STUDY OF COLLAPSE AND RECONDITIONING OF AFARES AND ZEEN OAK WOODS,FROM THE AKFADOU FOREST (ALGERIA)

Abstract

Within the framework of valorizing Algerian oak woods to reduce drying defects: collapse, splits, and deformations; drying and steam reconditioning tests were conducted on an experimental laboratory device. Starting from green wood, with macroscopic and microscopic analysis at the scale, drying splits and/or localized collapse, occurring in the wood rays or generalized during the treatment, which could occur during processing, were observed to aid in determining a good drying schedule and optimizing reconditioning parameters.

A physical characteristics analysis was performed to better adapt its applications to its characteristics. To this end, for each species of wood, we determined density, infra-density, total shrinkage: axial, radial, tangential, volumetric, coefficients of axial, radial, tangential, and volumetric shrinkage; as well as the fiber saturation point.

Finally, steam reconditioning tests were performed after drying to help recover some of the wood lost due to collapse. This involved determining the optimal moisture content for steam reconditioning in order to maximize recovery levels. The reconditioning of zeen and afares oak was studied after drying at five different humidity rates of 23%, 20%, 18%, 15% and 12%. Samples were reconditioned in an autoclave at 120 °C and a pressure of 1 atmosphere for 20 minutes, then dried to obtain a weight as close as possible to the initial moisture content before reconditioning.

The entire drying and reconditioning tests are accompanied by macroscopic and microscopic observations to establish a link between physical properties and structural factors, allowing for a better understanding of the collapse phenomenon.

The tests were conducted on a batch of 338 specimens taken according to current french AFNOR standards in each of the two afares and zeen oak trees. The main results obtained show that:

 – Total volumetric shrinkage, total volumetric shrinkage coefficient, and density at 12% moisture content place the afares oak and zeen oak in the category of high-shrinkage woods, nervous to very nervous, and from medium-heavy to heavy. The results attest that axial, tangential, and radial shrinkages remain high contrary to anisotropy, density, and infra-density for both species.

 – Collapse recovery is more significant in the tangential direction than in the radial direction. The optimal moisture content for recovery is 18% for both oaks in the two tangential and radial directions.

 – A clear decrease in recovery was observed in both tangential and radial directions when the wood’s moisture content is 12% for afares oak and zeen oak.

The results of this study confirm that steam reconditioning is an effective technique for recovering collapse in afares and zeen oak wood.

It will be necessary to generalize its application to the industrial field to obtain the best benefits from it.