How to verify concrete floor strength

[bmxdad]

I have a neighbor who had a new pad poured about 8 months ago, and it cracked on him when he drove a small excavator on it ... he's a bobcat mechanic. The people that poured the concrete said the base was soft, he thinks the concrete is to low of psi concrete.

Is there a easy way to get a rough idea of a concretes psi rating? Say you wanted 5000psi, but you got 2000psi ... how could you find this out?

 

[Thumper68]

Check around most cities have a test lab that will do this.

A quick google found this place.

http://www.ctlwa.com/index-4.html

 

[larry_g]

I'm curious to what the experts say, of which I am not, but the PSI is more to do with the durability of the finished product, not the resistances to cracking. Cracking in your friends case will depend on the sub-surface prep, amount of steel, and the thickness of the pour. Also did the break occour near the edge as he was driving on or out in the middle ofthe slab where he parked?

lg
no neat sig line

 

[Lx460]

You could take a core sample and have it tested, I suppose. Isn't going to make much difference. PSI strength is compressive strength and has zero to do with any surface cracking. Pad prep, Slab thickness, water/cement ratio (how much water was added), and finishing techniques all play a part.

 

[DekeT]

I have a neighbor who had a new pad poured about 8 months ago, and it cracked on him when he drove a small excavator on it ... he's a bobcat mechanic. The people that poured the concrete said the base was soft, he thinks the concrete is to low of psi concrete.

Is there a easy way to get a rough idea of a concretes psi rating? Say you wanted 5000psi, but you got 2000psi ... how could you find this out?

Cannot at all imagine why the contractor placed the concrete on a base that was not compacted to the correct density. Lowest bids usually get these kinds of results. I don't think compressive strength is a factor here.

 

[Slowgsr]

Sounds like it needed more rebar, mesh & fiber! Should have been min 6-7" for heavy equipment.

 

[LegacyIndustrial]

Lx460 hit it. Need to take core sample to a lab.


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[duneslider]

If you had the bill from when the concrete was ordered it would say what type was ordered.

If it cracked from driving a tractor on it the cause probably has nothing to do with the concrete mix and is a result of poor ground prep, insufficient thickness, not enough steel. The cracking wasn't a result of compression.

 

[Peoria Man]

Check around most cities have a test lab that will do this.

A quick google found this place.

http://www.ctlwa.com/index-4.html

They can probably test the concrete in-place using 1) a rebound hammer (also known as a Swiss hammer), or 2) a Windsor probe, or 3) by taking cores. #3 is the most accurate, #1 the least. But like has been said already, soft or uncompacted base course is probably a factor here.

Or who knows. Do we know how thick the slab is?

 

[rsanter]

Only way I know of is core samples.

I have heard that they have a newer system where they shoot a "nail" into the concrete and then they measure how far in it went. That will then tell them the strength. However I have no experience with them, just heard about it

Bob

 

[bmxdad]

They poured over a compacted dirt floor thats had heavy equipment on it for 50 years or more. I don't recall any rebar, but I'm guessing a 5-6" thickness.

Crack looks like it starts where they drove on the concrete ... it goes in and stops after about 3-4'. It's maybe the width of a dime at the widest. There is no lip, he poured a bunch of crushed rock to have a ramp up to the pad ... actually is an inch or so higher then the pad.

Thanks for the information, I'll pass it on, and let you know what comes of it.

 

[larry_g]

They poured over a compacted dirt floor thats had heavy equipment on it for 50 years or more. I don't recall any rebar, but I'm guessing a 5-6" thickness.

Crack looks like it starts where they drove on the concrete ... it goes in and stops after about 3-4'. It's maybe the width of a dime at the widest. There is no lip, he poured a bunch of crushed rock to have a ramp up to the pad ... actually is an inch or so higher then the pad.

Thanks for the information, I'll pass it on, and let you know what comes of it.

It won't help now, but whenever I drive the crawler or excavator into the shop I make a ramp from 2x material so that it bridges the edge of the concrete and then stays on the lumber track all the way into the shop. This prevents point load on the edge of the pad and prevents the tracks from marking up the floor. Even if the machine was on rubber tracks I would build the ramp and bridge the edge to prevent the point load.

I suspect the point load on the edge of the pad created the problem.

lg
no neat sig line

 

[Thumper68]

This is why the grade beam at my door opening is 24x24x36 with a bunch of extra rebar in it vs the 12x12x18 for the rest of the shop.

I also use wooden planks to bring machinery in on, but that is to protect the floor not to spread then footprint.

The heaviest thing I have brought in was my buddy's Case 450 dozer with a bucket.