Utilization of clay-containing aggregate sludge waste as structural concrete and asphalt aggregate

In the aggregate quarries in Çiftalan and Ağaçlı (Eyüpsultan, Turkey) regions, grovak-shale type rocks belonging to the Thracian Formation are used as concrete and asphalt aggregates. After crushing, these rocks are classified into 0-5 mm, 5-12 mm and 12-24 mm sizes and marketed as concrete and asphalt aggregates. Aggregates with sizes larger than 5 mm can be used directly in concrete and asphalt applications without any washing process, while aggregates with sizes smaller than 5 mm are called fine aggregates and are marketed after the washing process since the methylene blue value is too high for concrete and aggregate. After the washing process, grains smaller than approximately 100 microns in size (especially clay minerals) are stockpiled in waste sites. Within the scope of this study, it is aimed to produce sinter aggregates with strength that can be used in concrete from these waste materials. It was determined that the waste materials with a grain diameter of less than 100 micron consisted of 28.6% quartz, 21.9% albite, 17% muscovite, 24.9% chlorite and 3.6% calcite minerals. In addition to minerals, 3.4% organic matter was detected. In addition, the main oxide compositions of these wastes were determined, and it was found that 54.51% SiO₂, 18.1% Al₂O₃, 19.66% sum of fluxes (CaO, Na₂O, Fe₂O₃, K₂O, MgO) and 5.8% loss on ignition. Within the scope of determining the thermal properties of the wastes, DTA analyzes were carried out and it was determined that two different endothermic reactions took place in the range of 500-600 °C and 700-800 °C, thus dehydroxylation reactions took place in these temperature ranges. In the range of 1000-1100 °C, it was determined that an exothermic reaction, that is, a new phase or several phases were realized. Considering these thermal properties of the wastes, 1100 °C was determined as the sintering temperature. For the sintering process, the samples were first dried at 105 °C and then milled and powdered again. The powdered samples were placed in a metal cell with a diameter of 5 cm and a height of 10 cm and then compressed with a load of 200 kg per cm². The compressed samples were heated to 1100 °C in a high temperature furnace with a temperature increase of 10 °C per minute and kept at 1100 °C for 30 minutes and then allowed to cool in the furnace. Since the height of these sintered cylindrical specimens was less than 10 cm, the Brazilian test method was used to determine their strength. As a result of the experiment, it was determined that the Brazilian test strengths of 3 different specimens reached 8.8 MPa, 9.6 MPa and 15.7 MPa. Considering the strength values obtained, it was determined that ideal products for concrete and asphalt aggregate can be produced from the dust wastes released in these aggregate quarries.