A Molecular Dynamics study of the formation of Calcium (Alumino)Silicate Hydrate (C-A-S-H) particles

Transcription

1 A Molecular Dynamics study of the formation of Calcium (Alumino)Silicate Hydrate (C-A-S-H) particles Jorge S. Dolado LABEIN-TECNALIA 07 August 2009

2 Outline 1- Introduction 2- MD simulations of C-S-H particles 2.1- Three-dimensional us Linear features 2.2- MCL (Q factor) 3- MD simulations of C-A-S-H particles 3.1- Connectivity (Q3+Q4, MCL) 3.2- Position of Al atoms 4- Conclusions and some ongoing ideas

3 1- Introduction: NANO-STRUCTURE OF C-S-H gel - 29 Si NMR -TEM,SEM - XRD Silicate chain Calcium oxide layer Silicate chain Interlayer Calcium water Silicate chain Calcium oxide layer Silicate chain Distorted version Finite chain ES,PS,BSs guest ions

4 Introduction There are many experimental evidences ( 29 Si and 27 Al NMR) - Aluminum readily enters the Calcium Silicate Hydrate phase (C-S-H) of OPCs and others - Al atoms enlarge the chains - Al atoms promote the appearance of Q3 (3-D) sites - Al atoms seem to occupy internal positions within the chains We aim to reproduce these experimental facts by means of atomistic simulations (MD)

5 2- MD simulations of C-S-H particles Structural information 2.1 Connectivity of Si atoms OH HO HO Si HO HO OH Q 0 OH OH Si O OH HO Si Si OH HO O OH HO OH Q 3 +Q 4 (%) MCL HO HO OH Si HO O OH Q 2 Q 1 OH HO HO OH Si O HO Si OH OH HO HO Si O Si O Si OH OH HO HO Si O Si O Si Q 4 O O Q 3 HO HO Si OH 2.2 Bonds (Si-OH and Ca-OH) Si-OH Tobermorite Ca-OH Jennite

6 MD simulations of C-S-H particles J. S. Dolado et. al. A Molecular Dynamic Study of Cementitious Calcium Silicate Hydrate (C-S-H) Gels ; The Journal of American Ceramic Society 90 (2007) Si(OH) 4 Si(OH) 4 Si(OH) 4 Si(OH) 4 We have put together many Si(OH) 4 and Ca(OH) 2 4H 2 O Molecules, and we have studied the formation of C-S-H structures at different Ca/Si ratios

7 MD simulations of C-S-H particles J. S. Dolado et. al. A Molecular Dynamic Study of Cementitious Calcium Silicate Hydrate (C-S-H) Gels ; The Journal of American Ceramic Society 90 (2007) H 2 O (OH) 3 -Si-O-Si-(OH) 3 Si(OH) 4 H 2 O Si(OH) 4 We have put together many Si(OH) 4 and Ca(OH) 2 4H 2 O Molecules, and we have studied the formation of C-S-H structures at different Ca/Si ratios

8 Ca(OH) 2 4H2O MD simulations of C-S-H particles J. S. Dolado et. al. A Molecular Dynamic Study of Cementitious Calcium Silicate Hydrate (C-S-H) Gels ; The Journal of American Ceramic Society 90 (2007) H 2 O (OH)-Ca -O- -O- -O-Si(OH)4 (OH)-Si-O-Si-(OH) Ca(OH) -O- (OH)-Si-O-Si-(OH) H 2 O We have put together many Si(OH) 4 and Ca(OH) 2 4H 2 O Molecules, and we have studied the formation of C-S-H structures at different Ca/Si ratios

9 MD simulations of C-S-H particles B. P. Feuston and S. H. Garofallini, Onset of polymerisation in silica sols, Chem. Phys. Lett., (1990). V (2) ij = A exp(-r ij / ij ) + (q i q j /r ij ) (r ij / ij ) V (3) jik = jik exp{ r ij /(r ij -r ij0 ) + r ik /(r ik -r ik0 ) } jik =(cos jik + cos jik0 ) 2 jik

10 MD simulations of C-S-H particles 1800 K NVT 300 K NVT 500 ps NVT 300 K 10 ps 90 ps 1500 ps 100 ps t = [0, 1500 ps] T = 1800 K t = [1500, 2200 ps] T = 300 K N = ~ atoms V ~ 10 x 10 x 10 nm 3 canonical ensemble [NVT] TREMOLO CODE

11 MD simulations of C-S-H particles

12 MD simulations of C-S-H particles Q3+Q4 (%) 2.1-Q3+Q4 (%) Three-D features Ca/Si ratio The simulated C-S-H particles are LINEAR STRUCTURES

13 MD simulations of C-S-H particles 2.2-Main Chain Length (Q factor) Q=Q1/(Q1+Q2+Q3) ( = 2/Main Chain Length) Good agreement with 29 Si NMR data Good trend: Q Ca/Si Q {1.4 tobermorite, jennite} At low Ca/Si ratio Q factors exhibit a close proximity to 1.4 tobermorite. At high Ca/Si ratios our simulations are biased towards jennite-like features. X. Cong and R. J. Kirkpatrick, Adv. Cem. Based Mater, (1996).

14 3- MD simulations of C-A-S-H particles Connectivity of Si/Al atoms - Q3+Q4 (%) - MCL - Position of Al { Q n (mal) } Q 1 Q 2 (1Al) Q 3 (2Al) Al more environments Q 1 (1Al) Q 2 (2Al) { Q Al n(msi) } Q Al 2 (2Si) Q 1 (1Si) Q Al 1 (1Si)

15 MD simulations of C-A-S-H particles H. Manzano et al. A Molecular Dynamic Sutdy of the aluminosilicate chains structure in Al.rich Calcium Silicate Hydrate (C-S-H) gels ; Phys. Stat. Sol. (a) 205, No (2008) Si(OH) 4 Si(OH) 4 Al(OH) 3 Si(OH) 4 Al(OH) 3 We have put together many Si(OH) 4, Ca(OH) 2 4H 2 O, Al(OH) 3 and Na(OH) 5H 2 O molecules, and we have studied the formation of C-A-S-H structures at different Ca/(Si+Al) ratios

16 MD simulations of C-A-S-H particles 3.1-The connectivity of T-O-T bonds; T=Si,Al %(Q 3 +Q 4 ) Al/(Al+Si)=0 Al/(Al+Si)=0.125 Al/(Al+Si)=0.167 Al/(Al+Si)=0.250 The presence of Aluminium atoms favours the presence of threedimensional structures Ca/(Al+Si) ratio

17 Mean chain length MD simulations of C-A-S-H particles 3.1-The connectivity of T-O-T bonds; T=Si,Al Al/(Al+Si)=0 Al/(Al+Si)=0.125 Al/(Al+Si)=0.167 Al/(Al+Si)=0.250 Experimental data MCL Q1 Q 2 ( 3 / 2 )Q 2(1Al ) (1 / 2 )Q Al larger chains Good agreement with 29 Si NMR data (AACs) Ca/(Al+Si) ratio ED: I.G. Richardson et. al.; Cem. Concr. Res. 24 (1994) ; ED: I.G. Richardson and G.W. Grooves; J. Mat. Sci. 32 (1997)

18 Average number of bonds MD simulations of C-A-S-H particles 3.2-The position of Al atoms T=Si,Al 4 Al/(Al+Si)=0.125 Al/(Al+Si)=0.167 Al/(Al+Si)=0.250 ANB(T ) 1Q 2Q 3Q 4Q Q Q Q Q T T T T T T T T Al ANB (Si) is between 1 and 1.5 Q1 (terminal sites) Q2 sites (internal sites) 1 Si Ca/(Al+Si) ratio ANB (Al) is close to 2 Mainly Q2 sites (internal sites)

19 Q1 fraction of T in chains MD simulations of C-A-S-H particles 3.2-The position of Al atoms Si Al/(Al+Si)=0.125 Al/(Al+Si)=0.167 Al/(Al+Si)= Al atoms don t like the Q1 sites (when compared to the case of Si atoms) Al Ca/(Al+Si) ratio - At high Ca/(Al+Si) Q1 sites are not negligible!! Si-O-Al dimers might exist

20 MD simulations of C-A-S-H particles 3.2-The position of Al atoms Pairing sites Bridging sites Q 1 (1Al) Q 2 (1Al) Q 2 (1Al) Q 2 (1Al) Q 1 (1Al) + Q 2 (1Al) Q 2 (1Al) = = 2 Q 1 (1Al) + Q 2 (1Al) Q 2 (1Al) = 2 2 = 1

21 MD simulations of C-A-S-H particles 3.2-The position of Al atoms The formula Q 1 (1Al) + Q 2 (1Al) Q 2 (1Al) is OK for pentamers But we know that dimers can exist at high Ca/(Al+Si), andthey contribute to the term Q1(1Al) Fortunately their contribution can be calculated Q 1 (1Al) Q Al 1(1Si) Q * 1 (1Al)= Q 1 (1Al)-QAl 1 (1Si)*Al/Si Q * 1 (1Al) +Q 2 (1Al) Q 2 (1Al)

22 MD simulations of C-A-S-H particles 3.2-The position of Al atoms (Q * 1 (1Al)+Q 2 (1Al))/Q 2 (1Al) 3 2,5 2 Al/(Al+Si)=0.125 Al/(Al+Si)=0.167 Al/(Al+Si)=0.250 At low Ca/(Al+Si) ratios both PSs and BSs are occupied 1,5 1 0,5 Q 1 (1Al) Q 2 (1Al) Q 2 (1Al) Q 2 (1Al) At high Ca/(Al+Si) ratios PSs prevail. 0 0,6 0,8 1 1,2 1,4 1,6 1,8 Ca/(Al+Si)

23 4- Conclusions and Future MD simulations allow us to get structural information (Connectivity, Ca-OH and Si-OH bonds ) of C-S-H gels. From low to high Si/Ca ratios there is a gradual evolution from long to short chains, and from tobermorite-like to jennite-like features.

24 4- Conclusions and Future MD simulations allow us to reproduce the experimental evidences: - The presence of Al Larger presence of three-dimensional features An enlargement of the chains - The Al atoms occupy Q2 sites BSs and PSs at low Ca/(Al+Si) PSs at high Ca/(Al+Si)

25 4- Conclusions and Future MD simulations can serve us to establish the linkage between the structural models and the colloidal models

26 4- Conclusions and Future MD simulations can also serve us to monitor the hydration of C 3 S, C 2 S phases We have carried out some preliminary tests to monitor the hydration of small (~1nmx1nmx1nm) C 3 S and C 2 S pieces at different water-solid ratios LINKAGES WITH KINETIC AND HYDRATION MODELS

27 H. Manzano R. González Prof. M. Griebel J. Hamaekers F. Heber Funding Basque Government under the ETORTEK and SAIOTEK Programs Spanish Government under CONSOLIDER and PLAN NACIONAL Programs European Commission under the FP7 program

28 THANK YOU