What is the formula for determining the asphalt spread rate for an FC-5 mix?

The formula for determining the asphalt spread rate for an FC-5 mix involves the thickness of the layer and the bulk specific gravity (gsb) of the aggregate used in the mix design. The gsb represents the mass of the aggregate per unit volume, which is crucial for calculating the correct amount of material needed for the desired surface.

By using the gsb value, the formula incorporates how densely packed the aggregates are in the asphalt mix at a specific thickness, providing an accurate measure for the spread rate. The multiplication factor of 40.5 in the formula serves as a conversion constant that adjusts the units accordingly, ensuring the result is expressed in a meaningful way relevant to paving applications. This is essential for ensuring that the surface is durable and meets specified requirements.

The other formulas, while similar in structure, utilize either the maximum specific gravity (gmm) or incorrect constants that do not align with the industry standards for calculating spread rates, leading to potential inaccuracies in material application during paving. It's vital to apply the correct parameters to maintain the integrity of the pavement structure.