CEE3402 Reinforced Concrete StructuresSchool of Civil & Environmental EngineeringYonsei University, Seoul, Korea

Materials: Concrete and Steel

Kyoungsoo Park, Ph.D.

Spring, 2019

Kyoungsoo Park (k-park@yonsei.ac.kr)

Manufacture of Cement

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Kyoungsoo Park (k-park@yonsei.ac.kr)

Manufacture of Cement

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Limestonequarrying(crushing)

Other raw materials

Clay/shalequarrying(crushing)

Storage Storage

Grinding and blending

Grinding and blending

Storage and final blending

Finish grinding

Gypsum

Storage

Kyoungsoo Park (k-park@yonsei.ac.kr)

Cement Classification

Type I (Ordinary Portland Cement)

Type II (Moderate Heat Portland Cement)

Type III (High Early Strength Portland Cement) Smaller cement particles

Type IV (Low Heat Portland Cement)

Type V (Sulfate-Resisting Portland Cement)

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Kyoungsoo Park (k-park@yonsei.ac.kr)

Aggregate: Size Gradation

Economical Concrete

Uniform size versus Non-uniform size

Course Aggregate versus Fine Aggregate _______ mm Sieve (No. 4)

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Kyoungsoo Park (k-park@yonsei.ac.kr)

Concrete Mixing Design

Basic Consideration Economy

Reducing cement content Optimum ratio of coarse to fine aggregate

Workability Minimizing segregation and bleeding Slump test

Strength and Durability Minimum compressive strength at a given day Freezing & thawing (e.g. air content)

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Kyoungsoo Park (k-park@yonsei.ac.kr)

Water-Cement Ratio

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Kyoungsoo Park (k-park@yonsei.ac.kr)

Quality Control: Compressive strength

Specified design strength Compressive strength test

150 x 300 mm or 100 x 200 mm cylinder test Cylinder strength

Average compressive strength

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Freq

uenc

y

Compressive strength

Kyoungsoo Park (k-park@yonsei.ac.kr)

Concrete Mixing Design

Specified Mix (시방배합) Both coarse and fine aggregates are in the saturated-surface-dry

(SSD) condition All fine aggregate passes the No.4 (5 mm) sieve. All coarse aggregate is retained on the No.4 (5 mm) sieve.

Job Mix (현장배합) If aggregates do not satisfy the above requirements, the amount

of aggregates and mixing water should be modified

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굵은골재최대치수

(mm)

슬럼프범위(mm)

공기량범위(%)

물-결합재비

w/c(%)

잔골재율S/a(%)

단위질량(kg/㎥)

물W

시멘트C

잔골재S

굵은골재

G

혼화재료

혼화재¹ 혼화제²

Kyoungsoo Park (k-park@yonsei.ac.kr)

Special Placement

Shotcrete Spraying concrete from a nozzle Compacted on surfaces (e.g. vertical or steeply sloping

surfaces) Tunnel linings, stabilization of rock surface, surface supports No need for formwork

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Kyoungsoo Park (k-park@yonsei.ac.kr)

Special Placement

Tremie Pouring concrete under water Minimize entrapped air, and provide steady flow of concrete High slump

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Kyoungsoo Park (k-park@yonsei.ac.kr)

Consolidation

Elimination of void and entrapped air Corners of forms and around reinforcing steel Vibration: Internal and External Overvibration: bleeding, loss of entrained air

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Kyoungsoo Park (k-park@yonsei.ac.kr)

Curing

Objective As much hydration as possible

Strength & Durability Temperature & moisture during initial period Freezing of fresh concrete (4ºC or Lower): ____ of strength

Curing Maintenance of proper conditions for the initial period Protected from loss of moisture for _____ days / _____ days Springkling or covering with plastic film Low temperature: external heat High temperature: cooling concrete

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Kyoungsoo Park (k-park@yonsei.ac.kr)

Admixtures

Mineral Admixtures (Blended Cement) Supplementary cementitious material Fly ash, Silica fume, Blast furnace slag Heat of hydration, workability, strength development, durability Sustainable development: Reduce CO2 emission

Chemical Admixtures Water soluble compounds Air-entraining admixtures: Freezing and thawing resistance Accelerating admixture: Early strength development Set-retarding admixture: Workable for a long time Plasticizing admixtures: High-strength concrete Viscosity-modifier: Self-consolidating concrete

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Kyoungsoo Park (k-park@yonsei.ac.kr)

