by Asphalt, a sticky, black, and highly viscous liquid or semi-solid form of petroleum, is widely used in road construction around the world. While asphalt has excellent binding properties that make it suitable for paving applications, it also has some limitations. This is where asphalt additives come into play. Asphalt additives are materials that are added in small amounts to asphalt to enhance its engineering properties. Some common types and uses of asphalt additives are explained below.
Anti-stripping Additives
One key issue with asphalt is its inherent lack of adhesion to aggregate materials like stone, gravel, and sand that are used in asphalt mixes. Over time, this can cause the aggregate and asphalt to separate or “strip”, leading to cracks and potholes in the road surface. Asphalt Additives work by improving the adhesion between asphalt and aggregate through chemical and physical interactions. This prevents moisture from penetrating and weakening the bond. Common anti-stripping additives include amines and hydrated lime.
Viscosity Modifiers
The viscosity or thickness of asphalt is an important parameter that determines its workability and performance qualities. However, viscosity can fluctuate with changes in temperature. Viscosity modifiers are additives that impart elasticity and flexibility to asphalt at a wide range of temperatures. This allows the asphalt mix to be laid easily and also resist cracks from thermal expansion/contraction cycles. Some frequently used viscosity modifiers are styrene-butadiene-styrene and ethylene vinyl acetate.
Anti-oxidants
Prolonged exposure to oxygen and heat causes asphalt to oxidize or age prematurely over time. This oxidation leads to undesirable hardening and embrittlement of the asphalt. Anti-oxidant additives inhibit or slow down the oxidation reactions in asphalt by functioning as free radical scavengers. Common anti-oxidants added are amines and sulfonamides, thereby extending the service life of asphalt pavements.
Rejuvenators
Over several years of exposure to environmental stresses like ultraviolet radiation, moisture, and traffic loads, the binding asphalt in old pavements becomes oxidized and brittle. This accelerates cracking and deterioration of the road surface. Rejuvenators are additives designed to overcome this effect by restoring some of the lost properties in aged asphalt. Rejuvenators soften the asphalt binder and renew its flexibility. They find widespread application in asphalt pavement preservation and rejuvenation.
Fatty Amine Additives
Fatty amine compounds function as penetrating agents in asphalt. When added to fresh or recycled asphalt mixes, fatty amines aid the penetration and coating of aggregate particles for uniform binder distribution and adhesion. This results in mixes with optimized workability, reduced cracking, and enhanced moisture resistance. Fatty amines also act as corrosion inhibitors in asphalt. They are often used when recycling old reclaimed asphalt pavement in hot or warm mix recycling processes.
Polymer Modifiers
Adding synthetic polymers to asphalt binders can significantly boost the performance characteristics of the mix. Common polymeric modifiers includeStyrene-Butadiene-Styrene, Ethylene Vinyl Acetate, Ground Tire Rubber, etc. Polymer-modified asphalt mixes exhibit higher resilience, flexibility and resistance to reflective cracking compared to conventional mixes. The enhanced properties offset some limiting factors of unmodified asphalt and widen the range of applications as both surface course and stress-absorbing interlayers. However, polymer additives do increase the production cost of asphalt compared to other modifiers.
Application Techniques
Asphalt additives can be introduced at various stages of the asphalt production and paving process – during the manufacture of asphalt cement, incorporation into the hot mix plant, or at the job site during construction.
– At the refinery or terminal during asphalt cement production: Anti-oxidants and some viscosity modifiers are commonly blended in asphalt cement.
– In the dry form at the hot mix asphalt plant: Most modifiers can be metered and mixed with dry aggregate before the addition of asphalt binder.
– As an “on-site” additive applied during paving: Rejuvenators, anti-strip agents, etc. are sprayed onto fresh asphalt mats for maximum surface treatment effect.
Proper Selection and Quality Control
With the variety of available asphalt additives, selecting the right type and evaluating their effectiveness requires technical expertise. Field tests must be carried out to determine additive dosage, compatibility with local materials, and quality assurance during and after construction. Proper additive selection aligned with project needs and quality control ensures maximum performance benefits from asphalt pavements for their design life. Overall, asphalt additives play a crucial supporting role in improving the structural integrity and durability of roads.
*Note:
1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it.
