EXPERIMENTAL BEHAVIOUR AND ANALYSIS OF STRESS IN RIGID

PAVEMENT

Presented byM. VIVEK LOYOLA

09MK14II ME INFRASTRUCTURE ENGINEERING

Guided byMrs.A.THILAGAM.,D.Arch,B.E,M.Plan,M.Sc

ASSOCIATE PROFESSOR IN CIVIL ENGINEERINGDEPARTMENT OF CIVIL ENGINEERING

PSG COLLEGE OF TECHNOLOGYCOIMBATORE .

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INTRODUCTIONRigid pavements do not flex much under loading like flexible pavements. They are constructed using cement concrete. In this case, the load carrying capacity is mainly due to the rigidity and high modulus of elasticity of the slab (slab action).

H. M. Westergaard is considered the pioneer in providing the rational treatment of the rigid pavement analysis.

.

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METHODOLOGY

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LITERATURE REVIEW Yin - Wen Chan*, Shu - Hsien Chu, EFFECT OF

SILICA FUME ON STEEL FIBER BOND CHARACTERISTICS IN REACTIVE POWDER CONCRETE, Cement and Concrete Research 34 (2004) 1167–1172In this paper, the effect of silica fume on the bond characteristics of steel fiber in matrix of Reactive powder concrete (RPC), including bond strength, pullout energy, etc., are presented. The experimental results on steel fiber pullout test of different conditions are reported. Various silica fume contents ranging from 0% to 40% are used in the mix proportions. Fiber pullout tests are conducted to measure the bond characteristics of steel fiber from RPC matrix. 4

It is found that the incorporation of silica fume can effectively enhance the fiber–matrix interfacial properties, especially in fiber pullout energy. It is also concluded that in terms of the bond characteristics, the optimal silica fume content is between 20% and 30%, given the conditions of the experimental program. The microstructural observation confirms the findings on the interfacial-toughening mechanism drawn from the fiber pullout test results

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M. Khabiri Mohammed and R. Kargaran Bafqi Mohammed, EFFECT OF PAVEMENT BOUNDARIES DEPTHS ON THE STRUCTURAL STRENGTH OF ROADWAY, journals of applied sciences research, 4(1) : 103 – 109, 2008 Pavement thickness is highly variable in country roadways. The main objective of pavement engineers is to insure that these stresses do not exceed the strength of materials used in different pavement layers. The main objectives of this study were to examine the effect of pavement shoulders on the structural strength of highways. The finite element analysis and the kenlayer computer program were used in the structural analysis of pavement shoulders. The analysis indicated that shoulder width would result in a slight reduction of vertical stresses.

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OBJECTIVE & SCOPE To analysis the stresses in the rigid pavement using Westergaard’s & Bradbury's

analysis.

To determine mechanical property of silica fume concrete.

To evaluate the life cycle cost of the pavement.

To conduct model tests on rigid pavement slab using various mixes C0,C1 & C2.

To study the increase in flexural and compressive strength of concrete, this improves the pavement performance.

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ADMIXTURES & ITS PROPERTIES:Silica fume

It is also known as microsilica, is a byproduct of the reduction of high-purity quartz with coal in electric furnaces in the production of silicon and ferrosilicon alloys.

Silica Fume is also collected as a byproduct in the production of other silicon alloys such as ferrochromium, ferromanganese, ferromagnesian, and calcium silicon.

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Physical Properties of Silica Fume:  Particle size (typical): < 1 μm Bulk density:

(as-produced): 130 to 430 kg/m3

(densified): 480 to 720 kg/m3

Specific gravity: 2.29

Silica fume affects both the fresh and hardened properties of concrete. The effects on concrete are a result of the physical and chemical properties of silica fume.

Chemical Properties of Silica Fume

Amorphous Silicon dioxide > 85% Trace elements depending upon type of fume.

In concrete, cement is replaced with silica fume at 3%.

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Steel slag is produced as a by-product during the oxidation of steel pellets in an electric arc furnace.

