concrete pouring limitations 4

[katem]

The project I am working on has a concrete tank for an olympic swimming pool. On 2 previous projects there have been conflict as to the pour distance allowed for thje pool tank walls.
the first project the structural engineer wanted an area of no more than 5mtrs poured at any one time for the tank walls, and on the other it was 8mtrs. I have read the BS for waterproof structures and there doesnt seem to be any limitation. The engineer on my current project also wants 5mtrs , but experince tells me that the more joints there are the more potential for leaks. Please confirm whether there are actual limitations regarding the amount of concrete that should be poured in one go. Obviously we will be pouring the slab and a 150mm kicker , but want to pour the walls in maybe 2 hits rather than 5mtr runs.

 

[civilperson]

Joints increase the cost and potential for poor waterstop placement.

 

[katem]

that is exactly what i mean, I have checked BS8110 & Bs8007 there do not appear to be any restrictions and therefore we shouldn't have to justify why we want to do one big pour or a couple of larger pours. I was just putting the query 'out there' to see if i am infact crazy !!!! It would appear that I am NOT!.

Thanks

 

[Ron]

With current concrete technology and construction capability, I would place the concrete in one continuous placement per wall. Have two large pumps, a good concrete mix design with adequate plasticity and a large enough crew to do the job. Start and don't stop until it's topped off. Be sure your forms are designed for continuous, rapid placement.

Construction joints are not necessary if you do it right. If you need joints structurally, then put those in and you can use them as construction joints as well.

 

[hokie66]

I agree that joints are a nuisance, create maintenance issues, and are the most likely place for leaks to occur. If BS8007 is followed strictly in terms of the amount and placement of horizontal reinforcing, I would omit the joints. You should consider, however, that the walls will be restrained by the previously cast slab, so vertical shrinkage cracking is likely to occur at fairly regular intervals of about 3 or 4 metres, starting at the bottom of the wall. So to control these cracks, make sure you have reinforcing just above the horizontal joint, and I like to double up on those bars, as well as the ones at the top.

 

[katem]

Ron thanks for your advice.



Hokie66- your advice is appreciated too.


I'm aiming for a leak free structure .

Cheers .

 

[kieran1]

Katem,

I would recommend reading Ciria Report 135 'Concreting deep lifts and large volume pours'

Kieran

 

[JedClampett]

We design a lot of water tanks. The trade off is less joints, more shrinkage and temperature affects vs. more joints, more construction joints and potential leakage. Our normal criteria for spacing of joints is 25 to 30 ft. (8 to 9 m). If the British standards are anything like the ones on this side of the pond, they're very careful about prescribing anything regarding joint spacing. It's pretty much a black art and no one wants to require a spacing and get exposed to litigation.
More important than a specific spacing is enough shrinkage and temperature reinforcing (~.005%) and staggering the pours so adjacent pours do not occur too rapidly in succession.

 

[dik]

For an Olympic sized pool, I'd likely have a couple of joints along the length of the wall and across the bottom at this locaion. Use a good joint. Does the wall have tile applied; joints should match tile joints.

 

[dik]

Forgot to add... no need to consider alternate loading <G>.

 

[InDepth]

You should also look at your mix design very carefully. You should specify a maximum shrinkage (typical for Slabs on Grade - ASTM standard), verify your water/cementitious ratios, and verify flyash/pozzolanic replacement.

The type of cement should also be reviewed. Some cements shrink more than others and develop more heat than others. There are specific cements that should be used for slow curing to avoid thermal cracking and expansion.

You should probably look into the various concrete admixtures that are available that can reduce shrinkage while maintaining workability. Other admixtures you may also want to look into are migrating corrosion inhibitors and liquid crystalline waterproofing admixture (essentially seals cracks when moisture penetrates - see below).

One other admixture is Hycrete (

http://www.hycrete.com/).

Its an interesting admixture that claims no waterproofing membranes are required. At joints they have a specialized waterstop that they can post-inject to seal if a leak occurs there.

With any of these admixtures, testing is required.

You should also be very careful about specifying moist curing for several days. This should help reduce potetntial for shrinkage.


********************************
Aquafin-IC Admix is a liquid crystalline waterproofing admixture whose components react with moisture and free lime to grow tiny crystals that penetrate the concrete matrix. The crystals fill capillary voids and seal hairline cracks, enabling it to resist hydrostatic pressure.

 

[InDepth]

Oh, and you may want to make sure you have a polymer membrane below the pour to alleviate the concrete slab from being "restrained."

 

[hokie66]

Jed means 0.5% shrinkage reinforcing, not 0.005%. I would use not less than 0.6% for a 50 metre pool.