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    Evaluation and Multi-Objective Optimization of Lightweight Mortars Parameters at Elevated Temperature via Box-Behnken Optimization Approach
    (Mdpi, 2021) Kaya, Mehmet; Yildirim, Zeynel Baran; Koksal, Fuat; Beycioglu, Ahmet; Kasprzyk, Izabela
    In this research, the mechanical properties of lightweight mortars containing different percentages of additional powder materials has been investigated using response surface methodology (RSM). Box-Behnken design, one of the RSM techniques, was used to study the effects of silica fume content (5, 10, and 15%), vermiculite/cement (V/C) ratio (4, 6, and 8), and temperature (300, 600, and 900 degrees C) on the ultrasonic pulse velocity (UPV), bending strength, and compressive strength of lightweight mortars. Design expert statistical software was accustomed to determining and evaluating the mix-design of materials in mortar mixtures and temperature effect on mortars. After preliminary experimental research of the relationships between independent and response variables, regression models were built. During the selection of the model parameters, F value, p-value, and R-2 values of the statistical models were taken into account by using the backward elimination technique. The results showed a high correlation between the variables and responses. Multi-objective optimization results showed that the critical temperatures for different levels of silica fume (5-10-15%) were obtained as 371.6 degrees C, 306.3 degrees C, and 436 degrees C, respectively, when the V/C ratio kept constant as 4. According to the results obtained at high desirability levels, it is found that the UPS values varied in the range of 2480-2737 m/s, flexural strength of 3.13-3.81 MPa, and compressive strength of 9.9-11.5 MPa at these critical temperatures. As a result of this research, RSM is highly recommended to evaluate mechanical properties where concrete includes some additional powder materials and was exposed to high temperature.
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    Influence of Rock Dust Additives as Fine Aggregate Replacement on Properties of Cement Composites-A Review
    (Mdpi, 2022) Dobiszewska, Magdalena; Bagcal, Orlando; Beycioglu, Ahmet; Goulias, Dimitrios; Koksal, Fuat; Niedostatkiewicz, Maciej; Urunveren, Husamettin
    Concrete production consumes enormous amounts of fossil fuels, raw materials, and is energy intensive. Therefore, scientific research is being conducted worldwide regarding the possibility of using by-products in the production of concrete. The objective is not only to identify substitutes for cement clinker, but also to identify materials that can be used as aggregate in mortar and concrete productions. Among the potential alternative materials that can be used in cement composite production is rock dust of different geological origin. However, some adversarial effects may be encountered when using rock dust regarding the properties and durability of mortars and concrete. Therefore, comprehensive research is needed to evaluate the adequacy of rock dust use in cementitious composite production. This paper presents a comprehensive review of the scientific findings from past studies concerning the use of various geological origins of rock dust in the production of mortars and concrete. The influence of rock dust as a replacement of fine aggregates on cementitious composites was analyzed and evaluated. In this assessment and review, fresh concrete and mortar properties, i.e., workability, segregation, and bleeding, mechanical properties, and the durability of hardened concrete and mortar were considered.
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    Optimization Based on Toughness and Splitting Tensile Strength of Steel-Fiber-Reinforced Concrete Incorporating Silica Fume Using Response Surface Method
    (Mdpi, 2022) Koksal, Fuat; Beycioglu, Ahmet; Dobiszewska, Magdalena
    The greatest weakness of concrete as a construction material is its brittleness and low fracture energy absorption capacity until failure occurs. In order to improve concrete strength and durability, silica fume SF is introduced into the mixture, which at the same time leads to an increase in the brittleness of concrete. To improve the ductility and toughness of concrete, short steel fibers have been incorporated into concrete. Steel fibers and silica fume are jointly preferred for concrete design in order to obtain concrete with high strength and ductility. It is well-known that silica fume content and fiber properties, such as aspect ratio and volume ratio, directly affect the properties of SFRCs. The mixture design of steel-fiber-reinforced concrete (SFRC) with SF addition is a very important issue in terms of economy and performance. In this study, an experimental design was used to study the toughness and splitting tensile strength of SFRC with the response surface method (RSM). The models established by the RSM were used to optimize the design of SFRC in terms of the usage of optimal silica fume content, and optimal steel fiber volume and aspect ratio. Optimum silica fume content and fiber volume ratio values were determined using the D-optimal design method so that the steel fiber volume ratio was at the minimum and the bending toughness and splitting tensile strength were at the maximum. The amount of silica fume used as a cement replacement, aspect ratio, and volume fraction of steel fiber were chosen as independent variables in the experiment. Experimentally obtained mechanical properties of SFRC such as compression, bending, splitting, modulus of elasticity, toughness, and the toughness index were the dependent variables. A good correlation was observed between the dependent and independent variables included in the model. As a result of the optimization, optimum steel fiber volume was determined as 0.70% and silica fume content was determined as 15% for both aspect ratios.
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    Utilization of rock dust as cement replacement in cement composites: An alternative approach to sustainable mortar and concrete productions
    (Elsevier, 2023) Dobiszewska, Magdalena; Bagcal, Orlando; Beycioglu, Ahmet; Goulias, Dimitrios; Koksal, Fuat; Plominski, Blazej; Urunveren, Husamettin
    Production of concrete is consuming significant amounts of raw materials, high level of energy, and is heavily dependent on fossil fuels. This induces significant harmful impact on the environment. Scientific research is being conducted worldwide on the possibility of using different waste by-products in the production of concrete, particularly as a substitute for cement clinker. Rock dust of different geological origin can be considered as potential alternative material that can be used in cement composites production. However, there are some conflicting findings concerning the effect of rock dusts as partial cement replacement on the physical and mechanical properties and durability of cement composites as reported in the literature. Thus, a comprehensive assessment and analysis are needed to evaluate the value of rock dust application as cement replacement in concrete production. This paper presents a comprehensive review of the findings from scientific articles concerning the use of rock dust of different geological origins in mortar and concrete productions. The effect of rock dusts as partial cement substitution on cementitious composites properties were analyzed particularly on the cement hydration, the concrete and mortar mixture properties, mechanical properties and durability. The impact of rock dust is mainly related to the filler effect i.e., due to modification of particle size distribution, heterogenious nucleation, and cement dilution. This effect is more significant when cement is substituted with a rock dust of greater fineness than cement. Partial replacement of cement with up to about 10-15% of rock powder does not deteriorate cement composite properties. However higher substitution leads to reduction of mechanical properties and cement composite durability decline.