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    Effect of curing conditions during the first 24 hours after casting on the properties of mortar mixtures
    (Pontificia Univ Catolica Chile, Escuela Construccion Civil, 2020) Mardani-Aghabaglou, Ali; Özen, Süleyman; Altun, Muhammet Gokhan
    As it is well known, the curing method directly affects many properties of cementitious composites. In previous studies, the effect of different curing conditions on the properties of the cementitious systems has been generally investigated in the period after first 24 hours after casting. However, there are not many studies in the literature related to the effects of curing conditions on the specimens kept in mold during 24 hours after casting. In this study, strength development, ultrasonic pulse velocity (UPV) and water absorption capacity of mortar specimens subjected to steam-curing at different temperatures during keeping in mold for the first 24 hours after production were compared. In this regard, all mortar specimens were exposed to curing in a steam-curing cabin at 95% constant relative humidity (RH) under 5 different temperatures such as 20, 35, 50, 65 and 80 degrees C for the first 24 hours after the specimens were placed into the molds. Afterwards, the specimens were removed from the molds and cured in water conformed to the standard until the testing day. In this context, the water-cement ratio, sand- binder and slump-flow value of all mortar mixtures were kept constant as 0.485, 2.75, 25 +/- 2 cm, respectively. As a result, the application of steam-curing at high temperature for the first 24 hours positively affected the 1-day compressive strength and UPV values of the mixtures, while the 3,7 and 28-day compressive strength, UPV values and the 28-day water absorption capacity of mixtures were adversely affected.
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    Effect of main and side chain length change of polycarboxylate-ether-based water-reducing admixtures on the fresh state and mechanical properties of cementitious systems
    (Ernst & Sohn, 2021) Özen, Süleyman; Altun, Muhammet Gokhan; Mardani-Aghabaglou, Ali; Ramyar, Kambiz
    In this study, the effect of both main and side chain length changes of the admixtures on some properties of cementitious systems were investigated. Three different polycarboxylate-ether-based water-reducing admixtures (WRA) having constant molecular weights and different main and side chain lengths were synthesized. Single type of raw material and carboxylate functional group were used in all WRAs. The molecular weights, free nonionic contents, and anionic/nonionic ratios of the admixtures were kept constant. Test results showed that degree of fluidity was observed in cement paste and mortar mixtures in case the admixture main and side chain length is more or less than a critical value. This negative effect is thought to be due to the weakening of the adsorption ability by the chain length change of the admixtures, the being tendency of polymers to intertwine and the adsorbing of admixture on several cement particles simultaneous. Admixtures having excessive long or short main chain and side chain improved the time-dependent slump-flow retention of the mortar mixtures. The admixtures with short main and side chains had insufficient adsorption ability and the admixture with excessive long main and side chains had the interlacing risk of polymers. In both cases, time-dependent behavior improved because the amount of free admixture in solution increased. The change in the chain lengths of the WRAs affected the 1-day compressive strength of the mortar mixtures.
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    Effect of nonionic side chain length of polycarboxylate-ether-based high-range water-reducing admixture on properties of cementitious systems
    (Higher Education Press, 2020) Özen, Süleyman; Altun, Muhammet Gokhan; Mardani-Aghabaglou, Ali; Ramyar, Kambiz
    Despite the large variations in the behaviors of water-reducing admixtures upon changes in their structures, most previous reports on the cement-admixture compatibility did not provide sufficient information on the structure of the admixture. Hence, the evaluation and generalization of the reports on the cement-admixture compatibility are challenging. In this study, three different polycarboxylate-ether-based water-reducing admixtures with the same free nonionic content, anionic/nonionic molar ratio, and main chain length and different side chain lengths were produced. The compatibility of these admixtures with a CEM I 42.5 R-type cement was investigated. In addition, an analysis of variance was performed on the experiment results to evaluate the contributions of the admixture type, admixture/cement ratio, and elapsing time to the Marsh funnel flow time, mini-slump, slump flow, and compressive strength. The water-reducing admixtures having long or short side chains reduced the initial flow characteristics of the cementitious systems. However, the admixture having the shortest side chain was better with regard to flow retention. The side chain length of the admixture did not have significant effects on the compressive strength and water absorption capacity of the mortar mixtures and mini-slump performances of the cement paste mixtures. Regarding the behaviors of the admixtures in the cementitious systems, an optimal admixture side chain molecular weight is proposed.
