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Multiscale modeling of the mesotexture of C-S-H and ASR gels
Published in Günther Meschke, Bernhard Pichler, Jan G. Rots, Computational Modelling of Concrete and Concrete Structures, 2022
Calcium silicate hydrate (C-S-H) is the main product of cement hydration and is responsible for several important properties of concrete, including setting, hardening, shrinkage, and creep. Alkali-silica reaction (ASR) products are formed from the reaction between the alkali present in the cement paste (generally, sodium or potassium) and the disordered silica present in some of the aggregates (e.g., (Rajabipour etal. 2015)). Both C-S-H and crystalhne ASR products are calcium silicates in a hydrated form and present a layered molecular structure (i.e., they are phyllosilicates). C-S-H molecular structures share similarities with defective structures of tobermorite or jennite (Richardson 2004) as a function of the Ca/Si molar ratio, while crystalline ASR products structures are similar to that of shlykovite (Shi et al. 2019). Both C-S-H and ASR products present a gel mesostructure in which solid colloidal particles (i.e., particles with a characteristic size of 1-100 nm (Buckley & Greenblatt 1994)) are arranged in the mesoscale forming a phase with a gel mesoporosity.
3S grain interface over hydration time
Published in Günther Meschke, Bernhard Pichler, Jan G. Rots, Computational Modelling of Concrete Structures, 2018
Strength of cement largely depends on the formation of Calcium Silicate Hydrate (C-S-H) which imparts cohesive property to the hydrating mix. Cement hydration being a complex phenomenon (Kondo & Udea 1968, Bullard et al. 2011, Scrivener et al. 2011, Scrivener et al. 2015), the hydration of Tricalcium Silicate (C3S), the major constituent in cement has often been used as an approximation (Pommersheim et al. 1979, Pommersheim et al. 1982, Kumar et al. 2012). Most of these hydration models, which are used to design the performance of cement, have been developed at a larger length scale. Material heterogeneities and porosity at lower length scales have largely been ignored or approximated. However emerging techniques such as high resolution Electron Microscopy and Nanoindentation makes it possible to capture such microstructural and mechanical features at length scales lower than micrometer. Properly exploited, these methods will give us a deeper insight into the complexities of hydration. In this work we employ SEM and Nanoindentation to build a 2-Dimensional C3S-C3S grain interface model.
Cement
Published in A. Bahurudeen, P.V.P. Moorthi, Testing of Construction Materials, 2020
Hydration of cement is a complex process, as cement consists of different components. Consequently, the hydration rate is controlled by different significant parameters other than state parameters such as temperature and concentration. Some of the most critical parameters that control hydration are cement fineness, crystal defects in various components of the cement obtained from kiln and surface constituents. As mentioned earlier in previous sections, the principal constituent of cement is tri-calcium silicate (C3S); therefore, hydration of C3S is of utmost importance. That can also act as a good model for cement reaction with water. In a similar way, hydration of C2S is also identical to C3S. The reaction of C3S and C2S with water is schematically given in Equations 1.1 and 1.2, respectively. Tri-calcium silicate and di-calcium silicate react with water and form calcium silicate hydrate (C–S–H) and calcium hydroxide (CH). CH is generally developed as pore solutions. The formation of CH plays a vital role in the case of the usage of mineral admixtures such as class F fly ash, as reactive silicates in the case of a fly ash–like material tend to react with CH and fill the pores formed by this CH. 2C3S+6H2O→C3S2H3+3CH2C2S+4H2O→C3S2H3+CH
Technical and environmental assessment of hydrothermally synthesized foshagite and tobermorite-like crystals as fibrillar C-S-H seeds in cementitious materials
Published in Journal of Sustainable Cement-Based Materials, 2023
Somayeh Nassiri, Ananya Markandeya, Md Mostofa Haider, Antonio Valencia, Milena Rangelov, Hui Li, Aaron Halsted, David Bollinger, John McCloy
Calcium-silicate-hydrate (C-S-H) is the main phase of hydrated Portland cement and is the source of concrete’s strength and durability [9,10]. Thus, stimulating C-S-H to grow more of its own kind would lead to more strength and durability. To support this type of stimulated growth, synthesized C-S-H nanomaterials (referred to as C-S-H seeds) can be added during the production of cementitious composites [11]. Experimental evidence has shown that these C-S-H seeds speed up the hydration of silicate phases of clinker (especially C3S) and increase the early and total amount of hydration within the first 24 h. In addition, C-S-H seeds provide nucleation sites and growth templates, so additional C-S-H products grow away from clinker particles and on the dispersed C-S-H seeds in the pore solution [12]. This growth mechanism was shown to drive the acceleration seen in the dissolution of C3S and remove or shorten the dormant and induction periods of cement hydration [11, 13–15]. Thus, it is possible to multiply early strength with C-S-H seeding, which is paramount to high early strength in concrete blended with SCMs and other lower-CO2 cement types such as belite cements [16–23].
Effect of banana skin powder and coir fibre on properties and flexural behaviour of precast SCC beam
Published in International Journal of Sustainable Engineering, 2021
Muhammad Tahir Lakhiar, Noridah Mohamad, Abdul Aziz Abdul Samad, Khairunisa Muthusamy, Md Azree Othuman Mydin, W. I. Goh, Steafenie George
Mohamad et al. (2018a) investigated the effects of incorporating BSP and POFA in foamed concrete mixture as cement and sand replacement, respectively. From the chemical property tests conducted, it was found that BSP contained 55.98% silicon dioxide and 2.71% aluminium oxide, while POFA contained 51.83% silicon dioxide and 2.32% aluminium oxide. The particle size for these two materials as obtained from physical test showed that both materials are considered as fine particles, which is within 0.1–250 μm. The chemical composition and particle size of BSP and POFA contribute to the pozzolanic reaction in the foamed concrete mixture. The reaction between silicon dioxide and calcium hydroxide in the presence of water produced the calcium silicate hydrate gel (C-S-H), which plays important role in binding all the particles together in the mixture. From further investigations on the mechanical properties of foamed concrete incorporating BSP and POFA, it was found that the compressive strength, tensile strength and modulus of elasticity slightly increased compared to control mixture.
Impact of different hydrated cementitious phases on moisture-induced damage in lime-stabilised subgrade soils
Published in Road Materials and Pavement Design, 2018
Sayantan Chakraborty, Syam Nair
The long-term strength gain in lime-stabilised soil is a slow process as it depends on the pozzolanic reactivity of soil in the presence of lime. During this process, calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H) are formed when the dissolved silicates and aluminates from clay particles react with the Ca2+ ions provided by lime. Properties of C-S-H vary with the calcium-to-silica ratio of these phases. Broadly, there are two types of C-S-H, namely C-S-H I (with Ca/Si < 1.5) and C-S-H II (with Ca/Si > 1.5) (Gard & Taylor, 1976; Nonat, 2004; Taylor, 1950). The morphology of these C-S-H phases varies from leaf- plate-like to fibrous needle-like structure with the increase in Ca/Si ratio (Diamond, White, & Dolch, 1963; He, Zhao, Lu, Struble, & Hu, 2011). These C-S-H phases are the primary contributor of strength in stabilised soils and are similar to the cementitious product formed during hydration of cement (Little & Nair, 2009).