Doç. Dr. Halit YAZICI

D. E. U. Civil Engineering Department

http://kisi.deu.edu.tr/halit.yazici

PROPERTIES OF

HARDENED CONCRETE

� The principal properties of hardened concrete whichare of practical importance can be listed as:

1. Strength

2. Permeability & durability

3. Shrinkage & creep deformations

4. Response to temperature variations

Of these compressive strength is the most importantproperty of concrete. Because;

PROPERTIES OF

HARDENED CONCRETE

Of the abovementioned hardened propertiescompressive strength is one of the most importantproperty that is often required, simply because;

1. Concrete is used for compressive loads

2. Compressive strength is easily obtained

3. It is a good measure of all the other properties.

Factors Affecting Strength

� Effect of materials and mix proportions

� Production methods

� Testing parameters

STRENGTH OF CONCRETE

� The strength of a concrete specimen prepared, cured and tested under specified conditions at a given age depends on:

1. w/c ratio

2. Degree of compaction

COMPRESSIVE STRENGTH

�Compressive Strength is determined by loadingproperly prepared and cured cubic, cylindrical orprismatic specimens under compression.

COMPRESSIVE STRENGTH

� Cubic: 15x15x15 cm

Cubic specimens are crushed after rotating them 90° todecrease the amount of friction caused by the roughfinishing.

� Cylinder: h/D=2 with h=15

To decrease the amount of friction, capping of therough casting surface is performed.

Cubic specimenswithout capping

Cylindrical specimenswith capping

COMPRESSIVE STRENGTHCOMPRESSIVE STRENGTH

Bonded sulphur capping Unbonded neoprene pads

COMPRESSIVE STRENGTHCOMPRESSIVE STRENGTH

� The compressive strength value depends on the shapeand size of the specimen.

�Tensile Strength can be obtained either by directmethods or indirect methods.

Direct methods suffer from a number of difficultiesrelated to holding the specimen properly in the testingmachine without introducing stress concentration and tothe application of load without eccentricity.

Due to applied compression load a fairly uniformtensile stress is induced over nearly 2/3 of thediameter of the cylinder perpendicular to thedirection of load application.

� The advantage of the splitting test over the directtensile test is the same molds are used forcompressive & tensile strength determination.

� The test is simple to perform and gives uniformresults than other tension tests.

σst = 2P

πDlP: applied compressive load

D: diameter of specimen

l: length of specimenSplitting Tensile

Strength

FLEXURAL STRENGTH

The flexural tensile strength at failure or themodulus of rupture is determined by loading a prismatic concrete beam specimen.

TheThe resultsresults

obtainedobtained areare usefuluseful

becausebecause concreteconcrete

is is subjectedsubjected toto

flexuralflexural loadsloads moremore

oftenoften thanthan it is it is

subjectedsubjected toto

tensile tensile loadsloads..

P

M=Pl/4

d

b

cI =

bd3

12

2

3σ =

M c

I=

(Pl/4) (d/2)

bd3/12=

Pl

bd2

M=Pl/6

P/2 P/2

σ =(Pl/6) (d/2)

bd3/12=

Pl

bd2

Factors Affecting the Strength of

Concrete

1) Factors depended on thetest type:

� Size of specimen

� Size of specimen in relationwith size of agg.

� Support condition af specimen

� Moisture condition of specimen

� Type of loading adopted

� Rate of loading

� Type of test machine

2.2. FactorsFactors independentindependent of of

test test typetype::

–– TypeType of of cementcement

–– TypeType of of aggagg..

–– DegreeDegree of of compactioncompaction

–– MixMix proportionsproportions

–– TypeType of of curingcuring

–– TypeType of of stressstress situationsituation

porosity

STRESS-STRAIN RELATIONS IN CONCRETE

σult

(40-50%) σult

εult

σ-ε relationship forconcrete is nonlinear. However, specially forcylindricalspecimens withh/D=2, it can be assumed as linearupto 40-50% of σult

MODULUS OF ELASTICITY OF CONCRETE

Due to thenonlinearity of the σ-εdiagram, E is thedefined by:

1. Initial Tangent Method

2. Tangent Method

3. Secant Method

ACI → E=15200 σult½ → 28-D cylindrical comp.str.

