Thesis (M.S.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains x, 95 p. : ill. (some col.), col. maps. Includes abstract. Includes bibliographical references (p. 83-84).

Thesis (Ph. D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2006. / Dr. Jennifer Michaels, Committee Member ; Dr. Jacek Jarzynski, Committee Member ; Dr. Jianmin Qu, Committee Member ; Dr. Laurence J. Jacobs, Committee Chair ; Dr. Kimberly E. Kurtis, Committee Co-Chair.

Thesis (M.E.)--University of Canterbury, 2006. / Typescript (photocopy). Includes bibliographical references. Also available via the World Wide Web.

Thesis (M.S.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains vii, 64 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 58-59).

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 93-96). Also available via the Internet.

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The use of fibre-reinforced polymer (FRP) as an internal reinforcement for concrete has many advantages over steel, most notably lack of corrosion which is considered to be a major problem for structures incorporating steel. In Europe alone, it is estimated that the annual repairing and maintenance costs associated with steel corrosion in infrastructure are around £20 billion (Nadjai et al., 2005). Despite of its corrosion resistance, the widespread use of FRP as an internal reinforcement for concrete was hindered due to its relatively weak performance at elevated temperatures, such as in the event of fire. Under heating, the polymer matrix in FRP softens, which causes bond degrading between reinforcement and concrete. The softening of polymer matrices occurs around their glass transition temperatures, which is typically in the range of 65– 150 °C. The sensitivity of FRP bond to temperature is recognised in design guidelines, therefore many advise against utilising FRP as an internal reinforcement for concrete in structures where fire performance is critical. On the other hand, fibres, the other component of FRP, can tolerate temperatures much higher than polymer matrices. This research investigates a new design for FRP internal reinforcement, which exploits the fact that the FRP fibres in general and carbon fibres in particular are capable of sustaining a large proportion of their original strength at high temperatures. Instead of the traditional way of using separate bars, FRP reinforcement was made as closed loops produced through the continuous winding of carbon fibre tows. When the surface bond degrades at elevated temperatures, interaction with concrete can still be provided through bearing at loop ends. The concept of FRP loops was investigated through a series of experimental work. Firstly, the performance of carbon FRP (CFRP) loops was evaluated through a series of push-off tests in which specimens consisting of CFRP loops bridging two concrete cubes were tested in pull-out using hydraulic jacks. Specimens with straight and hooked reinforcement were produced as well for comparison. A total number of 18 specimens were tested at ambient temperature, glass transition temperature (Tg), and above Tg. Results showed that while at ambient temperature there was no distinction in performance. At elevated temperatures, CFRP loops developed strength about three times higher than specimens with straight or hooked bars. Also, while failure mode occurred due to de-bond in the case of straight and hooked reinforcement, rupture failure occurred with CFRP loops. For better demonstration of the concept in more realistic conditions, four-point bending tests were conducted upon 28 beam specimens reinforced either with CFRP loops or straight bars as flexural reinforcement. Beams were tested under monotonic loading at ambient temperature, or under sustained loads with localised heating over the midspan region that contained the reinforcement overlaps. The benefit of CFRP loops became evident in the elevated temperature tests. Beam specimens with spliced straight bars failed due to debonding after a short period (up to 15 minutes) of fire exposure. Conversely, the fire endurance increased four to five times when CFRP loop reinforcement was used. Unlike straight bars, debonding failure was avoided as failure occurred due to reinforcement rupture. The overlap length of the CFRP loops was found to be important in the order for the loop to develop full capacity. Premature failure can occur with short overlap length due to shear off concrete within the overlap zone. The presence of transverse reinforcement increases confinement levels for reinforcement, so the bond failure of straight bars at ambient temperature testing was eliminated when stirrups were provided. However, at elevated temperatures straight bars failed by pull-out even in presence of transverse reinforcement. To facilitate design with CFRP loops, a numerical analysis tool was developed to calculate the bond stress-slip response of reinforcement at ambient and elevated temperatures. A Matlab programme was designed based on a one-dimensional analytical model for steel. The bond law was modified to be used for CFRP reinforcement. Other analytical models from the literature to account for bond degradation with temperature and tensile strength of curved FRP were also utilised. The developed Matlab code has the capability of producing slip, axial stress, and bond stress distribution along reinforcement. The novel FRP loop reinforcement was demonstrated to be a promising solution for enhancing the fire performance of CFRP internal reinforcement at elevated temperatures. It contributes to removing a major obstacle preventing widespread use of FRP-reinforced concrete, and paves the way for CFRP reinforcement to be used in situations where fire performance is critical.

