Light Weight Concrete Form Blocks

[mmmbmf]

I have a builder that wants to produce his own lightweight concrete form blocks then infill the voids similar to reinforced masonry. The end result would be a wall (grid) of 5 inch thick normal concrete with voids where the webs of the block would be. The voids would be 6 inches by 6 inches at 16 inch on center horizontally and 12 inches on center vertically (with reinforcing in the solid sections). I am considering modeling this as a grid of concrete beams and columns. I do not believe that the beams and columns will fall into the technical definition in ACI, therefore I am thinking that this type of system could be designed as a wall in ACI. The blocks (forms) have 360 psi compressive strength so I do not want to use them for support nor design this system in accordance with ACI 530. Does ACI have design specifications for this type of systems yet? And if not, I would appreciate any thoughts on my design philosophy or similar specifications available for this type of design.

 

[concretemasonry]

You are describing a very common system - ICF (Insulated Concrete Forms). They are many different types of systems with good technical support and construction details.

The two different types are the molded EPS forms with formed voids and integral cross-webs in different configurations. The newer type are a system that uses parallel EPS foam exterior faces held together by a plastic truss-type with bar placement guides at different spacings to produce a wall with the reinforced concrete wall with the forms non-bearing forms left in place for future insulation. For a 6" concrete wall the outer dimension would be about 8" including the forms.

There is extensive documentation and specifications along with a massive amount of testing to achieve product approvals for the various codes.

The builder does not produce the forms - he or his sub-contractor just buy them. Find out what he is planning to use and then go from there on researching the acceptability.

Dick

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

 

[msquared48]

Sounds more like CMU made from lightweight concrete than ICF to me.

Mike McCann
MMC Engineering

 

[mmmbmf]

The blocks are made out of a super lightweight concrete. They will be very similar to a product like APEX Blocks. I have found some guidelines as per an ICC-ES Evaluation Report for the specific APEX product and it references various design methods with assumptions and prescriptive methods also. I believe a combination and comparison of design methods would give me some validity to the design methodology. Does anyone know of any design specifications or publications available for this type of system. If there are none, I would use the ICC report as a guideline as it appears to have been approved by AHJ. The main problem is that the construction is in a remote part of the world and buying an shipping existing products will not be economical. Thanks for your input.

 

[concretemasonry]

The ICF forms have nothing to do with the wall structure. There are left in place for insulation purposes (good or bad) and the only structural element is the concrete wall with reinforcement that is poured inside the forms.

Lightweight concrete forms would be very unpractical, too heavy and costly (materials and shipping). The bracing is critical as is the rate of pouring lifts to maintain tolerances and quality concrete (usually pumped because of access).

Most of the systems do provide good control of the rebar placement and concrete cover.

Dick

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