Filler

Filler or fly ash is a by-product of bitumen extraction process. It is a micron (μ) sized ash-like particle that rather than being disposed of, has been very useful to be used as a high quality, cost-effective mineral filler in hot mix asphalt (HMA) mixes.

Mineral fillers increase the stiffness of the asphalt mortar matrix, improving the rutting resistance of pavements. Mineral fillers also help reduce the amount of asphalt drain down in the mix during construction, which improves durability of the mix by maintaining the amount of asphalt initially used in the mix.

Fly ash will normally meet mineral filler specification requirements for gradation, organic impurities and plasticity. Carbon content, or LOI, is generally not a concern for HMA, as ashes with up to 10% LOI have performed well in laboratory tests.  Also, fly ash is hydrophobic (meaning it sheds water easily), reducing the potential for asphalt stripping; the presence of lime in some fly ashes may also reduce stripping.

The physical requirements for mineral filler in bituminous paving mixtures are defined in AASHTO M17 and are shown in Table 1 below. These requirements include gradation, organic impurities, and plasticity characteristics. Other properties of interest include fineness and specific gravity.

When used as a mineral filler in HMA, fly ash must be in a dry form. Typically, fly ash is handled in a similar manner to hydrated lime - it is transported to the HMA plant in pneumatic tankers; stored in watertight silos at the plant; and metered into the HMA using an auger. Sino Prosper Indocarbon (SIPINDO) Limited processes all orders for the supply filler locally and globally.