Www.tececo.com 1 New Materials Based on the Addition of Reactive Magnesia to Hydraulic Cements. All...

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New Materials Based on the Addition of Reactive Magnesia to Hydraulic Cements.

New Materials Based on the Addition of Reactive Magnesia to Hydraulic Cements.

All I ask is that the industry think about what I am saying.

John Harrison B.Sc. B.Ec. FCPA.

Hobart, Tasmania, Australia

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Materials - the Key to SustainabilityMaterials - the Key to Sustainability

The choice of materials controls emissions, lifetime and embodied energies, maintenance of utility, recyclability and the properties of wastes returned to the biosphere.

BIOSPHERE

Materials are the link between the biosphere and technosphere and the key to sustainabillity

TECHNOSPHERE

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The Construction IndustryThe Construction Industry

The built environment is our footprint on earth. TecEco estimate that building materials comprise some

70% of materials flows. Calcined minerals and their derivatives are the main

materials used to construct the built environment.– Globally around 2 billion tonnes of calcined minerals (cement,

lime and magnesia) are produced annually.– Portland cement is made by calcining limestone with clay and

concrete made with it is the most widely used material on Earth.

– Global Portland cement production is in the order of 1.7 billion tonnes. The largest producers of Portland cement are China at over 500 million tonnes followed by India at over 110 million tonnes. Globally this amounts to over 6 cubic kilometres of concrete per year.

Downloaded from www.dbce.csiro.au/ind-serv/brochures/embodied/embodied.htm (last accessed 07 March 2000)

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Embodied Energy of Building MaterialsEmbodied Energy of Building Materials


Concrete has a relatively low embodied energy

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Embodied Energy in BuildingsEmbodied Energy in Buildings


But because so much is used there is a huge opportunity for sustainability

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Sustainability = High PerformanceSustainability = High Performance Sustainability is not just about reducing emissions. Other properties of concrete such as the amount of cement

required for a given strength, durability, embodied energy, insulating capacity, weight etc. are also relevant.

Concretes should not be thought of as just cement and aggregate. They will become a composite material with a range of tailored properties offering vastly improved overall performance as well as meeting specific performance criteria such as strength.

As an ideal building material concrete should include other properties not usually provided such as insulating capacity and the ability to utilise wastes.– All sorts of other materials such as industrial mineral wastes, sawdust,

wood fibres, waste plastics etc. could be added for the properties they impart.

– More attention paid to the micro engineering of the material as well as the chemistry would result in improved properties.

Concretes can cost affectively be everything we would like them to be!

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EmissionsEmissions Calcined mineral materials and their derivatives used in

construction such as Portland cement, lime and magnesia are made from carbonates.

The process of calcination involves driving off chemically bound CO2 with heat.

MCO3 →MO + CO2 ∆

Heating requires energy. 98% of the world’s energy is derived from fossil fuels. Fuel oil, coal and natural gas are mainly directly or indirectly burned to produce the energy required for calcining of metal carbonates releasing CO2.

Most of the embodied energy in the built environment is in concrete.

The production of cement for concretes accounts for around 10% of global anthropogenic CO2.

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Opportunities for SustainabilityOpportunities for Sustainability The CO2 released by chemical reaction from the

calcined materials in TecEco Eco-cement concretes can be captured during manufacture and reabsorbed on a widely distributed basis in eco-cements.

A system using TecEco Eco-Cements to construct the built environment therefore offers enormous opportunities for sequestration, particularly if combined with mineral sequestration utilising magnesium silicates in a combined process.

Other TecEco cements are also much more sustainable but for different reasons that include durability and the use of less cement to make more material.

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Talked about– Rheology

• Workability, time for and method of placing and finishing

– Shrinkage• Cracking, crack control

– Durability and Performance• Permeability and Density• Sulphate and chloride resistance• Carbonation• Corrosion of steel and other reinforcing• Delayed reactions (eg alkali aggregate

and delayed ettringite)

– Bonding to brick and tiles – Efflorescence

Rarely discussed– Sustainability issues

• Emissions and embodied energies

Should the discussion be more about how we could fix the material, overcoming rather than tolerating and mitigating these problems?

Issues with OPC ConcreteIssues with OPC Concrete

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Engineering Issues are Mineralogical IssuesEngineering Issues are Mineralogical Issues

Problems with Portland cement concretes are usually resolved by the “band aid” application of engineering fixes. They are rarely discussed in terms of the mineralogy. e.g.– Use of calcium nitrite, silanes, cathodic protection or stainless steel to

prevent corrosion.– Use of coatings to prevent carbonation.– Crack control joins to mitigate the affects of shrinkage cracking.– Plasticisers to improve workability, glycols to improve finishing.

Many of the problems with Portland cement are better fixed by fundamentally fixing the mineralogy!

The flaw in the mineralogy of Portland cement concretes is the presence of Portlandite which is too soluble, mobile and reactive.

The TecEco technology is not a “band aid”, it is a fundamental fix.

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TecEco Technology - Simple Yet Ingenious?TecEco Technology - Simple Yet Ingenious?

The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them. -- Sir William Bragg

The TecEco technology demonstrates that magnesia, provided it is reactive rather than “dead burned” (or high density, periclase type), can be beneficially added to cements in excess of the amount of 5 mass% generally considered as the maximum allowable by standards

Reactive magnesia is essentially amorphous magnesia produced at low temperatures and finely ground.

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SUSTAINABILITY

DURABILITY STRENGTH TECECO CEMENTS

Hydration of the various components of Portland cement for strength

Reaction of alkali with pozzolans (e.g. lime with fly ash.) for sustainability, durability and strength

Hydration of magnesia → brucite. Carbonation of brucite → hydromagnesite and magnesite for plasticity, durability and sustainability.

