Effect of Wood on Setting of Portland Cement

Inhibition of the setting of Portland cement by finely ground wood can be measured quantitatively by the time required by the mixture to attain a maximum temperature in a Dewar flask. The method can distinguish between inhibitory and non-inhibitory batches of a single wood species. Calibration for the effect of wood particle size, Dewar heat loss, and system heat capacity is necessary. Decayed wood, heartwood, or spring-cut wood may greatly increase the normal setting time of a cement and wood mixture. Air-dry loblolly and slash pine boards and green loblolly boards were used in this study. Also several samples of southern pine excelsior were sent for test by an excelsior title manufacturer. Poria monticola, Polyporus versicolor, and Peniophora species were used as the decay fungi. Wood decayed by the brown rot Peniophora spp. may be severely inhibitory. Heartwood should not be cut into excelsior. Sapwood cut in the spring may be inhibitory because of the high starch content.

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