Effect of magnesium on the C-S-H nanostructure evolution and aluminate phases transition in cement-slag blend

Abstract

The microstructural study was conducted on cement and cement-slag pastes immersed in different concentrations of Mg(NO₃)₂ solutions utilizing ²⁹Si, ²⁷Al NMR spectroscopy and XRD techniques. The results show that the hydration of both the cement and cement-slag pastes is delayed when the pastes are cured in Mg(NO₃)₂ solutions as compared to the pastes cured in water. Moreover, Mg²⁺ ions also exhibit an decalcifying and dealuminizing effect on the C-A-S-H in cement and cement-slag pastes, and thereby decrease Ca/Si and Al[4]/Si ratios of the C-A-S-H. The dealuminization of C-A-S-H is mitigated for cement-slag paste as compared to pure cement paste. The depolymerized calcium and aluminum ions from C-A-S-H gel mainly enter the pore solution to maintain the pH value and form Al^[6] in TAH, respectively. On the other hand, Mg²⁺ ions exert an impact on the intra-transition between Al^[6] species, from AFm and hydrogarnet to hydrotalcite-like phase. NO₃ ^- ions are interstratified in the layered Mg-Al structure and formed nitrated hydrotalcite-like phase (Mg_1-xAl _x(OH)₂(NO₃) _x•nH₂O). Results from both ²⁷Al NMR and XRD data show that ettringite seems not to react with Mg²⁺ ions.

Keywords

²⁹Si and ²⁷Al NMR / magnesium ion / C-A-S-H microstructure / aluminate phases transition / hydration / slag incorporation

References

[1] Bonen D, Cohen M D. Magnesium Sulfate Attack on Portland Cement Paste-I. Microstructural Analysis[J]. Cement & Concrete Research, 1992, 22(1): 169-180.

[2] Bonen D, Cohen M D. Magnesium Sulfate Attack on Portland Cement Paste—II. Chemical and Mineralogical Analyses[J]. Cement & Concrete Research, 1992, 22(4): 707-718.

[3] Gollop R S, Taylor H F W. Microstructural and Microanalytical Studies of Sulfate Attack. IV. Reactions of a Slag Cement Paste with Sodium and Magnesium Sulfate Solutions[J]. Cement & Concrete Research, 1996, 26(26): 1013-1028.

[4] Kunther W, Lothenbach B, Skibsted J. Influence of the Ca/Si Ratio of the C–S–H Phase on the Interaction with Sulfate Ions and Its Impact on the Ettringite Crystallization Pressure[J]. Cement & Concrete Research, 2015, 69(1): 37-49.

[5] Taylor R, Richardson I G, Brydson R. Composition and Microstructure of 20-year-old Ordinary Portland Cement-ground Granulated Blast-furnace Slag Blends Containing 0 to 100% Slag[J]. Cement & Concrete Research, 2010, 40(40): 971-983.

[6] Dai Z, Tran T T, Skibsted J. Aluminum Incorporation in the C–S–H Phase of White Portland Cement-Metakaolin Blends Studied by 27Al and 29Si MAS NMR Spectroscopy[J]. Journal of the American Ceramic Society, 2014, 97(8): 2662-2671.

[7] Hou D, Li Z, Zhao T. Reactive Force Field Simulation on Polymerization and Hydrolytic Reactions in Calcium Aluminate Silicate Hydrate (C-A-S-H) Gel: Structure, Dynamics and Mechanical Properties[J]. Rsc Advances, 2015, 5(1): 448-461.

[8] Qomi M J A, Ulm F J, Pellenq J M. Evidence on the Dual Nature of Aluminum in the Calcium-Silicate-Hydrates Based on Atomistic Simulations[J]. Journal of the American Ceramic Society, 2012, 95(3): 1128-1137.

[9] Jackson M D, Moon J, Gotti E, et al. Material and Elastic Properties of Al-Tobermorite in Ancient Roman Seawater Concrete[J]. Journal of the American Ceramic Society, 2013, 96(8): 2598-2606.

[10] Jackson M D, Chae S R, Mulcahy S R, et al. Unlocking the Secrets of Al-tobermorite in Roman Seawater Concrete[J]. American Mineralogist, 2013, 98(10): 1669-1687.

[11] Ding Q, Wang H, Hu C, et al. Effect of Corrosive Solutions on C-S-H Microstructure in Portland Cement Paste with Fly Ash[J]. Journal of Wuhan University of Technology-Materials Science Edition, 2016, 31(5): 1002-1007.

[12] Ding Q, Liu K, Zhang G, et al. The Composition and Al-bearing Phases Transition of Cement Paste Subjected to MgSO₄ attack[J]. Journal of Wuhan University of Technology, 2016, 38(5): 1-7.

