accelerated hardening of wood-cement composites with carbon dioxide injection
Subtitle: mechanisms and applications.
Published: 2005
Language: eng
Number of pages: 157
Description: The initial strength of wood-cement composites was positively related to extent of carbonation reaction. However, the ultimate strength of wood-cement composites relied more on the hydration of cement after carbon dioxide injection. Excessive carbonation was not beneficial to the ultimate strength of wood-cement composites.The mechanisms of accelerated hardening of wood-cement composites with carbon dioxide injection and the application of this technique to recycle spent CCA-treated wood and medium density fibreboard (MDF) were studied.The rate of carbonation reaction could be increased by adding calcium hydroxide, increasing gas temperature and pressure, and decreasing the composite density. It was not affected by prolonging curing time of the composites prior to carbonation, nor by the addition of calcium chloride. The addition of wood slightly impeded the carbonation reaction at the beginning of carbon dioxide injection. Water/cement ratio was vital to the carbonation reaction but its optimal amount varied with wood/cement ratio.Spent MDF fiber was poorly compatible to cement under normal hydration, but could be used to make wood-cement composites under carbon dioxide injection, because their physical-mechanical properties and durability were significantly enhanced under carbon dioxide injection. The optimal conditions to produce wood-cement composites from this kind of fiber source with carbon dioxide injection were also obtained.The better compatibility of CCA-treated wood to cement was not found under carbon dioxide injection. Although the application of carbon dioxide did not change the general leaching properties of CCA-treated wood-cement composites, it led to higher leaching of chromium and Cr+6.The pH value of carbonated wood-cement composites remained as high as 11.7 even after 30 minutes of carbon dioxide injection, much higher than the expected value of around 9.Carbonation reaction followed a diffusion-controlled process, and the development of carbonation degree was very well predicted by the model developed by Kroger and Ziegler.Reactions during the accelerated hardening of wood-cement composites were those happening between calcium silicates and ettringite in the composites and the injected carbon dioxide. The reaction between calcium hydroxide and carbon dioxide was not the dominant one to give the composites high early strength.
Notes: Advisor: Paul Cooper.

Forestry theses.

Thesis (Ph.D.)--University of Toronto, 2005.

Electronic version licensed for access by U. of T. users.

Source: Dissertation Abstracts International, Volume: 66-06, Section: B, page: 2895.