Experimental Studies on Treated Sub-base Soil with Fly Ash and Cement for Sustainable Design Recommendations
Engineers in Malaysia often faced with problem of constructing roadbeds on problematic soils. These soils do not possess enough strength to support the wheel loads upon them either in construction or during the service life of the pavement. Thus, soil treatment must be conducted to provide a stable sub-base or a working platform for construction of pavement. One of the strategies to achieve this is soil stabilization. The soil stabilization includes both physical and chemical stabilization. Chemical stabilization involves mixing binding agents with natural soils to remove moisture and improve strength properties of the soil. Generally the role of stabilizing agent in the treatment process is either reinforcing of the bounds between the particles or filling of the pore spaces. There are two types of chemical stabilization depending to the depth of the problematic soil and the type of geotechnical application: surface or deep stabilization. The traditional surface stabilization begins by excavating and breaking up the clods of the soil followed by the addition of stabilizing agents. The known amount of water is mixed with the soil and additives and compacted. Approximately 150 to 250mm depth of soil can be strengthened by this surface method. Moreover, by using heavy equipment with appropriate modification, the depth of stabilized zone can be increased to 1m. These methods are used extensively to stabilized bases and sub-bases of highways and airfield pavements (3). The pavement soil qualities will be improved by thoroughly mixing and compacting with additives include portland cement, fly ash, bitumen, and combinations of any of the additives (4). The type of the additive and the amount required are dependent upon the soil classification and the degree of improvement desired (5). The pavement structure consists of a relatively thin wearing surface constructed over a base course and a sub-base course that rests upon a sub-grade course. Asphalt/concrete is primarily used for the wearing surface. The properties of all the pavement layers are considered in the design of the flexible pavement system (6). They suggested that construction of long-lasting, economical flexible pavement requires materials that exhibit good engineering properties. The sub-base should possess desirable properties to extend the service life of the roadway section and reduce thickness of the flexible pavement structure. Strength, drainage, and permanency of strength are the few desirable properties. The fly ash classified 'F' exhibits low self-cementing properties and however, with a addition of an activator such as lime the fly ash Class 'F' produces cementitious product (7). Even for very expansive clayey soil, unconfined compressive strength increased by 106% when fly ash content was increased from 0 to 25% (8).
Stabilized earth roads
Keywords: Stabilite des sols ; Fondation Reference Record created on 2004-09-07, modified on 2016-08-08
Effect of Aeration and Agitation Regimes on Lipase Production by Newly Isolated Rhodotorula mucilaginosa–MTCC 8737 in Stirred Tank Reactor Using Molasses as Sole Production Medium
The influence of media and process parameters (aeration and agitation) on fermentation broth rheology and biomass formation has been studied in 1.5-l stirred tank reactor for lipase production using Rhodotorula mucilaginosa MTCC 8737. Molasses, as sole production medium, is used for lipase production by varying aeration (1, 2, and 3 vvm) and agitation speeds (100, 200, and 300 rpm). Maximum lipase activity of 72 U/ml was obtained during 96 h of fermentation at 2 vvm, 200 rpm, pH 7, and 25 ± 2°C temperature. Lipase production kinetics with respect to dry cell weight of biomass showed YP/S of 25.71 U/mg, specific product formation of 10.9 U/mg DC, and YX/S 2.35 mg/mg. Maximum lipase activity (MC 2) of 56 U/ml was observed at 1% molasses, and a further increase in the molasses concentration of (%) 1.5 and 2 inhibited the product formation of lipase with 15 and 8.5 U/ml, respectively. The production kinetics of molasses media showed YP/X was 14 U/mg DC, YP/S 16 U/mg, and YX/S 1.14 mg/mg during 96 h of bioreactor operation. The kLa values for all batches (MC 1–MC 4) at 96 h of fermentation were 32, 28, 21, and 19/h, and the |oxygen transfer rate were 54.4, 56, 35.7, and 17.29 mg/l h, respectively. Increase in molasses concentration resulted in decreased lipase activity by increase in viscosity of the fermentation broth.