On Fri, 17 Nov 2017 10:07:04 +0000, Chris Hogg wrote:


Sure... but when used as pozzolan it needs to be extremely finely ground. Wood ash from your fireplace does not cut it.

If not so ground it acts more as a filler, replacing sand, making black mortar.

What makes you think that ash from a domestic coal fire isn't fine
enough? Granted, coal burnt in a power station to give PFA is milled
before being blown into the furnace to get it to burn rapidly and
completely, but this diagram suggests the ash from domestic coal fires
has a similar PSD to fly ash, with a maximum at about 10µm.
http://tinyurl.com/yafw9c8h or
https://www.researchgate.net/figure/...s-coal-fly-ash

You're not thinking just of the cinders, are you?

As the OP most of the coal ash I have does appear to quite fine.
Today in what turned out to be a successful attempt to find the
entrances to a rats nest where the rodent had burrowed into a raised
flower bed where the soil is kept between two 2ft high brick walls I
poured some of the ash into one entrance while at the same time
directing a flow of air from a small garden leaf blower into the hole
and as I hoped some emerged from the other holes it had dug.
It actually looked like smoke was emerging not unlike an old style
diesel exhaust.

G.Harman