huangyhg

water bar
im supervising a water tank consuction. the wall height is about 3.5m. because of the size of the tank, its impossible for the contractor to cast all concrete at one go. there are water bars specified at all construction joint. im not at all with the workmanshop(installation) of these water bars. i want to ommit the woater bars, but im afraid that the joint might leak! is there any compound which i can use to ensure the joint is water tight? want to hear from you.
i'm guessing you mean a pvc or other form of water stop when you say water bar...
my first choice would be a purpose made concrete additive (admixture) such as kryton kim. this will make the entirety of the concrete wall water tight, in addition to ensuring (properly installed, ssd etc) joints are water tight.
regarding cold joints in the concrete construction (ie: you concrete lifts), i don't believe you need to worry about water stopping them, so long as the construction is carried out in accordance with best practice. the surface of the "set" or already cast concrete typically is required to be surface saturated dry (ssd) prior to pouring the concrete above, in addition to ideally being a rough scabble face surface. personnally i do not like spray or paint on bonding agents as they can rather easily become bond breakers if not applied correctly.
also, in the case of a water tank, autogenous healing of concrete frequently means that any leaking through minor cracks is self-healing over time. i know that some concrete mix designers will add lime to their concrete to encourage autogenous healing for water retaining structures, although i do not know of any publication or reasearch discussing this topic.
that said, this question should be directed to the original design engineer, and i'm not entirely certain from your post whether or not you are the design engineer. you should be careful to check the original designer's intent and get their approval of any change.
i'd be very interested to hear back from you, and particularly to know which way you go, and what the ultimate outcome is!
good luck,
ys
b.eng (carleton)
working in new zealand, thinking of my snow covered home...
hydrophillic sealant strips are very forgiving. even if the joint has been poorly made the strips expand in contact with water, thus sealing the leaky joint. they do of course have a tolerance which they work over. they are not cast into the concrete but attached to the joint face once the surface has cured.
agree with ys that the decision should be made by the design engineer. an engineer who designs water tanks knows the answer to this question.
agree with ussuri about hydrophilic strips.
however, i think if the wall is not cast all at one time, the construction joints are best made vertically, not horizontally. horizontal joints inevitably cause undesirable restraint shrinkage cracking in the upper lift.
i've designed a few large tanks before. i have always avoided the use of water bars or hydrophillic strips as if they fail at some point in the life of the structure they can be difficult to repair.
when there are construction joints we specify that the surface of the poured concrete is cleaned to remove any latence and that the aggregate is exposed. when the next pour is placed with good workmanship you get a good bond and we have never had a problem with leaks (good workmanship is essential).
if the workmanship is not up to scratch it doesnt matter how the joint is detailed, it will more than likely leak.
the main factor to create a watertight joint is the quality of the workmanship (assuming sufficient rebar to control shrinkage and bending cracks).

i've designed numerous tanks for treatment works and clean water etc in the uk and wherever possible have tried to avoid using water bars. they're never installed correctly or very rarely and don't always perform as their suppose too as claimed. if you need joints allow the contractor to decide where to put them suit his pour sequence as simple day work joints. daywork joints using expanded metal are ok as these allow for better aggregate interlock, but if health and safety allows a joint that is sprayed with a retarder and then mechanically abraded to exposed the aggregate is the best. only use hydrophilic sealants if you really have too they again often get abused by contractors as an excuse for a poor construction detail, and if they absorb any water the will exert huge forces sufficient on an unrestrained edge to cause cracking.
regards
hannis
thanks guys!!for youngstructure, i have designed water tanks myself with the approval from seniour engineer. im confidend that the tanks will work properly as materials here are best (rural tanzania). just worried with water bars, im 100% that the contractor im dealing with can not put water bar to my satisfication, his workmanship is not good at all!
thanks all once again.
regargds

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