Transcript Document

An overview of Future Concretes
An overview of the alternative mineral binder systems
and composites made with them including novel concrete
technologies addressing practical supply chain and
economic issues including energy
17/07/2015
www.tececo.com
www.propubs.com
Why Future Concretes?
• What’s wrong with the concrete we use made with
Portland Cement?
– Embodied energy and emissions, shrinkage, durability,
placement, tensile strength etc. etc. Not optimised for
lifetime energy reduction.
• We can make better more environmentally friendly
materials but what about the cost?
– Better concretes don’t necessarily produce more and
those producing them will make more money.
• Concrete made for purpose = Higher Margin?
– Architectural façade, insulative properties, permeable
pavement etc.
The Business Model
• The industry model is like Woolworths or Coles. Head on
competition. Low margins resulting in a reliance on turnover
volume and cost control to produce profits.
– This model is past its use by date.
• "Firms need to embrace innovation to remain competitive.
Future job creation will come as companies transform and
adopt new practices. Putting it simply, firms that innovate will
survive and be the market leaders of tomorrow." Source: Senator
the Hon Kim Carr 24 Aug 2011
• The need to innovate under a carbon price and trading system
is significantly greater than without.
• Given our problems the need to innovate goes beyond the
immediate needs of the industry. There are other
stakeholders
• Innovation recognises new markets
Making Money Through Innovation
• In Australia rules relating to the new R & D Tax Incentive have
changed. The new scheme effective 1 July 2011 is more
generous.
– Make a $1 and pay 30c corporate tax
– Spend a $1 to innovate thereby ensuring future profits and adding
value to your balance sheet and the government will give you either 40
or 45c as a grant.
– That’s a 70 - 75c difference!
• Given the changes the industry business model needs to
change.
• TecEco are also changing their business model. We are going to
register as a Research Service Provider (RSP) and become more
aligned with the University of Tasmania to attract student
power under my supervision.
• The leverage provided by students will increase the value of
investing in R & D to well over a dollar.
What we Sell in the Industry
• Managers in the concrete industry seem to
misunderstand what we sell.
• They think we sell Portland cement and concrete
made with it.
• My analysis is that what we sell is the technical
confidence in a liquid that sets as a solid material
and it really would not matter what either was
provided we could demonstrate technical merit and
suitable properties.
Increases in Business Performance from the
Previous Year, by Innovation Status 2008-9
Some of the Issues?
The Techno Process
Primary Production Process Build, & Manufacture Use Dispose
Underlying Molecular Flows
Primary
Production
Methane
NOX &
SOX
Heavy
Metals
CO2
etc.
Embodied
& Process
Energy
Process,
Build
&
Manufacture
NOX &
SOX
Heavy
Metals CO2
etc.
Embodied
& Process
Energy
Use
NOX &
SOX
Heavy
Metals
CO2
etc.
Lifetime
Energy
Dispose
or Waste
Methane
NOX &
SOX
Heavy
Metals
CO2
etc.
Process
Energy
Predicted Global Cement Demand
and Emissions
Source: Quillin K. Low-CO2 Cements based on Calcium Sulfoaluminate [Internet]. Available from:
http://www.soci.org/News/~/media/Files/Conference%20Downloads/Low%20Carbon%20Cemen
ts%20Nov%2010/Sulphoaluminate_Cements_Keith_Quillin_R.ashx
Energy Outlook to 2035
Source: U.S. Energy Information Administration. International Energy Outlook 2010 [Internet].
U.S. Energy Information Administration; 2010 [cited 2010 Sep 5]. Available from:
www.eia.gov./oiaf/ieo/index.html
Global Waste – An Underestimate!
The challenge is to convert waste to resource.
There are Huge Change Opportunities
• A wide variety of possible end uses with higher potential
margins for which current solutions are sub-optimal.
– E.g. Addessing properties affecting lifetime energy.
• E.g. Mineral composites with higher “R” value
– E.g. Particle boards made with mineral binders
– E.g. Exterior structural panels with insulating properties
• Huge opportunities for reducing the cost base and improving
the properties of concretes by focusing on the process by
which they are made and what they are made with.
