Durability of aramid fiber reinforced plastic pretensioned elements under tidal/thermal cycles

This paper presents results from a 33-month exposure study to assess the li kely effect of diurnal/seasonal temperature change on the durability of ara mid fiber reinforced plastic (AFRP) pretensioned piles driven in tidal wate rs The aramid fiber composite ARAPREE was used in the investigation. Twelve precracked AFRP pretensioned beams, designed to fail by rupture of the pre stressing rods, were placed outdoors in two saltwater tanks. The beams were simultaneously exposed to wet/dry cycles (simulating tides) and hot/cold c ycles (simulating temperature variation). The effect of exposure was evalua ted from bending tests conducted periodically over the nearly 3-year exposu re period. The results showed that exposure led to visible cracking and a r apid deterioration in bond. Accompanying strength reductions ranged from 43 to 55 percent in specimens exposed for more than 21 months (15,500 hr). Th is provides persuasive evidence of the unsuitability of AFRP as a pretensio ning element for piles driven in tidal waters. Two-dimensional finite eleme nt analysis indicated that moisture absorption by the AFRP rods had been mo re important than temperature change for the bond degradation observed in t he study.