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Calcium silicates are produced by treating calcium oxide and silica in various ratios. Their formation is relevant to Portland cement. [5]Calcium silicate is a byproduct of the Pidgeon process, a major route to magnesium metal.
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.
These substances break down into dissolved ions as a result. For example, calcium silicate (CaSiO 3), or wollastonite, reacts with carbon dioxide and water to yield a calcium ion, Ca 2+, a bicarbonate ion, HCO 3 −, and dissolved silica. This reaction structure is representative of general silicate weathering of calcium silicate minerals. [9]
Upon addition of water, clinker minerals react to form different types of hydrates and "set" (harden) as the hydrated cement paste becomes concrete.The calcium silicate hydrates (C-S-H) (hydrates of alite and belite minerals) represent the main "glue" components of the concrete.
The other silicate, alite contributes "early" strength, due to its higher reactivity. Belite reacts with water (roughly) to form calcium silicate hydrates (C-S-H) and portlandite (Ca(OH) 2) according to the reaction:
Calcium ions then react with the soluble sodium silicate gel to convert it into solid calcium silicate hydrates (C-S-H). The C-S-H forms a continuous poorly permeable coating at the external surface of the aggregate. The penetrated alkaline solution (NaOH / KOH) converts the remaining siliceous minerals into bulky soluble alkali silicate gel.
Thaumasite is a calcium silicate mineral, containing Si atoms in unusual octahedral configuration, with chemical formula Ca 3 Si(OH) 6 (C O 3)(SO 4)·12H 2 O, also sometimes more simply written as CaSiO 3 ·CaCO 3 ·CaSO 4 ·15H 2 O. It occurs as colorless to white prismatic hexagonal crystals, typically as acicular radiating groups. It also ...
The calcium cycle is a transfer of calcium between dissolved and solid phases. There is a continuous supply of calcium ions into waterways from rocks, organisms, and soils. [1] [2] Calcium ions are consumed and removed from aqueous environments as they react to form insoluble structures such as calcium carbonate and calcium silicate, [1] [3] which can deposit to form sediments or the ...