AbstractThe scarcity of river sand is increasing due to worldwide fast-track urbanization and infrastructure development, which leads to high demand for fine aggregates. In recent years, the exploration and consumption of different types of fine aggregates other than natural sand in construction are growing across the globe. The existence of clay in alternative fine aggregates (AFA) is one of the formidable hurdles for their successful utilization in concrete and mortar. Clay content adversely affects the properties of concrete and mortar, such as strength, workability, and durability. Therefore, the objective of the present study represents the assessment of clay content in river sand and other types of alternative sands, such as recycled fine aggregate (RFA), crushed rock sand (CRS), and coal bottom ash (CBA), using an innovative phenol adsorption method. The activated clay effect on adsorption was also assessed. The phenol is adsorbed on the clay surface, resulting in an exothermic reaction that releases heat and causes an increase in the temperature of the solution. Standard correlation curves were developed to evaluate the clay content in different types of fine aggregates with the corresponding variation in temperature. The results were validated using a standard methylene blue value spot test, which was found in good agreement. Clay in different types of fine aggregates used in the present study was found to be less than 5%. Also found was that the activation process increases the phenol adsorption property of clay. The phenol adsorption method is relatively faster and more reliable than the methylene blue value spot test method for assessing clay content. The properties of mortar also indicated that workability and compressive strength decrease with an increase in the clay content in fine aggregates irrespective of activation. The phenol adsorption technique, which is novel, can be used to develop a sensor to evaluate the clay content in fine aggregates in the future by utilizing the exothermic property of clay.