Mechanical properties of gellan and polyacrylamide gels with implications for soil stabilization

Organic matter can stabilize soil aggregates against disintegration upon wetting. We examined the tensile strengths of two polymer gels that were chosen to represent features of soil organic matter. The mechanical properties of polyacrylamide and gellan gels (gellan is a natural polysaccharide) are remarkably similar despite large differences in molecular structure. The general shape of the stress strain curves for both gels is similar, although the method and mechanism of gelation differs drastically between the gels. The ultimate breaking stresses for both gels are also similar in magnitude (13 to 1100 kPa for polyacrylamide and 9 to 350 kPa for gellan), even though they differ fundamentally in type of gel cross-links and vary drastically in their ultimate breaking strain relations. Breaking strain tends to decrease with increased polymer and BIS concentration for polyacrylamide gels, whereas the relations tended to be more complex for gellan gels, These measurements allow some constraints to be placed on the effects of polymers on soil aggregate stability. For example, a 1-mum-thick layer of polyacrylamide, on a 1 mm-diameter aggregate, can support a range of maximum internal pressures from 0.046 to 2.5 kPa.