Doctoral Dissertations

Keywords and Phrases

Fiber alignment; Rheology; Shrinkage; Structural rehabilitation; Thixotropy; Ultra-high-performance concrete


"The objective of this research is to develop two classes of ultra-high-performance concrete (UHPC), one with self-consolidating consistency and the other with improved thixotropy. Tailoring the rheological properties of low yield stress UHPC can improve dispersion and orientation of steel fibers used in the design of UHPC, hence enhancing the tensile and flexural properties. Similarly, improving the thixotropy of UHPC can enable unique performance for the design of thin bonded bridge deck overlay. The research investigated various thixotropy enhancing admixtures to enhance the structural build-up at rest of UHPC. A total of 16 bonded overlay slab specimens were used to investigate the effect of overlay thickness, fiber volume, and shrinkage of self-consolidating UHPC on the performance of such composite elements.

Test results indicated that the key factors influencing the tensile/flexural properties of UHPC due to fiber orientation included the fiber embedment length, fiber number, and fiber-matrix bond strength. Fiber distribution of UHPC was found to depend on the rheological properties of the suspending mortar and casting method. The use of welan gum or diutan gum was more effective to enhance thixotropy compared to other specialty admixtures. Low-shrinkage UHPC led to crack-free overlay even after 30 months of outdoor exposure with temperature varying from -10 to 40°C. Such UHPC overlay slabs exhibited 85% to 135% higher flexural capacity compared to latex-modified concrete overlay slabs. The increase of overlay thickness from 25 to 50 mm led to 30% to 40% enhancement in flexural capacity of UHPC overlay slabs. Such improvement was 15% to 20% when the fiber volume increased from 2% to 3.25%"--Abstract, p. iv


Khayat, Kamal

Committee Member(s)

Kumar, Aditya
Ma, Hongyan
Sneed, Lesley
Chandrashekhara, K.


Civil, Architectural and Environmental Engineering

Degree Name

Ph. D. in Civil Engineering


Missouri University of Science and Technology

Publication Date

Spring 2022


xxviii, 370 pages

Note about bibliography

Includes_bibliographical_references_(pages 363-369)


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Document Type

Dissertation - Open Access

File Type




Thesis Number

T 12233