Protective coating for concrete in Sea Water Aeration Basin

[SShinde]

Guys,

I'am designing a 7m deep x 75 m long x 15m wide aeration basin, in which sea water is aerated using blowers.

My question pertains to provision of protective membrane or coating to be provided to protect concrete from deleterious
effect of sea water.

The sea water when entering the basin is rich in SO3 which then gets oxidized to SO4 through aeration.

The concrete being used is 40MPa using type I cement,with silica flume (min 5%, max 11% by mass of cement).
The temperature ranges from min 25C to maximum 61C.

Is the concrete itself capable of resisting sea water rich in sulphites and sulphates or is any protection needed.

Also providing any membrane type of protection will be very difficult as the shape of the basin is irregular with hundereds of penetrations for aerating pipes.

Rgds
Shinde

 

[Ron]

The concrete must be protected. Attack will occur otherwise and you will have a deteriorating structure. I suggest the following:

1. Increase the cover on the rebar to at least 75mm.
2. Provide very tight controls on the concrete mix and placement so that a very dense concrete is achieved. Make sure the mix is designed for durability, not just strength.
3. Use Type II cement at the least and consider using high sulphate resistant cement (Type V)
4. After concrete placement, but not sooner than about 28 days, carefully inspect the concrete surfaces for cracks. Use epoxy injection for cracks that are larger than about 1mm in width. Make sure the epoxy is compatible with subsequent coatings.
5. Coat the concrete with a very good bituminous coating such as Carboline Bitumastic 50.
6. Warn the owner that periodic inspections and maintenance will be required.

Good luck.

 

[SShinde]

Ron,

Thanks for the remarks.

We have provided 75mm of cover.

We had initially intended to use TYPE V cement, but the licensor insisted that it be TYPE I cement with silica flume as additive.I will renew the debate on using TYPE V cement, if it is compatible with silica flume.

Also we have limited the crack width as per ACI 318, by limiting stresses in the reinforcement.
The reinforcement is epoxy coated.

Providing bitumastic coating is not feasible, because there is going to be a lot of churning of water(120in dia pipe feeds the basin, 2 nos 422KW pumps ), this will erode the bitumastic coating.
But as per your suggestion , I will recomend that a protective coating be used.
Once again, thank you Ron, for clearing the muddle in my mind.
Regards
Shinde

 

[Ron]

Schinde....take advantage of the high volume, high velocity input and design diffusers to both initially aerate the water and allow the water to slow considerably before impinging the concrete....then the bituminous coating will work very well. It has been used for many years in aeration basins for sewage treatment, which happens to be similarly agressive.

Using influent aeration might allow you to reduce the blower sizes and save long term operation costs.

 

[Zambo]

What about using spray applied silane/siloxane. Silane and siloxane repellants penetrate into the substrate and react chemically with the alkalinity therein to form a resin. The resin that forms is designed to make the capillaries of the substrate smaller than that of a water molecule.

 

[bjb]

also, check into using xypex