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    Effects of mineral additive substitution on the fresh state and time-dependent hardened state properties of calcium alumina cement mortars
    (Turkish Chamber Civil Engineers, Turkish Journal of Civil Engineering) Eren, Faruk; Keskinateş, Muhammer; Felekoğlu, Burak; Tosun Felekoğlu, Kamile
    Calcium aluminate cements (CAC) are a candidate alternative binder to provide the requirements of a repair material such as accelerated hardening, good adhesion, compatibility with existing concrete, dimensional stability and corrosion resistance. The absence of water-soluble hydrated lime among the hydration products can also be accepted as an important advantage. However, the transformation reactions that may occur in the phase structure of the CAC depending on the ambient conditions over time may cause a loss of strength in the concrete produced with this cement. In this study, it is aimed to provide solutions to the problems arising from the conversion reactions in the hydration process of CAC, to improve the fresh state properties and to stabilize the strength development in the long term. Consequently, the effects of using CAC blended with different mineral additives (SiO2 and CaSO4) on the mortar consistency, setting time and rheological properties were investigated. In the hardened state, abrasion resistance and time-dependent compressive and flexural strength developments were determined. As a result of the experimental studies, it was concluded that the CAC mortars containing 16% SiO2 and 50% CaSO4 additives can provide improved properties in their fresh state, and they also demonstrate an improvement in strength after 400 days by obtaining stable products during the hydration process without any time-related strength loss.
  • Küçük Resim
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    The role of Pre-Heating and mineral additive modification on Long-Term strength development of calcium aluminate cement mortars
    (Elsevier Ltd., 2022) Eren, Faruk; Keskinateş, Muhammer; Felekoğlu, Burak; Tosun Felekoğlu, Kamile
    Strength development of Calcium Aluminate Cement (CAC) under various environmental conditions is an interesting subject of topic that pay attention of researchers for a long time. This special cement usually preferred in applications where quick setting ability, high early strength and resistance to chemical attack is required. However, uncertainty in the hydration process and long-term strength problems, due to conversion reactions in combination with high initial material cost, limit the application of this cement. In order to propose a solution to the above-mentioned problems, blended mortar mixtures were prepared by replacing CAC with variable amounts of microsilica, anhydrite CaSO4 and Portland cement within the scope of this study. The compressive strength development of mortar specimens up to 400 days were investigated under semi-dry curing conditions at 20 ± 5 °C and 60 ± 20% RH. During the initial stages of hydration, a distinct pre-heating based curing procedure was applied to the conjugate specimens. Preliminary stabilization of the unstable hydration products is targeted by this pre-heating method. Accordingly, the crystal structure of the hydration products of specimens was analyzed with the support of microstructural studies (XRD, DTA-TGA, SEM-EDS). The pore size distribution and sub-capillary porosity of specimens were also determined by mercury intrusion porosimetry. The effectiveness of the mineral modification and pre-heating based curing method (exposure to 50 ± 1 °C heating for 21 days) on the long-term strength development of CAC is discussed with the aid of microstructural analysis results. The results showed that it is possible to stabilize the hydration process of CAC and its strength becomes predictable in the long term, if appropriate mineral additives in proper replacement ratios are employed in the mixture design.