冻融循环对固化污泥力学及微观结构特性影响

冻融循环作用会改变固化污泥工程特性，影响固化污泥堆体稳定及安全。在封闭系统下对固化污泥进行冻融循环试验，每经历一次冻融循环，就测定固化体的无侧限抗压强度、渗透系数等工程指标，并根据试验结果选取试样进行扫描电镜和压汞试验。研究结果表明：第1次冻融循环作用使固化污泥强度衰减30%，渗透系数增大80%，随后变化幅度逐渐降低；经过约6次冻融循环后，固化污泥强度衰减幅度高达50%，渗透系数增加约1个数量级，随后基本保持恒定，渗透系数的变化较无侧限抗压强度变化表现出微弱的滞后性。随着冻融循环次数的增加，固化污泥孔隙体积逐渐增大，固化污泥强度逐渐降低，渗透系数逐渐增大。在封闭系统下，固化体内部水分结冰引起的总膨胀体积恒定，固化污泥内部水分分布均匀。当冻融循环作用达到一定次数后，孔隙体积不再持续增大，只是在空间上重新融合分布，使各参数逐渐达到恒定状态。研究成果对寒区污泥固化填埋的安全处理处置提供技术参数和指导。

Mechanical and microstructural properties changes of solidified sewage sludge due to cyclic freezing and thawing

The stability and safety of the solidified sludge pile will be threatened when the engineering properties change due to freezing and thawing cycles (FTC). Laboratory FTC tests are conducted on the solidified municipal dewatered sludge in the closed system. Unconfined compressive strength and permeability coefficient of the solidified sludge are tested after each FTC. According to the results of tests, some samples subjected to cyclic freezing and thawing are selected to perform mercury intrusion porosimetry (MIP) tests and to analyze with the scanning electron microscope (SEM). The results show that the 1st FTC results in a decrease in the strength by 30% and an increase in the permeability by 80% of the the solidified sludge. Whereafter the change range gradually decreases. The strength decreases by 50% and the permeability coefficient increases by about one order of magnitude after about 6 FTC, thereafter they both almost keep constant. The variation of the permeability coefficient lags slightly behind that of the unconfined compressive strength. The pore volume and the permeability coefficient gradually increase while the strength decreases little by little with the increase of FTC. In the closed system, the total swelling volume induced by the frozen water in the solidified body is constant and the internal moisture is uniformly distributed, so the pore volume doesn’t continue increasing any more while just the pores mix together and redistribute when reaching an certain number of FTC, then each parameter becomes constant. The investigation provides parameters and guiding for safe landfilling of the solidified sludge in the cold regions.