1. Highway materials

2. Aggregates
"Aggregate" is a collective term for the mineral materials such as sand, gravel and crushed stone that are used with a binding medium (such as water, bitumen, portland cement, lime, etc.) to form compound materials (such as asphalt concrete and portland cement concrete). 
By volume, aggregate generally accounts for 92 to 96 percent of HMA and
about 70 to 80 percent of portland cement concrete.
Aggregate is also used for base and subbase courses for both flexible and rigid pavements.

3. Aggregate Sources
Aggregates can come from either natural or manufactured sources. Natural aggregates come from rock, of which there are three broad geological classifications
Igneous rock.  These rocks are primarily crystalline and are formed by the cooling of molten rock material beneath the earth’s crust (magma).
Sedimentary rocks.  These rocks are formed from deposited insoluble material (e.g., the remains of existing rock deposited on the bottom of an ocean or lake). This material is transformed to rock by heat and pressure.  Sedimentary rocks are layered in appearance and are further classified based on their predominant mineral.

4. Cont..,
Metamorphic rock.  These are igneous or sedimentary rocks that have been subjected to heat and/or pressure great enough to change their mineral structure so as to be different from the original rock.

5. Cont..,
Manufactured rock typically consists of industrial byproducts such as slag (byproduct of the metallurgical processing typically produced from processing steel, tin and copper)
Slag is usually a mixture of metal oxides and silicon dioxide

6. Mineral Properties
An aggregate’s mineral composition largely determines its physical characteristics and how it behaves as a pavement material.  Therefore, when selecting an aggregate source, knowledge of the quarry rock’s mineral properties can provide an excellent clue as to the suitability of the resulting aggregate.

7. Chemical Properties
aggregate chemical properties are important in a pavement material.  In HMA, aggregate surface chemistry can determine how well an asphalt cement binder will adhere to an aggregate surface.  Poor adherence, commonly referred to as stripping, can cause premature structural failure.

8. Stripping (HMA)
Although the displacement of asphalt on the aggregate particle surface by water (stripping) is a complex phenomena and is not yet fully understood, mineralogy and chemical composition of the aggregate have been established as important contributing factors. 
In general, some aggregates have an affinity for water over asphalt (hydrophilic).  These aggregates tend to be acidic and suffer from stripping after exposure to water.  On the other hand, some aggregates have an affinity for asphalt over water (hydrophobic). 

9. Cont..,
These aggregates tend to be basic and do not suffer from stripping problems.  Additionally, an aggregate’s surface charge when in contact with water will affect its adhesion to asphalt cement and its susceptibility to moisture damage. 
In sum, aggregate surface chemistry seems to be an important factor in stripping. 

10. Alkali-Aggregate Reaction (PCC)
Alkali-aggregate reaction is the expansive reaction that takes place in PCC between alkali (contained in the cement paste) and elements within an aggregate.  The most common is an alkali-silica reaction. 
This reaction, which occurs to some extent in most PCC, can result in map or pattern cracking , surface popouts and spalling if it is severe enough.

11. Physical Properties
Aggregate physical properties are the most readily apparent aggregate properties and they also have the most direct effect on how an aggregate performs as either a pavement material constituent or by itself as a base or subbase material.  Commonly measured physical aggregate properties are

12. Cont.., Gradation and size Toughness and abrasion resistance
Durability and soundness
Particle shape and surface texture
Specific gravity
Cleanliness and deleterious materials

13. Gradation and Size
The particle size distribution, or gradation, of an aggregate is one of the most influential aggregate characteristics in determining how it will perform as a pavement material.  In HMA, gradation helps determine almost every important property including stiffness, stability, durability, permeability, workability, fatigue resistance, frictional resistance and resistance to moisture damage.

14. Cont..,
In PCC, gradation helps determine durability, porosity, workability, cement and water requirements, strength, and shrinkage.  Because of this, gradation is a primary concern in HMA and PCC mix design and thus most agencies specify allowable aggregate gradations for both.

15. Maximum Aggregate Size
Maximum aggregate size can affect HMA, PCC and base/subbase courses in several ways.  In HMA, instability may result from excessively small maximum sizes; and poor workability and/or segregation may result from excessively large maximum sizes. 
In PCC, large maximum sizes may not fit between reinforcing bar openings, but they will generally increase PCC strength because the water-cement ratio can be lowered. 

16. Gradation Test
The gradation of a particular aggregate is most often determined by a sieve analysis .  In a sieve analysis, a sample of dry aggregate of known weight is separated through a series of sieves with progressively smaller openings. Once separated, the weight of particles retained on each sieve is measured and compared to the total sample weight.  Particle size distribution is then expressed as a percent retained by weight on each sieve size.  Results are usually expressed in tabular or graphical format.

17.   Desired Gradation
It might be reasonable to believe that the best gradation is one that produces the maximum density. This would involve a particle arrangement where smaller particles are packed between the larger particles, which reduces the void space between particles. 
This creates more particle-to-particle contact, which in HMA would increase stability and reduce water infiltration. .

