[Stoves] brick making

[Crispin Pemberton-Pigott]

Dear Frank

I made an error in the explanation in the previous message regarding the
fact that all the remaining bricks were above the average-20% level. I have
re-written that sentence and included the whole test so you can replace that
message with this one.

Regards
Crispin

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Method for rating bricks

Crush 12 samples and obtain the load carrying capacity in p.s.i.
Ignore the weakest and strongest readings

Take the other 10 and calculate the average strength (sum, then total
divided by 10)
That is the rating of the set of bricks, provided that....the weakest sample
is not more than 20% weaker than the average.

If the lowest crushing strength of the weakest sample (of the remaining ten)
is lower than 80% of the average, you have to de-rate the bricks until the
weakest one is at -20%.

Taking your first 12 bricks as an example:
290
245
254
254
279
266
248
212*
227
315*
242

Highest = 315 and is disregarded
Lowest = 212 and is disregarded

Average of the remaining 10 = 230.5
80% of 230.5 = 184.4

All ten samples are above 184.4.   Therefore the strength rating of the
samples is 230.5 p.s.i.

If they were not all above 184.4, you have to de-rate the whole lot until
the weakest one has only 20% less strength that the rating value.

For example if one of the 12 bricks was 165 (and ignored) and one of the
remaining 10 bricks was 175, you would have to reduce the rating for all of
them to 175/0.8 = 219.

If your samples drilled from the bricks do not meet the p.s.i. rating the
architect specified when calculated in this matter, they should not be used.


The typical brick strength requirement for a load bearing wall in a house is
7 MPa and is calculated in this manner at the SABS (South African Bureau of
Standards).  Pavers for vehicular traffic 20 MPa and so on. The system is
simple and can be used by ordinary builders and brick makers.

Regards
Crispin