Supplementary cementitious Materials

Transcription

1 Supplementary cementitious Materials Karen Scrivener WORKING DOCUMENT

2 Most promising approach reducing the clinker factor CO 2 Process optimisation clinker factor Clinker Gypsum Cement SCMs Supplementary Cementitious Materials Limestone Fly ash Slag Natural pozzolan Often by-products or wastes from other industries

3 Evolution of Clinker substitution 25% Clinker substitution most successful strategy to reduce CO 2 20% 15% 10% 5% 0% 4% 1% 1% 4% 1% 1% 3% 3% 1% 1% 1% 1% 1% 1% 1% 1% 4% 4% 4% 4% 4% 4% 4% 3% 4% 4% 5% 5% 5% 5% 5% 5% 5% 5% 4% 5% 5% 6% 6% 6% 6% 6% 7% 7% 7% 4% Limestone Slag Fly ash Puzzolana Others 3 Almost no progress in last 5 years Only 3 substitutes used in quantity

4 Cement types in Europe, needs updating

5 Availability of Blast furnace is decreasing in relative terms Production (Mt) BF Slag \Cement (%) BF Slag BF Slag/Cement

6 Fly ash is already diminishing Coal (Mt) Coal (Mt) Europe & Eurasia

7 Availability of SCMs silica fume waste glass Vegetable ashes Natural Pozzolan Slag Fly ash Used Slag and useable fly ash 2017 ~ 17% 2050 ~ 8% Available Portland cement limestone Filler Calcined Clay Mt/yr

8 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 LC 3 project supported by SDC. Running to 2020 Work so far mainly in developing countries highest potential impact 8

9 Mass proportion (%) What is LC PC PPC30 LC3-50 LC3-65 Gypsum Limestone Calcined clay Clinker LC 3 is a family of cements, the figure refers to the clinker content Compressive strength (MPa) PC LC day 7 days 28 days 90 days 50% less clinker 30% less CO 2 Similar strength Better chloride resistance ASR resistant

10 Benchmark test of clay strength Compressive strength EN 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

11 11 Availability of suitable clays, yellow pink, light green regions, and others

12 Suitable clays presently stockpiled as waste

13 Trial productions in Cuba and India Housing materials produced in factories by unskilled workers with no special training at 1:1 replacement 13

14 Potential impact of LC3 technology Global cement production Billion tons/year Clinker factor, global average % Global SCM volume Billion tones/year (CSI study) 2050 (with LCC) Global CO 2 reduction Million tones/year IEA study for CSI of WBCSD Global potential of LC 3 = 400 million tonnes per yr Can replace whole of need for CCS in low demand scenario > whole of CO 2 emissions of France

15 Assumptions behind calculation 1 tonne clinker 850 kg CO2 1 tonne calcined clay 250 kg (figure quoted by Votorantim and internal calculation) 1 tonne limestone 0kg Clinker factor without calcined clay = 0.73 Clinker factor with calcined clay = 0.6 Replace 0.13 x 4.4 x 10 9 x ( x0.66) = 392 x 10 9 kg 400 million tonnes NB calcined clay plus limestone 2:1 is min CO2 reduction Higher possible with calcined clay plus limestone 1:1 or other SCMs with no attributable CO2

16 Calcined clay in Europe: Portugal EN 197-1: possible to replace 35% of clinker in CEM II B-M(Q-L) LC 3-65: 65% of clinker, 5% of gypsum, 20% of calcined clay, 10% of limestone Clay from Portugal (41,8% of kaolinite)» Higher strength than PC for LC 3-65 blend from 7 days onwards» Higher strengths than PC for all blends at 28 and 90 days 16

17 Calcined clay in Europe: Germany EN 197-1: possible to replace 35% of clinker in CEM II B-Q LC 3-65: 65% of clinker, 5% of gypsum, 20% of calcined clay, 10% of limestone Clay from Germany 27,6% kaolinite)» Possible to reach reach similar strength to PC for LC 3-65 blend from 7 day onwards 17

18 Obstacles to lowering clinker factor Durability concerns: Concrete standards (cement standards are sufficiently flexible) E.g. Norway almost only CEM I Need for better prediction Low early strengths Optimisation of particle size distributions: grinding 18

19 Summary Decreasing clinker factor requires new sources of SCM Unexploited wastes and by products are possible, e.g. slags other than blast furnace Clays which can be calcined are available in Europe this can allow higher clinker factor reductions Obstacles are durability (concrete standards) low early strength