SEEPAGE AND STRENGTH CHARACTERISTICS OF FLY-ASH SAND MIXTURES: AN EXPERIMENTAL STUDY

Abstract

ABSTRACT The aim of the present study is to utilize favourably the situation where sand is available in abundance, for example in the adjoining areas of rivers/streams. Very often civil engineers have to construct works like Dikes, Guide bund, Detention dams and Debris dams etc. So if we can make a low permeable mass by utilizing available sand/coarse sand mixed with otherwise problematic materials such as fly-ash, we shall be able to be benefited in two ways one by utilizing the available/otherwise discarded materials and at the same time by saving the cost of structure. With this background in mind an effort has been made in this paper to produce a low permeable mass by mixing fly-ash and sand in different proportions. Present paper is an attempt to study the effect of fly-ash in reducing the permeability of sand beds. The sand beds are highly permeable as compared to fly-ash (Parua, P. K., 1996). As a case study fly- ash has been collected from Dadri thermal power station situated in U.P. In an attempt to increase the seepage resistivity of sand beds, the fly-ash has been mixed in various percentages (0–100%) with fine sand and coarse sand. The study reveals that in case of fine sand minimum permeability is observed at 80% fly-ash, whereas in case of coarse sand it occurs at 60% fly-ash for a constant porosity of 40%. However, the minimum value of permeability achieved in case of coarse sand at 60% fly-ash is 21% less than the minimum permeability achieved in case of fine sand at 80% fly- ash. In an effort to achieve practically the same above minimum values of permeability in case of fine sand and coarse sand by using cement. Ordinary Portland Cement 43 grade was mixed to them instead of fly-ash in various percentages. It has been observed that in case of fine sand 20% cement is required against 80% fly-ash whereas in case of coarse sand 15% cement is required against 60% of fly-ash to get practically the same values of permeability. In order to further increase the seepage resistivity of the above two mixtures (i.e. 80% fly-ash 20% fine sand and 60% fly-ash 40% coarse sand), they were mixed with small percentages of cement (4–10%) and tested for permeability. It is observed that at 10% cement, the mixture of 60% fly-ash and 40% coarse sand gives the value of permeability in the initial range of clay, however, 15% cement is required in case of 80% fly-ash and 20% fine sand to get practically the same value of permeability. The compressive strength studies have also been conducted. The study reveals that at 10% cement the mixture of 60% fly-ash and 40% coarse sand gives the value of compressive strength which can also be achieved by adding 15% of cement to the mixture of 80% fly-ash and 20% fine sand.