Dimensonial Instability of Cement-Bonded Particleboard: Behavior of Cement Paste And Its Contribution To The Composite
Keywords:Cement-bonded particleboard, cement paste, relative humidity, cycle, hysteresis, adsorption and desorption, mass and dimensional changes
AbstractThis paper examines the behavior of cement paste under constant and changing relative humidity (RH) conditions to evaluate the contribution of cement paste to the dimensional instability of cement-bonded particleboard (CBPB). It was found that the trend of changes in cement paste was very similar to, but the degree of changes was different from, that of CBPB at various exposures. The comparison of the results of cement paste with those of CBPB indicated that the inclusion of wood chips accelerated the carbonation reaction, and that carbonation of the cement paste exerted additional stresses on the wood chips in CBPB; this resulted in a slightly higher increase in mass but an appreciably greater decrease in the dimension of CBPB under constant 20°C/65% RH. The cement paste had considerably lower changes in mass and dimension with a single change in RH between 35 and 90% RH (except for the increase in mass on adsorption at 90% RH) compared to CBPB. The inflection in the relationship between mass and dimensional changes of cement paste was more distinct than that of CBPB with the change of mass per unit length change after the "inflection point" being about eight times higher than that of CBPB on desorption. Under cyclic RH, the response to the level of RH and the history of sorption was different between cement paste and CBPB, with the difference in dimensional change between adsorption and desorption being more significant, while the adsorption at 90% RH for the cement paste was considerably higher. Fitting of models previously developed to the data permitted the prediction of accumulated change of the cement paste with a good degree of fit and established the suitability of using these formulae for modelling CBPB as a composite to be described in a further paper in this series.
Collins, R. J. 1986. Porous aggregates in concrete: Jurassic limestones. Building Research Establishment, Information Paper IP 2/86.nFan, M. Z. 1997. Dimensional instability of CBPB: Understanding its occurrence and reducing its magnitude. Doctorate Thesis, University of Wales, Bangor, Wales.nFan, M. Z., J. M. Dinwoodie, P. W. Bonfield, and M. C. Breese. 1999a. Dimensional instability of cement bonded particleboard: Part 1. Behaviour and modelling prediction under a constant and single change in RH. Wood Sci. Technol. (in press).nFan, M. Z., J. M. Dinwoodie, P. W. Bonfield, and M. C. Breese. 1999b. Dimensional instability of cement bonded particleboard: Part 2. Behaviour and its prediction under cyclic changes in RH. Wood Sci. Technol. (in press).nFan, M. Z., J. M. Dinwoodie, P. W. Bonfield, and M. C. Breese. 1999c. Dimensional instability of cement bonded particleboard: Behaviour of wood chips from various stages of manufacture of CBPB. J. Mater. Sci. (in press).nFeldman, R. F., and P. J. Sereda. 1963. Use of compacts to study the sorption characteristics of powdered plaster of paris. J. Appl. Chem. 13:158-167.nFeldman, R. F., and P. J. Sereda. 1964. Sorption of water on compacts of bottle-hydrated cement. I. The sorption and length change isotherms. J. Appl. Chem. 14:87-93.nHelmuth, R. A., and D. H. Turk. 1967. The reversible and irreversible drying shrinkage of hydrated Portland cement and tricalcium silicate pastes. J PCA Res. Dev. Labs. May 8-21.nLesage, F. C. 1985. Effect of concrete admixtures, composition and exposure on carbonation in Bahrain. Deterioration and Repair, Bahrain Proc. VI:467-483.nNagataki, S., H. Ohga, and E. K. Kim. 1986. Effect of curing condition on carbonation and corrosion in fly ash concrete. ACI SP 91, Madrid Proc. 1:521-540.nPowers, T. C. 1962. A hypothesis on carbonation shrinkage. J. PCA Res. Dev. Labs. 4(2):40-45.nPowers, T. C., and T. L. Brownyard. 1948. Studies of the physical properties of hardened Portland cement paste. The PCA Res. Dev. Labs. 992 pp.nSereda, P. J., and R. F. Feldman. 1963. Compacts of powdered material as porous bodies for use in sorption studies. J. Appl. Chem. 13:150-158.n
The copyright of an article published in Wood and Fiber Science is transferred to the Society of Wood Science and Technology (for U. S. Government employees: to the extent transferable), effective if and when the article is accepted for publication. This transfer grants the Society of Wood Science and Technology permission to republish all or any part of the article in any form, e.g., reprints for sale, microfiche, proceedings, etc. However, the authors reserve the following as set forth in the Copyright Law:
1. All proprietary rights other than copyright, such as patent rights.
2. The right to grant or refuse permission to third parties to republish all or part of the article or translations thereof. In the case of whole articles, such third parties must obtain Society of Wood Science and Technology written permission as well. However, the Society may grant rights with respect to Journal issues as a whole.
3. The right to use all or part of this article in future works of their own, such as lectures, press releases, reviews, text books, or reprint books.