Prabir K. Kolay

Physical, chemical, mineralogical, and thermal properties of cenospheres from an ash lagoon

Abstract A small percentage of the particles, present in the pulverized coal ash, consists of thin-walled hollow spheres or cenospheres. Their quantity depends on the carbon and iron contents present in the ash. The apparent density of these cenospheres is less than that of water and as such, they float on the ash slurry when it is impounded in the ash ponds or lagoons. Cenospheres are being used in different industrial applications, mainly due to their low density, high strength, and good thermal properties. However, it is important and mandatory to study and characterize these ash particles for a better and effective usage. As such, an effort has been made in this paper to study physico–chemico–mineralogical and thermal properties of the cenospheres obtained from an ash lagoon.

Synthesis of zeolites from a lagoon ash

Abstract The amount of ash, and its hazardous impact on the environment, produced from the coal fired thermal power plants is continuously increasing. This poses a very challenging task of safe handling, proper disposal and utilisation of the ash. A very common method of disposal of the ash is the wet disposal, in a slurry form, in the lands nearby thermal power plants, known as lagoons. During the process of wet disposal, the ash interacts with water and looses its original physical as well as the chemical properties. The ash–water interaction may also lead to the formation of zeolites over a period of time, which may be used for various industrial applications. This paper deals with the effect of water interaction, and hence the formation of zeolite, on a typical Class ‘F’ lagoon ash, from India.

Characterization of an alkali activated lagoon ash and its application for heavy metal retention

Abstract The wet disposal of ash, from the coal-fired thermal power plants, involves its mixing with water and its impoundment in the ash ponds or lagoons. This causes the interaction of ash and the alkalies present in it with water over a period and the formation of ash zeolites (i.e. zeolitization of the ash) takes place. In order to simulate such ash–water interactions, alkali activation of a typical lagoon ash, from India, has been conducted. Investigations have been conducted to identify the effect of zeolitization of the ash on its physical, chemical and mineralogical characteristics. Such studies are essential to explore the possibility of application of the lagoon ash, and the zeolitized ash, for various environmental applications, viz. retention and removal of heavy metals from the industrial sludge.

Effect of Zeolitization on Compaction, Consolidation, and Permeation Characteristics of a Lagoon Ash

A common method of disposing of ash generated from coal-fired thermal power plants is wet disposal, where the ash is mixed with water to make a slurry and is disposed of in ash ponds or lagoons. Such a disposal system allows for ash-water interaction, and alkalis present in the ash react with water, leading to the formation of ash zeolites. Formation of zeolites alters the overall properties of the ash. Controlled laboratory experiments have been conducted on a lagoon ash to determine the effects of zeolitization on its physico-chemico-mineralogical properties. Further investigations have been carried out to demonstrate the effect of zeolitization of the ash on its geotechnical properties such as its compaction, consolidation, and permeation characteristics. Such a study is required for bulk utilization of the ash (as a fill material) where compaction, consolidation, and permeation properties are most important.

Thermal characteristics of a class F fly ash

It is necessary to evaluate thermal properties of geotechnical materials, viz. soils and rocks, for power cables and oil pipe lines and disposal of nuclear wastes. A situation may arise where the heat dissipation through the soils and rocks may not be satisfactory, leading to adoption of a backfill. Fly ash can be used in conjuction with aggregates to design a proper backfill material. The thermal characteristics of this material, in terms of its resistivity, play an important role in the design of a thermally stable backfill, i.e., Fluidized Thermal Backfill (FTB). As such it is desired to establish thermal response of the fly ash based on its physical and moisture- holding characteristics. In this paper an effort has been made to evaluate the thermal resistivity of a Class F fly ash using a laboratory thermal needle/probe. The effect of density of compaction and the moisture content on the thermal response of the fly ash has been also studied.

Improvement of Bearing Capacity of Shallow Foundation on Geogrid Reinforced Silty Clay and Sand

The present study investigates the improvement in the bearing capacity of silty clay soil with thin sand layer on top and placing geogrids at different depths. Model tests were performed for a rectangular footing resting on top of the soil to establish the load versus settlement curves of unreinforced and reinforced soil system. The test results focus on the improvement in bearing capacity of silty clay and sand on unreinforced and reinforced soil system in non-dimensional form, that is, BCR. The results show that bearing capacity increases significantly with the increased number of geogrid layers. The bearing capacity for the soil increases with an average of 16.67% using one geogrid layer at interface of soils with equal to 0.667 and the bearing capacity increases with an average of 33.33% while using one geogrid in middle of sand layer with equal to 0.33. The improvement in bearing capacity for sand underlain silty clay maintaining and equal to 0.33; for two, three and four number geogrid layer were 44.44%, 61.11%, 72.22%, respectively. The finding of this research work may be useful to improve the bearing capacity of soil for shallow foundation and pavement design for similar type of soil available elsewhere.