Coal powered power plants account for more than 40 percent of the electricity production of the United States. The combustion of coal results in a large number of solid waste materials, or coal combustion byproducts (CCBs). These waste materials are stored in landfill or ponds. The construction industry is heavily reliant on concrete which is used to make the building blocks for any type of structures, bricks. Concrete is a composite material made of a binder and coarse and fine aggregate. The most widely used binder in concrete production is Ordinary Portland Cement (OPC). Since cement manufacture is costly and environmentally damaging, research has increased in recent years to find a more readily available binder. This study aims at investigating the properties of Illinois fly ash as a binder in the production of geopolymer concrete. Geopolymer concrete is an innovative material made by using Alumina and Silica rich materials of geological origins as a binder as well as an alkali activated solution. Sodium Silicate and Sodium Hydroxide were used to make the activator solution of two different ratios. Geopolymer Concrete with a ratio of 1:1 of Sodium Silicate to Sodium Hydroxide reached a compressive strength above 6000 psi while samples made with a ratio of 1:2 reached a compressive strength above 4000 psi. This environmentally-friendly, green concrete was also found to have a cost comparable to conventional concrete.

Doctor of Philosophy / Civil Engineering / Kyle Riding / Pre-stressed concrete is used for manufacturing railroad ties. Air entrainment is used in concrete railroad ties to provide durability in freeze-thaw conditions commonly present in track. Vibration practices in pre-stressed concrete railroad tie plants could contribute to excessive air loss during manufacture and thus poor freeze-thaw resistance. Rheological properties of fresh concrete significantly influence the determination of how much air is lost during vibration. This research attempted to increase understanding of the effect of vibration on air bubble distribution and freeze-thaw resistance of concrete given certain compositions and rheological properties of concrete. The objective was achieved by examining the effect of different admixtures combinations, vibration parameters, and rheological properties on the air void system and freeze-thaw resistance of concrete. This research also proposed a method to measure rheological properties of concrete when vibrated and for concrete mixtures too stiff to measure using conventional rheology measurements. Results showed that delaying the initiation of vibration can cause significant air loss but does not necessarily decrease freeze-thaw performance of concrete. Results also showed that a majority of air loss occurs in the first 30 seconds of vibration. The types of admixtures used in the concrete mixture can significantly affect the air system and freeze-thaw durability of concrete; this effect was shown to be more pronounced in mixtures with low yield stress and plastic viscosity. While the peak vibration acceleration had a mild effect, the frequency and peak velocity of vibration did not seem to have a noticeable effect on the air system and freeze-thaw performance of concrete. Results also showed that rheological properties of stiff mixtures can be estimated by running the rheology test during vibration.

Recycled concrete aggregates (RCA) are an eco-sustainable alternative to traditional aggregates. The equivalent mortar volume method has been developed to design RCA concrete with comparable mechanical and strength properties to natural aggregate concrete by accounting for the adhered mortar that distinguishes RCA from natural aggregates. This method also presents an opportunity to reduce the cement content of RCA concrete, increasing its cement efficiency. Modifications to mix design procedures were introduced to improve the fresh state properties of RCA concrete with a 19% cement reduction compared to the control mix. Beams cast with the RCA concrete had similar flexural capacity to corresponding control beams, however the shear strength varied as a function of RCA content in the concrete. Polished core samples taken from RCA members showed that crack development and aggregate interlock in RCA members is influenced by the aggregate properties and the spacing of coarse aggregates, indicating that knowing the compressive strength of RCA concrete is not the only parameter required for member design.