Concrete Durability - Field Checking

[BigH]

As many of you can see, we have many frustrations on our job. The latest is the contractor washing "grout" onto already placed floor slabs . . . if this hardens before washing off . . . weak. What tool can we use for measuring durability. My concrete guy - 45 years in the business can't remember what it is called . . . . senior moment. Thanks - and would it be suitable?

 

[Ron]

BigH..I'm not sure I fully understand your dilemma. Is the concrete onto which the grout is "washed" still in a plastic state? If so, the entire procedure would be an absolute no-no. If the concrete slab has hardened, then washing grout onto the surface is a nuisance and clean-up issue...if it hardens on the surface, then it becomes an even bigger cleaning issue, including potential mechanical scabbling.

As for durability, the only field measure I know is to measure the permeability of the concrete in the field. You can do this with a vacuum box to measure air flow or you could do a quick and dirty Rilem tube test.

 

[BigH]

In your first para - it is the fact that the surface has already hardened and the contractor is taking no steps to control his green-cutting runoff, or slick-line grout, or bleed water, or . . . . FRUSTRATING AS HELL - We are worried that it will be a big clean-up issue; suggestion - buy stock in Sika

 

[Ron]

BigH..got it. Yep, big cleanup issue. Abrasion of the grout will affect the surface of the slab.

Yes..Sika stock is a good bet!!

 

[BigH]

Wished I had bought some in Sika Indonesia before this project started - I'd likely retire. ESOTFMMR - Every strip of the formwork means MORE REPAIRS! It is un-f^&%in'-believable!

 

[oldestguy]

It may sound dumb, but I have found an ordinary (carpenter or geologist's) hammer tells a lot about concrete surface hardness, strength, voids, etc. A light bouncing across the surface.

 

[BigH]

My friend - nothing you say sounds "dumb"!! We'll give it a try - Some day maybe I'll post some of the crap we see. it is very difficult when one must use an unskilled work force in a complex project.

 

[Ron]

BigH...you should write a book!!

 

[BigH]

Actually Ron - I think it would be a gas . . . . nothing but stories in how to look at a problem; then handle it. Oldest Guy should lead - I bow to his life experience!

 

[Ron]

OK OG...the gauntlet has been thrown...start writing so BigH can edit and add!

 

[oldestguy]

Well guys, I have often wondered why some of the stuff I have learned, some thru experience the hard way, is not available in geotech texts. However, parallel experiences of some others have come up with the same methods, etc, and then published in papers. However, that is not to say some of these things are not also part of the knapsack of the "older" guys like Ron or Slide rule era and not published.

For instance, comparing "conventional" test boring work with test pits will sometimes show the error in using the boring results "blindly". This falls into one's general attitude about saving the client money versus how detailed you have to be, as well as experience in that area on other sites.

There is a thread running now about using SPT to test the "degree of compaction" and the questioner brought up the problem with 5 ft. sampling intervals. For many a year, before too much competition changed things, a firm I was with made it routine to continuous sample for the first 15 feet. Split spoons used were 30 inches long and driven that far each time. Nothing fancy about that, but quality of the result governed over doing it at least cost. Now how do you explain the desirableness of that thinking when competition may mean a job or no job? Not a real perfect way of sampling, but it did expose situations not otherwise likely to be found.

Another subject is how to interpret and time a surcharge job for organic soils. Attempting to relate lab tests to the field prediction of what to expect only worked two times as I recall. It took many a job to work out a quite reliable method for doing that with field data only. After I found a way that worked well, I come across a paper where someone was using about the same procedure.

So, who knows if such a discourse of these things might be useful. I have held back some on this last thing publicly, since there had been competition in the area and I didn't want to teach them anything.

On that hammer bouncing on concrete, loosely hold the handle and just ease it along with bounces about 2 to 5 inches high. Interesting as to what it can tell.

I was thinking that maybe you could modify a power trowel using carbide grit brazed onto the blades to just wear the crap off. Hard surfacing beads might do the same thing, but the thin trowels might not take the heat well, with burn thru likely with stick welding. I don't know if MIG welding wire comes as hard surfacing. If so, pulsed MIG would be the way to add the beads. Getting real fancy with diamond wheels, as is done to level out uneven highway slabs, might not be available there and the result might not be what you want.