[civilpaul]

Hi, I could really use some help from the science community on this one!

I'm a Civil Engineer constructing Bentonite Piles. I'm having major corrosion, sedimentation and discolouration problems with Cast Iron Pipes used for pumping grout to the base of the piles.

I'm using cement grout (ordinary portland cement and water) under pressure with a expansive additive called CAVEX (Silica sand 20-30% Sodium Carbonate30-40% Sodium Gluconate 5-10% Mineral Oil 1-3% White Spirit 3-5% and Uncoated Aluminium Powder 15%).

The CAVEX is used to expand the grout while it cures, which is fine. However, my pumping equipment made from polished cast steel is turning green, it looks like copper carbonate coating. There are thick white powder residues around the pressure seals, and some grout is curing 'hardening' within the pipes, around bends during the grouting process, which only takes 15-20 minutes.

This does not happen, or it is not noticed when using CAVEX in a regular not pressurized application.

Does anyone know why this occurs under pressure?

And how I can stop it from happening?

Any comments will be greatly appreciated.

[civilpaul]

I forgot to mention the quantities and pressure.

35 bar (500 PSI)

Mix Ratio 100 grams CAVEX to 100 Kg Cement

Hydrated with approx 50 litres of Water to reach specified consistency.

[IITian]

Not sure what might cause this, but you might recall that Fe(II) is usually green.

[civilpaul]

Good point about the green, I think the coating is Fe(II). I'm tring to figure out how much Hydrogen the reaction is producing, especialy since we are doing it a 500psi. I'm worried I might be sat on a time bomb!