Cynic Wrote in message:
Dave R wrote-

Most of the UK has sand and gravel quarries fairly close, so ballast (a
mixture of sand and gravel) is as cheap as anything else.

Possibly false economy, but then again I think you have more coal fired
power stations than we do.

Fly ash is very fine (not like an aggregate). I assume that you need the
lumps for strength.

I remember it being packed down beside a concrete gully under a dual
carriageway because it was very light and could be compacted to exert very
little side pressure on the concrete.

Also at one time proposed for spreading on marine oil spills to clump up
the oil.

As far as I know modern power stations grind the coal up very fine to make
it burn more efficiently so you probably don't get slag any more.

Cheers

Very few pulverized fuel (ground coal) fired stations now running in the UK due to being sacrificed on the altar of greentardery. Those that were best for concrete quality pulverized fuel ash or PFA (eggborough, Fiddlers Ferry, West Burton, Ironbridge and Longannet) required at least 3 days under baseload for the combustion to settle down and yield low carbon clean pale ash which could be used as a Pozzolan in the mix. Some of the ash particles in the flame would clump together and fuse then fall to the bottom of the furnace. This was Furnce Bottom Ash or FBA colloquially known as Clinker. Used in Breeze blocks and roads.
Adding pozzolan to concrete had many technical advantages. Thousands of tons were included in the Thames barrier and motorway bridges in the South West where alkali silicate reaction in mixes using local aggregate caused failure (concrete cancer).


PFA is an example of "a" pozzolan.....others exist...
--
Jimk


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