18. Cont..,
In PCC, this reduced void space reduces the amount of cement paste required.  However, some minimum amount of void space is necessary to:
Provide adequate volume for the binder (asphalt binder or portland cement) to occupy.
Promote rapid drainage

19. Toughness and Abrasion Resistance
Aggregates undergo substantial wear and tear throughout their life.  In general, they should be hard and tough enough to resist crushing, degradation and disintegration from any associated activities including manufacturing, stockpiling, production, placing, compaction (in the case of HMA) and consolidation (in the case of PCC) .
Furthermore, they must be able to adequately transmit loads from the pavement surface to the underlying layers (and eventually the subgrade).  Aggregates not adequately resistant to abrasion and polishing will cause premature structural failure and/or a loss of skid resistance

20. Los Angeles Abrasion Test
A common test used to characterize toughness and abrasion resistance is the Los Angeles (L.A.) abrasion test.  For the L.A. abrasion test, the portion of an aggregate sample retained on the 1.70 mm (No. 12) sieve is placed in a large rotating drum that contains a shelf plate attached to the outer wall (the Los Angeles machine). 
A specified number of steel spheres are then placed in the machine and the drum is rotated for 500 revolutions at a speed of revolutions per minute (RPM).  The material is then extracted and separated into material passing the 1.70 mm (No. 12) sieve and material retained on the 1.70 mm (No. 12) sieve.  The retained material (larger particles) is then weighed and compared to the original sample weight.  The difference in weight is reported as a percent of the original weight and called the "percent loss".

22. Cont..,
Aggregates having Abrasion value greater than 50% are rarely allowed.
Maximum recommended abrasion value for wearing course is 40% and for base course is 50%.

23. Durability and Soundness
Aggregates must be resistant to breakdown and disintegration from weathering (wetting/drying and freezing/thawing) or they may break apart and cause premature pavement distress.  Durability and soundness are terms typically given to an aggregate’s weathering resistance characteristic.  Aggregates used in HMA are dried in the production process and therefore should contain almost no water. 

24. Cont..,
Thus, for aggregate used in HMA, freezing/thawing should not be a significant problem.  This is not true for aggregate used in PCC or as base and/or subbase courses.  These aggregates typically contain some water (on the order of 0.1% to 3% usually) and are not dried prior to use.

25. Soundness Tests
The most common soundness test involves repeatedly submerging an aggregate sample in a saturated solution of sodium or magnesium sulfate.  This process causes salt crystals to form in the aggregate pores, which simulate ice crystal formation . The basic procedure is as follows
Oven dry the sample and separate it into specific sieve sizes. Immerse the sample in a saturated solution of sodium or magnesium sulfate and let it remain at a constant temperature for 18 hours.

26. Cont..,
Remove the sample from the solution and dry to a constant weight at 110 ± 5oC (230 ± 9oF). Repeat this cycle five times. Wash the sample to remove the salt; then dry. Determine the loss in weight for each specific sieve size and compute a weighted average percent loss for the entire sample. The maximum loss values typically range from 10 to 20 percent for every five cycles.
ASTM recommends max of 12 % loss if sodium sulphate is used and 18% when magnesium sulphate is used.

27. Particle Shape and Surface Texture
Particle shape and surface texture are important for proper compaction, deformation resistance, HMA workability and PCC workability.  However, the ideal shape for HMA and PCC is different because aggregates serve different purposes in each material. 
In HMA, since aggregates are relied upon to provide stiffness and strength by interlocking with one another, cubic angular-shaped particles with a rough surface texture are best.  .

28. Cont..,
However, in PCC, where aggregates are used as an inexpensive high-strength material to occupy volume, workability is the major issue regarding particle shape.  Therefore, in PCC rounded particles are better.  Relevant particle shape/texture characteristics are:

29. Particle shape.  Rounded particles create less particle-to-particle interlock than angular particles and thus provide better workability and easier compaction. 
However, in HMA less interlock is generally a disadvantage as rounded aggregate will continue to compact, shove and rut after construction. Thus angular particles are desirable for HMA (despite their poorer workability), while rounded particles are desirable for PCC because of their better workability (although particle smoothness will not appreciably affect strength)

30. Cleanliness and Deleterious Materials
Aggregates must be relatively clean when used in HMA or PCC.  Vegetation, soft particles, clay lumps, excess dust and vegetable matter are not desirable because they generally affect performance by quickly degrading, which causes a loss of structural support and/or prevents binder-aggregate bonding.

31. Moisture Content
Since aggregates are porous (to some extent) they can absorb moisture.  Generally this is not a concern for HMA because the aggregate is dried before HMA production. 
However, this is a concern for PCC because aggregate is generally not dried and therefore the aggregate moisture content will affect the water content
(and thus the water-cement ratio also) of the produced PCC and
the water content also affects aggregate proportioning (because it contributes to aggregate weight). 

32. Aggregate as a Base Material
Aggregate is often used by itself as an unbound base or subbase course.  When used as such, aggregate is typically characterized by the preceding physical properties as well as overall layer stiffness.  Layer stiffness is characterized by the same tests used to characterize subgrade stiffness.
Aggregate base = material passing ¾“ upto dust.
It is compacted to a minimum of 95% relative compaction.

33. Resilient modulus

34. Intoduction
The Resilient Modulus (MR) is a measure of subgrade material stiffness. A material’s resilient modulus is actually an estimate of its modulus of elasticity (E). While the modulus of elasticity is stress divided by strain for a slowly applied load, resilient modulus is stress divided by strain for rapidly applied loads – like those experienced by pavements.

35. Cont..,
Resilient modulus is determined using the triaxial test. The test applies a repeated axial cyclic stress of fixed magnitude, load duration and cycle duration to a cylindrical test specimen. While the specimen is subjected to this dynamic cyclic stress, it is also subjected to a static confining stress provided by a triaxial pressure chamber. It is essentially a cyclic version of a triaxial compression test; the cyclic load application is thought to more accurately simulate actual traffic loading.

36. Application of Resilient Modulus
The resilient modulus test provides a means of characterizing pavement construction materials including surface, base, and sub- base materials under a variety of temperatures and stress states that simulate the conditions in a pavement subjected to moving wheel loads.

37. Triaxial test