02 Concrete Fundamentals

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2 Concrete Fundamentals

K L 3 1 0 6 C L A S S 0 2

S E M E S T E R I 2 0 1 0 / 2 0 1 1

Introduction

Concrete is one of the most versatile and universal.

Available all over the globe.

Can be developed into diverse forms of construction.

Can be built with all different levels of technology.

Excellent durability and fire resistance characteristics.

Requires substantially less maintenance than other materials.

About 260 million m3 of concrete are used each yearin the US.


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Introduction

Concrete manufacturing process includes a numberof ste s:

Proportioning

Batching

Mixing

Placing

Compacting

n s ng Curing

Concrete

Concrete: rocklikematerial produced bym x ng coarse an neaggregates, hydrauliccement (usually portlandcement) and water andallowing the mixture toharden.


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Aggregates

Fine aggregates consistof sand with particlessma er t an 5 mm.

Coarse aggregates aregenerally gravel orcrushed stone larger than5 mm (usually 9.5 mmup to 37.5 mm).

Aggregates occupy 60-75% of the concrete

volume or 70-85% of itsmass.

Cement

H y d r a u l ic ce m e n t s set and harden by reacting.

hydration.

During hydration, cement combines with water to

form paste, which bind aggregates into concrete as ithardens.

Portland cement is the most common t e ofhydraulic cement.


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Historical Overview

300 BC 476 AD: early form of concrete was used inbridges, aqueducts, structures in Rome.

The concrete used volcanic sand called pozzuolana(available near Pozzuoli), which reacted with limeand water to solidify into rock-like mass.

1824: Joseph Aspdin invented Portland cement.

1855: J. Lambot introduced reinforced concrete

.Monier in 1867.

1930: Development of prestressed concrete byEugene Freyssinet.

Density of Concrete

Based on their density, fresh concrete are dividedinto: Lightweight concrete: 1350 1850 kg/m3

Normal-weight concrete: 2200 2400 kg/m3

Heavyweight concrete: 2800 6400 kg/m3

Normal-weight concrete is the most commonly usedconcrete in construction.

heat / fire insulation.

Heavyweight concrete is used for radiation-shieldingand concrete coating for pipelines.


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Mechanical Properties of Concrete

Concrete has a high compressive strength; however,its tensile stren th is low about 10% of itscompressive strength).

Compressive strength of concrete (fc) is obtained byuniaxial compression test of cylindrical concretesamples.

There are two commonl used concrete sam les:

15 cm diameter, 30 cm high, cylindrical sample (as in ACI andcurrent SNI).

15 cm 15 cm 15 cm cubic sample (as in PBI 1971).

Uniaxial Compression Test

c

or cu c samp es:

0.83 *c

f

where * is the compressive strengthobtained from cubic samples.


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Aggregates

Requirements

Aggregate should be:

Hard and strong

Free from absorbed chemicals

Free from coatings of clay

The distribution of aggregate size should follow thegrading limits (see tables in the next slide).

Grading is the particle-size distribution of aggregateas determined bys ieve an a lys is .


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Fine Aggre gateFine Aggre gateCoar se Aggr egate

( 2 5 m m m a x . s iz e )

Coar se Aggr egate

( 2 5 m m m a x . s iz e )

Grading Limits

Sieve s ize

[ m m ]

P e r c e n t p a s s in g ,

b y m a s s

9.5 100

4.75 (No. 4) 95 100

2.36 (No. 8) 80 100

1.18 (No. 16) 50 85

Sieve s ize

[ m m ]

P e r c e n t p a s s i n g ,

b y m a s s

37.5 100

25 95 100

12.5 25 60

4.75 0 10

0.60 (No. 30) 25 60

0.30 (No. 50) 5 30

0.15 (No. 100) 0 10

2.36 0 5

Grading Limits


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Fineness Modulus

Calculated by adding the cumulative percentages of massretained on each of a specified series of sieves anddividing the sum by 100.

The specified sieves for determining FM are: 150 m (No. 100)

300 m (No. 50)

600 m (No. 30)

1.18 mm (No. 16)

. .

4.75 mm (No. 4)

9.5 mm, 19.0 mm, 37.5 mm, 75 mm and 150 mm.

To be used in normal concrete, the fineness modulus offine aggregate should be between 2.3 3.1.

Example 1

A sample of fine aggregate is Sieve s ize[ m m ]

M a s s r e t a i n e d

[ g r a m ]and the masses retained on eachsieve are as shown.

Draw the grading of the fineaggregate and determine thefineness modulus.

9.5 0

4.75 9

2.36 681.18 101

0.6 102

0.3 121

0.15 93

0.075 10

Pan 5


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Sieve analysis is based on cumulative percentage of

aggregates that pass through the sieves, while finenessmodulus cumulative percentage of retained aggregates.