– A few tweaks to the formulations
– Major changes to the process and some
– Lateral thinking in relation to aggregates.
• Every improvement counts but quantum improvements really
matter – If implemented!
• Implementation issue because of the low level of skills in the
industry
Our Mantra
• Think outside the square.
• Spend more time thinking (R & D) less time doing
(earning low margins).
• We cannot solve problems doing the same old thing
in the same old way.
• The technology paradigm defines what is or is not a
resource.
• Improvements through innovation = profit!
• Think whole of material and whole of system
• Refine definition of what’s important and what is not
Example of a Decision Matrix to Help us
Improve the Future
ALTERNATIVES
Mg Hydraulic
Decision Model
Criterion
Weight Rating
Ea se of Pla cement
PC
Score Rating
Geopolymer
Score Rating
MgCarbonate
Score Rating
MgO
Score Rating
C4 A 3 S
Score Rating
Score
10
9
90
8.5
85
3
30
7
70
0
0
7
70
Cost
8
8
64
8.5
68
9
72
7
56
0
0
7
56
Sa fety
7
8
56
8
56
4
28
8
56
0
0
8
56
Compressive Strength
6
8
48
7.5
45
7.5
45
6
36
6
36
6
36
Tensile Strength
5
9
45
7.5
37.5
7.5
37.5
6
30
6
30
6
30
Dura bility
5
9
45
7
35
7
35
8
40
8
40
8
40
Use of Pozzola nic Wa stes
5
9
45
7
35
7
35
4
20
4
20
4
20
Use of Other Wa stes
5
9
45
4
20
5
25
9
45
9
45
4
20
Embodied Energy
8
7
56
7
56
8
64
7
56
7
56
7
56
Embodied Emissions
8
7
56
7
56
9
72
5
40
5
40
5
40
Therma l Ma ss
4
8
32
8
32
8
32
7
28
7
28
7
28
Therma l Flow
4
8
32
8
32
4
16
9
36
9
36
9
36
Supply Cha in
7
8
56
9
63
4
28
5
35
4
28
5
35
82
107
670
97
621
83
520
88
548
65
359
83
523
Total
Score = Rati ng * Wei ght
Rating
700
Score
600
500
400
Scores
300
200
100
0
Mg - Hydraulic
Alternatives
Score
PC
Rating
Geopolymer
Decision
Model
Future Cement Contenders
Portland Cement
PC
Current
Methods
PC
Permeable
Block
.369
formulation
PC
Split Process
– Lime then .369
clinker
.369
0.498
0.498
0.498
.868
.868
.868
None
.369
.369
.001
.144
.001
1. http://www.tececo.com/files/spreadsheets/TecEcoCementLCA12Oct2011.xls
Apply to
Comment
Notes
Cements
Process
Based on
Net
Absorpti Emissions
Emission on
(Sequestrat
Emissions s (kiln
(tonnes ion – No
Process
(if no kiln capture– CO2 /
kiln
CO2
Decarbonat
capture– tonnes
tonne
Capture)
(tonnes
ion CO2
tonnes
Compoun
Example of
CO2 /
CO2 /
(tonnes CO2
(tonnes
CO2 /
d,
Cement Type
tonne
tonne
/ tonne
CO
/
tonne
tonne
Compoun Assuming
2
Compound Compound)
Compound,
Compoun d)
100%
)
carbonati Assuming
d)
100%
on 1
carbonatio
year)
n 1 year)
.867
Split process
lime with
recapture then
clinker
No supplementary
Most dense cementitious or
pozzolanic
concretes
materials
1
.724
No supplementary
Ordinary
Most dense cementitious or
pozzolanic
Portland Cement concretes
materials
1
.368
Split process
lime with
recapture then
clinker
1
No supplementary
Most dense cementitious or
pozzolanic
concretes
materials
The Potential of CO2 Release and
Capture - Portland Cements
No Capture during
Manufacture
CO2 capture (e.g.