PORTLAND POZZOLAN

MAGNESIA

TecEco Concretes – A Blending SystemTecEco Concretes – A Blending System

TecEco concretes are a system of blending reactive magnesia, Portland cement and usually a pozzolan with other materials.

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Reactivity Overcomes Delayed Hydration Problems.Reactivity Overcomes Delayed Hydration Problems. Delayed hydration leads to dimensional distress.

– Magnesium was banned in Portland cements because when it goes through the high temperature process of making Portland cement it becomes periclase. It is “dead burned”, hydrates slowly and causes dimensional distress.

– Dead burned lime is much more expansive than dead burned magnesia(1), a problem largely forgotten by cement chemists.

TecEco have demonstrated that highly amorphous reactive magnesia can beneficially be added to concrete formulations– The reactivity of magnesia is a function of the state of disorder (lattice energy),

specific surface area and glass forming impurities.• The state of order or disorder is expressed in lattice energy and is dependent on the

temperature of calcining.• Specific surface area relates particle size. Make a particle small enough and it will

react with just about anything.• Glass forming impurities are formed when reactive magnesia reacts at high

temperatures with impurities such as iron. A new TecEco kiln technology which combines calcining and grinding

should make it possible to calcine at lower temperatures and produce more reactive magnesia with reduced problems due to impurities as well as capture CO2.– (1) Ramachandran V. S., Concrete Science, Heydon & Son Ltd. 1981,

p 358-360.

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Why Replace Portlandite with Brucite?Why Replace Portlandite with Brucite? Portlandite (Ca(OH)2) is not a suitable concrete matrix mineral. Ca(OH)2 is reactive, carbonates readily and being soluble can

act as an electrolyte. TecEco remove Portlandite in reactions with Pozzolans.

Brucite is much less soluble, mobile or reactive, does not act as an electrolyte or carbonate as readily.

The addition of magnesia which hydrates forming brucite improves the rheology, uses up bleed water as it hydrates, filling in the pores, increasing the density, reducing permeability, reducing shrinkage and providing long term pH control with many consequences including greater durability.

In porous eco-cements brucite carbonates forming stronger minerals.

The consequences of removing Portlandite (lime) with the pozzolanic reaction and filling the voids between hydrating cement grains with brucite, an insoluble alkaline mineral, need to be considered.

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Portlandite Compared to BrucitePortlandite Compared to BruciteProperty 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

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TecEco FormulationsTecEco Formulations Three main formulation strategies so far:

– Tec-cements (e.g. 10% MgO, 90% OPC.)• 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 without reaction problems.

– Enviro-cements (e.g. 25-75% MgO, 25-75% OPC)• In non porous concretes brucite does not carbonate readily.

– High proportions of magnesia are most suited to toxic and hazardous waste immobilisation and when durability is required. Strength is not developed quickly.

– Eco-cements (egg 50-75% MgO, 50-25% OPC)• Contain more reactive magnesia than in tec-cements.• Brucite in porous materials carbonates

– Forming stronger fibrous mineral carbonates.– Presenting huge opportunities for abatement.

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TecEco Formulations (2)TecEco Formulations (2)

OPC

Fly ash & other pozzolans Magnesia

Tec-cement

Eco-cement

Enviro-cement

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Porosity and Magnesia ContentPorosity and Magnesia Content

Note that TecEco eco-cements require a porous environment.

I n c r e a s in g D e n s i t y

I n c r e a s in g P o r o s i t y

Increasing Portlandi ceemnt

Increasing Magnesia

E c o – c e m e n t s f o r b r i c k s , b l o c k s p a v e r s m o r t a r s , r e n d e r s , t i l e c e m e n t s , g u n n i t e s a n d s h o t c r e t e s .

E n v i r o - c e m e n t s f o r t o x i c a n d h a z a r d o u s w a s t e i m m o b i l i s a t i o n & C L S M ’ s

E c o – c e m e n t s f o r p o r o u s p a v e m e n t s

T e c – c e m e n t s ( r e a d y m i x c o n c r e t e s e t c )

T e c – c e m e n t s f o r p o r o u s p a v e m e n t s

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Basic Chemical ReactionsBasic Chemical Reactions

Notice the low solubility of brucite compared to Portlandite and that magnesite is stronger and adopts a more ideal habit than calcite & aragonite

Magnesia Brucite

MgO + H2O Mg(OH)2

Hardness: 2.5 - 3.0 4.0 3.5

Form: Massive-Sometimes Fibrous Often Fibrous Acicular - Needle-like crystals

Solubility (mol.L-1): .00015 .0013 .0011

Silicates and aluminosilicates

Magnesia Brucite Magnesite Hydromagnesite

MgO + H2O Mg(OH)2 + CO2 MgCO3 + Mg(OH)2.4MgO.4CO2.4H2O

In Eco - Cements

In TecEco Modified Portland Cements

Hardness: 2.5-3.00 3.0

Form: Massive Massive or crystalline More acicular

Solubility (mol.L-1): .024 .00014

Portlandite Calcite

Ca(OH)2 + CO2 CaCO3

Compare to Portlandite

Aragonite

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Greater StrengthGreater Strength Tec-cements can be made with at least 25% less

binder for the same strength. Possible reasons for

– Low binder/total solids ratio– More rapid strength development even with pozzolans

• Reactive magnesia is an excellent plasticiser and results in:– Denser, less permeable concrete.– 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 caused by the removal of water by magnesia as it

hydrates.

Concrete technologists are obsessed by strength. They should be more interested in durability!

