Comparison of prehydration and polymer adding effects on Na activated Ca-bentonite by free swell index test

An experimental program is carried out to investigate the swelling properties of Na activated Ca-bentonite submitted to prehydration and polymer adding, using Free Swell Index (FSI). Three Na activated Ca-bentonite are used: S, T and V. Various concentrations (0.5, 1, 1.5 and 2%) of two polyelectrolyte polymers are mixed with bentonites to underline the effect of polymer adding on the mixture's FSI. FSI tests are performed with three testing fluids: NaCl 10− 3 M, synthetized leachate (LS) and a solution of 0.1 M of CaCl2. FSI and Electric Conductivity are followed for all configurations tested. Comparison between FSI ratios underlines the positive effect of prehydration compared to polymer adding. Polymer adding increases the chemical resistance of bentonites and has less impact on bentonite swelling. Statistic analysis demonstrates that the effect of bentonite activation is less significant in front of the influence of the testing fluid, type of treatment and the polymer concentration. The positive effect of polymer adding on bentonite's FSI is more effective for a polymer concentration ranged from 0.5% to 1%. The experimental results are in good agreement with literature but the positive effect of the polymer adding occurs to be misrepresented by standard FSI tests.