(kgf/cm2)

TS → E=15500 W ½→ 28-D cubic comp.str. (kgf/cm2)

PERMEABILITY OF CONCRETE

� Permeability is important because:

1. The penetration of some aggresive solution may resultin leaching out of Ca(OH)2 which adversely affects thedurability of concrete.

2. In R/C ingress of moisture of air into concrete causescorrosion of reinforcement and results in the volumeexpansion of steel bars, consequently causing cracks & spalling of concrete cover.

3. The moisture penetration depends on permeability & ifconcrete becomes saturated it is more liable to frost-action.

4. In some structural members permeability itself is of importance, such as, dams, water retaining tanks.

PERMEABILITY OF CONCRETE

� The permeability of concrete is controlled by capillarypores. The permeability depends mostly on w/c, age, degree of hydration.

� In general the higher the strength of cement paste, thehigher is the durability & the lower is the permeability.

PROPORTIONING CONCRETE

MIXTURES� W+C+C.Agg.+F.Agg.+Admixtures→ Weights / Volumes?

� There are two sets of requirements which enablethe engineer to design a concrete mix.

1. The requirements of concrete in hardened state. These are specified by the structural engineer.

2. The requirements of fresh concrete such as workability, setting time. These are specified by theconstruction engineer (type of construction, placingmethods, compacting techniques andtransportation)

PROPORTIONING CONCRETE

MIXTURES�Mix design is the process of selecting suitable

ingredients of concrete & determining their relativequantities with the objective of producing as economically as possible concrete of certain minimum properties such as workability, strength & durability.

�So, basic considerations in a mix design is cost & min. properties.

� Cost → Material + Labor

Water+Cement+Aggregate+Admixtures

Most expensive (optimize)

Using less cement causes a decrease in shrinkageand increase in volume stability.

�Min.Properties →Strength has to be more than..

Durability→Permeability has to be

Workability→Slump has to be...

�In the past specifications for concrete mix designprescribed the proportions of cement, fine agg. & coarseagg.

�1 : 2 : 4

Weight of cement

FineAgg.

CoarseAgg.

� However, modern specifications do not usethese fixed ratios.

�Modern specifications specify min compressivestrength, grading of agg, max w/c ratio, min/maxcement content, min entrained air & etc.

�Most of the time job specifications dictate thefollowing data:� Max w/c

� Min cement content

� Min air content

� Slump

� Strength

� Durability

� Type of cement

� Admixtures

� Max agg. size

PROCEDURE FOR MIX DESIGN

1. Choice of slump (Table 14.5)

PROCEDURE FOR MIX DESIGN

2. Choice of max agg. size

• 1/5 of the narrowest dimension of the mold

• 1/3 of the depth of the slab

• ¾ of the clear spacing between reinforcement

• Dmax < 40mm

PROCEDURE FOR MIX DESIGN

3. Estimation of mixing water & air content (Table 14.6 and 14.7)

PROCEDURE FOR MIX DESIGN

4. Selection of w/c ratio (Table 14.8 or 14.9)

PROCEDURE FOR MIX DESIGN

5. Calculation of cement content with selected wateramount (step 3) and w/c (step 4)

6. Estimation of coarse agg. content (Table 14.10)

PROCEDURE FOR MIX DESIGN

7. Calculation of fine aggregate content with knownvolumes of coarse aggregate, water, cement and air

8. Adjustions for aggregate field moisture

PROCEDURE FOR MIX DESIGN

9. Trial batch adjustments

� The properties of the mixes in trial batches arechecked and necessary adjustments are made to endup with the minimum required properties of concrete.

� Moreover, a lab trial batch may not always providethe final answer. Only the mix made and used in thejob can guarantee that all properties of concrete aresatisfactory in every detail for the particular job at hand. That’s why we get samples from the fieldmixes for testing the properties.