This by-product that mainly consists of calcium carbonate is broken down to smaller sizes to be used as aggregates in asphalt and concrete.

They are particularly useful in areas where good-quality aggregate is scarce.

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Steel slag:

EXPERIMENTAL WORKS EXPERIMENTAL WORKS CARRIED OUTCARRIED OUT

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EXPERIMENTAL MATERIALS

53 – Grade Portland Cement Silica Fume (SF) @ 3%

Steel slag 50% replacement for fine aggregate

Fine Aggregate: Grade II –Sand

Coarse Aggregate: 20mm

Powder content Aggregate Content

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EXPERIMENTAL WORKS

Cement concrete mix design (M40 grade) as per IS 10262 - 2009.

Mix Ratio:

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Water Cement Fine aggregate

Coarse aggregate

186 450 652.21 1193.84

0.40 1 1.44 2.65

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TRIAL DESCRIPTION

POWDER CONTENT

AGGREGATE CONTENT

W/C

Cement Fine Steel slag Coarse

C0 Conventional concrete

450 652.21 - 1193.84 186

C1(Silica fume

&Steel slag 50%)

SF ( 3%), 13.5

652.21 401.50 596.92 186Cement (97%) 436.5

C2(Steel slag 50%) Cement (100%) 450 652.21 401.50 596.92 186

C3(Silica fume)

SF ( 3%) 13.5652.21 - 1193.84 186

Cement (97%) 436.5

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EXPERIMENTAL EXPERIMENTAL INVESTIGATIONINVESTIGATION

TEST ON FLEXURAL STRENGTH Flexural Strength Of Concrete

Trial Description 7 14 28

C0 conventional 4.97 5.40 8.88

C1 50% Slag + 3% SF 5.30 6.80 8.06

C2 50% Slag 5.58 8.64 8.79

C3 3% SF 5.34 6.08 6.91

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TEST ON MODULUS OF ELASTICITY

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YOUNG'S MODULUS OF CONCRETE IN MPa

Trial Mix 7 days 14 days 28 days

C0 conventional 18214.41 25600.85 31454.67

C1 50% Slag + 3% SF 22863.05 22205.30 30620.10

C2 50% Slag 23808.05 30642.09 34493.67

C3 3% SF 22846.62 26669.30 32327.43

19Graph on C2 28days Young’s Modulus of concrete

TEST ON POISSON'S RATIO OF CONCRETE

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POISSION'S RATIO OF CONCRETE

Trial Description 7days 14days 28days

C0 conventional 0.13 0.17 0.20

C1 50% Slag + 3% SF 0.16 0.16 0.21

C2 50% Sla0g 0.14 0.18 0.27

C3 3% SF 0.15 0.17 0.25

TEST ON BOND STRENGTHBOND STRENGTH OF CONCRETE IN MPa

Trial Description 7 days 14days 28days

C0 Conventional 5.50 6.65 9.14

C1 50% Slag + 3% SF 6.86 7.52 9.84

C2 50% Slag 7.23 8.97 11.28

C3 3% SF 6.07 6.94 10.02

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TEST ON SPLIT TENSILE STRENGTHSPLIT TENSILE STRENGTH OF CONCRETE IN MPa

Trial Description 7days 14days 28days

C0 conventional 2.01 2.84 3.92

C1 50% Slag + 3% SF 1.70 2.81 3.88

C2 50% Slag 1.52 2.81 3.43

C3 3% SF 1.66 2.84 3.48

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TEST ON COEFFICIENT OF THERMAL EXPANSION

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COEFFICIENT OF THERMAL EXPANSION OF CONCRETE X 10-5

Trial Description 7 days 14 days 28 days

C0 conventional 0.475 1.901 3.153

C1 50% Slag + 3% SF 0.261 3.380 4.307

C2 50% Slag 0.188 1.474 -

C3 3% SF 0.020 2.912 4.162

MODEL TEST ON RIGID PAVEMENT

By conducting some model tests on rigid pavements made of various mixes C0, C1 & C2

The slab is resisting on sub grade (sand), with the modulus of subgrade reaction is 5.74 kg/cm3

The slab of size 0.6m x 0.75m x 0.05m were cast and cured for 7, 14 & 28days.

