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).
Stabilization of Black cotton soil using Fly ash
Expansive Black cotton clay soils are widely
distributed worldwide, and are a significant damage to
infrastructure and buildigs.It is a common practice around the
world to stabilize black cotton soil using fly ash to improve the
strength of stabilized sub- base and sub grade soil. Soil
stabilization is the improvement of strength or bearing capacity of
soil by controlled compaction, proportioning or addition of
suitable admixtures or stabilizers. The Black cotton soils are
extremely hard when dry, but lose its strength fully when in wet
condition. In monsoon they guzzle water and swell and in summer
they shrink on evaporation of water from there. Because of its
high Swelling and shrinkage characteristics the black cotton soils
has been a challenge to the highway engineers.So in this research
paper fly ash has been used to improve the various strength
properties of natural black cotton soil.The objective of this
research paper is to improve the engineering properties of black
cotton soil by adding different percentage of fly ash by the weight
of soil and make it suitable for construction. A series of standard
Proctor tests (for calculation of MDD and OMC) and California
Bearing Ratio (C.B.R) tests are conducted on both raw Black
cotton soil and mixed soil with different percentages of fly ash
(5%, 10%, 20%, 30%) by weight. A comparison between properties
of raw black cotton soil, black cotton soil mixed with fly ash are
performed .It is found that the properties of black cotton soil
mixed with fly ash are suitably enhanced.
Drivers of Live Cattle Price in the Livestock Trading System of Central Cameroon
Livestock production and trade are critical for the food security and welfare of rural households in sub-Saharan Africa. In Cameroon, animal trade consists mainly of live cattle commercialized through livestock markets. Identifying the factors contributing to cattle price formation is critical for designing effective policies for sustainable production and for increasing food availability. In this study, we evaluated the influence of a range of individual- and market-level factors on the price of cattle that were sold in all transactions (n = 118,017) recorded over a 12-month period from 31 livestock markets in the main cattle production area of the country. An information-theoretic approach using a generalized additive mixed-effect model was implemented to select the best explanatory model as well as evaluate the robustness of the identified drivers and the predictive ability of the model. The age and gender of the cattle traded were consistently found to be important drivers of the price (p < 0.01). Also, strong, but complex, relationships were found between cattle prices and both local human and bovine population densities. Finally, the model highlighted a positive association between the number of incoming trading connections of a livestock market and the price of the traded live cattle (p < 0.01). Although our analysis did not account for factors informing on specific phenotypic traits nor breed characteristics of cattle traded, nearly 50% of the observed variation in live cattle prices was explained by the final model. Ultimately, our model gives a large scale overview of drivers of cattle price formation in Cameroon and to our knowledge is the first study of this scale in Central Africa. Our findings represent an important milestone in designing efficient and sustainable animal health management programme in Cameroon and ensure livelihood sustainability for rural households.