A Study On Engineering Characteristics Of Phosphogypsum And Its Mixtures

Engineering characteristics of phosphogypsum are studied in detail by compaction test, gradation test, triaxial compression test and consolidation test. Engineering characteristics of two kinds of its mixtures, namely phosphogypsum-lime-flyash and phosphogypsum-lime-flyash-clay are also studied respectively by compaction test, unconfined compression test, water stability test, expansion test and shrinkage test.Experiments show that phosphogypsum has shear strength and water stability to some degree, so it can be used to fundament treatment. Based on building settlement control, choosing reasonable compressive coefficient of phosphogypsum, good safety request can be satisfied in engineering project.Adding phosphogypsum into lime-flyash mixtures or lime-flyash-clay mixtures, the more phosphogypsum added, the bigger unconfined compression strength of the new mixtures obtained before the ratio of phosphogypsum mass to new mixtures mass reaches 15%. When the ratio beyond 15%, the unconfined compression strength of the new mixtures decreases.Adding lime into phosphogypsum-flyash-clay mixtures, the new mixtures unconfined compression strength increases deeply before addition ratio of lime reaches 8%. When the ratio beyond 8%, the increase of new mixtures unconfined compression strength can be neglected.Adding flyash into phosphogypsum-lime-clay mixtures, the new mixtures unconfined compression strength increases before addition -ratio of flyash reaches 20%. When the ratio beyond 20%, the i new mixtures unconfined compression strength decreases.The optimum ratio of phosphogypsum: flyash: lime: clay is 15:20:6:5 or 15:25:8:52.The shrinkage test of phosphogypsum-flyash-lime mixtures show that its evaporation performs mainly in early 5 days beyond 90%, and its maximum shrinkage strain is 0.068%.The expansion test of phosphogypsum-flyash-lime mixtures show that its expansion performs mainly in early 3 days beyond 95%. Because of big expansion of phosphogypsum, the mixtures maximum expansion strain can reach 2.42%. Although its bigger expansion strain, it is available for us to use phosphogypsum mixtures as roadbed material beyond groundwater level.