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Öğe Autogenous Self-healing Assessment of 1-Year-Old Cementitious Composites(Springer Science and Business Media B.V., 2021) Yıldırım, Gürkan; Ulugöl, Hüseyin; Öztürk, Oğuzhan; Şahmaran, MustafaTraditional concrete materials are prone to cracking and as cracks form, durability issues arise which reduce the expected service life of the materials followed by structures incorporating them. This, in many occasions, may lead to repetitive repair and maintenance or even re-construction of certain structural/non-structural sections and structures. Thus, it is highly desirable to reduce the chance and/or further development of cracking. Engineered Cementitious Composites (ECC) are feasible materials to suppress cracking formation and progression through their strain-hardening response under uniaxial tensile loading conditions. Even at the stage of failure, these materials exhibit micron-size cracks which significantly improve the capability to resist against detrimental durability issues. Moreover, these microcracks are constantly reported to be closed through autogenous healing mechanisms with no external interference from outside which significantly improve the mechanical and durability performance and service life of these materials and structures incorporating them. However, the performance of autogenous self-healing in ECC is called into question, especially for late-age specimens since reactions which produce products to plug the micro-size cracks stabilize as the specimens get more and more mature. To clarify this subject, in this study, 1-year-old specimens produced from ECC mixtures incorporated with different mineral admixtures (i.e. Class-F fly ash and ground granulated blast furnace slag) were tested for their self-healing performance. For self-healing evaluation, specimens which were severely preloaded for creating microcracks, were subjected to four different curing conditions which included “Water”, “Air”, “CO2-water” and “CO2-air” for 90 additional days beyond initial 1 year. Tests used for self-healing assessments were electrical impedance (EI) and rapid chloride permeability (RCP). Results indicate that water is a must-have component for enhanced autogenous self-healing efficiency. “CO2-Water” curing results in the most effective self-healing performance regardless of the composition of ECC mixtures. By properly adjusting mixture proportions and curing conditions, microcracks as large as nearly half a millimeter (458 µm) can be healed in only 30 days of further curing. Overall, results clearly suggest that late-age autogenous self-healing capability of ECC can be made as effective as the early-age with proper further environmental conditioning and mixture design. © 2021, The Author(s), under exclusive license to Springer Nature Switzerland AG.Öğe Determination of Autogenous Self-healing Capability of Cementitious Composites Through Non-destructive Testing(Springer Science and Business Media B.V., 2021) Yıldırım, Gürkan; Öztürk, Oğuzhan; Ulugöl, Hüseyin; Hatem, Muhammed; Şahmaran, MustafaUnlike conventional concrete and fiber reinforced concrete, Engineered Cementitious Composites (ECC) display closely spaced multiple microcracks through strain/deflection-hardening response when subjected to tension-based loadings. These multiple microcracks allow ECC to be characterized with inherent autogenous self-healing capability. With the emergence of cement-based composites exhibiting multiple tight cracking, possibility for favoring the intrinsic self-healing behavior increased. Self-healing phenomenon in cementitious composites is being studied extensively nowadays. Although, great number of tests utilized to evaluate the self-healing mechanism in cementitious composites, implementation can be time consuming in some occasions and results from different tests may not always well-suit. Thus, different from other studies in literature, direct electrical impedance (EI) measurements were used in the present study to evaluate the self-healing performance of ECC mixtures along with rapid chloride permeability test (RCPT) and resonant frequency (RF) measurements. Experimental results revealed that EI testing is rather easy to perform and takes very limited time but it seems that the method itself is markedly influenced by anything modifying ionic state of specimens. Therefore, it looks like a hard task to very accurately assess the self-healing performance of ECC specimens considering the fact that both ongoing hydration and calcium carbonate precipitation which are regarded to be the main mechanisms contributing to the autogenous self-healing significantly changes the specimens’ pore solution chemistry. Well-fitting exponential relationship exists between EI and RCPT measurements at different ages regardless of the mixture and specimen type. However, results from RF tests do not correlate either with EI or RCPT results which is attributed to the different parameters having paramount influence on the individual tests. Although results from different tests do not always correlate well among themselves, three different tests used for the present study are capable of monitoring the self-healing behavior with differing efficiencies. © 2021, The Author(s), under exclusive license to Springer Nature Switzerland AG.Öğe Engineering Properties of Very High Volume Fly-ash Cementitious Composites Reinforced with Synthetic and 5D Steel Fibers(Kırıkkale Üniversitesi, 2022) Öztürk, OğuzhanIn cement-based mortars, using high volume of fly ash modifies several fresh and hardened properties besides an economical design. Although it varies according to the type of fly ash to be used, mixture design proving high amount of fly ash which is pre-targeted according to engineering properties may modify the relationship between matrix and fibers in the cement-based mortars. In this study, cement-based composites containing a very high percentage of fly ash (80%) by total binder weight were developed with polyamide fiber (PL) and five-dimensional steel fibers (5D-ÇL) in single and hybrid forms and investigated in terms of engineering properties. In addition, compressive strength of fiber reinforced composites were assessed at the curing ages of 7, 28, 60 and 90 days. The engineering properties of cementitious composites reinforced with single and binary use of different fibers were obtained by considering load and displacement values at yield and fracture points, maximum load-carrying capacities, ductility, rigidity and energy dissipation capacity. Results reveal that binary use of PL and 5D-ÇL provided a synergy in terms of matrix-fiber bond behavior compared to their single use thus increasing the ductility, initial rigidity and energy dissipation capacities. In addition, in the case of examining single use of fibers, it was found that 5D-ÇL was more effective than PL fibers for improving the engineering properties. It is considered that composites having fly ash/cement ratio of 4.0 by weight are sustainable in terms of economically and performance in the civil engineering applications where early-age mechanical properties is not significative.