Example:

� Slump → 75-100 mm

� Dmax → 25 mm

� f’c,28 = 25 MPa

� Specific Gravity of cement = 3.15

� Non-air entrained concrete

Coarse Agg. Fine Agg.

SSD Bulk Sp.Gravity 2.68 2.62

Absorption 0.5% 1.0%

Total Moist.Content 2.0% 5.0%

Dry rodded Unit Weight 1600 kg/m3 –

Fineness Modulus – 2.6

1. Slump is given as 75-100 mm

2. Dmax is given as 25 mm

3. Estimate the water and air content (Table 14.6)

Slump and Dmax → W=193 kg/m3

Entrapped Air → 1.5%

4. Estimate w/c ratio (Table 14.8)

f’c & non-air entrained → w/c=0.61 (by wt)

5. Calculation of cement content

W = 193 kg/m3 and w/c=0.61

C=193 / 0.61 = 316 kg/m3

6. Coarse Agg. from Table 14.10

Dmax and F.M. → VC.A=0.69 m3

DryDry WWC.A.C.A. = 1600*0.69 = 1104 kg/m= 1600*0.69 = 1104 kg/m33

SSD WSSD WC.A.C.A. = 1104*(1+0.005) = 1110 kg/m= 1104*(1+0.005) = 1110 kg/m33

7. To calculate the F.Agg. content the volumes of other ingredients have to be determined.

V = MSp.Gr.*ρwVwater = 193

1.0*1000= 0.193 m3

Vcement = 3163.15*1000

= 0.100 m3

VC.Agg. = 11102.68*1000

= 0.414 m3

Vair = 0.015 m3 (1.5%*1)

ΣV = 0.722 m3 → VF.Agg = 1-0.722 = 0.278 m3

WF.Agg = 0.278*2.62*1000 = 728 kg/m3

Summary of Mix Design� Based on SSD weight of aggregates

8. Adjustment for Field Moisture of Aggregates

WSSD =WDry *(1+a) WField =WDry *(1+m)

Correction for water

From coarse aggregate: 1127-1110 = 17

From fine aggregate: 759-728 = 31

48 kg

extra

Corrected water amount : 193 – 48 = 145 kg

Summary of Mix Design� Based on field weight of aggregates

9. Trial Batch

Usually a 0.02 m3 of concrete is sufficient to verifythe slump and air content of the mix. If the slumpand air content are different readjustments of theproportions should be made.

Cleaning Concrete

Surfaces

�Cleaning methods:

�Water

�Chemical

�Mechanical

Finishing Formed

Surfaces

� Rough-form finishes

� Smooth off-the-form finish

� Smooth, rubbed finish

� Sand-floated finish

� Grout cleandown

(sack-rubbed finish)

Special Surface Finishes

� Pattern and Textures

� Exposed Aggregate Concrete

� Colored Finishes

� Stains, Paints and Clear Coatings

Fiber Reinforced Concrete

Effect

of fiber

NEED� PCC has low tensile strength, limited ductility and little

resistance to cracking

� PCC develops micro-cracks, even before loading

� Addition of small, closely spaced and uniformly

distributed fibres act as crack arresters.

FIBRE REINFORCED CONCRETE is a composite

material consisting of mixtures of cement, mortar or

concrete and discontinuous, discrete, uniformly

dispersed suitable fibres.

69

FACTORS AFFECTİNG THE PROPERTIES OF FRC� Relative Fibre Matrix Stiffness

� Volume of Fibres

� Aspect Ratio of the Fibre

� Orientation of Fibres

� Workability and Compaction of Concrete

� Size of Coarse Aggregate

� Mixing

FIBRE REINFORCED CONCRETE

70

1. RELATİVE FİBRE MATRİX STİFFNESS� Modulus of elasticity of matrix must be

much lower than that of fibre. E.g.

steel, glass, carbon

� Fibres with low modulus of elasticity-

nylon, polypropylene

� Interfacial bond between the matrix

and the fibres determine the

effectiveness of stress transfer71

2. VOLUME OF FİBRES

72

3. ASPECT RATİO OF THE FİBRE

73

Aspect Ratio of a fibre = Length/Diameter

4. ORİENTATİON OF FİBRES

The effect of randomness, was tested

using mortar specimens reinforced with

0.5% volume of fibres, by orienting

them:

