Mortar and Grout on CMU wall

[kosrae]

Hi to everyone,

Our specs calls for 2500psi for mortar and 2000psi for grout. Could anybody help me any reference manual on the procedure for proportioning the said stuff.

I would appreciate responses.

Thanks

 

[Lion06]

They may be in different places in a different version, but in the '08 MSJC the grout proportion spec is in table SC-7, which is on page SC-17 in the '08 ACI 530 (MSJC).
The mortar proportions are in table SC-1 on page SC-11.

 

[Ron]

kosrae....don't mix up your specification by given both proportions and compressive strength...do one or the other, but not both.

Tell the contractor what you want (i.e., 2500 psi) and require that he submit a mix design that has been proven to achieve that strength. Do the same with the grout.

 

[kosrae]

Thanks guys,

StructuralEIT, where can i get the one your referencing. I do have ACI 530-02/ASCE 5-02/TMS 402-02 as references.

Ron, i am on the contractor and our inspector requires me to do the mix design for them but i dont have any references.

 

[Lion06]

Look in the spec commentary. That is where it is located in ACI 530-08, so I would imagine it is in the same part of the manual for '02.

 

[concretemasonry]

kosrae -

Ron is right about the method os specifying. Use either the proportion or property specifications, but not both.

The mortar spec (ASTM C270) appendix reommends using the lowest strength possible to carry the loads. Higher strength are non-productive and can be detrimentsl.

If you are just using grout to fill the cores for nominal reinforcing (at doors, windows, minimum steel, etc.) the important thing about grout is to have the proper aggregate and high enough slump (8"-11") to permit proper filling/contact and transfer any loads to to reinforcement.

Ideally, the grout should be approximately the same strength as the net compressive strength of the masonry units and never more than 25% above that. Grout is not used to increase the compressive strength of masonry and higher strength units should be specified if you are talking about higher loads. You want the outer fibers of the masonry to be capable of carrying the load and not fooling yourself by using high strength grout in the cores.

Mortar actally has a relatively small effect in the strength on a masonry prism (f'm). I have seen 4500 psi hollow prisms built using mortar the a compressive strength of aboutt 2000 psi (diffferent testing methods and failure mechanisms).

Refer the the commentary for the code and specifications in ACI 530.

Dick

 

[hokie66]

Guys, be kind to kosrae here. I think this is the same job he asked about before, and it is on Kosrae Island in the middle of the Pacific. He is trying to do a good job, but doesn't have the resources necessary, and his design engineer has been sacked for whatever reason.

Kosrae, what materials do you have available?

 

[frv]

I don't know if this is of any value to you, but a few months ago I attended a seminar on a somewhat unrelated topic.

One of the materials we were looking at was CMU, and the presenter (a very well known and respected researcher in this field) strongly suggested never using strength specification, only proportions.

The reason being that mortar tends to give unrealistically low strength results when tested independently from the prism. The mechanism for this is that the CMU itself tends to absorb a large amount of water, thus reducing the c/m ratio.

As Ron mentioned. You only specify one method; not both. Think about it. If you specify the compressive strength and the proportions, what happens if the tests come back under specified value? Who is liable?

 

[kosrae]

Hokie is right. Hokie, i can only used Portland Cement Type 1,we are lucky to have this on the island.

 

[hokie66]

You are going to need some lime or mortar admixture (cellulose based thickener) to make the mortar workable. With the admixture, about 1 part cement to 5 parts sand by volume should work. With lime, 1 cement, 1 lime, 6 sand.

For the grout, in an island environment, I would use not less than 300 kg/m^3 cement for protection of the reinforcement. Aggregates and water to suit workability and fill all cores. Not bigger than 10 mm for the coarse aggregate.

 

[kosrae]

Thanks Hokie for the info. How about if i will not use lime? Is there any effect?

StructuralEIT, thanks and i have found the Table that deals with the proportioning and could you please correct me if i didn't got things mix up. Under Mortar cement Type S 1/2 part cement for 2 1/4 aggregate but not less than 3x the sum of volumes for cementitious with no admixtures.

Thanks guys

 

[hokie66]

Kosrae,

The lime is to provide plasticity to the mortar. Portland cement provides strength, but a mortar with only Portland won't stick well to the block. Lime also improves the bond characteristics.

If you can't get lime, you may have to bring in some mortar admixture, which will tend to improve the workability similarly to the lime.

Who is going to lay the blocks? The masons should know how to mix mortar. Rely on their advice.

For the grout, I think that is too much cement. A mix to achieve 2000 psi should be about 1 part portland cement, 3 parts dry sand, and 1 to 2 parts pea gravel. But my recommendation of not less than 300 kg/m^3 Portland for protection of the reinforcement still stands.

 

[kosrae]

Hokie,

I really appreciate the way you impart.

With my few years here in the island, i haven't heard that they are using admixtures on there mortar. I believe this will be the first time to introduce this stuff on the island's construction so i don't think our mason are well aware of this.

I believe this is one of the first structure to stand here using a loadbearing blocks which amazed the islander why no columns supporting the upper floor.

 

[hokie66]

Kosrae,

One other thing to watch out for. If they don't use lime or any type of admixture, they may try to use "fat" sand, or sand with a lot of clay, which helps with workability but is deleterious to the mortar long term.

It would be interesting to know back from you what the masons say.