Optimization of magnesium phosphate cement: Stabilization of a kaolinitic soil

Abstract

Magnesium phosphate cement (MPC) can provide a resilient, sustainable, and low-CO2 emission alternative to conventional soil stabilization techniques. Changes in the mechanical properties of a kaolinitic, clay-textured soil were quantified after stabilization with 5, 12, and 20 % (w/w) MPC. The unconfined compressive strength (UCS) of the stabilized soils increased from 1.36 MPa when compacted without the stabilizer to 2.06 MPa with 5 % MPC, 3.51 MPa with 12 % MPC, and 3.47 MPa with 20 % MPC. Similarly, the elastic modulus of the compacted soils increased from 182.10 MPa in the unamended control soil to 266 MPa with 5 % MPC, 456 MPa with 12 % MPC, and 410 MPa with 20 % MPC. There were no significant differences observed in the UCS between 7- and 28-days curing time for samples stabilized with MPC (p < 0.05). The major MPC product, K-struvite, was present in the stabilized soil samples as determined by X-ray diffraction. Scanning electron micrographs of compressed MPC samples found hollow lens-shaped sections of pure struvite filled with aluminosilicates from the soil, and these structures appear to be the binding mechanism between the major soil minerals bind and the phosphate groups of K-struvite. Significant gain in the UCS of 12 % MPC stabilized soils to 8.12 MPa was observed with the addition of 1 % (w/w) 6.35 mm long dried jute fibers. Soils stabilized with 12 % MPC showed no significant change in strength after 3 cycles of capillary soaking with water and drying at 40 °C. Soil stabilization with MPC had similar strength to Portland cement stabilization.