AbstractIncrease in environmental awareness over the past decades has resulted in increasing attention to industrial pollution and waste management control. The use of waste is becoming increasingly important in construction. Such materials including Wastepaper Sludge Ash (WSA), can be used to modify certain engineering properties of soils for specific uses to conserve non-renewable natural resources.
hi lime-stabilization of sulfate-bearing clay soils, there has been increasing concern over the damage caused by the expansion which is produced when sulfate-bearing soils are encountered. The main objective of this research was to investigate the potential of utilizing WSA, an industrial by-product, as a soil stabilizer with or without blending it with quicklime (CaO), Portland Cement (PC) or with Ground Granulated Blastfurnace Slag (GGBS). The engineering behaviour (plasticity characteristics, compaction, unconfined compressive strength (UCS), linear expansion and California Bearing Ratio (CBR)) of the sulfate-bearing Lower Oxford Clay (LOG) soil and of a non sulfate-bearing soil-industrial Kaolinite (control)-were investigated.
Compacted cylinders of LOG and Kaolinite stabilized with quicklime ((CaO) at typical 2wt.%, 4wt.% and 6wt.%) and with various stabilizers incorporating WSA (WSA-Lime, WSA-PC and WSA-GGBS, at 10wt.%, 15wt.% and 20wt.%) were made
under controlled laboratory conditions. The cylinders were made under either mellowed (compacted 3 days after mixing) or unmellowed (compacted immediately after mixing) conditions and then moist cured for 7, 28, 90, 180 and 365 days prior to UCS tests. CBR tests were also carried out, but only on selected stabilized LOG samples, at the lowest and highest stabilizer contents. Linear expansion of stabilized cylinders during moist curing and during subsequent soaking was monitored for at least 100 days.
The results obtained showed that the blended stabilizers incorporating WSA reduced the plasticity index (PI), reduced the maximum dry density (MDD) and increased the optimum moisture content (OMC) of both LOG and Kaolinite. The UCS values of stabilized systems incorporating WSA for both LOG and Kaolinite were higher than those systems stabilized with the traditional CaO. When WSA was blended with lime, PC or GGBS, the results indicated that in the LOG stabilized system, the strength development of unmellowed samples was generally better than for the mellowed samples. This is in contrast with the Kaolinite stabilized system where it is the mellowed samples that recorded higher strength than the unmellowed samples. The CBR values of the unmellowed samples were also higher than those for the mellowed samples.
The linear expansion of unmellowed stabilized LOG system was significantly reduced. This is again quite the opposite in the Kaolinite system, where mellowed samples showed reduced expansion relative to the unmellowed ones. Sulfate and thermogravimetric analysis results suggest that the presence of sulfate in a soil plays a major role in the mellowing process. In conclusion, the findings in this research suggest that whether or not to mellow depends primarily on the stabilizer used. Other variables include the target material and site conditions, besides possibly other factors. There are technological, economic as well as environmental advantages of utilizing WSA and similar industrial by-products, in the stabilization of sulfate bearing and other clay soils, as an alternative to the traditional stabilizers of lime and/or Portland Cement.
|Date of Award
|Roderick Robinson (Supervisor)