Properties and microstructure of CO2 activated binder produced by recycling phosphorous slag

Abstract

This study examined the feasibility of producing CO2 activated binder by recycling phosphorous slag (PHS). The PHS specimen was shaped by compaction in view of its non-hydraulic activity at room temperature. Its reaction products, properties, including compressive strength and CO2 uptake, and microstructure were evaluated by multiple measurements. Results showed that CO2 activated binder could be produced by recycling phosphorous slag. The compressive strength of PHS specimens increased significantly up to 171.0 MPa after CO2 curing and presented an increasing trend with the increase of compaction pressure. The carbonation products of PHS were calcite and silica gel. CaCO3 formed firstly in spherical amorphous phase and then spindle calcite. The carbonated PHS particles showed a three-layer microstructure: unreacted core surrounded by a rim of silica gel with calcite filling up the spaces between PHS particles. The porosity and pore size decreased greatly after carbonation and with the higher compaction pressure. The degree of carbonation decreased with the increase of compaction pressure, while compressive strength increased. The improved compressive strength is attributed to the densified microstructure due to carbonation and compaction. CO2 uptake analysis shows that 1 t PHS can take up 110.9 kg CO2, presenting the potential of PHS to be used as a CO2 activated binder.