CEMENT BONDED COMPOSITES – A MECHANICAL REVIEW

Over the last years promising cement bonded wood composites for structural purposes have evolved. Durability, toughness, high dimen-sional stability, resistance against environmental influences such as biodegradation or weathering but also availability of the raw material as well as economic factors are features which can make cement-bonded composites superior to conventionally bonded composites. This paper reviews the relationship of diverse parameters, including density and particle size on mechanical and physical properties of cement bonded composites, based on published sources from the last 60 years. For general and recent information about bonding mechanisms, compatibility and setting problems, determination and improvement of compatibility, the used raw materials as well as accelerators are discussed. The main part deals with failure mechanisms in connection with several production parameters. Furthermore, the influence of particle size and geometry, orientation of the particles, cement-wood ratio and the effect of accelerators and treatment of the particles on modulus of elasticity, modulus of rupture as well as thickness swelling are discussed

INVESTIGATION OF THE MECHANICAL INTERACTIONS AT THE INTERFACE OF WOOD-CEMENT COMPOSITES BY MEANS OF ELECTRONIC SPECKLE PATTERN INTERFEROMETRY

This study investigates the bonding behaviour of Norway spruce wood strands to a surrounding cement matrix. Effects of wood swelling and shrinking during cement curing were studied by using strands of various thicknesses. The deformation of the spruce wood strands and the surrounding cement matrix, as well as the interface between the wood and the cement were examined using Electronic Laser Speckle Interferometry (ESPI) while applying a pull-out load. Sample deformation was transformed to shear strain maps, showing which side of the strand was tightly bonded to the cement matrix. The analysis of the strain maps proved that all strands were tightly bonded to the cement matrix on only one side. No shear deformation was observed on the loosely bonded side, meaning that there was no adhesion on that side between the wood strand and the cement matrix. Manufacturing of strands results in different surface characteristics and surface roughness. Bringing together the ESPI results with the roughness measurements, it was shown that only the comparably rougher surface adheres to the cement matrix. In a cement bonded composite (CBC) made of lignocellulosics to a greater or lesser extent, only half of the contact area is therefore able to transfer load