Browsing by Author "Das S.K."

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Characterization of coarse fraction of red mud as a civil engineering construction material
(2017) Alam S.; Das S.K.; Rao B.H.
Red mud is a highly alkaline (pH > 11) industrial solid waste produced by aluminum industries during extraction of alumina using Bayer process. The unutilized red mud stored either in slurry form or in dry stacking takes vast tract of usable land and has an adverse effect on the quality of ground water, surface water and also on animal and plant life. An attempt has been made here to characterize the coarse fraction (>75 ?m) of red mud as an alternate construction material (medium value utilization). Different physical, chemical and morphological properties are investigated and the results are compared with Indian standard sand. The morphology using particle size analyzer is elaborated and correlated with engineering properties like shear strength and flowability parameters. In addition, chemical properties like pH, electrical conductivity, total dissolve solids (TDS), zeta potential, lime reactivity and leachate analysis are also investigated along with thermal property and are compared with that of Indian standard sand. The result of zeta potential test shows that the point of zero charge of red sand lies between the pH values of 5.5�6.5. Based on the lime reactivity, the red sand is found suitable as fine aggregate for cement and concrete. Low thermal conductivity of red sand reveals that it can dissipate the heat more efficiently. Leachate analysis shows that most of the heavy metals are within acceptable limit except Al. Based on the present study, the red sand can be used as a sustainable construction material there by utilizing the industrial waste and conserving natural resources. � 2017 Elsevier Ltd
Correlations between swelling and suction properties of expansive soils
(2015) Rao B.H.; Sahu R.L.; Das S.K.
Expansive soils have long been identified as problematic soils because these soils cause potential damage to civil engineering structures mainly due to their significant volumetric deformation under seasonal moisture fluctuations. Hence, establishment of swelling characteristics such as swell potential and swell pressure of these soils becomes essential. Although, several methods have been developed, recent studies demonstrate that the prediction of swelling characteristics from suction measurements seems to be promising. Incidentally, both these properties are strongly influenced by physical, chemical and mineralogical characteristics of a soil. Apart from this studies also reveal that stress strain behavior of expansive soil is affected by soil suction. Further, most of the swell prediction methods are not standardized, while suction measuring techniques have been well established with standard guidelines. In the present study, an attempt was made to correlate suction properties with swelling characteristics of expansive soils. Correlations between (a) swell potential and (b) swell pressure versus suction measured at natural moisture content, optimum moisture content and air entry value (AEV) were developed. Results demonstrate that suction measurements are quite useful to predict the swelling characteristics of expansive soils, quickly and easily. � 2015 Taylor & Francis Group, London.
Decoupled periodic compensation for multi-channel output gain margin improvement of continuous-time MIMO plants
(2012) Ghosh A.; Das S.K.
This study achieves superior multi-channel output gain margin (MOGM), compensation of continuous-time, linear time-invariant (LTI), non-minimum-phase, unstable, multi-input-multi-output (MIMO) plants by first input-output decoupling these in open-loop and then effecting zero placements of the decoupled loops using single-input-single-output (SISO) periodic feedback. The condition that allows this controller to yield arbitrarily large MOGM is also found out. An example is considered to illustrate the design procedure and the capability of this controller. � 2012 The Institution of Engineering and Technology.
Strength and durability characteristic of alkali activated GGBS stabilized red mud as geo-material
(2019) Alam S.; Das S.K.; Rao B.H.
Red mud (bauxite residue) is generated during the Bayer's process of aluminium production in the ratio of one part aluminium to 0.8�1.5 part red mud and is considered as an industrial waste. The storage of unutilised red mud creates a geoenvironmental problem due to its highly alkaline nature (pH > 11) as it contaminates the groundwater as well as surface water. The present paper discusses the strength and durability properties of the stabilized red mud using alkali (Na 2 SiO 3 ) activated ground granulated blast furnace slag (GGBS) and its microstructural property for possible application as a geo-material. One of the major problems associated with the geo-materials is the strength loss and weathering due to the exposure to adverse environment. So, the emphasis has been given to the durability of the stabilized red mud by keeping in mind its various uses in geotechnical construction. The durability studies are performed by considering the effect of wet-dry cycles on compressive strength. In addition, the results of slake durability test and impact strength index are also discussed. The microstructural and chemical investigations are performed using scanning electron microscope (SEM) and X-ray diffraction (XRD), respectively, to correlate with the strength and durability characteristics. The chemistry of leachate in terms of heavy toxic metals (Hg, As, Pb, and Cr) as identified by EPA is also studied and it was found that the stabilized red mud is non-toxic. � 2019 Elsevier Ltd