The Brew Cabin

I have used the paving expert C20 concrete calculator which advises 300L of water per Cubic Meter of Concrete. This is incorrect.

Having researched this online; the water quantity should be approx half the weight of the cement i.e (C20 calculator suggests) 320Kg cement per Cubic Meter, which SHOULD be 160L of water NOT 300L. Can somebody please correct the calculator or slap me round the face and tell me i'm wrong. Thanks.

P.s. I have 1/5th Cubic meter of soft concrete that I now need to break up and re-lay as evidence!

Hi Hotdog - yes you are correct. I've checked the C20 calculator and the water content for one cubic metre is showing as 300 litres. It should be nearer 160 litres as you suggest. I wrote the Prescribed Concrete Mixes section for Tony and if you look at the table of free water content versus slump class (S1- S5) at the end of the section you'll see it gives typical figures for with and without a water reducing admixture. Note 'free' water content refers to the quantity of water per cubic metre with the coarse and fine aggregate being surface dry, ie no moisture.

Very sadly Tony passed away last year and I don't have access to the calculating methodology. Perhaps one of the administrators could help.

Hi Brucieboy, thanks for the response. As you say; hopefully one of the mods changes the calcs to save someone else!

Yes, very sad news about Tony. I didn't know him, but you definitely get a sense of what he was like when you read through the site and his posts. Hopefully someone keeps this site going, it's a wonderful source of knowledge and a good tribute to him.

I'll see what I can get sorted at the back end of the web stuff - can someone confirm the exact formula that the calculator should use?

This is the current formula:

{z=form.z.value;form.sand.value=Math.round(z*630);form.cem.value=Math.round(z*320);form.agg.value=Math.round(z*1170);form.water.value=Math.round(z*300)}

I'm guessing that the z*300 ought to be z*160 ?

Hi IanMelb - yes change z*300 to z*160

Thanks both.

I think that this should be OK now (updated this a couple of weeks ago)