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For decades, builders and engineers have used a uniform set of foundation practices in both residential and commercial.  The most common ones for a long time have been the original post-tensioned slab where a thin slab is combined with in-ground beams called ribs to provide stiffness; as well as the slightly different uniform thickness post-tensioned slabs where thicker slabs were used with or without in-ground beams.

However, the problem with these slabs is that the entire slab area touches the soil when installed. And since the soil experiences differential swelling or shrinking under changing conditions, upwards pressure is exerted onto the complete area of the slab, which overpowers its stiffness, thus leading to deflection up to unacceptable limits.

Wafflemat Slabs were tested for this deflection over a twenty-year period to gauge its performance under extreme conditions.

What made these slabs different is that this is a completely new third-generation post-tensioned slab where hollow forms, or “Waffleboxes,” are placed in a grid arrangement directly on grade, which creates voids in a waffle-like pattern, along with ribs installed in both directions with post-tensioning tendons located in the ribs. Concrete is then placed over the forms, creating the “Wafflemat” foundation.

The best feature of this slab structure is that it only touches the ground at the bottom of the ribs; So that if and when the soil swells, the upward pressure is applied to a much lesser area than before, which increases the bearing stress from the structure and decreases deflection. Additionally, the voids allow the soil to expand up to several vertical inches which also contributes to the decrease in movement.

Ultimately, observation over the years proved that the foundation movement in Wafflemat Slabs was well within acceptable limits and it provided all the benefits of in-ground ribs or uniform thickness slabs, but with better resistance to deflection.

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