Effect of fly ash modified plastic particles using heat welding method on performance and interface modification mechanism of mortars

The weak bonding of plastic/paste caused by the hydrophobicity of plastic surface is a significant bottleneck for the large-scale application of plastics in concrete, which seriously affects the macro and micro structure of plastic concrete. To address this issue, a heat welding modification method was proposed in this paper, which utilized the thermoplastic of the plastic, fly ash was welded to the polypropylene (PP) surface to form a composite aggregate with fly ash properties (F@PP). Experimental results revealed that F@PP exhibited better wettability (contact angle = 75 degrees) and pozzolanic activity compared to unmodified PP. Moreover, compared to PP mortar or F/PP mortar (simply add fly ash to PP mortar), the microscopic interface of F@PP/paste was more compact and its Ca/Si was mostly reduced to less than 2.0. The porosity of F@PP mortar was significantly reduced by 50-57% at 28d and the compressive strength was increased by 11-28% at 3d, 7d, and 28d. These findings highlight the effectiveness of the proposed heat weld method in enhancing the plastic/paste interface and the performance of plastic mortars.