What makes good concrete?
The question what makes good concrete probably depends on who you talk with. If its the concreter they usually err on the side of saying most concrete mixes are rubbish. If its the batch plant they prefer mixes that only just reach their 28 day strength targets. That means they are not wasting cement, the most costly raw material in their mix design. If its the engineer they believe good concrete meets and exceeds flexural and compression testing specifications at 7, 28 and 56 days. Whilst if its the mixer driver he or she is going to suggest its any concrete that they don’t cop abuse for when delivering. And whilst we are there its probably not a good idea to ask the concrete pumper what makes good concrete. You might not have long enough to hear their answer…
Concreter’s, placers and finishers of concrete prefer creamier mix designs with large amounts of fines or 10mm aggregates which prove easier to move around, shovel, screed and finish. Mixes that do not tend to “go off” or set during placement. Concrete mixes with a slightly higher slump than otherwise specified, with the additional water making the fresh concrete more pliable when in its plastic state, prior to hardening. This concrete tends to be of a slightly lower strength e.g., N,S, or M20 and 25 mixes. Stronger mixes tend to be heavy and at times difficult to manoeuvre and place. Even sticky at times.
The batcher at the Ready Mix Concrete plant often holds the key, as it were, to making good concrete. By adding just the right amount of sand, aggregates and cementitious materials, together with chemicals and water, they are able to produce a consistent mix of concrete that is fit for purpose. Hot and cold weather can influence the setting time of your concrete, as can the distance travelled to site. Therefore it is important for the batcher to vary the mix to suit the prevailing conditions. A good batcher is capable of adjusting their mixes in line with customer requests and these variables.
And lets not forget the raw materials themselves. They most definitely play a role in determining what makes good concrete. Sharp, incongruous or elongated aggregates and stone can make concrete difficult to place and uneven at the surface. Whilst contaminated, dusty or dry material can prove deleterious to concrete both before and after it has been placed. Therefore ensuring raw materials are appropriately screened at the quarry and conditioned effectively at the plant, are crucial to making good concrete. To ensuring your concrete is what concreters would call a good brew. That is if they are over 40. If under 40 they might call it a “sick mix”.
Either way, happy concreting!
This article was written by and is the property of Tim Harrison……..All Rights Reserved