N-Mg process etc.)
CO2 in atmosphere
Hydrated
Cement
Paste
H 2O
Clinker
Net Energy
3962 kJ/kg
product
Hydrated
Cement
Paste
Carbon positive. Chemical and
process emissions
Carbon positive. Chemical and
process emissions
CO2 capture (e.g.
N-Mg process etc.)
CaCO3
CaCO3 + Clays
CaCO3 + Clays
Net Energy
3962 kJ/kg
product
Net Emissions
(Sequestration) 0.369
Kg CO2/Kg product
Net Emissions
(Sequestration) 0.369
kg CO2/kg product
Net Emissions
(Sequestration) 0.867
kg CO2/kg product
H 2O
Split Process with
Capture during
Manufacture
Capture during
Manufacture
H 2O
Clinker
Net Energy
3962 kJ/kg
product
Hydrated
Cement
Paste
CaO + Clays
Clinker
Net sequestration less carbon
from process emissions
Use of non fossil fuels => Low or no process emissions
Source Data: http://www.tececo.com/files/spreadsheets/TecEcoCementLCA12Oct2011.xls
Future Cement Contenders
Mg Group
Absorpti
on
(tonnes
CO2 /
tonne
Compou
nd,
Assumin
g 100%
carbonati
on 1
year)
Net
Emission
s
(Sequestr
ation)
(tonnes
CO2 /
Example of Cement
tonne
Apply to
Type
Compou
nd,
Assumin
g 100%
carbonati
on 1
year)
Cements
Process
Based on
Emission
Emission
s (kiln
Decarbona s (if no
capture–
Process
tion CO2 kiln
tonnes
CO2
(tonnes
capture–
CO2 /
(tonnes
CO2 /
tonnes
tonne
CO2 / tonne tonne
CO2 /
Compou
Compound) Compoun tonne
nd)
Compou
d)
nd)
<750 oC
MgCO3
.403
1.092
1.495
.403
-1.092
.-.688
Eco-cement concrete,
TecEco Eco-Cement
TecEco, Cambridge
pure MgO concretes.
Force carbonated
& Novacem
Novacem concretes
pure MgO
3
<450 oC
MgCO3.3H2O
.693
1.092
1.784
.693
-1.092
-.399
Eco-cement concrete,
TecEco, Cambridge N-Mg route
pure MgO concretes.
& Novacem
University of Rome
Novacem concretes?
3
.693
1.092
1.784
.693
-2.184
-1.491
Eco-cement concrete,
TecEco, Cambridge N-Mg route
pure MgO concretes.
& Novacem
University of Rome
Novacem concretes?
3
<450 oC
Modified
Ternary
Blends
(50% PC)
MgCO3.3H2O
Including
capture during
production of
nesquehonite
Silicate route
Split Process –
Lime (with
capture) then
clinker
?
.185
Novacem
.185
.002
.183
1. http://www.tececo.com/files/spreadsheets/TecEcoCementLCA12Oct2011.xls
2. http://www.tececo.com/files/newsletters/Newsletter93.php
Ternary mix with MgO Most dense
additive.
concretes
Notes
Comment
After Klaus Lackner?
Faster setting and
2
higher early strength
The Potential of CO2 Release and Capture
Magnesium Carbonating System
MgCO3 Route using TecEco Tec-Kiln
No Capture during
Manufacture
With Capture during
Manufacture
<7250C
CO2
CO2 from
atmosphere
Net Emissions
(Sequestration)
0.403 Kg CO2/Kg
product
Net Emissions
(Sequestration) .085 kg
CO2/kg product
CO2 capture
(e.g. N-Mg
process etc.)
