Presentation downloadable from 1 Tec and Eco-Cement Update I will have to race over some slides but the presentation is always downloadable

1Presentation downloadable from www.tececo.com

Tec and Eco-Cement UpdateTec and Eco-Cement Update

I will have to race over some slides but the presentation is always downloadable from the TecEco web site if you missed something. John Harrison B.Sc. B.Ec. FCPA.

TecEco Masonry Products utilising Tec and TecEco eco-cements


TecEco CementsTecEco CementsSUSTAINABILITY

DURABILITY STRENGTHTECECO 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 for strength, workability, dimensional stability and durability. In Eco-cements carbonation of brucite => nesquehonite, lansfordite and an amorphous phase for sustainability.

PORTLAND

+ or - POZZOLAN

MAGNESIA

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


The Magnesium Thermodynamic CycleThe Magnesium Thermodynamic Cycle

An alkaline environment in which silicates form

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

Carbonation Mg(OH)2 + CO2 + 2H2O MgCO3.3 H2O ΔH = -175.59 kJ.mol-1 ΔG = -38.73 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 Nesquehonite

? Representative of other hydrated mineral carbonates including an amorphous phase and lansfordite Magnesite*

Magnesia

Dehydration

CO2

Brucite*

Tec - Cements

Eco - Cements


TecEco Cement SustainabilityTecEco Cement Sustainability TecEco technology will be pivotal in bringing

about sustainability in the built environment.– The CO2 released by calcined carbonates used to make binders

can be captured using TecEco kiln technology.– Tec-Cements Develop Significant Early Strength even with

Added Supplementary Materials.• Around 25 = 30% less total binder is required for the same strength.

– Eco-cements carbonate sequestering CO2

– Both tec and eco=cements provide a benign low pH environment for hosting large quantities of waste overcoming problems of:

• 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• Durability issues


TecEco FormulationsTecEco 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.


TecEco Cement TechnologyTecEco Cement TechnologyPortlandite (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 forming brucite which is another alkali,

but much less soluble, mobile or reactive than Portlandite.In Eco-cements brucite carbonates

The consequences of need to be considered


Why Add Reactive Magnesia?Why Add Reactive Magnesia? To maintain the long term stability of CSH.

– Maintains alkalinity preventing the reduction in Ca/Si ratio.

To remove water.– Reactive magnesia consumes water as it hydrates to possibly

hydrated forms of brucite.

To reduce shrinkage.– The consequences of putting brucite through the matrix of a

concrete in the first place need to be considered.

To make concretes more durable Because significant quantities of carbonates are

produced in porous substrates which are affective binders.

Reactive MgO is a new tool to be understood with profound affects on most properties


What is Reactive MgO? or Lattice Energy Destroys a MythWhat is Reactive MgO? or 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 (Ramachandran V. S., Concrete Science, Heydon & Son Ltd. 1981, p 358-360 )


Summary of Reactions InvolvedSummary of Reactions Involved

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

Magnesia Brucite

MgO + H2O Mg(OH)2

M3A + 6H + M3AH6 (or similar ?)

Hardness: 2.5 - 3.0 2.5

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

Solubility (mol.L-1): .00015 .01 .013 (but less in acids)

Silicates and aluminosilicates

Magnesia Brucite Amorphous Lansfordite

MgO + nH2O Mg(OH)2.nH2O + CO2 MgCO3.nH2O + MgCO3.5H2O + MgCO3.3H2O

In Eco - Cements

In Tec-Cements

Hardness: 2.5 3.5

Form: Massive Massive or crystalline More acicular

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

Portlandite Calcite

Ca(OH)2 + CO2 CaCO3

Compare to the Carbonation of Portlandite

Aragonite

Nesquehonite

We think the reactions are relatively independent.


Strength with Blend & PorosityStrength with Blend & Porosity

0

50

100

150

100-15050-1000-50

High OPC High Magnesia

High Porosity

STRENGTH ON ARBITARY SCALE 1-100

Tec-cement concretes

Eco-cement concretes

Enviro-cement concretes


Eco-CementsEco-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 nearly six times more efficient.

