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1. Prestress Concrete Design Sessional
CE-416
Presented by
Md Mashqur Ul Alam
Student ID: 08.02.03.053
Department of Civil Engineering
Ahsanullah University of Science and Technology
3. Definition:
Concrete is a mixture of aggregate and often controlled amounts of
entrained air held together by a hardened paste made from cement and
water. Although there are other kinds of cement, the word cement, in
common usage, refers to portland cement.
4. Classification of Concrete
Based on unit weight
Ultra light concrete <1,200 kg/m3
Lightweight concrete 1200- 1,800 kg/m3
Normal-weight concrete ~ 2,400 kg/m3
Heavyweight concrete > 3,200 kg/m3
Based on strength (of cylindrical sample)
Low-strength concrete < 20 MPa compressive strength
Moderate-strength concrete 20 -50 MPa compressive strength
High-strength concrete 50 - 200 MPa compressive strength
Ultra high-strength concrete > 200 MPa compressive strength
Based on additives:
Normal concrete
Fiber reinforced concrete
Shrinkage-compensating concrete
Polymer concrete
5. States of concrete
Concrete has three different states:
PLASTIC : Plastic concrete in a relatively fluid state can be
readily
molded by hand like a clump of modeling clay.
SETTING: The stiffening of concrete, when it is no longer soft
HARDENING: This is the end product of any concrete design.
6.
7. Material Properties of Concrete
The Properties of Concrete are its characteristics or basic qualities :
Workability
Uniformity
Non-segregation
Strength
Durability
Watertightness
Plastic concrete
Hardened concrete
8. Workability
Workability means how it is easy to place, handle, compact and finish a
concrete mix.
Facts needed to be considered for good workability:
Proportions of fine and coarse aggregate
Consistency
Amount of slump
10. Penetration Test
It is a measure of consistency
The ratio of slump to penetration is
usually between 1.3 and 2.0
Fig: Kelly Ball
Penetration
11. Nonsegregation
Plastic concrete must be homogeneous and carefully handled
to keep segregation to a minimum. For example, plastic concrete
should not drop (free-fall) more than 3 to 5 feet nor be transported
over long distances without proper agitation.
12. Uniformity
The uniformity of plastic concrete affects both its economy and
strength. Uniformity is determined by how accurately the ingredients
are proportioned and mixed according to specifications. Each separate
batch of concrete must be proportioned and mixed exactly the same to
ensure that the total structural mass has uniform structural properties.
13. Strength
The ability of concrete to resist a load in compression, flexure, or shear
is a measure of its strength. This is the most important property of
concrete for engineers.
Concrete strength is largely determined by w/c ratio in the mixture.
Time
Curing
17. Durability
Concrete's ability to resist the effects of wind, frost, snow, ice,
abrasion, and the chemical reaction of soils or salts is a measure of
its durability.
Climate and weather exposure affect durability.
As the w/c ratio increases, durability decreases
correspondingly.
Air-entrained concrete has improved freeze-thaw durability.
Durability should be a strong consideration for concrete
structures expected to last longer than five years.
18.
19. Watertightness
The watertightness of concrete is judged by the depth of penetration
of water forced in under pressure with the mechanism of flow of
seepage water examined theoretically and experimentally.
depends on the w/c ratio and the
extent of the chemical reaction
progress between the cement
and water.
W/C ratio should be 0.48 for
concrete exposed to fresh water
and 0.44 for concrete exposed to
salt water.
The watertightness of airentrained concrete is superior to
that
of
non-air-entrained
concrete.
20. Admixtures
Admixtures are mixed into the concrete to change or alter its properties.
Chemical Admixture:
Retarders: sugar, sucrose, sodium gluconate,
glucose, citric acid, and
tartaric acid
Air entrainment agent: Lime
Plasticizers: Lignosulfonate
Accelerator: CaCl2, Ca(NO3)2 and NaNO3
Mineral Admixture:
Fly ash
Ground granulated blast furnace slag
Silica fume
High reactivity Metakaolin(HRM)
