Construction Tips

Should you wish to accelerate the curing of concrete that might be exposed to tide driven seawater or any other reason for that matter, instead of racing to beat the tide you can accelerate the curing by adding Calcium Chloride. A trick used by the worlds biggest concreting specialists. The more you add the quicker it sets.



Adding sugar has the reverse effect btw.

Nice tip for when I build my sea front mansion!

What a bizarre thread?
I`ll try to remember this little gem when I build my very first oil rig platform!!

I was thinking more of your water deposit tank for the "house" that you are building now by the sea.

Whats it got to do with oil platforms?

Ahhh!!! Sorry..I had no idea that you knew about my little project near the sea!
We put 5 tons of fresh water in it last week and no leaks.. So far.
The big test will be when we fill it with its 25 ton capacity.. Thats a lot of pressure.

Take the height of the water in the tank in feet. Multiply by 8.33 ( weight of freshwater in pounds per US gallon ) and divide by 0.052 and you will have the pressure in psi felt at the bottom of the tank.

Its a metric sized tank John.. Do you know the metric math formula?
Cheers.

No calculation required if you go completely metric.

But, to get feet, multiply the metric depth by 3.281. Then multiply by 8.33 and then multiply by 0.052 (sorry I said divide by 0.052 above - mistake)

So 10 metres in height of water would give:

10 x 3.281 x 8.33 x 0.052 psi = 14.2 psi or 1 bar of pressure at the bottom of the tank.

It comes to 14.2 the imperial way round, due to rounding.....

Or another way of putting it : 10 meters in depth of freshwater will give 1 bar of pressure at the bottom of the water column.

This would be the same, regardless of width of tank. The height is the key.

Yeah I do read your stuff.

Thanks!
Thats very useful and interesting..
What about the pressure on the sides? The same as the floor?
So a large and shallow fish pond would be low pressure?

Well, if you consider two tanks that have the same 25 ton capacity but are different heights, then the shallower tank of the two will have the lowest hydrostatic pressure at the bottom, of the two tanks. So a tall narrow tank will have a greater pressure at the bottom than a short wide tank.

Ignoring ambient air pressure then at the top of any tank the hydrostatic pressure is zero. At the bottom of a 10m tank the hydrostatic pressure is 1 bar or 14.5psi and at halfway it will be half of that.

The volume has nothing to do with the pressure at the bottom, its the height that counts.

Another way of looking at this. If you have 25 tonnes of water acting on the bottom of a tank that is really narrow then that weight is spread out over a small area. However, if you have the same 25 tonnes acting on the bottom of a tank with a large area then that same weight is more "thinly" distributed across the wider tank floor.

Here's a handy calculator. Though this adds atmospheric pressure to the figures.

http://www.calctool.org/CALC/other/games/depth_press

And heres a table, saving any calcs...

http://www.engineeringtoolbox.com/hydrostatic-pressure-water-d_1632.html

The pressure at any point in the tank is the same in all directions. The pressure only varies with water column vertical height.

So, did it hold water?

We have only ever had 6 tons (6.000 liters) in at a time.
It certainly holds that at least..
The tank walls need to go up another 500 mm so a bit of a wait to find out if it will hold all of its water!

From the UK Concrete Society

"Accelerators containing calcium chloride are restricted to unreinforced concrete due to the increaed risk of reinforcement corrosion. Accelerators based on calcium formate have been used in the UK with no reported harmful effects since the mid-1960s and thiocyanates since the 1970s."

However calcium chloride is used as an accelerator to cement that cents up steel linings in many oil and gas wells. Hence my reference to Cuadrilla. I await a reply from the geezer who spends half his time in a yacht on the med these days so it will be a while yet. Though he will be here in 2 weeks from now.

Here it is from the horses mouth:

"I don’t doubt that Calcium Chloride has the potential for provide a corrosive environment for wet steel. However the purpose of Calcium Chloride in oil well cementing is to make cement set at low temperatures. Once it has reacted with the cement and the cement has set it should not provide long term corrosion hazard. Calcium Chloride is a tried and tested cement accelerator which has been used in the oil field since the beginning of time and I have never heard of any corrosion related hazards in connection with that application. The quantity of Calcium Chloride required will depend upon the temperature and formulation of the cement and is determined by lab testing using samples of cement additives and mix water taken from the rig. Another thought- seawater will also corrode steel!"

Corrosion is indeed a problem with steel. Calcium chloride as an accelerator in cement isn't one of them.

No use of local sand or lime in construction here..(apart from hollow block production)
All sand and gravel shipped in from Leyte.