Calcined Clays and LC3
Professor Karen Scrivener Karen Scrivener
» English » MA Cambridge, PhD Imperial College
» Head of Calcium Aluminate Research Lafarge 1995-2001
» Professor and Director of Laboratory of Construction Materials , EPFL 2001- present
» Editor in Chief Cement and Concrete Research
» Founder and Co-ordinator of Nanocem. Industrial Academic Partnership for Fundamental Research on Cementitious Materials
» Fellow Royal Academy of Engineering Main messages » We have to be realistic about the composition of cementitious materials in the future » >90% will be based on Portland cement with SCMs » Classic SCMs – fly ash and slag are only around 15% of current cement production, will drop to < 10% in near future » We need to use new sources of SCMs - calcined clay » Calcined clays even with only 40-60% Kaolin give very good performance in terms of strength and durability Concrete is an environmentally friendly material
Material MJ/kg kgCO2/kg
Cement 4.6 0.83 2 Concrete 0.95 0.13 Masonry 3.0 0.22 Wood 8.5 0.46 Wood: multilayer 15 0.81 Steel: Virgin 35 2.8 Steel: Recycled 9.5 0.43 Aluminium: virgin 218 11.46 Relative energy,Relative CO Aluminium recycled 28.8 1.69
Glass fibre 100 8.1 composites Glass 15.7 0.85
ICE version 1.6a Hammond G.P. and Jones C.I 2008 Proc Instn Civil Engineers www.bath.ac.uk/mech-eng/sert/embodied/ Origins of CO2 emissions in cement production
1 tonne of cement leads to the emission of 650 – 900 kg CO2
The production process is highly optimised Around 80% of CaCO3 thermodynamic limit. decomposition 40 it is estimated that < 2% (CHEMICAL) further savings can be Fuel made here 60 Use of waste fuels, which can be > 80% reduces the demand
for fossil fuels CaCO3 CaO + CO2 What can be done to lower environmental impact? What is available on earth?
Mg rest K Na2O Na Too soluble K2O Ca Fe2O3 Fe Too low mobility in alkaline solutions MgO CaO Al O
SiO2 The most useful Al O Si 2 3
Slag cement blend Hydraulic materials in CaO-SiO2-Al2O3 system SiO2 BUT, what sources of minerals are
there which contain Al2O3 >> SiO2 ? Bauxite – localised, under increasing demand for Aluminium production, EXPENSIVE
Also resource limited. All current bauxite production diverted to produce CSA would Calcium aluminate / cover <15% of need Portland calcium sulfo aluminate Cement
CaO Al2O3 Partial replacement of Portland clinker Traditionally Portland Cement consists of clinker ground with about 5% of calcium sulfate (e.g gypsum) Clinker Gypsum Cement
Now the majority of cement Supplementary contain other materials as a cementitious partial substitution for materials clinker. SCMs Supplementary cementitious materials
Limestone Fly ash Slag Natural pozzolan Calcined clay
Often by-products or wastes from other industries Local availability very important! Evolution of Clinker substitution
Clinker substitution most successful strategy to reduce CO2 25%
20% 1% 1% 1% 1% 1% 1% 1% 2% 2% 1% 2% 2% 2% 2% 1% 2% Limestone 15% 1% 2% 4% 4% 2% 4% 4% 2% 4% 4% 4% 2% 3% Slag 3% 3% 2% 10% 4% 5% 5% 5% Fly ash 2% 5% 5% 5% 5% 5% 1% 4% 4% 1% Puzzolana 4% 5% 4% 6% 7% 7% 7% Others 5% 5% 6% 6% 6% 6% 4% 0% 2% 1990 2000 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014
• Almost no progress in last 5 years • Only 3 substitutes used in quantity Availability of SCMs
silica fume waste glass Vegetable ashes Natural Pozzolan Used Available Slag Fly ash Portland cement
limestoneFiller Calcined Clay
0 2000 4000 6000
Mt/yr There is no magic solution
. Blended with SCMs will be best solution for sustainable cements for foreseeable future . Only material really potentially available in viable quantities is calcined clay. . Blend containing combination of calcined clay and limestone are particularly interesting: EPFL led LC3 project supported by SDC. Started 2013 What is LC3 70 100 60 50 80 1 day 40 Gypsum 60 7 days Limestone 30
(MPa) 28 days 40 Calcined clay 20 Clinker 10 90 days
Mass Mass proportion(%) 20 Compressive strength 0
