Civil Engineering / İnşaat Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/13
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Conference Object Citation - WoS: 6Development of a New Test Method To Evaluate Dynamic Stability of Self-Consolidating Concrete(RILEM Publications SARL, 2016) Alami, Mohammad Musa; Erdem, Tahir Kemal; Khayat, Kamal H.Although many different test methods have been proposed to evaluate the static stability of self-consolidating concrete (SCC), limited test methods have been developed to determine dynamic segregation of SCC. In this study, a new apparatus was developed for testing the dynamic stability of SCC. The new method was called as "Dynamic Sieve Segregation Test" (DSST) which provides a numerical result referred to the "dynamic segregation ratio" (DSR). Higher DSR values indicate dynamically less stable mixtures. Several correlations were successfully established between the test results. SCC mixtures with higher slump flow, higher coarse aggregate-to-total aggregate ratio or higher maximum aggregate size (Dmax) resulted in higher DSR values. A maximum DSR value of 30% was proposed for a dynamically stable SCC. The repeatability of DSST was found to be high with a COV value of 5.30%. Based on the results, DSST was found to be a suitable method to evaluate the dynamic stability of SCC.Article Citation - WoS: 1Citation - Scopus: 1Generalized Regression Neural Network and Empirical Models To Predict the Strength of Gypsum Pastes Containing Fly Ash and Blast Furnace Slag(Springer Verlag, 2020) Erdem, Tahir Kemal; Cengiz, Okan; Tayfur, GökmenGypsum is widely used in constructions owing to its easy application, zero shrinkage, and excellent fire resistance. Several parameters can affect the properties of gypsum pastes. To study the strength of the gypsum pastes experimentally by trying all these parameters is time-consuming and costly. Therefore, artificial intelligence methods can be very useful to predict the paste strength, which, in turn, can reduce the number of trial batches. Based on experimental data, the generalized regression neural network (GRNN) and empirical models were developed to predict strength of gypsum pastes containing fly ash (FA) and blast furnace slag (BFS). Gypsum content, pozzolan content, curing temperature, curing duration, and testing age constituted the input variables of the models while the paste strength was the target output. The trained and tested GRNN model was found to be successful in predicting strength. Sensitivity analysis by the GRNN model revealed that the curing duration and temperature were important sensitive parameters. In addition to the GRNN model, empirical models were proposed for the strength prediction. The same input variables formed the input vectors of the empirical models. The same dataset used for the calibration of the GRNN model was employed to establish the empirical models by employing genetic algorithm (GA) method. The empirical models were successfully validated. The GRNN and GA_based empirical models were also tested against the multi-linear regression (MLR) and multi-nonlinear regression (MNLR) models. The results showed the outperformance of the GRNN and the GA_based empirical models over the others.Article Citation - WoS: 2Citation - Scopus: 3A New Method To Quantify the Robustness of Self-Consolidating Grouts(Elsevier, 2019) Erdem, Tahir Kemal; Bilgiç, Esra; Kanpara Cıvaş, ZüleyhaThere are different methods in literature to evaluate the robustness of highly fluid cementitious mixtures. However, no one of them gained widely acceptance due to the relative advantages and disadvantages involved in each of them. Therefore, there is still need for further research on this topic. This study proposes a new and relatively easy method for quantifying the robustness of self-consolidating grouts by calculating so-called robustness indices. Due to the more difficulty to produce robust mixtures for highly fluid mixtures obtained by very powerful chemicals, the method is based on the variations in the superplasticizer (SP) type and amount. Mineral admixture (fly ash or limestone powder) usage and water-to-binder ratio (w/b) were other parameters investigated in this study. It was found that SP type was the most important factor affecting the robustness. The effect of w/b was less when compared to SP type. The mixtures containing naphthalene-based SP were more robust than those containing polycarboxylate-based SP. Mineral admixture type and amount had the least effect on robustness. (C) 2019 Elsevier Ltd. All rights reserved.Article Citation - WoS: 19Citation - Scopus: 22Influence of Thixotropy Determined by Different Test Methods on Formwork Pressure of Self-Consolidating Concrete(Elsevier Ltd., 2018) Tuyan, Murat; Ahari, Reza Saleh; Erdem, Tahir Kemal; Andiç Çakır, Özge; Ramyar, KambizIn this experimental study, the influence of thixotropy determined by different test methods on the formwork pressure of