Road Construction & Materials

• The notes cover several aspects of road construction and materials, including subbases, wearing courses, bituminous materials, asphalt testing, aggregate properties, asphalt mix design, and pavement performance evaluation.

Subbases

• The function of subbases is to decrease construction costs.
• Aggregate sizes can reach a maximum of 3 inches.
• Subbases can be stabilized using cement or asphalt.

Stabilized Bases

• Stabilized bases are not selected due to difficulties in obtaining suitable materials, improving material quality, or reducing pavement's total cost

Wearing Course (Surface Layer)

• Wearing courses protect vehicle tires.
• Wearing courses are less resistant.
• Wearing courses minimize water infiltration into the pavement.

Surface Treatments

• Surface treatments involve the successive distribution of bituminous material and aggregates.
• They're suitable for roads bearing heavy traffic.
• Asphalt cements with penetration grades of 85-100 are utilized.

Asphalt Concretes

• Asphalt concretes are prepared in a central facility.
• They are applied on heavily trafficked roads.
• Asphalt concretes exhibit a lifespan of approximately 20 years.
• Asphalt concrete surfaces usually incur higher costs.

Hot Mixes

• Hot mixes need semi-solid asphalt cement for the construction.
• Asphalt cements with penetration grades of 60-70 are used for light traffic.
• Grades 85-100 are suggested for heavy traffic.

Bituminous Material Types

• The different types of bituminous materials include asphalt cements, cutback asphalts, asphalt emulsions, and asphalt concrete

Asphalt Tests

• Tests carried out on asphalts evaluate penetration, softening point, ductility, and abrasion resistance.

Flash Point

• Flashpoint does not measure the tendency of a sample to form an inflammable mixture.
• Flashpoint cannot indicate the presence of highly volatile materials.
• Flashpoint is not the temperature at which a flame causes oil to burn for 5 seconds.

Ductility

• Ductility is the distance a cement asphalt briquette stretches before breaking.
• It's tested at 25 ± 0.1ºC with a speed of 50 ± 2.5 mm/min.
• Ductility measures the tensile properties of bituminous materials.

Saybolt-Furol Viscosity

• This is measured in seconds.
• It fills a 60cc recipient with liquid.
• Liquid goes through a calibrated orifice (furol).

Asphalt Emulsions

• Asphalt emulsions utilize an asphalt volume concentration of 50 to 60%.
• Non-ionic types are used in pavement construction.
• Asphalt emulsions constitute dispersion systems consisting of two non-miscible liquids.

Aggregates for Asphalt Concrete

• Coarse aggregate consists of particles retained by sieve #4.
• Fine aggregate includes material passing sieve #4 and is retained by sieve #200.
• Mineral filler is the portion of material passing sieve #200.
• Coarse aggregates should have a wear percentage no greater than 35%.

Wearing Course

• A wearing course is not necessarily stable, durable, permeable, or slip-resistant.

Aggregate Gradation in Asphalt Mixes

• The gradation of material depends on work characteristics and according to the technical specification used.
• An amount of smaller particles leads to high stability.
• Maximum size cannot be greater than 2/3 of the carpet thickness.

Asphalt's Effect on Stability

• Asphalt stability doesn't always increase with an increase in asphalt percentage.
• Asphalt's effect varies with the type of aggregate.
• The grade of asphalt's effect is significant to the stability, but barely influences the flow.

Aggregate Grading in Asphalt Mixtures

• Choose aggregates that permit a wide variance in the % of asphalt.
• Have a greater % of voids in the mineral aggregate, as stability permits.
• You can obtain a higher % of voids in the aggregate, decreasing the % of sand.
• Less % of voids in the aggregate can be obtained, augmenting the % of mineral filter.

Void Percentage in Asphalt Mix

• Lowering the % of voids reduces porosity.
• Reducing air penetrability results in slower asphalt oxidation.
• Slower asphalt oxidation results in reduced durability.
• A minimum volume of voids prevents asphalt flushing.

Durability of Asphalt Concrete

• Durability of asphalt concrete consists of resistance to the abrasive effect of traffic, destructive action of atmospheric agents, and flexibility to resist breaks during repeated load applications.

Asphalt Quantity in Mix

• The goal is to keep the aggregates bound under traffic's abrasion.
• The concrete should retain flexibility at low temperatures.
• Abrasion and disintegration should decrease with fragility.
• The pavement must also be resistant to breaks.

Marshall Method

• This is a process for stability and flow testing of asphalt mixes.
• It assesses physical characteristics of the mixes.
• It analyzes parameters defining asphalt content.

Mixture Preparation Criteria

• Air void percentage in the total mix is considered for mix preparation.
• Minimum void percentage in mineral aggregate is another criteria.
• Maximum stability value, and range of flow values also play a role.

Marshall Test

• Examines a series of specimens.
• Each is prepared with the same gradation.
• Each contains different asphalt contents.
• Asphalt content varies less than 0.5%.
• Specimens measure 4 inches thick and 2.5 inches in diameter.
• Three briquettes must be made per asphalt content.

Specific Gravity Measurements

• That includes the total volume of aggregate particles and the volume of pores in water after 24 hours of immersion.
• Specific gravity measurements include apparent dry specific gravity, bulk dry specific gravity, saturated surface dry bulk specific gravity, and effective specific gravity.

Voids in Mineral Aggregate (VMA)

• Corresponds to volume occupied by the effective asphalt volume.
• Corresponds to the volume of voids trapped between the coated aggregates.
• VMA is expressed as a percentage of the total volume of the mix.

Voids Filled with Asphalt (VFA)

• The amount of volume occupied by effective asphalt.
• It refers to the percentage of voids in the mineral aggregate occupied by asphalt.
• It represents the volume of voids trapped between coated aggregates.

Serviceability Index

• The initial index hinges on the design and the quality of construction.
• The end index corresponds to the lowest level the pavement can bear before rehabilitation.
• Its decrease shows the loss of service quality due to pavement deterioration.

Drainage Coefficient

• It relies on the amount of time it takes for water to evacuate the pavement.
• It depends on the percentage of time the pavement is exposed to near-saturation moisture.
• AASHTO sets correction factors a2 for bases and a3 for granular subbases without stabilization.

Load Equivalent Factors

• Factors are tabulated based on axle type, initial serviceability index, load per axle, and structural number (SN) of the pavement.

Truck Factor

• The truck factor defines the number of Equivalent Single Axle Loads (ESALs) per vehicle.
• This can be calculated for each vehicle type.
• This can be calculated for all vehicles.

Structural Number SN

• It relies on the total number of equivalent W18 axles, reliability, and loss of serviceability.