Browsing by Author "Ahmed, Tasnia"

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Evaluation of Physical, Mechanical, and Durability Properties of Limestone Powder Blended Concrete
(Research and Development Wing, MIST, 2025-12-30) Islam, Md. Jahidul; Ahmed, Tasnia; Naila Meghna, Nishat; Abida, Ismat; Mashfiq, Nayeem Mohammad
Reducing the amount of cement in construction has become a challenge in the 21st century. In this study, limestone powder (LSP) is adopted to partially replace cement at different weight percentages (5%, 10%, 15% and 20%). The influence of LSP on engineering properties such as workability, compressive strength, splitting tensile strength, flexural strength and toughness, water permeability, and surface resistivity is investigated to assess the acceptability of LSP blended concrete and to find the optimum replacement level considering these properties. At low replacement levels (5% and 10%), the mechanical and durability properties are improved due to the nucleation effect of LSP. Beyond 10% replacement, the dilution effect dominates which disadvantages the concrete. The workability linearly rises with the increase in the LSP content. The compressive and tensile strength does not vary much from the control specimen up to a 10% replacement level. The highest compressive and flexural strength is recorded for 10% LSP replacement. Toughness calculated from the beam load-deflection curve showed an increased value with increased LSP replacement. In comparison to the control specimens, 6.4% higher flexural strength and 90% higher toughness index are achieved for 10% LSP. An equation has been proposed using a machine learning approach to predict the tensile strength of LSP blended concrete with 87% accuracy. Water permeability and chloride ion penetrability are reduced for higher LSP content as LSP works as a filler and enhances pore structure. This study summarizes that 10% cement substitution with the LSP can be adopted for overall better mechanical and durability properties of concrete.
Physical, Mechanical, and Durability Properties of Concrete with Class F Fly Ash
(Research and Development Wing, MIST, 2023-12) Islam, Md Jahidul; Ahmed, Tasnia; Salehin, Md Riadus; Sadman Sakib, Mohammad; Shariar, Md Shakil; Hossain, Monowar
Concrete is one of the most used manufactured materialsin the world. Fly ash (FA) is a byproduct produced from pulverized coal combustion in power generation. A total of 0.08 million tons of class F fly ash is produced from a coal-based power plant yearly in Barapukuria, Bangladesh, whose disposal is of a great issue. Therefore, this study aimsto explore the possibility of using class F FA in concrete construction as a supplementary cementitious material. In this study, two different water-to-cement ratios (0.4 and 0.5), each with five cement replacement levels numerically, 0%, 10%, 20%, 30%, and 40% with FAare used. Various tests are performed on cylinder and beam specimens to assess physical, mechanical, and durability properties, such as workability, density, compressive strength (CS), splitting tensile strength (STS), flexural strength (FS), chloride ion penetrability (CIP), and shrinkage. Analyzing the results, it is reported that workability increases and density decreases with the increasingFA replacement. Mechanical properties mostly decrease with increasing FA content. However, the strength gained with age is higher for concrete with FA compared to the control concrete. The CIP reduces with FA replacement, especially at 56 days of age. Shrinkage value reduces 82% at 40% replacement FA replacement and w/c ratio 0.4. However, at 10% FA replacement and concrete age of 56 days, mechanical strength loss is infinitesimal or even better compared to the control concrete. Thus, a low replacement percentage of FA with a high curing period is a suitable concrete cement alternative.