2 nd Mechanisms and modelling of waste/cement interactions, Le Croisic, October 13, 2008. Hydration of calcium sulfoaluminate cement by a zinc chloride solution Application to nuclear waste conditioning S.Berger 1 , C. Cau dit Coumes 1 , D. Damidot 2 , P.Le Bescop 3 1. Atomic Energy Commission, Marcoule Research Center, France. 2. Civil & Environmental Egineering Departement – Ecole des Mines de Douai, France. 3. Atomic Energy Commission, Saclay Research Center, France.
Context Zinc chloride is a soluble salt contained in ashes resulting from the incineration of α radioactive wastes including neoprene and polyvinylchloride . Deleterious effects on Portland cement: • setting is strongly delayed and can be inhibited at high zinc chloride loading (Arliguie 1985), • hydration and hardening are slowed down (Ortego 1989) . 35 Precipitation of β 2 -Zn(OH) 2 or Temperature rise (°C) Portland Cement From Cau-dit-Coumes and al, ICCC 2007 Zn 2 Ca(OH) 6 .2H 2 O over the cement 30 without ZnCl 2 grains has been postulated to explain Portland Cement with 25 the delay in cement hydration 0,1 mol/L ZnCl 2 (Arliguie 1985) . 20 15 10 < 24 h > 4 days 5 It is necessary to select a binder having a different chemistry, more compatible 0 with the waste: 0 20 40 60 80 100 120 140 a calcium sulfoaluminate cement . Time (h) S.Berger, Cau dit Coumes and al ; Hydration of calcium sulfoaluminate cement by a zinc chloride solution 2
Objective: to investigate the influence of zinc chloride on the hydration of CSA cements. Overview I. Materials and Methods II. Kinetics of hydration III. Mineralogical evolution IV. Conclusion and prospects S.Berger, Cau dit Coumes and al ; Hydration of calcium sulfoaluminate cement by a zinc chloride solution 3
Materials: cement composition and hydration Mineralogical composition of the CSA clinker (KTS 100 provided by Bellitex): Minerals (% weight) C 4 A 3 S C 2 S C 3 FT C 12 A 7 Periclase CS Quartz 16 6.6 3.1 2.6 0.5 0.5 71 Two main features of CSA cement hydration: Hydrates proportion depend of the amount Major heat output of gypsum mixed with the clinker. 100 Modified from Glasser and al, CCR 2001 80 90 AH 3 semi-adiabatic Langavant calorimetry Temperature (°C) 80 70 % hydrates Calcium monosulfo 70 CSA cement 60 60 aluminate 50 50 Ettringite hydrate 40 40 30 Portland cement 20 30 Gypsum 10 20 CSH 0 0 10 20 30 40 9 4 4 1 5 7 6 2 7 1 2 3 2 , , , , , , , , , , , , , 3 7 0 3 6 9 1 4 6 8 0 4 9 1 1 2 2 2 2 3 3 3 3 4 Time (h) % gypsum Influence of temperature and gypsum content has to be studied. S.Berger, Cau dit Coumes and al ; Hydration of calcium sulfoaluminate cement by a zinc chloride solution 4
Materials and methods: preparation of specimens • CSA cements preparation: mixing of ground CSA Two kinds of specimens clinker with gypsum (0-10%, 20% and 35%). were prepared: • Mixing solution: dissolution of ZnCl 2 salt (0 or 0.5 • pastes for XRD analysis, mol/l) into distilled water. (hydration stops at 5min, 1h, 2h, 5h, 24h, 7days,…) • Water to cement ratio: 0.55 for pastes and mortars. • mortars for semi-adiabatic • Sand to cement ratio : 3, sand and cement pre-mixed. Langavant calorimetry. After mixing, samples were cured 7 days in sealed plastic bag at 20°C or were submitted to a thermal cycle in an oven. 80 semi-adiabatic Langavant calorimetry Thermal cycles: temperature profiles made Temperature (°C) Temperature evolution 60 from the temperature evolution of mortars under recorded on CSA mortars semi-adiabatic conditions and applied on pastes to reproduce the temperature rise and decrease 40 which may occur in a massive structure during cement hydration. 20 0 50 100 150 Time (h) S.Berger, Cau dit Coumes and al ; Hydration of calcium sulfoaluminate cement by a zinc chloride solution 5
Materials and methods: preparation of specimens 80 semi-adiabatic curing Temperature (°C) Differences between the thermal 60 evolution of two mortar samples cured at 20°C or under semi- mortars, 10% gypsum adiabatic conditions were very 40 significant. 20°C curing 20 0 2 4 6 8 10 12 14 16 18 20 Time (h) inner temperature 80 Temperature profiles were defined Temperature (°C) by interpolating in 20-40 segments the curves recorded on mortars. 60 calorimetry paste recorded on 20% gypsum Some corrections were required to mortar 0.5 mol/l ZnCl 2 40 keep the inner temperature of the temperature profile paste near that of the mortar under applied to the paste semi-adiabatic curing. 20 0 1 2 3 4 5 Time (h) S.Berger, Cau dit Coumes and al ; Hydration of calcium sulfoaluminate cement by a zinc chloride solution 6
