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Öğe Characterization of carbon fiber reinforced conductive mortars filled with recycled ferrochrome slag aggregates(2022) Maraşlı, Muhammed; Doğan, Fatih; Dehghanpour, Heydar; Subaşı, SerkanRecently, it has been known that carbon fiber, a conductive fiber, is used in different mix- ture designs and the development of electrically conductive cementitious materials. Howev- er, the evaluation of ferrochrome slag as a recycled aggregate in the mixture of these special concretes has still not been investigated. In this study, electrically conductive mortars were produced using 100% recycled ferrochrome slag aggregate with a particle size of less than 1 mm as filling material and using carbon fiber in 4 different ratios, 0%, 0.5%, 0.75%, and 1%. To investigate the electrical conductivity properties, the resistivity values of the samples were measured at five different times within 2–180 days. In addition, 28-day compressive strength, flexural strength, dynamic resonance, ultrasonic pulse velocity, Leeb hardness, scanning elec- tron microscope, and X-Ray Diffraction tests were performed on all samples. The results were compared with the literature, proving that ferrochrome slag could be used as a reasonable aggregate in conductive mortars. The age effect was minimal in CF-added mixtures. With the addition of 1% CF, the resistivity values decreased approximately 40 times compared to the ref- erence. Moreover, SEM analyses of the CF-0.75 sample showed that the CFs adhered to form a conductive network between the components in the ferrochrome-filled compact structure.Öğe Development of a maturity method for GFRC shell concretes with different fiber ratios(Taylor & Francis Ltd, 2022) Maraşlı, Muhammed; Subaşı, Serkan; Dehghanpour, HeydarThe use of glass fiber reinforced concrete (GFRC) in the construction industry is increasing due to its mechanical and physical properties. Waiting time of concrete in the mold and the removal of the mold at the right time are important in terms of strength. In conventional concretes, maturity models are widely used as a non-destructive method for early strength estimate. In this study, it is aimed to develop an estimate model of flexural and compressive strength in GFRCs using the maturity index method. In this context, glass fiber reinforced concretes were produced at the rates of 0%, 1%, 2% and 3%. Calcined kaolin and acrylic polymer were used as modification materials in the mixtures. Properties such as compressive, flexural, hardness, and shrinkage of specimens were investigated at different ages. The maturity-strength relationships of mixtures at different ages were examined by weighted maturity and Nurse-Saul methods. At the end of the study, two new models were developed to estimate the compressive and flexural strengths of GFRCs, taking into account all the data. The suggested models have been confirmed by examining them on all mix-age groups and comparing them with the literature.Öğe Effects of single-walled carbon nanotubes and steel fiber on recycled ferrochrome filled electrical conductive mortars(2022) Doğan, Fatih; Dehghanpour, Heydar; Maraşlı, Muhammed; Subaşı, SerkanThe production of electrically conductive concrete was introduced years ago among construction materials, generally for anti-icing. The present study investigates the electrical, mechanical, dynamic, and microstructural properties of recycled ferrochrome filled cementitious mortars, containing single-walled carbon nanotubes (SWCNTs) and steel fiber. 7, 14, and 28-day non-destructive and 28-day compressive and bending tests of cementitious conductive mortars obtained from five different mixtures were performed. Two-point uniaxial method was used to determine the electrical conductivity properties of the samples. The damping ratio of the samples was obtained by performing dynamic resonance tests. Ultrasound pulse velocity (UPV) and Leeb hardness tests were performed as other non-destructive testing methods. Microstructure analysis at the interfaces of conductive concrete samples were characterized by scanning electron microscopy (SEM), EDS (Energy-Dispersive X-ray Spectroscopy), and X-ray diffraction (XRD). According to the experimental results, all data agreed and confirmed each other. When SWCNT is used in combination with steel fiber, the conductive mortar samples exhibited reasonable conductivity, while their mechanical properties turned out to below.