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    Examination of mechanical properties and microstructure of alkali activated slag and slag-metakaolin blends exposed to high temperatures
    (Ernst & Sohn, 2022) Akcaozoglu, Semiha; Ciflikli, Murat; Bozkaya, Omer; Atis, Cengiz Duran; Ulu, Cuneyt
    This paper reports an experimental study of the influence of elevated temperature on alkali activated slag (AAS) and slag-metakaolin (MK) systems. The residual compressive and flexural tensile strengths, ultrasonic pulse velocity (UPV) and porosity and water absorption ratios of AAS and AAS-MK composites after subjected to elevated temperatures of 200, 400, 600, 800, and 1000 degrees C were investigated. Two different procedures were applied for cooling the specimens. The changes in the microstructure of the composites after subjected to high temperature were examined with scanning electron microscope and X-ray diffraction. Test results reveal that depending on the increasing temperature, the residual compressive strength, flexural tensile strength, and UPV values of the specimens decreased, and porosity and water absorption ratios increased. The minimum strength results of AAS and AAS-MK specimens were observed at 800 and 600 degrees C, respectively. In particular, there have been significant changes in the internal structure of AAS and AAS-MK specimens exposed to 1000 degrees C and new reaction products were observed. Test results have shown that AAS specimens are a new alternative that can be developed for use in environments exposed to high temperatures. Since this new composite contains only slag binder and slag aggregate, it can be an economical product that use fully recycled material and these properties can increase the application areas of environmentally friendly material.
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    Recycling of waste PET granules as aggregate in alkali-activated blast furnace slag/metakaolin blends
    (ELSEVIER SCI LTD, 2014) Akcaozoglu, Semiha; Ulu, Cuneyt
    In this study the utilization of waste PET aggregate in alkali-activated slag and slag/metakaolin blended mortar was investigated. Sodium hydroxide (NaOH) pellets and liquid sodium silicate were used as activators. Eighteen different mortar mixtures were prepared for the laboratory tests. In the reference mixture, unground slag (max Size of 4 mm) was used as aggregate. In PET aggregate mixtures, slag aggregate was replaced with waste PET aggregate, in amount of 20%, 40%, 60%, 80% and 100% by volume. The water-binder (w/b) ratio and aggregate-binder ratio used in the mixtures were 0.50 and 2.75, respectively. The unit weight, compressive strength, flexural tensile strength, ultrasonic wave velocity and water absorption and porosity ratios of the mixtures were measured. The test results showed that, using PET aggregate contributed to decrease of unit weight of alkali-activated mortars due to the low density of PET aggregate. Although the strength values of the specimens decreased depending on increasing waste PET aggregate amount, the compressive strength values of the alkali-activated slag mortars containing waste PET aggregate were satisfactory. In addition, alkali-activated slag mixtures containing 60% and 80% waste PET aggregate were drop into structural lightweight concrete category in terms of unit weight and strength properties. However, the compressive strengths of alkali-activated slag/metakaolin blended mixtures were lower than alkali-activated slag mixtures at the same cure condition. It is concluded from the test results that there is a potential for the use of waste PET as aggregate in the production of alkali-activated slag mortar. Because of using waste materials as binder and aggregate for mortar production in this study, alkali-activated slag mortar with PET aggregate is thought to be a good alternative for recycling of waste materials. (C) 2014 Elsevier Ltd. All rights reserved.