– Magnesium hydroxide in particular and to some extent the carbonates are less reactive and mobile and thus much more durable.


Eco-Cement pH CurvesEco-Cement pH Curves

13.7

pH

Log Time

10.5

Eco – Cement Concrete with 75% reactive magnesia (red). Ph maintained by brucite and hydrated carbonates

OPC Concrete

HYPOTHETICAL pH CURVES OVER TIME

Plastic Stage

? ?

? 11.2

PC Concrete – Ph maintained by lime and calcite (Ca(OH)2 carbonates more readily.)


Eco-Cement Strength DevelopmentEco-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 volumentric expansion from magnesium oxide to lansfordite is for example 473 volume %.


Eco-Cement Concrete Strength Gain CurveEco-Cement Concrete Strength Gain Curve

Eco – Cement Concrete with 50% reactive magnesia

OPC Concrete

HYPOTHETICAL STRENGTH GAIN CURVE OVER TIME (Pozzolans added)

MPa

Log Days Plastic Stage

?

?

?

?

7 14 28 3

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.


Eco-Cement Micro-Structural StrengthEco-Cement Micro-Structural Strength

Elongated growths of lansfordite and nesquehonite near the surface, growing inwards over time and providing microstructural strength.

Portland clinker minerals (black). Hydration providing Imperfect structural framework.

Micro spaces filled with hydrating magnesia (→brucite) – acting as a “waterproof glue”

Flyash grains (red) reacting with lime producing more CSH and if alkaline enough conditions bonding through surface hydrolysis. Also acting as micro aggregates.

Mysterious amorphous phase?


CarbonationCarbonation Because magnesium has a low molecular weight,

proportionally a greater amount of CO2 is captured. Carbonation results in significant sequestration

because of the shear volumes involved. Carbonation adds strength. Carbonates are the stable phases of both calcium

and magnesium. The formation of carbonates lowers the pH of

concretes compromising the stability of the passive oxide coating on steel.

Some steel reinforced structural concrete could be replaced with fibre reinforced porous carbonated concrete.


Chemistry of CarbonationChemistry of Carbonation 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.


Ramifications of CarbonationRamifications of Carbonation Magnesium Carbonates.

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

– Lansfordite and nesquehonite are stronger and more acid resistant than calcite or aragonite.

– The curing of eco-cements in a moist - dry alternating environment seems to encourage carbonation.

Portland Cement Concretes– Carbonation proceeds relatively rapidly at the surface. Vaterite

followed by Aragonite and Calcite is the principal product and lowers the pH to around 8.2


Proof of Carbonation - Minerals Present After 18 MonthsProof of Carbonation - Minerals Present After 18 Months

XRD showing carbonates and other minerals before removal of carbonates with HCl in a simple Mix (70 Kg PC, 70 Kg MgO, colouring oxide .5Kg, sand unwashed 1105 Kg)


Proof of Carbonation - Minerals Present After 18 Months and Acid Leaching

Proof of Carbonation - Minerals Present After 18 Months and Acid Leaching

XRD Showing minerals remaining after their removal with HCl in a simple mix (70 Kg PC, 70 Kg MgO, colouring oxide .5Kg, sand unwashed 1105 Kg)


TecEco Binders - Solving Waste ProblemsTecEco Binders - Solving Waste Problems

There are huge volumes of concrete produced annually ( 2 tonnes per person per year.)

An important objective should be to make cementitous composites that can utilise wastes.

TecEco cements provide a benign environment suitable for waste immobilisation

Many wastes such as fly ash, sawdust , shredded plastics etc. can improve a property or properties of the cementitious composite.

There are huge materials flows in both wastes and building and construction. TecEco technology will lead the world in the race to incorporate wastes in cementitous composites


TecEco Binders - Solving Waste Problems (2)TecEco Binders - Solving Waste Problems (2)

TecEco cementitious composites represent a cost affective option for both use and immobilisation of waste.– 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


Role of Brucite in ImmobilizationRole of Brucite in Immobilization

In a Portland cement brucite matrix– PC takes up lead, some zinc and germanium– 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.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 substances trapped between the layers.