The slab is placed over the wooden box of size 0.8m x 0.8m x 0.4m filled with sandy soil, that was acting as a sub grade.

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CBR TEST ON SAND (SUBGRADE) I conducted test on sand, to determine the modulus of subgrade reaction.Trail I:

for CBR2.5 = 10%

for CBR5 = 11.5%

As per IRC : 58 – 2002, The modulus of subgrade reaction corresponding to

CBR 11.5% = 5.74 kg/cm3

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TEST ON RIGID PAVEMENT SLAB  

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For 28days test result for C2 slab

load at failure, P = 2.79 tonnes. Young’s modulus, E = 34493.67 MPa. Thickness of slab, h = 50mm. Poisson's ratio, µ = 0.15.

Corner load stress = 3.96 MPa

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Failure Pattern

Loading Set up

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ANALYSIS AND DESIGNANALYSIS AND DESIGN

TYPE OF

SLAB

 

DAYS

SIZE OF

SLAB

(M)

LOAD

(CORNER)

AT FAILURE

IN

DIVISIONS

CORNER

LOAD

STRESS

(MPA)

BASE

COURSE

USED AND

TYPE OF

LOAD

 

C0

7 

0.75 X 0.6 X

0.05

25 11250 

Sandy soil and

corner load.

14 38 17100

28 62 27900

 

C1

7 

0.75 X 0.6 X

0.05

30 13500 

Sandy soil and

corner load.

14 48 21600

28 52 23400

 

 

C2

7  

0.75 X 0.6 X

0.05

20 9000  

Sandy soil and

corner load.

14 45 20250

28 60 27000 29

RIGID PAVEMENT DESIGN

The design procedure is explained for mix C2. INPUT DATADesign life : 20 yearsCommercial vehicles per day : 2000cvFlexural strength : 8.79 MPaModulus of subgrade reaction : 60MN/m3

Modulus of elasticity of concrete : 34493.67MPaPoisson’s ratio : 0.27Coefficient of thermal expansion : 0.0000336/cTyre pressure : 0.6MPaRate of increase of traffic intensity : 7.5%Spacing of contraction joints : 4.5mWidth of slab : 3.5m

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STEP 1:The cumulative number of repetitions of axles during the design period may

be computed from the following formula

Cumulative traffic, C = A * 365 * { (1+r)n – 1} / rWhere A = initial number of axles per day in the year when the road is operational.r = annual rate of growth of commercial traffic.n = design period in years.

Design traffic:25% of total repetitions of commercial vehicles are expected to use the edge

of the pavement.

STEP 2:Assuming that midpoint of the axle load class represents the group, the total

repetitions of single axle and tandem axle loads are follows. 31

SINGLE AXLE TANDEM AXLE

Load in tonnes Expected repetition Load in tonnes Expected repetition

20 39516 36 15806

18 102740 32 15806

16 395155 28 39516

14 885148 24 126450

12 1722877 20 110643

10 1857229 16 39516

10 less 2426253 16 less 126450

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STEP 3:Assume trial thickness, say 24cm

Calculate stress from charts in IRC: 58 – 2002

Calculate fatigue life (N) as followsN = unlimited for stress ratio < 0.45N = {4.2577 / (SR – 0.4325) }3.268 , when 0.45 ≤ SR ≤ 0.55Log10N = (0.9718 – SR ) / 0.0828 , when SR > 0.55

Axle load,

al (tonnes)AL * 1.2

Stress

kg/cm2

(from

charts)

Stress ratioExpected

repetition

Fatigue life

n

Fatigue life

consumed

1 2 3 4 5 6 5/6

Single axle

20 24 40 0.46 39516 14335235 0.00275

18 21.6 36 0.143 102740 ∞ 0

16 19.2 34 0.390 395155 ∞ 0

Tandem axle

36 43.2 32 0.36 15806 ∞ 033

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DESIGN OF TIE BARDesign of tie bar as per IRC: 58 – 2002

For concrete mix for C2 28days.INPUT DATA:Slab thickness = 30cmLane width = 3.5mCoefficient of friction, f = 1.5Density of concrete = 2400 kg/m3

Allowable tensile stress in deformed bars = 2000 kg/m2

Allowable bond stress in deformed tie bars = 50.3Diameter of tie bar, d = 12mm.

