The application of CO2-fixed recycled fine aggregate as filler of sand compaction piles-PPT Presentation

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This study examined whether carbonated recycled fine aggregate (RFA), produced from demolished concrete, can replace natural sand as filler in sand compaction piles (SCPs). SCPs use compacted columns to mitigate liquefaction in sandy soils and promote consolidation in clayey soils. Natural sand is increasingly costly and environmentally burdensome, motivating alternative materials.<br /><br />RFA was carbonated in a chamber for one week. Thermal analysis showed that carbonation increased the material’s calcium carbonate content, with an estimated CO₂ fixation capacity of about 5% of the RFA’s mass. Its particle-size distribution met Japanese guidelines for SCP filler, and compaction testing found a maximum dry density of 15.1 kN/m³, comparable to natural sand. Triaxial testing produced a friction angle of 34.8°, also comparable to natural sand; the measured cohesion was relatively high, attributed to the particles’ angularity.<br /><br />A potential concern is that carbonation can increase the leaching of toxic hexavalent chromium (Cr⁶⁺). Adding 0.3% iron(II) sulfate reduced Cr⁶⁺ leaching below the Japanese regulatory limit of 0.05 mg/L.<br /><br />Overall, the results indicate that carbonated RFA has suitable particle-size, compaction, and shear-strength properties for SCP use, while also enabling CO₂ utilization. Further work is needed to develop cost-effective manufacturing and achieve production at scale.

Keywords

carbonated recycled fine aggregate

natural sand replacement

sand compaction piles

liquefaction mitigation

consolidation improvement

CO2 fixation

particle size distribution

dry density

friction angle

hexavalent chromium leaching