Van der waals bonding holding the layers together.


Lower Solubility of Metal HydroxidesLower Solubility of Metal Hydroxides

Pb(OH) 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.

There is a 104 difference


TecEco Materials as Fire RetardantsTecEco Materials as Fire Retardants The main phase in TecEco tec - cement concretes is Brucite. The main phases in TecEco eco-cements are Lansfordite and

nesquehonite. Brucite, Lansfordite and nesquehonite are excellent fire

retardants and extinguishers. At relatively low temperatures

– Brucite releases water and reverts to magnesium oxide.

Mg(OH)2 ↔ MgO + H2O

– Lansfordite and nesquehonite releases CO2 and water and convert to magnesium oxide.

MgCO3.nH2O ↔ MgO + CO2 + H2O 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.


Tec-Cement Concrete Strength Gain CurveTec-Cement Concrete Strength Gain Curve

strength gain with less cement and added pozzolans is of great economic and environmental importance.

Tec – Cement Concrete with 10% reactive magnesia

OPC Concrete

HYPOTHETICAL TEC-CEMENT STRENGTH GAIN CURVE MPa

Log Days Plastic Stage

? ?

?

?

7 14 28 3

Concretes are more often than not made to strength. The use of tec-cement results in

– 20-30% greater strength or less binder for the same strength.

– more rapid early strength development even with added pozzolans.

– Straight line strength development for a long time


Reasons for Strength Development in Tec-Cements.Reasons for Strength Development in Tec-Cements. Reactive magnesia requires considerable water to hydrate

resulting 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 of alkalis caused by the removal of water?

Micro-structural strength due to particle packing (Magnesia particles at 4-5 micron are a little over ½ the size of cement grains.)

Slow release of water from hydrated Mg(OH)2.nH2O supplying H2O for more complete hydration of C2S and C3S?

Formation of MgAl hydrates? Similar to flash set in concrete but slower??


Water Reduction During the Plastic PhaseWater Reduction During the Plastic Phase

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

Water

Log time

Observable Characteristic

Relevant Fundamental

Voids

Binder + supplementary cementitious materials

Hydrated Binder Materials

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

Unhydrated Binder


Tec-Cement Compressive StrengthTec-Cement Compressive Strength

3 14.365 18.095 19.669 5.5163 16.968 19.44 20.196 6.6569 19.466 20.877 13.39 3.4179 24.248 24.408 15.39 4.4349 29.03 27.939 17.39 5.451

21 24.54 35.037 25.493 11.99221 28.403 36.323 28.723 13.93321 32.266 37.609 31.953 15.874

TEC-CEMENT COMPRESSIVE STRENGTH

0

5

10

15

20

25

30

35

40

0 2 4 6 8 10 12 14 16 18 20 22 24

CURING TIME (days)

ST

RE

NG

TH

( M

Pa

)

OPC(100%)

OPC(90%)+MgO(10%)

Graphs by Oxford Uni Student


Tec-Cement Tensile StrengthTec-Cement Tensile Strength

TEC - CEMENT TENSILE STRENGTH

0

1

2

3

4

5

6

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

CURING TIME (days)

ST

RE

NG

TH

(M

Pa)

OPC(100%)

OPC(90%)+ MgO(10%)

Graphs by Oxford Uni Student

Tensile strength is thought to be caused by change in surface charge on MgO particles from +ve to –ve at Ph 12 and electrostatic attractive forces


Other Strength Testing to DateOther Strength Testing to DateBRE (United Kingdom)•2.85PC/0.15MgO/3pfa(1 part) : 3 parts sand - Compressive strength of 69MPa at 90 days.•Note that there was as much pfa as Portland cement plus magnesia. Strength development was consistently greater than the OPC control

TecEco Large Cement Company

0

20

40

60

17 30 56 89

Days

MP

a

Sample 1Sample 2

Strength Development of Tec-Cement Concrete

0

5

10

15

20

25

30

0 5 10 15 20 25 30

Days water cured

Str

eng

th,

MP

aCompressiveStrength

Modified 20 MPa mix


Concretes have a high percentage (around 18% - 25%) of voids.

