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Life365 with concrete cover greater than 75 mm

Life365 with concrete cover greater than 75 mm

Life365 with concrete cover greater than 75 mm

(OP)
The current version of Life 365 does not allow running with cover > 75 mm. I want to run with larger cover to get 75 year design life to first repair, for raft foundation slab with granular plus paving and parking above it. Since the cracks are not visible, they should not be an issue. The surface crack width (as opposed to crack width at the bar level) is not a significant factor in the rebar corrosion. Earlier versions allowed running >75 mm cover. Any idea how to get around this?

RE: Life365 with concrete cover greater than 75 mm

Why not revise the concrete dimensions so that you have 75mm cover but the effective depth is maintained?

BA

RE: Life365 with concrete cover greater than 75 mm

(OP)
Sorry, but I am not following you. 75 mm cover results in only 28 years till first cycle of repairs are required, based on the C-1 concrete mix as outlined in S413 Annex H (with 30% slag, 1.4% silica fume,and w/cm = 0.40)and the exposure factors and other parameters therein. For a raft in a parking garage under a tall superstructure I would want much more than that, probably 75 years if possible, so I need much more than 75 mm concrete cover. To add a corrosion inhibitor in the concrete for the raft would be very expensive. Anyway, to get back to my original question of how to run Life 365 for cover > 75 mm, I found a CD with an earlier version of the software, which does allow greater cover.

RE: Life365 with concrete cover greater than 75 mm

You completely misunderstood what I meant, but if you have found your answer, I'll let it go.

BA

RE: Life365 with concrete cover greater than 75 mm

(OP)
My apologies. I always look forward to your responses, highly value your advice which has been very helpful on a number of occasions, and I did not intentionally misunderstand what you meant. (Since Life 365 determines the time to corrosion based on the cover that the user inputs, and the effective depth is not an input variable and is not used by the program, I did not understand).

RE: Life365 with concrete cover greater than 75 mm

Maybe the confusion is because BA wasn't familiar with "Life 365", whatever that is.

RE: Life365 with concrete cover greater than 75 mm

It is true that I am unfamiliar with "Life 365" and perhaps my suggestion is off base for that reason.

My suggestion was not to alter the actual dimensions of the concrete slab but to alter the dimension input into your program such that a cover of 75mm could be used instead of the actual cover. Let's say the depth of the concrete slab is 600mm and a cover of 150mm is required; I was suggesting you input a slab depth of 525mm with a cover of 75mm which should result in the same structural performance. The slab shown on your drawings would be 600mm with 150mm cover; in that way, you have tricked the program into thinking the slab was thinner than it was.

BA

RE: Life365 with concrete cover greater than 75 mm

(OP)
ok, that is very clear. I sort of suspected that was what you meant, i.e. to try to trick the program, and that is something I have done with other programs. Unfortunately with this program, that is not possible. They diminished the usefulness of the program when they restricted the cover to 75 mm maximum, whereas earlier versions could be greater. I guess they were concerned about he appearance of crack widths, although I think that surface crack widths are not a major factor in the mechanism of rebar corrosion. I think the user friendliness of a program varies inversely with the number of revised versions that are brought out!

To Hokie66 - Life 365 models the time to rebar corrosion in chloride environments, using Ficks law of diffusion and based on user defined Canadian Standards Association (CSA) concrete classifications, concrete cover, protection system, and other input parameters. You can download Life 365 from the internet, free of charge. It is almost essential software for the engineer where greater than the standard 40 year service life (CSA S413 Parking Structures) is desired. However, as you live in Australia, where I would guess they have no need for road deicing chemicals (generally corrosive chlorides) you may have no need for it.

RE: Life365 with concrete cover greater than 75 mm

I don't know that surface cracking would not affect rebar corrosion - I would think a crack that allows greater chloride ingress would lead to more rapid formations of the corrosion microcell, specifically localized pitting corrosion.

RE: Life365 with concrete cover greater than 75 mm

(OP)
Crack width at the rebar level is more significant than crack width at the surface of the slab. But more importantly the overwhelming mechanism of rebar corrosion is ingress of the corrosive chlorides through the pore structure of the uncracked concrete. Note the Beebe cautions against more smaller size bars to control crack width, where corrosion is a concern, because they may cause more extensive plains of delamination, rather than the local spalls associated with larger farther spaced bars. The ingress of chlorides through uncracked concrete was powerfully brought home to me in the Bell Canada vs. O&Y litigation, where the post tensioned floor slabs of the garage were completely free of cracks, the top surface being entirely in compression due to the unusually large amount of prestress used, yet the top rebars were extensively corroded and the top surface of the concrete was very extensively delaminated due to the corroded rebars (the expansive oxide split the concrete apart). When I walked over the floor with hard heeled shoes, you heard "clomp clomp".

Note that CSA S413 "Parking Structures") does not have provisions about crack width. Its provisions are mainly directed at preventing ingress of the chlorides into the uncracked concrete.

In any event, the bars could likely be chosen to control the crack width, so that would not seem to be a compelling reason to have limited the input cover for Life365 to 75 mm in Life 365.

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