Kinetics of hydration: influence of gypsum content 500 450 5% 400 7% Cumulated heat (J/g of cement) 350 10% 300 3% 2% 1% 0% 250 200 150 100 50 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Time (h) Two effects were observed when the gypsum content increased from 0 to 10%: • the cumulated heat output was reduced when the gypsum content exceeded 5%, • the induction period decreased strongly especially at low gypsum contents. S.Berger, Cau dit Coumes and al ; Hydration of calcium sulfoaluminate cement by a zinc chloride solution 7
Kinetics of hydration: influence of gypsum content 500 450 0% 400 Cumulated heat (J/g of cement) 350 35% 300 250 20% 200 10% 150 100 50 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Time (h) Beyond a gypsum content of 10%, heat output and induction period did not vary anymore. S.Berger, Cau dit Coumes and al ; Hydration of calcium sulfoaluminate cement by a zinc chloride solution 8
Kinetics of hydration: influence of gypsum content Mineralogical study on 100% (based on XRD relative peak areas) pastes with thermal cycles : Reacted yeelimite / 5 min (%) 90% 80% Without gypsum: 70% 60% • yeelimite started to react much later, 50% in agreement with the long induction 40% 0% gypsum period previously observed. 30% 10% gypsum • Yeelimite was almost totally depleted 20% 20% gypsum at 24h while with gypsum, 10 to 20% 10% 35% gypsum 0% were still unreacted. 0 5 10 15 20 25 100% Time (h) (based on XRD relative peak areas) Reacted gypsum and yeelimite /5min (%) gypsum, 10, 20 and 35% gypsum 80% yeelimite, 10, 20 and 35% gypsum Gypsum reactivity: 60% • gypsum dissolution before that of yeelimite, • almost total depletion at 5h. 40% 20% 0% 5min 1h 2h 5h Time S.Berger, Cau dit Coumes and al ; Hydration of calcium sulfoaluminate cement by a zinc chloride solution 9
Kinetics of hydration: influence of thermal cycle 100% cycle 1 day (based on XRD relative peak areas) Reacted yeelimite at 1 day /5min (%) 90% no cycle 1 day no cycle 7 days 80% 70% 60% 50% 40% 30% 20% 10% 0% 0% 10% 20% 35% Gypsum content (%) The thermal cycle promoted the dissolution of yeelimite: amount of yeelimite consumed at 1 day higher than that depleted at 7 days when curing is performed at 20°C. S.Berger, Cau dit Coumes and al ; Hydration of calcium sulfoaluminate cement by a zinc chloride solution 10
Kinetics of hydration: influence of zinc chloride addition 500 450 0.5 mol/l Cumulated heat (J/g of cement) 400 350 0 mol/l 300 0.5 mol/l 250 0 mol/l 200 150 With gypsum Without gypsum 100 50 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 Time (h) • A retardation was observed, but its magnitude was much smaller than that recorded with OPC. • Setting inhibition was never observed: setting occurred in less than 2h with gypsum, and in less than 24h without it. S.Berger, Cau dit Coumes and al ; Hydration of calcium sulfoaluminate cement by a zinc chloride solution 11
Kinetics of hydration: influence of zinc chloride addition Investigating the reactivity of zinc cations and chloride anions 500 500 Cumulated heat (J/g of cement) Cumulated heat (J/g of cement) 450 450 CaSO 4 400 400 ZnSO 4 0% gypsum 350 350 ZnCl 2 300 300 H 2 O 250 250 200 200 150 150 CaCl 2 100 100 50 50 0 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 Time (h) Time (h) 500 Zn(NO 3 ) 2 Cumulated heat (J/g of cement) 450 Temperature of the mixing solution: 20°C 400 350 Salt concentration : 0.5 mol/l 300 Ca(NO 3 ) 2 250 200 acceleration Zn 2+ > Ca 2+ delay 150 100 50 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 Time (h) S.Berger, Cau dit Coumes and al ; Hydration of calcium sulfoaluminate cement by a zinc chloride solution 12
Kinetics of hydration: influence of zinc chloride addition Investigating the reactivity of zinc cations and chloride anions 500 500 Cumulated heat (J/g of cement) Cumulated heat (J/g of cement) 450 ZnSO 4 450 CaSO 4 400 400 350 350 Ca(NO 3 ) 2 300 300 250 250 ZnNO 3 ) 2 200 200 150 150 100 CaCl 2 ZnCl 2 100 50 50 0 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 Time (h) Time (h) Temperature of the mixing solution: 20°C 2- >> 2 NO 3 - > 2 Cl - acceleration SO 4 delay Salt concentration : 0.5 mol/l Chloride anions strongly slowed down hydration but zinc cations accelerated it. S.Berger, Cau dit Coumes and al ; Hydration of calcium sulfoaluminate cement by a zinc chloride solution 13
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