On hydration magnesia expands 116.9 % filling voids and surrounding hydrating cement grains and compensates for the shrinkage of Portland cement.

Brucite is 44.65 mass% water. Lower voids:paste ratios than water:binder ratios

result in little or no bleed water less permeability and greater density.– Compare the affect to that of vacuum dewatering.

Increased Density – Reduced PermeabilityIncreased Density – Reduced Permeability


Reduced PermeabilityReduced 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.

Consequences:– Tec - cement concretes tend to dry from

within, are denser and less permeable and therefore stronger more durable and more waterproof. Cement powder is not lost near the surfaces.

– Tec-cements have a higher salt resistance and less corrosion of steel etc.


Tec-Cement pH CurvesTec-Cement pH Curves

13.7

pH

Log Time

10.5

Tec – Cement Concrete with 10% reactive magnesia (red). Ph maintained by brucite

OPC Concrete

HYPOTHETICAL pH CURVES OVER TIME (with fly ash)

Plastic Stage

? ?

?

Tec-Cement (red) - more affective pozzolanic reactions

11.2

OPC Concrete – Lower long term pH due to consumption of lime and carbonation


Lower More Stable Long Term pH with Less CorrosionLower More Stable Long Term pH with Less Corrosion

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 Fe3O4 stable in reducing conditions.

Steel corrodes below 8.9


Reduced Steel CorrosionReduced Steel Corrosion

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.

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.)


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.


Reduced Delayed ReactionsReduced 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.


Reduced Delayed Reactions (2)Reduced Delayed Reactions (2)

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, probably holding it for slow release to extended hydration reactions of Ca silicates.

– Magnesia dries concrete out from the inside. Reactions do not occur without water.


Brucite has always played a protective role during salt attack. Putting it in the matrix of concretes in introduces considerable durability.

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

Durability - Reduced Salt & Acid AttackDurability - Reduced Salt & Acid Attack


Bingham Plastic RheologyBingham Plastic Rheology

Reactive Magnesia grains Mean size 5 - 6 micron

Portland cement grains Mean size 10 - 15 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.

Finely ground reactive magnesia consumes water but also acts as a plasticiser

There are also surface charge affects


Bingham Plastic RheologyBingham Plastic Rheology

O

O

O

O Mg++

+

- +

+

+

+

+

+

+

+

+

O +

+

+

+

+

+

O

O O

- -

- -

-

-

The strongly positively charged small Mg++ atoms attract water (which is polar) in deep layers affecting the rheological properties and making concretes less “sticky” with added pozzolan

It is not known how deep these layers get

Etc.

Etc.

Ca++ = 114, Mg++ = 86 picometres


RheologyRheology

TecEco concretes and mortars are:– Very homogenous and do not segregate easily. They exhibit good

adhesion and have a shear thinning property.

– Exhibit Bingham plastic qualities and react well to energy input.

– Have good workability.

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

Second layer low slump tec-cement concrete Tech Tendons

First layer low slump tec-cement concrete

A range of pumpable composites with Bingham plastic properties will be required in the future as buildings will be “printed.”


Reduced ShrinkageReduced Shrinkage

Log Time, days

Stoichiometric (Chemical) Shrinkage

Portland Cement Concretes

Tec-Cement Concretes

Plastic Settlement

Drying Shrinkage

Stoichiometric (Chemical) Expansion

Legend

Dimensional change such as shrinkage results in cracking and reduced durability

Net shrinkage is reduced due to stoichiometric expansion of Magnesium minerals, and reduced water loss.


Reduced Shrinkage – Less CrackingReduced Shrinkage – Less Cracking

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. Tec-cements also have greater tensile strength.

Test Age (days) Microstrain

7 133

14 240

28 316

56 470

Large Cement Company

Tec-cements exhibit higher tensile strength and less shrinkage and therefore less cracking


When magnesia hydrates it expands: MgO (s) + H2O (l) ↔ Mg(OH)2.nH2O (s)

40.31 + 18.0 ↔ 58.3 (minimum) molar mass

11.2 + liquid ↔ 24.3 (minimum) 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 less as the water comes from mix and bleed water.

