Grout vs Mortar in reinforced masonry 3

[enginerding]

I am looking for an article that a contractor (he is bright, but not an engineer) could read to give the reasons why it is important to make sure that grout is used to fill the cells of reinforced masonry rather than the cells being simply packed with mortar. He tells me that mortar is used for this purpose all the time and he has never seen a problem with it. He says that without evidence of problems, it will be a hard sell to make sure his subs use grout the right way. Does anyone know of something that I can show him that shows the actual in-use effects in a wall built this way?

I have plenty of small articles showing the importance of vibrating the grout to make sure it fills all voids, but nothing to show that replacing the grout with mortar has had adverse effects on strength or durability.

 

[UcfSE]

The building code will point out that grout is required and what ASTM spec it must meet. I imagine you would have similar requirements in your code if you are not in the US. If mortar does not meet the required ASTM it cannot be used, per the building code. Done. Do note though that mortar is commonly used to fill the cells of reinforced fence brick.

 

[miecz]

Go to maconline.com, click on "Grout", then on "What is grout". Here you find that grout has a slump of 8 to 10 inches, mortar, 5 to 8 inches. The difference is that grout can be poured and will fill the cells, while mortar is too stiff and will leave voids that weaken the wall.

 

[concretemasonry]

engineering -

Refer the "well meaning" contractor to the National Concrete Masonry Association TEK Note series (ncma.org).

Just pick any state and member to get access to the TEK Note series. The TEK notes (over 100) are written in a manner that is understandable by all and contain the specific code and material standards.

TEK 9-4A gives a good discussion on materials, specifications and the properties of grout.

TEK 3-2A gives a good discussion on the proper construction of fully and partially grouted masonry.

It sound like the contractor has just seen a lot of small projects and not enough of the correct materials, which have been used for many years.

Dick

 

[samdamon]

There is no reference in any building code I am aware of that allows mortar to be used as a substitute for grout in filling cmu cells. Contractors do it all the time but that doesn't mean its correct. I would expect that mortar used to fill cells will shrink more and bond less well to both bars and block than properly placed coarse or fine grout.

 

[DarthSoilsGuy]

If you specified the specified strength of your structural masonry construction (f'm) and it's 1500 psi or higher....

The masonry won't qualify as STRUCTURAL MASONRY unless F'M is met and usually by Unit Stength design. The mortar, probably "S" won't by definition cover this. So... now the contractor is taking the project in the direction where Unit Strengths must be met by field testing in order for code to be met. Now the contractor has to feel comfortable enough that his mortar will meet grout spec by field testing(probably 2000 psi for f'm=1500psi which is the most typical).

The reality of the situation is that you might shoot yourself in the foot trying to get the masons to change their practice. I've seen a bunch of times where grout-as-you-go masons just can't deal with pumped grout and you would have a better product if you just let them mortar it in. Some masons will try to skip bond-beams in inconvenient locations for scaffolding or too near another bond beam when truck grout comes. That is just one example of many possibilities.

In my experience, (this may raise some eyebrows) the mason should have no issue with working in a batch of site grout every couple of courses by mixing portland cement in lieu of mortar cement or masonry cement. With a good mix (use the damn measuring box!) and occasional grout compression test specimen, you should get above 3000psi and feel comfortable justifying F'm.

 

[haynewp]

I know you shouldn't allow them to substitute concrete for grout because it doesn't bond to the units. It may be that you also get a reduced bond with mortar when compared to what is required for grout.

 

[concretemasonry]

Units meeting the ASTM C90 minimum strength and mortar meeting ASTM C470 requirements can be assumed to have a f'm of 1500 psi. From a practical standpoint, mortar has a very minor effect on prism strengths(f'm) when compared to the unit strength of the CMU, if you use the prism test method.

By all means avoid getting highter strength masonry by using high strength grout and/or mortar. It is far more economical, safer and easier to justify and test by using higher strength masonry units. This puts the higher stregth material at the out fibers of the section and eliminates the errors of using an average strength. - CMUs can also be tested before they are in place, resulting in increased reliability, which is a luxury you do not have with many other materials like concrete.

The reason for using grout and NOT mortar is because of specifications! - It is as clear as that.

Mortar is designed to be workable with a trowel, not to "fill" voids. Grout also makes the constructability of the wall more reliable because of the ability to fill all the voids and the proven lower in-place shrinkage.

 

[haynewp]

Additional

http://www.lime.org/BLG/Biggs.pdf

 

[DarthSoilsGuy]

I bet my house the blocks are on-site already.

I'm assuming the mortar mix is a 3:1 sand to cement mix (mortar cement or masonry cement). I think that's a safe assumption because that is the easiest (and i think cheapest) to do. switching the masonry/mortar cement bag to a bag of Portland makes Fine Grout per Table 2103.10 of the IBC, not concrete. ok, so it's still concrete... But it's not hi-test.

If i'm wrong,... that's my landlord's problem.

 

[MarcbSE]

haynewp:
I've never heard that concrete should not be used for grout and I've seen a lot of masonry constructed with 3,000 psi for grout.

ASTM C476 specifies that portland cement is an acceptable cementitious material. The only other requirements in C476 is the cement to aggregate ratio, and a minimum compressive strength of 2,000 psi.

