Date of Graduation

5-2023

Document Type

Thesis

Degree Name

Master of Science in Civil Engineering (MSCE)

Degree Level

Graduate

Department

Civil Engineering

Advisor/Mentor

Prinz, Gary S.

Committee Member

Murray, Cameron D.

Second Committee Member

Hale, W. Micah

Keywords

Prestressing; Concrete; Shape memory alloy

Abstract

Prestressing concrete is common practice in the construction industry. Current prestressing methods are often used for large, straight members and come with geometric limitations for curved or thin-walled members. Shape memory alloy short fibers embedded within concrete mixes may allow for the prestressing of geometries not possible with traditional methods. This study reviews past research on prestressing concrete with shape memory alloys, evaluates the achievable recovery stress within an Fe-SMA (when deformed at room temperature), and examines the mechanical behavior of Ductal dark grey UHPC when heated to 250 °C. The flexural behavior, compressive strength, and fiber-to-concrete bond strength of heated and non-heated UHPC specimens are investigated to better understand the effect high temperatures on concrete properties. Results from flexure tests indicate heating specimens increases stiffness and modulus of rupture by 6.8% and 28.1 %, respectively. The compressive strength of heated specimens was on average 53.5% higher than non-heated specimens. Steel fiber pullout tests show that fiber-to-concrete bond strength typically increases when specimens are heated to 250 °C. The tests on heated UHPC specimens show that the Ductal mix used behaves favorably upon heating and would likely work well for Fe-SMA prestressing applications. Fe-SMA recovery stress was found to reach approximately 50 ksi. This indicates that Fe-SMA fibers may be able induce about 354 psi of prestress for every 1% (per volume) of Fe-SMA fibers added to a UHPC mix.

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