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When the plaster is dry, the pH falls to about 8.6. Non-hydraulic lime plaster requires moisture to set and has to be prevented from drying for several days. The number of qualified tradesmen capable of plastering with lime has declined due to industrialization, deskilling of trade crafts, and widespread adoption of drywall and gypsum veneer ...
The conditions and compounds present during each step of the lime cycle have a strong influence of the end product, [8] thus the complex and varied physical nature of lime products. An example is when slaked lime (calcium hydroxide) is mixed into a thick slurry with sand and water to form mortar for building purposes.
Calcined gypsum is an alternative material in industrial plasters and mortars. Cement, cement kiln dust, fly ash, and lime kiln dust are potential substitutes for some construction uses of lime. Magnesium hydroxide is a substitute for lime in pH control, and magnesium oxide is a substitute for dolomitic lime as a flux in steelmaking. [28]
John Smeaton is credited with pioneering hydraulic lime in the 18th century, which led to the development of Portland cement and thus modern concrete. Painting by John Lynn. Painting by John Lynn. Hydraulic lime (HL) is a general term for a variety of lime different from calcium oxide (quicklime), that sets by hydration and consists of calcium ...
Lime comes from Old English lim ('sticky substance, birdlime, mortar, cement, gluten'), and is related to Latin limus ('slime, mud, mire'), and linere ('to smear'). [7] Mortar is a mixture with cement and comes from Old French mortier ('builder's mortar, plaster; bowl for mixing') in the late 13th century and Latin mortarium ('mortar'). [7]
The theoretical heat (the standard enthalpy) of reaction required to make high-calcium lime is around 3.15 MJ per kg of lime, so the batch kilns were only around 20% efficient. The key to development in efficiency was the invention of continuous kilns, avoiding the wasteful heat-up and cool-down cycles of the batch kilns.
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).
Calthemite straw stalactite growing from the concrete ceiling of an undercover car-park Calthemite straw stalactites, the rightmost example demonstrating bending due to the direction of air currents during its formation. Calthemite is a secondary deposit, derived from concrete, lime, mortar or other calcareous material outside the cave environment.