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Formation of the desired clinker minerals involves heating the rawmix through the temperature stages mentioned above. The finishing transformation that takes place in the hottest part of the kiln, under the flame, is the reaction of belite (C 2 S = 2CaO·SiO 2, or Ca 2 SiO 4) with calcium oxide to form alite (C 3 S = 3CaO·SiO 2, or Ca 3 SiO 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 ...
A fairly well-defined reaction front can often be observed in thin sections; ahead of the front the concrete is normal, or near normal. Behind the reaction front, the composition and the microstructure of concrete are modified. These changes may vary in type or severity but commonly include: Extensive cracking; Expansion
Samples of "ground granulated blast furnace slag" (left) and "granulated blast furnace slag" (right) Ground granulated blast-furnace slag (GGBS or GGBFS) is obtained by quenching molten iron slag (a by-product of iron and steel-making) from a blast furnace in water or steam, to produce a glassy, granular product that is then dried and ground into a fine powder.
The ancient Romans used a type of lime mortar that has been found to be self-healing. [8] The stratlingite crystals form along the interfacial zones of Roman concrete, binding the aggregate and mortar together and this process continued even after 2000 years and it was discovered by the geologist Marie Jackson and her colleagues in 2014.
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