presentation downloadable from 1 tec and eco-cement update i will have to race over some slides but...
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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
2Presentation downloadable from www.tececo.com
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.
3Presentation downloadable from www.tececo.com
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
4Presentation downloadable from www.tececo.com
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
5Presentation downloadable from www.tececo.com
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.
6Presentation downloadable from www.tececo.com
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
7Presentation downloadable from www.tececo.com
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
8Presentation downloadable from www.tececo.com
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 )
9Presentation downloadable from www.tececo.com
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.
10Presentation downloadable from www.tececo.com
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
11Presentation downloadable from www.tececo.com
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.
12Presentation downloadable from www.tececo.com
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.)
13Presentation downloadable from www.tececo.com
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 %.
14Presentation downloadable from www.tececo.com
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.
15Presentation downloadable from www.tececo.com
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?
16Presentation downloadable from www.tececo.com
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.
17Presentation downloadable from www.tececo.com
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.
18Presentation downloadable from www.tececo.com
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
19Presentation downloadable from www.tececo.com
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)
20Presentation downloadable from www.tececo.com
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)
21Presentation downloadable from www.tececo.com
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
22Presentation downloadable from www.tececo.com
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
23Presentation downloadable from www.tececo.com
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.
24Presentation downloadable from www.tececo.com
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
25Presentation downloadable from www.tececo.com
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.
26Presentation downloadable from www.tececo.com
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
27Presentation downloadable from www.tececo.com
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??
28Presentation downloadable from www.tececo.com
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
29Presentation downloadable from www.tececo.com
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
30Presentation downloadable from www.tececo.com
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
31Presentation downloadable from www.tececo.com
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
32Presentation downloadable from www.tececo.com
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
33Presentation downloadable from www.tececo.com
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.
34Presentation downloadable from www.tececo.com
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
35Presentation downloadable from www.tececo.com
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
36Presentation downloadable from www.tececo.com
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.)
37Presentation downloadable from www.tececo.com
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.
38Presentation downloadable from www.tececo.com
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.
39Presentation downloadable from www.tececo.com
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.
40Presentation downloadable from www.tececo.com
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
41Presentation downloadable from www.tececo.com
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
42Presentation downloadable from www.tececo.com
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
43Presentation downloadable from www.tececo.com
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.”
44Presentation downloadable from www.tececo.com
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.
45Presentation downloadable from www.tececo.com
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
46Presentation downloadable from www.tececo.com
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
47Presentation downloadable from www.tececo.com
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).
48Presentation downloadable from www.tececo.com
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.
49Presentation downloadable from www.tececo.com
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.
50Presentation downloadable from www.tececo.com
Tec - Cement Concretes – Less or no Dimensional ChangeTec - Cement Concretes – Less or no Dimensional Change
90 days 28
? ?
? ?
?
? ?
?
-.05%
+.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.
51Presentation downloadable from www.tececo.com
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
52Presentation downloadable from www.tececo.com
TecEco Cement Implementation
Summary
TecEco Cement Implementation
Summary
53Presentation downloadable from www.tececo.com
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?
54Presentation downloadable from www.tececo.com
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.
55Presentation downloadable from www.tececo.com
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
56Presentation downloadable from www.tececo.com
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
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TecEco Doing Things
TecEco Doing Things
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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.
59Presentation downloadable from www.tececo.com
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.
60Presentation downloadable from www.tececo.com
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
61Presentation downloadable from www.tececo.com
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
0
5
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0 5 10 15 20 25 30
Days water cured
Str
eng
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aCompressiveStrength