DEVELOPMENT OF ULTRA-HIGH PERFORMANCE STRAIN-HARDENING CEMENTITIOUS COMPOSITES WITH STRAIN CAPACITY OVER 10%

Abstract

This thesis describes a process of developing ultra-high performance strain-hardening cementitious composites (UHP-SHCCs) with tensile strength, strain capacity, and energy absorption capacity of 9.8 MPa and 14.9%, and 1310 kJ/m3. Also, its flexural behaviors under static and impact loading conditions along with its reinforcing efficiency on flexural behavior of non-reinforced normal concrete were evaluated from the material perspective. As fiber-reinforced cementitious composites have a complex network of influential factors affecting their physical and chemical properties, many factors were specifically inspected through repetitive mechanical tests followed by microstructural and micromechanical analyses that were performed before, after, and even during the tests. Types and aspect ratios of reinforcing fibers, development of the microstructure of the matrix based on different matrix compositions, curing conditions influencing hydration and shrinkage mechanisms, and properties at the fiber-matrix interface were all taken into consideration. From ultra-high performance cementitious composite (UHPCC) to engineered cementitious composite (ECC) and strain-hardening cementitious composite (SHCC) were designed and improved based on previous studies, the author’s knowledge, and database obtained from preliminary experiments and research. To specify the influence of fiber-matrix interaction on the mechanical performance of the composite, steel and polyethylene fibers were hybridized in the UHPCC matrix. This was to improve the matrix damage mechanism. Subsequently, the development of UHP-SHCCs progressed based on the repetition of designing mixture composition and performing mechanical tests followed by diverse analyses. Lastly, one of the devised UHP-SHCC mixtures was proved to be more effective than ultra-high performance fiber-reinforced cementitious composite and ECC considering overall mechanical performances: tensile performance, static and impact flexural performance, and strengthening of the flexural behavior of normal concrete.