The Application of CO2-Fixed Recycled Fine Aggregate as Filler of Sand Compaction Piles

The sand compaction pile method improves the bearing capacity of the ground and prevents liquefaction by constructing compacted sand columns in the ground, and natural sand is usually used as filler in this method. In recent years, there has been great public interest in technologies to reduce CO2 emissions from ground improvement. Therefore, in this study, the applicability of carbonated recycled fine aggregate (RFA) as a filler for sand compaction piles was investigated to reduce CO2 emissions from ground improvement. RFA is a carbon capture and utilization material that can absorb 3-5% CO2 by mass by reacting CO2 with cement hydrates adhered around sand particles to form calcium carbonate. To verify the applicability, particle size distribution tests, soil compaction tests, constant head permeability tests, triaxial CD tests, and hexavalent chromium elution tests of carbonated RFA were conducted. Particle size distribution tests showed that the particle size distribution of RFA was similar to that of natural sand and that it could be used as a filler in sand compaction piles. Soil compaction tests results showed that the optimum water content of carbonated RFA was 20.8% and the maximum dry unit weight was 14.79 kN/m3. The hydraulic conductivity, the cohesion, and the internal angle of friction of carbonated RCF compacted at the optimum water content was 10-5 m/sec, 27.7 kN/m2, and 34.8 degrees, respectively. Also, by adding 1% iron (II) sulfate, dissolution of hexavalent chromium of carbonated RFA was less than 0.01 mg/l which is lower than the environmental standard in Japan (0.05 mg/l). From these tests results, we have concluded that carbonated RFA could be used as an eco-friendly filler of sand compaction piles.