What could be the reasons for such cracks?
What could be the reasons for such cracks?
(OP)
Hello
A concrete tunnel wall (30m length x 6.5 m height x 1.2 m thick) cast using 35 Mpa triple blended concrete mix saw vertical cracks(please see attachment) from the kicker up to mid height and diminishing at top. The fresh concrete temperature at placement was kept under control at 28 Deg C. Proper workmanship measure were taken care during casting.
Please note that there is no expansion joint in the entire 30 m length of the concrete wall.
What could be the reasons for such cracks? Thermal gradient or restraint? or any other
Thanks in advance
A concrete tunnel wall (30m length x 6.5 m height x 1.2 m thick) cast using 35 Mpa triple blended concrete mix saw vertical cracks(please see attachment) from the kicker up to mid height and diminishing at top. The fresh concrete temperature at placement was kept under control at 28 Deg C. Proper workmanship measure were taken care during casting.
Please note that there is no expansion joint in the entire 30 m length of the concrete wall.
What could be the reasons for such cracks? Thermal gradient or restraint? or any other
Thanks in advance





RE: What could be the reasons for such cracks?
RE: What could be the reasons for such cracks?
How about after the concrete placement? What steps were taken to cure the concrete?
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RE: What could be the reasons for such cracks?
The third party inspection agency concluded that the cracks are due to early thermal contraction. Are these not due to lack of expansion joint because the length of the wall is 30 meters ! Please see the attached photo of the wall
RE: What could be the reasons for such cracks?
"Early age thermal contraction" is a European term, and is the same as drying shrinkage. Your reference to "expansion joints" is not logical, as only contraction joints would have been useful in this case. But these restraint cracks tend to form at about 3-4 metre intervals, so that would be a lot of joints, and you still might get cracking that doesn't follow the joints.
How much horizontal reinforcement do you have in the wall? It takes about 0.6% Ag to control cracks when you have heavy restraint such as provided by that base slab.
RE: What could be the reasons for such cracks?
RE: What could be the reasons for such cracks?
It then cools and shrinks due to the reduction in temperature plus the drying shrinkage effect.
Agree with Hokie that the minimum reinforcement in this sort of situation is at least .6% possibly up to 1% if the section is thick resulting in higher thermal effect.
If you have foll;owed standard BS8110 minimum of .13% in a wall, you have no chance.
RE: What could be the reasons for such cracks?
Dik
RE: What could be the reasons for such cracks?
He did say that it was 35 MPa, thus a normal strength concrete.
It is 30 metres long, with no attempt at crack control joints. And we don't know how much reinforcement. The cracking was inevitable, but for those cracks to be uncontrolled in width was not inevitable.
sarabia05,
Do the cracks affect the serviceability of the tunnel? In other words, does water leak through? Is there an external membrane?
RE: What could be the reasons for such cracks?
Dik
RE: What could be the reasons for such cracks?
RE: What could be the reasons for such cracks?
Dik
RE: What could be the reasons for such cracks?
Was your mix design hot? by that I mean did you design it to reduce thermal issues? (slag,silica fume, cold water?)
Johnny at cast stone and precast concrete http://premier-stoneworks.com