CE 2030 Chapter 9 - Asphalt

Questions and Answers from Textbook

What is the difference between tar and asphalt cement?

- Tar is a byproduct of the destructive distillation of coal or the cracking of petroleum vapors. It is primarily used for waterproofing membranes, such as roofing. Tar has a higher viscosity and is more brittle than asphalt cement.

- Asphalt Cement, on the other hand, is derived from the refining of crude oil. It is a blend of hydrocarbons and is primarily used in pavement construction due to its excellent adhesive properties and flexibility.

Main Uses of Asphalt

Pavement Construction, Sealing and Waterproofing, and Maintenance

Define Pavement Construction

Asphalt is primarily used for constructing roads, highways, and airport runways due to its durability and ability to withstand traffic loads.

Define Sealing and Waterproofing

It is used in roofing materials and to seal foundations and other structures to prevent water infiltration.

Maintenance

Includes patching, resurfacing, and sealing existing pavements.

What are the ingredients of asphalt cutbacks?

Composed of asphalt cement dissolved in lighter hydrocarbon solvents (e.g., kerosene, gasoline).

What are the ingredients of asphalt emulsions?

Composed of asphalt cement, water, and an emulsifying agent (usually a soap).

Name three uses of asphalt emulsion

  1. Tack coats between layers of asphalt.

  2. Fog seals to protect existing pavements.

  3. Chip seals for surface treatment.

Why is asphalt emulsion preferred over asphalt cutback?

asphalt emulsion is preferred over cutbacks because it does not contain volatile solvents, making it safer and more environmentally friendly. It can also be applied without heating.

Define what is meant by temperature susceptibility of asphalt

Refers to how the viscosity of asphalt changes with temperature. As temperature increases, viscosity decreases, affecting the performance of asphalt concrete.

Briefly discuss the chemical composition of asphalt

Asphalt is primarily composed of hydrocarbons, such as Aliphatic Compounds and Aromatic Compounds. Minor components include heteroatoms such as sulfur, nitrogen, and oxygen, which can affect the chemical behavior and performance of asphalt.

Flash Point Test:

Determines the safety of handling and storage of asphalt by identifying the temperature at which it can ignite.

RTFO Procedure:

Simulates short-term aging of asphalt during mixing and placement, helping to predict performance in service.

Rotational Viscometer Test:

Measures the viscosity of asphalt at specific temperatures, which is critical for determining mixing and compaction temperatures

Dynamic Shear Rheometer Test:

Evaluates the viscoelastic properties of asphalt, predicting its performance under load and temperature conditions.

Penetration Test:

Measures the consistency of asphalt, indicating its softness or hardness, which is important for selecting appropriate grades.

Discuss the aging that occurs in asphalt cement during mixing with aggregates and in service. How can the different types of aging of asphalt cement be simulated in the laboratory?

  - Short-Term Aging: Occurs during mixing and placement, leading to increased viscosity and stiffness.

  - Long-Term Aging: Occurs during service, resulting in further hardening and potential cracking.

- Laboratory Simulation:

  - RTFO (Rolling Thin-Film Oven): Simulates short-term aging by exposing asphalt to heat and air.

  - PAV (Pressure Aging Vessel): Simulates long-term aging by subjecting asphalt to elevated temperatures and pressure.

Show how various Superpave tests used to characterize the asphalt binder are related to pavement performance

Dynamic Shear Rheometer (DSR), Bending Beam Rheometer (BBR), Direct Tension Test (DTT)

Define the four methods used to grade asphalt binders.

Performance Grading, Penetration Grading, Viscosity Grading, Aged Residue Grading

To select an asphalt binder for a specific location, the mean seven-day maximum pavement temperature is estimated at 55°C with a standard deviation of 2.5°C. The mean minimum pavement temperature is -9°C with a standard deviation of 1.5°C. What PG grade asphalt is needed at 98% reliability?

  Maximum Temperature: 55C + (2.5C * 2) = 60C

  Minimum Temperature: -9C - (1.5C * 2) = -12C

  Recommended PG Grade: PG 60-12.

For the following temperature conditions, calculate the proper PG grade for both 50% and 98% reliabilities (show your calculation)

- Seven-day maximum pavement temperature of 48°C with a standard deviation of 2.5°C.

  - 50% Reliability: 48°C

  - 98% Reliability: 48°C + (2.5°C * 2) = 53°C

- Minimum pavement temperature of -21°C with a standard deviation of 3°C.

  - 50% Reliability: -21°C

  - 98% Reliability: -21°C - (3°C * 2) = -27°C

- Recommended PG Grade: PG 53-27.

What are the differences between CRS-2 and SS-1 emulsions?

- CRS-2: Cationic rapid-setting emulsion; sets quickly and is used for applications requiring rapid bonding.

- SS-1: Anionic slow-setting emulsion; sets more slowly, allowing for better workability and is often used for surface treatments.

Discuss how asphalt emulsions work as a binder in asphalt mixtures

Asphalt emulsions consist of asphalt particles dispersed in water, stabilized by emulsifying agents. When applied, the water evaporates, allowing the asphalt particles to coalesce and form a strong bond with aggregates, providing effective adhesion and sealing properties.

What are the components of hot-mix asphalt? What is the function of each component in the mix?

- Asphalt Binder: Provides adhesion and waterproofing.

- Aggregates: Provide structural support and stability.

- Filler: Fills voids and improves stability.

- Additives: Enhance performance characteristics (e.g., polymers for flexibility).

What are the objectives of the asphalt concrete mix-design process?

To determine the optimal asphalt content that provides the desired performance characteristics, including stability, durability, resistance to cracking, and moisture damage.

Why is it important to have optimum binder content in asphalt concrete?

Ensures proper coating of aggregates and optimal performance.

What would happen if a less-than-optimum binder content is used?

Can lead to inadequate coating, resulting in reduced stability and increased susceptibility to cracking.

What would happen if more than the optimum value is used?

Can cause excessive lubrication, leading to instability and deformation under load.

What is the typical range of binder content in asphalt concrete?

ranges from 4% to 7% by weight of the total mix

Explain why the strength of asphalt concrete is not necessarily the most important property of the material

While strength is important, other properties such as flexibility, resistance to thermal cracking, and moisture susceptibility are critical for long-term performance. Asphalt pavements must withstand dynamic loads and environmental conditions, making a balance of properties essential.

Air Voids (Va):

The percentage of voids in the total mix, indicating the amount of air present in the compacted asphalt concrete.

Voids in the Mineral Aggregate (VMA):

The volume of voids in the mineral aggregate, which includes both air voids and the voids filled with asphalt.

Voids Filled with Asphalt (VFA):

The percentage of the VMA that is filled with asphalt binder, indicating the effectiveness of the binder in the mix.

Briefly describe the volumetric mix design procedure of Superpave

- Volumetric Mix Design Procedure:

  1. Selection of Aggregates: Choose aggregates based on source and consensus requirements.

  2. Selection of Binder: Choose an appropriate binder based on temperature and traffic conditions.

  3. Trial Mixes: Prepare trial mixes with varying asphalt contents to determine the optimal binder content.

  4. Compaction: Compact samples using the Superpave gyratory compactor.

  5. Volumetric Analysis: Measure bulk specific gravity, theoretical maximum specific gravity, and calculate air voids, VMA, and VFA.

  6. Adjustments: Adjust the mix design based on performance criteria and ensure compliance with specifications.

The Marshall method of mix design has been widely used by many highway agencies

- Steps of Marshall Mix Design:

  1. Aggregate evaluation.

  2. Asphalt cement evaluation.

  3. Specimen preparation.

  4. Marshall stability and flow measurement.

  5. Density and voids analysis.

  6. Design asphalt content determination.

- Parameters Calculated: Stability, flow, bulk specific gravity, voids in total mix, voids in mineral aggregate, and voids filled with asphalt.

- Graphs: Typical graphs include stability vs. asphalt content, flow vs. asphalt content, and air voids vs. asphalt content.

- Purpose of Graphs: To visually determine the optimum asphalt content that meets the design criteria.

Describe the process for determining the stripping potential for an asphalt concrete mix

- Stripping Potential Determination:

  - Conduct the AASHTO T 283 test, which involves preparing specimens, conditioning them through freeze-thaw cycles, and measuring the tensile strength to assess moisture susceptibility.

Briefly discuss how the indirect tensile resilient modulus is determined in the lab.

  - A cylindrical specimen is subjected to a compressive load along its vertical diameter, and the resulting tensile stress is measured. The resilient modulus is calculated based on the applied load and the resulting strain.

Name three methods of asphalt pavement recycling

Central Plant Recycling, In-Place Recycling, Surface Recycling

Central Plant Recycling:

Involves milling the old pavement and sending the RAP to a central asphalt concrete plant, where it is mixed with virgin aggregates and asphalt binder.

In-Place Recycling:

Involves milling the existing pavement and reusing it on-site.

Surface Recycling:

A method that involves treating the surface layer of existing pavements.

Which one of the asphalt pavement recycling method is the predominant method? Briefly summarize this method.

- Central Plant Recycling:

  - Involves milling the old pavement and sending the RAP to a central asphalt concrete plant, where it is mixed with virgin aggregates and asphalt binder.

State four advantages of recycling asphalt pavement materials

  1. Economic savings of about 25% of the price of materials.

  2. Energy savings in manufacturing and transporting raw materials.

  3. Environmental benefits by reducing the amount of required new materials.

  4. Reduces the dead load on bridges due to overlays.

Why can we not mix the RAP materials with aggregates in a conventional hot-mix asphalt concrete plant?

- Mixing Limitations: RAP materials cannot be exposed to high temperatures used to dry aggregates in conventional hot-mix plants, as this can burn the asphalt binder.

Show the proper ways of recycling the RAP materials in the two types of hot-mix asphalt plants

 - Recycling Methods:

  - Central Plant: RAP is added mid-length in the drum to prevent burning.

- In-Place Recycling: Uses specialized equipment to reprocess the existing pavement without exposing it to high temperatures.

State four different asphalt modifiers that can be added to asphalt or asphalt mixtures

Polymer Modifiers, Rubber Modifiers, Filler Materials, Antistripping Agents

What is the purpose of adding fly ash to asphalt concrete?

used as a filler to improve the workability and stability of asphalt concrete. It can also enhance the durability and resistance to moisture damage.

What is the most common polymer used for modifying asphalt cement?

- Common Polymer: Styrene-Butadiene-Styrene (SBS) is the most widely used polymer modifier.

Briefly describe the interaction that occurs when asphalt and SBS are mixed

- Interaction: When SBS is mixed with asphalt, it forms two phases: a polymer-rich phase and an asphalt-rich phase. The polymer phase swells as it absorbs aromatics from the asphalt, enhancing the elasticity and performance of the binder.

List three advantages of warm mix asphalt technology

1. Reduced energy consumption during production.

2. Lower greenhouse gas emissions.

3. Improved workability in cooler temperatures, allowing for extended paving seasons.