182 research outputs found
Microstructural properties of lithium-added cement mortars subjected to alkali-silica reactions
No full textDemir, Ilhami/0000-0002-8230-4053; Sevim, Ozer/0000-0001-8535-2344Little comparative research has been done on the efficiency of lithium additives to reduce the alkali-silica reaction (ASR) expansion. To reduce the ASR effects of reactive aggregate, different mortar bars were obtained by adding lithium additives (Li2SO4, LiNO3, Li2CO3, LiBr and LiF) to the mixing water by the following mass percentages of cement: 0%, 0.5%, 1%, 1.5%, 2%, 2.5% and 3%. The ASR expansions of the mortar bars at 2, 7 and 14 days were identified according to ASTM C 1260-14. The morphology of the specimens subject to the ASR effect was analysed using a scanning electron microscope, and their chemical composition was analysed by electron dispersion spectroscopy. Among all specimens, the lowest level of 14-day ASR expansion was obtained in mortar bars with 3% Li2CO3 additive
Optimization of fly ash particle size distribution for cementitious systems with high compactness
No full textSevim, Ozer/0000-0001-8535-2344; Demir, Ilhami/0000-0002-8230-4053Compactness is of special importance for aggregates in concrete; however, the particle-size distribution (gradation) of powdery ingredients is commonly disregarded especially for pozzolanic materials such as fly ash. Without good gradation, powdery materials will result in higher void ratios, as in the case of aggregates, and the products obtained after hydration will still have some voids. Using a vacuum sieve, this study found the particle-size-distribution of fly ash in accordance with the Dinger-Funk particle-size distribution modulus, q, and explored the effects of various fly ash particle-size distributions on the compressive and flexural strengths of 7-, 28- and 90-day-old fly ash-blended cement mortars. After defining the optimal size distribution, the mechanical properties of cement mortars were assessed for several fly ash replacement levels. Results reveal that q of 0.4 yields the best mechanical property results. Further, the cement mortar with a 20% fly ash replacement level and a previously optimized particle-size distribution offered improved mechanical properties and high-compactness results over the control cement mortar after 90 days. Experimental results clearly indicate that only by properly adjusting the particle size distribution of fly ash used in the mixtures, better mechanical properties than the control mixtures without any fly ash addition can be achieved at a fly ash replacement ratio of 20%. The findings of current study are believed to greatly contribute to new lines of research on more effective replacement techniques for different pozzolanic materials without risking basic properties expected from cement-based materials. (C) 2018 Elsevier Ltd. All rights reserved.Scientific and Technical Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [215M081]The authors gratefully acknowledge the financial assistance of the Scientific and Technical Research Council of Turkey (TUBITAK) provided under Project: 215M081
Physical and permeability properties of cementitious mortars having fly ash with optimized particle size distribution
No full textSevim, Ozer/0000-0001-8535-2344; Demir, Ilhami/0000-0002-8230-4053Gradation of powder materials is often avoided in pozzolanic materials, such as fly ash and slag. Without good gradation, powder materials result in high void ratios similar to the case of aggregates and the products obtained after hydration would still have voids. It is therefore necessary to optimize the particle size distributions (PSDs) of pozzolanic materials for improved compactness. This study calculated the PSDs of fly ash using a vacuum sieve in accordance with the Dinger-Funk PSD modulus. The optimal PSD was defined, and the compressive strength of fly ash-blended cement mortars at 7, 28 and 90 days was explored. Properties including water absorption capacity, dry density, rapid chloride permeability and consistency of mortars having optimized fly ash compositions were analysed by varying the replacement levels. Results reveal that the water absorption capacity of the optimized fly ash-blended cement mortar was lower than that of the blended cement mortar having non-optimized fly ash. Moreover, at 90 days, the chloride permeability of the cement mortar blended with optimized fly-ash improved up to 39.1% when compared to that of blended cement mortar having non-optimized fly ash. The results showed that it is possible to use 20% optimized fly ash instead of 10% non-optimized fly ash by simply changing the PSD of fly ash used. Findings of this study clearly show that even slight modifications in the PSDs of pozzolanic materials can make marked contributions to the certain properties of mortars.Scientific and Technical Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [215M081]The authors gratefully acknowledge the financial assistance of the Scientific and Technical Research Council of Turkey (TUBITAK) provided under Project: 215M081
Enhancement on mechanical and durability performances of binary cementitious systems by optimizing particle size distribution of fly ash
