Browsing by Author "Turkoglu M."

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Effect of cement clinker type, curing regime and activator dosage on the performance of one-part alkali-activated hybrid slag/clinker composites
(2023-06-01) Turkoglu M.; Bayraktar O.Y.; Benli A.; Kaplan G.
One candidate for a novel binder is alkaline hybrid cement, which has more than 70% supplemental cementitious materials (SCMs) and a trace amount of an alkali activator but less than 30% Portland cement. This cementitious material offers high early strength, a more compact microstructure, and outstanding resistance to chloride penetration and sulphate attack, in addition to the benefits of alkali-activated materials (AAMs) and Portland cement. This study presents the findings of an experimental investigation that aims to clarify the effect of cement clinker type, curing regime, and activator dosage on the fresh, mechanical, durability, and microstructure properties of one-part alkali-activated hybrid slag/cement clinker composites (AAHC). Flow diameter, setting time, compressive strength, dry unit weight, flexural strength, drying shrinkage, sorptivity, and transport properties were evaluated. It was also aimed to investigate its effectiveness at high-temperatures, sulphate exposure, alkali-silica reaction (ASR), and freeze-thaw (F-T) cycles. A total of twelve AAHC mixtures were made with two GBFS/Clinker ratios of 70/30 and 90/10 and an external addition of 10% and 20% one-part alkali activator. Three cement clinker types and three curing regimes were adopted including oven, water, and steam. The results indicated that the water-cured mixture with GBFS/C3 ratio of 90/10 and activated by 20%MS had the greatest compressive strength of about 65 MPa. Steam and oven-cured mixtures with GBFS/C3 ratio of 90/10 and activated by 10%MS performed the best high-temperature resistance. The same mixtures cured in steam also had the best F-T resistance.
Effect of cement dosage and waste tire rubber on the mechanical, transport and abrasion characteristics of foam concretes subjected to H2SO4 and freeze–thaw
(2021-10-04) Bayraktar O.Y.; Soylemez H.; Kaplan G.; Benli A.; Gencel O.; Turkoglu M.
This paper presents an experimental study of the effects of cement dosage and waste tire rubber as aggregate on the mechanical, transport and abrasion characteristics of foam concretes subjected to H2SO4 and freeze–thaw cycles. Foam concrete mixtures were made with two percentages 0, and 20 of silica fume (SF) as partial substitution of Portland cement (PC) and with 100% of waste tire rubber (WRA) as substitution of fine aggregates. Two groups of mixtures were prepared with SF contents of 0% and 20%. At each group of mixtures, three cement contents of 300, 400 and 500 kg/m3 and three foam contents of 20, 40 and 60 kg/m3 were used to produce concretes mixtures having water/binder (w/b) ratio of 0.75. Workability of fresh concretes were assessed by performing slump test. Compressive and flexural strength of the mixtures were determined after 7 and 28 days and transport properties were measured by means of porosity and water absorption after 28 days. Tests for shrinkage, sorptivity, abrasion, acid attack and freeze–thaw cycles of 30 and 60 were also performed in addition to microstructure investigations. An optimization was also performed. The results exhibited that increase in cement dosage resulted in the compressive strength by 204.50% maximum increment at cement content of 500 kg/m3 as compared to the mixture with dosage of 300 kg/m3 at foam content of 20 kg/m3. Based on the results, it was concluded that the lowest and highest shrinkage values of 5032 × 10−6 and 7065 × 10-6 mm/mm were gained for the mixtures with cement dosages of 300 kg/m3 and 500 kg/m3 and foam content of 20 kg/m3 respectively. The results also indicated that SF blended mixture with cement content of 500 kg/m3 foam content of 20 kg/m3 showed the best resistance after abrasion, F-T cycles and acid attack exposure.
Hemp fiber reinforced one-part alkali-activated composites with expanded perlite: Mechanical properties, microstructure analysis and high-temperature resistance
(2023-01-11) Bayraktar O.Y.; Tobbala D.E.; Turkoglu M.; Kaplan G.; Tayeh B.A.
