why testing compressive strength and flexural strength of concrete for 7 days, 14 days, 28 days?

Question

Why we choose this day to test the compressive strength and flexural strength? What happened to the strength of concrete by these times?

Answer 1

28 days is the real strength test - the one that is specified on the construction drawings. This is the big one. But we test early for a couple of reasons. First, if there's a problem with the concrete, the sooner you can fix the concrete the less you'll have to rip out and replace. Second, a lot of times, the builder wants to remove forms at around 7 days. Having a strength test can tell him that the concrete is strong enough to stand up on it's own. Finally, concrete should get stronger as it sits. If you plot the relationship between time and strength it's a curve. Engineer's can check that curve and see if there's a potential problem by it's shape.

One other thing - having the tests is a safeguard not only for life safety (to make sure the concrete structure won't fall down) but also for the protection of the contractor and/or engineer. If a lawsuit arises out of a project, having those records can demonstrate that there was or wasn't a problem with the concrete - and a cause of failure is easier to determine

Answer 2

The strength characteristics are checked to assure the concrete placed meets or exceeds what was designed for the particular application. Most people generally will break a cylinder at 7 days to get an idea of what strength the concrete will end up at. Most concrete mixes used have a history of strength characteristics that can be compared to the value obtained at 7 days to verify if the strength is on track to make it or not. a brak at 14 days is usually optional, unless it was questionable if the required strength was going to be made. The 28 day break is usually used to document the final strength of the concrete used. So, the 7 day break is used to give the engineer and contractor an early indication of strength and allow them to make modifications if needed (up to and including tearing out the concrete placed and redoing it). It can also be used as an indication of when it is safe to remove any formwork (and can be done earlier, like at day 2 or 3 if needed).

Answer 3

the maximum strength of cement is achieved in 28 days that is
95% of strength is acheived 28 days .according to standards there are certain percentage of strength has to be acheived in 2,7,and 28 days.example for according to BS standards a 43 grade ordinary portland cement
the 2 day ,7 days ,28days, strength are 10 mpa,33 mpa ,43mpa.

Answer 4

7 days.