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    Effect of side chain length change of polycarboxylate-ether based high range water reducing admixture on properties of self-compacting concrete
    (Elsevier Sci Ltd, 2020) Altun, Muhammet Gokhan; Özen, Süleyman; Mardani-Aghabaglou, Ali
    In this study, the effect of side chain length, molecular weights changes and adsorption amount of polycarboxylate ether-based high range water reducing admixtures having constant main chain length, free non-ionic amount and anionic/non-ionic ratio on fresh properties, early and advanced age compressive strength, water absorption capacity and ultrasonic pulse velocity value of self-compacting concretes (SCC) were investigated. FTIR (Fourier transform infrared) and GPC (Gel Permeation Chromatography) analyzes were carried out to characterize admixtures. According to the test results, all SCC mixtures produced within the scope of the study provided EFNARC criteria. If the admixture side chain length is higher or shorter than a certain value, the admixture requirement is increased for providing the desired target slump-flow value in SCC mixtures. This negative effect is thought to be due to the weakness of the steric hindrance effect for admixture with short side chain, the low adsorption amount and interlacing risk of side chains for admixture with the long side chain. On the other hand, the increase in the side chain length of the admixtures had a positive effect on the time-dependent fresh state performance of the mixtures. This positive effect is thought to be due to the low adsorption amount of the admixture, the increase in the side chain length and the increase of the non-adsorbed free polymer content in the mixture. While side chain length change of the water reducing admixture affected the 1 and 2-day compressive strength values of SCC mixtures, the 3, 7 and 28-day compressive strengths and the 28-day water absorption, ultrasound and dynamic elasticity modulus values did not significantly affect. (C) 2020 Elsevier Ltd. All rights reserved.
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    Effect of the polycarboxylate based water reducing admixture structure on self-compacting concrete properties: Main chain length
    (Elsevier Sci Ltd, 2020) Özen, Süleyman; Altun, Muhammet Gokhan; Mardani-Aghabaglou, Ali
    In this study, the effect of polycarboxylate ether-based water reducing admixture (WRA) main chain length on fresh state properties, compressive strength, ultrasonic pulse velocity (UPV) and water absorption capacity of self-compacting concrete (SCC) mixtures were investigated. Within this aim, three polycarboxylate ether-based high range WRAs with stabilized polyethylene oxide side chain molecular weight, free non-ionic content and constant anionic/non-ionic ratios, but different main chain length were synthesized. FTIR (Fourier transform infrared) and GPC (Gel Permeation Chromatography) analyzes were carried out to characterize admixtures. According to test results, the admixture requirement for reaching targeted main chain length in SCC increased and adsorption of admixture decreased in case the admixture main chain length is higher and lower than a certain value. However, time-dependent flow performance of the mixtures improved with the increase of admixture main chain length and a reverse situation was observed when the length was decreased. Similar behaviors were also observed in V funnel flow, L box and U box passing tests. While the admixture main chain length change affected early age strength, it showed no effect on the strengths of later ages. No considerable differences were observed in the 28-day water absorption, UPV and dynamic modulus of elasticity values of the mixtures with the change of admixture main chain length. (C) 2020 Elsevier Ltd. All rights reserved.
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    EFFECT OF WATER CURING TEMPERATURE ON COMPRESSIVE STRENGTH DEVELOPMENT AND WATER ABSORPTION CAPACITY OF MORTAR MIXTURES
    (Yildiz Technical Univ, 2020) Mardani Aghabaglou, Ali; Özen, Süleyman; Altun, Muhammet Gokhan; Faqiri, Zia Ahmad
    In this study, the effect of different curing temperature processes on the 1, 3, 7 and 28-day compressive strength and 28-day water absorption ratios of mortar mixtures were investigated. All mortar mixtures were prepared according to ASTM C109. The water/cement ratio, sand/binder ratio and flow values of mortar mixture were kept constant as 0.485, 2.75 and 25 +/- 2 cm, respectively. Polycarboxylate ether-based high range water reducing admixture was used for providing desired flow value. All mortar mixtures were cured at fresh state in a curing room under the same conditions (Temperature of 20 degrees C and Relative humanity (RH) of 95%) during 24 hours from casting. Then, specimens were subjected to 6 different water-curing conditions. According to test results, the 3-day compressive strength of mixtures cured in water having a temperature of 40 degrees C was higher than that of mixtures cured at 20 degrees C in water. At early ages, the high curing temperature negatively affected the 7 and 28-day compressive strength of mixtures. Specimens cured in water at 20 degrees C and 40 degrees C had the highest and lowest 28-day compressive strengths, respectively. Different curing conditions had no significant effect on the 28-day water absorption ratios of mortar mixtures.
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    Effects of anionic monomer type of water-reducing admixture on fresh properties, compressive strength and water adsorption of self-compacting concrete
    (Taylor & Francis Ltd, 2021) Özen, Süleyman; Altun, Muhammet Gokhan; Mardani-Aghabaglou, Ali; Unlu, Ayda; Ramyar, Kambiz
    In this study, the effects of anionic monomer functional group type of the water-reducing admixture (WRA) on the fresh properties and compressive strength of self-compacting concrete (SCC) mixtures were investigated. Nine types of polycarboxylate ether-based high-range WRAs with the same main chains but different anionic monomers linked to the main chain were synthesized and used in different dosages to provide the desired slump-flow value in SSC mixtures. For this motivation, in addition to the control admixture consisted of 100% carboxylate functional group, 5, 10, 20 and 30% of carboxylate functional group was replaced by either phosphate or sulfonate group. Test results revealed that the admixtures containing sulfonate and phosphate anionic monomer improved the fresh properties of SCC mixtures compared to those of the control admixture. However, anionic monomer exchange in the structure of the WRA did not significantly affect the compressive strength and water absorption capacity of the SCC mixtures.