Browsing by Author "Koksal F."

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Insulating and fire-resistant performance of slag and brick powder based one-part alkali-activated lightweight mortars
(2022-01-01) Koksal F.; Bayraktar O.Y.; Bodur B.; Benli A.; Kaplan G.
Waste brick powder (WBP) has enough pozzolanic characteristics to be employed as a supplemental cementing material in Portland cement-based concrete or as a precursor in the manufacture of alkali activated materials. This study was aimed to study the strength, thermal, microstructural and durability properties of ground blast furnace slag (GBFS) and WBP based one-part alkali-activated lightweight mortars (AAMs) produced with expanded vermiculite. One-part AAM mixtures were produced by using GBFS and WBP as binary precursors. Sodium metasilicate powder was used as the alkali activator. Two curing regimes namely heat curing at 75°C for 24 h and air curing at ambient conditions were adopted. GBFS was used as main binder and WBP was added at the rates of 0%, 10%, 25%, and 50% instead of GBFS. Four different mixtures were prepared by replacing GBFS at the rates of 0%, 10%, 25%, and 50% with WBP for each curing regime (totally eight mixtures). Expanded vermiculite powder were used as lightweight aggregates in all mixtures. The effects of WBP on AAM mixtures properties, including flowability, compressive strength, flexural strength, dry bulk density, thermal conductivity, porosity, and water absorption were studied. The effects of WBP and curing regime on drying shrinkage, sorptivity were also investigated. High temperature performance of the produced mixtures were determined. Results showed that air-cured WBP incorporated AAM mixtures exhibited better compressive strength, flexural strength, shrinkage, and sorptivity performance than the heat-cured WBP incorporated AAM mixtures. The air-cured AAM mixtures containing 25% WBP achieved the best results of 5.69 and 1.43 MPa for compressive strength and flexural strength at test age of 28 days. The heat-cured 50% WBP incorporated AAM mixture showed the best high temperature resistance and the lowest thermal conductivity.
Mechanical and durability properties of steel fiber-reinforced concrete containing coarse recycled concrete aggregate
(2021-10-01) Kaplan G.; Bayraktar O.Y.; Gholampour A.; Gencel O.; Koksal F.; Ozbakkaloglu T.
The focus of this study is to investigate the effect of using coarse recycled concrete aggregates (RCAs) as an alternative material to natural coarse aggregate on the fresh, mechanical and durability behavior of concrete reinforced with steel fiber. Eighteen unique concrete mixes with RCA content of 0%, 50%, and 100% and steel fiber content of 0%, 1%, and 2% were prepared, and tests were performed to study slump, density, compressive and splitting tensile strengths, flexural behavior, surface hardness, surface abrasion resistance, water absorption, and sorptivity of each mix. It is shown that concrete containing RCA has a lower unit weight, compressive, splitting tensile and flexural strength, flexural toughness, surface hardness, and abrasion resistance, and a higher water absorption and sorptivity in comparison with conventional concrete. An increased compressive, splitting tensile and flexural strength, flexural toughness, surface hardness, and abrasion resistance, and a decreased water absorption and sorptivity of concrete with an increased steel fiber content from 1% to 2% is less significant compared to those from 0% to 1%. The results also show that, at RCA content of 50%, incorporating 1% steel fiber develops a concrete mix with similar or even better properties compared to unreinforced conventional concrete. At 100% RCA content, incorporating 2% steel fiber develops a concrete mix with similar properties to unreinforced conventional concrete having water to cement ratio of 0.3, but inferior properties to unreinforced conventional concrete having water to cement ratio of 0.5. These findings indicate that recycled aggregate concrete with similar or even better properties compared to concrete with natural aggregate can be developed through properly designing mixes, providing a great avenue toward the production of green construction material for structural applications.
Sustainable one-part alkali activated slag/fly ash Geo-SIFCOM containing recycled sands: Mechanical, flexural, durability and microstructural properties
(Elsevier B.V., 2023) Bayraktar O.Y.; Bozkurt T.H.; Benli A.; Koksal F.; Türkoğlu M.; Kaplan G.
Slurry Infiltrated Fiber Concrete or Composite (SIFCOM) is a unique form of steel-fiber-reinforced cement composite that possesses exceptional toughness and superior mechanical properties like compressive, shear, tensile, and flexural strengths. New supplies of fine aggregate are required since the construction industry is experiencing natural sand shortage. By thoroughly evaluating workability, mechanical properties, flexural toughness, durability and microstructure, this study demonstrates the potential of various recycled sands from different sources in the manufacture of sustainable slag/fly ash one-part alkali activated SIFCOM (Geo-SIFCOM). Recycled concrete, brick and ceramic sands were used as a substitute of 10, 25 and 50% by volume of silica sand. Steel fiber ratios of 5%, 10%, and 15% were used and exposed to heat curing for 6, 24 and 48 h at 80 °C. Taguchi method was used to investigate the optimum mixture. The results showed that 24 h heat-cured mixture containing 25% recycled concrete sand and 15% fiber (C25F15) had the largest compressive strengths of 68.49 MPa, 74.53 MPa and 80 MPa at 7, 28, and 91 days, respectively. All 6 h – cured mixtures containing 100% slag exhibited the best resistance to freeze-thaw and the mixtures heat cured for 6 h demonstrated the best compressive strength resistance to elevated temperature and F-T cycles regardless of FA content. The largest flexural toughness was also assessed for the mixture with 50% brick sand and 15% fiber (B50F15) heat-cured for 6 h. The mixture with 50% FA and 50%slag (50% ceramic sand and 15% fiber) exhibited the best high temperature resistance.
The use of waste marble for cleaner production of structural concrete: A comprehensive experimental study
(2022-12-26) Gencel O.; Nodehi M.; Yavuz Bayraktar O.; Kaplan G.; Benli A.; Koksal F.; Bilir T.; Siddique R.; Ozbakkaloglu T.
Waste marble is a byproduct that is produced as a result of cutting and reshaping marble stone that is commonly used in the construction sector. From a sustainability perspective, waste marble can be a potential alternative to limestone sand with slightly reduced ecological footprint which is aligned with novel concepts, such as circularity of construction industry. To provide a comprehensive outline of marble's use as coarse aggregate in concrete production, this study adopted utilizing waste coarse marble aggregate (WCMA) at a quantity of 50% and 100% to substitute coarse limestone aggregates (also natural coarse aggregate (NCA)). Likewise, since marble stone is considered as a metamorphic rock with slightly different microspores, compared to limestone, three different water-to-cement ratios (w/c) of 0.35, 0.42 and 0.49 have also been used. Results show that concretes incorporating WMCA exhibit a slightly better mechanical performance than concretes incorporating NCA, given that the w/c ratio is enough to lubricate WMCA's surface but not to the point of increasing free water in concrete's microstructure. In other words, it is found that WMCA is relatively sensitive to the mixture's w/c ratio which can have a large impact on the resulting physico-mechanical and thermo-durability properties of the specimens. In this regard, despite the WMCA's slightly enhanced performance in certain thermo-durability tests, the interfacial transition zone (ITZ) areas are found to be more susceptible to deteriorating factors. Nonetheless, the result of this study is found to be significant and point to the suitability of utilizing WMCA as an alternative to NCA.