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Rapid Water ReductionRapid Water Reduction

Water

Binder + supplementary cementitious materials

Log time

Primary Observation

Relevant Fundamental

Voids

Paste

Binder + supplementary cementitious materials

Paste

High water for ease of placement

Less water for strength and durability

Variables such as % hydration of mineral, density, compaction, % mineral H20 etc.

Consumption of water during plastic stage

Water is required to plasticise concrete for placement, however once placed, the less water over the amount required for hydration the better. Magnesia rapidly removes water as it hydrates.

Less water results in less shrinkage and cracking and improved durability. Concentration of alkalis and increased density result in greater strength.

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Concretes have a high percentage of voids. On hydration magnesia expands 116.9 % filling voids

and surrounding hydrating cement grains. Brucite is 44.65 mass% water. Lower voids:paste ratios than water:binder ratios

result in less bleed water and greater density. Greater density results in greater strength, more

durable concrete with a higher salt resistance and less corrosion of steel etc.

Self compaction of brucite may add to strength.– Compacted brucite is as strong as CSH (Ramachandran,

Concrete Science p 358)

Durability & Strength - Increased DensityDurability & Strength - Increased Density

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Hypothetical Tec-Cement pH CurvesHypothetical Tec-Cement pH Curves

13.7

pH

Log Time

10.5 Tec – Cement Concrete with 10% reactive magnesia

OPC Concrete

HYPOTHETICAL pH CURVES OVER TIME

Plastic Stage

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Hypothetical Tec-Cement Concrete Strength Development CurveHypothetical Tec-Cement Concrete Strength Development Curve

The possibility of high early strength gain with added pozzolans is of great economic importance.

Tec – Cement Concrete with 10% reactive magnesia

OPC Concrete

HYPOTHETICAL STRENGTH GAIN CURVE OVER TIME (Pozzolans added)

Mpa

Log Days Plastic Stage

?

?

?

?

7 14 28

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Durability - A Lower More Stable Long Term pHDurability - A Lower More Stable Long Term pH

Eh-pH or Pourbaix Diagram The stability fields of hematite, magnetite and sideritein aqueous solution; total dissolved carbonate = 10-2M.

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 Fe2O3 and Fe3O4 stable in reducing conditions.

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The Passive Coating of Iron Oxide The Passive Coating of Iron Oxide

The passive coating on steel is iron oxide. According to the Pourbaix diagram it is magnesite but some authors such as Neville report the oxide is γFe3O(1).

One of the problems associated with examining iron oxides is that they change rapidly from one form to another and are therefore difficult to characterise(2).

The author would be interested in definitive information of any papers on this subject!

(1) Neville, A. M. Properties of Concrete, 4th Ed. Pearson Prentice Hall, England, 2003, page 563.

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Durability – Reduced Delayed ReactionsDurability – Reduced Delayed Reactions

A wide range of delayed reactions can occur in Portland cement based concretes– Delayed alkali silica and alkali carbonate reactions– The delayed formation of ettringite and thaumasite– Delayed hydration of minerals such as dead

burned lime and magnesia.Delayed reactions cause dimensional

distress and possible failure.

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Durability – Reduced Delayed Reactions (2)Durability – Reduced Delayed Reactions (2)

Delayed reactions do no 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 Tec-cement concretes are dried out from the inside by the water demand of reactive magnesia as it hydrates.

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Durability – CarbonationDurability – Carbonation Carbonates are the stable phases of both calcium and

magnesium. Carbonates lower the pH of concretes compromising the

stability of the passive oxide coating on steel. The Portlandite in Portland cement concretes carbonates

readily starting at the surface. Brucite in tec - cement concretes carbonates less readily

(for the main kinetic pathway) because:– The carbonation reaction has a less negative Gibbs free energy.

Gor Brucite = -19.55 Gor Portlandite = -64.62

– Carbon dioxide cannot enter the dense impermeable concrete matrix.

– The magnesium carbonates that form at the surface of tec – cement concretes expand, sealing off further carbonation.

Eco-Cement Concretes– Magnesite is formed deliberately and is stronger and more acid

resistant than calcite or aragonite.

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Durability – Reduced PermeabilityDurability – 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 cement powder is not lost near the surfaces.

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Reduced ShrinkageReduced Shrinkage

Log Time, days

Stoichiometric (Chemical) Shrinkage

Portland Cement Concretes

Tec-Cement Concretes

Plastic Settlement

Drying Shrinkage

None

Dimensional change such as shrinkage results in cracking and reduced durability

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Reduced Cracking in TecEco Cement ConcretesReduced Cracking in TecEco Cement Concretes

After Richardson, Mark G. Fundamentals of Durable Reinforced Concrete Spon Press, 2002. page 212.

Cracking, the symptomatic result of shrinkage, is undesirable for many reasons, but mainly because it allows entry of gases and ions reducing durability. Cracking can be avoided only if the stress induced by the free shrinkage strain, reduced by creep, is at all times less than the tensile strength of the concrete.

Reduced in TecEco tec-cements because they do not shrink.

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Corrosion in Portland Cement ConcretesCorrosion in Portland Cement Concretes

Passive Coating Fe3O4 intact

Both carbonation, which renders the passive iron oxide coating unstable or chloride attack (various theories) result in the formation of reaction products with a higher electrode potential resulting in anodes with the remaining passivated steel acting as a cathode.Corrosion

Anode: Fe → Fe+++ 2e-Cathode: ½ O2 + H2O +2e- → 2(OH)-

Fe++ + 2(OH)- → Fe(OH)2 + O2 → Fe2O3 and Fe2O3.H2O (iron oxide and hydrated iron oxide or rust)

The role of chloride in Corrosion

Anode: Fe → Fe+++ 2e-Cathode: ½ O2 + H2O +2e- → 2(OH)-

Fe++ +2Cl- → FeCl2FeCl2 + H2O + OH- → Fe(OH)2 + H+ + 2Cl-

Fe(OH)2 + O2 → Fe2O3 and Fe2O3.H2O

Iron hydroxides react with oxygen to form rust. Note that the chloride is “recycled” in the reaction and not used up.

