CE 382 Asphalt ConcreteFall 2015

Lecture 1 - Asphalt Cement Introduction

Learning Objectives

• Understand the components of asphalt concrete

• Understand manufacturing asphalt cement• Understand the types of asphalt• Understand asphalt specifications– Historical– Viscosity

Asphalt Concrete

% by weight955

• Asphalt concrete is commonly referred to as Hot Mix Asphalt (HMA)

• 94% of roads in US are surfaced with asphalt

MaterialsAggregatesAsphalt (Binder)Air

HMA Components

Asphalt Stress Response

Two Types of Asphalt• Natural Asphalts: Occurs in geologic strata

as both soft and hard asphalt material.

• Petroleum Asphalts: Colloidally dispersed hydrocarbons in crude petroleum and are obtained by refining crudes.

Asphalt Legends and Myths

• La Brea Tar Pits in Los Angeles

• Canadian Tar Sands

• Roofing Tar

• Brother-in-law says he needs to “Tar” his driveway

Myth Busted!

• La Brea Tar Pits in Los Angeles

• Canadian Tar Sands

• Roofing Tar

• Brother-in-law says he needs to “Tar” his driveway

Asphalt versus Tar

• Asphalt Cement (bitumen): Naturally occurring or produced by petroleum distillation– asphalt pavements– driveway sealcoats – roofing shingles

• Tar: Naturally occurring or manufactured by distillation of coal – Coal tar is listed at number 1999 in the United Nations

list of dangerous goods

Trinidad Lake Asphalt

Background

• First US hot mix asphalt (HMA) constructed in 1870’s– Pennsylvania Ave– Used naturally occurring asphalt from surface of lake

on Island of Trinidad

• Demand for paved roads exceeded the supply of lake asphalts in late 1800’s– Led to use of petroleum asphalts

Asphalt Components• Asphaltenes

– Large, discrete solid inclusions (black)– High viscosity component

• Resins– Semi-sold or solid at room temperature– Fluid when heated– Brittle when cold

• Oils– Colorless liquid– Soluble in most solvents– Allows asphalt to flow

Petroleum Asphalt

Refinery Operations

Crude Petroleum Variation• Can vary significantly, resulting in very different levels of

performance.• American Petroleum Institute– API Gravity (60º F) = [141.5/specific gravity] - 131.5– API Gravity of Water is 10.– Low API gravities (<25) have relatively low %’s of distillable

overhead fractions & high %’s of asphalt cement. These crudes are known as heavy crudes. If they contain a lot of sulfur, they are known as sour.

– High API gravities are the converse. Are known as light crudes. If they contain little sulfur, they are known as sweet.

Asphalt Types

• Asphalt cements– Generally refinery produced materials– Air blown asphalt cements

• Cutbacks– Asphalt cements “cut” with petroleum solvents

• Emulsions – Mixture of asphalt cement, water, and emulsifying

agent

Air-Blowing• Air blowing is used to increase the viscosity of the

vacuum resids.• Used for roofing industry products (batch

blowing).• Used to “improve” the temperature susceptibility

of asphalt cements (continuous blowing).

Oxidization is occurring.

Cutbacks = Asphalt + Solvent

• Rapid-Curing (RC): Gasoline or naptha• High volatility of solvent• Tack coats, surface treatments

• Medium-Curing (MC): Kerosene• Moderate volatility• Stockpile patching mix

• Slow Curing (SC): Road oils• Low volatility• Prime coat, dust control

Emulsions = Asphalt + H20 + Emulsifying agent

• Emulsifier gives surface charge to asphalt droplets suspended in water medium

• Selection of emulsifier type is dependent upon aggregate used (electrical charge)

• Asphalt Emulsions are needed to “set” or “break” Anionic Emulsion (-) Cationic Emulsion (+)

Asphalt Distributor (for emulsions)

Grades of EmulsionsANIONIC EMULSIFIED ASPHALT CATIONIC EMULSIFIED ASPHALT

RS-1 CRS-1 RS-2 CRS-2 MS-1 --- MS-2 CMS-2 MS-2h CMS-2h HFMS-1 --- HFMS-2 --- HFMS-2h --- HFMS-2s --- SS-1 CSS-1 SS-1h CSS-1h

Early Specifications

• Chew test• Penetration

• Solubility• Ductility• Flash Point

• Softening Point (Ring-and-Ball Method)• Specific Gravity

Penetration (early 1900’s)

Pen Grades

Flash Point (Cleveland Open Cup)

Solubility Test

Ductility

Measure of a materials ability to undergo deformation without breaking.

Thin Film Oven

Outside of Oven

Rotating Shelf

Pan Thermometer

Temperature

25C (77F)

Penetration, 0.1 mm

High

Medium

Low

Softening Point (Ring-and-Ball Method)

The temperature at which the bituminous material touches the bottom of the container.

Viscosity Graded Specifications(1970’s)

Viscosity: the ratio between the applied shear stress and the rate of shear.

h = t / g

Definition

Absolute and Kinematic Viscosity

• Absolute– Viscosity at 60ºC– Time required for a fixed volume of liquid to be

drawn through a capillary tube with a vacuum.– (flow time) x (viscometer calibration) = poises

• Kinematic– Viscosity at 135ºC– Measured in cm2/sec = stokes (centistokes)

• Abs. Visc. = Kin. Visc.(in stokes)x spec. gr.

Types of Viscosity

Viscosity Specifications

• AC Grades– AC 2.5, AC 5, AC 10, AC 20, AC 40

• AR Grades (Aged Residue)– AR 1000, AR 2000, AR 4000, AR 8000, AR 16000

.1

.2

.3

.5

1

105

100 110 120 130 140 150 160 170 180 190 200

Temperature, C

Viscosity, Pa s

Compaction Range

Mixing Range

Mixing/Compaction Temps

Rotational Viscometer

• Pumpability

• Mixability

• Workability

Pavement Performance Related to A.C. Rheological Properties

• Ravelling• Cracking

– Load-Associated– Non-Load Associated

• Rutting• Stripping

Temperature Dependency

Superpave Physical Tests for Asphalt Binders

• Rolling Thin Film Oven (RTFO)• Pressure Aging Vessel (PAV)• Rotational Viscometer (RV)• Dynamic Shear Rheometer (DSR)• Bending Beam Rheometer (BBR)• Direct Tension Tester (DTT)