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Concrete pad and sidewalk

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Posted by: from Surrey
9/10/2012 at 3:08:22 PM

A concrete pad that is approx 35x20. Would it need expansion joints?

Rebar was not used nor was it tamped down and they didnt use sand, its already cracking and it was just poured at the beginning of summer.

concrete pad and sidewalk
REPLIES (8)
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Date/Time9/10/2012 at 4:08:05 PM

The following document from the NRMCA should be able to clarify your question: http://www.nrmca.org/aboutconcrete/cips/06p.pdf

Control joints should no more than 2-3 times the slab thickness (in inches). A 4" slab should have joints 8-12 feet apart.

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Date/Time9/10/2012 at 5:08:16 PM

Is that a door in the back ground as well?

There are rules regulating sidewalk and door intersections as well. If not followed water will pour into your house in some circumstances. (like snow damning)

That is a sizable pad with no expansion joints, if there is thermal differences between the surface of the pad it is likely to crack. (like one side is in sunlight and one in shade). No mesh, no compaction, compressible sub straight, all are also ingredients to a cracked slab.

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Date/Time9/10/2012 at 5:10:50 PM

Kathie,

In response to the concrete pad, you will get some more professional concrete poeple responding but I will provide my opinion based on previous experience.

Depending on the thickness, the strength, the temperature at the time of pouring the concrete, the amount of water used by the truck driver to keep the concrete loose, and how the concrete was "worked", all have a bearing on the outcome.

The gound should be as level as possible, a gravel base, and sand. All to provide for a solid foundation for the concrete to rest on and to allow for some drainage as may be needed. We always use re-bar and wire mesh. Depending what will be parked on the pad, thickness may vary but should be a minimum of four inches. Cracking can be caused by several factors including some of what was previously mentioned, ie. temperature, poor material, etc., but also if the ground underneath moved.

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Date/Time9/10/2012 at 6:35:30 PM

The pad definitely needed expansion joints and should have been installed with at least wire mesh, rebar would have been better. The area should have been excavated to accommodate the thickness of the slab, minimum of 4" preferably 6" and minimum of 10" of compacted Granular A. If the ground conditions were poor more gravel may have been needed. The type of concrete used and weather conditions are obviously important factors for success as well.

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Date/Time9/10/2012 at 10:48:47 PM

A concrete pad of that size would not need expansion joints if some one competent had built it.

When pouring a concrete patio or walkway for that matter in our climate, there are a number of steps to be taken.

To many contractors act as if we live in Florida, and winter does not exist. A construction site that is not settled properly will also cause cracking without winters harsh effects.

First the site should have been excavated ten inches throughout. Every eight feet a hole should have been auged 4' below the new excavation level. About two feet of sono tube should be installed in each hole. Then install 4" of 3/4 cut clear stone in the entire patio area. Then 1/2" rebar is run up from each hole (three peices eight feet long) You then bend the rebar down into the new patio area. Connect ten to fifteen foot lengths of rebar to the peices coming out from the auged holes. These lengths of rebar should run paralell from one side of you patio to the other and the entire length. By now a six inch high form will have been constructed for the whole exterior of the patio to be constructed.

My company lays six inch thick boards steaked twenty feet long about every seven feet from the outside perimiter of the form, These boards allow us to screet the concrete and level the pad. We now install 3500 P.S.I earated concrete, six inches thick to the whole patio area Now we remove the screeter boards and smooth out the entire surface. You now have a patio that will not crack nor break even after ten to fifteen years of harsh winters. Sadly good quality costs money, But that is the only way I build, and ny clients have come back to me for project after project for years, because I live by the rule "do it right or don't do it at all".

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Date/Time9/11/2012 at 5:57:43 PM

Since the pad is there already the only thing you can to is to cut crack control lines into it. you can't put in expansion joints in now but if the pad was placed up to existing concrete a bond break should have been used.

Think about how often a sidewalk is cut to control where the cracking occurs.

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Erroll from MVP Construction in Surrey
Date/Time9/12/2012 at 6:57:54 PM

Was this the same contractor that did your deck? If so this guy is a fraud.

The post above mine was correct in his statement" only thing you can do now is cut in some controle joints". The bottom line is concrete allways cracks, the controle joints give the conc. a place to crack. The rebar will hold the concrete together when it does crack and prevent it fom seperating to the point where the crack goes right through. Knowing how hot it was in vancouver a month ago your contractor should have put a sprinkler on the slab once it set up to slow down the curing of the concrete. This will also help against cracking. But this guy made a lot of mistakes and skipped a lot of steps. He dosn't deserve to stay in buisness.

Once again Good Luck

Erroll

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Kathie in Surrey
Date/Time9/12/2012 at 9:39:44 PM

Thanks again for the information errol, no it was a concrete company i hired to do the slab and he didnt put rebar in he said he was using a concrete with some kind of fibre in it,,,,

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