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).
Using Resilient Modulus to Determine the Subgrade Suitability for Forest Road Construction
Forest roads are often constructed in environments with low bearing capacity of the subgrade. The subgrade then has an effect on their service life and damage. According to the methodology of the American Association of State Higway and Transportation Officiales AASHTO, the design of pavement is divided into three levels according to the intensity of the traffic load. For pavements with the highest load intensity, preparing the resilient modulus from a cyclic triaxial test is required. For other traffic load classes, including forest roads, the methodology allows the use of the estimate of resilient modulus value determined from other tests. In the laboratory at the Faculty of Forestry, Mendel University of Brno, the method from the Delft University 2009 was tested and subsequently modified, using a standard CBR machine for repeated loading. A total of 276 samples from various types of forest road subgrade from the Czech Republic were tested by the method of repeated loading on the CBR machine, from which the values of the Resilient Modulus were newly labelled Mr,CBR. The results of the statistical analysis showed a large variability of Mr,CBR values and wide intervals of its occurrence for individual types of subgrade. The variability was subjected to analysis and the influence of basic geotechnical parameters on the values of Mr,CBR was analyzed. A fundamental correlation was found between the value of Mr,CBR and the value of the plunger stress, which reached values exceeding the bearing capacity of the soil types using the Delft University method. It is necessary to limit the plunger stress during cyclic loading up to the failure limit or even better to the expected traffic load. The modified procedure results show a more consistent behavior of the modulus.
Investigation of large strain extrusion machining (LSEM) of pure magnesium (Mg)
Abstract Large strain extrusion machining (LSEM) is used to produce pure magnesium strips directly from as-cast billets. LSEM reduces manufacturing steps and the special shear direction inclines the unfavorable strong basal texture of Mg. Finding suitable parameter ranges to control geometry and properties of the produced strip is a great challenge. In the present research, a finite element model is proposed and verified with experiments and previous findings. Next, effects of process parameters (temperature and pressure) on geometrical and microstructural properties of the produced strips are investigated. Studying the involved failure micro-mechanisms shows that the process temperature and hydrostatic pressure have adverse effects on the production of a flawless strip. To reduce the temperature and hydrostatic pressure throughout the LSEM process many different conditions are tested by the FEM model. Among all the examined conditions, 0.85 m m R e v feed and 530 R e v m i n rotation speed yields the most promising results it terms of low temperature, low hydrostatic pressure, and stable machining force. The proposed conditions are applied in the experimental setup and a uniform and flawless strip is obtained.