Sieve

size

m m

M a s s

r e t a i n e d

r a m

Cu m u l a t i ve

r e t a i n e dCumula t ive

p a s s

%

9.5 0 0 0 100

4.75 9 9 2 98

2.36 68 77 15 85

1.18 101 178 35 65

0.6 102 280 55 45

0. 121 01 21

0.15 93 494 97 3

0.075 10 504 99 1

Pan 5 509 100 0

fineness modulus calculation

50

60

70

80

90

100

tivePass[%]

0

10

20

30

40

0.01 0.1 1 10

Cumula

SieveSize[mm]

0 2 15 35 55 79 972.83

100FM

Note: The 0.075 mm sieve is not included in the FM calculation.


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Example 2

A sample of coarse aggregate isassed throu h a series of

Sieve s ize

[ m m ]

M a s s r e t a i n e d

[ g r a m ]sieves and the masses retainedon each sieve are as shown.

Draw the grading anddetermine the finenessmodulus.

25 0

19 405

12.5 2850

9.5 2435

4.75 2030

2.36 375

Pan 35

Sieve

size

[ m m ]

M a s s

r e t a i n e d

[ g r a m ]

C u m u l a t i v e

r e t a i n e dC u m u l a t i v e

p a s s

[%][gr a m ] [%]

25 0 0 0 100

19 405 405 5 95

12.5 2 50 3255 40 0

9.5 2435 5690 70 30

4.75 2030 7720 95 5

2.36 375 8095 100 0

Pan 35 8130 100 0

Note: The 25 mm and 12.5 mm sieves are not included in the FM calculation.


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50

60

70

80

90

100

lativePass[%]

0

10

20

30

1 10 100

Cumu

SieveSize[mm]

5 70 95 100 100 100 100 1006.70

100FM

80

90

100

Combined grading of fine and coarse aggregates fromExamples 1 and 2:

10

20

30

40

50

60

70

Cumula

tivePass[%]

0

0.01 0.1 1 10 100

SieveSize[mm]


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Bulk Density and Voids

Bulk density (or unit weight): mass (or weight) ofa re ate re uired to fill a container of a s ecifiedunit volume.

The volume above is occupied by aggregates andvoids between particles.

Aggregates commonly used in normal concrete havebulk densit in the ran e of 1200 1 0 k m3.

Void contents range from 30 45% for coarseaggregates to 40 50% for fine aggregates.

Relative Density

Relative density (or specific gravity): ratio of

of water.

Most aggregates have relative density between 2.4

2.9.

In concrete mix design, the density of aggregate iscalculated b multi l in its relative densit with thedensity of water.


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Absorption and Surface Moisture

Moisture conditions of aggregates are designated as:,

Air dry: dry at the surface, but contain some interior moisture,absorbent.

Saturated surface dry (SSD): neither absorbent, norcontributing water to the concrete mixture.

Damp or wet: containing excess moisture on the surface.

Portland Cement


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Main Ingredients

Raw materials, , ,

clinker

Gypsum

Important minerals

Calcium, iron, silica, alumina, sulfate

Primary chemical compounds

Tricalcium silicate (3CaO-SiO2 or C3S) Dicalcium silicate (2CaO-SiO2 or C2S)

Tricalcium aluminate (3CaO-Al2O3 or C3A)

Tetracalcium aluminoferrite (4CaO-Al2O3-Fe2O3 or C4AF)

Type of Portland Cement

Type I : normal / general-purpose cement

For concrete exposed to soil, ground water, or seawater wheresulfate concentration are higher than normal but not severe.

Must be used with low water-cement ratio.

Type III : high early strength

Physically and chemically similar to Type I, but the particleshave been ground finer.

Type IV : low hydration heat Develop strength at slower rate than other types of cement.

Type V : sulfate resistant


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Mix Design

Required Strength

The required average strength , as the targetcrf

,of the following equations:

1.34

2.33 3.45 for 35 MPa

0.9 2.33 for 35 MPa

cr c

c c

cr

c c

f f s

f s ff

f s f

= specified compressive strength (MPa)

s = standard deviation (MPa)

cf


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Required Strength

If there are no field strength test data available, thefollowin values of avera e com ressive stren thshould be used (Table 9-11):

S p e c if ie d c o m p r e s s i ve

s t r e n g t h , [ M P a ]

R e q u i r e d a v e r a g e

c o m p r e s s i ve st r e n g t h ,

[ M P a ]

crfcf

21 35

> 35

c

8.5cf

1.1 5c

f

Water-Cement Ratio

Relationship between water-cement ratio and-

Co m p r e s s iv e s t r e n g t h

a t 2 8 d a y s [ M P a ]

W a t e r - ce m e n t r a t i o

N o n - a i r - e n t r a i n e d

c o n c r e t e

A i r - e n t r a i n e d

c o n c r e t e

45 0.38 0.30

40 0.42 0.34

. .

