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Concrete is damaged if it does not reach a strength of 500 pounds per square inch (3.4 MPa) before freezing. [3]: 19 Typical chemicals used for acceleration today are calcium nitrate (Ca(NO 3) 2), calcium nitrite (Ca(NO 2) 2), calcium formate (Ca(HCOO) 2) and aluminium compounds.
A single concrete block, as used for construction. Concrete is a composite material composed of aggregate bonded together with a fluid cement that cures to a solid over time. . Concrete is the second-most-used substance in the world after water, [1] and is the most widely used building material
Most densifiers can react within 1-2 hours with concrete surface, however the chemical reaction with the calcium and free lime in the concrete will continue for up to 2 months after the application of it to the surface of the concrete. Densifiers may use various carrying agents to accomplish the hardening process, potassium, sodium, lithium, or ...
The chemical reaction results in mineral hydrates that are not very water-soluble. This allows setting in wet conditions or under water and further protects the hardened material from chemical attack. The chemical process for hydraulic cement was found by ancient Romans who used volcanic ash with added lime (calcium oxide).
Superplasticizers (SPs), also known as high range water reducers, are additives used for making high-strength concrete or to place self-compacting concrete. Plasticizers are chemical compounds enabling the production of concrete with approximately 15% less water content. Superplasticizers allow reduction in water content by 30% or more.
The calcium silicate hydrates (C-S-H) (hydrates of alite and belite minerals) represent the main "glue" components of the concrete. After initial setting the concrete continues to harden and to develop its mechanical strength. The first 28 days are the most critical for the hardening. The concrete does not dry but one says that it sets and hardens.
They are the main binding phase (the "glue") in most concrete. Only well defined and rare natural crystalline minerals can be abbreviated as CSH while extremely variable and poorly ordered phases without well defined stoichiometry , as it is commonly observed in hardened cement paste (HCP), are denoted C-S-H.
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 ...
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