In fact, steel that's exposed to the soil will corrode and weaken the slab.
Reinforcing steel that's on the ground is not reinforcing at all.
When the steel is raised by way of 'hooking,' the traffic and activity of the installation process will likely cause the steel to fall back to the ground, leaving the slab structurally compromised.
The answer is to raise the steel using small concrete blocks or 'chairs. On this job, the crew unfortunately failed to do so.
The improper placement of reinforcement within a slab continues unabated — despite codes, standards and training to the contrary. One of the most egregious examples of these substandard practices is known as "hooking."
In this context, the term does not refer to the world's oldest profession but, in my opinion, should be equally illegal. It's the absurd jobsite practice of leaving the rebar on the soil and then lifting it as the concrete is placed, using some kind of makeshift hook. As a result, the rebar is placed in a random position within the slab. Ongoing foot traffic, concrete screeding and gravity, as well as lifting the steel in random locations, settling and lifting to varying heights, all result in steel at incorrect elevations. Often times, it settles directly back on the soil.
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This can leave the concrete completely unreinforced with voids where water can accumulate and destroy the slab. In other words, in this poor attempt to lift the steel into place, the installer winds up making the concrete weaker. It would be better to have no steel at all.
EASY TO AVOID
Why do contractors do this, especially when inexpensive concrete blocks are available to properly space the rebar? Is it laziness, force of habit or just a lack of knowledge?
I have heard that one of the reasons for leaving the steel on the ground before the concrete is poured is that the installers don't have to lift their feet to step over the elevated steel. If that's the case, hooking is laziness taken to an extreme.
Whatever the reason, this practice should be forever banned.
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And the fix is so simple: use small concrete blocks — some people call them "dobies" — to securely raise the steel into proper position. The funny thing is simply using blocks, or chairs, to raise the steel into place requires very little effort. In this case, doing it wrong actually requires more work.
Standards for proper steel encasement in a slab are clearly defined in ACI 318.
