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A cement accelerator is an admixture for the use in concrete, mortar, rendering or screeds. The addition of an accelerator speeds the setting time and thus cure time starts earlier. [1] This allows concrete to be placed in winter with reduced risk of frost damage. [2]
The setting time of the concrete is an important criterion to determine the delay period. Generally, the delay period is equal to the initial setting time which has been found to give satisfactory results. Lesser delay periods result in compressive strength losses. [1]
Manufacturing costs were therefore considerably higher, but the product set reasonably slowly and developed strength quickly, thus opening up a market for use in concrete. The use of concrete in construction grew rapidly from 1850 onward, and was soon the dominant use for cements. Thus Portland cement began its predominant role.
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. [2] Its usage worldwide, ton for ton, is twice that of steel, wood, plastics, and aluminium combined. [3]
Concrete has a limited lifespan between batching / mixing and curing. This means that ready-mixed concrete should be placed within 30 to 45 minutes of the batching process to hold slump and mix design specifications in the US, [15] though in the UK, environmental and material factors, plus in-transit mixing, allow for up two hours to elapse. [16]
(The last two requirements were already set out in the German Standard, issued in 1909). Clinkers make up more than 90% of the cement, along with a limited amount of calcium sulphate (CaSO 4, which controls the set time), and up to 5% minor constituents (fillers) as allowed by various standards. Clinkers are nodules (diameters, 0.2–1.0 inch ...
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Self-consolidating concrete or self-compacting concrete (SCC) [1] is a concrete mix which has a low yield stress, high deformability, good segregation resistance (prevents separation of particles in the mix), and moderate viscosity (necessary to ensure uniform suspension of solid particles during transportation, placement (without external compaction), and thereafter until the concrete sets).
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