Deep-mix Stabilization of Quick Clay:A Potential Areafor Utilization of Wastepaper Sludge Ash
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A study has been carried out to investigate the suitability of wastepaper sludge ash (WSA) andits potential for partial or full replacement of cement in binder mixtures for deep-mix stabilization of quick clay. The motives for the study have been the anticipated technical, environmental and economic advantages of converting this industrial waste into a valuable construction material. A successful utilization of WSA for soil stabilization would help to check the installation costs associated with the use of cement, convert WSA into a valuable material, reduce WSA disposal expenses, mitigate environmental pollution and degradation, conserve the cement natural raw materials and, in general, promote the overall sustainability. Technically, the lime-WSA stabilized columns are anticipated to provide a better soil-column interaction than lime-cement columns. Besides, the study intended to study the geomechanical behaviour of quick clay as it changes from a gel-like remoulded liquid mass to a stiff to hard stabilized material, and the effects of cementation on the stress-strain properties of stabilized quick clay. Accordingly, a series of laboratory tests was conducted on the natural materials as well as stabilized quick clay samples. Chemical and mineralogical analyses of WSA were done to establish the conformity of WSA to the international limits on heavy metal contents and its potential for producing cementitious products in the pozzolanic reactions with lime, i.e. qualifying as a binder material. A new method for laboratory preparation of stabilized quick clay samples was devised, which produced samples of acceptable quality for geomechanical testing. The new method is described herein and appraised against the traditional methods. The samples were cured at the temperature of 5º C for periods of 7, 14, 28, 56, 90 and 180 days before being subjected to different types of laboratory tests. Unconfined compression test was conducted for each of the above mentioned curing periods at a constant strain rate of 1% per minute. The Atterberg limits were determined for each set of the UCT samples. CIU triaxial compression tests were done for the curing periods of 28, 90 and 180 days at a constant rate of strain of 0.02% per minute and a back pressure of about 400 kPa. Incremental loading and CRS oedometer tests were conducted on natural quick clay as well as the stabilized samples for the curing periods of 28, 56 and 90 days. The permeability of stabilized quick clay samples was determined on samples cured for a period of 90 days. UCT and permeability test were also conducted on cored field samples from the actual in-situ columns stabilized with an L-C-WSA binder mixture of mix ratio 25:65:10. All test results are presented and discussed in this thesis. Lime-WSA and limecement-WSA mixtures gave comparable results to those of the traditional lime-cement mixtures. Based on these results, a constitutive model for stabilized quick clay, called QUICKSTAB, has been formulated. The model takes into account the actual mechanical properties of the stabilized material, such as the cohesion, friction angle and stiffness variations. It also simulates fairly well the stress-strain behaviour, including the cohesion-softening and destructuration phenomena. The results of this study have highlighted the potential for utilizing WSA (in a mixture with lime) as a binder for deep-mix stabilization of quick clay. A lime to WSA mix proportion of 50:50 together with a mixture water content of 53% were found to give the samples of optimum quality, using the devised sample preparation method. A more rapid strength development was realized by partial replacement of cement compared with full replacement. However, incorporation of WSA was found to give higher long-term strength. This could be explained by the relatively slow pozzolanic reaction between WSA and lime. The study recommends installation of trial columns using the results of this study for in-situ testing as well as laboratory tests on cored samples. Also, the study recommends additional tests using other types of loading, such as the direct shear test and the oedometric, extension and cyclic triaxial tests, for a better understanding of the behaviour of stabilized quick clay and data for validation the proposed constitutive model.