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    Effects of reactive MgO and metakaolin on compressive strength and chloride migration coefficient of sodium carbonate activated slag mortars
    (YILDIZ TECHNICAL UNIV., 2023-02) Abolfathi, Mehrnosh; Ulukaya, Serhan; Aktürk, Büşra
    This paper presents an investigation of the compressive strength and chloride migration of sodium carbonate (NC) activated slag-based mortars. In the experimental study, NC was preferred to use as an activator since it can be designated as an environment-friendly activator. To improve the performance of sodium carbonate-activated slag-based mortars (NCAS), reactive MgO (M) and metakaolin (MK) were replaced with slag up to 15% by mass and five mortar mixtures were prepared with different M and MK replacement ratios. It was found that replacing the slag with a combination of 10% M and 5% MK achieved the highest compressive strength for both early age and ultimate strength. In addition, the mix which was composed of 85% slag, 10% M and 5% MK, was the most resistant one against chloride migration. Based on the compressive strength and chloride migration test results, it was concluded that the compressive strength and chloride migration performances of NCAS could be enhanced by the combination of M and MK.
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    Fresh state properties and compressive strength development of reactive MgO-based systems
    (Elsevier, 2022) Taj, Khalilullah; Aktürk, Büşra; Ulukaya, Serhan
    In this study, flowability, setting time, and strength gain of mortars containing reactive magnesium oxide cement (RMC) and a combination of micro-silica (MS), nano-silica (NS), slag, and fly ash (FA) as precur-sors without employing accelerated carbonation have been investigated. To increase the flowability and hydration degree, sodium hexametaphosphate (SHMP) was incorporated. The series containing RMC and MS simultaneously, had the greatest 3-day compressive strength value of about 25 MPa, whereas further strength gains in all the mixtures until the 7th day was minimal, which establishes that strength gains were due to hydration degree, not carbonation. RMC and MS simultaneously in a series, a combination of extremely high fineness materials dropped the flowability; the presence of slag and FA, on the other hand, enhanced it. The inclusion of NS in the mix didn't demonstrate a perceptible change in any of the properties measured in this study; its inertness could be attributed to the unsuitable dispersion method. Setting time of reference mix was the shortest, which was in conformity with its fast initial strength gain. Replacement of RMC with any other binder extended both the initial and final setting time. It was hypothesized that a major difference in this study is the use of SHMP as a dispersant and hydration agent. The outcomes of this study confirm that RMC can be a potential binder material to be used in mor-tar productions.Copyright (c) 2022 Elsevier Ltd. All rights reserved.Selection and peer-review under responsibility of the scientific committee of the International Confer-ence on Advances in Construction Materials and Structures.
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    Lightweight Cement-Based Composites Incorporating Hollow Glass Microspheres: Fresh and Hardened State Properties
    (Turkish Chamber of Civil Engineers, 2022-01) Aktürk, Büşra
    Abstract: This research aims to develop a lightweight cementitious composite with satisfying mechanical and good thermal insulating properties. Two different types of hollow glass microspheres (HGM) were used as lightweight aggregates and were substituted with fine aggregate by 10, 20, and 40% by volume. The rheological, physical, mechanical, and microstructural properties of the resulting HGM-incorporated composites were investigated and correlations were established between physical and mechanical test results. The results showed that the physical and mechanical properties of individual HGM particles play a dominant role in the properties of lightweight mortars. HGM addition provided reductions up to 20% in the density and 45% in the thermal conductivity values of mortars compared to the reference. The best HGM ratio in the tested range was found as 20%, which provides benefits such as reduced density and enhanced thermal insulation capability without causing a significant reduction in compressive strength. It was concluded that HGMs can be used in the lightweight cementitious mortar production which has great potential in building applications to reduce the heating energy consumption. © 2022 Turkish Chamber of Civil Engineers. All rights reserved.