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Is concrete strength primarily a function of water content? E.g., let's say:

concrete mixture A contains (per cubic metre)

  • 400kg cement
  • 180kg water
  • 1900kg aggregate

for a slump of 10cm

And let's say that for 10cm slump we can also make concrete mixture B, which is not as strong

  • 250kg cement
  • 300kg water
  • 2000kg aggregate

If we aim to make concrete mixture A, but end up adding 300kg water instead of 180kg, does this result in the same strength as concrete mixture B, which has much less cement, but was properly mixed?

I.e. is concrete strength primarily a function of the actual quantity of water added, or does the mixture somehow shed excess water without losing strength, or only losing partial strength?

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No. Overwatering results in a much weaker mix. The water eventually leaves the concrete, resulting in a very porous structure. You also get more cure shrinkage, and the aggregate mix can settle.

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  • weaker than a mix with the same amount of water but less cement? – thelawnet Oct 26 '16 at 19:42
  • Maybe I misunderstood the question. It would help if you'd normalize the proportions for easier comparison. It all comes down to ratios, not absolute quantities. – isherwood Oct 26 '16 at 20:06
  • basically if the amount of water is constant, but the cement quantity changes – thelawnet Oct 26 '16 at 20:32
  • The ingredients are measured by volume not weight. Increasing the water content will weaken the finished product. A standard mix is 1 part cement 2 parts sand and 3 parts gravel, water is approximately 1/2 part depending on how wet the sand and gravel are. Additional cement will make a stronger mix additional water will make a weaker mix. + – Ed Beal Oct 30 '16 at 18:32

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