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RE: Masonry Cement

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While we are off on this tangent of masonry strength.  I have had a lot of
heart burn about specifying acceptance criteria for masonry prism strengths.
I have written my own.  The issue becomes more glaring when you compare the
masonry strength testing versus concrete.  Concrete (ACI 318) is fairly well
written.  It is poorly understood, but it is well written.

To determine the mix design (per ACI 318 Sec.5.3) the average strength of
the confirmation cylinders must exceed the specified strength by the
standard deviation determined from the quality and consistency of the
production plant, and number of tests.  The field breaks (ACI Sec. 5.6) have
clear acceptance criteria and a method of investigation low-strength test

In contrast the UBC and the ACI 530 deems compliance as merely equaling or
exceeding the f prime m.  With such a limited amount of testing required
(understandable due to expense) it is odd that there is no default standard
deviation to adjust for the unknowns such as variables in materials and
workmanship.  From probabilities, it is easily conceivable to construct a
standard deviation curve that would indicate 40% of masonry on a given
project to be understrength.

What do others do regarding acceptance criteria regarding masonry?

Harold O. Sprague

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