1. CON 121
Concrete Aggregate
Session 5
Special Consideration in Concrete &
Lightweight Aggregate

2. Part 1
Special Consideration in Concrete

3. Concrete Aggregates Influence
Important Concrete Characteristics
 Placeability
 Workability
 Finishability
 Appearance

4. Workability
 Workability: that property of freshly mixed
concrete that determines its working
characteristics, i.e. the ease with which it
can be mixed, placed, compacted and
finished.

5. Factors for Workable Mix
 Formwork
 Reinforcement Spacing
 Placement Procedures
 Consolidation Technique
 Fill spaces
 Flow into corners
 Homogeneous mass
 Without segregation or air entrapment

6. Workability
 Workable concrete
should flow sluggishly
into place without
segregation.

7. Additional Mix Design Considerations
 Cohesiveness
 Harshness
 Segregation
 Bleeding
 Ease of Consolidation
 Finishability
 Durability

8. Factors Affecting Segregation and
Cohesiveness
 Maximum size of coarse aggregate
 Combine grading of fine and coarse aggregate
 Amount of clay-size fines
 High cement factor fines provide cohesion
 Low cement factor requires presence of fines
in aggregates
 Air entrainment

9. Factors Affecting Bleeding of Concrete
 Mixture Proportions
 Air Content
 Slump
 Chemical Admixtures
 Cementitious Materials
 Angularity and grading of fine aggregate

10. Bleeding and Settlement
 Bleed water on the surface
of a freshly placed concrete
slab.
 Bleeding is the development
of a layer of water at the top
or surface of freshly placed
concrete.
 It is caused by
sedimentation (settlement)
of solid particles (cement
and aggregate) and the
simultaneous upward
migration of water.

11. Factors Affecting Workability
Aggregate grading, Shape & Surface Texture
 Quantity and characteristics of cementing materials
 Concrete consistency (slump)
 % entrained air
 Water content
 Admixtures

12. Aggregate Properties Influencing Fresh
Concrete Proportions
 Aggregate Grading
 Particle Shape
 Maximum Size
 Texture
 Bulk Unit Weight
 Absorption
 Specific Density
 Amount of fines

13. Aggregate Grading
 Influence the proportions
 Economy of mix
 Amount of mixing water
 Maximum size of coarse aggregate
 Particle size range
 Aggregate Fines
 Coarse aggregate limit 3/8” sieve
 Fine aggregate limit #50 mesh sieve

14. Aggregate Testing
 Maximum Size
 Nominal size

15. Aggregate Particles
 Angularity and roughness
 Increased Water Demand
 Higher Mortar Content
 Flat and Elongated pieces
 Harshness for placement
 Voids and honeycombing
 Pump blockages

16. Aggregate Particle Degradation
 Increased water demand
 Slump Loss
 Decreased air content
 Absorption of mix water by porous aggregate
 Extended mixing time

17. Relationship Between Aggregate Size -
Cement Content - Air Content
 Relationship between
aggregate size, cement
content, and air content
of concrete.
 The air-entraining
admixture dosage per
unit of cement was
constant for air-
entrained concrete.

18. Relationship Between Aggregate Size -
Cement Content - Air Content
 Relationship between
percentage of fine
aggregate and air
content of concrete.

19. Relationship Between Freeze-Thaw Resistance, W/C-
Ratio, and Different Concretes and Curing Conditions (1)
 Relationship between
freeze-thaw resistance,
water-cement ratio, and
drying for air-entrained and
non-air-entrained concretes
made with Type I cement.
 High resistance to freezing
and thawing is associated
with entrained air, low Type I
cement
water-cement ratio, and a
drying period prior to
freeze-thaw exposure.

20. Relationship Between Freeze-Thaw Resistance, W/C-
Ratio, and Different Concretes and Curing Conditions (2)
 Relationship between
freeze-thaw resistance,
water-cement ratio, and
drying for air-entrained and
non-air-entrained concretes
made with Type I cement.
 High resistance to freezing
and thawing is associated
Type I cement
with entrained air, low
water-cement ratio, and a
drying period prior to
freeze-thaw exposure.

21.  Effect of weathering on
boxes and slabs on
ground at the Long-
Time Study outdoor test
plot, Project 10, PCA,
Skokie, Illinois.
 Specimens at right are
air-entrained,
specimens.
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22.  At right exhibiting severe
crumbling and scaling are non-
air-entrained.
 All concretes were made with
335 kg (564 lb) of Type I
portland cement per cubic
meter (cubic yard).
 Periodically, calcium chloride
deicer was applied to the
slabs.
 Specimens were 40 years old
when photographed (see
Klieger 1963 for concrete
mixture information). (69977,
69853, 69978, 69854)

23. Part 2
Lightweight Aggregate

24. Structural Lightweight Aggregates:
ASTM C 330
 Rotary kiln expanded
clays, shale, and slates
 Sintering grate
expanded shale and
slates
 Pelletized or extruded
fly ash
 Expanded slag

25. Structural Lightweight Aggregate Density
 560 to 11120 kg/m3 (35 to 70 pcf)
 Absorption range: 5% to 20% by weight
 Lightweight aggregates are prewetted (not
saturated)

26. Structural Lightweight Concrete
 Air-dry density:
1350 to 1850 kg/m3
(85 to 115 lb/ft3)
 28-day compressive strength:
> 17 MPa (2500 psi)

27. Structural Lightweight Concrete
 Workability
 Placeability
 Finishability
 Appearance
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28. Factors Affecting Compressive
Strength of Structural Lightweight Concrete
 Cement Content
 Slump
 Air Content
 Typical ranges: 20 to 35 MPa (3000 to 5000
psi)

29. Structural Lightweight Concrete
Strength vs. Cement Content
 Relationship between
compressive strength
and cement content of
field structural
lightweight concrete
using lightweight fine
aggregate and coarse
aggregate.

30. Structural Lightweight Concrete Air
Entrainment
 Resistance to Freezing and thawing
 Resistance to Deicer Applications
 Improves workability, reduces bleeding, and
segregation
 Compensates for minor grading deficiencies
 Air Contents range 5% to 8% depending on max size
of aggregate
 Tested by Volumetric method (ASTM C 173)

31. Lightweight Concrete Considerations
 Bleeding
 Workability
 Pumpability (slump loss/absorption)
 Segregation
 Vibration
 Minimum amount of floating and troweling

32. Lightweight Aggregate
Please return to Blackboard and watch the
following videos:
 Video 1: Particle Shape & Surface Texture
 Video 2: Gap Graded Aggregate
 Video 3: Max Size
 Video 4: Nominal Size