Which type of sieving equipment is utilized for gradation testing on coarse aggregate?

The correct option for gradation testing on coarse aggregate is the use of box screen sieves. These sieves are specifically designed to effectively separate larger aggregate particles based on size during testing. The rigid structure and design of box screen sieves allow for the reliable collection of samples and facilitate thorough analysis of the aggregate's size distribution. Their box-like shape helps in containing the sample, preventing any loss of material during the sieving process, which is crucial for accurate gradation results.

While round sieves, flat screens, and mesh screens have their own applications, they are not as well-suited for grading coarse aggregates. Round sieves are often associated with smaller particles and might not maintain the integrity of larger aggregates as effectively. Flat screens and mesh screens can vary greatly in their openings and may not provide the structured environment necessary for consistent coarse aggregate testing, leading to potentially inaccurate results. Therefore, box screen sieves are the preferred choice for this particular application in aggregate gradation testing.