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RE: Low mortor prism test results

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Alden:

Strength tests of mortar are not specifically required to determine f'm if
the mortar proportions are verified as noted in other responses.  IBC 2103.7
[ACI 530.1 1.5B] indicates mortar needs to meet the proportions of IBC Table
2103.7(1) [ASTM 270 Table 1] or have the strengths in IBC Table 2103.7(2)
[ASTM 270 Table 2].  This means that mortar should either have proportions
verified or strength tested but not both.  ASTM 270 does not talk about
water in conjunction with strength and only talks about the importance of
workability.

There are two ways to determine f'm: 1) Unit strength method or 2) Prism
test method.  The prism test method tests prism assemblies.  The unit
strength method tests the units per ASTM C140, tests grout per ASTM C 1019
[or has it proportioned per ASTM C 476].  For the unit strength method, the
required unit strength is based on the type of mortar used per IBC Table
2105.2.2.1.2 [ACI 530.1 Table 2].  Per the code if the mortar proportions
are right per ASTM 270, f'm can be determined using either method. 

Respectfully,

Scott M. Haan P.E. 
Chief of Building Inspections
Municipality of Anchorage
Development Services  Department





-----Original Message-----
From: Alden Manipula [mailto:amanipula(--nospam--at)novagroupinc.net]
Sent: Wednesday, September 03, 2003 6:22 AM
To: SEAINT Listserve
Subject: Low mortor prism test results


I have test results for mortor in an 8" CMU wall as 800 psi for type S
mortor.

I was told by a local masonry representative that he wasn't concerned
because the mix they used was pre-approved/pre-packaged as type s mortor and
that they are allowed to add as much water as needed to make it workable.

This doesn't seem right.  Wouldn't adding water incrase the w/c ratio and
decrease compressive strength?

Also, ACI 530-02 Section 1.14.7.1 says "Compressive strength of masonry
shall be considered satisfactory if the compressive strength of each masonry
wythe and grouted collar joint equals or exceeds the value of f'm"

So shouldn't there be a concern if the mortor test results are so low if the
specified f'm=1500 psi?  ACI318 is clear on acceptance criteria, but 530 is
not.

Any advice appreciated.

TIA

Alden






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