Mechanical properties of sawdust and woodchips

Abstract

Mechanical characteristics useful for design and process control were determined for sawdust and woodchips at five levels of moisture content. The density, the modulus of elasticity and relaxation curves were determined using uniaxial compression tester that allowed for measurement of horizontal pressure. The strength properties, the flowability and coefficient of friction against popular construction materials were determined using direct shear tester having 210mm in diameter shear box. The modulus of elasticity was found to be under strong influence of moisture content of the material. In the case of dry woodchips modulus of elasticity of 0.33MPa was obtained, while at 50% of moisture content it was of 0.25MPa. Mean value of angle of internal friction for sawdust was found 27° while that for woodchips was approximately equal to 33°. Effective angle of internal friction ranged from 34° for sawdust to 42° for woodchips. Flow index of sawdust was characteristic for cohesive/easy flowing materials while it was characteristic for cohesive materials in the case of woodchips. Strong negative correlation was observed in relationship between angle of internal friction and moisture content of sawdust. Weak or no correlation of cohesion versus moisture content relationships was observed for both tested materials, while cohesion was found under strong influence by consolidation stress.Friction against construction materials was found higher in the case of woodchips. No influence of consolidation stress on coefficient of friction was noted. With an increase of moisture content above 30% for sawdust and 20% for woodchips decrease in friction coefficient took place.