Search results
Results from the WOW.Com Content Network
Carbonatation is a slow process that occurs in concrete where lime (CaO, or Ca(OH) 2 ) in the cement reacts with carbon dioxide (CO 2) from the air and forms calcium carbonate. The water in the pores of Portland cement concrete is normally alkaline with a pH in the range of 12.5 to 13.5.
When atmospheric carbon dioxide (CO 2), or carbonate ions (HCO − 3, CO 2− 3 dissolved in water) diffuse into concrete from its external surface, they react with calcium hydroxide (portlandite, Ca(OH) 2) and the pH of the concrete pore water progressively decreases from 13.5 – 12.5 to 8.5 (pH of water in equilibrium with calcite).
A prompt reaction initiated at the early stage of concrete hardening on very fine silica particles will help to suppress a slow and delayed reaction with larger siliceous aggregates on the long term. Following the same principle, the fabrication of low-pH cement also implies the addition of finely divided pozzolanic materials rich in silicic ...
900 to 1050 °C – the remaining calcium carbonate decomposes to calcium oxide (CaO) and CO 2. 1300 to 1450 °C – partial (20–30%) melting takes place, and belite reacts with calcium oxide to form alite (Ca 3 O·SiO 4) (also known as C3S in the Cement Industry). Typical clinker nodules. Alite is the characteristic constituent of Portland ...
Silicic acid (H 4 SiO 4) in the silica-enriched fluids forms lenticular, nodular, fibrous, or aggregated quartz, opal, or chalcedony that grows within the rock. [5] Silicification happens when rocks or organic materials are in contact with silica-rich surface water, buried under sediments and susceptible to groundwater flow, or buried under ...
The only other major sink of silica in the ocean is burial along continental margins (3.6 ± 3.7 Tmol Si year −1), primarily in the form of siliceous sponges. [15] Due to the high degrees of uncertainty in source and sink estimations, it's difficult to conclude if the marine silica cycle is in equilibrium.
Hydrotalcite – Hydrated Mg-Al layered double hydroxide (LDH) containing carbonate anions; Tacharanite – Calcium aluminium silicate hydrate mineral (Ca 12 Al 2 Si 18 O 33 (OH) 36, and also Ca 12 Al 2 Si 18 O 51 (OH) 2 · 18 H 2 O) Mechanisms of formation of C-S-H phases: Alkali–silica reaction – Chemical reaction damaging concrete
This figure describes the geological aspects and processes of the carbonate silicate cycle, within the long-term carbon cycle. The carbonate–silicate geochemical cycle, also known as the inorganic carbon cycle, describes the long-term transformation of silicate rocks to carbonate rocks by weathering and sedimentation, and the transformation of carbonate rocks back into silicate rocks by ...