Yazar "Bakbak, Derya" seçeneğine göre listele
Listeleniyor 1 - 4 / 4
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe Mechanical behavior of fiber reinforced slag-based geopolymer mortars incorporating artificial lightweight aggregate exposed to elevated temperatures(ELSEVIER SCI LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND, 2022) Kadhim, Sarah; Çevik, Abdulkadir; Niş, Anıl; Bakbak, Derya; Aljanabi, MaysamThe present research investigates the effects of artificial lightweight aggregate (ALWA) and polyvinyl alcohol (PVA) fiber utilization on the mechanical performance of slag-based lightweight geopolymer mortar (LGPM) specimens cured at ambient temperature. Also, the influence of elevated temperature (250 ?C and 500 ?C) on the resulting performance of LGPM samples was studied. For the production of LGPM specimens, 60% and 80% ALWA were utilized as a partial replacement of river sand. The slag-based LGPM samples were activated by a mixture of sodium silicate and 12 M sodium hydroxide solutions. The fresh and hardened state properties of LGPM specimens with and without fibers were assessed by workability, density, compressive strength, uniaxial tensile strength, and flexural strength tests. Also, the micro-scale variations were evaluated by scanning electron microscopy (SEM). The findings revealed that the incorporation of ALWA reduced the workability, density, and compressive strength of the LGPM, and the reductions in all these properties were more with 1% PVA inclusions. Meanwhile, inclusions of 1% PVA fibers significantly enhanced the uniaxial tensile and flexural behaviors of LGPM. After exposure to 250 ?C, all mechanical strengths were improved due to the further geopolymerization, while mechanical strength reductions were observed at 500 ?C due to the vapor impact and difference in thermal expansion. The uniaxial tensile strength of fiber-reinforced LGPM samples was improved from 1.47 MPa to 2.16 MPa at 250 ?C, while uniaxial tensile strength reduced at 500 ?C, and the samples exhibited a brittle failure mode due to the melting of PVA fibers. The results pointed out that tensile and flexural properties of LGPM significantly enhanced with ALWA and 1% PVA fiber utilization.Öğe Modeling the Shear Strength of Reinforced Aerated Concrete Slabs via Support Vector Regression(İstanbul Gelişim Üniversitesi Yayınları / Istanbul Gelisim University Press, 2019-03-29) Kurtoğlu, Ahmet Emin; Bakbak, DeryaAbstract- Autoclaved aerated concrete (AAC) attracts attention as it provides superior material characteristics such as high thermal insulation and environmentally friendly properties. Apart from non-structural applications, AAC is being considered as a structural material thanks to its characteristics such as lighter weight compared to normal concrete, resulting in lower design costs. This study focuses on the feasibility of support vector regression (SVR) in predicting the shear resistance of reinforced AAC slabs. An experimental dataset with 271 data points extracted from eleven sources is used to develop models. Based on random selection, the dataset is divided into two portions, 75% for model development and 25% for testing the validity of the model. Two SVR model types (epsilon and Nu) and four kernel functions (linear, polynomial, sigmoid and radial basis) are used for model development and the results of each model and kernel type is presented in terms of correlation coefficient (R 2 ) and mean squared error (MSE). Results show that epsilon model type with radial basis function yields the best SVR model. Keywords Autoclaved aerated concrete, reinforced concrete slab, shear strength, support vector regression, modelling.Öğe New Model for Compressive Strength Loss of Lightweight Concrete Exposed to Elevated Temperatures(VINCA INST NUCLEAR SCI, MIHAJLA PETROVICA-ALASA 12-14 VINCA, 11037 BELGRADE. POB 522, BELGRADE, 11001, SERBIA, 2019) Kurtoğlu, Ahmet Emin; Bakbak, DeryaThis study proposes a new model for the residual compressive strength of structural lightweight concrete after exposure to elevated temperatures up to 1000 degrees C. For this purpose, a database of residual compressive strengths of fire exposed lightweight concrete was compiled from the literature. Database consisted a total number of 289 data points, used for generating training and testing datasets. Symbolic regression was carried out to generate formulations by accounting for various input parameters such as heating rate, cooling regime, target temperature, water content, aggregate type, and aggregate content. Afterwards, predictions of proposed formulation is compared to experimental results. Statistical evaluations verify that the prediction performance of proposed model is quite high.Öğe Residual mechanical performance of lightweight fiber-reinforced geopolymer mortar composites incorporating expanded clay after elevated temperatures(Sage Publications Ltd, 2022) Aljanabi, Maysam; Cevik, Abdulkadir; Nis, Anil; Bakbak, Derya; Kadhim, SarahThis research provides an experimental investigation on the properties of fiber reinforced composite materials consisting of lightweight expanded clay aggregates (LECA) and polyvinyl alcohol (PVA) fibers. The influence of temperature (room temperature, 250 degrees C, and 500 degrees C) on the lightweight geopolymer mortar (LWGM) composite materials is also explored. LECA is used as a partial replacement to river sand with 60% and 80%. The base material utilized for LWGM is slag activated by a mixture of sodium silicate and sodium hydroxide solutions. The fresh properties in terms of workability and density were performed. A series of experiments, such as compression, flexural and uniaxial tensile strength tests, were executed to assess the mechanical properties of LWGM composite materials. In addition, the microscopic variations due to the elevated temperature were also evaluated by scanning electron microscopy (SEM) to understand the macro-scale behavior of the samples. The results indicated that increasing the level of LECA replacement caused a reduction in the density and compressive strength of the LWGM. Also, incorporating a 1% PVA fiber volume fraction significantly enhanced the flexural and uniaxial tensile behavior of LWGM composite materials. The compressive strength enhancements were observed at 250 degrees C due to further geopolymerization, while compressive strength reductions were obtained at 500 degrees C due to the vapor impact and difference in thermal expansion. In addition, the load-carrying capacity of all samples increased, and displacement capacity decreased under flexural tests at 250 degrees C. However, the ductile behavior of the PVA incorporating specimens changed to brittle due to the melting of PVA fibers.
