Impermeability and shear strength of phosphogypsum-based impermeable materials under drying-wetting cycles
New sodium polyacrylate modified bentonite-sand-phosphogypsum(PMB-S-PG)impermeable material was developed for PG slag field or roadbed impermeable layers,which can provide a new idea for multiple ways to dispose PG.The properties of impermeability and shear strength for PMB-S-PG,raw bentonite-sand-phospho gypsum(RB-S-PG)and sodium polyacrylate modified bentonite-sand(PMB-S)under the drying-wetting(DW)cycles were compared,and the micro-mechanisms of the impermeability and the strength weakening for the specimens under the action of DW cycles were investigated by scanning electron microscope(SEM)and mercury intrusion porosimetry(MIP)tests.Results showed that the coefficients of permeability for the RB-S-PG,PMB-S-PG and PMB-S specimens increased by 146.50,6.14 and 1.59 times after 9 DW cycles,respectively,indicating that the PMB can effectively improve the resistance of the specimens for DW cycles.The relationship of the shear strength for three specimens was as follows:PMB-S-PG>RB-S-PG>PMB-S,indicating that the PG and the PMB both helped to improve the shear strength of the specimens.The shear strength of the specimens showed a change trend of decreasing first and then stabilizing with the increasing number of DW cycles.By the MIP tests,it was found that the pore structure of the PMB-S-PG specimen changed from single-peak to three-peaks structure with the increasing number of DW cycles.The pore volume and number corresponding to the particle size of the three peaks increased continuously,which led to the weakening of interparticle cementation,but the increment of the pore volume of the specimen decreased gradually.In the effect of DW cycles,the properties of impermeability and strength for the specimen first weakened and then tended to be stable.
phosphogypsum(PG)drying-wetting(DW)cyclescoefficient of permeabilityshear strengthpore structure
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