CGN3501C Test 4 Study Guide

superpave binder tests: pressure aging vessel (PAV)

simulates long term (3-5 years) aging of binders in service

superpave binder tests: dynamic shear rheometer test (DSR)

measures the viscoelastic properties of a binder by testing it in an oscillatory mode. measured properties: G* and delta (we want high G* bc very stiff and low delta bc elastic in high temperatures, low G* and low delta in intermediate temperatures)

significance of DSR test results

G*/sinδ at the highest pavement temperature should be greater than 1.0 kPa before aging and 2.2 kPa after RTFOT to control rutting

G*sinδ at intermediate pavement temperature should be less than 5000 kPa after PAV to control fatigue cracking

bending beam rheometer test

measures stiffness of binders at low service temperatures. measured properties: Stiffness S should be less than 300 MPa & m should be > 0.3 at 60 seconds at test temperature in order to reduce low temperature cracking

direct tension test

measures the failure stress and failure strain of a binder after PAV at low service temperature

PG 52-46 means

suitable for pavement with maximum temp. of 52 C and minimum temp of -46 C

PG 76-16

Suitable for pavement with max temp. of 76 C & min temp. of -16 C

benefits of asphalt pavement recycling

cost savings
conservation of aggregate and asphalt & energy

preservation of existing pavement geometrics & environment

elimination of reflective cracking due to overlay

reclaimed asphalt pavement (RAP) contains:

hard asphalt binder and degraded aggregate

recycling of RAP involves:

adding appropriate type and amount of recycling agent (or soft asphalt) to soften the binder. adding appropriate type and amount of virgin coarse aggregate to correct the gradation of the degraded aggregate

hot mix (central plant) recycling

RAP (Reclaimed Asphalt Pavement) is combined with new aggregate and asphalt binder or recycling agent in a hot mix plant. Mix is transported to paving site, placed, and compacted

cold mix (central plant) recycling

RAP is combined with new aggregate and asphalt binder or recycling agent in a central plant without application of heat. Mix is transported to paving site, placed and compacted. A wearing course is usually placed over the cold recycled mixture.

hot in place (surface) recycling

existing asphalt surface is heated, scarified to a depth from ¾ to 2 inches (20-50 mm). Scarified material is combined with aggregate and/or asphalt binder and/or recycling agent and compacted. New overlay may or may not be provided

cold in place (surface) recycling

existing asphalt surface is milled. RAP is reduced if needed, mixed with recycling agent in place, placed, and compacted. A hot mix asphalt wearing course is usually placed over the finished surface.

Full depth reclamation (or cold in place surface and base recycling)

all asphalt surface layers and predetermined thickness of underlying base materials are pulverized, stabilized with additives, spread and compacted as a base course. A surface course is applied over it.

rolling sequence for thick lifts

1. Transverse Joints: rolling transversely with static steel-wheel roller

2. Longitudinal Joints

3. Initial Rolling

4. Outside Edge (For thin lifts, do step 4 before 3)

5. Intermediate Rolling

6. Finish Rolling

two major parts of a paver

Power unit (Tractor unit) provides moving power to the paver

Screed unit strikes off the mix to the specified thickness and smoothness and provides initial compaction

paver

a self-propelled machine for placing asphalt mix to a specified depth and providing initial compaction

thin film oven test (TFOT)

to simulate the effects of heating in a hot-mix plant operation on an asphalt cement

rolling thin film oven test (RTFOT)

to simulate the effects of heating in a hot-mix plant operation on an asphalt cement

AR-6000 asphalt

Absolute Viscosity of RTFOT residue at 60 C: 6000 ± 1500 Poises

AR-10000 asphalt

Absolute Viscosity of RTFOT residue at 60 C: 10000 ± 2500 Poises

solubility test

determines the amount of Bitumen (in %) in an asphalt. Bitumen content should be close to 100%

absolute viscosity test

determines units of Poise (P). AC-20 is softer (used in colder environments) than AC-30 (Florida)

AC-30 asphalt

Absolute Viscosity at 60 C: 3000 ± 600 Poises

AC-40 asphalt

Absolute Viscosity at 60 C: 4000 ± 800 Poises

kinematic viscosity test

units of Stokes (St) = cm² / s. To convert kinematic viscosity to absolute viscosity: Stoke x (specific gravity) = Poise

saybolt furol viscosity test

units of seconds, used mainly in measuring viscosity of emulsified asphalt (run on liquid asphalt). The higher the number, the higher the viscosity (harder)

ring & ball softening point test

measures temperature at which an asphalt reaches a certain softness (Penetration = 800)

ranges of PI

PI = - 2 to +2 normal asphalt

> 0: better than average

< 0: worse than average

PI > 2 low temp. susceptibility (abnormally good)

