Thermal analysis in eco-concrete research

Transcription

1 Thermal analysis in eco-concrete research Els Bruneel, Mieke De Schepper, Ruben Snellings, Joris Schoon, Isabel Van Driessche, Nele De Belie, Klaartje De Buysser SCRiPTS, Department of Inorganic and Physical Chemistry, UGent Magnel Laboratory for Concrete Research, UGent Sagrex N.V., Brussel Magnel Laboratory for Concrete Research 1

2 Introduction Concrete production: 10 billion ton concrete each year, 3 billion ton cement Consumption of natural raw materials» 42% of produced aggregates is for concrete production» 1 kg cement = 1.6 kg raw materials Production of waste» 850 million tons construction and demolition waste whereof 40-67% is concrete Emission of CO 2» 1.6 billion tons each year which is around 5-8% of the total CO 2 emissions ~ 40% energy required for cement production ( at > 1400 C) ~ 60% calcination of limestone (to produce cement) CaCO 3 CaO + CO 2 2

3 Evolution 3

4 What is concrete Overview Portland Clinker CO 2 Cement hydrates = creation of adhesive bonds CSH gel, ettringite, portlandite H 2 O hydration 1450 C Fine and coarse granulates >60 % Ca-source Si-source Al-source Fe-source Formation of alite, belite, aluminate, ferrite 4

5 What can be done? Portland Clinker / alternative binders Clincker production using industrial byproducts and waste. slag, fly ash, silica (glass powder) Replacement of clinker and cement by industrial byproducts and waste : supplementary cementitious materials (SCMs) fly ash, slag, silica (glass powder) H 2 O hydratation 1450 C Use of the best technology Thermal efficiency of kiln and cooler systems Use of demolition waste as aggregate Use of alternative fuels (i.e. solvent waste) 5

6 What can be done? H 2 O hydratation 1450 C Granulates Sand >60% 6

7 What can be done? Complete recyclable concrete Cradle to cradle Concept M. De Schepper Design of a concrete which could be used for making a new clincker 7

8 Necessary condition: Chemical composition CRC = Chemical composition cement raw meal Completely Recyclable Concrete Most important ratios: LSF: lime saturation factor Ca versus (Si, Al, Fe) SM: silica modus Si versus Al, Fe AM: alumina modus Al versus Fe Bekaert - meeting 21/08/09 8

9 To make a good clincker: composition should lie between certain limits 1. Cement paste: hydrated + crushed CEMI 52.5N 2. CRC: hydrated + crushed CEMI 52.5N + Components: Limestone aggregates (Gaurain, Soignies) Limestone filler Diorite (Lessines) Fly ash Copper slag Two raw materials: a CRC and a CEMENT PASTE (CP) CRC CP CaO SiO Al 2 O Fe 2 O MgO SO K 2 O Na 2 O LSF SM AM Good for clincker production 9

10 Cement paste Question: How does this mixture behave during reclinkering? CRC 1450 C Formation of alite, belite, aluminate, ferrite Bekaert - meeting 21/08/09 10

11 Bekaert - meeting 21/08/09 11

12 CO 2 CaCO 3 CaO C 3 S = aliet Bekaert - meeting 21/08/09 SiO 2 Al 2 O 3 Fe 2 O 3 C 2 S= beliet C C 4 AF 3 A Other oxides Liquid phase

13 Clinckering Reactions, Ruben Snellings 1. Thermogravimetry /Differential thermal analysis 2. XRD-HTXRD Bekaert - meeting 21/08/09 13

14 Clinckering Reactions TGA-DTA, heating and fast cooling of a CRC DT TG /% Temp. / C DTA /(µv/mg) Dehydr. Decarb. exo Base line is not flat - Geometry of furnace Heat transfer towards cup Compare with blanc Dry air C/min C/min There is a sample * emissivity * Thermal conduction 70 [3] Bekaert - meeting 21/08/ Time /min

