Zafer Kurt

The substitution of conventional materials with alternative resources is a significant approach for enhancing the engineering performance and sustainability of foamed concrete (FC). While supplementary cementitious materials, volcanic materials, and waste-derived materials have been extensively investigated, the use of obsidian as an alternative aggregate in FC systems remains largely unexplored, and the combined, systematic comparative use of obsidian, waste ceramic powder (WCP), and recycled concrete powder (RCP) within a unified experimental framework has not been previously investigated. This paper evaluates the use of obsidian, WCP, and RCP as alternative aggregates in hydroxypropyl methylcellulose (HPMC)-stabilized FC by replacing standard sand at 25%, 50%, and 100% levels. The thermal, durability and mechanical characteristics of the mixtures were assessed through density, compressive strength (CS), ultrasonic pulse velocity (UPV), water absorption (WA), elevated temperature resistance (200 °C, 400 °C, 600 °C and 800 °C), freeze–thaw performance, thermal conductivity (TC), and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDS) and X-ray diffraction (XRD) analyses. The results showed that the 28-day CS increased from 0.545 MPa in the control mixture to a maximum value of 2.590 MPa in the obsidian-based FC. Moreover, WA decreased markedly from 117.7% to 46.9% in the obsidian-based FC. The UPV varied from 1355 to 1795 m/s due to the incorporation of RCP, WCP and obsidian at different replacement ratios in the mixture designs. The lowest TC of 0.08185 W/(m·K) was recorded in the obsidian-based FC at 50% substitution level. Under elevated-temperature exposure, the mixture with 100% obsidian replacement retained a compressive strength of 0.5936 MPa at 800 °C. To conclude, the use of obsidian, WCP and RCP as alternative aggregates in FC shows promising potential for the development of durable, thermally efficient, and sustainable lightweight construction materials.

Although there are ongoing studies on innovative green materials, building materials are mostly composed of cementitious compounds as binders. Cement is known to significantly increase CO₂ emissions both during its production and utilization. Furthermore, while the utilization of industrial by-products in waste storage and disposal processes offers positive contributions to the circular economy, this approach does not constitute a holistic and adequate solution in terms of the environment and human health. This study presents the results of the effect of mud powder obtained from Rize province on the mechanical and microstructural properties of cement mortars to the academic environment. The mud was dried and ground, then calcined at 600, 700 and 800 °C. The calcined mud powder obtained at the optimum calcination temperature was substituted into cementitious mortars at 0%, 10%, 20%, 30% and 40% by weight. The parameters used in the study were material/ball weight = 1/12 and binder/cement weight = 0.45. Compressive and flexural tests were performed for mechanical strength and XRD, SEM-EDS, FTIR, Specific gravity, and UPV tests were performed to explain the microstructures. The numerical and test data imply that the maximum 28-day compressive strength of 46. 65 MPa was obtained as a result of 10% substitution of calcined mud powder, which is a natural resource. These results indicated that calcined powder mud (CPS) has strong potential as a sustainable material for construction and structural applications.

Functionally Graded Materials (FGMs) represent a highly advanced solution for the repair of cracked aircraft structures, offering superior performance compared to conventional homogeneous materials. FGMs contribute to more durable, lightweight, and structurally effective repairs, extending service life while maintaining safety and performance standards. This study investigates the effectiveness of functionally graded material (FGM) patches for reinforcing cracked aluminum alloy plates. Using three-dimensional finite element analysis implemented in ABAQUS with a USDFLD subroutine, spatial variations of the Young’s modulus were applied according to linear, logarithmic, and exponential gradation laws. The fracture behavior was quantified through J-integral calculations under plane strain conditions. Results show that FGM patches significantly reduce the J-integral at the crack tip compared to unrepaired plates: up to 56% reduction for linear gradation, 52% for logarithmic, and 44% for exponential gradation. Linear gradation is most effective in mitigating longitudinal crack propagation, while logarithmic gradation efficiently reduces local principal stresses. Contour convergence and comparison with homogeneous patch and unrepaired plate benchmarks confirm the reliability of the numerical results. These findings provide mechanistic insight into stiffness-gradient-driven stress redistribution, guiding the optimal design of FGM repairs for enhanced durability.

In this study, the effects of impacts caused by freely falling rocks from different heights on the structural performance of concrete domes were investigated. The variations of the maximum stresses induced by rocks falling from different elevations depending on the diameter of the falling rock and the cross-sectional wall thickness of the concrete domes are presented. Domes are important structural elements frequently preferred by designers due to their aesthetic appearance and engineering properties. As they are frequently preferred, they are exposed to different natural disasters. Rockfalls are an important natural disaster that causes damage to structures built on rugged terrains with unstable soils. Knowing the extent of the damages caused by this disaster will shed light on the design of the structures built or to be built. The results of the structural analyses show that the kinetic energy caused by the increase in the elevation of the rock fall increased the structural damages (maximum stress) considerably, and these increased structural damages were tried to be controlled with the section wall thickness. As a result of the analyses, the stress values of the dome were determined according to the height at which the rock falls. It is thought that the results of these analyses will give a preliminary idea to structural engineers and architects at the design stage.