If that is the case, then what exactly is the problem with using 3,000 psi concrete as grout?

 

[concretemasonry]

DarthSoilsGuy -

The block are probably there and they probably do meet the specifications since it is not enonomical to make anything as weak as the ASTM C90 specs.

The spec you referred to (IBC 2103.10) is for "Ceramic tile Mortar Composition" and not for structural grout to fill the cells of block. It applies to grout for ceramic tile floors, ceilings and walls. All must contain hdrated lime.

The applicable core filling grout standard is IBC 2103.12 for both fine and coarse grout. Both of these types of grout refer to either portland or blended cements and to the option addition of a small percentage of lime. The slump requiremetn for proper plcement is much different.

If the mortar meeting the proportions of ASTM C470 can meet all the gradation and physical requirements of ASTM C476 for grout, it could be used if verified in advance by testing the raw materials used and is reformulated by adding water and also meeting the compressive strength requirements of the grout with require different sampling, procedures and performance. - In short, the mortar is not adequate and that is why there are two different standards.

If you look at the appendix if ASTM C270 for mortar, you find that the most important factor in the selection of mortar is workability, since the strength is really secondary. This section recommends using the weakest mortar possible to carry the load since other factor can be more important. Grout on the other hand, is intended to have the ability to fully fill all voids and bond the block/steel together. - Grout and moratr are two different material designed to perform two different purposes. The only thing in common is cement, aggregate and water, after that there are many different materials with the same raw material but with different compositions and different end properties.

It is just the best and easiest to follow the material standards and placement methods and schedules.

 

[samdamon]

I would never specify concrete as a substitution for grout. Even in placements just a few courses high the concrete can snot up in the cells as the water gets sucked out of it by the block.

 

[concretemasonry]

samdamon -

I have never seen the word "snot" in a construction specification/description or a placement procedure. Usually, grout is vibrated or "puddled"(in the case of low lifts). - Certainly, the people that routinely build load bearing high-rise structures do not have that word in their engineering vocanulary.

It is intended that the excess placement water necessary in the grout is absorbed by the masonry units. Even the ASTM grout testing procedures recognize this and use a grout "prism" sampling/curing procedure in the ASTM C1019 method to simiulate this.

Grout is not just wet concrete.

 

[enginerding]

"Snot" is used more verbally than in a specification -

Examples
"You would have to weld the snot out of it."
"Tighten the bolt with the DTI until it snots"
and
"...concrete can snot up in the cells..."

 

[DarthSoilsGuy]

i've got an old IBC (2003) in my hands. Ceramic Tile Mortar Compositions is Table 2103.9 in mine. My IBC doesn't even have a 2103.12.

that's it for me quoting code on the web. i'll catch up with yall in 2009. We're still saving up for Windows Vista or was it Civil3D, i'm not sure anymore.

"If it ain't broke, sell an update."
-dsg

 

[haynewp]

MarcSE

Besides the fact that it doesn't meet the masonry code definition of grout as is being re-iterated in this thread over and over, I understand that it doesn't bond to the units as well as grout.

I can only guess as for the reason why it doesn't bond-- It may have to do with the flowability being a lot less than grout so it does not get sucked into the pores of the units like grout does. Or, the amount of moisture that is available is sucked out of the concrete directly adjacent to the units and this concrete does not fully hydrate, thus causing a weak interface.

I don't really know, I just remember my concrete/masonry professor telling me to never allow this substitution particularly because it does not bond to the units. And contractors have come to me and wanted to substitute concrete for grout before also, and I got the impression they did this often-but I did not allow it.

 

[MarcbSE]

haynewp:

Thanks for the comments. But what I'm having a hard time with is that concrete DOES meet the masonry code definition of grout unless I'm missing something (which is entirely possible).

ACI 530-02 Specification section 2.2 states "...provide grout that conforms to the requirements of ASTM C476."

ASTM C476-02 section 3.1.1.1 gives portland cement as an acceptable cementitious material and Table 1 (Grout Proportions by Volume) lists the following proportions for fine grout (coarse grout similar):
Portland Cement or Blended Cement = 1 part
Hydrated Lime or Lime Putty = 0 to 1/10 part
Fine Aggregate = 2 1/4 to 3 parts (+/-)

Now, assuming the aggregates meet ASTM A404 and the slump is the same, I don't see where the problem is from a code perspective. Any additional thoughts or input would be appreciated.

 

[concretemasonry]

DarthSoilsGuy -

My appologies, I was referring to my 2006 IBC code. The older table was about 2 pages earlier.


Heynewp -

You are right about the moisture transfer. Because of the aggregate gradation and fines in mortar, the moisture does not get absorbed into into the masonry usit and is tied up in the hydration process.

With grout, and the amount of aggregates that have a lower area per volume, the water is available for absorption, which tends to compact/late consolidate the grout. That is the reason for the requirement for re-consolidation and "topping off" of the grout well after the actual placement. The saturated masonry units provide an ideal curing condition for the grout.

dick

 

[samdamon]

concretemasonry- Please re-read my post. I was not writing about grout, but about concrete being improperly substituted for grout. No, no one uses the word snot in a spec. Lighten up, sheesh.