HMA Modifier

Some pavement concretes need alteration with a specific end goal, which is to meet details. Bitumen alteration has been polished for over 50 years but has accepted united regard in the past decade or somewhere in the vicinity. The put consideration might be ascribeed in the emulating components (Roberts et al., 1996[1]):

Increased demand on HMA pavements. Traffic volume, loads and tire pressures have increased substantially in recent years, which can cause increased rutting and cracking. Many modifiers can improve the asphalt binder’s stiffness at normal service temperatures to increase rut resistance, while decreasing its stiffness at low temperatures to improve its resistance to thermal cracking.
Superpave asphalt binder specifications. Superpave asphalt binder specifications developed in the 1990s require asphalt binders to meet stiffness requirements at both high and low temperatures. In regions with extreme climatic conditions this is not possible without asphalt binder modification.
Environmental and economic issues. It is both environmentally and economically sound to recycle waste and industrial byproducts (such as tires, roofing shingles, glass and ash) in order to gain added benefit. Thus, when they can benefit the final product without creating an environmental liability they are often used as additives in HMA.
Public agency willingness to fund higher-cost asphalt additives. Modified asphalt cement is usually higher in initial cost than unmodified asphalt cement, but it should provide a longer service life with less maintenance.

There are various Binder added substances good to go on the business sector today. The profits of altered black-top bond can just be apprehended by a reasonable determination of the modifier(s); not all modifiers are fitting for all provisions. In across the board, black-top bond might as well be adjusted to attain the taking after sorts of enhancements (Roberts et al., 1996[1]):

Lower stiffness (or viscosity) at the high temperatures associated with construction. This facilitates pumping of the liquid asphalt binder as well as mixing and compaction of HMA.
Higher stiffness at high service temperatures. This will reduce rutting and shoving.
Lower stiffness and faster relaxation properties at low service temperatures. This will reduce thermal cracking.
Increased adhesion between the asphalt binder and the aggregate in the presence of moisture. This will reduce the likelihood of stripping. Figure 1 shows two aggregate samples from the same source after they have been coated with asphalt binder. The asphalt binder used with the sample on the left contain no anti-stripping modifier, which resulted in almost no aggregate-asphalt binder adhesion. The asphalt binder used with the sample on the right contains 0.5% (by weight of asphalt binder) of an anti-stripping modifier, which results in good aggregate-asphalt binder adhesion.

Common Types of Asphalt Modifiers

The following table lists some common asphalt cement and HMA modifiers and their general purpose/use.

Table 1. Asphalt Cement and HMA Modifiers (from Roberts et al., 1996^[1])
Type	General Purpose or Use	Generic Examples
Filler	Fill voids and therefore reduce optimum asphalt content Meet aggregate gradation specifications Increase stability Improve the asphalt cement-aggregate bond	Mineral filler crusher fines lime portland cement fly ash Carbon black
Extender	Substituted for a portion of asphalt cement (typically between 20 – 35 % by weight of total asphalt binder) to decrease the amount of asphalt cement required	Sulfur Lignin
Rubber	Increase HMA stiffness at high service temperatures Increase HMA elasticity at medium service temperatures to resist fatigue cracking Decrease HMA stiffness at low temperatures to resist thermal cracking (see Figure 2)	Natural latex Synthetic latex (e.g., Polychloroprene latex) Block copolymer (e.g., Styrene-butadiene-styrene (SBS)) Reclaimed rubber (e.g., crumb rubber from old tires)
Plastic		Polyethylene/polypropylene Ethylene acrylate copolymer Ethyl-vinyl-acetate (EVA) Polyvinyl chloride (PVC) Ethylene propylene or EPDM Polyolefins
Rubber-Plastic Combinations		Blends of rubber and plastic
Fiber	Improving tensile strength of HMA mixtures Improving cohesion of HMA mixtures Permit higher asphalt content without significant increase in draindown	Natural: Asbestos Rock wool Manufactured: Polypropylene Polyester Fiberglass Mineral Cellulose
Oxidant	Increase HMA stiffness after the HMA is placed	Manganese salts
Antioxidant	Increase the durability of HMA mixtures by retarding their oxidation	Lead compounds Carbon Calcium salts
Hydrocarbon	Restore aged asphalt cements to current specifications Increase HMA stiffness in general	Recycling and rejuvenating oils Hard and natural asphalts
Antistripping Agents	Minimize stripping of asphalt cement from aggregates	Amines Lime
Waste Materials	Replace aggregate or asphalt volume with a cheaper waste product	Roofing shingles Recycled tires Glass