DIVISION S-6 SOIL AND WATER MANAGEMENT AND CONSERVATION - MECHANICAL STRENGTH OF CLAY-MINERALS AS INFLUENCED BY AN ADSORBED POLYSACCHARIDE

The water-stabilizing action of polysaccharides on soil aggregates has been ascribed to the binding together of soil particles by polymer bridges. This study was conducted to investigate the ability of polysaccharides to increase the strength of interparticle bonds by measuring the mechanical strength of clay-polysaccharide complexes. Kaolinite, montmorillonite, and the polysaccharide scleroglucan were used. Cores were prepared from dilute suspensions of the complexes, air dried, and manufactured either into small briquets or into spherical aggregates to measure respectively the modulus of rupture and the tensile strength. The polysaccharide increased the mechanical strength of both clay minerals. The modulus of rupture of montmorillonite increased from 265 to 580 x 10(5) Pa at the maximum adsorption of scleroglucan, which was 140 g kg-1 clay. In the case of kaolinite, modulus of rupture measurements indicated that particle-orientation effects were small and could be neglected. The tensile strength of kaolinite increased from 1 to 20.6 x 10(5) Pa at the maximum adsorption of scleroglucan (29.9 g kg-1 clay). In this case, the mechanical properties were not due to changes in the clay microorganization, since scleroglucan affected neither the fabric nor the porosity of the kaolinite. Increases in strength were thus intercepted as the formation of polymer bridges between the clay particles and were related to the progressive coverage of the surface area of the clay by the polysaccharide. We concluded that the aggregating action of polysaccharides is predominantly due to an increased strength of interparticle bonds.