Effect of material properties on the behaviour of sand-cement-fibre composites

Saturated drained triaxial compression tests with local strain measurement were carried out to evaluate the effects of using three different randomly distributed fibres (polyester, polypropylene and glass fibres) and rapid hardening Portland cement to improve the engineering behaviour of a uniform fine sand. In addition to the nature of the fibres, also analysed have been the separate and combined effect of fibre content (up to 0.5% by weight), fibre length (up to 36 mm), cement content (from 0% to 7% by weight) and initial mean effective stress (20, 60 and 100 kN/m2) on the deformation and strength characteristics of the soil. The present work searches for the establishment of a relation between the properties of the fibres and the mechanical behaviour of the composite material, originated from their combination with soil and cement. The cementation itself notably increased modulus, peak cohesive intercept, peak friction angle and brittleness of the sand. Inclusion of polyester and glass fibres (both relatively stiff) slightly reduced the stiffness and increased the peak friction angle of both the cemented and uncemented sand, and also slightly reduced the peak cohesive intercept and brittleness of the cemented composite. On the other hand, relatively flexible polypropylene fibre reinforcement dramatically reduced the brittleness (changing the mode of failure of the cemented sand from brittle to ductile for longer fibres) and stiffness, while increasing the'ultimate strength of the cemented composite.