MgCO3
MgCO3
H2O
H2O
Net Energy
4084 kJ/kg
product
MgO
H2O
H2O
Net Energy
4084 kJ/kg
product
MgO
Mg(OH)2
Mg(OH)2
H2O
Carbon neutral except for carbon from
process emissions
H2O
Net sequestration less carbon from
process emissions
Use of non fossil fuels => Low or no process emissions
Source Data: http://www.tececo.com/files/spreadsheets/TecEcoCementLCA14Feb2011.xls
The Potential of CO2 Release and Capture
Magnesium Carbonating System
MgCO3.3H20 Route using TecEco Tec Kiln
No Capture during
Manufacture
With Capture during
Manufacture
<4200C
CO2
CO2 from
atmosphere
Net Emissions
(Sequestration)
0.693 Kg CO2/Kg
product
CO2 capture
(e.g. N-Mg
process etc.)
MgCO3.3H2O
MgCO3.3H2O
H2O
H2O
Net Energy
7140 kJ/kg
product
Net Emissions
(Sequestration) .399kg CO2/kg
product
MgO
H2O
H2O
Net Energy
7140 kJ/kg
product
MgO
Mg(OH)2
Mg(OH)2
H2O
Carbon neutral except for carbon from
process emissions
H2O
Net sequestration less carbon from
process emissions
Use of non fossil fuels => Low or no process emissions
Source Data: http://www.tececo.com/files/spreadsheets/TecEcoCementLCA14Feb2011.xls
Gaia Engineering
kg CO2-e/kg product
1 -1.092
2 -.399
3 -1.092
>2 kg CO2-e/kg Mg
product
2
3
1
Or similar. The annual world production of HCl is about 20
million tons, most of which is captive (about 5 million tons
on the merchant market).
The N-Mg Process
HCl
NH3 and a small amount of CO2
CO2
H2O
Tec-Kiln
Mg rich water
Ammoniacal Mg rich water
MgCO3.3H2O
MgO
MgO
Mg(OH)2
Steam
MgCO3.3H2O
Filter
Filter
NH4Cl and a small amount of NH4HCO3
A Modified Solvay Process for Nesquehonite
The Tec-Reactor Hydroxide
Carbonate Capture Cycle
• The solubility of carbon dioxide gas in seawater
– Increases as the temperature approached zero and
– Is at a maxima around 4oC
• This phenomenon is related to the chemical nature of CO2 and
water and
• Can be utilised in a carbonate – hydroxide slurry process to
capture CO2 out of the air and release it for storage or use in a
controlled manner
Gaia Engineering
Portland Cement
Manufacture
CaO
Industrial CO2
Brine,
Sea
water,
Oil
Process
water,
De Sal
Waste
Water
etc .
N-Mg
Process
TecEco
Tec-Kiln
MgO
MgCO3.3H2O
Clays
TecEco
Cement
Manufacture
GBFS
Fly ash
Fresh
Water
EcoCements
NH4Cl or HCl
Building
components &
aggregates
Other wastes
TecCements
Man Made Carbonate
Aggregate?
Tonnes 20,000,000,000
18,000,000,000
16,000,000,000
World Production PC
14,000,000,000
Tonnes CO2 from unmodified PC
12,000,000,000
World Production Concrete
10,000,000,000
8,000,000,000
Calculated Proportion Aggregate
6,000,000,000
4,000,000,000
CO2 Sequestered in Mg Carbonate
Aggregate
2,000,000,000
Net Sequestration
2009
2006
2003
2000
1997
1994
1991
1988
1985
1982
1979
1976
1973
1970
1967
1964
1961
1958
1955
1952
1949
1946
0
Assumptions - 50% non PC N-Mg mix and Substitution by Mg Carbonate Aggregate
Percentage by Weight of Cement in Concrete
Percentage by weight of MgO in cement
Percentage by weight CaO in cement
Proportion Cement Flyash and/or GBFS
1 tonne Portland Cement
Proportion Concrete that is Aggregate
CO2 captured in 1 tonne aggregate
Source USGS: Cement Pages
15.00%
6%
29%
50%
0.867Tonnes CO2
85%
1.092Tonnes CO2
Magnesium Carbonate Cements
• Magnesite (MgCO3) and the di, tri, and pentahydrates known as
barringtonite (MgCO3·2H2O), nesquehonite (MgCO3·3H2O),
and lansfordite (MgCO3·5H2O), respectively.
