Hi AllOne of the reasons for a 20kg bag is that the additive is...

Hi All

One of the reasons for a 20kg bag is that the additive is more often than not added manually at the concrete depot. It is also very convenient for measuring the quantity which will be added i.e. 1 bag (20kg) per cubic metre of concrete. This is the current practice when introducing additives such as xypex (waterproofing) or a colour. Keeps the process very simple and measuring simple. I guess if the additive became the norm/ standard then the plants would become automated.
Currently the concrete plants add a surcharge of of somewhere between $10 and $20 for manually adding each bag. Note: that rate may have changed in recent years....its been a while since I have ordered concrete with an additive).
I should add that if the bags were 25kg that would probably be an issue with Workplace Health and Safety representatives/advocates.

kippax