MECHANISMS AND MODELLING OF WASTE/CEMENT INTERACTIONS 2 nd International Workshop Low pH concrete resistance Low pH concrete resistance against underground water against underground water aggression aggression José Luis García Calvo 1 , Ana Hidalgo 1 , Mª Cruz Alonso 1 , Luis Fernández Luco 2 1 - Eduardo Torroja Institute for Construction Sciences, CSIC, Madrid, Spain 2 - IECA- Spanish Institute for the Cement and its Applications, Madrid, Spain
Mechanisms and modelling of waste/cement interactions-2 nd International Workshop/ October 12-16, 2008, Le Croisic SCOPE • Design of low- -pH cements for underground pH cements for underground Design of low • repositories of HLRW repositories of HLRW • Microstructure evolution of low- -pH cement pH cement Microstructure evolution of low • pastes pastes • OPC based • OPC based • • CAC based CAC based • Resistance of low- -pH pH cementitious cementitious materials materials • Resistance of low to underground waters aggression to underground waters aggression
Mechanisms and modelling of waste/cement interactions-2 nd International Workshop/ October 12-16, 2008, Le Croisic Design of low- -pH cements for underground repositories of HLRW pH cements for underground repositories of HLRW Design of low Role of Cementitious Materials in Deep HLRW Surface instalations 10000 Concrete Tons Granitic Reposit. Liner 2 m 2.40 m Bentonite plug Concrete plug Canisters Access tunnel Concrete Plug Deep Instalations (ESDRED) Structural cast concrete : road paving, floors or operational structures. Structural cast concrete Shotcrete: : either for tunnels linings, rock support or for plug tunnels Shotcrete Rock bolts Rock bolts Grouting : Grouting : to inject fractures, for sealing
Mechanisms and modelling of waste/cement interactions-2 nd International Workshop/ October 12-16, 2008, Le Croisic Need of Low-pH Cements for HLRW Repositories Interaction of concrete with Bentonite ground waters liberates 2 m 2 m “Hyper-alkaline plume” pH>12.6 perturbs the Concrete integrity of Bentonite barrier Ground Waters Interface Acceptable Acceptable pH pH Desired Desired Uncertain Uncertain Bad Bad 7 7 8 8 9 9 10 10 11 11 12 12 13 13 The risk corrosion alteration of bentonite barrier is higher if pH >>11 USE LOW pH CONCRETE ⇒ LOW-pH CEMENT REQUIREMENT: Pore water pH ≤ 11
Mechanisms and modelling of waste/cement interactions-2 nd International Workshop/ October 12-16, 2008, Le Croisic Criteria for designing low-pH cements from OPC 1 4 1 4 Alkaline plume origin N a + , K + , O H - N a + , K + , O H - 1 3 1 3 C a (O H ) 2 C a (O H ) 2 p H= 1 2 .5 p H= 1 2 .5 1 2 1 2 Cement components responsible for C S H C S H 1 1 1 1 pH = 1 0 pH = 1 0 high alkaline pH of pore water: 1 0 1 0 pH pH A l a n d F e p h a s e s A l a n d F e p h a s e s Na + , K + and Portlandite (Ca(OH) 2 ) 9 9 8 8 p H =7 p H =7 7 7 6 6 0 0 2 0 2 0 4 0 4 0 6 0 6 0 8 0 8 0 1 0 0 1 0 0 1 2 0 1 2 0 V H N O 3 ( m l) V H N O 3 ( m l) Elimination of OH - sources % of CH at 90 days of curing % of CH at 90 days of curing 18% 18% Portlandite Crystals 14 14 * %SiO 2 in binder * %SiO 2 in binder 29% 29% 12 12 10 10 8 8 % CH % CH Pozzolanic Reaction Reaction Pozzolanic 6 6 Ca(OH) 2 + Mineral Admix. 4 4 47% 47% 51% 51% 2 2 55% 55% 65% 65% 0 0 No addition No addition 10%SF- 10%SF- 40% SF 40% SF 35%SF- 35%SF- 50% SF 50% SF 50%SF- 50%SF- 10%FA 10%FA 30%FA 30%FA 30%FA 30%FA
Mechanisms and modelling of waste/cement interactions-2 nd International Workshop/ October 12-16, 2008, Le Croisic Criteria for designing low-pH cements from OPC 13,5 Pastes based on OPC Ref 13 10SF+10FA 20SF 50FA 12,5 SF is very efficient ↓ pH 40 SF 12 SF>>>FA pH 11,5 50SF OPC ↑ %MA ↓ pH 11 35SF+30FA OPC-SF 10,5 OPC-FA 10 OPC-SF-FA 50HS+30FA 9,5 0 20 40 60 80 100 Curing time (days) 13,5 % of CH at 90 days of curing % of CH at 90 days of curing 18% 18% 14 14 13 * %SiO 2 in binder * %SiO 2 in binder 29% 29% 12,5 12 12 12 10 10 pH 11,5 ⇑ %CH ⇑⇑ pH 8 8 % CH % CH 11 6 6 10,5 4 4 47% 47% 51% 51% 10 2 2 55% 55% 65% 65% 9,5 0 0 0 2 4 6 8 10 12 14 No addition No addition 10%SF- 10%SF- 40% SF 40% SF 35%SF- 35%SF- 50% SF 50% SF 50%SF- 50%SF- CH (%) 10%FA 10%FA 30%FA 30%FA 30%FA 30%FA