0 PC LC3-50 PC PPC30 LC3-50 LC3-65 • 50% less clinker
• 30% less CO2 LC3 is a family of cements, • Similar strength the figure refers to • Better chloride resistance the clinker content • ASR resistant Why can we get such high replacement levels » Calcined kaolinite (metakaolin) is much » Alumina in metakaolin can more reactive than react with limestone to glassy SCMs give space filling hydrates
Ms Mc Hc Strät.AFt Hc C 4AFAFt CH AFt Ms Strät . AFt
OPC
28d 1d 5 10 1520 25 Position [ 2Q ]
Ms Mc Hc Strät.AFtHc C4AFAFt CH AFt Ms Strät. AFt
LC3-50
28d 1d
5 10 1520 25 Position [2Q ] What kinds of clay are suitable? Three basic clay structures
Kaolinite (1:1) Montmorillonite (2:1) Illite (Micas) (Smectites) (2:1)
+ ++ Na , Ca , H2O
silicon aluminium
“Metakaolin”, sold as high purity product for paper, ceramic, refractory industries Requirements for purity, colour, etc, mean expensive 3-4x price cement
Clays containing metakaolin often available as wastes – over or under burden Much much less expensive About 50 clays studied from around the world
Different calcination conditions Different compositions, impurities Different physical properties
0%17.0% 35.0%38.9% 50.3% 66.2% 79.4% 95%
Quartz% of calcined kaolinite in the calcined clay Pure kaolinite Benchmark test of clay strength
Compressive strength EN 196-1 at 1, 3, 7, 28 and 90 d Linear increase of strength with the MK content of calcined clays Similar strength to PC for blends containing 40% of calcined kaolinite from 7d onwards At 28 and 90 days, little additional benefit >50% Minor impacts of fineness, specific surface and secondary phases Calcined kaolinite content overwhelming parameter Availability of suitable clays, yellow pink and light green regions, and others Suitable clays presently stockpiled as waste Trial productions in Cuba and India
Housing materials produced in factories by unskilled workers with no special training at 1:1 replacement Potential impact of LC3 technology
Clinker Global cement Global SCM Global CO factor, 2 production volume reduction IEA study for global average Billion Billion Million CSI of tons/year tones/year tones/year % WBCSD 2006 2.6 79 0.5 2050 4.4 73 1.2 200 3 (CSI study) Global potential of LC 2050 4.4 60 1.8 600 (with LCC) ∆ = 400 million tonnes per yr
Can replace whole of need for CCS in low demand scenario
> whole of CO2 emissions of France In fact little extra benefit above ~ 60% kaolin
Similar strength to PC for blends containing 40% of calcined kaolinite from 7d onwards At 28 and 90 days, little additional benefit for clays >60% of kaolinite Clinker hydration degree
Higher DoH for LC3-50 blends due to the filler effect of calcined clay and limestone DoH constant for LC3-50 (95.0%) from 3 days onwards: significant slowing down of clinker hydration Clinker hydration continues for LC3-50 containing less than 65% of calcined kaolinite Clinker hydration slowing down due to a too low relative humidity?
Measurement of the relative humidity
Higher relative humidity for the LC3-50 (95.0%)
Lack of water is not responsible for the slowing down of clinker hydration Amount of reacted metakaolin
Increase of the amount of reacted metakaolin with the calcined kaolinite content This increase becomes lower with the increase of the calcined kaolinite content Porosity characterization by MIP Significant refinement of porosity already at 3 days of hydration
LC3-50 (95%) 3d
» Porosity already well defined at 3 days for high-grade calcined clays » Kinetics difference depending on the grade of calcined clays Competition of clinker and metakaolin reactions
Clays containing > 65% of calcined kaolinite: Slowing down of clinker hydration and stabilization of porosity observed by MIP However, metakaolin keeps reacting (not seen by MIP) Characterization of metakaolin reaction Carboaluminate increase until 50% of kaolinite Decrease then due to lack of large capillary pores . Incorporation of Si and Al in C-A-S-H. Significant increase of the Al/Ca for LC3-50 (95.0%)
Hc+Mc
28 days