[13] Mendes A, Gates W P, Sanjayan J G, et al. NMR, XRD, IR and Synchrotron NEXAFS Spectroscopic Studies of OPC and OPC/Slag Cement Paste Hydrates[J]. Materials & Structures, 2011, 44(10): 1773-1791.

[14] Jakobsen H J, Hall C. Quantification of Calcium Silicate Phases in Portland Cements by 29Si MAS NMR Spectroscopy[J]. Journal of the Chemical Society Faraday Transactions, 1995, 91(24): 4423-4430.

[15] Brough A R, Dobson C M, Richardson I G, et al. In Situ Solid-State NMR Studies of Ca₃SiO₅: Hydration at Room Temperature Using 29Si Enrichment[J]. Journal of Materials Science, 1993, 29(15): 3926-3940.

[16] Girão A V, Richardson I G, Porteneuve C B, et al. Composition, Morphology and Nanostructure of C–S–H in White Portland Cement Pastes Hydrated at 55 °C[J]. Cement & Concrete Research, 2007, 37(12): 1571-1582.

[17] Richardson I G. Tobermorite/Jennite-and Tobermorite/Calcium Hydroxide-based Models for the Structure of C-S-H: Applicability to Hardened Pastes of Tricalcium Silicate, β-dicalcium Silicate, Portland Cement, and Blends of Portland Cement with Blast-furnace Slag, Metakaol[J]. Cement & Concrete Research, 2004, 34(9): 1733-1777.

[18] Wang Z, Ding Qingjun. Comparative Study on Characterization Methods of Integrate Hydration Degree of Fly Ash and Cement Composite Blend Pastes[J]. Journal of Wuhan University of Technology, 2014, 36(1): 17-23.

[19] Lumley J S, Gollop R S, Moir G K, et al. Degrees of Reaction of the Slag in Some Blends with Portland Cements[J]. Cement & Concrete Research, 1996, 26(1): 139-151.

[20] Rodger S A, Groves G W, Clayden N J, et al. A Study of Tricalcium Silicate Hydration from Very Early to Very Late Stages[J]. Materials Research Society Symposium Proceedings, 1987, 85: 13-20.

[21] Cong X, Kirkpatrick R J. 29Si MAS NMR Study of the Structure of Calcium Silicate Hydrate[J]. Advanced Cement Based Materials, 1996, 3(3): 144-156.

[22] Fernández-Jimenez A, Torre A G D L, Palomo A, et al. Quantitative Determination of Phases in the Alkali Activation of Fly Ash. Part I. Potential Ash Reactivity[J]. Fuel, 2005, 85(5-6): 625-634.

[23] Fernández-Jiménez A, Torre A G D L, Palomo A, et al. Quantitative Determination of Phases in the Alkaline Activation of Fly Ash. Part II: Degree of Reaction[J]. Fuel, 1960, 85(14-15): 1960-1969.

[24] Andersen M D, Jakobsen H J, Skibsted J. Incorporation of Aluminum in the Calcium Silicate Hydrate (C-S-H) of Hydrated Portland Cements: a High-field 27Al and 29Si MAS NMR Investigation[J]. Inorganic Chemistry, 2003, 42(7): 2280-2287.

[25] Andersen M D, Jakobsen H J, Skibsted J. A New Aluminium-hydrate Species in Hydrated Portland Cements Characterized by Al and Si MAS NMR Spectroscopy[J]. Cement & Concrete Research, 2006, 36(1): 3-17.

[26] Sun G K, Young J F, Kirkpatrick R J. The Role of Al in C–S–H: NMR, XRD, and Compositional Results for Precipitated Samples[J]. Cement & Concrete Research, 2006, 36(1): 18-29.

[27] Le S G, Mohsen B H, Frank W, et al. Hydration Degree of Alkali-Activated Slags: A 29Si NMR Study[J]. Journal of the American Ceramic Society, 2011, 94(12): 4541-4547.

[28] Jin F, Gu K, Al-Tabbaa A. Strength and Drying Shrinkage of Reactive MgO Modified Alkali-activated Slag Paste[J]. Construction & Building Materials, 2014, 51(4): 395-404.

[29] And Z P X, Zeng H C. Decomposition Pathways of Hydrotalcite-like Compounds Mg_1-xAl_x(OH)₂(NO₃)_x·nH₂O as a Continuous Function of Nitrate Anions[J]. Chemistry of Materials, 2001, 13(12): 4564-4572.

[30] Myneni S C B, Traina S J, Logan T J. Ettringite Solubility and Geo-Chemistry of the Ca(OH)2–Al2(SO4)3–H2O System at 1 atm Pressure and 298 K[J]. Chemical Geology, 1998, 148(148): 1-19.