Physical properties:

Density (kg/m3)

  • oven-dry 540-740-870
  • air-dry (12% MC) 580-770-900
  • green 800-900-950

Freshly felled black locust contains only 35-45% of water, therefore it burns well even without drying. The fibre saturation point of black locust was determined by various studies to be at 21.8-22.5%.

Shrinkage (%):

  • longitudinal 0.1
  • tangential 5.4-7.2
  • radial 3.2-4.6
  • volumetric 11.4-12.2

Porosity (%): 52

The ratio of the tangential and radial shrinkage (shrinkage anisotropy) is rather favourable in black locust. However, significant internal stresses were observed in black locust. They might have been introduced by the fast growth, the inhomogeneous growth ring structure, the high proportion of juvenile wood and the frequently occurring eccentric growth. The internal forces often cause various deformations and splits.

Thermal properties:
Because of its high density, black locust is rather hard to get ignited. The minimum radiation heat intensity necessary for ignition is 2.6 W/cm2. For designing structural fire resistance, the burning rate recommended for calculations is 1.0 mm/min for conifers, 1.3 mm/min for poplars, and a very favourable 0.5 mm/min for black locust.
According to our studies, the calorific value of oven-dry black locust in kJ/kg is :

  • bark-free wood: 17,777
  • bark 19,145
  • bole (in bark) 18,047
  • thick roots 17,223

Assuming a density of 700 kg/m3 (bark included), the volumetric calorific value is 12,633 MJ/m3, i.e., 2.5 tons (or 3.5 m3) of air-dry black locust wood would replace 1 ton heating oil. Due to its low initial moisture content, black locust needs to be stored as firewood for only one year, and it will not be damaged by fungi or insects if appropriately stored.