Why is it crucial to achieve less than 0.5% retained weight on each sieve?

Achieving less than 0.5% retained weight on each sieve is crucial because it ensures greater sample accuracy. When performing particle size analysis, particularly in asphalt mixtures, having a minimal retained weight helps verify that the distribution of aggregate sizes is consistent with desired specifications. This low retention indicates that the sieving process has effectively separated out the finer materials from coarser ones, thus providing a more representative and accurate sample of the aggregate gradation.

Accurate gradation is essential for the performance characteristics of asphalt mixtures, affecting how well the asphalt binds and how it will perform under various traffic and weather conditions. If the sieving process shows a higher retention weight, it could suggest that the sample does not reflect the actual size distribution or that there are inconsistencies in the material being tested. Maintaining a low retained weight therefore plays a significant role in quality control and assurance for asphalt production.