Particle size distribution is an important factor when it comes to aggregates. It is used to determine the dimensions of the pore space in cultivated soils, and is also used to classify particles according to their size. This is done through tests such as the flake index, which uses a slotted thickness gauge and a separate length gauge to classify particles. The gradation of aggregates is typically reported graphically by plotting each of the particle sizes on a semi-logarithmic graph and drawing a best-fit curve between the points.
The values obtained from these tests can be used to qualitatively group the aggregate with classification terms such as by space, open grade, or uniform grade to describe the particle distribution. Scanning electron microscopy results have shown that adding fine aggregates to coarse-grained aggregates provides more bridging contacts between the coarse-aggregate particles, which can increase the maximum UCS achieved. Particle size determinations on large aggregate samples are necessary to ensure that aggregates perform as intended for their specified use. The ASTM D4791 test method uses a proportional gauge to test and grade a representative sample of approximately 100 individual aggregate particles of each size fraction.
A sieve analysis or gradation test determines the distribution of aggregate particles by size within a given sample. The flat and elongated particle test measures the dimensional ratios of the individual coarse-grained aggregate particles. Once the proportions of the individual fractions are determined and graphically represented as a gradation curve, the information can be used for more than just a grain size report. It is also used to determine the maximum UCS achieved with a particle size distribution containing 75% coarse-grained aggregate and 25% fine aggregate.
In conclusion, particle size distribution is an important factor when it comes to aggregates. Tests such as the flake index, sieve analysis, and flat and elongated particle test are used to measure particle size distribution, which can then be used to determine the maximum UCS achieved with a given particle size distribution.