30 0.54 0.45

25 0.61 0.52

20 0.69 0.60

15 0.79 0.70


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Slump

Recommended slumps for various types ofconstruction Table -6 :

Co n s t r u c t i o n t y p eS lu m p [m m ]

M a xim u m M in im u m

Reinforced foundation walls and footings 75 25

Plain footings, caissons, and substructure walls 75 25

eams an re n orce wa s 100 25Building columns 100 25

Pavements and slabs 75 25

Mass concrete 75 25

Mixing Water and Air Content

Mixing water and air content as a function of slump- -,

air-entrained concrete:

S lu m p [m m ]W a t e r [ k g p e r m

3

c o n c r e t e ] ,f o r i n d i ca t e d m a x . a gg r e g a t e s iz e s [ m m ]

9 .5 12 .5 19 2 5 3 7.5 50 75 150

25-50 207 199 190 179 166 154 130 113

75-100 228 216 205 193 181 169 145 124

150-175 243 228 216 202 190 178 160 -

Air content [%] 3 2.5 2 1.5 1 0.5 0.3 0.2


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Coarse Aggregate Content

Bulk volume of dry coarse aggregate per unit volumeof concrete Table - :

Max. s i ze o f

a g gr e g a t e [ m m ]

B u l k v o lu m e p e r u n i t vo l u m e o f co n c r e t e ,

fo r d i f fe r en t FM of fine aggrega te

2 .4 0 2 .6 0 2 .8 0 3 .0 0

9.5 0.50 0.48 0.46 0.44

12.5 0.59 0.57 0.55 0.53

19 0.66 0.64 0.62 0.60

25 0.71 0.69 0.67 0.65

37.5 0.75 0.73 0.71 0.69

50 0.78 0.76 0.74 0.72

75 0.82 0.80 0.78 0.76

150 0.87 0.85 0.83 0.81

Mix-Design Procedure(ACI 211.1, Absolute Volume Method)

Determine the required average strength, , usingACI formula or Table 9-11.

crf

Determine the water-cement ratio based on concretestrength, using Table 9-3.

Choose an appropriate slump based on constructiontype, using Table 9-6.

Determine mixing water and air content based on, - .

Determine the coarse aggregate content based onmaximum aggregate size and FM of fine aggregate,using Table 9-4.


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Mix-Design Procedure(ACI 211.1, Absolute Volume Method)

By now, we have had the volume of cement, coarsea re ate air and water er unit volume ofconcrete. The rest of the volume should be filled bythe fine aggregate.

Adjust the content of water, coarse aggregate, andfine aggregate due to absorption or water content ofthe aggregates.

Example 3

Design the proportioning of concrete for pavement.

maximum size of aggregate is 25 mm, and noprevious statistical data available are available.

The properties of the materials are as follows: Cement: type I, with relative density of 3.15

Coarse aggregate: max. size 25 mm, ovendry density 2.68,absorption 0.5%, bulk density 1600 kg/m3, moisture content2%.

Fine aggregate: ovendry relative density 2.64, absorption0,7%, fineness modulus 2.80, moisture content 6%.


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Required average strength:

8.5 35 8.5 43.5 MPacr c

f f

Water-cement ratio (Table 9-3):45 43.5w . . . .45 40c

Slump (Table 9-6):

Slump for pavement: 25 75 mm, choose 75 mm.

Air and water content (Table 9-5):.

Water: 193 kg for 1 m3 of concrete

Cement content:193

0.392 ; 193 kg 492 kg0.392

w w cc

Coarse aggregate (Tabel 9-4):

Max. size 25 mm, FM of fine aggregate = 2.80volume of coarse aggregate = 0.67 m3 for 1 m3 concrete.

Mass of coarse aggregate (ovendry):

Now, for 1 m3 concrete we need:

Water: 193 kg 0.193 m3

Cement: 492 kg 0.156 m3

Coarse aggregate: 1072 kg 0.400 m3

1600 0.67 1072 kgw

r: 1.5 0.015 mTotal: 0.764 m3

Fine aggregate content = 1 0.764 = 0.236 m3

Mass of fine aggregate = 0.236 2.64 1000 = 623 kg


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Total mass = 193 + 492 + 1072 + 623 = 2380 kg

Estimated concrete density =

193 + 492 + (1072 1.005) + (623 1.007) = 2390 kg/m3

Coarse aggregate: 1072 1.02 = 1093 kgFine aggregate: 623 1.06 = 660 kg

Water: 193 (1072 0.015) (623 0.053) = 144 kg

ustment or mo sture content:

Concrete density =

144 + 492 + 1093 + 660 = 2389 kg/m3

Admixtures

Cementitious materials

strength, reduce permeability, improve workability, reduceshrinkage and creep

Silica fume: byproduct of semiconductor, about 100 timesfiner than cement; increase strength, reduce permeability.

Blast furnace slag: byproduct of iron manufacture; improveworkability, reduce temperature rise during curing, improvesulfate resistance.


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Admixtures

Chemicals-

Water-reducing

Superplasticizer (high range water reducing)

Accelerating / retardant

Shrinkage-reducing

Corrosion inhibitor

reeze pro ec on Coloring agents

Curing

Concrete strength increases with age provided that:.

The concrete remains moist (humidity > 80%).

The temperature remains favorable.

Sufficient space is available for the hydration product to form.

02 Concrete Fundamentals

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