CEE 395- Materials for Constructed Facilities
Civil Engineering Materials
Aggregate I
Week 3, Lecture 05
Aggregate
Mass of crushed stone, gravel, sand, etc.. predominantly
composed of individual particles ranging from between 0.005
mm to 150 mm in size.
Function of aggregate:
1. Main ingridient in making concrete:
- As a low cost filler in Portland Cement Concrete (PCC)
- As a source of stiffness and stability in Asphalt Cement
Concrete (ACC, HMA)
2. Used as underlying foundation in pavements and
foundations.
Aggregate Sources
 Natural
- Gravel Pits (gravel)
- River Run Deposits (gravel)
- Rock Quarries (crushed stones)

Manufactured
- Slag waste (steel mill), Steel slugs and bearings
- Expanded shale and clay (light weight)
- Syrofoam beads (insulation)

Geological Formations
- Igneous rocks
- Sedimentary rocks
- Metamorphic rocks
Evaluation of Aggregate Sources
Primary Challenge:
How to use local materials in the most cost effective manner ?
Sources (quarries or pits) are evaluated for
1. Quality of the larger particles (soundness, toughness,..)
2. Nature and amount of fines (sieve analysis tests)
3. Gradation of aggregate
Characteristics vary within a quarry/gravel pit
Transportation cost is a major component of cost
Aggregate Uses
Base for pavements:
Provides stability and drainage.
Tradeoff between stability (more fines) and better drainage
(larger aggregate)
Portland Cement Concrete
- 60-75% of volume, 79-85% of weight
- Maximize aggregate for greater stability at lowest cost
- It is a filler; Friction between particles should be minimal
Notes:
Aggregate #1 (Continued)
Asphalt Concrete
- 0+% of volume, 92-96% of weight
- Asphalt cement serves as a binder for aggregates
It is the main load-bearing component.
Friction (interlock) needs to be maximized.
Aggregate Properties (Table 5.1.)
 Physical (particle shape, size, surface texture, soundness)
 Chemical (solubility, surface charge, reactivity, affinity)
 Mechanical (compressive strength, toughness, abrasion
resistance, stiffness, etc).
I. Particle Shape
How the material will pack into a dense configuration
The mobility of the particles within a mix
Angular aggregates:
- From crushing rocks
- Generally produce higher stability
Rounded aggregates:
- From angular rocks weathering and tumbling in water
- Easier to work with because particles can more easily slide
past one another
Flakiness
- Ratio of smallest to largest dimensions of the aggregate
- Undesirable because they are difficult to compact during
construction and easy to break
II. Surface Texture
How the aggregate compacts and bonds with the binder.
Rough texture
- better bonding and increased inter-particle friction
- desirable for asphalt concrete and base courses for greater
stability and reduced rutting.
Smooth texture
- Easier to compact into a dense configuration
- Desirable for a more workable mix in preparing Portland
cement concrete
Test for uncompacted void content of fine aggregate
(AASHTO TP33 Method A) for indirect measure of angularity
and surface texture
III. Soundness and Durability
The ability to withstand weathering. Extremely important
since materials are subject to severe weather changes.
Aggregate soundness test is covered in ASTM C88
Durability in Portland Cements
- Rapid Freezing and Thawing (ASTM C666)
- Critical Dilation by Freezing (ASTM D4792)
Notes:
Aggregate #1 (Continued)
IV. Toughness, Hardness, and Abrasion Resistance
Collectively refer to the ability of an aggregate to resist the
damaging effects of loads.
Test commonly used is Los Angeles Abrasion Test (ASTM
C131, C535)
V. Absorption
Surface pores. Extremely important in making PCC and ACC.
- Determines the correct water mixture for cement
- Important in determining workability
- Some absorption required for bonding purposes
- Cost Issue and higher absorption rates require greater
amounts of cement and asphalt binder
4 moisture conditions:
- Bone dry (aggregate contains no moisture)
- Air dry (aggregate may have some moisture)
- Saturated Surface Dry (voids are filled with moisture but
surface is dry)
- Moist (moisture content above SSD condition)
VI. Specific Gravity
Different volumes used in calculation of aggregate's specific
gravity:
- Vs, Volume of solids
- Vi, Volume of impermeable voids
- Vp, Volume of water permeable voids
- Vc, Volume of ????
- Ws, Weight of solids
- Wp, Weight of permeable void in SSD condition
- gw, Specific gravity of water
Bulk Dry Weight
Bulk SSD Specific Gravity
Apparent Specific Gravity
Effective Specific Gravity
Ws / (Vs + Vi + Vp).γw
(Ws + Wp) / (Vs + Vi + Vp).γw
Ws / (Vs + Vi ).γw
Ws / (Vs + Vic ) γw
Bulk Specific Gravity Test
ASTM C127 (Coarse Aggregates)
Different weights used in calculation in bulk specific gravity
test:
- A, Dry Weight
- B, Saturated Surface Dry Weight
- C, Submerged weight
Bulk Dry Specific Gravity
Bulk SSD Specific Gravity
Apparent Specific Gravity
Absorption (%)
A / (B - C
B / (B - C)
A / (A - C)
(B - A) / A (100)
ASTM C128 (Fine Aggregates)
- Same as the previous test using a 500 gram sample and a
constant volume flask called the pycnometer
- Equations are the same, except:
C is the submerged aggregate in pycnometer, which is defined
as (weight of flask with aggregate and water) - (weight of
flask and water)
Notes:
Aggregate #1 (Continued)
VII. Strength
Portland Cement Concrete and Asphalt Concrete
- cannot exceed the strength of the aggregates
- aggregate strength is very important in high strength concrete
and High Volume asphalt surface coarse
Aggregates strength requirement:
- Tensile strength (0.7 MPa to 16 MPa)
- Compressive strength (35 MPa to 350 MPa)
Modulus
Modulus of Resilience (Mr)
- Resilience modulus test (Figure 5.6)
Simulates a moving truck
- Deformation response
- recoverable or resilience
- permanent
Layer Coefficients:
Used in pavement design as an estimate of structural capacity
of base layer. Also used for design of gravel roads.
Drainage Capacity (permeability)
Used to estimate the amount of water that can be drained
through a layer
Notes: