective pozzolanic reactions.
 More complete hydration of PC .
– Small substitutions of PC by MgO result in water being trapped
inside concrete as Brucite and Brucite hydrates which can later self
desiccate delivering water to hydration reactions of calcium
silicates (Preventing so called “Autogenous” shrinkage).
Presentation downloadable from www.tececo.com
65
Bleeding is a Bad Thing
 Bleeding is caused by:
– Lack of fines
– Too much water
Better to keep concretes
as closed systems
 Bleeding can be fixed by:
– Reducing water or adding fines
– Air entrainment or grading adjustments
– Adding kosmotropic ions like Mg++
 Bleeding causes:
–
–
–
–
–
–
–
–
Reduced pumpability
Loss of cement near the surface of concretes
Delays in finishing
Poor bond between layers of concrete
Interconnected pore structures that allow aggressive agents to enter later
Slump and plastic cracking due to loss of volume from the system
Loss of alkali that should remain in the system for better pozzolanic reactions
Loss of pollutants such as heavy metals if wastes are being incorporated.
 Concrete is better as a closed system
Presentation downloadable from www.tececo.com
66
Dimensional Control in Tec-Cement Concretes over Time
 By adding MgO volume changes are
minimised to close to neutral.
– So far we have observed significantly less shrinkage in
TecEco Tec - Cement concretes with about (8-10%
substitution OPC) with or without fly ash.
– At some ratio, thought to be around 15-18% reactive
magnesia there is no shrinkage.
– The water lost by concrete as it shrinks is used by the
reactive magnesia as it hydrates eliminating shrinkage.
 Note that brucite is > 44.65 mass% water and
it makes sense to make binders out of water!
 More research is required to accurately
establish volume relationships and causes for
reduced shrinkage.
Presentation downloadable from www.tececo.com
67
Reducing Cracking as a Result of Volume
Change caused by Delayed Reactions
An Alkali Aggregate Reaction Cracked Bridge Element
Photo Courtesy Ahmad Shayan ARRB
Presentation downloadable from www.tececo.com
68
Types of Delayed Reactions
 There are several types of delayed reactions that
cause volume changes (generally expansion) and
cracking.
–
–
–
–
–
Alkali silica reactions
Alkali carbonate reactions
Delayed ettringite formation
Delayed thaumasite formation
Delayed hydration or dead burned lime or periclase.
 Delayed reactions cause dimensional distress,
cracking and possibly even failure.
Presentation downloadable from www.tececo.com
69
Reducing Delayed Reactions
 Delayed reactions do not appear to occur to the
same extent in TecEco cements.
– A lower long term pH results in reduced reactivity after the
plastic stage.
– Potentially reactive ions are trapped in the structure of
brucite.
– Ordinary Portland cement concretes can take years to dry
out however the reactive magnesia in Tec-cement concretes
consumes unbound water from the pores inside concrete.
– Magnesia dries concrete out from the inside. Reactions do
not occur without water.
Presentation downloadable from www.tececo.com
70
Reduced Steel Corrosion Related Cracking
Rusting Causes Dimensional Distress
 Steel remains protected with a passive oxide coating of
Fe3O4 above pH 8.9.
 A pH of over 8.9 is maintained by the equilibrium
Mg(OH)2 ↔ Mg++ + 2OH- for much longer than the pH
maintained by Ca(OH)2 because:
– Brucite does not react as readily as Portlandite resulting in
reduced carbonation rates and reactions with salts.
 Concrete with brucite in it is denser and carbonation is
expansive, sealing the surface preventing further
access by moisture, CO2 and salts.
Presentation downloadable from www.tececo.com
71
Reduced Steel Corrosion
 Brucite is less soluble and traps salts as it forms resulting
in less ionic transport to complete a circuit for electrolysis
and less corrosion.
 Free chlorides and sulfates originally in cement and
aggregates are bound by magnesium
– Magnesium oxychlorides or oxysulfates are formed. ( Compatible
phases in hydraulic binders that are stable provided the concrete is
dense and water kept out.)
 As a result of the above the rusting of reinforcement does
not proceed to the same extent.
 Cracking or spalling due to rust does not occur
Presentation downloadable from www.tececo.com
72
Long Term pH control
 Important if you wish to also add wastes
 TecEco add reactive magnesia which hydrates forming
brucite which is another alkali, but much less soluble,
mobile or reactive than Portlandite.
 Brucite provides long term pH control.
Tec-Cement (red) - more affective
pozzolanic reactions
Surface hydrolysis and more polymeric species?
pH
13.7
11.2
10.5
HYPOTHETICAL pH CURVES
OVER TIME (with fly ash)
?
Tec – Cement Concrete with 10% reactive
?
? magnesia (red). Ph maintained by brucite
OPC Concrete
OPC Concrete – Lower long term pH due
to consumption of lime and carbonation
Log Time
Plastic
Stage
Presentation downloadable from www.tececo.com
A pH in
the
range
10.5 –
11.2 is
ideal in a
concrete
73
Steel Corrosion is Influenced by Long Term pH
In TecEco cements the long
term pH is governed by the low
solubility and carbonation rate
of brucite and is much lower at
around 10.5 -11, allowing a
wider range of aggregates to
be used, reducing problems
such as AAR and etching. The
pH is still high enough to keep
Fe3O4 stable in reducing
conditions.
Eh-pH or Pourbaix Diagram
The stability fields of hematite,
magnetite and siderite
in aqueous solution; total
dissolved carbonate = 10-2M.
Steel corrodes below 8.9
Equilibrium pH of Brucite and of lime
Presentation downloadable from www.tececo.com
74
Reducing Cracking Related to Autogenous Shrinkage
 Autogenous shrinkage tends to occur in high
performance concretes in which dense
microstructures develop quickly preventing the entry
of additional water required to complete hydration.
– First defined by Lynam in 1934 (Lynam CG. Growth and movement in
Portland cement concrete. London: Oxford University Press; 1934. p. 26-7.)
 The autogenous deformation of concrete is defined as
the unrestrained, bulk deformation that occurs when
concrete is kept sealed and at a constant temperature.
Presentation downloadable from www.tececo.com
75
Reducing Cracking Related to Autogenous Shrinkage
 Main cause is stoichiometric or chemical shrinkage as
observed by Le Chatelier.
– whereby the reaction products formed during the hydration of
cement occupy less space than the corresponding reactants.
 A dense cement paste hydrating under sealed
conditions will therefore self-desiccate creating empty
pores within developing structure. If external water is
not available to fill these “empty” pores, considerable
shrinkage can result.
Le Chatelier H. Sur les changements de volume qui accompagnent
Ie durcissement des ciments. Bulletin de la Societe
d'Encouragement pour I'Industrie Nationale 1900:54-7.
Presentation downloadable from www.tececo.com
76
Reducing Cracking Related to Autogenous Shrinkage
 Autogenous shrinkage does not occur in high strength TecCement concretes because:
– The brucite hydrates that form desiccate back to brucite delivering water in
situ for more complete hydration of Portland cement.
Mg(OH)2.nH2O (s) ↔ MgO (s) + H2O (l)
• As brucite is a relatively weak mineral compressed and densifies the
microstructure.
– The stoichiometric shrinkage of Portland cement (first observed by Le
Chatelier) is compensated for by the stoichiometric expansion of magnesium
oxide on hydration.
MgO (s) + H2O (l) ↔ Mg(OH)2.nH2O (s)
40.31 + 18.0 ↔ 58.3 molar mass (at least!)
11.2 + liquid ↔ 24.3 molar volumes (at least 116% expansion,
probably more initially before desiccation as above!)
Presentation downloadable from www.tececo.com
77
Improved Durability
Materials that last longer need
replacing less often saving on
energy and resources.
 Reasons for Improved Durability:
– Greater Density? = Lower Permeability
• Physical Weaknesses => Chemical Attack
– Removal of Portlandite with the Pozzolanic Reaction.
• Removal or reactive components
– Substitution by Brucite => Long Term pH control
• Reducing corrosion
Presentation downloadable from www.tececo.com
78
Reduced Permeability
 As bleed water exits ordinary Portland
cement concretes it creates an
interconnected pore structure that remains
in concrete allowing the entry of aggressive
agents such as SO4--, Cl- and CO2
 TecEco tec - cement concretes are a closed
system. They do not bleed as excess water is
consumed by the hydration of magnesia.
– As a result TecEco tec - cement concretes dry
from within, are denser and less permeable and
therefore stronger more durable and less
permeable. Cement powder is not lost near the
surfaces. Tec-cements have a higher salt
resistance and less corrosion of steel etc.
Presentation downloadable from www.tececo.com
79
Greater Density – Lower Permeability
 Concretes have a high percentage (around 18% – 22%) of
voids.
 On hydration magnesia expands >=116.9 % filling voids and
surrounding hydrating cement grains => denser concrete.
 On carbonation to nesquehonite brucite expands 307%
sealing the surface.
 Lower voids:paste ratios than water:binder ratios result in
little or no bleed water, lower permeability and greater
density.
Presentation downloadable from www.tececo.com
80
Densification During the Plastic Phase
Observable
Characteristic
Water
Binder +
supplemen
tary
cementitio
us
materials
High water
for ease of
placement
Consumption
of water during
plastic stage
Variables such as %
hydration of mineral,
density, compaction,
% mineral H20 etc.
Log time
Relevant
Fundamental
Voids
Hydrated
Binder
Materials
Unhydrated
Binder
Less water
for strength
and durability
Water is required to
plasticise concrete
for placement,
however once
placed, the less
water over the
amount required for
hydration the better.
Magnesia consumes
water as it hydrates
producing solid
material.
Less water results in increased density and concentration of alkalis less shrinkage and cracking and improved strength and durability.
Presentation downloadable from www.tececo.com
81
Durability - Reduced Salt & Acid Attack
 Brucite has always played a protective role during salt
attack. Putting it in the matrix of concretes in the first place
makes sense.
 Brucite does not react with salts because it is a least 5
orders of magnitude less soluble, mobile or reactive.
– Ksp brucite = 1.8 X 10-11
– Ksp Portlandite = 5.5 X 10-6
 TecEco cements are more acid resistant than Portland
cement
– This is because of the relatively high acid resistance (?) of
Lansfordite and nesquehonite compared to calcite or aragonite
Presentation downloadable from www.tececo.com
82
Less Freeze - Thaw Problems
 Denser concretes do not let water in.
 Brucite will to a certain extent take up internal stresses
 When magnesia hydrates it expands into the pores left
around hydrating cement grains:
MgO (s) + H2O (l) ↔ Mg(OH)2 (s)
40.31 + 18.0 ↔ 58.3 molar mass
11.2 + 18.0 ↔ 24.3 molar volumes
39.20 ↔ 24.3 molar volumes
At least 38% air voids are created in space that was occupied
by magnesia and water!
 Air entrainment can also be used as in conventional
concretes
 TecEco concretes are not attacked by the salts used on
roads
Presentation downloadable from www.tececo.com
83
Rosendale Concretes – Proof of Durability



Rosendale cements contained 14 – 30% MgO
A major structure built with Rosendale cements commenced in 1846 was Fort Jefferson near
key west in Florida.
Rosendale cements were recognized for their exceptional durability, even under severe
exposure. At Fort Jefferson much of the 150 year-old Rosendale cement mortar remains in
excellent condition, in spite of the severe ocean exposure and over 100 years of neglect. Fort
Jefferson is nearly a half mile in circumference and has a total lack of expansion joints, yet
shows no signs of cracking or stress. The first phase of a major restoration is currently in
progress.
