Adding 12" to Caisons

Hello Jarrow

If you intend adding a 12 inch thick layer of concrete on anything, you are going to need it to be strong.

The "standard mixture of cement/aggregate/sand/clean drinking quality water in correct proportions" has been determined by many years of experience to be generally the best.

A mixture of cement and sand is normally known as concrete plaster, and if long-term-strength is required, will probably not stand up well to abrasion and/or temperature changes.

If your caissons are going to need a 12 inch "horizontal only coating on a top face only", just to act as ballast, and will not be abraded or have temperature changes, then your proposed cement/sand plaster may survive for the job.

Whatever you use, a 12 inch thick concrete cover, is going to require reinforcing steel anyway, as well as needing a bonding compound to bond it to the steel or original concrete.

Advise further, with

Kind Regards....

Yes for structural concrete you must use aggregate suitable for the concrete stength required for the caisson. Also, you need to dowel and connect the structural reinforcement from the caisson into the 12-inch of new concrete and install the spiral compression reinforcement. Concrete without aggregate technically is not concrete, it is a grout. Also you do not need drinking water. In general drinking water is much cleaner in many constituents, like iron, calcium and magnesium, than you ever need to consider, and can have higher levels than you'd like to see of others, like sodium, chloride, sulfate and potassium. Drinking water will also have residual disinfectants in it that are reactive with reinforcing steel and concrete, though typically in low quantities. You just need clean water low in suspended solids, sulfates, sodium/potassium, chlorides and organics.