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Reduced Steel CorrosionReduced Steel Corrosion

A pH of over 8.9 is maintained for much longer and steel remains passive due to a stable oxide coating.

Brucite does not react readily resulting in reduced carbonation rates and reactions with salts.

Concrete with brucite is denser and carbonation is expansive, sealing the surface preventing further access by moisture, CO2 and salts.

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 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.)

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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 of it’s low solubility (reactivity, mobility) and lower pH (reactivity)– Ksp brucite = 1.8 X 10-11 – Ksp Portlandite = 5.5 X 10-6

- 5 orders of magnitude

Durability - Reduced Salt AttackDurability - Reduced Salt Attack

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Improved WorkabilityImproved Workability

Finely ground reactive magnesia acts as a plasticiser.– Improving rheology– Lower water cement ratio results in greater

strength and reduced porosity.– The proportion and cost of binders and

plasticisers can be reduced.

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Reasons for Improved WorkabilityReasons for Improved Workability

There are also surface charge affects and water reducing agents are not required. Reactive Magnesia is a plasticiser as well.

Reactive Magnesia grains Mean size 5 -8 micron

Portland cement grains Mean size 20 - 40 micron

The magnesia grains act as ball bearings to the Portland cement grains and also fill the voids densifying the whole

Smaller grains (eg microsilica) for even better rheology.

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RheologyRheology

TecEco concretes are– very homogenous– very thixotropic and react well to energy input.

• (Slump is therefore not a good measure of workability)

TecEco concretes with the same water/binder ratio have a lower slump but greater plasticity and workability.

Second layer low slump TecEco modified Portland cement concrete

Tech Tendons

First layer low slump TecEco modified Portland cement concrete

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Dimensionally Neutral TecEco Tec - Cement Concretes During Curing?

Dimensionally Neutral TecEco Tec - Cement Concretes During Curing?

Portland cement shrinks around .05%. Over the long term much more (>.1%).– Mainly due to chemical shrinkage, plastic and drying shrinkage,

as well as carbonation. Hydration:

– When magnesia hydrates it expands:

MgO (s) + H2O (l) ↔ Mg(OH)2 (s) 40.31 + 18.0 ↔ 58.3 molar mass 11.2 + liquid ↔ 24.3 molar volumes– Up to 116.96% solidus expansion depending on whether the water is

coming from stoichiometric mix water, bleed water or from outside the system. In practice much less as the water comes from mix and bleed water.

– So far we have not observed shrinkage in TecEco tec - cement concretes (10% substitution OPC) also containing fly ash.

– The water lost by Portland cement as it shrinks is used by the reactive magnesia as it hydrates eliminating shrinkage.

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Volume Changes on CarbonationVolume Changes on Carbonation Carbonation:

– Consider what happens when Portlandite carbonates:Ca(OH)2 + CO2 CaCO3

74.08 + 44.01 ↔ 100 molar mass33.22 + gas ↔ 28.10 molar volumes

• 18.22% shrinkage. Cracks appear allowing further carbonation.– Compared to brucite forming magnesite as it carbonates:

Mg(OH)2 + CO2 MgCO3

58.31 + 44.01 ↔ 84.32 molar mass24.29 + gas ↔ 28.10 molar volumes

• 15.68% expansion and densification of the surface preventing further ingress of CO2 and carbonation. Self sealing?

Combined - Curing and Carbonation are close to Neutral.– At some ratio, thought to be around 10% reactive magnesia and 90% OPC

volume changes cancel each other out.– More research is required for both tec - cements and eco-cements to

accurately establish volume relationships.[1] The molar volume (L.mol-1)is equal to the molar mass (g.mol-1) divided by the density (g.L-1).

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Tec - Cement Concretes - Potential for Neutral CureTec - Cement Concretes - Potential for Neutral Cure

90 days 28

? ?

? ?

?

? ?

?

-.05%

+.05%

Portland Cement

Reactive Magnesia

Composite Curve

+- Fly Ash?

HYDRATION THEN CARBONATION OF REACTIVE MAGNESIA AND OPC

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Are the Texts all Wrong About Carbonation?Are the Texts all Wrong About Carbonation?

Most texts maintain the carbonation reaction is one between ions in solution yet carbonation is observable in very dry conditions. The transport of carbon dioxide is much more rapid in air than in water and adherence to Le Chatelier’s principal would also indicate dry conditions as the removal or water as a product would help the reactionCa(OH)2 + CO2 CaCO3 + H2O (Gof - 64.62 kJ.mol-1)

To proceed towards products (the right). The highly negative Gibbs free energy of the reaction

indicates this should occur spontaneously. The author would be very interested in some definitive

information on this as most of the texts seem to take a bet both ways!

Please contact me if you know more about this than me!

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Safety – Reduced Fire DamageSafety – Reduced Fire Damage The main phase in TecEco tec - cement concretes is brucite. The main phases in TecEco eco-cements are magnesite and

hydromagnesite. Brucite, magnesite and hydromagnesite are excellent fire

retardants and extinguishers. At relatively low temperatures

– Brucite releases water and reverts to magnesium oxide.– Magnesite releases CO2 and converts to magnesium oxide.– Hydromagnesite releases CO2 and water and converts to magnesium

oxide. Fires are therefore not nearly as aggressive resulting in less

damage to structures. Damage to structures results in more human losses that

direct fire hazards.