The molar volume (L.mol-1)is equal to the molar mass (g.mol-1) divided by the density (g.L-1).

Volume Changes on HydrationVolume Changes on Hydration


Volume Changes on CarbonationVolume Changes on CarbonationConsider what happens when Portlandite

carbonates:Ca(OH)2 + CO2 CaCO3

74.08 + 44.01 ↔ 100 molar mass33.22 + gas ↔ 36.93 molar volumes

– Slight expansion. But shrinkage from surface water loss

Compared to brucite forming nesquehonite as it carbonates:

Mg(OH)2 + CO2 MgCO3.3H2O58.31 + 44.01 ↔ 138.32 molar mass24.29 + gas ↔ 74.77 molar volumes

– 307 % expansion (less water volume reduction) and densification of the surface preventing further ingress of CO2 and carbonation. Self sealing?

The molar volume (L.mol-1)is equal to the molar mass (g.mol-1) divided by the density (g.L-1).


Dimensionally Control Over Concretes During Curing?

Dimensionally Control Over Concretes During Curing?

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

The use of some wastes as aggregates causes shrinkage e.g. wood waste in masonry units, thin panels etc.

By varying the amount and form of magnesia added dimensional control can be achieved.


TecEco Cement Concretes –Dimensional ControlTecEco Cement Concretes –Dimensional Control

Combined – Hydration and Carbonation can be manipulated to be close to neutral.– So far we have not observed significant shrinkage in

TecEco tec - cement concretes (5% -10% substitution OPC) also containing fly ash.

– At some ratio, thought to be around 10% reactive magnesia and 90% PC volume changes are optimised as higher additions of MgO reduce strength.

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


Tec - Cement Concretes – Less or no Dimensional ChangeTec - Cement Concretes – Less or no Dimensional Change

90 days 28

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+.05%

Portland Cement

Reactive Magnesia

Composite Curve

+- Fly Ash?

HYDRATION THEN CARBONATION OF REACTIVE MAGNESIA AND OPC

Tec-Cement Concrete

It may be possible to engineer a particle with slightly delayed expansion to counterbalance the expansion and then shrinkage concretes containing gbfs.


Less Freeze - Thaw ProblemsLess 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 volumes38% 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


TecEco Cement Implementation

Summary

TecEco Cement Implementation

Summary


High Performance-Lower Construction CostsHigh Performance-Lower Construction Costs

Less binders (OPC + magnesia) for the same strength. Faster strength gain even with added pozzolans. Elimination of shrinkage reducing

associated costs. Tolerance and consumption of water. Reduction in bleed water enables finishing of lower

floors whilst upper floors still being poured and increases pumpability.

Cheaper binders as less energy required Increased durability will result in lower

costs/energies/emissions due to less frequent replacement.

Because reactive magnesia is also an excellent plasticiser, other costly additives are not required for this purpose.

A wider range of aggregates can be utilised without problems reducing transport and other costs/energies/emissions.

Foolproof Concrete?


TecEco Concretes - Lower Construction Costs (2)TecEco Concretes - Lower Construction Costs (2) Homogenous, do not segregate with pumping or work. Easier placement and better finishing. Reduced or eliminated carbon taxes. Eco-cements can to a certain extent be recycled. TecEco cements utilise wastes many of which improve

properties. Improvements in insulating capacity and other properties will

result in greater utility. Products utilising TecEco cements such as masonry and

precast products can in most cases utilise conventional equipment and have superior properties.

A high proportion of brucite compared to Portlandite is water and of Lansfordite and nesquehonite 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.


Relevance to the Masonry IndustryRelevance to the Masonry Industry

The Canadian masonry industry is ideally placed to take advantage of the Kyoto protocol to solve the world’s global warming problem as the country:– Making bricks, blocks, pavers and mortars using tec or eco-cements in

Canada would help the country meet its Kyoto objectives and together with the raw materials required provide a new export. Canada:

Canada:– Is close by countries that are big emitters (Europe, the US)– Has abundant Mg minerals suitable for a silicate reactor process to

sequester CO2 from concentrated sources such as power stations etc.– Has abundant non fossil fuel energy (hydro, wind) to power TecEco

kilns– Is close to markets that could use Mg carbonate products with

associated carbon credits


SummarySummary Simple, smart and sustainable?