PI < -2 high temp. susceptibility (abnormally bad)

approximate correspondences

60/70 Pen = AC-30 = AR-8000

85/100 Pen = AC-20 = AR-6000

120/150 Pen = AC-10 = AR-3000

cutback asphalt

a liquid asphalt made by dissolving an asphalt in a petroleum solvent (such as gasoline or kerosine). Can be mixed and placed with little or no application of heat.

types of cutback asphalts

Rapid Curing (RC): Relatively hard asphalt (600-2400 P at 60 C or 80-120 Pen) dissolved in gasoline

Medium Curing (MC): Intermediate hardness (300-1200 P at 60 C or 120-250 Pen) dissolved in kerosene (or kerosine)

MC-250 is more viscous (more asphalt) than MC-70

Slow Curing (SC): Soft asphalt dissolved in diesel oil (Kinematic viscosity of asphalt residue from SC - 70 = 4 - 70 St at 60 °C)

RC-70

Rapid Curing Cutback with a kinematic viscosity of 70 - 140 cSt at 60 °C

MC-250

Medium Curing Cutback with a kinematic viscosity of 250-500 cSt at 60 °C

emulsified asphalts

a colloidal mixture of asphalt cement, water and emulsifying agent

two kinds of asphalt emulsion

1. anionic

Asphalt droplets are negatively charged

More compatible with aggregate with positive surface charges (such as limestone)

Typical emulsifying agent: fatty acids

2. cationic

Asphalt droplets are positively charged

More compatible with agg. with negative surface charges (such as siliceous aggregate)

Typical emulsifying agent: fatty amines

two main types of hot mix plants

batch plant

-Produces one batch at a time (3,000-10,000 lbs/batch)

-Dries and heats the aggregate in a dryer, and mixes the aggregate and asphalt in a separate mixer

-Major parts: cold bins, cold feed gate, cold elevator, dryer, dust collector, exhaust stack, hot elevator, screening unit, hot bins, weigh box, mixing unit (or pugmill), mineral filter storage, hot asphalt cement storage, asphalt weigh bucket, baghouse

drum mix plant

-Produces mixes in a continuous process

-Dries the aggregate and blends it with asphalt in the same piece of equipment

-Major parts: cold feed bins, cold feed conveyor, automatic weighing system, drum mixer, asphalt pump, asphalt storage tank, dust collector, hot-mix conveyor, mix surge silo, control van

asphalt pavement structure

seal coat, surface, tack coat, binder, prime coat, base, subbase, compacted subgrade, natural subgrade

Bitumen definition

black or dark brown sticky substance composed principally of high-molecular-weight hydrocarbons soluble in Carbon Disulfide (CS2).

category 1: natural asphalt

Lake asphalt (occurs in form of a lake), rock asphalt (found impregnated in sandstone or limestone, good skid resistance), gilsonite (hard and brittle asphalt mined in Utah)

category 2: petroleum asphalt

derived from the refining of crude oil

asphalt characteristics

Insoluble portion in natural asphalt is mineral matter

More weather resistant

Can occur in natural form or as a by-product of petroleum refinery

tar characteristics

Distinguished by odor (tar has an aromatic odor)

Insoluble in tar is free carbon

Tar molecules tend to be aromatic (ring or cyclic), while asphalt molecules tend to be aliphatic (straight chain)

More temperature susceptible

Can coat aggregates better and is more water resistant

Fumes from heated tar cause health hazards such as severe eye and skin irritation

Does not occur in natural form, but comes as a by-product in the manufacture of coke or water-gas

asphalt and tar similarities

Composed principally of Bitumen

Black or dark brown in color

Cementitious

Water repellent

penetration test

a consistency test used to identify an asphalt as to its hardness or grades

Other uses: measure changes in hardness due to heating or changes in temperature

The penetration value (in 0.1 mm) is used to classify asphalt cement into grades, such as 40-50, 60-70, 85-100, 120-150, and 200-300. Use softer asphalts (bigger number) in colder temperatures

40/50 pen asphalt

Penetration at 25 C: 40-50

flashpoint test

determines max temperature to which an asphalt can be safely heated in the presence of an open flame. Other uses: detect contaminating material, such as gasoline or kerosine

Cleveland Open Cup or Tag Open Cup. Cleveland method is used on asphalt cements or asphalts with relatively higher flash points, while Tag method is used on cutback asphalts or asphalts with flash points of less than 79 C.

ductility test

measures the distance a standard asphalt sample will stretch without breaking under a standard testing condition

Standard asphalt can stretch without breaking at rate of 5 cm/min at 25 C

Low ductility is related to poor adhesive property (we want high ductility)