• Some basic forms such as artinite (MgCO3·Mg(OH)2·3H2O),
hydromagnestite (4MgCO3·Mg(OH)2·4H2O) and dypingite
(4MgCO3· Mg(OH)2·5H2O) also occur as minerals.
• We pointed out as early as 2001 that magnesium carbonates are
ideal for sequestration as building materials mainly because a
higher proportion of CO2 than with calcium can be bound and
significant strength can be achieved.
• The significant strength is a result of increased density through
carbonation (high molar volume increases) and the
microstructure developed by some forms.
TecEco Eco-Cements
Eco-Cements are blends of one or more
hydraulic cements and relatively high
proportions of reactive magnesia with or
without pozzolans and supplementary
cementitious additions. They will only
carbonate in gas permeable substrates forming
strong fibrous minerals. Water vapour and CO2
must be available for carbonation to ensue.
Eco-Cements can be used in a wide range of
products from foamed concretes to bricks,
blocks and pavers, mortars renders, grouts and
pervious concretes such as our own
permeacocrete. Somewhere in the vicinity of
the Pareto proportion (80%) of conventional
concretes could be replaced by Eco-Cement.
Left: Recent Eco-Cement blocks made, transported and erected in a week.
Laying and Eco-Cement floor. Eco-Cement mortar & Eco-cement mud
bricks. Right: Eco-Cement permeacocretes and foamed concretes
TecEco Tec-Kiln, N-Mg route
The calcination of nesquehonite has a relatively
high enthalpy but there is significant scope for
reducing energy using waste heat
Initial weight loss below 1000 C consists almost
entirely of water (1.3 molecules per molecule
of nesquehonite). Between 100 and 1500C
volatilization of further water is associated with
a small loss of carbon dioxide (~3-5 %).
From 1500C to 2500C, the residual water
content varies between 0-6 and 0-2 molecules
per molecule of MgC03. Above 3000C, loss of
carbon dioxide becomes appreciable and is
virtually complete by 4200C, leaving MgO with a
small residual water content.
Dell, R. M. and S. W. Weller (1959). "The
Thermal Decomposition of Nesquehonite
MgCO3 3H20 And Magnesium Ammonium
Carbonate MgCO3 (NH4)2CO3 4H2O." Trans
Faraday Soc 55(10): 2203 - 2220.
Energy could be saved using a two stage
calcination process using waste energy for the
first stage.
Modified PC 50% Ternary Mix with
N-Mg Route Mg Carbonate Aggregate
•
•
•
•
•
•
•
25-30% improvement in strength
Fast first set
Better Rheology
Less shrinkage – less cracking
Less bleeding
Long term durability
Solve autogenous shrinkage?
Criteria
Good
Energy Requirements and Chemical Releases, Use >50% replacements and still set like “normal”
Reabsorption (Sequestration?)
concrete!
Speed and Ease of Implementation
Rapid adoption possible
Barriers to Deployment
Cost/Benefit
Use of Wastes? or Allow Use of Wastes?
Performance
Engineering
Thermal
Architectural
Safety
Audience 1
Audience 2
Bad
Permissions and rewards systems see
http://www.tececo.com/sustainability.permissions_rewa
rds.php
Excellent until fly ash runs out!
Uses GBFS and fly ash and manufactured
nesquehonite based aggregate
Excellent all round
High thermal capacity
Excellent
No issues
Magnesium Phosphate Cements
• Chemical cements that rely on the precipitation of insoluble magnesium
phosphate from a mix of magnesium oxide and a soluble phosphate.
• Some of the oldest binders known (dung +MgO)
• Potentially very green
– if the magnesium oxide used is made with no releases or via the nesquehonite
(N-Mg route) and
– a way can be found to utilise waste phosphate from intensive agriculture and
fisheries e.g. feedlots. (Thereby solving another environmental problem)
Criteria
Good
Energy Requirements and Chemical Releases,
Reabsorption (Sequestration?)