15 Clinckering Reactions TGA-DTA, mass-difference baseline method Yang & Roy, Thermochimica acta, 1999 DTA curve derived from a small mass sample as the baseline for a large mass sample using the same material. 100 TG /% [3] CRC4M_Air.ngb-ss3 TG DTA Temp. [4] CRC4M_Air2.ngb-ss3 TG DTA Temp. low mass 25 mg (green) high mass 50 mg (blue) Temp. / C DTA /(µv/mg) exo [4] [3] [4] [3] diminishes - ``apparatus effect'' asymmetric heat transfer problem attributed to the and -``sample influence' improving the linearity between the DTA curve and enthalpy change. 70 [4] [3] Time /min

16 Clinckering Reactions TGA-DTA, heating and fast cooling of a CRC Much better resolution on endothermal and exothermal events Higher temp: possible explanations: melt formation and crystallisation, polymorphic transformations of alite and belite 100 TG /% exo Temp. / C DTA /(µv/mg) exo [1] subtr_crc4m_air.ngb-ss340_crc4m_air2.ngb-ss340.ngb-ms3 TG Temp. [2] subtr_crc4m_air.ngb-ss3230_crc4m_air2.ngb-ss3230.ngb-ms3 DTA Temp. [1] [2] [2] aluminate =C3A formation α L to α H C 2 S transition Melt formation Time /min [1]

17 Clinckering Reactions TGA-DTA DTA curves for CRC and Cement Paste (CP) CRC : endoth. decarbonation during heating (B) and cooling (C) Lower T of melt formation and cooling exotherms C 3 A formation from Ca-aluminates Indicative for better burnability of CP α L to α H C 2 S transition Melt formation C 3 A, C 4 AF crystallisation C 2 S polymorp. transitions cement CSH, CAH dehydration Ca(OH)2 dehydroxylation 17

18 Clinckering Reactions HTXRD In situ XRD measurements C: Calcite & dolomite decomposition Decomposition of quartz Formation of intermediate phases CaCO 3 CaO Ca-(alumino-)silicates Gehlenite (C2AS) Yeelimite (C4A3S) Belite (C 2 S) Mayenite (C12A7) Lime :CaO Aluminate: celiet (C3A) Ferrite (C4AF) Bekaert - meeting 21/08/09 CaMg (CO 3 ) 2 18

19 Clinckering Reactions XRD, after calcination Ex situ XRD measurements, C, dwell 1h C2S + CaO C3S Decomposition of intermediate phases to form main clinker phases End product Alite (C3S = Ca 3 SiO 5 ) Belite (C2S = Ca 2 SiO 4 ) Aluminate (C3A = Ca 3 Al 2 O 6 ) Ferrite ( C4AF= Ca 2 (Al,Fe) 2O 5 ) ZnO intern standard for Rietveld analysis Bekaert - meeting 21/08/09 19

20 Clinckering Reactions Rietveld Other C2S = aliet Gehlenite C4AF_Jupe C3A cubic C12A7 Lime Dolomite Quartz low Calcite HTXRD Bekaert - meeting 21/08/09 T ( C) Rietveld analysis gives a quantitative view on the occurring reactions: Using : internal standard Using data from TGA: mass loss,melt formation Furnace, 1h + XRD T ( C) C: Extensive crystallisation of C 2 S C 2 AS, C 4 AŠ (yeelimite), C 12 A 7, C Quartz decomposition C Intermediate Ca-aluminates form C 3 A C 2 S + C C 3 S (gradual increase) C C 4 AF and C 3 S are formed at the expense of C 3 A Other Periclase Alkali Sulphates C3S_M3_DLT beta-c2s Gehlenite Yeelimite C4AF_Jupe C3A_Na_cubic C12A7 Lime Quartz low 20

21 Weight percentage [wt%] Weight percentage [wt%] Clinckering Reactions CRC versus Cement paste Lime Gehlenite Belite Burning temperature [ C] CRC Alite Other Magnetite Quartz Gehlenite Periclase Alkali sulphates Mayenite Ye'elimite Aluminate Ferrite Alite Belite Lime Belite Alite 10 Lime Burning temperature [ C] Cement Paste Comparison with CRC: in cement: Lower aliet / beliet due to solid solution in C 2 S Higher C 4 AF = ferrite (higher Fe 2 O 3 content) Why?: more S => more / melt at low temperature. : faster S in Belit: less alite 21

