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Posted by Matt Whiting on June 30, 2005, 5:38 pm
Bob Morrison wrote:
> In a previous post Matt Whiting says...
>
>>>CF&SG is correct in that rebar and lower water content will improve
>>>structural performance. However, only the latter will have any effect
>>>on crack control.
>>
>>Yes, but rebar will help prevent problems is there is a soft spot in the
>>ground under the slab that settles a little. It can also prevent cracks
>>from opening up or shifting vertically.
>>
>>
>
>
> Matt:
>
> Quite true. However, I tell the contractors to spend their time and
> effort on subgrade preparation. It's easier to do than correctly
> placing rebar, and with the current price of steel may even be cheaper.
>
> A good unreinforced slab on properly prepared subgrade with adequate
> crack control should not have any problems.
Yes, unfortunately, a soft spot can go quite deep and be sizeable. It
may not even be noticed by most excavators. Unless you dig down 6' and
fill with gravel, it is hard to be sure that you won't have problems in
the future. This depends greatly, obviously, on location and soil type.
Here in PA, it isn't unusual to have challenging soil conditions. I
figure a few bucks worth of rebar is cheap insurance. You still want
proper preparation, however, I like suspenders with my belt for things
that are hard to fix later. And cured concrete that has cracked and
heaved an inch isn't cheap to fix.
Matt
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