Öğe Experimental investigation of engineering properties of silica sand filled mortars containing high doses of SWCNT(2023) Doğan, Fatih; Dehghanpour, Heydar; Subaşı, Serkan; Maraşlı, MuhammedRecently, great efforts have been made by researchers on the mixture of electrically conductive concretes that have been developed for different purposes. In this study, an experimental research was carried out on electrically conductive mortar mixtures especially for shell elements produced for building facade cladding. Six different mixtures were produced, including the non-conductive reference mixture. Single-walled carbon nanotube (SWCNT) was used as nano-sized conductive additive material. SWCNT was added at 0.2% and 0.3% of cement weight. SF was added to the same mixtures as another group at the rate of 4% by total weight. 2, 14, 28, 90 and 180 days electrical resistivities of the obtained conductive mortar samples were measured. As a non-destructive method, dynamic resonance testing was performed and the 28-day damping rates of the samples were determined. Ultrasonic pulse velocity (UPV) and Leeb hardness tests were performed, respectively, by using other non-destructive testing methods to obtain information about the internal structure voids and surface hardness of the samples. SWCNT, which causes low machinability and therefore internal structure voids, caused a decrease in compressive strength and flexural strength, as well as a significant increase in electrical conductivity.Öğe Experimental Study on Engineering Properties of Recycled Olivine Aggregate Filled CF Reinforced Electrically Conductive Mortars(2024) Dehghanpour, Heydar; Doğan, Fatih; Subaşı, Serkan; Maraşlı, MuhammedElectrically conductive concretes produced for different purposes were introduced years ago and since then, intensive scientific research has been going on. Studies in the literature have generally been carried out on conventional concretes with electrical conductivity for floor applications. The current study investigates carbon fiber reinforced mortars filled with fine olivine aggregate. Fine aggregate filled mortars are generally produced for building facade applications. Within the scope of the study, the mechanical, electrical, dynamic and microstructural properties of cementitious mortars containing 0.5%, 0.75% and 1.0% carbon fiber and 100% recycled olivine aggregate were investigated. The purpose of performing dynamic resonance tests was to investigate the effect of carbon fiber on damping ratio. 28-Day compressive, flexural, dynamic resonance, ultrasonic pulse velocity (UPV), Leeb hardness and dry density tests of conductive mortar samples obtained from four different mixtures were performed. In addition, 2, 14, 28, 90 and 180 days electrical conductivity tests were carried out to determine their resistivity in different time intervals. The purpose of performing dynamic resonance tests was to investigate the effect of carbon fiber on damping ratio. While a significant positive effect of CF on electrical conductivity and damping ratio was observed, a negligible decrease in mechanical results was observed. Calcium silicate hydrate (C-S-H) structure formed by hydration using olivine filler in the cement mixture confirmed the binding formations.Öğe Investigation of Different Superplasticizers Effect on Workability and Strength Parameters in Ultra High Performance Concretes(2022) Maraşlı, Muhammed; Dehghanpour, Heydar; Seis, Muhammet; Kula, Betül İşbilir; Özdal, Volkan; Subaşı, SerkanThe use of ultra-high performance concretes (UHPC) in the modern construction industry is increasingly widespread. UHPCs are a type of concrete that provides advantages in solving many engineering problems. UHPCs have superior properties compared to conventional concretes in terms of workability, self-settling, as well as high strength and durability. However, although UHPCs have many advantages, achieving the desired workability is one of the biggest challenges of the production procedure, since they contain high amounts of powder materials. Therefore, the aim of this study is to determine the most suitable superplasticizer (SP) additive in terms of workability and strength by using different SP additives in UHPC mixtures. In this study, workability and strength parameters were tested on UHPC mixtures using 8 different SP additives. The SPs used were named A, B, C, D, E, F, G, H. First of all, the spreading diameters of the obtained mixtures were measured. For each mixture, compressive strength, unit weight, ultrasound velocity, Schmidt hammer rebound and Leeb hardness measurements were performed on 70x140 mm sized cylindrical samples taken on days 2, 7 and 28. Since SPs have a working principle at the interfaces of particles in the internal structure of concrete, different behaviors were observed on workability, even if a little. All the results obtained have been compared with the literature and it has been proven that they meet the UHPC specifications. As a result of the study, the best compressive strength value (127.83 MPa) was achieved with the G superplasticizer, and the flow diameter value was determined as 230 mm.Öğe Investigation of fracture mechanics, physical and dynamic properties of UHPCs containing PVA, glass and steel fibers(Elsevier Sci Ltd, 2022) Dehghanpour, Heydar; Subaşı, Serkan; Güntepe, Sefa; Emiroğlu, Mehmet; Maraşlı, MuhammedFracture energy, non-destructive testing, some physical and mechanical tests and microstructural investigations were performed on 18-month 0.7 V%, 1.3 V% and 2.0 V% PVA fiber, glass fiber (GF) and steel fiber (SF) reinforced Ultra High Performance Concretes (UHPCs). Fracture test was performed on Single Edge Notched Beams (SENB) to investigate fracture energy, dissipated energy, flexural strength, crack resistance index (CRI), and flexibility index (FI) of UHPCs. Dynamic modulus of elasticity and damping ratios of the UHPCs were calculated by performing resonance frequency tests on the SENB samples by ASTM C215 standard. In addition, compressive strength, static modulus of elasticity, electrical resistivity, ultrasonic pulse velocity (UPV), Leeb hardness, Schmidt hammer, and density tests were also performed on the cylindrical samples. Field Emission Scanning Electron Microscopy (FE-SEM) and Energy Dispersive X-Ray (EDX) analyzes were performed to examine the interaction between the UHPC matrix and different fibers. Among all the mixtures, an exceptionally positive effect of SFs on the all mechanical properties of the UHPCs was observed. Dynamic test results showed that the increase in fiber ratio increased the damping ratio of UHPCs irrespective of fiber type. The UPV and electrical resistivity results offered promising results regarding the internal structure of UHPCs.Öğe Investigation of mechanical and electrical properties of ultra-low rate SWCNT added UHPC(Gazi Univ, Fac Engineering Architecture, 2023) Seis, Muhammet; Subaşı, Serkan; Maraşlı, Muhammed; Dehghanpour, HeydarWith the development of nanotechnology, the use of nano materials with specific features in the construction industry, especially in the field of building materials, attracts attention by many researchers. According to the literature, carbon nanotubes (CNTs) are among the highly usable nanomaterials in the mixtures of cementitious materials. Although there are many studies on multi-walled carbon nanotube (MWCNT) added concretes, there are limited studies investigating the behavior of single-walled carbon nanotubes (SWCNTs) on concrete. In the present study, the mechanical and electrical properties of ultra-high performance concretes (UHPCs) produced by using SWCNT at the ratios of 0.0125, 0.020 and 0.025 % of cement weight were investigated. By adding 4.2 % steel fiber to the same mixtures, a total of 8 mixes with the reference were obtained. Conductivity and bending tests were carried out on 12X3X2 cm specimens. For electrical resistance measurement, the two-point uniaxial method, which is common in measuring cementitious materials, was used. According to the results, positive effects of SWCNT on mechanical properties have been observed. With the addition of SWCNT and increasing its ratio, the electrical resistance decreased, but it was found that high rates of SWCNT were required to increase the current rate. In addition, the effect of SWCNT was more pronounced in steel fiber added mixtures.Öğe Production and Characterization of GRC-SWCNT Composites for Shell Elements(Kaunas Univ Tech, 2022) Subaşı, Serkan; Dehghanpour, Heydar; Maraşlı, MuhammedNano-sized defects in Glass fiber Reinforced Concrete (GRC) shell elements can cause damage over time, leading to mechanical and durability problems. Therefore, in this study an experimental program was conducted to investigate the application of single-walled carbon nanotube as a nano-additive material in GRC. Since there is no study on GRCcarbon nanotube (CNT) composites in the literature, the behavior of CNTs on conventional concretes was discussed. Five different GRC-SWCNT composite mixtures containing 0, 0.007, 0.010, 0.015 and 0.020 wt.% single walled carbon nanotube (SWCNT) were obtained. Calcined kaolin and acrylic polymer were used as pozzolanic and chemical modification materials in the mixtures, respectively. Workability, density, capillarity, pressure, flexural, tensile, impact, Leeb hardness and FE-SEM tests of the produced samples were carried out. According to the results obtained, the optimum SWCNT ratio in GRC mixtures was found to be 0.015 %. It was observed that there was a linear relationship between the mechanical results. FE-SEM images confirmed that SWCNTs act as bridges for micro-cracks and reinforce the microstructure.
