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Öğe Development of gravitational search algorithm model for predicting packing density of cementitious pastes(ELSEVIER, 2020) Banyhussan, Qais S.; Hanoon, Ammar N.; Al-Dahawi, Ali; Yildirim, Gurkan; Abdulhameed, Ali A.Wet packing approach is recently used to design different kinds of concrete. To achieve an optimal particle packing density, the particles should be chosen in a way to fill the voids between larger particles with smaller ones for obtaining a dense and stiff particle structure. The majority of past research on packing density has focused on the evaluation of the particle size distribution of granular matrix to gain improvements in the packing density of cementitious materials, while limited attention has been paid to the construction of a model to estimate the packing density value. To serve that purpose, in this study, a series of 216 collected samples were used for proposing a model. The dataset was divided into two main sets for construction and verification of the model. As the basis for the packing density modeling, use of the gravitational search algorithm (GSA) was proposed. Design of experiment (DOE) software was used to evaluate the contribution of each variable on the proposed model. The outcomes indicate that among different parameters, water amount has the largest effect on the packing density value of cementitious pastes. Moreover, increases in the amounts of supplementary cementitious materials up to certain levels increase the packing density. The coefficient of variation (CoV) of the proposed model is 6.3% which reflects the accuracy and consistency of the model.Öğe Dimensional stability of deflection-hardening hybrid fiber reinforced concretes with coarse aggregate: Suppressing restrained shrinkage cracking(Ernst & Sohn, 2019) Yildirim, GurkanHigh Performance Fiber Reinforced Concretes (HPFRCs) with deflection-hardening capability are relatively novel materials with high damage tolerance. However, mixture proportions of such materials are mostly designed with fine aggregates for easier/homogenous fiber distribution and low matrix fracture toughness which increases the amount of cementitious materials as the main binder and related risk for dimensional instability, high cost, and environmental unfriendliness. Here, with the idea of developing concrete that is free of shrinkage-related cracking at a more reasonable price, deflection-hardening HPFRC mixtures incorporating different amounts of coarse aggregates (with maximum size of 12mm) were developed with different mixture parameters (fiber types/dosages and fly ash contents) and tested for their dimensional stability by focusing mainly on the drying and restrained shrinkage measurements. Experimental results reveal that the combined effectiveness of utilizing hybrid fiber reinforcement and high amounts of coarse aggregates by properly adjusting the matrix properties without compromising high ductility (deflection-hardening behavior) can help the realization of possible producibility of HPFRC mixtures that are completely free of restrained shrinkage-related cracking. The findings of this study are believed to make a significant impact on the wide-spread usage of deflection-hardening HPFRC mixtures with similar ingredients to that of conventional concrete in actual field conditions.Öğe Effects of Mixture Design Parameters on the Mechanical Behavior of High-Performance Fiber-Reinforced Concretes(ASCE-AMER SOC CIVIL ENGINEERS, 2020) Erdem, Tahir K.; Demirhan, Serhat; Yildirim, Gurkan; Banyhussan, Qais S.; Sahin, Oguzhan; Balav, Mohammad H.; Sahmaran, MustafaThe main purpose of this research is to assess the influence of different design parameters on the mechanical performance of high-performance fiber-reinforced concrete (HPFRC) mixtures. Special attention is also paid to achieving deflection-hardening behavior in the presence of a large amount of coarse aggregates. Different mixture design parameters were the initial curing ages (3, 7, 28, and 90 days), ratios of Class F fly ash (FA) to portland cement (PC) (0.0, 0.2, and 0.4), addition/type of nanomaterials [nanosilica (NS), nanoalumina (NA), and nanocalcite (NC)], and combinations of fibers [polyvinyl-alcohol + steel (P, S) or brass-coated microsteel + steel (B, S)]. The experimental program included the evaluation of compressive strength, flexural strength, and midspan