Small-Scale Mechanical Properties of Biopolymers

The use of biopolymers to improve the engineering properties of soil has received attention in recent years, stimulated by potential cost savings and the low environmental impact of this class of materials. The purpose of this work is to improve the understanding of precisely how biopolymers strengthen soil and to quantify the small-scale mechanical properties of biopolymers for implementation in physics-based numerical models. The authors describe the initial efforts to develop viable methods to form biopolymer bonds between grains of naturally occurring materials and present the results of mechanical properties experiments on these bonds. The subject biopolymer was an exopolysaccharide from Rhizobium tropici (ATCC #49672). The initial experiments indicate that the stiffness of bonds ranged from 1 GPa after approximately 1 h of curing to plateau values as high as 3.8 GPa for extended cure times. For bonds with neck areas in the range of 0.01-0.06 mm(2), the cohesive tensile strength of the bonds ranged from 16 to 62 MPa, but averaged approximate to 20 MPa. The associated cohesive failure strains in tension ranged from 0.013 to 0.042. Cyclic loading experiments were conducted to provide information on the mechanical behavior of the biopolymer and to support subsequent constitutive modeling. The results are analyzed and discussed in terms of the underlying viscoelastic behavior, paying particular attention to the variations in stiffness and internal friction as functions of cure time, frequency, and amplitude. DOI: 10.1061/(ASCE)GT.1943-5606.0000680. (C) 2012 American Society of Civil Engineers.