Effect of Wood Waste and Sunflower Husk Biochar on Tensile Strength and Porosity of Dystric Cambisol Artificial Aggregates

Abstract

This paper focuses on the tensile strength (Q) and porosity of Dystric Cambisol cylinders with and without biochars (0.1% or 5% dose) obtained from wood waste (BC1) and sunflower husks (BC2). The experiments were performed on air-dried and wetted artificial aggregates remolded from unfractionated soil and its selected fractions (1−0.25, 0.25−0.1, 0.1−0.05, and <0.05 mm). The obtained results indicated that the biochar addition reduced the tensile strength of all examined samples, regardless of the type of biomass used in pyrolysis. This effect was more significant with the larger biochar dose of 5%. When cylinders formed from a wetted 1−0.25 mm fraction with 5% BC2, the Q reduction equaled as much as 0.048 MPa. The noted decrease in tensile strength was mainly associated with the formation of macropores in the cylinders (of maximum radii: 4.77 µm BC1 and 5.78 μm BC2). The highest tensile strength was observed in the air-dried samples formed from the largest silica-rich fraction (1−0.25 mm) without biochar (0.078 MPa for the air-dried cylinders and 0.066 MPa for the wetted ones). The higher Q parameter for the air-dried remolded soil aggregates was probably related to the dehydration of soil gels and the thermal transformation of iron and alumina oxides during drying.

Keywords

• remolded soil aggregates
• cylinders
• biochar
• tensile strength
• organic carbon content
• porosity