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The mono-sulfate (AFm) now more soluble at low temperature slowly dissolves to recrystallize as the less soluble ettringite (AFt). AFt crystal structure hosts more water molecules than AFm. So, AFt has a higher molar volume than AFm because of its 32 H 2 O molecules. During months, or years, after young concrete cooling, AFt crystallizes very ...
If the ambient temperature is too high in the summer, no concrete casting is allowed, or special precautions need to be taken such as making concrete with ice and cold aggregates in desertic conditions. Selecting a cement with a low-alkali content (Na 2 O eq < 0.60 wt. % according to the European cement norm EN 197).
4 ions to precipitate CaSO 4 ·2H 2 O . A fraction of SO 2− 4 ions can also be trapped, or sorbed, into the layered structure of C-S-H. [3] These successive reactions lead to the precipitation of expansive mineral phases inside the concrete porosity responsible for the concrete degradation, cracks and ultimately the failure of the structure.
Changes of pore water content due to drying or wetting processes cause significant volume changes of concrete in load-free specimens. They are called the shrinkage (typically causing strains between 0.0002 and 0.0005, and in low strength concretes even 0.0012) or swelling (< 0.00005 in normal concretes, < 0.00020 in high strength concretes).
The ultimate strength of concrete is influenced by the water-cementitious ratio (w/cm), the design constituents, and the mixing, placement and curing methods employed.All things being equal, concrete with a lower water-cement (cementitious) ratio makes a stronger concrete than that with a higher ratio. [2]
These are created during concrete mixing (while the slurry is in its liquid state), with most surviving to remain part of it when hardened. Air entrainment makes concrete more workable [1] during placement, and increases its durability when hardened, particularly in climates subject to freeze-thaw cycles. [2] It also improves the workability of ...
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The second consideration is the high thermal mass of concrete slabs, which applies similarly to walls and floors, or wherever concrete is used within the thermal envelope. Concrete has a relatively high thermal mass, meaning that it takes a long time to respond to changes in ambient temperature. [9]