I am thinking about hiring a concrete company to redo out driveway and
other concrete work. What I really want is that the driveway should
stay level and crack-free for years, as cracks seriously nterfere
with my material handling. How would I ensure that? Is that a matter
of putting more gravel, more concrete, different concrete, or what?
A RELLY GOOD base with proper drainage, then thick concrete with mesh
and rebar tying the sections together.adding fibre to the concrete and
a high strength mix helps too. how heavy loads on this driveway?
you can build iut to airport runway specs if you dont mind spending a
poor drainage is a major trouble, and realize concrete doersnt last
I think you are joking. If not, the rebar should
be in the lower third of layer. How do you
explain the lack of spalling on exposed concrete
pillars, e.g., bridge supports, basement supports,
etc. since they have lots of rebar.
On Sun, 07 Jan 2007 23:30:41 GMT, "George E. Cawthon"
Do a little net search.
Spalling is an IMMENSE problem in concrete structures.
They generally know what they are doing.
In Quebec recently an overpass collapsed killing people. Spalling is the probable
Spalling in concrete on the ground can be very bad due to the moisture. There is
a thing as TOO much rebar.
Spalling is an IMMENSE problem in concrete structures. <<<<<
Rebar corrosion....one of the causes of spalling
is strongly dependent on the thickness of the cover (amount of concrete
over the rebar), soundness of the concrete & the local environment.
a marine environment is probably one of the worst as is one where snow
removal chemicals are used
general cover suggestions
marine environment a lot more
another cause of spalling is freeze thaw but I doubt we're concerned
with this on the OP's driveway
plus to add "too much rebar" to a slab it would have to be quite a
bit....I'm sure the OP's driveway project will get less than minimum
temperature (if it get's any)
btw I'd wait until some investigation work has been done before
suggesting a reason for the Quebec overpass collapse you mention.
This isn't the first collapse.
Spalling on bridge trusses, coated beams, etc, is a very big problem here in
SW Michigan. I know several 40 year old bridges where they had to replace or
cast over and make thicker the pillars, and parge the supporting beams. All
recent projects around here are designed with coated steel and replaceable
decks instead of concrete over steel. Sure, there is still concrete in them,
but they are designed so the salty crud doesn't saturate the concrete and
rot the rebar. A couple historic bridges had to be torn down, due to the
left-in-place steel forms under the concrete arches rotting out.
Didn't somebody develop rust-resistant rebar a few years back? Special
alloy, some sort of coating, and some sort of field prep kit for welded and
alloy, some sort of coating, and some sort of field prep kit for welded
twisted joints? <<<<<
Epoxy coated rebar but the coating is easily damaged during placement
care must be taken
Stainless steel rebar does exist but the cost is high.
Salt (more properly, chloride ion from whatever source, i.e. sodium chloride
or calcium chloride) used for deicing is the primary factor causing the
failure of concrete structures on highways. Also, you'll find contractors
who'll want to add calcium chloride to the mix to accelerate strength gain
so that they can get the finishing over with and move on to the next job.
Except in emergency repair situations, DOT's generally won't allow the use
of calcium chloride in concrete. There are accelerators that don't cause
corrosion, but they're more expensive than calcium chloride.
In a normal concrete mix, reinforcing steel will quickly form a passive
coating and no rusting will occur for many, many years. If you apply
chloride deicers, the chloride ions will gradually work their way down to
the reinforcing steel. When the concentration of chloride ion gets high
enough at the surface of the steel, the passive coating breaks down and
rusting ensues. Since the rust takes up considerably more space than the
steel it was produced from, the pressures can become high enough to rupture
the concrete overlaying the steel (much like a tree root opening a crack in
a rock). Concrete bridge decks fail at the highest rate since they have so
much steel and more deicer is applied to them because ice forms there first
but the rest of the bridge suffers also from splash and seepage.
Concrete slabs will crack eventually and it will happen more quickly if you
haven't added sufficient expansion joints. Since you can't totally prevent
the cracks, your best bet is to use reinforcing steel so that the cracks
won't go anywhere once they form. If you put really heavy loads on the
driveway, you'll have to include load transfer steel at each expansion
If you absolutely must use large amounts of chloride deicers, then consider
reinforcing with epoxy coated rebar. If you use epoxy coated rebar, you'll
have to be on your toes to ensure that the epoxy coating isn't damaged
during placement of the steel and you'll have to inspect the epoxy coating
before placement to be sure it wasn't damaged (chipped, cracked) during
shipping/handling. Damaged epoxy coating can sometimes cause more problems
than not having epoxy coating at all.
Another Idea to make sure it doesn't crack is to make sure that u try
and keep it as cool as possible while it is curing,spraying water on it
at different times,but be sure not to mess up the finish,and u could
use expansion joints,good concrete co. should already know this.
Hope this helps
Keeping it damp is what is important not cool.
High temperature steam curing is often used for high strength concrete.
You can't re wet concrete. Once it dries it stops curing.
10- 30 days of keeping it damp will get you very strong concrete.
check out these threads about driveway thickness, prep & design
short answer: good base, 6" thickness & crack control joints every 150
prep is more important than mix but a low water ratio & a decent amount
of cement in the mix help (3000 psi min)
I like rebar or mesh but lots of people (more expert than me) don't.
think it's necessary
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