How can a post-tension slab be identified?

A post-tension slab can be identified primarily by noting small circle patches or a sign stamped in the concrete. These small circle patches are typically where the post-tension tendons are anchored. When the concrete is poured, these areas are usually marked to indicate the presence of the tendons, which are tensioned after the concrete has cured to improve its structural integrity and resistance to cracking.

The other options might not provide reliable identification methods. For instance, the color of the concrete can vary based on the mix and does not specifically denote the tensioning technique used. Similarly, the thickness of the slab can differ based on design requirements and does not inherently indicate whether it is post-tensioned or not. Lastly, the weight of the slab will also depend on various factors, including the density of the materials used and the overall size, making it an unreliable identification method in determining if it's a post-tension slab. Therefore, identifying post-tension slabs is most accurately achieved through visual inspection of the markings or patches on the surface.