Properties and behavior of raw sludge mixed with pulverized fuel ash and lime

Raw sludge from a water treatment plant and Pulverized fuel ash (PFA) from a coal-fired power plant are normally considered to be waste. The raw sludg e is usually soft and weak, and takes a large area for storage if stockpile d on open ground, or requires a heavy dam/retaining structure if impounded. Strength and stiffness of the sludge are important parameters for the desi gn and construction of facilities for sludge storage. This paper presents r esults from a series of tests on geotechnical properties and behavior of lo cal raw sludge mixed with PFA and lime. The focus is on the improvement of the shear strength and stiffness of the sludge by mixing with different rat ios of PFA and percentages of lime. Test results are presented and analyzed . Relationships between unconfined compression strength (UCS), PFA/Sludge ( PIS) ratios, and lime contents are obtained. Relationships between the effe ctive friction angle (and cohesion) and PIS ratios for 8% lime are also obt ained from consolidated undrained (UC) triaxial tests. Correlation between secant Young's modulus Eso and the peak deviator stress q(peak) is establis hed.