Reinforced masonry using internally-insulated CMU 2

[Enginerdad]

I was hoping someone could help me with a detailing question. I'm designing a reinforced masonry building, but our client has inquired about using internally insulated block. I can't think of any way this would work except to eliminate the insulation in the reinforced/grouted cells. But I'm probably going to end up with reinforcement @16" (every other cell), so at that point, there's more un-insulated wall area than insulated. Is this actually the typical approach, or am I missing something.

Note: I've looked at some of the proprietary high-R-value products like NRG blocks which claim to be fully reinforceable, but this project doesn't need that level of insulation (it's a truck wash building for a public works department), and the cost wouldn't be justified.

Thanks for any insight you can provide.

 

[concretemasonry]

I have over 40 years experience in the production of masonry units (domestically and internationally) and have seen hundreds of different concepts for insulation methods/materials and even the basic masonry units.

Calculations of "U" values and "R" values of walls and single units are rampant in the claims. It is a shame to see the values based on singular method of calculating when there is no single method recommended by the NCMA, but just listed as a possible method depending on the results desired by the organization making the claims.

It is similar to the claims made by other organizations that say you get an R19 wall when you are just using R19 insulation in a part of the wall when there may also be significant heat loss through the "structural" framing.

Unfortunately, the insulation claims are rampant in the business of supplying all materials for a wall.

The engineering of the wall can be a basic problem. Different aggregates can be used in the masonry units and still get the required structural strength. All it takes is simple adjustment to the mix design if you are using good aggregates.

I hope the proprietary masonry units proposed were tested in a 2 block high masonry hollow prism that is referred to in the ACI 530 design standards for engineered masonry. - The grout in the walls does little to compressive strength of the wall, since the masonry units control the f'm used in the structural design. - Was there a 2 block prism test conducted on the proprietary shaped units?

Also, a actual guarded hot-box test results on the block and inserts should be made available rather than a questionable calculation based on some thermal assumptions.

We were able to get an f'm of well over 3000 psi with lightweight aggregates. Some of the exotic specialized shapes are costly to lay because of weight and configurations and the need for additional labor for inserting inserts.

A simple 8x8x16 CMU with 2 webs at 8" on center provides perfectly alighted webs and face shells with cores that can be reinforced at 16", 24" or 32" on center with easier grouting and more reliable construction. Depending on the location they can be available in 8", 10" or 12" wall thicknesses. There are different types of bulk insulation materials that can be used periodically as the wall is built up.

I hope this describes an option for your structural design since this was considered when the ACI 530 was first written.

Dick

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

 

[hokie66]

You can't insulate and grout in the same core. So the idea of insulating within a reinforced block wall is silly.

 

[concretemasonry]

Insulation half of the cores is commonly done with reinforced walls. It is not "silly" for the contractors that use them daily in some markets. The same units are used for partially grouted walls.

It is not required that all of the cores must be grouted, but only those with reinforcement. The double "H" block as it is referred to in many counties, is the prime example. - The block has 2 webs and center core in the middle portion and 2 "half cores" on each end and it has 2 webs.

This configuration provides a wall with totally clean cores with no obstructions and the webs can also have a mortar bed that is not possible with some other units. - The only disadvantage is that the masons that are accustomed to laying one handed do not have a center web to provide a balanced unit for one handed setting.

The large cores make it easier to get good installation if bulk insulation (vermiculite, perlite etc.) or foam is desired. The webs and the cores of the block align in both stack and running bond.

The company I worked for supplied a series of molds for the stretcher units, corner units and pour through bond beams for 8" wall thicknesses. They also supplied metric versions for many international markets. Similar units are also available in 6" and 12" units.

Sometimes engineers do not look to see what could be available for specific applications. The actual availability depends on the local suppliers.

Dick

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

 

[hokie66]

But what does insulation of half the cores accomplish? I think it is indeed silly.

 

[JAE]

In my area, with required adherence to an energy code, reinforcing some cells, but not all, is not allowed anymore... so it is indeed silly, or fruitless to try.

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[JAE]

I suppose some specialty blocks like this might be an option.

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[concretemasonry]

JAE -

You found the photo of the "poster-child" of the most costly block made. It is for an 8" structural wall, but the assembly weighs about 60# with normal weight block. It would be a real chore to handle and lay, let alone be able to have 1/2 length units and corners for running bond. The foam portion is EPS foam and not XPS. I always wondered if they were actually made and used somewhere. The cores for grouting do align reasonably well for running bond, but the actual use was questionable.

That unit could be used as partially grouted with steel at 8", 12", 16" or 24"O.C. Partial grouting is real aid for reinforcing masonry for 6", 8" 10" or 12" CMUs.

I did see a variant of CMU the unit you posted somewhere along the east coast.

Dick

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

 

[XR250]

Why not do a 2-wythe wall with foam in-between? I imagine partially insulating a CMU wall provides minimal R-value.

 

[Enginerdad]

XR250,
The 2-wythe approach is certainly an option, but may not be the most economical option due to the added cost of building two walls. However, it may be the best option in regards of performance, since we have a big moisture concern on this project. Thanks for the suggestion!

 

[dik]

I couldn't believe it... I figgured that JAE was having fun with sketchup or something of that ilk...

Dik

 

[rdubs]

If insulation is important, so much so that specialty CMU and multi-wythe is being considered, why not look at insulated concrete forms? Insulation and strength are both potentially better and labor goes way down.

 

[concretemasonry]

Very often a hard wall surface is required, so the forms would have to be covered with and approved, durable surface.

Dick

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

 

[rdubs]

Very good point Dick. Too much of my time is spent in non-industrial projects.