Sealants & backstop water bar for concrete reservoir

[BarryEng]

I have designed several reservoirs (up to 300,000 m3) & the subject of sealants & waterstops has not been satisfactorily resolved. I would like to find out if other designers have had good or bad experiences of backstop water bars.

I have two reservoirs next to each other - both 165 m X 125 m in plan & 13 m deep. Total volume 400,000 m3. The concrete lining is 150 mm with N12-100 each way & located in the centre of the slab. The base is excavated in a residual material (clay) with 150 mm pipe drains under all joints. The banks are also clay with some rock fill & rock facing with an internal bank slope of 1.7H:1V & an outside bank slope of 2H:1V.

In previous reservoirs, the joints have consisted of a 'primary' water retaining sealant of polyurethane with dimensions of 40mm wide X 20mm deep. A PVC bondbreaker strip is located across the base of the groove but NO polyurethane backup tube is used (high water pressure will deform the backup tube & the resulting peel stresses will fail the bond of the sealant at the top of the groove).

Reinforcement is continuous through most joints (except for movement joints around pipe blocks, overflows, corners & the transition from the sloping wall to the floor joint). Previous reservoirs have had joints 10m wide & floor pours up to 150m long. Some have used backstop water bars.

I propose to use a 'bandage' type of sealant (Parchem in Australia) for the primary sealant but without a water bar. The sealant can be inspected & if leaking, can be easily repaired. The concern I have for waterbars, is that a water bar (centre of slab) can result in problems if not installed correctly. A backstop water bar (I have used these to prevent the ingress of ground water up thru' a joint) if damaged or leaking, is relatively impossible to locate a leak & repair.

Generally, very few people (owners, designers, sealant & waterbar manufacturers, installers & applicators) like to discuss failures or unsatisfactory performance of their products.

I would like to find out what problems (& successes) have been experienced with:-
* Primary sealants such as polyurethanes.
* Primary sealants such as 'bandage' sealants.
* Centre water bars.
* Backstop water bars.
* Are primary sealants generally replaced every 20 years (or so) to maintain water tightness or has experience shown that a longer life is possible?

BarryEng

 

[JedClampett]

Here in the U. S. of A., we typically use PVC waterstops centered in the walls. Polyurethane sealants are only used as dressing for joints to keep dirt and grit out of them. We use the bandage type sealants (Sikadur Combiflex)exclusively as a retrofit, where a non water bearing wall is to be made waterbearing or where the waterstop has failed. If constructed correctly, embedded waterstops are pretty much permanent.
You are correct that centering waterstops in walls is difficult. But once the contractors get the hang of it, it's not so bad. They have to be made to understand that their responsibility is to construct a bottle tight facility and that any repairs required are under their cost. That's part of their learning curve. If the waterstop isn't doing its job, they send divers in with dye wands and expanding sealants, such as Sikafix HH (by the way, I don't work for Sika, but I am impressed by their products) and the repairs are pretty straightforward.