Abstract: Polyvinyl alcohol fibers (PVAF) and basalt fibers (BF) were selected to be incorporated into concrete in different proportions and volume rates, and mixed fiber recycled aggregate concrete was configured with 30% recycled coarse aggregate as an equal mass replacement of normal coarse aggregate. 90 times dry-wet sulfate cycles tests were conducted to measure the changes in mass loss, dynamic elastic modulus and compressive strength of concrete after different times of dry-wet cycles. The study showed that the mass loss rate of concrete in the PVAF group was 0.22%, which was 42% lower than that of normal concrete, and the mass loss rate of concrete in the BF group was 0.19%, which was 50% lower than that of normal concrete, when PVAF∶BF was 1∶4, 1∶2, 1∶1 and 4∶1, and the fiber volume ratio was 0.2%, the minimum mass loss rate. When PVAF∶BF was 1∶1 and 2∶1 with 0.3% fiber volume ratio, after 90 times of wet-dry cycles of sulfate, the minimum values of relative dynamic elastic modulus reduction of concrete were 102.2% and 99.4%, respectively; however, when PVAF∶BF was 1∶2, 1∶4 and 4∶1 with 0.2% fiber volume ratio, the relative dynamic elastic modulus of concrete was reduced to the lowest values of 99.4%, 94.1% and 99.4%. After 90 times of dry-wet cycles of sulfate, when the fiber volume rate was less than 0.2%, the magnitude of compressive strength loss rate of concrete was in the following order: 1∶1 mix<4∶1 mix=1∶2 mix<1∶4 mix<2∶1 mix; when the fiber volume rate was greater than 0.2%, the magnitude of compressive strength loss rate of concrete was in the following order: 2∶1 mix<1∶2 mix<1∶1 mix<4∶1 mix<1∶4 mix. Mixing PVAF and BF on the concrete resistance to sulfate erosion than single PVAF or BF, showing a better “positive effect”.

Key words: recycled aggregate concrete, wet-dry cycles, sulfate, polyvinyl alcohol fibers, basalt fibers, composites