Effect of paper mill ash on properties of expansive soils

[摘要] ENGLISH ABSTRACT: Expansive soils, one of the problematic soils, are encountered on all continents with exception of polar continents. Problems caused by their heaving and shrinking behaviour, particularly to light structures, have been reported from different countries to place large financial burden on developers. For this reason, many techniques have been developed and applied to prevent and/or remediate the damage caused by these soils. Soil stabilization with traditional chemical additives has been applied successfully since ancient times. In addition to traditional additives such as lime, cement, fly ash, etc., some non-traditional additives, such as polymer based products, salts, etc. have been used effectively for soil treatment.On the other hand, industries are increasingly challenged by waste management in an acceptable and environmentally friendly manner. In this regard, a number of researches have been done on using industrial waste for soil improvement purposes. The study and understanding of basic reactions involved in lime-soil stabilization persuaded many researchers to study the applicability of lime-rich products for soil treatment. Studies conducted by Khalid et al. (2012); Muchizuki et al. (2004) and Thacker (2012) showed that lime-rich products such as pulp fly and bottom ashes and CaO by-products, can be applied for soil stabilization. This research was thus performed to investigate the effect of lime-rich paper mill waste ash on expansive soil properties.Two commonly listed soil engineering properties namely volume change and strength were investigated. Soil strength was examined in terms of unconfined compressive strength (UCS), due to its correlations with a number of other soil properties, and the volume change in terms of free swell and swelling pressure. In addition to these two engineering properties, dry density and moisture content were also studied due to their involvement in structural design, as well as gradation, Atterberg limits and California Bearing Ratio (CBR). The choice of these properties was also influenced by the availability of a standard (ASTM D4609-08) specifically developed to assess the effectiveness of admixtures for soil stabilization.Two main types of materials were used namely three clay materials and paper mill ash. According to the index properties, commonly used for expansive soil classification, three clays were classified into low, medium and high degrees of potential expansiveness. The ash results from the combustion of paper mill sludge, sawdust, bark, coal ash and bituminous coal in a multi-fuel boiler for the purpose of electricity and steam production. The tests mentioned above were conducted on both untreated and treated clays and the results were compared. Since the study was carried out on this material based on the fact that it contains lime, the procedure applied for lime-soil stabilization was considered.In general, it was observed that ash-soil treatment has a number of effects similar to lime-treatment and almost all studied properties were enhanced for all clays. It can thus be concluded that the paper mill ash from a multi-fuel boiler can be efficiently used for expansive soil treatment. For optimum use of this material for expansive soil treatment, more tests and further researches have been recommended.

[发布机构] Stellenbosch University