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TecEco Eco-Cements - Solving Waste ProblemsTecEco Eco-Cements - Solving Waste Problems The best thing to do with wastes is if at all possible

to use them. If they cannot directly be usedthen they have to be immobilised.

Concretes represent a cost affective option: Chemically and physically enviro-cements are more

suited to toxic and hazardous waste immobilisationthan either lime, Portland cement or Portland cementlime mixes and they are more predicable than geopolymers.

In a Portland cement brucite matrix– OPC takes up lead, some zinc and germanium– Brucite and hydrotalcite are both excellent hosts for toxic and hazardous

wastes. Brucite has a layered structure and traps neutral compounds between the layers.

– Heavy metals not taken up in the structure of Portland cement minerals or trapped within the brucite layers end up as hydroxides.

The pH which is controlled in the long term by brucite is around 10.52, and is an ideal long term value at which most heavy metal hydroxides are relatively insoluble.

TecEco cements are also more durable, dense, impermeable and homogenous. They do not bleed water, are not attacked by salts in ground or sea water and dimensionally more stable with less cracking.

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Toxic and Hazardous Waste ImmobilisationToxic and Hazardous Waste Immobilisation

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.

Layers of electronically neutral brucite suitable for trapping balanced cations and anions as well as other substances

Salts and other toxic and hazardous substances between layers

Brucite is an ideal mineral for trapping toxic and hazardous wastes.

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Lower Solubility of Metal HydroxidesLower Solubility of Metal Hydroxides

Pb(OH) 2 Cr(OH) 3 Zn(OH) 2 Ag(OH)

Cu(OH) 2 Ni(OH) 2

Cd(OH) 2

10 -6

10 -4

10 -2

10 0

10 2

Co

nce

ntr

atio

n o

f D

isso

lved

Met

al, (

mg

/L)

14 6 7 8 9 10 11 12 13

Equilibrium pH of brucite is 10.52 (more ideal)*

Equilibrium pH of Portlandite is 12.35*

*Equilibrium pH’s in pure water, no other ions present. The solubility of toxic metal hydroxides is generally less at around pH 10.52 than at higher pH’s.

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High Performance = Sustainability=Lower CostHigh Performance = Sustainability=Lower Cost

High Performance = Sustainability=Lower Cost

Comprehensive high performance will include improvements in:– Compressive and tensile strength/binder ratios– Durability, insulating capacity, ability to host wastes– Weight etc. etc.

Increased durability will result in lower costs/energies/emissions due to less frequent replacement.

Improvements in insulating capacity will mean lower lifetime as well as embodied energies in buildings.

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TecEco Concretes - Lower Construction CostsTecEco Concretes - Lower Construction Costs

Lower water binder ratio means less binders (eg OPC) for same strength.

Faster strength gain even with added pozzolans. Cheaper binders as less energy required and a

higher proportion is water. Elimination of shrinkage reducing associated costs. Elimination of bleed water enables finishing of

lower floors whilst upper floors still being poured. A high proportion of brucite compared to

Portlandite is water and of magnesite compared to calcite is CO2.– Every mass unit of TecEco cements therefore produces a

greater volume of built environment than Portland and other calcium based cements. Less need therefore be used reducing costs/energy/emissions.

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TecEco Concretes - Lower Construction Costs (2)TecEco Concretes - Lower Construction Costs (2)

Homogenous, so no under plastic necessary. Because reactive magnesia is also an excellent

plasticiser, other costly additives are not required for this purpose.

Easier placement and better finishing. A wider range of aggregates can be utilised without

problems reducing transport and other costs/energies/emissions.

Greater durability reduces costs over time. Reduced or eliminated carbon taxes. Eco-cements can to a certain extent be recycled. TecEco cements utilise wastes many of which

improve properties.

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Characteristics of TecEco Cements (1)Characteristics of TecEco Cements (1)Portland Cement Concretes


Enviro-Cement Concretes

Eco-Cements

Typical Formulations

100 mass% PC 8 mass% OPC, 72 mass % PC, 20 mass% pozzolan

20 mass% OPC, 60 mass % PC, 20 mass% pozzolan

50 mass% OPC, 30 mass % PC, 20 mass% pozzolan

Setting Main strength from hydration of calcium silicates.

Main strength is from hydration of calcium silicates. Magnesia hydrates forming brucite which has a protective role.

Magnesia hydrates forming brucite which protects and hosts wastes. Carbonation is not encouraged.

Magnesia hydrates forming brucite then carbonates forming magnesite and hydromagnesite.

Suitability Diverse Diverse. Ready mix concrete with high durability

Toxic and hazardous waste immobilisation

Brick, block, pavers, mortars and renders.

Mineral Assemblage (in cement)

Tricalcium silicate, di calcium silicate, tricalcium aluminate and tetracalcium alumino ferrite.

Tricalcium silicate, di calcium silicate, tricalcium aluminate, tetracalcium alumino ferrite, reactive magnesia.

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Eco-Cements

Final mineral Assemblage (in concrete)

Complex but including tricalcium silicate hydrate, di calcium silicate hydrate, ettringite, monosulfoaluminate, (tetracalcium alumino sulphate), tricalcium alumino ferrite hydrate, calcium hydroxide and calcium carbonate .

Complex but including tricalcium silicate hydrate, di calcium silicate hydrate, ettringite, monosulfoaluminate, (tetracalcium alumino sulphate), tricalcium alumino ferrite hydrate, calcium hydroxide, calcium carbonate, magnesium hydroxide and magnesium carbonates.

Strength (S19-21)

Variable. Mainly dependent on the water binder ratio and cement content.

Variable. Mainly dependent on the water binder ratio and cement content. Usually less total binder for the same strength development

Variable, usually lower strength because of high proportion of magnesia in mix.

Variable.

