ABSTRACT
Cellulose fiber reinforced cement composites provide the highest performance-to-cost ratio among fibrous cement composites considered for the replacement of asbestos. Cellulose fibers being fairly strong and stiff are particularly suited for the reinforcement of thin-sheet cement products. The research reported herein is concerned with the effects of repeated wetting-drying, freezing-thawing, and also variable moisture conditions on the performance characteristics of cellulose fiber reinforced cement composites. The effectiveness of pozzolans in improving the moisture sensitivity of cellulose fiber reinforced cement composites were also assessed.
An experimental study was undertaken in order to investigate the performance of cellulose fiber reinforced cement composites containing 1 % and 2% mass fractions of kraft pulp. The results generated in this investigation were indicative of the adverse effects of wetting-drying cycles on toughness characteristics of composites. Microstructural studies confirmed that the precipitation of cement hydration products within cellulose fiber cores (petrification) and at interface zones is the key deterioration mechanism in composites. The flexural strength of composites, however, was not adversely influenced by the repeated cycles of wetting and drying. Cellulose fiber reinforced cement composites performed desirably under repeated freeze-thaw cycles.
High moisture contents were observed to reduce the flexural strength and increase the flexural toughness of cellulose fiber reinforced cement composites. Microstructural investigations showed that adverse effects of moisture on fiber-to-matrix bond are the main factors contributing to the moisture-sensitivity of composites. Pozzolanic admixtures were found effective in reducing the moisture-sensitivity of composites.
