Asphalt

Batch type Mixing Plant

-Hot aggregates removed from storage bins in quantities desired -Mixing chamber is known as pugmill where asphalt goes into -Materials emptied from the pugmill into the truck one mix at a time

Difference between Asphalt and Tar

Asphalt is soluble in petroleum, tar is not. Asphalt has bitumens, tar has low bitumens

Anionic

Negatively charged Emulsion

Stability

-Ability to resist shoving and rutting under traffic loads -Maintain shape

Durability

-Ability to resist weather/traffic, stripping of asphalt

Flash Point Test

-Asphalt cements are heated before use in construction -Must understand what the max temp the material can be heated to safely -Flash point = temp at which an instantaneous flash occurs

Stationary plants

-Considered central mix plants -Can be either batch or continuous/drum-mix

Solubility

-Determines the purity of the asphalt cement -The Asphalt cement will soluble in a particular solvent

Portable Plants

-Easily moved from job site to job site (trucks or rails) -Can either be batch or continuous/drum-mix

Rolling Operation #2

-Roller wheel should be kept moist to avoid picking up material -Move slowly and uniformly -Line of rolling should not change suddenly or reverse

Mix Design Properties

-Stability -Durability -Impermeability -Workability -Flexibility -Fatigue Resistance -Skid Resistance

Penetration test

-Test hardness and consistency

Continuous-type Mixing Plant

-Uninterrupted flow of materials in and materials out -Mixing occurs in the pugmill -Inclined mixer allows for flow of material from one end to the other -Surge bin silo is used for storage of mix. Usual maximum time allowed for storage is 24 hrs.

Thin-film oven test

-Used to simulate the aging that takes place during the production of hot mix and during 1st year of pavement's life

3 tests performed on Hockey pucks

1. BSG 2. Stability and flow 3. Density and voids content

Rolling Operations and Purpose

1. Breakdown/Initial Rolling: compacts the material beyond that imparted by the paver, to obtain practically all of the density it needs. 2. Intermediate rolling: densifies and seals the surface 3. Finish rolling removes roller marks and other blemishes left from previous rolling

Asphalt is selected based on...

1. Climate 2. Traffic 3. Location

Two Different Distillation Process to Produce Asphalt

1. Fractional Distillation: Crude oil is heated, lighter oils vaporize and are drawn off, leaving behind asphalt cement 2. Destructive Distillation: crude oil heated under pressure to higher temperatures than fractional distillation

Basic requirements for an asphalt pavement

1. Have sufficient total thickness and internal strength to carry expected traffic loads 2. Prevent penetration or internal accumulation of moisture. 3. Have top surface that's smooth and resistant to wear, distortion, skidding, and deterioration by weather and de-icing chemicals

General Mixture Characteristics

1. Mic density 2. Air Voids 3. Voids in mineral aggregate 4. Asphalt content

Courses of Asphalt Pavement (Top to Bottom)

1. Surface Course 2. Binder Course 3. Base Course 4. Sub-base course 5. Subgrade

Typical order of pavement operations

1. The subgrade under the pavement will be properly graded and uniformly compacted to the required density. 2. Trucks with the asphalt mix will dump its content into the paver. 3. Pavers will place and initially compact the asphalt mixture to a specific width and depth. 4. Immediately after, steel wheeled and rubber-tired rollers are driven over the pavement to compact the mix until the pavement reaches its required density or until the temp has dropped to a point where further compaction may produce detrimental results. 5. IT'S READY FOR TRAFFIC

Factors that determine asphalt pavement thickness

1. Traffic 2. Subgrade strength 3. Strength and other influencing characteristics of the material available or chose for the layers or courses in the total asphalt pavement structure 4. Any other special factors

Typical density of Asphalt

125 lb/ft3

Typical percentage of RAP used in recycle hot mix

20-30%

Typical Air Void Content

> 8%

Flexibility

Ability of the pavement to move without cracking

Skid resistance

Ability to minimize skidding or slipping

Superpave binder

Another name for asphalt

HMA (hot mix asphalt)

Asphalt concrete paving mixtures prepared in a hot mix plant -Considered highest quality type of asphalt mixture bc the plant removes all ambient moisture from aggregates which ensures the best bond between aggregates and asphalt binder

Paving Machines/Equipment

Asphalt paver, roller, distributor, motor grader

Superpave pucks are ___ than Marshall pucks

Bigger

Asphalt can be modified into liquid form known as ___ or ____

Cutback Asphalt or an Emulsion

Asphalt Content

Dependent on aggregate (gradation and % absorption) -CA = less asphalt -FA = more asphalt

Superpave Mix Method

Design based on PERFORMANCE of the final product -Attention is paid to the % voids (by volume)

Settlement test

Detects the tendency of asphalt globules to "settle out" during storage of emulsified asphalt

Sieve test

Determine quantitatively the percentage of asphalt cement present in the form of pieces, strings, or relatively large globules

Subgrade Evaluation

Determine the strength of the subgrade to evaluate its ability to carry load 1. Loading tests in the field directly on the subgrade 2. Loading tests in lab using representative samples (California Bearing Tests) 3. Evaluations based on classification of soil by identifying and testing the constituent particles on the soil

Mixed-in-place construction

Emulsified asphalt and many cutback asphalts are fluid enough to be sprayed onto and mixed into aggregate at moderate- to warm-weather temperatures Benefits: 1. Utilization of aggregate already on the roadbed 2. Elimination of the need for central mixing plant.

Marshall Mix Method

Intent was to provide a simple design procedure for pavements that could quickly and easily be constructed -Tested materials should be identical to those that will be used in field

Low Density

Means there is low volume/air voids = will not last long

Saybolt Furol Viscosity Test

Measures anionic and cationic emulsions

Marshall mix design is based on ____ of the asphalt product.

Physical characteristics

Cationic

Positively charged Emulsion

RAP

Recycled Asphalt Pavement -Milling (grinding) removal of old asphalt pavements and reused in new hot mic asphalt pavements

Fatigue Resistance

Resistance to repeated loading

Impermeability

Resistance to the movement of air and water

SHRP

Strategic Highway Research Program

Tons of asphalt concrete required

T = (A x h x uw)/2000lb = (Area x thickness x unit weight) / 2000 lb uw = 140 to 150 lb/ft3

Hockey Pucks

Test specimens -- 2.5 in thick, 4 in. diameter

Viscosity test

Tests resistance to flow

Slurry Seal

Thin asphalt overlay applied by a continuous process machine to worn pavements to seal them and provide a new wearing surface

The weight and volume of ____ that a road is expected to carry initially and throughout its design life influence the required thickness of asphalt pavement structure, as well as mix selection and mix design.

Traffic

Distillation test

Used to determine the relative proportions of asphalt cement and water in the asphalt emulsion

VMA

Voids in Mineral Aggregate in % (by volume)

Ductility test

Workability