Studay On The Engineering And Expansive Properties Of Solidified Dredged Sludge-Phosphogypsum Blends

It’s a new technology of filling materials use cement (lime) to solidify the mixture of dredged sludge and phosphogypsum. The technology can effectively change two kinds of waste into soil resources. As a new waste treatment technology, it’s valuable to systematic study the properties of solidified mixed soil, in order to develop the technology of treatment mixed-soil.In this paper, A series of laboratory tests has done, such as the unconfined compression test, direct shear test, consolidation test, variable head permeability test and linear expansion ratio test a series of laboratory tests, considering the mixture ratio of the mixed-soil, the moisture content of dredged sludge, curing age, curing agent and dosage. The engineering properties of treated mixed-soil are studied; the remoulded properties of solidified soil are recoveried; the law of expansion of treated mixed-soil is revealed, and the mechanism of treated mixed-soil is analyzed.The researches of the engineering properties of solidified mixed-soil have shown:(1) the strength, compressive properties, moisture content and permeability coefficient of treated mixed-soil are found to be mainly affected by the mixing ratio of dredged sluge and phosphogypsum, the initial moisture content of dredged sluge, curing agent and its dosage, curing age. According to the experimental results, the strength model of treated mixed-soil with phosphogypsum content is established; the strength change is divided into three stages:the strength rising stage, the strength transitional stage, the strength stable stage.(2)The treatment of solidified mixed-soil is better than treated dredged sludge, its strength is far higher, so can save the curing agent. And the failure strain more than single solidified dredged sludge. It shows that the solidified mixed-soil has good toughness and engineering applicability.(3) The technology of solidified the mixed-soil is feasible, which can cheaply treat a great amount of dredged sludge and phosphogypsum at the same time.The researches of the remoulded properties solidified soil have shown:(1) the strength of solidified dredged sludge and solidified mixed soil will be significantly reduced after being remolded, the strength of the remolded solidifiedly soil will be restored to a certain extent after curing. The remolded timing is the most important factor to affect the remoded strength reduction and recovery, and there are some other factors such as the mixing ratio of dredged sluge and phosphogypsum, curing agent and its dosage, curing time.(2) Remolded soil strength reduction is mainly due to the crushing process for the destruction of cohesion; and strength recovery is derived from the increase of cohesion and internal friction. Remolded soil strength of solidified dredged sluge recovery is the interaction effect of the friction bite force increased of particles and the gel repair, the remolded timing is the most important factor to affect the ablitity of the gel repair. But remolded soil strength of solidified mixed-soil recovery is the synergistic effect of the three factors that the friction bite force increased of particles, the interaction of restoration of soil structure and the expansive damage results; the remoded timing of is important factors to affect their coordination.(3) The remolded soil has better better compression characteristics and smaller permeability coefficient comparing to the original solidified mixed-soil.(4)The Remolded soil has better engineering properties, the remolded solidified soil as fill materials is feasible, and the optimum remolded timing of solidfited dredged sludge and solidified mixed-soil is studied.The expansibility and mechanism study shows that the solidified mixed soil has the following characters:(1) solidified mixed soil basically has some swelling, and the swelling increased its strength, which is beneficial to it. Linear expansion is related with the initial moisture content of dredging silt, curing agent content, dredging silt and phosphogypsum ratio, curing time and other factors. The variation patterns of linear expansion under different factors circumstance are given.(2) the mechanism analysis found the hydration conversion process in the solidified mixed soil has three steps, soil moisture conversion has significant impact to the volume stability and strength of solidified mixed soil; the macroscopic volume of solidified mixed soil is the combined action of contraction and expansion, and its macroscopic strength is the combined action of expansion damage and stregth recovery.(3) the criteria of the expansion character of the solidified mixed soil is proposed, based on the relevant information, the solidified mixed soil has small or medium expansion character, and has good engineering applicability.