Posted on 05/06/2017 7:38:09 PM PDT by Lorianne
Good to know that the rebar is coated. The new bridge portion is full of leaks into the internal concrete under the roadbed. I recall that they screwed up on the guard rail construction, placing them without an intervening seal layer, then later caulking from the sides to seal the joints, all of which leaked during rainstorms. The internal cavities under the roadbed are full of water that can't be reached, particularly at the support tower area.
I don’t know what kind of “Ice Melt” you are using but NEVER put rock salt (road salt) on concrete. I use Driveway Melt and never had a problem.
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Microscopic cracks at the surface, yes, but destructive open cracks can only occur in tension.
But the funny thing is that the most disastrous failures occur in compression where a structure was excessively reinforced.
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Here is an article by Peter’s Chemical about chemical deicers.
http://www.peterschemical.com/seven-things-facility-managers-must-know-about-ice-melters/
This shows them viewed from several perspectives.
“Independent testing of commonly used deicers has shown that calcium chloride is the least harmful to concrete”
(I worked for 2 wholesale hardware distribution companies in a number of capacities for 35 years. We sold a lot of different brands of deicers.)
IceMelt is a brand name but commonly used as type of product
Reviews of their product on Amazon:
I suspect they make more than 1 type of deicer under the name IceMelt.
I did state the 1st response wrong. It was not calcium carbonate, but calcium chloride.
Here is a Dow Chemical Calcium Chloride ice melt .pdf
http://icemeltchicago.com/MSDS-Peladow-Calcium-Chloride.pdf
After looking back at my post, it appears I was wrong on what IceMelt brand contained. Reviews on Amazon indicated it was primarily rock salt. That is very damaging.
Yeah I can’t argue that. I know there are some old concrete structures performing just fine and that too much water can be a cause of terrible cracking... but I am just a drafter, that did some intspecting, not an engineer.
I have seen a few extreme cases in my career, we did a project in San Francisco pre-cad days that had intregal columns built within 6” tunnel form walls that sure seemed like did not have enough concrete to work. We had to draw a bunch of full scale details to show there was room for aggregate after all the layers of steel was tied together, it was tight on paper, I felt sorry for guys in field, it had to be tied perfect.
The firm i worked for at the time sent engineers to do inspections after the earthquake in 89, If memory serves, that freeway pancake was mostly because the column vertical steel did not have proper containment ties to keep them together...
My mom had just drove under that section minutes before it hit.
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Are you talking about the Cypress fwy in Oakland?
That failure was predicted by the resident engineer for the construction project, Jim See, who noticed that the only containment for the columns was #4 hoops at 12” when it should have been at 3” per the calcs of the designer.
They ignored him. Soon after, he became the City Engineer for the City of Pleasant Hill, where he was a constant thorn in the side of Caltrans.
He lived long enough to say “I told you so.”
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If you’re not building a beam then rebar or wire mesh is a waste of money. For driveways, patios, sidewalks, etc, well compacted base of crushed 3/4”-0” gravel is all you need. Just make sure you place your joints in the right places. Slabs should be no larger than 15x10. Make sure your garage slab joints line up with your driveway slab joints, which should line up with the sidewalk joints. If the don’t, then the crack will jump across from a good joint and transfer to the other slab and it will crack there and become a problem
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For large slabs, a hexagonal weakened plane joint pattern works best. The smaller, the better.
Also, covering the base rock with a thin layer of Blow-Sand will provide more stress relief when expanding or contracting thermally.
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The most important thing when dealing with concrete is not to use to much water. The stiffer the better. Do that slump test!
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Correct, water = voids.
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To much water equal weak chemical bonds in the cement. Most people think concrete dries like paint. But concrete doesn’t dry, it hardens, the process is called hydration. The H20 is part of the concrete itself. But too much water is a bad thing.
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If you have more water than fits into the crystalline pattern, it simply makes a void, and eventually evaporates.
No, I am a licensed civil engineer. Trust me it doesn't evaporate. LOL. All you have is very weak concrete.
Have a copy of TY Lin?
Yes exactly, the containment hoops at 3” o.c. I did not realize that deficiency was known before the earthquake, I thought that was learned from the aftermath. I also thought they did not have proper lap or hooks at the ends besides the wide spacing. The round columns got hoops with a lap and square or rectangular got ties with a 90, 135 or 180 hook at ends... Those 135/180 degree hooks were what was causing problems with aggregate jamming up in the narrow walls I was talking about. But anyway that freeway failure was used as an example to me about importance of showing those ties correctly, because I was also learning to draw structural drawings for bridges at the time...
I only had about 6 years drawing time in when that occurred. The project we were working on was Filmore Center in San Francisco. It was a big super block project, There were some towers and a bunch of shorter apartment buildings with underground parking etc. Our engineers went and inspected those buildings that were finished and under construction and also a whole bunch of post offices in the area. I remember drawing a lot of wall elevations with epoxy crack repairs for awhile after that.
Isn’t salt how they get an exposed aggregate finish?? Salt the top and hose it down the next day? I cant remember, should just look it up, maybe it is some other chemical. I had a concrete truck driver tell me they always carried a 5# bag of sugar in case the truck broke down or they got stuck, they could add it to the load so the concrete would not set up fully and ruin the drum.
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