Dimensional instability of cement bonded particleboard: contributions to its occurrence

Abstract

An intensive programme of research has been carried out to understand the dimensional instability of cement bonded particleboard (CBPB) and establish methods of improving its stability. The quantitative appraisal and qualitative interpretation of the instability were through investigations on CBPB, wood chips and cement paste. Aspects studied included the sorption of all three materials, SEM, image analysis and carbonation of CBPB, and stabilisation of CBPB using various pre-treatments. As part of this programme, this paper discusses the occurrence of instability of CBPB. It was found that the movement of CBPB was attributable to the contributions of its components, the distribution of wood chips and cement paste, carbonation, and residual stresses in CBPB. The behaviour of wood chips and cement paste dominated the movement of CBPB, with the effect of wood chips being greater than that of cement paste; but the behaviour of the cement paste dominated the behaviour of CBPB over a prolonged exposure. Carbonation resulted in a significantly irreversible increase in mass and decrease in dimension of CBPB under both constant and changing RH. The distribution of wood chips in CBPB determined that the change between length and width was almost identical due to a random distribution of wood chips on the horizontal surface (about 45° to the longitudinal edge), and the thickness change was much higher than length change due to wood chips almost lying flat (about 11° to the horizontal). The generation and distribution of stresses had a significant influence on the behaviour of CBPB.