Study on Mix Proportion Design and Performance of High Volume Phosphogypsum Road Base Material
The phosphogypsum road base material designed by traditional mineral mixture is difficult to meet the demand of large-scale consumption of phosphogypsum.In order to realize the large-scale utilization of phosphogypsum in road base ma-terial,the mix ratio design of high-volume phosphogypsum road base material was explored with aggregate substitution method to determine the propriate graded gravel ratio(mass ratio of 5～10 mm and 10～25 mm fraction of 39∶61).As a substitute for the phosphogypsum-based cementitious material system,the aggregate with different dosages were employed to reach the opti-mum water content and maximum dry density by compaction.The performance test was carried out with the designed mix ratio to screen the propriate ratio as P85S60.For P85S60,the 28 d compressive strength reached 5.39 MPa,but the volume change rate was low,and the volume growth became stable after 7 days with the ultimate volume change rate as about 0.5%,which was conducive to the application of on-site road construction.The fluorine and phosphorus content in the leaching of all ratios meets the first-level limit of Integrated Wastewater Discharge Standard(GB 8978-1996),and the pH of the leaching solution would not increase additional adverse effects compared with conventional cement stabilized crushed stone materials.According to re-sults from XRD and SEM,it can be found that ettringite and hydrated calcium silicate produced by the hydration of the cemen-titious material wrapped around the unreacted dihydrate gypsum.In addition,needle-shaped ettringite and hydrated calcium sil-icate fill tiny pores,making the overall structure dense to form big strength and volume stability.
road base materialmix ratio designperformance testphosphogypsumcompressive strengthvolume change rate
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