Dear all
currently, I am working on research that involves sodium bentonite
I am facing difficulties in finding the plastic limit of the bentonite using the traditional method (rolling a 3mm thread)
I observed that cracks can be obtained at different water contents
and the moment I roll the thread to 3 mm it is hard to reform a ball out of it
which makes the thread break apart upon the second iteration of rolling
this causes my trials to be inconsistent
is there a technique that I should follow, or am I missing something?
best regards
To gain knowledge of the shrinking and swelling nature of smectitic soils, you may try to measure COLE (co-efficient of linear extensibility), which is generally done in soils' laboratory..
As an alternative way, the plastic limit of bentonite can be measured by the cone penetration method corresponding to the specific penetration depth using a suitable cone. You can use this result as a reference to compare with the conventional thread rolling procedure. For details, you can refer to the book "Emerging Trends in Geotechnical Engineering, 2012 - Page 99-111".
If the value of plastic limit is not so important for your study, you can rely on correlations for reporting PL value. Like , if you know the OMC of your bentonite sample, your PL has to be somewhere around 1.03 times OMC.
However, it is advised to better look for some alternative laboratory procedure rather than relying on empirical equations.
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