Component Distinction and Content Optimization of Fine Powder in Crushed Sand for High-Fluidity Concrete

Crushed sand is becoming a main substitute for river sand in the concrete industry. The quality of crushed sand production is crucial for concrete. Fine powder refers to the particles less than 0.075 mm in crushed sand, mainly consisting of rock powder (limestone with CaCO3 as the main component) from the parent rock, and clay powder (yellow clay with Al2(Si2O5)(OH)4 as the main component) from the clay minerals. These particles possess a strong adsorption effect, significantly impacting the performance of high-fluidity concrete. This study addresses the issues of distinguishing and optimizing the content of each component in the fine powder of crushed sand used for preparing high-fluidity concrete. To this end, a method has been established to determine the content of each component based on the methylene blue value (MBV). Furthermore, rational content classifications based on MBV have been proposed through a series of tests on crushed sand mortar, including rheological properties, workability, strength, and scanning electron microscopy (SEM) analysis. Finally, a correlation has been established between the initial yield shear stress and the slump flow of mortar, which can be used to predict the workability of mortar and provide guidance for controlling the fine powder content.