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After sufficient setting and hardening of concrete (after 28 days), the progressive loss of capillary water is also responsible for the "drying shrinkage". It is a continuous and long-term process occurring later during the concrete life when under dry conditions the larger pores of concrete are no longer completely saturated by water. Thermal ...
Cement manufacture is a source of the following airborne contaminants: particulate matter, nitrogen oxides, sulfur dioxide, carbon monoxide, and carbon dioxide. [3] Cement production releases carbon dioxide by sintering limestone or shells. It is also very energy-intensive, with the result that the cement industry is a large emitter of carbon ...
The alkali–silica reaction (ASR), also commonly known as concrete cancer, [3] is a deleterious internal swelling reaction that occurs over time in concrete between the highly alkaline cement paste and the reactive amorphous (i.e., non-crystalline) silica found in many common aggregates, given sufficient moisture.
Alteration of hardened cement paste composition, with monosulfate aluminates phase converting to ettringite and, in later stages, gypsum formation. The necessary additional calcium is provided by the calcium hydroxide and calcium silicate hydrate in the cement paste; The effect of these changes is an overall loss of concrete strength.
Chromium present in the cement as Cr[III] is of no consequence. Mn 2 O 3 is not deleterious, acting as a substitute for iron. But it contributes more color to the cement than iron, and high-Mn 2 O 3 cements (>1%) are almost black. ZnO is encountered in some rawmix additives (as well as tires used as kiln fuel). At levels above 0.2%, it causes ...
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[28] Pore structures in fresh concrete and air entrained in concrete. Concrete can be carbonated by two main methods: weathering carbonation and early age carbonation. [29] Weathering carbonation occurs in concrete when calcium compounds react with carbon dioxide (CO 2) from the atmosphere and water (H 2 O) in the concrete pores. The reaction ...