Browsing by Author "Das, Mitu"

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    Mechanical and durability properties of nylon fiber reinforced concrete with recycled brick aggregate concrete as coarse aggregate
    (Department of Civil Engineering (CE), BUET, 2024-02-10) Das, Mitu; Mutsuddy, Dr. Rupak
    This research investigates the synergistic effects of incorporating nylon fibers and recycled brick aggregate (RBA) as coarse aggregate in conventional concrete mixtures to meet the increasing demand of concrete and reduce the impact of waste concrete produced from construction and demolition on the environment. Recycled brick aggregate, derived from waste bricks, is employed as a sustainable alternative to traditional coarse aggregates, contributing to the reduction of environmental impact associated with construction materials. Simultaneously, nylon fibers, renowned for their tensile strength and flexibility, are introduced as a reinforcing element to augment the ductility and toughness of the concrete matrix. The study aims to assess the mechanical (i.e. compressive strength, split tensile strength, flexural strength) and durability properties (level of permeability and service life prediction) of the resulting recycled brick aggregate concrete (RBC), exploring the potential enhancements in structural performance and sustainability. The experimental program involves the formulation of various concrete mixtures with varying proportions of nylon fibers and recycled brick aggregate. Stone chips were replaced with recycled brick chips by the volume fraction of 0%, 10%, 20%, 30%, and 40% with the widely used mixing ratio of 1:1.5:3 and the water-cement ratio of 0.42. After that, nylon fiber (NF) was added to those mixtures with volume fractions of 0%, 0.1%, 0.25%, 0.4%, and 0.5%. Mechanical properties such as compressive strength, flexural strength, and split tensile strength are assessed to quantify the impact of these additives on the concrete's structural performance. Additionally, durability aspects, including resistance to chloride ion penetration and service life prediction, are investigated to evaluate the material's long-term resilience under adverse environmental conditions through Rapid Chloride Penetration Test (RCPT) and Rapid Migration Test (RMT). This research aims to provide insights into the feasibility of using nylon fibers and recycled brick aggregate as viable alternatives in concrete production, focusing on achieving a balance between mechanical strength, durability, and environmental sustainability. It was found that incorporating nylon fiber with 0.4% volume fraction and 10% recycled brick aggregate increased the compressive strength by about 8.5% compared to that of the control mix. The optimum dose for improving splitting tensile strength and flexural strength is 0.25% Vf of NF and 10% recycled brick aggregate. For a certain mix proportion, water cement ratio, and cement type, RBC always demonstrates a significantly higher value of diffusion coefficient than that of natural stone concrete (NSC), which means RBC without any fiber possesses lower resistance to chloride ion penetration. Concrete prepared using 0.25% Vf of NF and 10% recycled brick aggregate have higher resistance to chloride ion penetration and thus can be said to have a lower range of susceptibility to chloride-induced corrosion. Based on these diffusion coefficient values, the service life of various concrete mixes is determined, which shows NSC possesses higher service life with the incorporation of 0.25% Vf of NF. Considering the combined effect of nylon fiber and RBA on the mechanical and durability properties, the results will contribute to sustainable construction practices.
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    REPRODUCTIVE BIOLOGY OF Acanthopagrus datnia COLLECTED FROM THE BAY OF BENGAL, BANGLADESH
    (Faculty of Fisheries Chattogram Veterinary and Animal Sciences University Chattogram-4225, Bangladesh, 2024-06) Das, Mitu
    Studying the life-history traits and reproductive biology of commercially important species are important for successful conservation and management of fishery resources. Bengal yellowfin seabream, Acanthopagrus datnia, is a commercially important species from the Bay of Bengal, Bangladesh with scanty information on the reproductive biology and life history. A total of 169 samples, both male and female, were collected from January 2023 to July 2024. Biological parameters such as length-weight relationship (LWR), condition factor (K), gonadosomatic index (GSI), hepatosomatic index (HSI), length at first maturity (Lm), fecundity, oocyte diameter and gonadal histology were investigated to find out the overall life-history of the fish. Histological analysis revealed that this species is protandric hermaphrodite. The coefficient of regression ‘b’ was 2.88, 3.01 and 2.34 for all fishes (combined), males and females respectively showing the negative allometric growth pattern for the pooled and females, however isometric for males. Mean K value was always higher than 1 indicating the good condition of the fishes. Length at first maturity (Lm) was estimated 15.9−18.4 cm for males and 16.8−17.4 cm for females. Oocyte diameter ranged from 23.9−232.6 μm, lowest in August and highest in February having a moderate alignment with the GSI that peaked in February. Histological examination shows that the highest number of yolk granule stage in females and spermatozoa in males in February which indicates the spawning season in this month. Fecundity ranged from 33,005−1,38,330 eggs/females. This study is the first record of life-history characteristics of this hermaphrodite fish from the Bay of Bengal. Information gathered in this research work will be helpful for successful conservation and management in the Bay of Bengal.