This study presents the effects of using pyrite aggregate in field concretes on the mechanical, surface performance, and algal growth tendency of concrete. The substitution of pyrite influences the process of hydration, as the gradual release of its iron- and sulfur-bearing components shifts the reaction mechanism, leading to differences in phase formation and some modification in the pore structure of the cement matrix. Three different concrete mixes (PB0, PB2.5%, and PB7.5%) were designed by replacing 0%, 2.5%, and 7.5% of the total weight of sand and crushed sand with ground pyrite as a fine aggregate. Prismatic specimens of 80 × 100 × 200 mm were produced from these mixtures and mechanical properties such as flexural, splitting tensile, and abrasion were investigated after 28 days of curing. Then, to determine the effect of pyrite on concrete surface properties, pyrite was substituted on the surface of three concrete specimens produced in 50 × 240 × 500 mm dimensions at rates of 0, 1, and 3 kg/m². These specimens were divided into two groups: one group was exposed to clean water drops at a constant flow rate in a closed environment, and the other group was exposed to dirty water in an open environment, and observed for 2 months. At the end of the process, sections of 50 × 80 × 200 cm³ were taken from the specimens and friction, abrasion and flexural tests were carried out. The results of the study demonstrate that a 7.5% pyrite substitution improves both flexural and shear strength by 38%. At the same time, pyrite substitution prevented algal growth on the surface of field concrete under clean water and delayed its formation in those under contaminated water. Finally, it was observed that pyrite, when used in concrete mix and surface applications, optimizes mechanical performance and environmental durability.

This paper presents the mechanical and micro-structure results of concrete parquet blocks. The blocks were generated by utilizing the same part in the bottom part and by substituting different proportions (40%, 30%, 20%, and 10%) of heavy aggregate like chromite aggregate, magnetite aggregate, normal aggregate, and surface hardener in the upper part. The parquet sample tests were conducted on TS 2824 EN 1338. The test outcomes indicated that utilizing diverse aggregate and chemical materials boosted the abrasion resistance, 40% magnetite and quartz-based concrete parquet block samples demonstrated the best abrasion resistance values. Also, the minimum amount of mass loss was discovered in the samples that possess high water absorption at the freezing-thaw test. The different material substitutions in the sheet of the surface of the concrete parquet block samples altered the tensile strength of the samples, even though they did not bring about an outstanding variation in the compressive strength of the concrete parquet samples.

Geopolymer mortars, which cause less CO ₂ emissions than concrete and its raw material cement, are an innovative, environmentally friendly and sustainable building material. Geopolymers are formed by activating silica and alumina materials with alkaline activators. In this study, a geopolymer mortar containing obsidian (OB), also known as volcanic glass, which is free, and silica fume (SF), which is the waste material of the silicon and ferrosilicon industry, was investigated. The behavior of OB‐based geopolymer mortars under different curing times ranging from 2 to 120 h and different thermal treatment temperatures such as 90, 150, and 200°C were examined. The effectiveness of OB and SF on the physical features, compressive strength (CS), and micro‐structural of the geopolymers were characterized. Results demonstrated that the peak CSs were acquired in 96 h at 90 and 150°C heat treatment temperatures, while the highest CSs were acquired in 72 h for specimens subjected to 200°C heat treatment. Reduces in CSs were detected when the curing time exceeded the ideal limit. OB‐based geopolymer was found to be stable with SF and there was a linear relationship between SF substitution ratio and CS. The density of the mortar pieces decreased with increasing thermal curing hours. Devolving on the thermal temperature and curing time, the microstructures became more compact and microvoids and cracks decreased. It was observed that SF substitution reduced the total pore size of the geopolymers and allowed the pore structure size to be reduced. The results obtained from the study are expected to encourage the utilize of industrial wastes and new binders in the manufacture of geopolymers.

Concrete has been the world's most produced and utilized building material for years due to its economic and easy accessibility. However, it attracts attention due to the CO2 emitted from cement, the raw material of concrete, during the production and consumption stages. Although there are different research studies to reduce this emission, one of the most logical solutions is to use pozzolanic materials with cement and reduce the need for cement. This paper investigated the general material characteristics of mortar samples generated by substituting obsidian pow- der with pozzolanic properties into cement at different ratios by weight. Mortar specimens with varying proportions of obsidian, such as 0%, 10%, 20%, and 30% by weight, were subjected to mechanical tests at 3, 7, 14, and 28 days. Material tests like X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to characterize the material. As a result of the me- chanical tests, 42.52 MPa compressive strength was obtained from the 28-day reference sample, while 44.331 MPa compressive strength was obtained from the mortar sample with 30% obsid- ian substitution. The outcomes of this paper noted that obsidian powder, which has pozzolan- ic properties, increased the mechanical strength of cementitious mortar specimens. This work indicates the suitability of using obsidian as pozzolan material with cement was determined.