Concrete and styrofoam object

Just had this idea and would like to hear from someone with experience with concrete. Can I make an object - a concrete shape ( box) which which has inside full of styrofoam? I am thinking about the posibility to make staircase from concrete with styrofoam inside - the role of styrofoam is to make the the box lightweight.

sort by: active | newest | oldest
that would be cool
lemonie7 years ago
You can do this, it's a technique used for floating platforms. However you do need enough thickness of concrete for structural strength. It's still going to be heavy if it doesn't fall apart. Wood is better for light structures, concrete stair cases are best made solid. If you have a go at it, make sure to buy good structural concrete (preferably pre-mixed) and use steel reinforcing. L
Kiteman7 years ago
How about using styrofoam (is that expanded polystyrene?) pellets as the agregate in a concrete mix? You would retain bulk, but reduce mass.
sasham (author)  Kiteman7 years ago
I think that would make it to weak structurally. The general idea was to make the stairs of less wight yet strong enough.
As Kiteman said it would reduce the mass and retain the bulk. But you would also be losing the strength of normal concrete, as pointed out buy the links Kiteman posted below will show. Since styrofoam is "fluffed" it is comprised of a lot of air, not solid mass, like gravel. This is referred to in one of those links that there was too much air in the bricks made with it. This is the reason it becomes lighter and weaker in the same amount of space. Just think about centerblock brick construction. They are made with holes in the middle to reduce weight. They are strong when stacked with the holes facing vertical. But stacked horizontal they don't have the same amount of strength.
Kiteman sasham7 years ago
Certainly weaker than normal concrete, but the matrix of cement around the beads would (I think) retain a significant amount of strength.

Oh - somebody tried it!

So did this guy

Arkansas considered it for bridges

So, the idea has potential at least.
I think what you should be asking yourself is can you make a mold from the styrofoam to pour the concrete into to make the steps, and how could you engineer it to be strong enough to be safe? At my parents house they have steps of concrete to the front door, and I think the landing is about 3 inches thick. The landing is hollow after you get to the top. I think this is along the lines of what your thinking.
sasham (author)  RedneckEngineer7 years ago
What do you mean by "The landing is hollow after you get to the top." ? Thanks.