No full textSevim, Ozer/0000-0001-8535-2344Fly ash is a well-known supplementary cementitious material that is the by-product of coal-fired thermal power plants. The contribution of fly ash to the enhancement of the mechanical and durability properties of cementitious materials has been documented in concrete technology for many years. In this study, to allow superior mechanical and durability properties, fly ash-based mixtures have been produced after optimization of particle size distribution (PSD) of Class F and Class C fly ash according to the formula of Fuller-Thompson. Different distribution modulus values ranging from 0.3 to 0.6 were used to achieve ideal PSD in accordance with the Fuller-Thompson equation. 30% of F- and C-class fly ash by weight of cement were used to replace with cement in cementitious composites by optimizing PSD with help of air jet sieve. The recommended optimization technique improved the 7-, 28- and 90-day compressive and flexural strength results of mortars. Compressive and flexural strength tests and rapid chloride permeability test of cement-based systems incorporating fly ash up to 15% replacement ratio with optimized PSD at 90-days exhibited better results than those of plain samples owing to the filler effect.Scientific and Technical Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [115M325]The authors wish to thank the Scientific and Technical Research Council of Turkey (TUBITAK) for financial support (Project: 115M325)
Restrained shrinkage cracking of self-consolidating concrete roads
No full textSevim, Ozer/0000-0001-8535-2344; AKGUNGOR, ALI PAYIDAR/0000-0003-0669-5715; Demir, Ilhami/0000-0002-8230-4053The present study is dedicated to investigate the liability of continuously reinforced concrete pavement (CRCP) cast with self-consolidating concrete (SCC) to restrained shrinkage cracking and the values of restraint stresses in these pavements. SCC, which is becoming increasingly popular due to its several superiorities over conventionally vibrated concrete (CVC), has higher amounts and rates of shrinkage compared to CVC. The higher risk of restrained shrinkage cracking of SCC is a great cause of concern in pavement construction as the penetration of water, chemicals, and salts increases the risk of corrosion of reinforcement. In the present study, an analytical restraint stress expression was developed for typical CRC pavements by modifying the restraint stress equation developed previously for RC beams. Using this equation, the restraint stresses induced to the longitudinal reinforcement by the rigid pavement, cast with CVC or SCC, were calculated for eight different example sections. These restraint stress values were found to reach up to 50% of the limit stresses of bars, allowed by the design guidelines, when the pavement is cast with SCC. The amounts of longitudinal reinforcement used in typical CRCP roads were found to be more critical when the pavement is cast with SCC
Mechanical properties and microstructure of cement multicomponent systems containing pozzolan materials under sulfate attack
No full textKalkan, Ilker/0000-0002-5987-631X; Sevim, Ozer/0000-0001-8535-2344Sulfates are a significant chemical components that may lead to failures of cement concrete composites. The present study is dedicated to analyzing the effects of sulfate on the microstructure of cement composite mortars. For this purpose, cementing composite specimens were prepared with 20% pozzolan mixture [fly ash + granulated blastfurnace slag + bottom ash] by mass of cement, together with the reference additive-free specimen of cement concrete, without any mineral admixtures. These cementing composite mortar specimens were then treated for 2, 7, 28, 90, and 360 days in tap water and 10% sodium sulfate solution. The microstructure of the additive-free mortar and composite cement mortar, partially replaced with 20% pozzolan, was then investigated using a scanning electron microscope. The results showed that increasing curing time also increases the formation of C-S-H [calcium silicate hydrate] gel in the cement mortar, when the microstructural changes in the cement are explored in detail. Ettringite formation [3CaO center dot Al2O3 center dot 3CaSO(4)center dot 32H(2)O] in the specimens cured in 10% Na2SO4 was also noticed, in the present experiments.Kirikkale University Scientific Research CentreKirikkale University [2011/73]The authors gratefully acknowledge the financial assistance of the Kirikkale University Scientific Research Centre provided under Project: 2011/73
Effects of sulfate on cement mortar with hybrid pozzolan substitution
No full textSevim, Ozer/0000-0001-8535-2344; Demir, Ilhami/0000-0002-8230-4053Sulfate is one of the most important chemical risks which affect the durability of concrete and reinforced concrete structures. Therefore, this study investigates the effects of sulfate on blended cement mortars. In this paper, cement mortar specimens were prepared with the substitution of CEM I 42.5 R cement with Fly ash + Bottom ash + Blast-furnace Slag at the ratios of 5%, 10%, 15%, and 20% along with a control specimen without additives. These prepared cement mortar specimens were then cured for 2, 7, 28, 90, 180, and 360 days either in potable water or 10% sodium sulfate (Na2SO4) solution. Cement paste specimens were subjected to the initial setting, final setting, and volumetric expansion tests in accordance with the TS EN 196-3 standard. Cured for 2, 7, 28, 90, 180, and 360 days, cement mortars were subjected to compressive strength tests as per the TS EN 196-1 standard while length change tests were conducted as per the ASTM C 1012 standard. It was found that the compressive strength of cement mortars blended with 5% Fly ash + Bottom ash + Blast-furnace Slag cured in sodium sulfate for 360 days was approximately 2% higher than that of the cement mortar without additives. The length change of specimens obtained from cured in sodium sulfate solution shows best results in higher additive ratio. These all length changes ratio are greater than 0.087% ratio which is maximum length change expansion in potable water. This study suggests that 15% and 20% additive ratios are effective in reducing unfavorable effects of sulfate. (C) 2018 Karabuk University. Publishing services by Elsevier B.V
