An investigation of the hybrid effect of pre-absorbed lightweight aggregate and basalt-polypropylene fiber on concrete performance

Although fibers have been extensively adopted to modify the mechanical performance of concrete containing lightweight aggregate (LWA), the composite impact of fibers and LWA's internal curing has not been addressed yet. In this study, a comprehensive investigation of basalt-polypropylene (BF-PF) fiber reinforced lightweight aggregate concrete was carried out to investigate the interactions between BF-PF fibers and LWA's internal curing, considering multiple LWA contents and BF:PF ratios. Results showed that adding LWA benefited the flexural strength but lowered the compressive strength, as the multi-pore structure of LWA increased the porosity and pore size of concrete while the internal curing of LWA optimized the overall pore structure. Nonetheless, adding BF-PF fibers could alleviate LWA's negative effect on compressive strength given that a positive hybrid effect was identified between LWA and BF-PF fibers. The discharged water from LWA benefited cement hydration and contributed to an increased Ca(OH)(2) content in the paste and a lowered Ca/Si ratio in the interfacial transition zone, thereby enhancing the bond between BF-PF fibers and the paste. Given a fixed fiber volume, increasing the PF ratio was more conducive to concrete's post-cracking behavior while increasing the BF ratio benefited concrete's pore structure. Furthermore, a multi-dimensional evaluation accommodating fresh properties, mechanical performance, pore characteristics, cost and environmental sustainability indicated that a mix of 20% LWA and 0.20% fiber at a BF:PF ratio of 3:1 was the optimum one. The results demonstrate the enhancing mechanism of fiber reinforced lightweight aggregate concrete, providing insight into concrete design in practical engineering.