2.4. Durability of T. cacao pod husk and A. boonei sawdust biochar briquettes

The ability to resist and withstand an amount of load was assessed for each biochar briquette [28]. Geometric analysis was made on the briquette to determine its width and thickness. In the geometry, a simulated crack was introduced to the briquette by manufacturing a notch with a depth of 0.45 to 0.55 mm. A continuous load was applied to the cracked briquette to determine the critical stress intensity. The load ratio used was R = 0.0258 kN and 15 Hz frequency. The crack opening displacement was recorded using an extensometer mounted at the notch edges created on the briquette. The fracture toughness was determined by this formula [28]:

Where: K₁ = Fracture toughness or stress intensity (N/cm²).

P = Load applied to the briquette (N).

B = Thickness crack length of the briquette (cm).

W = Width of the briquette (cm).

The resistance to shattering of each biochar briquette was determined using the tumbling test. This involved a cuboid formed by an angle iron frame measuring 16 cm high and 6 cm wide. A sample of each briquette (45 g) inside the cuboid was rotated for about 15 min after which the percentage mass loss of the briquette was calculated [29]:

Where: w₁ = Mass of biochar briquette before shattering (g),

w₂ = Mass of biochar briquette after shattering (g).

The Shatter Resistance (%) of each biochar briquette was calculated as [29]: