Potential of Wood Waste Ash as an Additive in Concrete

The enormous amount of wastes produced during wood processing operations in many countries provides challenging opportunities for the use of wood waste as a construction material. In this research, wood waste (sawdust and wood shaving) ash (WWA) of pretreated timber of 0, 5, 10, 15, 20, 25, and 30% by weight of cement was added as a supplement to a concrete of mix proportion 1:2:4:0.56 (cement:sand:coarse aggregate:water cement ratio), and the strengths and the water absorption of the matrix were evaluated. Also, the metal leachability of WWA was analyzed. The compressive and the flexural strengths of WWA concrete for the ages investigated ranged from $12.83\text{to}28.66\mathrm{N}∕{\mathrm{mm}}^2$ , and $3.65\text{to}5.57\mathrm{N}∕{\mathrm{mm}}^2$ , respectively, with the lowest values obtained at 30% additive level of ash. When compared with the strength of plain concrete (control), the compressive and flexural strengths of WWA concrete were between 62 and 91% and 65 and 98%, respectively, of the former. The trend of the water absorption of WWA concrete was a reversal of those of the strengths, that is, the highest water absorption values were recorded for concrete specimens with the highest additive level of ash. A batch leaching test also performed at an ash-leachant volumetric ratio of 20 produced leachate containing chromium, arsenic, iron, copper, and zinc at the following concentrations: 410, 6720, 150, 280, and $1690\mu \mathrm{g}∕\mathrm{L}$ , respectively, when leached at a pH of 4, and 400, 10,670, 0, 100, $1470\mu \mathrm{g}∕\mathrm{L}$ , respectively, when leached at a pH of 5. These concentration levels exceed the EPA fresh water acute criteria limits.