The MgO used could be made without releases
Speed and Ease of Implementation
Rapid adoption possible
Barriers to Deployment
Cost/Benefit
Use of Wastes? or Allow Use of Wastes?
Performance
Engineering
Thermal
Architectural
Safety
Audience 1
Audience 2
Economies of scale issue for MgO to overcome
With technology could use waste phosphate reducing
water pollution
Excellent all round
High thermal capacity
No issues
Bad
There is not much phosphate on the planet
If barrier overcome (see below)
Permissions and rewards systems see
http://www.tececo.com/sustainability.permissions_rewa
rds.php. Must find a way to extract phosphate from
organic pollution.
Sorel Type Cements and Derivatives
Sorel Type Cements and Derivatives are all nano
or mechano composites relying on a mix of ionic,
co-valent and polar bonding.
There are a very large number of permutations
and combinations and thus a large number of
patents
Criteria
Good
Energy Requirements and Chemical Releases,
Reabsorption (Sequestration?)
The MgO used could be made without releases
Speed and Ease of Implementation
More could be used
Barriers to Deployment
Cost/Benefit
Economies of scale issue for MgO to overcome
Use of Wastes? or Allow Use of Wastes?
Performance
Engineering
Excellent except
Thermal
High thermal capacity
Architectural
Safety
No issues
Audience 1
Audience 2
Bad
If barrier overcome (see below)
Not waterproof even with modification.
Not waterproof
Not waterpoof, salt affect metals
Future Cement Contenders
(tonnes
CO2 /
Example of
tonne
Cement Type
Compoun
d,
Assuming
100%
carbonati
on 1 year)
0.785
-0.332
>0.578
>0.511
?
?
>0.578
>0.511
0.594
>0.594
?
>0.594
0.216
>0.216
?
?
CaO
Conventional .453
0.785
1.237
C3S
C2S
Conventional ?
Conventional ?
0.578
0.511
C3A
Conventional ?
C4A3S
Conventional ?
.453
Net
Emissions
(Sequestr
ation)
Carbonating
lime mortar
Apply to
Comment
Notes
Cements
Process
Based on
Absorpt
ion
Emission
Emission
(tonnes
Decarbon
s (kiln
s (if no
CO2 /
ation
capture–
Process
kiln
tonne
CO2
tonnes
CO2
capture–
Compou
(tonnes
CO2 /
(tonnes CO2
tonnes
nd,
CO2 /
tonne
/ tonne
CO2 /
Assumi
tonne
Compou
tonne
ng
Compound)
Compoun
nd)
Compou
100%
d)
carbona
nd)
tion 1
year)
Small net
Calera, British Lime sequestration
Assn. & many others with TecEco
kiln
Belite cement Chinese & others
Tri calcium
aluminate
Increased proportion
cement
Calcium
sulfoaluminate Chinese & others
cement
1. http://www.tececo.com/files/spreadsheets/TecEcoCementLCA12Oct2011.xls
3. Quillin, K. and P. Nixon (2006). Environmentally Friendly MgO-based cements to support sustainable construction - Final report, British Research
Establishment.
1
3
3
3
Future Cement Contenders
Cements
Based on
Process
Alakali
Activated
Ground
Granulate
d Blast
Furnace
Slag
(GBFS)
GBFS
(“slag”) is
a waste
product
Nil to
from the cement
manuf
industry
acture of
iron and
steel
Net
Emissions
(Sequestr
ation)
(tonnes
CO2 /
Example of
tonne
Cement Type
Compoun
d,
Assuming
100%
carbonati
on 1 year)
Apply to
Comment
Notes
Absorpt
ion
Emission
Emission
(tonnes
Decarbon
s (kiln
s (if no
CO2 /
ation
capture–
Process
kiln
tonne
CO2
tonnes
CO2
capture–
Compou
(tonnes
CO2 /
(tonnes CO2
tonnes
nd,
CO2 /
tonne
/ tonne
CO2 /
Assumi
tonne
Compou
tonne
ng
Compound)
Compoun
nd)
Compou
100%
d)
carbona
nd)
tion 1
year)
GBFS with
MgO activator
Patented by
TecEco
Many other
activators
1
Not patented
Geopolymer Alliance,
Geo
polymers
Fly ash +
NaOH
0.16
1. http://www.tececo.com/files/spreadsheets/TecEcoCementLCA12Oct2011.xls
4. http://www.geopolymers.com.au/science/sustainability
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Geopolymer
Institute, University
Melbourne
6
CaO-Lime
Criteria
Good
Energy Requirements and Chemical Releases,
Reabsorption (Sequestration?)
The CaO used could be made without
Speed and Ease of Implementation
Barriers to Deployment
Cost/Benefit
Use of Wastes? or Allow Use of Wastes?
Performance
Engineering
Thermal
Architectural
Safety
Audience 1
Audience 2
Easily implemented as no carbonation rooms etc
reqd.
Good
Engineered thermal capacity and conductivity.
An irritating dust
Bad
Permissions and rewards systems see
http://www.tececo.com/sustainability.permissions_rewa
rds.php.
We need carbon trading!
Geopolymers
Criteria
Good
Energy Requirements and Chemical Releases,
Reabsorption (Sequestration?)
Low provided we do not run out of fly ash
Speed and Ease of Implementation
Barriers to Deployment
Cost/Benefit
Use of Wastes? or Allow Use of Wastes?
Performance
Engineering
Thermal
Architectural
Safety
Audience 1
Audience 2
Process issues to be overcome
Bad
Permissions and rewards systems see
http://www.tececo.com/sustainability.permissions_rewa
rds.php.
We need carbon trading!
Good but inconsistent
Engineered thermal capacity and conductivity.
Caustic liquors
Geopolymers as a future concrete suffer from two basic flaws on one very high risk
Flaw. 1. The nanoporisity flaw which leads to durability problems and Flaw. 2. The fact that
water is not consumed in the geopolymerisation process resulting in the almost
impossible task of making them fluid enough for placement. Too much water reduces
alkalinity and hence the high risk.
Other Contenders
• Slag cements a variant of Portland cement as CSH is the main product.
• Supersulfated cements have potential as they are made mostly from GBFS
and gypsum which are wastes and only a small amount of PC or lime. The
main hydration product is ettringite and they show good resistance to
aggressive agents including sulphate but are slow to set. (A derivative)
• Calcium aluminate cements are hydraulic cements made from limestone
and bauxite. The main components are monocalcium aluminate CaAl2O4
(CA) and mayenite Ca12Al14O33 (C12A7) which hydrate to give strength.
Calcium aluminate cements are chemically resistant and stable to quite
high temperatures.
• Calcium sulfoaluminate cements & belite calcium sulfoaluminate
cements are low energy cements that have the potential to be made from
industrial by products such as low calcium fly ash and sulphur rich wastes.
The main hydration product producing strength is ettringite. Their use has
been pioneered in China (A derivative)
Other Contenders
• Belite cements can be made at a lower temperature and contains less
lime than Portland cement and therefore has much lower embodied
energy and emissions. Cements containing predominantly belite are
slower to set but otherwise have satisfactory properties. Many early
Portland type cements such as Rosendale cement were rich in belite like
phases. (a variant, See
http://www.tececo.com/links.cement_rosendale.php.)
• PC - MgO – GBFS – fly ash blends. MgO is the most powerful new tool in
hydraulic cement blends since the revelation that reactive magnesia can
be blended with other hydraulic cements such as Portland cement. 2530% improvements in compressive strength and greater improvements in
tensile strength, faster first set, better rheology and less shrinkage and
cracking less bleeding and long term durability have been demonstrated. It
is also possible autogenous shrinkage has been solved.
• MgO blended with other hydraulic cements, pozzolans and
supplementary cementitious materials (SCM’s). Amazingly very little real
research has been done on optimised blends particularly with cements
other than Portland cement.