The Mechanical and Microstructural Properties of Artificially Frozen Sawdust-Ice Mixture (Pykrete) and Its Usability as a Retaining Structure

Abstract

The application of soil bracing systems through the artificial ground freezing (AGF) method is developing in the field of geotechnical engineering. Retaining structures cannot be stabilized if the strength of the material used at the construction stage is not sufficient. For this reason, this study aims to investigate the usability of an innovative composite material named pykrete, which contains sustainable sawdust obtained with natural pinewood after a recycling process. The mechanical properties are inferred from different types of pine sawdust (fine, medium and coarse) with various densities (dense, medium dense and loose) at two freezing temperatures (- 20 and - 10 degrees C) as an advanced temporary retaining structure against lateral earth pressure. Unconfined compression tests (UCC) are applied on 60 types of pykrete samples after a freezing application in a CDF/CIF freezing-thawing machine. In addition, the micro-textural structures of the samples were examined by a light microscope in terms of freezing and thawing performance. The strain ratio's mean values of the samples increased from 3.10 and 4.81 to 4.95% at - 20 degrees C, and from 5.45 and 6.04 to 6.65% at - 10 degrees C, according to the fine, medium and coarse sawdust types, respectively. The innovative pykrete material with a fine pinewood sawdust type and a density of 18% by weight can be used as a high-strength composite material with 4.83 MPa compressive strength within retaining structures in civil engineering applications, according to the experimental results.