Hi, just joined this great forum. Anyone know about light weight concrete? I am trying to build light weight concrete slabs that are 1-2-inches in thickness with good strength. I realize they cannot be as strong as regular concrete. Any help is much appreciated.

Dimitri, there is a better way, Give me a call, I will explain, and I am not talking SF.

Are you back in CA.

Mark Ross

dimitri, how light do you need 1.5"to be ? Reg concrete is 18.5 # per sq ft at 1.5" which can easily be adjusted with any floor system at minimal cost. Give us more in sight.

Dave

Dave and Mark, thanks for replying.

I make concrete castings (copies of original flagstone panels which I make) using polyurethane rubber molds.

First I cut random pieces of flagstone which I embed in concrete inside of a 2' X 4' X 1.5" wooden box. Into this box I pour about 1 inch of regular concrete mix i(Sackrete Brand) which I buy from Home Depot. I embed small chips of flagstone in the concrete and place the shaped flagstone pieces so that they fstick out about 1/4" above the level of the concrete. This gives the appearance of grout joints between the fitted flagstone pieces. I wait 7 days for it to cure. Then I remove the concrete panel which has a beautiful flagstone facing and I lay it inside of a box that is 1/2 inch bigger all around it. I pour the polyurethane rubber over it and 15 hours later I have a "negative" rubber mold. Now I pour concrete into this rubber mold to make a copy of the original. Then, 7 days later when it cures I stain the 'flagstone' areas avoiding the grout joints. The problem is that this copy weighs about $140 lbs. It is way too heavy for handling and very expensive to ship anywhere.

It would be great if this 2" X 4" X 1.5" concrete panel weighed 50 lbs or thereabouts. I understand that when concrete is made lighter using different aggregates, there is a sacrifice in its strength. Is it possible to make these panels weigh 50 lbs (or less!) and have a strength of, say, 1000 psi instead of the typical 3,000 psi.

Thank you for your help.

Dimitri

Your pieces have ±1 cubic foot of concrete.  Normal weight concrete is nominally 150 lbs/cf.  Lightweight concrete will weigh ±110-115 lbs/cf depending on aggregate.  It is typically used in high rise buildings to reduce dead load.  I don't think this is the solution to your problem.  The only way you could do this on a small scale is to buy your own cement and aggregates and mix your own. 

The loss of strength due to lightweight aggregates for concrete in  the 3000-4000 PSI range is minimal and is easily corrected in the mix design process.  Depending on the aggregate (open or closed cell), pumping a lightweight mix can be problematic.

xexpat

Dimitri : You will have to experiment with lightweight aggregates.
Expanded shale is the common material for Ready Mix concrete, but the quantities you need are way too small for RM.

Perlite is a material that might work for you.
It is available at Landscape Supply houses.