Asphalt Properties and Sources

Asphalt Characteristics

• Asphalt is a dark brown to black, highly viscous, hydrocarbon produced from petroleum distillation residue

Sources of Asphalt

• Natural Deposits: Trinidad Asphalt lakes
• Petroleum Refinery
• Bituminous Materials

Types of Asphalt

• Asphalt Cement: prepared for use in hot-mix asphalt (HMA) and other paving applications
• Asphalt Binder: the principal binding agent in HMA, including asphalt cement and any added materials to modify its properties

Cutback Asphalt

• A combination of asphalt cement and petroleum solvent
• Classified into three types:
  • Rapid Curing (RC)
  • Medium Curing (MC)
  • Slow Curing (SC)

Emulsified Asphalt

• A suspension of small asphalt cement globules in water, assisted by an emulsifying agent (such as soap)
• Classified into three types:
  • Rapid Setting (RS)
  • Medium Setting (MS)
  • Slow Setting (SS)
• Can be anionic (negatively charged) or cationic (positively charged)

Foamed Asphalt

• Formed by combining hot asphalt binder with small amounts of cold water

Prime Coats

• A sprayed application of cutback or emulsion asphalt applied to the surface of untreated subgrade or base layers
• Purpose: to fill surface voids and protect the subbase from weather

Asphalt Properties

• Asphalt: a dark brown to black, highly viscous, hydrocarbon produced from petroleum distillation residue
• Asphalt Cement: prepared for use in hot-mix asphalt (HMA) and other paving applications
• Asphalt Binder: principal binding agent in HMA, including asphalt cement and materials added to modify its properties

Types of Asphalt

• Cutback Asphalt: combination of asphalt cement and petroleum solvent
• Emulsified Asphalt: suspension of small asphalt cement globules in water, assisted by an emulsifying agent
• Foamed Asphalt: formed by combining hot asphalt binder with small amounts of cold water

Asphalt Applications

• Prime Coat: sprayed application of cutback or emulsion asphalt to untreated subgrade or base layers
• Tack Coat: thin bituminous liquid asphalt, emulsion, or cutback layer applied between HMA pavement lifts to promote bonding

Asphalt Characteristics

• Durability: measure of how asphalt binder physical properties change over time (age hardening)
• Rheology: study of deformation and flow of matter
• Volatility: asphalt cement volatilizes (gives off vapor) when heated
• Purity: asphalt cement should consist of almost pure bitumen

Asphalt Grading Systems

• Penetration Grading: based on the depth a standard needle will penetrate an asphalt binder sample
• Viscosity Grading: measures penetration and an asphalt binder's viscosity at 140°F and 275°F
• Superpave Performance Grading (PG) System: uses a common battery of tests to determine an asphalt binder's performance at specific temperatures dependent on climatic conditions

Asphalt Mix Design

• HMA Mix Design: process of determining what aggregate to use, what asphalt binder to use, and the optimum combination of these two ingredients
• Job Mix Formula: recommended mixture, including aggregate gradation and asphalt binder type