� parallel to the direction of the load

� perpendicular to the direction of the

load

� in random 74

5. Workability and Compaction of

Concrete

Fibres reduce workability

6. Size of Aggregate

Size of CA is restricted to 10mm

75

7. MİXİNGCement content : 325 to 550 kg/m3

W/C Ratio : 0.4 to 0.6

% of sand to total aggregate : 50 to 100%

Maximum Aggregate Size : 10 mm

Air-content : 6 to 9%

Fibre content : 0.5 to 2.5% by

vol of mix

: Steel -1% - 78kg/m3

: Glass -1% - 25 kg/m3

76

FIBRE REINFORCED CONCRETE

TYPES OF FRC’S

77

STEEL FİBRE REİNFORCED CONCRETE (SFRC)� Aspect ratios of 30 to 250

� Diameters vary from 0.25 mm to 0.75

mm

� Hooks are provided at the ends to

improve bond with the matrix

78

79

FIBRE REINFORCED CONCRETE

80

FIBRE REINFORCED CONCRETE

INTRODUCTION OF STEEL FIBRES MODIFIES:1. Tensile strength2. Compressive strength3. Flexural strength4. Shear strength5. Modulus of Elasticity6. Shrinkage7. Impact resistance8. Strain capacity/Toughness9. Durability10.Fatigue

81

APPLICATIONS OF SFRC� Highway and airport pavements

� Refractory linings

� Canal linings

� Industrial floorings and bridge-decks

� Precast applications - wall and roof

panels, pipes, boats, staircase steps &

manhole covers

� Structural applications

82

POLYPROPYLENE FIBER REINFORCED CONCRETE (PFRC)

� Cheap, abundantly available

� High chemical resistance

� High melting point

� Low modulus of elasticity

� Applications in cladding panels and shotcrete

83

FIBRE REINFORCED CONCRETE

GLASS FIBER REINFORCED CONCRETE (GFRC)� High tensile strength, 1020 to 4080 N/mm2

� Lengths of 25mm are used

� Improvement in impact strengths, to the tune

of 1500%

� Increased flexural strength, ductility and

resistance to thermal shock

� Used in formwork, swimming pools, ducts and

roofs, sewer lining etc.

84

OTHER FIBRES

85

ASBESTOS FIBERS� High thermal, mechanical and chemical

resistance

� Short in length (10 mm)

� Flexural strength is 2 to 4 times that

of unreinforced matrix

� Contains 8-16% of asbestos fibres by

volume

� Associated with health hazards, banned

in many countries86

CARBON FIBERS� Material of the future, expensive

� High tensile strengths of 2110 to 2815

N/mm2

� Strength and stiffness superior to that of

steel

87

ORGANIC/VEGETABLE FIBERS

� Jute, coir and bamboo are examples

� They may undergo organic decay

� Low modulus of elasticity, high impact

strength

88

Load Induced Volume ChangesLoad Induced Volume Changes

u Instantaneous, 1D

ε=σ E

ε

σ

Secant modulus

Tangent modulus

c

.

concrete 'fE 5133γ=

ftcubic/lbs,concreteofweightunit=γ

psi,strengthecompressiv'f c =

Load Induced Volume ChangesLoad Induced Volume Changes

u Time dependant ε

Creep deformationDeformation

Time

Creep in ConcreteCreep in Concrete

Creep in ConcreteCreep in Concrete

water

Creep

Consequences of creepConsequences of creep

u Loss in pre-stress

u possibility of excessive deflection

u stressing of non load bearing members

EconomyEconomy

u Cement Content

u 50-60$/ton

u Aggregates

u 5-6 $/ton

u minimum cement required at the minimum

water cement ratio, with the maximum

strength and durability

Shrinkage

and Creep

Doç. Dr. Halit YAZICI

D. E. U. Civil Engineering Department

http://kisi.deu.edu.tr/halit.yazici