[Stoves] brick making

[Crispin Pemberton-Pigott]

Dear Frank

I am impressed by your approach and the simple method.  Very good. Remember
to check and record the density and plot the crushing strength against the
density.  If you use different mixes, keep different charts for each. You
will learn a lot.

I have something small to contribute, which is how to rate the bricks.

Ratings of bricks are important to know if they will, when assembled, give
you a wall that stands to an acceptable load.

This is one approach, or protocol, that is something applied in
certifying/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 are within the range of 184.4 to 230.5

Therefore the strength rating of the samples is 230.5 p.s.i.

If your samples drilled from the bricks do not meet the p.s.i. rating the
architect specified when calculated in this matter, it will not be allowed
to 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