The Brew Cabin

Looking at your cement mixes page (http://www.pavingexpert.com/concmix1.html) i am confused by the zone sections in the Prescribed Mixes for Ordinary Structural Concrete section. A C20 mix has a ratio of 1:2:4 but what are the zone 1,2 &3 percentages?

Zones?? The only place the term 'zones' is used in relation to sands is in their suitability as a bedding material for different block paving projects. The 'zone' of a particular sand has nowt to do with its suitability as a fine aggregate for concrete.

Can you explain why you think zones are relevant to concrete? :confused:

See section below relating to C25 concrete taken from the mentioned page...

25
(1:1½:3) Cement (kg) 340 360 360 390 380 420 400 450
Total Agg. (kg) 1800 1750 1750 1700 1700 1650 1700 1600
Zone 1 (%) 35 40 40 45 45 50 50 55
Zone 2 (%) 30 35 35 40 40 45 45 50
Zone 3 (%) 30 30 30 35 35 40 40 4

For a C25 mix with medium workability and using 40mm aggregate I need 340KG cement, 1800KG total aggregate, 35% zone , 30% zone 2, 30% zone 3 to produce 1 cubic meter. What are the zones and why do they only add up to 95%?

Hope this is clearer, thanks
Chris

Aaah, now I'm with you!

The percentages shouldn't add up to 100%, as they are distinct values, not related. So, in the example you quoted, A C25 grade concrete, using a 40mm aggregate (the first column) would use 340kg of cement and 1800kg of aggregate. Of that 1800kg, if the fine aggregate were a zone 1, then it should make up 35% of the 1800kg aggregate total, but if you were using a zone 2 or zone 3 sand, then only 30% of the 1800kg aggregate total should be made up of that sand.

The percentage figure refers to the percentage of the total aggregate content represented by that particular zone of fine aggregate (sand). The definitions for each 'zone' is given on the Aggregates page, in the section dealing with sands.

This is all very technical, and is the sort of thing only ever used in batch plants ands civil projects where the strength of the concrete is hyper-critical. For DIY jobs and most residential paving, it's way, way, way too involved, and the basic 1:2:4 type proportions are near enough.