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Eco-Cements

Rate of Strength Development (S28)

Variable. Addition of fly ash can reduce rate of strength development.

Variable. Addition of fly ash does not reduce rate of strength development.

Slow, due to huge proportion of magnesia

Variable, but usually slower as strength develops during carbonation process.

pH (S20,21)

Controlled by Na+ and K+ alkalis and Ca(OH)2 in the

short term. In the longer term pH drops near the surface due to carbonation (formation of CaCO3)

Controlled by Na+ and K+ alkalis and Ca(OH)2 and high in the short term. Lower in

the longer term and controlled by Mg(OH)2

and near the surface MgCO3

High in the short term and controlled by Ca(OH)2. Lower in

the longer term and controlled by MgCO3

Rheology (S32-35)

Plasticisers are required to make mixes workable.

Plasticisers are not necessary. Formulations are generally much more thixotropic.

Plasticisers are not necessary. Formulations are generally much more thixotropic and easier to use for block making.

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Eco-Cements

Durability(S22-25)

Lack of durability is an issue with Portland cement concretes

Protected by brucite, are not attacked by salts, do not carbonate, are denser and less permeable and will last indefinitely.

Protected by brucite, are not attacked by salts, do not carbonate, are denser and will last indefinitely.

Density (S25)

Density is reduced by bleeding and evaporation of water.

Do not bleed - water is used up internally resulting in greater density

Permeability(S28)

Permeable pore structures are introduced by bleeding and evaporation of water.

Do not bleed - water is used up internally resulting in greater density and no interconnecting pore structures

Shrinkage (S36-39)

Shrink around .05 - .15 %

With appropriate blending can be made dimensionally neutral as internal consumption of water reduces shrinkage through loss of water and magnesium minerals are expansive.

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Eco-Cements

Insulating Properties

Relatively low with high thermal conductivity around 1.44 W/mK

Depends on formulation but better insulation as brucite is a better insulator

Depends on formulation but better insulation as brucite is a better insulator and usually contains other insulating materials

Thermal Mass

High. Specific heat is .84 kJ/kgK

Depends on formulation but remains high

Depends on formulation but remains high

Embodied Energy (of concrete)

Low, 20 mpa 2.7 Gj.t-1, 30 mpa 3.9 Gj.t-1 (1)

Approx 15-30% lower due to less cement for same strength, lower process energy for making magnesia and high pozzolan content(2).

Lower depending on formulation(2).

Depends on formulation Even lower due to lower process energy for making magnesia and high pozzolan content(2).

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Eco-Cements

Re-cyclability

Concrete can only be crushed and recycled as aggregate.

Can be crushed and recycled as aggregate.

Can be crushed and fines re-calcined to produce more magnesia or crushed and recycled as aggregate or both.

Can be crushed and fines re-calcined to produce more magnesia or crushed and recycled as aggregate or both.

Fire Retardant

Ca(OH)2 and

CaCO3 break down

at relatively high temperatures and cannot act as fire retardants

Mg(OH)2 is a fire retardant and releases

H2O at relatively low temperatures.

Mg(OH)2 and

MgCO3 are both

fire retardants and release H2O or

CO2 at relatively

low temperatures.

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Eco-Cements

Sustainability A relatively low embodied energy and emissions relative to other building products. High volume results in significant emissions.

Less binder for the same strength and a high proportion of supplementary cementitous materials such as fly ash and gbfs. Can be formulated with more sustainable hydraulic cements such as high belite sulphoaluminate cements. A wider range of aggregates can be used. Greater durability.

A high proportion of supplementary cementitous materials such as fly ash and gbfs. Can be formulated with more sustainable hydraulic cements such as high belite sulphoaluminate cements. A wider range of aggregates can be used. Greater durability.

A high proportion of supplementary cementitous materials such as fly ash and gbfs. Carbonate in porous materials reabsorbing chemically released CO2

A wider range of aggregates can be used. Greater durability.

Carbon emissions

With 15 mass% PC in concrete .32 t.t-1

After carbonation approximately .299 t.t-1

With 15 mass% PC in concrete approx.29 t.t-1 After carbonation approximately .26 t.t-1

Could be lower using supplementary cementitous materials and formulated with other low carbon cement blends.

With 11.25 mass % magnesia and 3.75 mass % PC in concrete .241 t.t-1

With capture CO2

and fly ash as low as .113 t.t-1

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TecEco Challenging the WorldTecEco Challenging the World Although the technology is new and not yet fully

characterised, TecEco challenge universities governments and construction authorities to come to grips with the new cement technology and quantify performance in comparison to ordinary Portland cement and other competing materials.

At TecEco will do our best to assist. Negotiations are underway in many countries to

organise supplies to allow such scientific endeavour to proceed.

The invention of the new TecEco cement system is an enormous opportunity for the world to take materials science, which is the key to sustainability, more seriously.

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Addressing Issues in Concrete ScienceAddressing Issues in Concrete Science Addressing the research objectives of concrete science.

– Durability salt resistance and steel corrosion may become problemsof the past.

• Lower use of materials and energyover time saving money and the environment.

– Lower more stable long term alkalinity.• Reduced AAR and steel corrosion etc.

– Better rheology.• Lower water cement ratio, less shrinkage, and easier placement.

– Other improved properties:• Greater density, adjustable placing and finishing times. Fire retarding

properties– Lower Costs

• Making reactive magnesia is a benign process with potential for using waste energy and capture of CO2.

• A wider range of aggregates including wastes will be availablereducing cartage costs and emissions.

