Concrete compresive strength prediction
Concrete compresive strength prediction
(OP)
Dear friends, usually we crush test cubes at 7, 14 and 28 days after casting and use attached figure to verify the compressive strength. But sometimes we missed exact date. May be we have to crush it on 10th or 29th day due to practical matters occurred at site. So I want to know if there is any formula to calculate compressive strength at any age. Please help...!!






RE: Concrete compresive strength prediction
Further, there is no point in testing to the exact desired compressive strength. Concrete design doesn't work that way.
While we use a specific design strength for our designs, the goal of the mix design is to achieve that value within a reasonable tolerance and predictability. Such predictablity comes from specific strength gain curves for each mix design; however, not all ready mix suppliers provide such curves. If the concrete is mixed on site, there is little predictability of strength gain until enough testing is done to validate the design.
If you use 35 MPa for your design, your mix design should be proportioned to achieve that design strength in 28 days, typically. There are other design strength days; however, 28 days is the norm.
If you are using conventional portland cement concrete with Type I cement (US designation) and without much in the way of admixtures, you can predict that the concrete will achieve about 70 percent of its design strength in 7 days. This is a generalization, of course, but based on generalized strength gain curves from copious amounts of data over the years for various mix designs.
If that value is not achieved in 7 days, it becomes a "flag" for us to watch the strength gain of those test specimens. Use such generalizations carefully, as they might not be accurate for your specific mix design.
RE: Concrete compresive strength prediction
You could plot your results form a series of previous tests on the same type of concrete and determine if there is a sensible relationship for the concrete mixes you are using!
RE: Concrete compresive strength prediction
RE: Concrete compresive strength prediction
RE: Concrete compresive strength prediction
If you're breaking samples on another day, the question is why? To make sure you can remove support/scaffolding/forms and start the next floor? Because of bad communication and timing with your testing lab?
RE: Concrete compresive strength prediction
The tests before 28 days are really just to flag whether crazy things are happening and to verify that it's safe to partially load if necessary.
RE: Concrete compresive strength prediction
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.