Updating Physical And Chemical Characteristics Of Fly Ash For Use In Concrete

Author : Zacharia Sao
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (134 download)

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Download or read book Strategies for Improving the Early Age Strength of High Volume Fly Ash Cementitious Mixtures for Precast Concrete Applications and In-situ Stiffening and Upgrading of Ballasted Rail Track Beds Via Cement Grout Injection written by Zacharia Sao and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Using supplementary cementitious materials (SCMs) as a replacement of portland cement is a viable solution to meet the growing infrastructure needs in a sustainable manner. In concrete production today, fly ash is the most commonly used SCM due to its availability and ability to improve fresh and long-term properties of concrete. Despite the benefits that fly ash provides, the replacement level used in construction is limited. This is mainly attributed to extended set times and slow strength development associated with the use of large quantities of fly ash in concrete. Consequently, this limits the use of fly ash in applications where high early strength is required, such as the precast industry. To address this challenge, the first part of this thesis evaluates strategies to improve the early age strength of high-volume fly ash concrete (HVFA) to promote their use in the precast industry. In this thesis, strategies to improve strength of HVFA concrete were summarized based on a literature review. Accordingly, a number of innovative material formulation strategies were developed to achieve high early age strength with HVFA concrete, thus meeting the specifications of the precast industry. The strategies were evaluated with three types of fly ash, including a fresh class F fly ash, a fresh class C fly ash, and a harvested landfilled Class F fly ash. Prior to testing, the fly ashes were characterized according to ASTM C618 test methods to determine their physical properties, chemical properties, and reactivity. Finally, ternary and binary mortar mixtures were designed and tested with fly ash dosages ranging between 40% to 60% and proportions that had the best chance to meet the performance criteria were recommended for precast application. While some strategies evaluated in this study were found to be successful, other strategies failed to meet the target early age strength requirements. Railways allow the transportation of goods and people in a cost effective and sustainable manner. In the United States, most railway tracks use the ballasted track bed design due to their relative advantages when compared to other designs. This includes low investment cost, ease of construction, and good drainage performance. However, there are several disadvantages associated with their use such as ease of deformation, need for frequent maintenance, and poor life expectancy. To address these issues, the second part of this dissertation seeks to develop an insitu technology for reinforcing and stiffening of ballast track beds. This will consist of injecting a grout with appropriate rheology and hardened properties to convert the bottom third of ballast assemblies into portland cement concrete. To allow in situ conversion of ballast beds to hybrid concrete track beds, this study aims to use the technology of preplaced aggregate concrete casting where coarse aggregates are placed in a formwork and cementitious grout is injected to fill the voids. To develop this technology a comprehensive literature review was conducted to understand the mechanism behind ballast deterioration and treatment strategies proposed in literature. In addition, the literature on preplaced aggregate concrete technology was also summarized, and an experimental plan was developed to allow the implementation of this technology in practice. A series of tests were conducted with the aim of understanding the link between aggregate void space and grout rheology on filling ability. This included aggregate characterizations tests, grout fluidity experiments, and bench scale filling experiments. In addition, X-ray CT was used to determine aggregate morphology that will be further used for reconstruction of virtual ballast assemblies and simulation of grout flow experiments via computational fluid dynamics (CFD) modeling. While the modeling parameters are not discussed in this thesis, a qualitative experimental validation was conducted and is discussed. Overall, this thesis proposed innovative strategies that address challenges related to concrete production and railway transportation. The first part of this thesis is directed towards improving the early age strength of HVFA concrete. The successful outcomes of this project will mitigate a currently existing major barrier to HVFA adoption in the precast concrete industry. The second part of this thesis is directed towards developing a rapid and in-situ method for converting ballast track beds into hybrid concrete track beds. This will provide significant benefits to the railway industry by reducing maintenance cost of rails tracks. Additionally, the service life of the railway track will be reduced if this technology is successfully implemented in practice.