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

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The study evaluates carbonated recycled fine aggregate (RFA), produced from crushed waste concrete, as a lower-carbon filler for sand compaction piles (SCP). During carbonation, CO₂ reacts with cement hydrates attached to the aggregate particles and forms calcium carbonate.<br /><br />RFA was dry-carbonated for seven days at 20°C, 60% relative humidity, and 10% CO₂. Thermogravimetric analysis indicated that it fixed approximately 5% of its mass as CO₂. Tests of particle-size distribution, compaction, permeability, drained triaxial strength, and chromium leaching assessed its suitability for SCP.<br /><br />The carbonated RFA had a particle-size distribution suitable for SCP and compaction properties comparable to natural sand. Its optimum water content was 20.8%, maximum dry unit weight about 15 kN/m³, hydraulic conductivity approximately 3.1 × 10⁻⁵ m/s, and internal friction angle 34.8°. However, carbonation increased hexavalent chromium (Cr⁶⁺) leaching above the Japanese environmental limit. Adding iron(II) sulfate reduced leaching: 0.1% brought it below the limit, while 1% or more nearly eliminated it.<br /><br />The authors conclude that treated, carbonated RFA can serve as an SCP filler while conserving natural sand and potentially reducing CO₂ emissions. Its estimated cost is currently about twice that of natural sand, so lower-cost production and carbonation processes are needed for widespread adoption.

Keywords

carbonated recycled fine aggregate

sand compaction piles

CO2 sequestration

waste concrete

calcium carbonate

particle size distribution

permeability

triaxial strength

hexavalent chromium leaching

iron sulfate treatment