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).
Reusing coal ash of thermal power plant in a pavement base course
Abstract Nowadays, the disposing of coal bottom ash from thermal power plants is increasing day by day and creates serious environmental problems, especially in Vietnam. The utilization of coal ash from Vietnam’s thermal power plants in a pavement base course has been attempted in this study. A total of 345 specimens in California bearing ratio, proctor compaction, compressive strength, resilient modulus, and splitting tensile strength test of bottom ash–cement, coarse aggregate–fly ash–cement, and local soil–fly ash–cement mixtures are investigated to find the mixtures that meet the technical requirements of the pavement base course. First, bottom ash was mixed with (3, 5, 7, 9, 11, and 13)% cement by weight. Second, coarse aggregates were mixed with 3% cement and (5, 10, 15, and 20)% fly ash by weight. Last, local soil was mixed with 5% cement and (5, 10, 15, and 20)% fly ash. Test results show that the optimal mixtures that have qualified properties for a pavement base course are mixtures of bottom ash+11% cement, coarse aggregates+20% fly ash+3% cement, and local soil+10% fly ash+5% cement. These results demonstrate that Vietnam’s coal ash can be reused in a base course pavement.
Determining the Jaw Relationship
Contacts between the upper and lower posterior teeth of complete dentures take place during the opening and closing strokes of mastication (Brudvik and Howell 1990). These contacts are fast, gliding impacts of the mandibular teeth which contact close to the position of maximal intercuspation of the teeth, called the “intercuspal occlusion”. The intercuspal position is the position adopted by the mandible when the teeth are in intercuspal occlusion.