Physical and geotechnical characteristics of stabilized and unstabilized tropical peat soil

This paper presents physical and geotechnical characteristics of unstabilized (original) and stabilized peat soil samples from Sarawak, Malaysia. Peat soil is heterogeneous, with high compressibility, high water content, low specific gravity and has medium to low permeability. As a result, evaluation of physical and geotechnical properties are very important for any types of construction on it. Different physical and geotechnical properties e.g. organic content, loss on ignition, liquid limit, specific gravity, fiber content, compaction and Unconfined Compressive Strength (UCS) tests have been carried out on peat soil sample. Locally available fly ash (FA) from coal fired thermal power plant and commercially available quick lime (QL) were used as stabilizers. The amount of FA and QL added to the peat soil sample, is 5 to 25% and 2 to 8%; respectively, for curing periods of 7 to 120 days. The standard Proctor compaction test and UCS test were carried out on original and stabilized peat soil samples with the above mentioned percentages of stabilizer and results show that the UCS value increases significantly with the increase of FA and QL percentage and also with curing periods. But, with 15 to 20 % FA and 6 % QL added with peat soil, the UCS values slightly decreases up to 28 days and again increases after 120 days curing periods. Furthermore, liquid limit and specific gravity tests have been carried out with only for the FA stabilized peat soil samples, in order to comprehend their stabilized behavior.

Effect of alkali on tropical peat stabilized with different stabilizers

Abstract The paper presents the effect of alkali on tropical peat stabilized with ordinary portland cement (OPC), fly ash (FA) and different chemicals e.g., accelerator (a combination of 2.0% sodium sulfate, 0.5% sodium chloride and 0.1% triethanolamine); 2.6% aluminum sulfate; and 2.6% calcium sulfate. Various physical and engineering properties tests were conducted on original peat, FA and stabilized peat samples to check the effect of alkali and chemicals. Unconfined Compressive Strength (UCS) tests were carried out on treated (i.e., peat treated with 2% NaOH to reduce its acidity) and untreated stabilized peat samples with OPC, FA, and different chemicals for various curing periods. The results show that UCS value increases with curing periods and treated peat samples show better results than untreated peat for both OPC and FA stabilized peat samples. The highest UCS value was found on treated stabilized peat where calcium sulfate and OPC were used as stabilizers for 120 days curing period. In addition, specific gravity (Gs), pH, loss on ignition (N), Organic Content (OC) and Scanning Electron Microscope (SEM) studies were also carried out on stabilized peat samples to investigate the stabilized behavior and micro-structure of the peat.

GEOTECHNICAL CHARACTERIZATION OF COAL ASHES FROM SARAWAK FOR BULK UTILIZATION

The utilization of the coal, for the generation of electrical energy, has been increased substantially from 4.2 to 13 million tones during the years 2000 to 2005 in Malaysia. As a result, it produces a large quantity of ashes as a by-product. The coal ash can be, and is being successfully used, for different applications e.g., a stabilizer of sub-grade and sub-bases in pavement construction; as a fill material; as a foundation material etc. But before utilization in different fields mainly as a bulk its physical and geotechnical properties (e.g., compaction, compressibility and shear strength) must be studied. The advantages of using coal ash as a bulk fill material include low cost, low unit weight, and good strength. However, not much attention has been paid locally to the characterization of the coal ashes and its utilization in Sarawak. Hence this paper describes some physical, chemical and geotechnical properties of coal ashes collected from Sejinkat Thermal Power Plant, Sarawak, Malaysia.

Effect of salt and NAPL on electrical resistivity of fine-grained soil-sand mixtures

Electrical resistivity of soils are very important for various engineering projects, for example, subsurface transmission of either heated fluids or high-voltage buried power cables; storage and contamination of radioactive waste. Electrical resistivity mainly depends on the type of soil and its water content or saturation. The present study measures the electrical resistivity of commercially available kaolinite clay mixed with various percentages of sand & tried to establish a relationship between electrical resistivity and water content of the soil mixtures. Also, electrical resistivity has been measured with the addition of salts and non-aqueous phase liquid (NAPL) contamination into the kaolinite and/or kaolinite–sand mixture. The results show that electrical resistivity reduced drastically with the addition of salt but the resistivity increases with the addition of NAPL for kaolinite and kaolinite–sand mixtures.