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Twenty eight days is a long wait to determine if desired strengths are going to be obtained, so three-day and seven-day strengths can be useful to predict the ultimate 28-day compressive strength of the concrete. A 25% strength gain between 7 and 28 days is often observed with 100% OPC (ordinary Portland cement) mixtures, and between 25% and 40 ...
S is the strength of concrete A and B are constants and A=96 N/mm2, B=7 (this is valid for the strength of concrete at the age of 28 days) w/c is the water–cement ratio , which varies from 0.3 to 1.20
The compressive strength of concrete is given in terms of the characteristic compressive strength of 150 mm size cubes tested after 28 days (fck). In field, compressive strength tests are also conducted at interim duration i.e. after 7 days to verify the anticipated compressive strength expected after 28 days.
The gypsum level may also be increased a small amount. This gives the concrete using this type of cement a three-day compressive strength equal to the seven-day compressive strength of types I and II. Its seven-day compressive strength is almost equal to 28-day compressive strengths of types I and II. The only downside is that the six-month ...
HPC is concrete that develops a strength greater than 50 megapascals (7,300 psi) at 28, 56, or 90 days. These strengths generally require well-graded hard rock aggregates, a fairly high proportion of cement plus fly ash, water-reducing admixtures, and the silica fume, with relatively low water content.
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Bagwork concrete will generally reach full strength within 28 days. Each bag must be pierced by at least one, and preferably up to four pins. Bagwork is a simple and convenient method of underwater concrete placement which does not require pumps, plant, or formwork, and which can minimise environmental effects from dispersing cement in the water.
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