The bentonite powder and bentonite suspension used for pilling work shall satisfy the following requirements:
The liquid limit of bentonite when tested in accordance with IS 2720 (Part 5) shall be 400 percent or more.
The bentonite suspension shall be made by mixing it with fresh water using a pump for circulation. The density of the freshly prepared bentonite suspension shall be between 1.03 and 1.10 g/ml depending upon the pile dimensions and the type of soil in which the pile is to be bored. The density of bentonite after contamination with deleterious material in the borehole may rise upto 1.25 g/ml. This should be brought down to at least 1.12 g/ml by flushing before concreting.
The marsh viscosity of bentonite suspension when tested by a marsh cone shall be between 30 to 60 stoke; in special cases it may be allowed up to 90s.
The pH value of bentonite suspension shall be between 9 and 11.5.