The objective of the current research is to find out what impacts hemp fibers (HF) lengths and percentages have on the fresh, physical, mechanical, sorptivity, dry shrinkage, and thermal properties of HF-reinforced alkali-activated composite (AAC) reinforced with ground blast furnace slag (GBFS). Two groups of AAC mixes with 10 and 20 mm HF lengths were produced. Each group contained different percentages of HF with varying fiber lengths added to mixes at 0.5 %, 1 %, 2 %, and 3.0 % by weight of cement, respectively. Flow diameters were measured to determine the fresh-state properties of the AACs. Water absorption and apparent porosity were determined as physical properties. The unit weights of AAC mixtures are between 1045–1672 kg/m3. Measurements were made on compression and flexural characteristics at 7 and 28 days. The 28-day compressive strengths of AAC mixtures vary between 1.28 and 2.73 MPa, and the bending strengths vary between 0.48 and 1.65 MPa. AAC was also tested for water absorption, drying shrinkage, thermal conductivity, fresh and dry unit weight and porosity. The resistance of high temperatures at 250, 500, and 750 °C was determined. There is a significant improvement in compressive and flexural strength and thermal conductivity when HF is added at a 20 mm length. This improvement was confirmed and emphasized through scanning electron microscopy (SEM). According to study results, high-temperature alkali cooking treatments up to 250 °C may improve the thermal stability of HF cellulose. The best HF mix, M2-2 %, increased the 28-day compressive strength by 28.8 % and produced the best results at temperatures as high as 750 °C. The compressive strength of the mixtures exposed to 750 °C was obtained as approximately 2 MPa.
The effect of steel fiber aspect-ratio and content on the fresh, flexural, and mechanical performance of concrete made with recycled fine aggregate
(2023-03-03) Yavuz Bayraktar O.; Kaplan G.; Shi J.; Benli A.; Bodur B.; Turkoglu M.
In order to solve the problem of low toughness and easy cracking of recycled aggregate concrete, steel fibers were incorporated to recycled fine aggregate concrete (RAC) to prepare a sustainable fiber-reinforced concrete. Steel fibers of various contents (20, 35, 50 and 65 kg/m3) and aspect ratios (l/d = 40 and 55) were incorporated to the RAC, and their fresh properties, mechanical properties and microstructure were investigated. The results show that the slump of RAC decreases with increasing fiber aspect ratio and content. Meanwhile, incorporating a small amount of steel fibers (l/d = 40, 20 kg/m3) improves the 28-d compressive strength of RAC, but with further increase in fiber aspect ratio and content, the compressive strength of RAC decreases. The incorporation of steel fibers greatly improves the splitting tensile strength and flexural strength of RAC, and the steel fibers with high aspect ratio have a higher gain in strength. The 28-d flexural strength of concrete with 65 kg/m3 steel fibers (l/d = 40) increases by 148.11 % relative to plain RAC, while the 65 kg/m3 steel fibers with an aspect ratio of 55 makes RAC with increases by 243.78 %. The mass loss of fiber-reinforced RAC under abrasion is also lower than that of plain RAC, and the steel fiber with high aspect ratio performs better. For the load–deflection response, the incorporation of fibers increases the peak load, and also increases the flexural toughness and post-cracking toughness, with the greatest gain for high aspect ratio fibers.
Usage of recycled fine aggregates obtained from concretes with low w/c ratio in the production of masonry plaster and mortar
(2022-02-01) Kaplan G.; Turkoglu M.; Bodur B.; Bayraktar O.Y.
In this study, fresh and hardened aspects of mortars being produced from RFAs (recycled fine aggregates) obtained from concretes, w/c (water/cement) ratio of which varies in the range of 0.47–0.55 have been examined. On the mortars experiments such as those relating with workability, mechanical properties, drying shrinkage, sorptivity, and apparent porosity have been conducted. As flow diameters of mortars are kept at the value of 16 ± 2 cm, as a/c (aggregate/cement) ratio increased, w/c ratios of mortars also increased. As paste volume of mortars decreased, their mechanical properties got diminished. Increase in a/c ratio has impacted flexural strength negatively. In a mortar with a/c ratio of 5 and RFA ratio of %75, compressive strength of nearly 12 MPa has been obtained. As a/c ratio and compressive and flexural strengths of mortars increased, drying shrinkage values got reduced. Drying shrinkage value of mortars having a/c ratio of 7 and RFA ratio of %100 on 56th day has fallen below 1000 µm. By means of high grains below 75 µm within body of RFA, water penetration depth values of mortars have reduced. However, in mortars being produced by using RFA, attention should be paid to a/c ratio with regard to capillarity. Due to older cement paste situated on RFA surface, as RFA content increases, apparent porosity values of mortars have increased. As a conclusion, it has been determined that RFA will be used in production of mortar and plaster and it will be recycled and hence, sustainable building material could be obtained.