self-consolidating concrete (SCC) with varying compositions was investigated. In order to determine the effect of water/binder (w/b) ratio, slump flow diameter and coarse aggregate/total aggregate (CA/TA) ratio on thixotropy and formwork pressure of SCC, fifteen concrete mixtures were prepared. Four different test methods i.e., “structural break-down area” (SBDA), “break-down percentage” (BDP), “drop in apparent viscosity” (DAV) and “yield value at rest” (YVR) were performed to determine the thixotropy of the SCC mixtures. Test results showed that the SBDA, DAV and YVR methods were more appropriate to evaluate the thixotropy of SCC than the BDP method. A strong correlation between thixotropy and formwork pressure was found using SBDA, DAV and YVR methods in SCC mixtures having low w/b ratio. There was a strong relationship between thixotropy determined by SBDA, BDP and DAV methods and formwork pressure in low slump flow SCC mixtures, while thixotropy determined by the YVR method showed good correlation with the formwork pressure in SCC mixtures having high slump flow values. Finally, new models were developed to estimate the formwork pressure of all kinds of mixtures as a function of thixotropy and time. The models were found to be successful for each of the thixotropy measurement method.Conference Object Citation - WoS: 1Development of a Proper Mix-Design for Impact Loading of Deflection Hardening Hybrid Fiber Reinforced Concrete(Springer Verlag, 2018) Alami, Muhammad Musa; Erdem, Tahir Kemal; Yardımcı, Mert Yücel; Aydın, SerdarThis study aims to develop a low-cost Hybrid Fiber Reinforced Concrete (HyFRC) that exhibits deflection hardening behavior under bending and has high energy absorption capacity under impact loading by determining proper combination of steel and polyvinyl alcohol (PVA) fibers. More than forty mixtures were prepared including two mixtures of conventional concrete, six mixtures of Engineered Cementitious Composites (ECC), and thirty-six mixtures of HyFRC. The design parameters were chosen as fly ash to cement ratio (1.2, 1.7 and 2.2), steel fiber type and amount (0.5%, 0.75%, and 1.25% by volume), PVA fiber amount (0.25% and 0.50% by volume), and maximum aggregate size (Dmax) of 8 mm and 16 mm. Several tests were carried out on fresh and hardened specimens such as bending, compression, and low-velocity flexural impact loading. Based on the results, it is found that the mixture with 0.75% steel fiber and 0.25% PVA showed the best performance for the aim of the study.Article Citation - WoS: 11Citation - Scopus: 12Cement Based Strain Sensor: a Step To Smart Concrete(Foundation Cement, Lime, Concrete, 2011) Teomete, Egemen; Erdem, Tahir KemalAccording to a report published in USA, 30% of the bridges in USA were found to be structurally de cient while concrete infrastructures have a state of material deterioration before the design life is reached (1). Earthquakes, material degradations and other environmental effects decrease the performance of the structures. The assessment of structures by structural health monitoring is very important to protect the lives of people. The best decision about a damaged structure after an earthquake can be made by use of structural tests and structural health monitoring. Structural tests and structural health monitoring are important steps in the decision making of asset management for maintenance and repair of infrastructures. The classical sensors (strain gauges, piezo-electric sensors) have low durability, low sensitivity and high cost. The low durability of classical sensors disables long term measurement while their high cost limits the amount of sensors that can be used (2). The addition of carbon ber to cement based material decreases the electrical resistance of the material. By application of load, the electrical resistance of the material changes (3-5).Article Citation - WoS: 5Citation - Scopus: 7Experimental and Modeling Study of Strength of High Strength Concrete Containing Binary and Ternary Binders(Foundation Cement, Lime, Concrete, 2011) Erdem, Tahir Kemal; Tayfur, Gökmen; Kırca, ÖnderSilica fume (SF), fl y ash (FA) and ground granulated blastfurnace slag (S) are among the most widely utilized mineral additions for normal strength concrete (NSC) and high strength concrete (HSC). High Reactivity Metakaolin (HRMK) is a relatively new mineral addition, produced by calcination of highly pure kaolin. The replacement of cement with HRMK increases the strength, especially at early ages, and improves durability of concrete. (1-3). Pumice (P) is a porous volcanic glass containing 60-75 SiO2% and 13-17% Al2O3. When fi nely ground, it shows pozzolanic characteristics but it is generally used as a lightweight aggregate in the concrete industry (4, 5). HRMK and P have white color and, therefore, are useful for production of white concrete when applied with white Portland cement (WPC)Article Citation - WoS: 123Citation - Scopus: 140Effect of