Structure of Cement Phases from ab initio Modeling Crystalline C-S-HC

Structure of Cement Phases from ab initio Modeling Crystalline C-S-HC Sergey V. Churakov sergey.churakov@psi.ch Paul Scherrer Institute Switzerland

Cement Phase Composition C-S-H H Solid Solution Model C-S-H C-S-H Lothenbach &Winnefelf(2006) after Kulik & Kersten (2001) Lothenbach et al. (2008)

Possible end-members for Amorphous C-S-H C H Solid Solutions CSH C-S-H (I): H Tobermorite (I): Anomalous Solid Solution Normal Tobermorite Ca 5-x Si 6 O 17-2x 2x(OH) Solid Solution 2x 5H 2 O Ca/Si = = 0.60 0.60 0.75 0.75 Ca 4 Si 6 O 15 (OH) 15 2 5H 2 O Ca 4.5 Si 4.5 6 O 16 (OH) 16 5H 2 O C-S-H H (II): Normal Tobermorite Jennite Solid Solution Ca/Si = 0.75 1.50 Ca 4.5 Si 6 O 16 (OH) 5H 2 O Ca 9 Si 6 O 18 (OH) 6 8H 2 O Further relevant C-S-H C H Phases Xonotlite: Ca 6 Si 6 O 17 (OH) 2

Nuclear Energy and Safety Research Department Basic Structural Elements of C-S-H Phases Xonotlite 11 Å Tobermorite Jennite Ca6Si6O17(OH)2 Ca4+xSi6O15+2x(OH)2-2x 5H2O Ca9Si6O18(OH)6 8H2O 11 Å 7Å Silicate chain Ca-Layer c b a c b b

Method Molecular Dynamics (MD) Newton Equation M k 2 d R dt k 2 = U ( R) R k Must be known Γ({ R k},{ R& k}) Ensemble of position and velocities Average over Ensemble Structure: Bond distances Crystallographic positions Thermodynamics: Energies Temperature Dynamics: IR spectra Diffusion

Interaction Potentials Nuclear Energy and Safety Research Department Ab Initio methods Solve Schrödinger equation to obtain energy and forces 2 h 2m 2 Ψ + UΨ = EΨ Empirical force field methods intra-molecular: harmonic bond stretching, bending inter-molecular: electrostatic and van der Waals interaction Ab Initio <=> Empirical Computationally expensive Valid for any P-T conditions and chemistry Correct description of bond breaking/forming up to ~ n 10 2 atoms up to ~ n 10 ps Fast computation Must be calibrated for the system of interest Fail to describe bond breaking/forming up to ~ n 10 6 atoms up to ~ n 10 2 ns

Density functional theory Hohenberg & Kohn, 1964; Kohn & Sham 1965; Nuclear Energy and Safety Research Department Schrödinger Equation HΨ( R N ) = EΨ( R3 3 N Kohn-Sham Equation ) Exact Hamiltonian 3N dimensional problem far too complex :-(( H H KS KS ψ ( r ψ 1 N 3 ( r ) = ε... 3 ) = ε KS 1 ψ ( r KS N 1 ψ N 3 ) ( r 3 ) Approximate Hamiltonian 3 dimensional problem but can be solved! :-)) H KS = Kinetic Energy Coulomb Interactio n of Electrons 678 Nuclei Electrons Electrons 64748 64748 1 2 el + Vˆ ext ( Rnuc ) + Vˆ Hartree [ ρ ] + 142 4444 44 244444443 Exact Coulomb Interactio n Quantum effects 64748 el Vˆ xc[ ρ ] 14243 Approximat ion el ρ ( r) = ψ i ( r) i 2 Major uncertainty

xc Nuclear Energy and Safety Research Department Approximations for Exchange and Correlation functional el local density approximation (LDA) Vˆ xc[ ρ ( r homogeneous electron gas generalized gradient approximation (BLYP, PBE,...) ˆ el el V [ ρ ( r), ρ ( r)] Vˆ )] Pseudopotential approximation Radial Electron Wavefuctions in Si Atom an example for Si atom all electro vs. pseudo wavefunctions xc Core Region Valence Region Core Region Valence Region 1s 3s Plane Waves ψ = e i k 2s 0 1 2 3 4 R [bohr] c i, k ikr Basis set 3s pseudowavefunction 3s true wavefunction 0 1 2 3 4 R [bohr] Gaussian basis set ψ = i,μϕ μ ϕ μ ( α, l, m, n) = Ne i c αr l m n μ 2 x y z