Stress-Strain Curves of Concrete

Normal Concrete Lightweight Concrete

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Kyoungsoo Park (k-park@yonsei.ac.kr)

Stress-Strain Curves of Concrete

Effect of the Strain Rate

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Stre

ss

Strain

Kyoungsoo Park (k-park@yonsei.ac.kr)

Elastic Modulus

Definition of Elastic Modulus

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Stre

ss

Strain

fc′

Stre

ss

Strain

Kyoungsoo Park (k-park@yonsei.ac.kr)

Elastic Modulus

In Practice

wc = 1440 ~2560 kg/m3

Overestimate for compressive strength (42 ~ 84 MPa)

wc = 2300 kg/m3

Normal-density concrete: 21 ~ 84 MPa Lightweight concrete: 21 ~ 62 MPa

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𝐸 0.043𝑤 . 𝑓 ′

𝐸 3320 𝑓 6900𝑤

2300

.

𝐸 4700 𝑓 ′

Kyoungsoo Park (k-park@yonsei.ac.kr)

Tensile Strength Measurement

Splitting Test

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Plane of tensile failure

Concrete cylinder

Testing machine bed

Dis

tanc

e fr

om to

p of

spe

cim

en

Stress x πLD/2P

Kyoungsoo Park (k-park@yonsei.ac.kr)

Tensile Strength Measurement

Flexure Test (Modulus of Rupture)

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𝐿/3 𝐿/3 𝐿/3

𝐿

ℎ

𝑃2

𝑃2

Kyoungsoo Park (k-park@yonsei.ac.kr)

Approximate Range of Tensile Strength

Normal weight concrete Light weight Concrete

Direct tensile strength 0.25 to 0.58 𝑓 ′ 0.17 to 0.25 𝑓 ′

Split-cylinder strength 0.50 to 0.66 𝑓 ′ 0.33 to 0.50 𝑓 ′

Modulus of rupture 0.66 to 1.00 𝑓 ′ 0.50 to 0.66 𝑓 ′

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Kyoungsoo Park (k-park@yonsei.ac.kr)

Time-Dependent Deformation

Creep Increase of ____________ under __________________

Creep coefficient at time t (days), 𝐶

Ultimate creep coefficient, 𝐶

𝜀 : Instantaneous strain of concrete (or elastic strain) 𝜀 : Creep strain of concrete at time t (days) 𝜀 : Ultimate creep strain of concrete (Table 2.2)

𝐶.

. 𝐶

Effect of w/c ratio Effect of moist curing time & temperature

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Kyoungsoo Park (k-park@yonsei.ac.kr)

Creep of Concrete

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Cre

ep s

trai

n

Time (days)

Kyoungsoo Park (k-park@yonsei.ac.kr)

Time-Dependent Deformation

Shrinkage Decrease of _________ Cracking when each side is restrained Effect of w/c ratio Effect of aggregate content Self-desiccation

Water is consumed by hydration Low w/c ratio & no water during curing

Shrinkage strain after t days, εsh,t

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𝜀 ,𝑡

35 𝑡 𝜀 ,

εsh,u: Ultimate drying shrinkage strain (≈ 780x10-6)

Kyoungsoo Park (k-park@yonsei.ac.kr)

Shrinkage of Concrete

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Shrin

kage

str

ain

Time (days)

Kyoungsoo Park (k-park@yonsei.ac.kr)

Steel vs. Concrete

Compressive Strength 15 times higher than general concrete

Tensile Strength Over 100 times higher than general concrete

Thermal expansion coefficients Steel: 11.7 x 10-6

Concrete: 9.9 x 10-6

Corrosion resistance Concrete cover

Fire resistance High thermal conductivity Decrease of strength

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Kyoungsoo Park (k-park@yonsei.ac.kr)

Reinforcing Bars

Higher strength Reduce steel congestion

Less than fy = 550 MPa for most applications Minimum yield strength

Strain NOT exceed 0.0035

Types of deformed bars

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Kyoungsoo Park (k-park@yonsei.ac.kr)

Stress-Strain Relationships

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800

600

400

200

100

80

40

20

60

120

140

20010000

Grade 620

Grade 520

Grade 420

Grade 280

Stress, MPa

Strain, 0.001

ksi

800

600

400

200

100

80

40

20

60

120

140

201000

Grade 620

Grade 520

Grade 420

Grade 280

Stress, MPa

Strain, 0.001

ksi

3.5