– TecEco cement technology has resulted in potential solutions to a number of problems with Portland and other cements including shrinkage, durability and corrosion 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

“There is a way to make our city streets as green as the Amazon rainforest”

Fred Pearce New Scientist Magazine


TecEco Doing Things

TecEco Doing Things


The Use of Eco-Cements for Building Earthship BrightonThe Use of Eco-Cements for Building Earthship BrightonBy Taus Larsen, (Architect, Low Carbon Network Ltd.)The Low Carbon Network (www.lowcarbon.co.uk) was established to raise awareness of the links between buildings, the working and living patterns they create, and global warming and aims to initiate change through the application of innovative ideas and approaches to construction. England’s first Earthship is currently under construction in southern England outside Brighton at Stanmer Park and TecEco technologies have been used for the floors and some walling.

Earthships are exemplars of low-carbon design, construction and living and were invented and developed in the USA by Mike Reynolds over 20 years of practical building exploration. They are autonomous earth-sheltered buildings independent from mains electricity, water and waste systems and have little or no utility costs.

For information about the Earthship Brighton and other projects please go to the TecEco web site.


Repair of Concrete Blocks. Clifton Surf ClubRepair of Concrete Blocks. Clifton Surf ClubThe Clifton Surf Life Saving Club was built by first pouring footings, On the footings block walls were erected and then at a later date concrete was laid in between.

As the ground underneath the footings was sandy, wet most of the time and full of salts it was a recipe for disaster.

Predictably the salty water rose up through the footings and then through the blocks and where the water evaporated there was strong efflorescence, pitting, loss of material and damage.

The TecEco solution was to make up a formulation of eco-cement mortar which we doctored with some special chemicals to prevent the rise of any more moisture and salt.

The solution worked well and appears to have stopped the problem.


Mike Burdon’s Murdunna WorksMike Burdon’s Murdunna WorksMike Burdon, Builder and Plumber.

I work for a council interested in sutainability and have been involved with TecEco since around 2001 in a private capacity helping with large scale testing of TecEco tec-cements at our shack.

I am interested in the potentially superior strength development and sustainability aspects.

To date we have poured two slabs, footings, part of a launching ramp and some tilt up panels using formulations and materials supplied by John Harrison of TecEco. I believe that research into the new TecEco cements essential as overall I have found:

1. The rheological performance even without plasticizer was excellent. As testimony to this the contractors on the site commented on how easy the concrete was to place and finish.

2. We tested the TecEco formulations with a hired concrete pump and found it extremely easy to pump and place. Once in position it appeared to “gel up” quickly allowing stepping for a foundation to a brick wall.

3. Strength gain was more rapid than with Portland cement controls from the same premix plant and continued for longer.

4. The surfaces of the concrete appeared to be particularly hard and I put this down to the fact that much less bleeding was observed than would be expected with a Portland cement only formulation


Tec-Cement Slab Whittlesea, Vic. AustraliaTec-Cement Slab Whittlesea, Vic. Australia On 17th March 2005 TecEco

poured the first commercial slab in the world using tec-cement concrete with the assistance of one of the larger cement and pre-mix companies.

– The formulation strategy was to adjust a standard 20 MPa high fly ash (36%) mix from the company as a basis of comparison.

– Strength development, and in particular early strength development was good. Interestingly some 70 days later the slab is still gaining strength at the rate of about 5 MPa a month.

– Also noticeable was the fact that the concrete was not as "sticky" as it normally is with a fly ash mix and that it did not bleed quite as much.

– Shrinkage was low. 7 days - 133 micro strains, 14 days - 240 micro strains, 28 days - 316 micros strains and at 56 days - 470 microstrains.

Strength Development of Tec-Cement Concrete

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Documents

Presentation downloadable from 1 Tec and Eco-Cement Update I will have to race over some slides but the presentation is always downloadable