DFT approach used in this work CPMD code (used for oblique supercell) Plane Wave basis set 70 Ry cut-off BLYP functional, MT-pseudopotentials Car-Parrinello MD CP2K/Quickstep code (used for orthogonal supercell) Gaussian and Plane Wave basis set Triple-ζ basis for O and H, double-ζ for Si and Ca PBE functional, Goedeker - pseudopotentials Born Oppenheimer MD

Q 2 Xonotlite Ca 6 Si 6 O 17 (OH) 2 Ideal structure from X-ray X studies: Q 3 Experimental Observations NMR: Presence of both Q 2, Q 3 and Q 1 sites Presence OH with different environment and molecular H 2 O IR and TG/DTA: Presence of molecular H 2 O Calculated IR spectra EDS: Ca:Si > 1.0 in disordered samples Experimental arb. units 3800 3600 4000 3000 2000 3200 2800-1 ν Η [cm ] 2400 2000 Possible defect formation mechanism {Si} X Si + 2H 2 O ={4H} X Si + SiO 2 CPMD, BLYP, MT-PP, 80 Ry

Assumed Defect Formation Mechanism {Si} X Si + 2H 2 O ={4H} X Si + SiO 2 Δ57 kj/mol Δ40 kj/mol Δ5 5 kj/mol Δ0 0 kj/mol {4H} x Q3 {4H} x Q2 {8H} x {Q3,Q3} {8H} x {Q2,Q3} CPMD, BLYP, MT-PP, 80 Ry Churakov & Mandaliev (2008) CCR

Thermodynamics of Defects in Xonotlite 2{H = 4 } Q {Si} + 3 Q {Si 3 2} Q3, Q {H 3 8} Q3, Q 3 [{Si2} ][ {H8} ] 3 3 3 3 ΔE Q, Q Q, Q = exp 2 [{H } {Si} ] RT 4 Q 3 Q { Si } 2 Q 3, Q3 1.0 { H } 8 Q Q 3 3, 3 mole fraction 0.8 0.6 0.4 0.2 300K 500K { H 4 } Q { Q 3 Si} 3 0 0 0.2 0.4 0.6 0.8 1.0 + 2 Churakov & Mandaliev (2008) CCR

Structure of Defects in Xonotlite Nuclear Energy and Safety Research Department Idealized Structure Structure with Defects Si-OH {4H} x Q3 Ca-OH {8H} x {Q3,Q3} H 2 O Churakov & Mandaliev (2008) CCR

IR spectra Nuclear Energy and Safety Research Department Ideal arb. units Experimental 4000 3000 2000 3800 3600 3200 2800-1 ν Η [cm ] 2400 2000 arb. units Q 3 O10 O9 O5 O6 Structure with defects O1 3800 3600 3200 2800-1 ν Η [cm ] 2400 2000 Churakov & Mandaliev (2008) CCR

Structure of 11 Å Tobermorite Nuclear Energy and Safety Research Department Anomalous Tobermorite Ca 4 Si 6 O 15 (OH) 2 5H 2 O Normal Tobermorite Ca 4.5 Si 6 O 16 (OH) 5H 2 O

Anomalous 11 Å Tobermorite Ca 4 Si 6 O 15 (OH) 2 5H 2 O Nuclear Energy and Safety Research Department 20 ps NVE ab initio MD trajectory T~ 310 K cp2k/quickstep/gpw, PBE, DZP(Ca,Si), TZ2P(O,H)

Preserential orientation of water molecules in anomalous 11 Å Tobermorite A B C D O2 O1 W2 O7 W2 W6 W1,3 O6 W6 O1,O7 W2 W6 W1,3 O6 W6 O1,O7 W2 W3 O1,W2 O7,W2 W1 W6 O6 W3 W2 W1 W6 c c c c b a a b Churakov (2009) Amer. Miner.