22 Clinckering Reactions Microscopy, CRC versus cement paste, burned at 1450 C Traditional clinker phases are formed! Open porosity of about 24v% Melt (mainly grey) rich in aluminate Belite mainly as inclusions in alite Melt (mainly bright/white) rich in ferrite Belite as individual crystals Closed porosity of about 11v% Bekaert - meeting 21/08/09 CRC At 1450 C more open pores More alite Alite Cement Paste more and earlier melt formation earlier formation of well-formed alite/belite crystals better distribution of the crystals in the melt lower porosity 22 cement paste clinker has a better burnability

23 General conclusions In the cement paste clinker more and earlier melt formation earlier formation of well-formed alite/belite crystals better distribution of the crystals in the melt lower porosity cement paste clinker has a better burnability This effect is probably caused by its higher sulfur content S: acts as flux -Lowering melitng temp. (seen in TGA) -Reduces melt viscosity -Stabilizes belite => less alite CRC CP CaO SiO Al 2 O Fe 2 O MgO SO Bekaert - meeting 21/08/09 23

24 Next step : hydration hydratation 1450 C Granulates Sand Formation of alite, belite, aluminate, ferrite Cement hydrates = creation of adhesive bonds 24

25 CRC clincker + CaSO 4 cement + 40% H 2 O hydratation Question: How does the cement behave during hydration? 1450 C Commercial Cement CEM I 52.5 N + 40% H 2 O hydration Bekaert - meeting 21/08/09 25

26 Cement hydration Alite + water: 2Ca3OSiO4 + 6H2O 3CaO.2SiO2.3H2O + 3Ca(OH)2 (= fast) Belite + water: 2Ca2SiO4 + 4H2O 3CaO.2SiO2.3H2O + Ca(OH)2 (= slow) Aluminate + water + gypsum: Ca3(AlO3)2 + 3CaSO4 + 32H2O Ca6(AlO3)2(SO4)3.32H2O KJ/mol KJ/mol KJ/mol Ferrite +water + gypsum: 2Ca2AlFeO5 + CaSO4 + 16H2O Ca4(AlO3)2(SO4).12H2O + Ca(OH)2 + 2Fe(OH)3 Reaction rate: formation Ca(OH)2 bound H2O heat of hydration 26

27 Isothermal calorimetry Early stage of hydration Apparatus: TAM air, TA instruments : 2 ampules, temp constant Dormant period reference= sand Sample= Cement+ H 2 O 1 period Ca 2+ OH - Hydration of alite, rapid crystallization of CH and C-S-H Seebeck heat flow sensor Bekaert - meeting 21/08/09 27

28 Isothermal calorimetry - Shows us the reaction speed in the first couple of hours, days. More aluminate = 7d Hydration of regenerated cement is slower, but after 7 days the cumulative hydration heat is approaching the one of CEM I 52.5 N Size of grains is of major importance.. 28

29 TGA, DTA Cement + H2O -> react for 1h, 3 h, 6h, 9h, 1d, 2d, 3d, 7d, 28 d and stop the reaction by - Freeze drying - Solvent Exchange: soaking in dry solvent to replace capillary water ethanol / isopropanol + drying. Measure of hydration: - % bound water - formation of Ca(OH) 2 Bekaert - meeting 21/08/09 29

30 Mass [m%] TGA, 10 C/min, N 2 100,00 95,00 90,00 85,00 free water Y x : Bound water x C : decomposition of calcite (CaCO 3 ) CaCO 3 CaO + CO 2 = carbonated Ca(OH) 2 => correction 80,00 75,00 70, C : decomposition of portlandite Ca(OH) 2 Ca(OH) 2 CaO + H 2 O 28d 65,00 Ca(OH) 2 CaCO 3 60,00 Bekaert - meeting 0 21/08/ Temperature [ C] 30

