This document discusses several physical characteristics and properties of aggregates, including: 1. Particle shape, surface texture, moisture content, porosity, and specific gravity are described. 2. Formulas for calculating moisture content, bulk specific gravity, saturated surface dry specific gravity, and apparent specific gravity are provided. 3. Aggregate strength, toughness, surface chemistry, durability, and alkali-silica reactivity are discussed as important factors that affect the performance of aggregates in concrete.

1. Lecture #3:
Aggregate Moisture and
Physical Characteristics

2. Particle Shape
and Surface
Texture
•Results from processing
•Difficult to characterize
•Function of:
•Angularity:
•Sphericity:
•Described in terms of particle
dimensions:
Equidimensional
Flaky
Elongated
•Surface texture:

3. Moisture Content States
Physical Properties: Porosity & Voids
Content

4. Moisture Content Equations
100
% x
W
W
W
AC
OD
OD
SSD 

100
% x
W
W
W
MC
OD
OD
AGG 


5. Moisture Analysis
Water 500kg
cement 250kg
coarse agg 800kg (SSD) AC = 1.50%
fine agg 450kg (SSD) AC = 0.75%
•If MCca = 1% and the MCfa = 1% what
is the stock water amount to maintain the
same water demand?
•Will the aggregate absorb or release water?

6. Specific Gravity
Specific gravity is the ratio of the weight oa a unit volume of material to the
Weight of the same volume of water at 20º to 25ºC.
2
w H O
Wt
γ
V
G= =
Wt γ
V
w
:
G = specific gravity
Wt = weight of material
V = volume
Wt = weight of water
where

7. Archimedes Principle
H O
2
OD
Aggregate
WOD
Wg. of OD
Aggregate under H O
WSW
2
OD
OD SW
W
=
W W
a
G

2
/
od SSD sw Displ H O
w W w
 

8. Apparent Specific Gravity
  2
s
V
OD
a
ip H O
W
G
V 


Overall volume of the aggregate exclusive of the volume of the pores or
Capillaries which become filled with water in 24 hrs of soaking
OD
s
ip
w
where:
= apparent specific gravity of solids (aggregate)
W oven dry weight of aggregae
V = volume of solids
V = volume of impermeable pores
γ = unit we
a
G

ight of water (1 g/ml)

9. Bulk Specific Gravity
 
 
 
 
2
2
ssd
s
OD
s
s
ip
pp
w
W
=
V *
W
=
V *
oven dry weight of aggregate
V = volume of solids
V = volume of impermeable pores
V = volume of water permeable pores
= unit
b ssd
ip pp H O
b od
ip pp H O
OD
G
V V
G
V V
Wt



 
 

 
weight of water 1 g/ml

10. Specific Gravity Equations
Bulk Specific Gravity
Saturated Surface-Dry
Apparent Specific Gravity
Lab Formula
OD
a
pyc w OD pyc w agg
W
G
W W W
  

 
 
 
OD
OD
W
=
W
OD
b OD
SSD SW
SSD
b ssd
SSD SW
a
SW
W
G
W W
W
G
W W
G
W






11. OD Aggregate Container
with H2O
Container
with H2O
and with
Aggregate
Specific Gravity Test for Sand

12. Specific Gravity Relationships
Gb < Gb(ssd)< Ga < Gtrue

13. Moisture Content in Field
100
% x
W
W
W
MC
OD
OD
AGG 

sw
a
a
OD W
G
G
W
1



14. Aggregate Strength and Toughness
•Aggregate strength dependent upon:
a) properties of constituent materials
b) bonding between grains
c) porosity
•These properties are difficult to measure.
•LAAbrasion test measures aggregate
degradation
•Affects particle breakdown

15. Aggregate Surface Chemistry
•Aggregate surface chemistry affects bonding to cement
Hydrophobic: water-repellent such as limestone and dolomites
have a positive surface charge. Work well in asphalt concrete.
Hydrophilic: water-attracting such as gravels and
silicates (acidic) have a negative surface charge. Gravels may
tend to create a weaker interfacial zone in concrete than lime-
stone aggregates.
•Surface coating (dust of clay, silt, gypsum, etc.)
tend to reduce bond strength.

16. Aggregate Durability
•Physical durability: resistance to physical processes
1. Unstable volume changes: due to freezing of
absorbed water.
2. Mechanical breakdown during handling,
stockpiling, or placement.
•Chemical durability: resistance to chemical processes
1. Alkali-silicate reaction

17. Alkali-Silica Reactivity

18. What is ASR?
 ASR only a concern if deleterious, e.g. causes
cracking.
 Needs three factors to be deleterious :
- Source of alkali - Internal and external
- Reactive silica (aggregate)
- Water ( humidity) > 80 %

19. What is ASR?
Onset of ASR results in formation of expansive gels
which produce internal stresses which may
cause cracking of concrete. Problem is often
misdiagnosed.
Environmental factors such as freeze-thaw cycles,
wetting/drying cycles, and traffic loading
propagate cracking.
Deicing salts, marine environments, can accelerate
ASR expansion and deterioration processes.
ASR can accelerate corrosion deterioration.

20. What is ASR?

21. Deleterious Substances
•Absorbent particles: shale, leached chert, or porous flint
•Clay lumps
•Coal or wood particles
•Organic impurities
•Flat or elongated particles