Calcium silicate hydrates (CSH orC-S-H) are the main products of the hydration ofPortland cement and are primarily responsible for thestrength of cement-based materials.[1] They are the main binding phase (the "glue") in mostconcrete. Only well defined and rare natural crystalline minerals can be abbreviated as CSH while extremely variable and poorly ordered phases without well definedstoichiometry, as it is commonly observed inhardened cement paste (HCP), are denoted C-S-H.
When water is added to cement, each of the compounds undergoes hydration and contributes to the final state of the concrete.[2] Only calcium silicates contribute to the strength. Tricalcium silicate is responsible for most of the early strength (first 7 days).[3] Dicalcium silicate, which reacts more slowly, only contributes to late strength.Calcium silicate hydrate (also shown as C-S-H) is a result of the reaction between the silicate phases of Portland cement and water. This reaction typically is expressed as:
Thestoichiometry of C-S-H incement paste is variable and the state of chemically and physically bound water in its structure is not transparent, which is why "-" is used between C, S, and H.[4]
Synthetic C-S-H can be prepared from the reaction of CaO and SiO2 in water or through the double precipitation method using various salts. These methods provide the flexibility of producing C-S-H at specific C/S (Ca/Si, or CaO/SiO2) ratios. The C-S-H from cement phases can also be treated with anammonium nitrate solution in order to induce calcium leaching, and so to achieve a given C/S ratio.
C-S-H is a nano sized material[5][6] with some degree of crystallinity as observed byX-ray diffraction techniques.[7] The underlying atomic structure of C-S-H is similar to the naturally occurring mineraltobermorite.[8] It has a layered geometry with calcium silicate sheet structure separated by an interlayer space. The silicates in C-S-H exist as dimers, pentamers and 3n-1 chain units[9][10] (where n is an integer greater than 0) and calcium ions are found to connect these chains making the three dimensional nano structure as observed bydynamic nuclear polarisation surface-enhancednuclear magnetic resonance.[11] The exact nature of the interlayer remains unknown. One of the greatest difficulties in characterising C-S-H is due to its variablestoichiometry.[citation needed]
The scanning electron microscope micrographs of C-S-H do not show any specific crystalline form. They usually manifest as foils or needle/oriented foils.
Synthetic C-S-H can be schematically divided into two categories, depending on whether their Ca/Si molar ratio is below or above a threshold value of 1.1. There are several indications that the chemical, physical and mechanical characteristics of C-S-H vary noticeably between these two categories.[12][13]
Afwillite – Nesosilicate alteration mineral also sometimes found in hydrated cement paste
Gyrolite – Rare phyllosilicate mineral crystallizing in small spheres (a rare mineral from hydrothermal alteration, or an ageing product of alkali-silica reaction)
Jennite – Inosilicate alteration mineral in metamorphosed limestone and in skarn
Thaumasite – Complex calcium silicate hydrate mineral
Tobermorite – Inosilicate alteration mineral in metamorphosed limestone and in skarn
Pozzolanic reaction – Capacity of silica-rich materials to react with calcium hydroxyde to form calcium silicate hydratesPages displaying short descriptions of redirect targets
^Allen, Andrew J.; Thomas, Jeffrey J.; Jennings, Hamlin M. (25 March 2007). "Composition and density of nanoscale calcium–silicate–hydrate in cement".Nature Materials.6 (4):311–316.Bibcode:2007NatMa...6..311A.doi:10.1038/nmat1871.PMID17384634.
^Andalibi, M. Reza; Kumar, Abhishek; Srinivasan, Bhuvanesh; Bowen, Paul; Scrivener, Karen; Ludwig, Christian; Testino, Andrea (2018). "On the mesoscale mechanism of synthetic calcium–silicate–hydrate precipitation: a population balance modeling approach".Journal of Materials Chemistry A.6 (2):363–373.doi:10.1039/C7TA08784E.ISSN2050-7488.S2CID103781671.
^Renaudin, Guillaume; Russias, Julie; Leroux, Fabrice; Frizon, Fabien; Cau-dit-Coumes, Céline (December 2009). "Structural characterization of C–S–H and C–A–S–H samples—Part I: Long-range order investigated by Rietveld analyses".Journal of Solid State Chemistry.182 (12):3312–3319.Bibcode:2009JSSCh.182.3312R.doi:10.1016/j.jssc.2009.09.026.
^Taylor, Harry F.W. (June 1986). "Proposed Structure for Calcium Silicate Hydrate Gel".Journal of the American Ceramic Society.69 (6):464–467.doi:10.1111/j.1151-2916.1986.tb07446.x.
^Cong, Xiandong; Kirkpatrick, R. James (April 1996). "29Si and17O NMR investigation of the structure of some crystalline calcium silicate hydrates".Advanced Cement Based Materials.3 (3–4):133–143.doi:10.1016/S1065-7355(96)90045-0.
^Brunet, F.; Bertani, Ph.; Charpentier, Th.; Nonat, A.; Virlet, J. (October 2004). "Application of Si Homonuclear and H−Si Heteronuclear NMR Correlation to Structural Studies of Calcium Silicate Hydrates".The Journal of Physical Chemistry B.108 (40):15494–15502.doi:10.1021/jp031174g.
