Title:	PROPERTIES OF HIGH-VOLUME FLY ASH SELF-COMPACTING CONCRETE CONTAINING RECYCLED CONCRETE AGGREGATES AND COAL BOTTOM ASH
Authors:	Meena, Amardeep
Keywords:	Department of Civil Engineering
Issue Date:	2024
Publisher:	NIT Jalandhar
Abstract:	Results of an investigation on strength and durability properties of High-Volume Fly Ash Self￾Compacting Concrete (HVFA-SCC) made with Coal Bottom Ash (CBA) and Recycled Concrete Aggregates (RCA) as partial replacement of Natural Fine Aggregates (NFA) and Natural Coarse Aggregates (NCA) respectively are presented. A total number of thirty HVFA￾SCC mixes were prepared and their workability was established to meet the requirements of EFNARC/ACI guidelines. To assess the strength properties of various HVFA-SCC mixes, tests such as Compressive Strength, Splitting Tensile Strength, Direct Shear Strength and Ultrasonic Pulse Velocity (UPV) tests were conducted at the curing ages of 7, 28, 56, 90 and 120 days, whereas, Flexural Strength tests were conducted after 28 and 120 days of curing. To assess the durability properties of various HVFA-SCC mixes, tests such as Sorptivity, Rapid Chloride Penetration, Accelerated Carbonation and Electrical Resistivity were conducted at the curing ages of 28, 56, 90 and 120 days of curing. The mixes were further divided into three different Series containing ten mixes in each on the basis of the content of FA, i.e., 50% (Series-1), 60% (Series-2) and 70% (Series-3). A total number of 1050 cylindrical specimens of size 200 mm × 100 mm, 450 cubical specimens of size 100 mm × 100 mm × 100 mm, 450 cubical specimens of size 150 mm × 150 mm ×150 mm and 332 prisms specimens of size 100 mm x 100 mm x 500 mm were cast and tested wherein the replacement levels of NFA with CBA were kept at 0%, 10%, 20% and 30% and the replacement levels of NCA with RCA were kept at 25% and 50%. In addition, the microstructure analysis of all the mixes was conducted using different petrographic techniques such as Scanning Electron Microscopy (SEM), X-ray diffraction analysis (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). All HVFA-SCC mixes of three different Series successfully met with the desired workability conditions in accordance to ACI/EFNARC guidelines. The compressive strength test results indicate that an increase in replacement levels of NFA with CBA (10-30%), increased the compressive strength at extended curing ages (120 days), while the same was found to decrease at lower curing ages (28 days) in all HVFA-SCC mixes. In all three Series, the HVFA-SCC mixes made with 25% of RCA exhibited an increase in compressive strength compared to respective control mix up to 120 days of curing. On the other hand, the HVFA-SCC mixes with 50% RCA resulted in the decrease of compressive strength after 120 days of curing. More or less similar trends were observed for other strength tests such as Splitting Tensile, Direct Shear and Flexural Strength for all HVFA-SCC mixes in comparison to respective control HVFA￾SCC mix up to 120 days of curing. iii The influence of CBA and RCA was duly noticed in all durability tests results as ample variation in the durability performance was noted after initial and extended ages of curing. The maximum resistance of the HVFA-SCC mixes towards Sorptivity, Chloride Permeability and Carbonation was observed for replacement of NFA and NCA with 20% of CBA and 25% of RCA respectively at higher curing ages (>28 days). A similar trend was observed in the Electrical Resistivity and UPV tests results for all of HVFA-SCC mixes comprising in all the Series. However, most of the HVFA-SCC mixes resulted in satisfactory performance as described in relevant Standards after higher curing ages. The synergistic effect of both FA and CBA contributed towards additional pozzolanic action during the hydration process leading to noticeable variation in both strength and durability properties. Various microstructural characteristics such as hydrated cement paste, nature of aggregates and interfacial transition zones, phase composition of hydrated and anhydrated cementitious products, functional groups etc., were analysed for validation. The SEM, XRD and FTIR analysis of different CBA and RCA based HVFA-SCC mixes was found to be highly beneficial in understanding the microstructure as well as supplementing the strength and durability properties. Scanning Electron Microscopy analysis revealed the presence of platy, hexagonal and layered cloud form(s) of dense C-S-H gel indicating the enhanced pozzolanic action of CBA and FA in all the three Series of HVFA-SCC mixes containing 20% CBA and 25% RCA. Similarly, XRD and FTIR analysis successfully indicated the ongoing/continuous pozzolanic actions during hydration of cement and due to presence of CBA and FA in all HVFA-SCC mixes. Based on the experimental results and keeping all aspects in view i.e. strength, durability and microstructural properties, the present investigation assures the use of CBA (up to 20%) and RCA (up to 25%) in HVFA-SCC with greater confidence in concrete construction applications. It is worthwhile to mention that the results obtained in the present investigation are applicable for the materials, their source and proportions used in the present investigation. Therefore, additional research work is required for other materials, proportions and sources, which forms the ‘Future Scope for Research’. The findings of this research have been published in refereed Journals and Conference.
URI:	http://localhost/xmlui/handle/1/61
Appears in Collections:	PHD - Thesis

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