Microstructure And Macroscopic Mechanical Property Of Solidified Sludge

As a by-product of the sewage treatment plants, the sludge can bring secondary pollution to the environment, making hunman activities under huge threat.The traditional method to manage the sludge is poor and expensive. The curing effect of traditional method is poor and it has a high cost. In order to solve these problems, a new method is considered. On the basis of cement solidification, combining with the skeleton construction principle, adding coal gangue as skeleton material, clay and fiber as secondary curing materials to solidify sludge.Through shrinkage and cracking experiment, the deformation rule of different solidified sludge in the process of maintenance was analyzed. Through microstructure tests, the evolution of morphology and pore structure of cement solidified sludge was analyzed. Through the triaxial shear test, the strength of solidified sludge was tested. This study has great value to the harmless treatment and resource utilization of sludge. Based on the tests and theoretical analysis, the main conclusions can be drawn as follows:(1)The shrinkage of nine kinds of solidified sludge has shown a rising trend with the increase of curing age. At the 30 th day of the curing period,the radial shrinkage, axial shrinkage and volume shrinkage of the solidified sludge with 0.05kg/kg cement,0.1kg/kg coal gangue and 0.001 kg/kg fiber were the largest of all, which were 37%, 22% and 50%, respectively. The cracking phenomenon of the solidified sludge with 0.1kg/kg cement,0.2kg/kg coal gangue,0.001 kg/kg fiber and 0.05 clay was the most significant,its cracking factor was 0.033.(2)With the increasing of curing age, the secondary pore and average pore diameter in the solidified sludge decreased.The solidified sludge which was added 0.1kg/kg cement,0.2kg/kg coal gangue,0.001 kg/kg fiber and 0.05 clay had the largest average aperture with 13.378 nm.(3)In the curing process of solidified sludge, the moisture content decreased, organic matter in sludge was changed, and calcium carbonate content became more and more. The material composition and crystalline phase transition of different solidified sludge were similar during curing period.(4)With the increasing of curing age, the stress strain curve of solidified become strain softening model from strain hardening model under the condition of lower confining pressure. The strength, cohesive force and internal friction angle of the solidified sludge increased with the increasing of curing age. On 28 th day, the sample with 0.15kg/kg cement,0.2kg/kg coal gangue,0.002 kg/kg fiber had the maximum cohesive force, c = 55.4kPa, φ= 25.7 °.