AAC 1

[haynewp]

I just got introduced to autoclaved aerated concrete. What is the design standard for AAC? Is there an ACI document similar to 318 for design or is it all based on testing? If I was going to check an AAC floor panel designed by an AAC mfr, what ultimate stress block is applicable for AAC?

 

[concretemasonry]

AAC (Autoclaved Aerated Concrete) is an old product that was used frequently in Europe in the 1950's (maybe earlier), but never got any real acceptance elsewhere. It is a factory produced material and not site cast. The compressive strengths are much lower than normal concrete or concrete block. The main use is for masonry (solid blocks for 1 and 2 story residential construction). Some manufacturers do make slab panels.

The properties of the AAC vary widely from manufacturer to manufacture and depend on the make-up of the raw materials and the manufacturing process. It has a unigue property that the strength of the ACC material can vary with the orientation when it was expanded prior to final curing (it rises like bread in most processes). There was one manufacturer in the U.S. that made imterior wall panels and could conceivably make a floor panel.

Because of the wide variability in the properties between the manufacturers, you should contact the manufacturer to find out what the basis is for the claimed strength and capacity. Chances are you will find it is a German standard of some type. The next trick will be to determine the actual strength of the AAC itself.

 

[haynewp]

"you should contact the manufacturer to find out what the basis is for the claimed strength and capacity"

So it sounds like the strengths are likely test based per the manufacturer for construction under U.S. model codes.

 

[concretemasonry]

Does the floor panel manufacturer claim the panels meet an existing U.S. standard or are equivalent using a different standard?

The last time I was involved, there were no U.S. standards for factory manufactured AAC panel products. I do recall reviewing/voting on the specs for the ASTM standards for masonry units. I suspect there may not very much information for comparing the U.S. codes and specifications for AAC panels because of the limited availability in the country. The non-bearing wall panels I saw were 4" to 6" thick and used wire reinforcement.

They may have some physical tests (under some recognized testing procedure) that could be correlated to an existing U.S. standard. Correlation will be the challenge if the tests are applicably and there is a way to compare a U.S. standrad to a european standard.

You must be after the insulation benefits since the lower strength and much higher cost (energy, production, freight) cost must be justified in some way. I inspected some buildings (built about 1960-65)in Minnesota that used AAC for wals, but they were not load bearing. That plant closed in about 1966.

The major plants in the U.S. were originall built about 25 years ago under licenses held by Ytong and Hebel and were in southern Georgia and just south of Orlando. I think the names have changed through years because of ownership changes. It would be interesting to know where your floor panels are coming from.

Good luck!!

Dick

 

[hokie66]

haynewp,

A lot of this AAC is used in Australia under the brand name Hebel, blocks and panels. The big building products company CSR markets it, and architects like the idea, but not many engineers that I know agree. It is generally glued together, and is very brittle. I don't know if there is a standard for its use in this country, and even if there is, it wouldn't help you. For general interest, you may want to google Hebel or CSR.

 

[frv]

Requirements are addressed in Appendix A of ACI-530-08 "Building Code Requirements for Masonrt Structures"

 

[haynewp]

That covers floor panels?

 

[concretemasonry]

The inclusion of AAC is new to ACI 530 since the ASTM masonry unit standards have now been approved along with the specialized mortar. - It takes time to get agreement of all the associated material amd product standards.

I do not think that a floor panel normally does not use masonry units. Even in Europe and othe countries, the block floor systems are not included in the masonry codes because the construction method and lack of mortar. There are European standrds for block floor systems, but AAC would not normally meet them. They are for normal concrete masonry units, ceramic masonry units and in some cases for concrete/wood fiber masonry filler units.

If the panels you are considering are factory produced (which is required/normal for AAC) and include reinforcement in the manufactered panels (similar to precast concrete), I suspect it will be difficult to find a national standard.

Dick

 

[concretemasonry]

haynewp -

Where is the project located?

I did some Googling and found the only real information on a Hebel floor system was from Australia. The Australian company was owned by CSR (Colonial Sugar Refiners?) that previously also had owned Rinker (the major block and ready-mix producer) in Florida. If I recall correctly, they never did have an interest in the Florida AAC plant (Ytong process/marketing), but it is possible they were involved in the south Georgia plant. - I have been in both plants, but never saw a structural floor system.

I saw model homes being built in both Florida and in Atlanta.

I ask these questions because I have followed the AAC products for 40 years, mainly in both eastern and western Europe and similar ptoducts in Russia. They have always been basic building masonry materials located at or near national energy sources (subsidized power plants with fly ash and some excess steam) and geared for residential construction where they could easily be cut with a hand saw and laid using thinset mortar and covered with a veneer plaster/rendering. In Florida, there was an attempt to use non-bearing wall panels, but they did not fit the traditional construction cycle/techniques.

Any information you can provide on the products, technical information or applications would be appreciated.

Thanx in advance.

Dick

 

[haynewp]

It's Hebel south Georgia. They have a technical manual online now that has floor and wall panels they label as "preliminary". I was just curious how the manufacturers are getting their allowable load info whether it is from testing or a design code/standard for AAC. There are a couple of projects they have done listed on the website also.

http://www.xella.com/html/us/en/hebel_technical_manual.php

 

[haynewp]

Multi-story they did

http://oxblue.com/pro/open/xella/xellaaircretenorthamerica

 

[aaceng]

Hello haynewp,

I want to add that ACI 523.5R Guide for Design and Construction with Autoclaved Aerated Concrete Panels is currently in final review and publication. This publication should be available within the next few months.

AAC blocks and reinforced panels(wall and floor) can be designed as non-load bearing and load bearing building components. Manufacturers of AAC produce in compliance with ASTM C 1386 and ASTM C 1452.

The preliminary panel thickness table mentioned is used for determining the typical floor/roof panel thickness for common loading conditions. All floor/roof panel reinforcing is determined from final contract documents.

Kind regards,

Bruce.