31 Mass [m%] TGA, DTA Bound water Ca(OH)2 CaCO3 60 Bekaert 0- meeting 21/08/ Temperature [ C] 1h 3h 6h 9h 1d 2d 3d 7d 28d 31

32 Mass [m%] TGA Bound water content CEM I 52.5 [SEM] CRC2e [SEM] ,01 0, Time [days] 32

33 Mass [m%] Mass [m%] TGA Portlandite 25 CEM I 52.5 N 25 CRC2e ,01 0, Time [days] 0 0,01 0, Time [days] CEM I 52.5 [SEM] Bekaert - meeting 21/08/09 CEM I 52.5 N [SEM] corrected for CO2 CRC2e [SEM] CRC2e [SEM] corrected for CO2 33

34 Mass [m%] Mass [m%] XRD, Rietveld Hydration of clinker minerals Resulting in hydration products CRC2e 0 0,01 0, Age [days] Alite_SEM [XRD] Belite_SEM [XRD] 0 0,01 0, Age [days] Other_SEM [XRD] Portlandite_SEM [XRD] Bekaert - meeting 21/08/09 Ferrite_SEM [XRD] Aluminate_SEM [XRD] AFm_SEM [XRD] Ettringite_SEM [XRD] Monosulfate aluminate 34

35 Mass [m%] Mass [m%] Portlandite: TGA vs. XRD CEM I 52.5 N CRC2e ,01 0, Age [days] CEM I 52.5 N [XRD] CEM I 52.5 N [TGA] Bekaert - meeting 21/08/09 CEM I 52.5 N [TGA not corr.] 5 0 0,01 0, Age [days] CRC2e_SEM [XRD] CRC2e_SEM [TGA] CRC2e_SEM [TGA not corr.] 35

36 Future: design of the next CRC Bekaert - meeting 21/08/09

37 Use of Waste fibrecement Joris Schoon, Sagrex Fibrecement: a non carbonate CaO source Fibrecement: composite material consisiting of portland cement, inert and or reactive mineral filler and a available as waste mixtrure of sevreal typrs of organic fibers. less energy consumption to heat up less C0 2 emission = recycling: fibrecement is Again: To make a good clincker: composition should lie between certain limits Most important: LSF: lime saturation factor Ca/ (Si, Al, Fe) SM: silica modus Si / Al, Fe AM: alumina modus Al / Fe Ca : 60-65% 37

38 Use of Waste fibrecement 1. Thermogravimetry /Differential thermal analysis - Mass loss => - amount CO 3 ( C) - DTA => energy needed to heat till 1450 C - endotherm: decomp of CO3 (CaCO3 -> CaO +CO2 : 1782kJ/kg) - Endotherm: dehydration - TGA of fillers: determine decomposition temp. and products. Bekaert - meeting 21/08/09 38

39 DTA (m V/mg) Use of Waste fibrecement 0,5 0,4 PVA decomp CO 3 decomp 0,3 0,2 0,1 0-0,1-0,2-0,3 classic composition fibrecement -0, temp ( C) Emission of CO 2» 1.6 billion tons each year Bekaert - meeting 21/08/09 ~ 40% energy required for cement production ( at > 1400 C) ~ 60% calcination of limestone (to produce cement) CaCO 3 CaO + CO 2 Energy to decompose fibres is small enough 39

40 Conclusions Use of TGA, DTA, (HT- XRD) and calorimetry Completely recyclable concrete Characterise end products and study the reactions During clinckering And hydration Identify end products and intermediates Identify the difference in burnability Follow reactions rate Use of fibrecement Could lead to Re-Use of fibrecement waste Energy gain Low CO2 emisions Information for new design industrial tests are the next step Clinckering Reactions during firing of recyclable concrete R. Snellings J Am Cer Soc, 2012 The hydration of cement regenerated from completely recyclable concrete M. De Schepper, J Am Cer Soc, 2012 Bekaert Waste Fibrecement: - meeting 21/08/09 An interesting alternative raw material for a sustainable Portland clinker production, J. Schoon, Construction and building materials, 36 (2012) 40