Mechanisms and modelling of waste/cement interactions-2 nd International Workshop/ October 12-16, 2008, Le Croisic Microstructure evolution of low-pH cement pastes – OPC based 1200 -Dissaprearance of CH OPC+SF 1000 - C 2 S and C 3 S 2 days 800 pH=11.2 I (counts) 7 days 600 - ettringite pH=12.3 30 days 400 pH=12.7 90 days 200 pH=12.8 0 5 10 15 20 25 30 35 40 45 50 55 60 2 θ OPC 90 d OPC+SF • No micro cracks. 100 100 100 TG(%) f 0 50 DTA 96 96 0 • Good texture. -4 92 TG (%) -50 DTA -8 88 DTA ( μ V) 92 -100 DTA( μ V) TG (%) TG(%) • Anhydrous grains of SF 84 -150 g -12 88 -200 h 80 -16 • C/S ratios of the CSH gel -250 76 f -20 84 g -300 between 1-0.7 0 200 400 600 800 0 200 400 600 800 Temperature (ºC) Temperature (ºC) • Anhydrous cement
Mechanisms and modelling of waste/cement interactions-2 nd International Workshop/ October 12-16, 2008, Le Croisic Criteria for designing low-pH cements from CAC 1st.- CAC achieves an acceptable 13,5 Pastes based on OPC Ref pore fluid pH 13 10SF+10FA 20SF 50FA 12,5 13.5 40 SF 13 12 Ref 12.5 20%SF pH 11,5 30%SF 50SF 12 11 OPC 50%SF pH 11.5 35SF+30FA OPC-SF 30%FA 10,5 11 OPC-FA 50%FA 10 10.5 OPC-SF-FA 20%SF-10%FA 50HS+30FA Pastes based on CAC 9,5 10 0 20 40 60 80 100 9.5 0 20 40 60 80 100 Curing time (days) Curing Time (days) 90 days: pHs < 12. MA do not significantly ↓ pH (50% MA ↓ pH in 0.5 points) 2 nd .- Conversion Process : 3 CAH 10 � C 3 AH 6 + 2 AH 3 + 18 H 3 C 2 AH 8 � 2 C 3 AH 6 + AH 3 + 9 H ↑ Porosity → ↓ compressive strength
Mechanisms and modelling of waste/cement interactions-2 nd International Workshop/ October 12-16, 2008, Le Croisic Microstructure evolution of low-pH cement pastes – CAC based Short Ages (< 7d) Long Ages (>30d) CAC + SF CAC and CAC+SF CAC alumina gel CAH 10 AH 3 AH 3 C 2 ASH 8 C 2 AH 8 C 3 AH 6 C 3 AS 3-X H 2X AH 3 BSEM confirms the existence of 700 C 3 AH 6 C 3 AH 6 hexagonal platelets of gehlenite C 3 AH 6 600 REF 500 CAC+MA I (counts) 400 300 200 100 0 2 Theta 30 40
Mechanisms and modelling of waste/cement interactions-2 nd International Workshop/ October 12-16, 2008, Le Croisic Resistance of Low-pH concretes to 2 m 2 m water aggression: Percolation test Concrete + ground waters leaching of pore solution alteration of the solid phases loss of concrete properties Although the degradation rate is very slow its evaluation is important for structures near field RWR, where extremely long-term stability is needed. In laboratory accelerated tests are used to qualify the different concretes for deep repositories Cement degradation depends on: composition, porosity, density, leachant characteristics, flow rate, Tª and water chemical composition
Mechanisms and modelling of waste/cement interactions-2 nd International Workshop/ October 12-16, 2008, Le Croisic Interaction of low-pH concretes with ground waters Basic concretes samples 60%OPC+40%SF 70%CAC+30%SF Constituents Kg/m 3 Kg/m 3 Constituents Water (kg/m 3 ) 160 Water (kg/m 3 ) 128 Binder (kg/m 3 ) 320 Binder (kg/m 3 ) 320 Water/binder 0.5 Water/binder 0.4 Fine Gravel (4-8 cm) (kg/m 3 ) 855 Fine Gravel (4-8 cm) (kg/m 3 ) 855 1033 Sand (0-4 cm) (kg/m 3 ) 1033 Sand (0-4 cm) (kg/m 3 ) Superplasticizer (kg/m 3 ) 3.2 Superplasticizer (kg/m 3 ) 3.2
Mechanisms and modelling of waste/cement interactions-2 nd International Workshop/ October 12-16, 2008, Le Croisic Interaction of low-pH concretes with ground waters Cores from shotcreted concrete (Äspö) 60%OPC+40%SF Low pH basic concrete design Low pH cement Shotcreting formulations Fresh concrete discharge from the Fresh concrete discharge from the truck mixer to te pump truck mixer to te pump Compatibility with chemical admixtures 150 x 300 mm cylinder 150 x 300 mm cylinder cast at Santa Barbara cast at Santa Barbara Constituents Kg/m 3 Water (kg/m 3 ) 277.2 Binder (kg/m 3 ) 307.2 Water/binder 0.9 Coarse Aggregate (8-12 mm) (kg/m 3 ) 615.6 Medium Aggregate (4-8 mm) (kg/m 3 ) 199.7 Shotcreted plug 818.1 Sand (0-4 mm) (kg/m 3 ) Superplasticizer (kg/m 3 ) 5.5 Accelerator (kg/m 3 ) 18.5
Mechanisms and modelling of waste/cement interactions-2 nd International Workshop/ October 12-16, 2008, Le Croisic Interaction of low-pH concretes with ground waters Cores from shotcreted concrete (Äspö) 60%OPC+40%SF Extraction of cores for testing Core
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