Concrete Strength Using Water Reducers
Posted by Pete on January 19, 2007
I do not have the concrete mix design to share with you but my question has to do with typical strength gain that can be expected at 7, 14, 28 and 56 day tests.
There is a project we are looking at for a contractor where strength gains range from of 18% to 25% from 3 to 28 days. In some cases the strength gain is from 28 days to 56 days is relatively flat, 6% gain.
Is this normal, especially during winter construction.
The rate of strength development of concrete depends on factors such as the water to cement ratio, cement type, use of any mineral admixture and the curing temperature.
From a published research article, the rate of development of the strength of concrete made with ordinary Portland cement and having a w/c of 0.40 is 18%, 54%, 78% for 1, 3 and 7 days respectively of the 28 days strength, considering the 28 days strength as 100% strength.
Whereas for an ordinary Portland cement concrete having a w/c of 0.60, the 1, 3 and 7 days strength is 12%, 42% and 58% of the 28 days strength, the 28 days strength again being considered as 100% strength.
This means that as the water to cement ratio of the concrete reduces, the rate of development of strength of the concrete with respect to the 28 days strength increases.
For concretes made with plain cement the strength gain after 28 days is not very high. For concretes containing fly ashes or slags used as cement replacement materials, the strength continuous to grow beyond 28, 56 and 90 days due to the pozzolanic reaction.
The rate of development of strength during cold season is slow.