• Water or CO2 from the air comprise a high mass % and volume % of the magnesium minerals in TecEco cements. Water and CO2 are free or attract carbon credits

• Expensive plasticisers are not required

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TecEco’s Immediate FocusTecEco’s Immediate Focus Form strategic alliances with major companies. Raise money for Research – Around 1 million dollars worth in

the pipeline. Concentrate on defined markets for low technical risk

products that require minimal research and development and for which performance based standards apply. – Carbonated products such as bricks, blocks, stabilised earth blocks,

pavers, roof tiles pavement and mortars that utilise large quantities of waste and products where sustainability, rheology or fire retardation are an issue. (Mainly eco-cement technology using fly ash).

– The immobilisation of wastes including toxic hazardous and other wastes because of the superior performance of the technology and the rapid growth of markets. (Eco-cements and tec - cements).

– Products such as oil renders and mortars where excellent rheology and bond strength are required.

– Products where extreme durability is required.– Products for which weight is an issue.

Continue our awareness campaign regarding TecEco cements, the new TecEco kiln design and the Tech Tendon method of prestressing, partial prestressing and reinforcing.

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TecEco Minding the FutureTecEco Minding the Future TecEco are aware of the enormous weight of

opinion necessary before standards can bechanged globally for TecEco tec - cementconcretes for general use.– TecEco already have a number of institutions and universities

around the world doing research.

TecEco have received huge global publicity – not all of which is correct and have therefore publicly released the technology.– TecEco research documents are available from TecEco by request.

Soon they will be able to be purchased from the web site.

– Other documents by other researchers will be made available in a similar manner as they become available.

Technology standing on its own is not inherently good. It still matters whether it is operating from the right value system and whether it is properly available to all people.

-- William Jefferson Clinton

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TecEco Technology SummaryTecEco Technology Summary Simple, smart and sustainable?

– TecEco cement technology has resulted in potential solutions to a number of problems with Portland and other cements including durability and corrosion, the alkali aggregate reaction problem and the immobilisation of many problem wastes and will provides a range of more sustainable building materials.

The right technology at the right time?– TecEco cement technology addresses important triple bottom line issues

solving major global problems with positive economic and social outcomes.

Climate Change Pollution

Durability Corrosion

Strength Delayed Reactions

Placement , Finishing Rheology

Shrinkage Carbon Taxes

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The Magnesium Thermodynamic CycleThe Magnesium Thermodynamic Cycle

CO2

Magnesite*

Magnesia Brucite*

An alkaline environment in which silicates form

Cementitious phases

Dolomite*

Ca++

Thermal decomposition MgCO3 MgO + CO2 ΔH = 118.28 kJ.mol-1 ΔG = 65.92 kJ.mol-1

Carbonation Mg(OH)2 + CO2 MgCO3 + H2O ΔH = -37.04 kJ.mol-1 ΔG = -19.55 kJ.mol-1

Hydration MgO + H2O Mg(OH)2 ΔH = -81.24 kJ.mol-1 ΔG = -35.74 kJ.mol-1

Reactive phase

TOTAL CALCINING ENERGY (Relative to MgCO3) Theoretical = 1480 kJ.Kg-1 With inefficiencies = 1948 kJ.Kg-1

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Manufacture of Portland CementManufacture of Portland Cement

CO2

Calcite and Aragonite

Quicklime Portlandite

Cementitious phases

Clay

OPC Tri calcium silicate hydrate ΔH = - 114 kJ.mol-1

+ Pozzolan

Tri calcium aluminate ΔH = - 362 kJ.mol-1 Calcium alumino ferrite

Di calcium silicate hydrate ΔH = - 43 kJ.mol-1

Rotary Kiln

Thermal decomposition CaCO3 CaO + CO2 ΔH = 178.77 kJ.mol-1 ΔG = 130.98 kJ.mol-1

Carbonation Ca(OH)2 + CO2 CaCO3 + H2O ΔH = - 69.58 kJ.mol-1 ΔG = - 64.62 kJ.mol-1

Hydration CaO + H2O Ca(OH)2 ΔH = -109.19 kJ.mol-1 ΔG = - 66.35 kJ.mol-1

Reactive phases

Portland Cement

SUMMARY

Limestone + Clay

Estimated* ΔH = 1807 kJ.kg-1 ΔG = 1287 kJ. kg-1

*Note the measure is relative to Kg as mixed molar amounts are used.

TOTAL CALCINING ENERGY. (Relative to CaCO3) Theoretical = 1807 kJ.Kg-1

With inefficiencies = 3306 kJ.Kg-1

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TecEco Eco - Cements for Sustainable CitiesTecEco Eco - Cements for Sustainable Cities

RAW MATERIALS

RECYCLABLE MATERIALS

ECO-CEMENT PRODUCTS

MINING

RECYCLING CITIES

CO2

PERMANENT SEQUESTRATION (Man Made Carbonate Rock As A

Building Material)

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Manufacture of TecEco-CementsManufacture of TecEco-Cements

Caustic Magnesia Calcined using waste heat and/or sustainable energy

Flyash

Other ingredients Eco-Masonry Products e.g. Bricks & blocks

Hydration using flue cooling &/or scrubbing water & flue steam. Carbonation using warm CO2 rich gases

Coal Combustion

TecEco - Cements

Magnesite Coal

Bottom ash & other wastes as aggregates

Eco-Cement – One of Many Possible Manufacturing Scenarios

Portland Cement

CO2

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Embodied Energy and EmissionsEmbodied Energy and Emissions

Energy costs money and results in emissions and is the largest cost factor in the production of mineral binders.– Whether more or less energy is required for the manufacture of reactive

magnesia compared to Portland cement or lime depends on the stage in the utility adding process it is measured.

– Utility is greatest in the finished product which is concrete. The volume of built material is more relevant than the mass and is therefore more validly compared. On this basis the technology is far more sustainable than either the production of lime or Portland cement.

