f'm values in ACI 530-05/ASCE 5-05/TMS 402-05

[Berniedog]

I need some verification. f'm is the specified compressive strength of masonry (pg. C-9). Does the right column of Table 2 (pg. S-8) give the value of f'm? Also, according to 1.4 B.2 (pg. SC-4) if the grout strength equals or exceeds f'm then we are OK. Is this right?

How do I know how to proportion grout to obtain a specified grout strength?

Thanks for the help. I think the masonry code could be clearer on these issues.

 

[henri2]

We are dealing here with compliance with f'm by the unit strength method. To the best of my knowledge, the net area compressive strength values in ACI 530.1 Table 2 (page S-8) are the same as the f'm values in UBC Table 21-D. And yes the f'g must be equal to or exceed f'm and not be less than 2,000 psi.

If you don't mind me asking; why do you have to know how to proportion the grout? Will you be reviewing a grout mix or designing/proportioning one? Fine and Coarse grout proportions (by loose volume) are in Tables in IBC Chapter 21, Sec 2102 or 2103 and ASTM C476. They should be good for f'g of 2,000 psi.

 

[Berniedog]

Thanks henri2:

The reason I want to proportion the 2200 psi grout is that I read somewhere that it is better to do that. But as I am thinking about it, it would mean that I have to be a specialist in this field and I am a generalist.

 

[concretemasonry]

Many experienced engineers place a maximum limit on the strength of the grout to preserve the joint action of the masonry units and the grout working together. The masonry units essentially carry the vertical loads and the grout distributes the loads from the units to reinforcement. Testing grouted prisms is misleading and a waste of time and money.

Specific proportioning of percentages of materials in grout may give comfort, but the key is to have 8"-11" slump (forget about relating to concrete since concrete is placed for a different purpose in non-absorbent forms) so it is placed so it can perform as intended.

Keep in mind the various materials (brick, CMUs, mortar and grout) are tested separately using different shapes and/or proportions and formations and do not relate to each other directly. The over-riding item the the f'm of the masonry units when tested in hollow prisms. Mortar has a minor effect on the wall strength but has other properties that are needed.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[Berniedog]

Thank you all