Why should I specify water-stops in relatively dry construction joint 3

[IJR]

The situation is as follows

1) A rectangular duct 6ft*6ft top slab in level with ground.
2) No precasting, will be cast in trench
3) Final backfill is wet but no water table nearby
4) Casting sequence is base-walls-top
5) so there will be total 4 construction joints


Question:

1) What is the sense in installing waterstops(PVC or metal) in these 4 construction joints. The inside of the duct is dry, a typical cable channel

2) If the idea is to prevent moisture, well that may work but I have 2 layers of vertical reinforcement in walls and I have moisture insulation outside, if moisture penetrates then how does the waterstop save reinforcement? The barrier is between reinforcement layers.


Thanks and nice weekend

 

[Ron]

The waterstop is not to protect the rebar as much as it is to provide long-term protection against moisture/water infiltration and exfiltration at the construction joints.

You do not mention the type of waterproofing you are using, but keep in mind that much of the waterproofing effort used in today's construction does not compare favorably with waterproofing used in the past, so construction joint protection is a good measure.

You say that the water table is not an issue nearby, but that too could change. Also, unless this is being installed in an arid environment, you will have a transient water issue each time it rains.

Bottom line...I think it is a good idea to use the waterstops. They are the only redundancy you have in the system.

 

[Gourile]

Water stops are normally used in expansion joints to compensate with its movements and keep the moisture out. If you perform a good construction joint, its permeability won't be different much more than the concrete of the duct. So what would be the significance of using a water stop? In my opinion, you had better concentrate on detailing for connection between old and fresh concretes at the construction joint location. Offcourse, in expansion joints where all reinforcements are cut, you will need water stops.

 

[emmgjld]

The issue is probably the climate involved. If semi-arid to arid, such as I deal with in Western Colorado, Drainage (to include drainage boards and subsurface drains) and other protection (such as good backfill compaction) may be pratical. If the climate or particular circumstances involve the possibility of future water increases, either short or longterm, the water stop may be required.

The area practices have much to do with the decision. If water stops are commonly installed, then go with them. In my area, water stops are not the norm, the contractor experience is scant and actual applications are often flawed. My personal experience with water stops is that many faults are present (probably due to inexperienced contractors) and I tend to go with other measures. As I said earlier, local practice and experience is important.