– The new TecEco kiln technology will result in around 25% less energy being required and the capture of CO2 during production resulting in lower costs and carbon credits.

The manufacture of reactive magnesia is a benign process that can be achieved with waste or intermittently available energy.

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Energy – On a Mass BasisEnergy – On a Mass Basis

Relative to Raw Material Used to make Cement

From Manufacturing Process Energy Release 100% Efficient (Mj.tonne-1)

From Manufacturing Process Energy Release with Inefficiencies (Mj.tonne-1)

Relative Product Used in Cement



Relative to Mineral Resulting in Cement



CaCO3 +

Clay 1545.73 2828.69

Portland Cement 1807 3306.81

Hydrated OPC 1264.90 2314.77

CaCO3 1786.09 2679.14 Ca(OH)2 2413.20 3619.80

MgCO3 1402.75 1753.44 MgO 2934.26 3667.82 Mg(OH)2 2028.47 2535.59

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Energy – On a Volume BasisEnergy – On a Volume Basis

Relative to Raw Material Used to make Cement

From Manufacturing Process Energy Release 100% Efficient (Mj.metre-3)

From Manufacturing Process Energy Release with Inefficiencies (Mj.metre-3)

Relative Product Used in Cement



Relative to Mineral Resulting in Cement



CaCO3

+ Clay 4188.93 7665.75Portland Cement 5692.05 10416.45

Hydrated OPC 3389.93 6203.58

CaCO3 6286.62 8429.93 Ca(OH)2 5381.44 8072.16

MgCO3 4278.39 5347.99 MgO 9389.63 11734.04 Mg(OH)2 4838.32 6085.41

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CO2 Abatement –TecEco Eco-CementsCO2 Abatement –TecEco Eco-Cements

Eco-cements in porous products absorb carbon dioxide from the atmosphere. Brucite carbonates forming hydromagnesite and magnesite, completing the thermodynamic cycle.

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.

Portland Cements 15 mass% Portland cement, 85 mass% aggregate

Emissions

.32 tonnes to the tonne. After carbonation. Approximately .299 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.

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.

On the basis of the volume of building materials produced the figures are even better!

85 wt% Aggregates 15 wt% Cement

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Global AbatementGlobal Abatement

Without CO2 Capture during manufacture (billion tonnes)

With CO2 Capture during manufacture (billion tonnes)

Total Portland Cement Produced Globally 1.80 1.80

Global mass of Concrete (assuming a proportion of 15 mass% cement)

12.00 12.00

Global CO2 Emissions from Portland Cement 3.60 3.60

Mass of Eco-Cement assuming an 80% Substitution in global concrete use

9.60 9.60

Resulting Abatement of Portland Cement CO2

Emissions

2.88 2.88

CO2 Emissions released by Eco-Cement 2.59 1.34

Resulting Abatement of CO2 emissions by

Substituting Eco-Cement

0.29 1.53

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Abatement from SubstitutionAbatement from Substitution

Figures are in millions of Tonnes

Building Material to be substituted

Realistic % Subst-itution by TecEco technology

Size of World Market (million tonnes

Substituted Mass (million tonnes)

CO2 Factors (1)

Emission From Material Before Substitution

Emission/Sequestration from Substituted Eco-Cement (Tonne for Tonne Substitution Assumed)

Net Abatement

Emissions - No Capture

Emissions - CO2 Capture

Abatement - No Capture

Abatement CO2 Capture

Bricks 85% 250 212.5 0.28 59.5 57.2 29.7 2.3 29.8

Steel 25% 840 210 2.38 499.8 56.6 29.4 443.2 470.4

Aluminium 20% 20.5 4.1 18.0 73.8 1.1 0.6 72.7 73.2

TOTAL 426.6 20.7 633.1 114.9 59.7 518.2 573.4

Concretes already have low lifetime energies.

If embodied energies are improved could substitution mean greater market share?

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Tripling Mineral SequestrationTripling Mineral SequestrationAs a method of capturing CO2 the kinetics of the following reactions are being examined:

½Mg2SiO4 + CO2 → MgCO3 + ½SiO2 + 95kJ/mole

1/3Mg3Si2O5(OH)4 + CO2 → MgCO3 + 2/3SiO2 + 2/3H2O + 64kJ/mole

Of the above the second reaction with chrysotile or serpentine as it is sometimes called is favoured as the mineral is abundant.

At low partial pressures of CO2 and relatively low temperatures, MgCO3 will break down yielding MgO and CO2.

MgCO3 →MgO + CO2

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Tripling Mineral Sequestration (2)Tripling Mineral Sequestration (2)

CO2

Utilising a closed system such as with TecEco Kiln technology the CO2 re-emitted can be captured for industrial use (replacing alternative production) or direct sequestration.

If the MgO is then used to make eco-cement products the total CO2 captured is three moles to the mole of serpentinite mined.

MgO +H2O → Mg(OH)2

Mg(OH)2 +CO2 → MgCO3 + H2O

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Tripling Mineral Sequestration (3)Tripling Mineral Sequestration (3)

One tonne of chrysotile will sequester .588 tonnes CO2

producing 1.263 tonnes of magnesite. 1.263 tonnes of magnesite will yield .538 tonnes of

reactive magnesia. .588 tonnes CO2 driven off by the low temperature

calcination of magnesia can be captured. The magnesia when it carbonates (directly or via the

hydroxide) will yield 1.263 tonnes of magnesite again absorbing a further .588 tonnes of CO2

A total of 1.176 tonnes of CO2 can therefore be directly sequestered and a further .588 tonnes captured.

Captured CO2 can be used to replace commercially produced CO2 or sequestered by other means.

Total sequestration possible is therefore three times that possible with direct mineral sequestration alone!

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