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Therefore, when concreting at cold temperature cannot be avoided, it is essential to have a minimum curing time at a temperature sufficiently above the freezing point of the concrete pore water, so that the early strength of concrete is high enough to resist the inner tensile stress caused by water freezing. [5]
A slab of pykrete Pykrete is made of 14% sawdust and 86% water by mass.. Pykrete (/ ˈ p aɪ k r iː t /, PIE-creet) [1] is a frozen ice composite, [2] originally made of approximately 14% sawdust or some other form of wood pulp (such as paper) and 86% ice by weight (6 to 1 by weight).
During the curing period, concrete is ideally maintained at controlled temperature and humidity. To ensure full hydration during curing, concrete slabs are often sprayed with "curing compounds" that create a water-retaining film over the concrete. Typical films are made of wax or related hydrophobic compounds.
Concrete has immersed from natural resources into man-made processes; evidence of the use of concrete dates back over 8,000 years ago. Today, many construction companies and concrete manufacturers have cut the use of Portland cement in their mixtures due to its production process emitting significant amounts of greenhouse gases into the atmosphere.
Depending on the climate, the curing process may take longer and require more frequent wetting. Once the concrete is cured, it sits for two to three weeks before the process is complete. [citation needed] When hydrophobic concrete is made through the use of an admixture, a powder with the hydrophobic chemicals is added during the batching process.
This effect aids in reducing water penetration, but has no known effect on reducing water vapor transmission and emission. [29] A chemical reaction occurs with the excess Ca(OH) 2 ( portlandite ) present in the concrete that permanently binds the silicates with the surface, making them far more durable and water repellent.
Concrete sealers are applied to concrete to protect it from surface damage, corrosion, and staining. They either block the pores in the concrete to reduce absorption of water and salts or form an impermeable layer which prevents such materials from passing.
Precast concrete molds can be made of timber, steel, plastic, rubber, fiberglass, or other synthetic materials, with each giving a unique finish. [3] In addition, many surface finishes for the four precast wall panel types – sandwich, plastered sandwich, inner layer and cladding panels – are available, including those creating the looks of ...