A study on ASR mitigation by optimized particle size distribution
No full textSevim, Ozer/0000-0001-8535-2344In this study, the effect of alkali-silica reaction on binary cementitious composite systems incorporating fly ash or slag having optimized particle size distribution has been investigated. Specimens have been exposed to ASR effect according to ASTM C227 and ASTM C1260 methods. Test results, which were conducted after ASR exposure, have been discussed in terms of use of additive having optimized particle size distribution. The characterization of specimens was investigated using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopic analyzer (EDS), Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis instrument (TGA). As a result of the experimental program, it was seen that the ASR effect is reduced with fly ash and slag replacement. Even, fly ash addition has been more effective than slag addition in reducing the ASR effect for the same additive ratio. In addition, addition of fly ash and slag with optimized particle-size distribution were found to be more effective in reducing the ASR effect as compared to addition of fly ash and slag without optimized particle-size distribution. (C) 2020 Elsevier Ltd. All rights reserved
Effect of sulfate on cement mortars containing Li2SO4, LiNO3, Li2CO3 and LiBr
No full textSevim, Ozer/0000-0001-8535-2344The purpose of this study is to explore the influence of sulfate on the fresh and hardened mortars containing lithium additives added with the aim to prevent alkali-silica reaction (ASR). Four different types of lithium additives (Li2SO4, LiNO3, Li2CO3 and LiBr) were added to the cement at the ratios of 0.5%, 1%, 1.5%, and 2% by mass in order to produce mortar specimens. Influence of sulfate on the specimens was then investigated. Used in order to keep the expansion under control, expansion characteristics and mechanical properties of Li2SO4, LiNO3, Li2CO3 and LiBr were defined. Initial setting and final setting tests were conducted on the cement pastes as per the provisions of TS EN 196-3 standard. Flexure and compressive tests were conducted in accordance with TS 196-1 in order to identify the mechanical properties of cement mortars. Prisms of 25 x 25 x 285 mm in dimension were produced as per ASTM C 1012-95 in order to measure the length change of the cement bars and results were analyzed. The results showed that Li2CO3 among the other lithium additives was effective in shortening the initial setting and final setting times, while LiNO3 and LiBr additives gave the best results in terms of strength and length change when tested for 1% additive ratio by mass. The highest length change was observed for the specimens with Li2CO3 cured both in water and sulfate solution. The lowest length change was observed for the specimens with LiNO3 cured both in water and sulfate solution. 1% LiNO3 additive gave the best results under sulfate effect for all test days. The length change of cement mortar with 1% LiNO3 additive was decreased by 53%, 25%, and 41% under sulfate effect for the 90th, 180th, and 360th day, respectively. It is believed that the use of LiNO3 and LiBr additives at the ratio of 1% by mass will reduce the unfavorable influence of sulfate. Li2CO3 and LiSO4 should not be used because they have negative effects on mechanical properties and length changes. (C) 2017 Elsevier Ltd. All rights reserved
Microstructural, Physical And Mechanical Properties Of Aerated Concrete Containing Fly Ash Under High Temperature And Pressure
No full textSevim, Ozer/0000-0001-8535-2344This study analyzed the effects of the use of fly ash as a replacement for the quartz sand on the compressive strength, dry density, moisture content and thermal conductivity of the aerated concrete. Based on the production of Class G2/04 aerated concrete, a commercially available wall construction element, aerated concrete samples were produced using the fly ash as a replacement for the silica sand (quartz sand) at additive ratios of 5%, 10%, 15%, 20%, and 25%. After steam curing the samples for 4 hours at 60 degrees C, they were cured in an autoclave for 6.5 hours at 180 degrees C under 11 bar pressures. As a result, the samples showed an increase in their dry density directly proportional to the fly ash addition ratio; and the highest dry density was found in the aerated concrete with 25% fly ash content. It was further observed that the moisture content increases as the fly ash addition ratio increases. Compressive strength was reduced with the fly ash addition. Thermal conductivity was found to be reduced up to fly ash addition ratio of 10%, however, it was then increased again up to fly ash addition of 25%. 25% fly ash replacement ratio is recommended in this study in terms of thermal conductivity, dry density, which are the most important properties of aerated concrete. Higher levels of fly ash replacement with sand can be actualized which can further enhance to the utilization of fly ash, raise awareness regarding waste minimization and reduce the overall costs of aerated concrete mixtures
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