Preferential orientation of water molecules in anomalous 11 Å Tobermorite 506K 321K c W3 O7,W2 O1,W2 W6 W1 O6 W3 W2 W6 W1-3 -2-1 0 1 2 3 c, [Å] arb. units W3 W1 arb. units ΔR HB, [Å] h(t) 2 1 0-1 -2 1-1 321K 506K W1 W3-3 -2-1 0 1 2 3 c, [Å] 0 5 10 15 20 b Churakov (2009) Amer. Miner. ΔR HB, [Å] h(t) 2 1 0-1 -2 t, [ps] 1-1 0 5 10 15 20 t, [ps]

Normal 11 Å Tobermorite Ca 4.5 Si 6 O 16 (OH) 5H 2 O Nuclear Energy and Safety Research Department Merlino et al. (2001) X-ray diffraction

Supercell setup Normal 11 Å Tobermorite Ca 4.5 Si 6 O 16 (OH) 5H 2 O Nuclear Energy and Safety Research Department Set 0 Set I Set II Ca2* b a Set III Set IV Set V Merlino et al. (2001) X-ray diffraction

Normal 11 Å Tobermorite Nuclear Energy and Safety Research Department Ca 4.5 Si 6 O 16 (OH) 5H 2 O Snapshot form ab initio MD AI MD, PBE, cp2k/quickstep/gpw, 310 K Churakov (2009) EJM

X-ray diffraction Normal Tobermorite Nuclear Energy and Safety Research Department Snapshot form ab initio MD Merlino et al. (2001) cp2k/quickstep/gpw, PBE, 310 K

Structure of interlayer Ca ion in Normal Tobermorite W6 O7 O6 O1 W6 O1,7 O6 W3 W2 W1 W2 W1,3 W6 O6 W6 O1,7 O2 O6 c c b a Churakov (2009) EJM

Calculated vibrational density of state Normal 11 Å Tobermorite W6 O7 W3 W6 O6 W2 O6 O1 W1 b c arb. units CaW1, CaW3 W1, W3 W6 W2 CaW2 c O2 O1 W2 O7 b W2 c W6 W1,3 O6 W6 a O1,O7 W2 OH6 2600 2800 3000 3200 3400 3600 3800 4000 ν, cm -1 Measured IR spectra 3300 3600 2800 3200 3600 ν, cm -1 Yu et al. (1999) 4000 Churakov (2009) EJM

Jennite Experimental Observations Ca 9 Si 6 O 18 (OH) 6 8H 2 O XRD: Presence of both Q 2 sites only Presence >Ca-OH linkage only NMR: Presence of both Q 2, and Q 1 sites Presence both >Si-OH and >Ca-OH linkage Bonaccorsi et al. (2004)

Jennite Ca 9 Si 6 O 18 (OH) 6 8H 2 O Dynamic Proton Distribution log(ρ H (Γ)) ~ -ΔE/kT O13 O12 R[O8-W1] 2.0 2.5 3.0 O8..H..O13 O8..H..O13 W2 W1 O14 R[O8-W1] 2.0 2.5 3.0 O8..H..W2 R[W1H] - R[O8H] O8..H..W2 c O11 O13 O12 O2 O11 O2 R[O8-W1] 2.0 2.5 3.0 R[W1H] - R[O8H] O8..H..W1 O8..H..W1 b -1.0-0.5 0.0 0.5 1.0 R[W1H] - R[O8H] ΔE = 10-15 kj mol -1 310 K MD CPMD, BLYP, MT-PP, 70 Ry Churakov (2008) CNR

Summary structure of C-S-H C H phase Xonotlite, Tobermorite and Jennite Nuclear Energy and Safety Research Department Distribution of water and cations in the interlayer of tobermorite and jennite IR and NMR spectra are interpreted on the basis of calculation Preferential formations of defects in Q 3 sites in xonotlite Preferential stability of defects in bridging tetrahedra of CSH phases Dangling O-sites O on the bridging Si tetrahedra of jennite are de-protonated The dangling de-protonated sites are likely sorption sites

Acknowledgments Peter Mandaliev Jan Tits Erich Wieland Dmitri Kulik Marcella Iannuzzi-Mauri Matthias Krack