Cement hydration tests using wood flour may not predict the suitability of Acacia mangium and Eucalyptus pellita for the manufacture of wood-wool cement boards

Wood-wool cement boards (WWCBs) are manufactured in many tropical countries which have extensive eucalypt and acacia plantations. Wood from such plantations could act as a potential raw material for WWCBs, but the suitability of most tropical eucalypts and acacias for the manufacture of such products is unknown. This study was undertaken to assess whether the standard laboratory test for wood-cement compatibility, which measures heat of hydration in wood flour-cement mixtures, is an appropriate method for screening tropical eucalypts and acacias for their compatibility with cement and suitability for the manufacture of WWCBs. Wood samples from a tropical eucalypt (E. pellita) and a tropical acacia (A. mangium) were tested in two forms, i.e. flour and wool, for their compatibility (expressed by maximum hydration temperature and C_A-factor) with Portland cement. Form significantly influenced the effect of the wood on cement hydration, resulting in a different species compatibility ranking for flour and wool. As the heartwood content of wood-wool-cement hydration test samples increased, T_max. and C_A factor increased whereas the opposite occured for those containing wood flour. Tests using wood flour ranked E. pellita as being more compatible with cement than A. mangium whereas the ranking was reversed when wood-wool was used. Furthermore at low wood levels the compatibility of samples containing wood-wool or wood flour with cement was similar whereas at high wood levels, samples containing wood-wool were much more compatible with cement than those containing wood flour. Laboratory tests designed to screen eucalypts and acacias for their compatibility with cement should use wood in a coarser form with a lower surface-to-volume ratio than flour. Caution should be exercised if using results from wood flour-cement hydration tests to estimate the suitability of wood species for the manufacture of WWCBs and possibly other wood-cement composites.