Various Supplementary Cementitious Materials on Rheological Properties of Self-Consolidating Concrete(Elsevier Ltd., 2015) Saleh Ahari, Reza; Erdem, Tahir Kemal; Ramyar, KambizIn design of self-consolidating concrete (SCC) for a given application, the mixture's rheological parameters should be adjusted to achieve a given profile of yield stress and plastic viscosity. Supplementary cementitious materials (SCM) can be useful for this adjustment in addition to their other advantages. In this study, the rheological properties of 57 SCC mixtures with various SCM were investigated for a constant slump flow value. For this aim, various amounts of silica fume (SF), metakaolin (MK), Class F fly ash (FAF), Class C fly ash (FAC) and granulated blast-furnace slag (BFS) were utilized in binary, ternary, and quaternary cementitious blends in three water/binder ratios. Results showed that SF and BFS decreased plastic viscosity and V-funnel time values in comparison with mixtures containing only Portland cement (PC). However the opposite tendency was observed when MK, FAC and FAF were incorporated with PC. Substitution of PC with SF, MK and FAC increased high range water reducer (HRWR) demand in the SCC mixtures having constant slump flow. Use of SCM in SCC mixtures increased yield stress values. Good correlations were established between plastic viscosity and V-funnel flow time values for all w/b ratios.Article Citation - WoS: 70Citation - Scopus: 86Permeability Properties of Self-Consolidating Concrete Containing Various Supplementary Cementitious Materials(Elsevier Ltd., 2015) Saleh Ahari, Reza; Erdem, Tahir Kemal; Ramyar, KambizIn this study, permeability properties of 17 self-consolidating concrete (SCC) mixtures containing various supplementary cementitious materials (SCM) were investigated by different experimental approaches. The effects of SCM type and content on the compressive strength, rapid chloride ion permeability (RCPT), water penetration depth, water absorption and sorptivity were studied. For these purposes, various amounts of silica fume (SF), metakaolin (MK), Class F fly ash (FAF), Class C fly ash (FAC) and granulated blast-furnace slag (BFS) were utilized in binary, ternary, and quaternary cementitious blends. Results showed that partial replacement of PC by SCM increased the compressive strength of control mixtures at 28 and 90 days (except for FAF at 28 days). Mixtures containing MK presented a better performance compared to other SCM at 7 days. The utilization of SCM reduced the RCPT results of almost all mixtures compared to the control mixtures and the reduction was more significant with an increase in the SCM content. All of the mixtures containing SCM had lower penetration depths when compared to reference mixtures at 28 and 90 days. Good correlations were established between the percentage of permeable voids and water absorption. Moreover, there was an inverse but almost linear relationship between permeable voids content and compressive strength of the mixtures.Article Citation - WoS: 55Citation - Scopus: 64High-Early Ductile Cementitious Composites With Characteristics of Low Early-Age Shrinkage for Repair of Infrastructures(Springer Verlag, 2015) Şahmaran, Mustafa; Al-Emam, Muhannad; Yıldırım, Gürkan; Şimşek, Yunus Emre; Erdem, Tahir Kemal; Lachemi, MohamedReduced performance in concrete infrastructures is mainly caused by the formation of cracks, which may arise due to deteriorating mechanisms during service life. In most cases, reduced performance calls for urgent repairs to the degraded section. Therefore, it is highly desirable to develop dimensionally stable, ductile repair materials that can attain adequately high strength in a limited amount of time, compensate for significant deformation due to mechanical and environmental loadings, and prevent early-age shrinkage cracks. In this paper, the performance of such a material (high-early-strength engineered cementitious composites, HES-ECC, with very low early-age shrinkage capacity) was investigated by studying mechanical properties and dimensional stability. Composites were produced with different water to cementitious materials and slag to Portland cement ratios. In order to enhance composite properties in terms of ductility and early-age shrinkage characteristics, saturated lightweight aggregates replaced sand in the mixtures. The experimental results show that the majority of HES-ECC mixtures developed in this study attained compressive strength values of more than 20.0 MPa and minimum flexural strength of 6.0 MPa within 6 h. Moreover, the HES-ECC mixtures exhibited strain-hardening behavior with strain capacities comparable to normal strength ECC, as well as substantially reduced autogenous shrinkage strain, both of which are unlikely to trigger the formation of cracks in tension at early ages. The integration of these conflicting parameters suggests that HES-ECC can easily meet the need for fast and durable repairs.