Research Information System
Mediterranean Geosciences Union (MedGU)-24, Barcelona, Spain, 25 - 28 October 2024, (Unpublished)
One of the most important aggregate resources of İstanbul is the rocks consisting of greywacke-shale sequence belonging to the Trakya Formation. Aggregate mining is carried out on these rocks and aggregates of different sizes obtained from these rocks by crushing method are widely used in concrete production plants. The widespread use of these aggregates in concrete production requires a thorough assessment of their alkali-silica reaction (ASR) potential. ASR poses a significant threat to the durability of concrete structures, leading to cracking, expansion, and ultimately compromising their structural stability. Understanding the ASR characteristics of these aggregates is crucial for ensuring the long-term performance and safety of concrete constructions in the region. The study employed the ASTM C1260 standard to conduct ASR tests on greywacke-shale samples collected from an aggregate quarry in Istanbul. The mineral composition of the aggregates was determined using XRD analysis. Mortar bars prepared from these aggregates were subjected to accelerated ASR tests for a duration of 21 days, with length change measurements taken at regular intervals. The accelerated ASR tests revealed a length extension (expansion) of 0.21% in mortar bars after 21 days. The aggregates were found to consist predominantly of quartz, albite, chlorite, muscovite, and calcite minerals. The observed expansion exceeding 0.2% indicates a potential for ASR in these aggregates. The presence of quartz minerals, which are known to trigger ASR when they have undergone metamorphism, in the non-metamorphosed greywacke-shale rocks (Trakya Formation) suggests that these quartz minerals were likely sourced from pre-existing metamorphic rocks during the formation of the sedimentary greywacke-shale sequence. This metamorphic origin of the quartz minerals contributes to the observed ASR risk in these aggregates. Additionally, the clayey matrix of the aggregates may contribute to ASR by facilitating moisture movement and silica dissolution. The study highlights the potential for deleterious ASR in greywacke-shale aggregates from Istanbul's Trakya Formation. These findings underscore the importance of considering ASR mitigation strategies, such as the use of supplementary cementitious materials or chemical admixtures, when utilizing these aggregates in concrete construction to ensure the long-term durability and safety of concrete structures. In addition, this study emphasizes the relevance of these findings to the construction industry by highlighting the importance of assessing aggregate reactivity during the planning and design stages of concrete production. This approach is essential for developing mitigation strategies tailored to the specific characteristics of greywacke-shale aggregates, thereby ensuring the safety and longevity of concrete structures in İstanbul.