More information from http://www.rosendalecement.net/rosendale_natural_cement_.html
Presentation downloadable from www.tececo.com
84
Solving Waste & Logistics Problems
 TecEco cementitious composites represent a cost affective option
for
– using non traditional aggregates from on site reducing transports costs and
emissions
– use and immobilisation of waste.
 Because they have
– lower reactivity
• less water
• lower pH
– Reduced solubility of heavy metals
• less mobile salts
– greater durability.
• denser.
• impermeable (tec-cements).
• dimensionally more stable with less shrinkage and cracking.
– homogenous.
– no bleed water.
TecEco Technology - Converting Waste to Resource
Presentation downloadable from www.tececo.com
85
Role of Brucite in Immobilization
 In a Portland cement Brucite matrix
– PC derive CSH takes up lead, some zinc and germanium
– Pozzolanic CSH can take up mobile cations
– Brucite and hydrotalcite are both excellent hosts for toxic and
hazardous wastes.
– Heavy metals not taken up in the structure of Portland cement
minerals or trapped within the brucite layers end up as hydroxides
with minimal solubility.
Layers of
electronically
neutral brucite
suitable for
trapping
balanced
cations and
anions as well
as other
substances.
Van de
waals
bonding
holding the
layers
together.
Salts and
other
substances
trapped
between
the layers.
The Brucite in TecEco cements
has a structure comprising
electronically neutral layers and
is able to accommodate a wide
variety of extraneous
substances between the layers
and cations of similar size
substituting for magnesium
within the layers and is known
to be very suitable for toxic and
hazardous waste
immobilisation.
Presentation downloadable from www.tececo.com
86
Concentration of Dissolved Metal, (mg/L)
Lower Solubility of Metal Hydroxides
There is a 104 difference
10
Pb(OH)
2
Cr(OH) 3
Zn(OH) 2
10 0
Ag(OH)
Cu(OH) 2
Ni(OH) 2
Cd(OH) 2
10 -2
Equilibrium pH of brucite
is 10.52 (more ideal)*
10 -4
10 -6
6
7
8
9
10
Equilibrium pH of PC
CSH is 11.2
11
12
13
*Equilibrium
pH’s in pure
water, no
other ions
present. The
solubility of
toxic metal
hydroxides is
generally less
in the range
pH 10.52 11.2 than at
higher pH’s.
14
Equilibrium pH of
Portlandite is 12.35
All waste streams will contain heavy metals and a
strategy for long term pH control is therefore essential
Presentation downloadable from www.tececo.com
87
Using Wastes and Non-Traditional Aggregates to Make
TecEco Cement Concretes
 Many wastes and local materials can contribute physical
property values.
– Plastics for example are collectively light in weight, have tensile
strength and low conductance.
 Tec, eco and enviro-cements will allow a wide range of
wastes and non-traditional aggregates such as local materials
to be used.
 Tec, enviro and eco-cements are benign binders that are:
– low alkali reducing reaction problems with organic materials.
– stick well to most included wastes
 Tec, enviro and eco-cements can utilize wastes including
carbon to increase sequestration preventing their conversion
to methane
 There are huge volumes of concrete produced annually
(>2 tonnes per person per year)
Presentation downloadable from www.tececo.com
88
Sustainable Materials in the Built Environment - 2007
Technical Focus
Sustainable Materials in the Built
Environment
2007
Innovation - Process – Design
Announcement and Call for Papers
18th to 20th February 2007
Melbourne, Australia
www.materialsaustralia.com.au/SMB2007
This Conference will focus on:
 The impacts and connectivity
of different parts of the supply
chain.
 Fabrication, performance,
recycling and waste
 New developments in
materials and processes
 Reviewing existing materials
assessment tools
 Future directions in regulation
 Opportunities/barriers to
introduction of sustainable
materials and technologies in
the building industry.
 New materials and more
sustainable built
environments: the evidence?
Joint Venture Websites
ASSMIC Website: www.aasmic.org
Materials Australia Website: www.materialsaustralia.com.au
Presentation downloadable from www.tececo.com
89