deflection results in addition to test parameters recorded under biaxial flexural loading via a series of square panel tests, including peak load and energy absorption capacities. Test results revealed that deflection-hardening response coupled with multiple microcracks can be obtained when large amounts of coarse aggregates are available for all HPFRC mixtures. As expected, experimental results change depending on the different curing ages and FA/PC ratios. The most distinctive parameters affecting the results are addition/type of nanomaterials and the presence of different fiber combinations. In the presence of nanomaterials, all results from the different tests improved, especially for NA and NS inclusions. With slight concessions in flexural deflection results, B fiber is shown to be a successful candidate to fully replace costly P fibers because most properties of B, S fiber-reinforced HPFRC mixtures outperformed those with P, S fibers, both under four-point bending and biaxial flexural loading.Öğe Evaluation of Mechanical and Microstructural Properties of Engineered Geopolymer Composites with Construction and Demolition Waste-Based Matrices(Asce-Amer Soc Civil Engineers, 2024) Kul, Anil; Ozcelikci, Emircan; Ozel, Behlul Furkan; Gunal, Muhammed Faruk; Yildirim, Gurkan; Bayer, Ismail Raci; Demir, IlhamiThe main purpose of this work was to combine the advantages of increased material greenness, waste upcycling, reduced raw material demand, and the superior characteristics of traditional engineered cementitious composites (ECCs). To this end, engineered geopolymer composites (EGCs) with matrices based entirely on components from construction and demolition waste (CDW) as precursors and aggregates were developed. The CDW-based precursors included roof tiles, red clay bricks, hollow bricks, glass, and concrete. Different combinations of sodium hydroxide, sodium silicate, and calcium hydroxide were used as alkaline activators. Hybridized polyethylene and nylon fibers were used as fibers. To investigate the influences of the additional calcium source, slag-substituted versions of the same mixtures were produced. At the fresh state, Marsh cone and mini-slump tests were performed. At the hardened state, mechanical property tests (compressive strength and four-point bending) and microstructural characterization tests (X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy) were conducted. The findings revealed that, regardless of the mixture composition, all EGCs exhibited a deflection-hardening response coupled with multiple microcracking behavior. The 28-day average ranges for compressive strength, flexural strength, and midspan deflection results were 25.2-42.1 MPa, 6.2-9.5 MPa, and 14.1-28.3 mm, respectively. Slag substitution mostly improved the mechanical performance of EGCs. The main geopolymerization products were sodium aluminosilicate hydrate (NASH), calcium aluminosilicate hydrate (CASH), and C-(N)-ASH gels, the formation of which varied depending on the type of precursor and activator.Öğe Impact behaviour of nanomodified deflection-hardening fibre-reinforced concretes(ICE PUBLISHING, 2020) Demirhan, Serhat; Yildirim, Gurkan; Banyhussan, Qais Sahib; Koca, Kemal; Anil, Ozgur; Erdem, Recep Tugrul; Sahmaran, MustafaThe behaviour of concrete under sudden impact loads is complex. Moreover, very little is known about the impact behaviour of high-performance fibre-reinforced concretes (HPFRCs). To account for this, nanomodified deflection-hardening HPFRC mixtures incorporating coarse aggregates were produced with three ratios of fly ash to Portland cement (0.0, 0.2 and 0.4), three nanomaterials (nanosilica, nano-alumina and nanocalcite) and two hybridised fibre combinations (hooked-end steel with polyvinyl alcohol, or hooked-end steel with brass-coated microsteel) and tested for basic mechanical properties and flexural impact resistance. After experimental testing, beams used in impact testing were modelled using Abaqus. Cubic compressive strength did not change significantly with the differences in mixture parameters, although this was not the case for flexural parameters. For a given fly ash/Portland cement ratio and nanomaterial type, mixtures with hooked-end steel and polyvinyl alcohol fibres exhibited higher displacement and lower flexural strength capacity than those with hooked-end steel and brass-coated microsteel fibres. Nano-alumina contributed best to the development of mechanical properties and impact resistance of HPFRCs, followed by nanosilica and nanocalcite. Results validate the idea that costly polyvinyl alcohol fibres can be fully replaced with brass-coated microsteel fibres without risking mechanical properties and impact resistance, as long as matrix properties are properly controlled.Öğe Impact resistance of deflection-hardening fiber reinforced concretes with different mixture parameters(Ernst & Sohn, 2019) Banyhussan, Qais S.; Yildirim, Gurkan; Anil, Ozgur; Erdem, R. Tugrul; Ashour, Ashraf; Sahmaran, MustafaThe impact behavior of deflection-hardening High Performance Fiber Reinforced Cementitious Concretes (HPFRCs) was evaluated herein. During the preparation of HPFRCs, fiber type and amount, fly ash to Portland cement ratio and aggregate to binder ratio were taken into consideration. HPFRC beams were tested for impact resistance using free-fall drop-weight test. Acceleration, displacement, and impact load versus time graphs were constructed and their relationship to the proposed mixture parameters were evaluated. The paper also aims to present and verify a nonlinear finite element analysis, employing the incremental nonlinear dynamic analysis, concrete damage plasticity model, and contact surface between the dropped hammer and test specimen available in ABAQUS. The proposed modeling provides extensive and accurate data on structural behavior, including acceleration, displacement profiles, and residual displacement results. Experimental results which are further confirmed by numerical studies show that impact resistance of HPFRC mixtures can be significantly improved by a proper mixture proportioning. In the presence of high amounts of coarse aggregates, fly ash, and increased volume of hybrid fibers, impact resistance of fiberless reference specimens can be modified in a way to exhibit relatively smaller displacement results after impact loading without risking the basic mechanical properties and deflection-hardening response with multiple cracking.Öğe Nano-tailored multi-functional cementitious composites(ELSEVIER SCI LTD, 2020) Ozturk, Oguzhan; Yildirim, Gurkan; Keskin, Ulku Sultan; Siad, Hocine; Sahmaran, MustafaThis paper explores the effects of single and binary use of nano-additions on the self-sensing and self-healing efficiencies of cementitious composites in achieving a material that combines high mechanical and multifunctional performances. The researchers studied three nano-tailored cementitious compositions incorporating nano-silica (NS), multi-walled carbon nanotubes (CNT) and binary NS/CNT, as well as control composites prepared without nano-additions. The study included compressive strength testing on sound specimens and an evaluation of combined self-sensing/self-healing capabilities with electrical resistivity (ER) measurements conducted before and after preloading and during the self-healing recovery stage. Recovery rates were also evaluated via crack width measurements recorded by video microscope and compared to ER testing results. To account for different self-healing products, microstructural characterization was performed on healed cracks using scanning electron microscopy coupled with EDX (SEM/EDX) and thermo-gravimetric (TG/DTG) analyses. Results show that while the single use of CNT can promote self-sensing and self-healing properties, using binary NS/CNT can significantly enhance these performances. The density and amounts of C-S-H and CaCO3 in healed cracks increased with the addition of nano-materials, especially for the binary NS/CNT.Öğe Performance of engineered cementitious composites under drop-weight impact: Effect of different mixture parameters(Ernst & Sohn, 2019) Yildirim, Gurkan; Khiavi, Farhad Emami; Anil, Ozgur; Sahin, Oguzhan; Sahmaran, Mustafa; Tugrul Erdem, RecepCurrent research focuses on the experimental and numerical determination of impact performance of engineered cementitious composites (ECC). Performance assessment of ECC beams with different mixture parameters was made. Mixtures were produced with different replacement rates of Class-F fly ash and slag with Portland cement, water to binder ratios and fiber types (polyvinyl alcohol [PVA] and nylon [N]). Experimental works were validated with incremental dynamic analyses performed by ABAQUS finite element software. Impact testing results were further supported by mechanical property results. Results reveal that each individual mixture parameter used is distinctively effective in modifying the properties under both sudden impact and slow static loading. In brief, enhanced impact resistance is noted when ECC is produced with slag, low amounts of pozzolanic materials, low W/B ratio, fiber addition and PVA fibers. Experimental results were also in line with the numerical results from ABAQUS largely. Significantly, cost-effective N fibers were also shown to be fully replaceable with costly PVA fibers without jeopardizing mechanical/impact performance, if mixture design parameters are adjusted suitably. Current research is likely to attract further research on the development of ECC that is with lower cost and comparable impact/mechanical performance with regards to widely studied more expensive counterparts in the literature.Öğe Role of Nanosilica on the Early-Age Performance of Natural Pozzolan-Based Blended Cement(Amer Concrete Inst, 2018) Yildirim, Gurkan; Dundar, Burak; Alam, Burhan; Yaman, Ismail Ozgur; Sahmaran, MustafaThis investigation focused on the microstructural, workability, mechanical, and hyration evolution of blended cements composed of natural pozzolan with nanosilica (NS). In Turkey, the most common supplementary cementitious materials are natural pozzolans of volcanic origin. Volcanic pumice is a natural pozzolan produced by the release of gases during the cooling and solidification of lava. In this study, pumice powders with two different levels of fineness were used to replace ordinary portland cement (OPC) at 15%, 30%, and 45% by weight. Seven mixtures were proposed with different levels of pumice fineness and OPC replacement rates, as well as an additional control mixture without pumice powder. Companion mixtures were also produced by adding 3% NS (by total weight of cementitious materials) into the proposed mixtures for a total of 14 different mixtures. Fresh properties measured by flow test and mechanical performance validated by microstructural analyses show that in the presence of NS, up to 30% pumice powder can be replaced with OPC without risking workability and 2-day strength measurements. In cases where the early-age strength is necessary after the first 7 days, the same level of replacement can be increased up to 45%. The successful outcomes of this study may compensate for the drawbacks of OPC use in concrete mixtures and popularize the use of natural pozzolans in locations where they are more commonly available.Öğe Self-sensing capability of Engineered Cementitious Composites: Effects of aging and loading conditions(ELSEVIER SCI LTD, 2020) Yildirim, Gurkan; Ozturk, Oguzhan; Al-Dahawi, Ali; Ulu, Adem Afsin; Sahmaran, MustafaSelf-sensing capability of 7-, 28-, 90- and 180-day-old Engineered Cementitious Composites (ECC) incorporated either with carbon fibers (CF/ECC-CF) at micro-scale or multi-walled carbon nanotubes (CNT/ECC-CNT) and carbon black (CB/ECC-CB) at nano-scale were investigated herein. Mechanical properties (compressive strength, splitting tensile strength/deformation, flexural strength/deformation) of different-age mixtures were evaluated. Control mixture (ECC-Control) without any carbon-based material was also produced and tested for comparison. Depending on the loading condition, equipment utilizing either direct current (DC) or alternating current (AC) was used for self-sensing assessments. Results showed that carbon-based materials generally improve the mechanical properties of ECC-Control specimens depending on the type of carbon-based materials, specimens' age and loading conditions. All specimens sensed different types of damage except 180-day-old ECC-Control specimens loaded under uniaxial compression and splitting tension due to abrupt increments in impedance results exceeding the limits of testing device which revealed the importance of presence of electrically-conductive materials for achieving enhanced self-sensing capability independent of aging, testing configuration/equipment, loading conditions and microcrack characteristics. CF is the best to improve self-sensing capability of ECC-Control specimens for all ages and loading conditions. Self-sensing performances of ECC-CNT and ECC-CB are comparable and utilization of nano-size carbon-based materials is suggested in cases where reversibility in self-sensing is needed. (C) 2019 Elsevier Ltd. All rights reserved.
