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Durability of kraft pulp fiber–cement composites to wet/dry cycling

2004; Elsevier BV; Volume: 27; Issue: 4 Linguagem: Inglês

10.1016/j.cemconcomp.2004.07.006

1873-393X

Benjamin J. Mohr, Hiroki Nanko, Kimberly E. Kurtis,

Innovations in Concrete and Construction Materials

If pulp fiber–cement composites are to be used for exterior applications, the effect of cyclical wet/dry exposure must be known. In this research program the effects of three fiber treatments—beating, bleaching, and drying—were investigated to identify those that may minimize effects of environmental aging and degradation during wet/dry cycling. After 25 wet/dry cycles, all composites showed significant losses in first crack strength, peak strength, and post-cracking toughness. The majority of losses in mechanical properties occurred within the first 5 wet/dry cycles, though ductile fiber failure was still observed by scanning electron microscopy (SEM). A three-part progressive degradation mechanism during wet/dry cycling is proposed: (1) initial fiber–cement debonding, (2) reprecipitation of hydration products within the void space at the former fiber–cement interface, and (3) fiber embrittlement due to fiber cell wall mineralization. Unbeaten fiber–cement composites exhibited greater peak strength and post-cracking toughness, prior to cycling, while no significant differences were seen after 25 cycles. The effects of fiber beating varied prior to and after cycling. Unbleached fiber–cement composites exhibited the slowest progression of degradation during cycling. The initial drying state appeared to have no effect on composite performance after 25 wet/dry cycles.