The Shrinkage Intersection Point–Its Significance and the Method of Its Determination

The shrinkage intersection point is defined as the moisture content at which the extended linear portion of the shrinkage-moisture content curve intersects the line of zero shrinkage. Practical importance of the intersection point is in the estimation of variation of any property with moisture content. This paper describes the shrinkage intersection point obtained by each of two methods. Two specimen sizes were used: 1) the basic shrinkage specimens which are 1 inch by 1 inch cross section and 4 inches in length and 2) 0.5 inch by 0.5 inch in cross section and about 0.04 inches along the grain. The more important results are summarized as follows: 1) In the absence of collapse, the means of the tangential and radial shrinkage intersection points were not significantly different for either size of specimens. 2) The intersection point calculated from green to 12 and to 5 percent moisture content was not significantly different from that determined by using the whole linear portion of the shrinkage-moisture content relationship. However, the point calculated from green to 12 percent and to oven-dry state was definitely too high because of non-linearity in the low moisture content area. 3) When collapse occurred, the intersection point was greater. 4) The tangential intersection point was consistently greater than the radial value, but the mean of the two was not significantly different from the volumetric shrinkage values. 5) The correlation between volumetric shrinkage and basic density for 131 Australian and Pacific Island species was poor, only 57 percent. 6) A rough estimate of the intersection point could be made by using the volumetric shrinkage from green to 12 percent moisture content and basic density, however, the correlation coefficient between this estimated value and that obtained from the shrinkage moisture contents relationship was only 0.86. 7) The equilibrium moisture content of species with low intersection points were considerably less than those species with normal intersection points. This suggests that the intersection point is a characteristic property of the species and is related to its hydroscopicity.

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