STEP 1: (Spacing And Length Of Diameter Of Tie Bar)Area of steel bar per meter width of joint to resist the frictional force at slab

bottom.As = (b x f x w) / s= (3.5 x 1.5 x 0.3 x 2400) / 2000= 1.89 cm2/m

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Diameter of tie bar is 12mm, the cross sectional areaA = d2/4

= 1.131 cm2

Perimeter of tie bar, P = d= 3.769 cm.

Spacing of bars = A/As= (100 x 1.131) / 1.89= 59.84 cm

Provide at a spacing of 60 cm c/cLength of tie bar, L = (2 x S x A) / (B x P)

= (2 x 2000 x 1.131) / ( 50.3 x 3.77)= 23.85 cm

Increase length by 10cm for loss of bond due to painting and another 5cm for tolerance in placement. Therefore, the length is

= 23.85 + 10 + 5 = 38.85cm, say 40cm.

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FINITE ELEMENT ANALYSIS: It can represent both linear and non-linear

analysis.

The linear stage, the concrete is assumed to be isotropic material upto cracking.

The non-linear stage, the concrete may undergo plasticity and/or creep.

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It is used in all types of application to calculate a field quantity.

For a stress analysis, it could be displacement or stress.

For a thermal analysis, it could be temperature or heat flux.

For a fluid flow analysis, it could be velocity potential.

FEA is a way getting a numerical solution to a specific problem.

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ABOUT ANSYS 12 PACKAGEThe ansys id the software package developed by ANSYS Group Engineering that was used to perform the finite element analysis in this study.

Inputs: The geometrics of the problem. Material properties. Loading conditions. Boundary conditions.

Outputs: Load and deflection behaviour. Stress and strain behaviour. Cracking pattern of the slabs. 39

NUMERICAL EXAMPLE:

For concrete mix C2, the Material properties are;

Elastic modulus of concrete = 34493.67 MPaPoisson’s ratio = 0.27Size of Slab = 0.60m x 0.75m Thickness of Pavement Slab = 0.15m

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41Fig : Model of Pavement slab with corner loadings.

42Fig : Stress along X direction of the Slab.

43Fig : Stress along Y direction of the Slab.

44Fig : Deformation of the Slab.

45Fig : Moment of the Slab.

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CONCLUSIONS The earlier stage flexural strength is obtained by C2 mix. This leads

to increase the performance of pavement.

From the various mix replacements, the earlier stage flexural strength is obtained. This leads to increase the performance of pavement at various temperature conditions.

  Using experimental results, 3D modeling is created using Ansys 12.

These results are been compared and analyzed.   Using mat lab program, the rigid pavement design of IRC: 58 –

2002 is to be executed.

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REFERENCES F. Tahmasebinia, Investigating Failure Mode In

Concrete Pavements Subjected To Impact Loading, the indian concrete journal, july 2010.

Mohammed N.S. Hadi, B.C. Budhinayake, Non-linear Finite Element Analysis Of Flexible Pavements, advance in engineering software 34(2008) 657 – 662.

R. Y. Xiao, T. O’ Flaherty, Finite Element Analysis Of Tested Concrete Connections, computer and structures 78(2000) 247 – 255.

Neville A.M, ‘Properties of Concrete’, Prentice Hall, 4th

Edition, Pg: 666, 667,1995.48

Yin - Wen Chan, Shu - Hsien Chu, Effect Of Silica Fume On Steel Fiber Bond Characteristics In Reactive Powder Concrete, Cement and Concrete Research 34 (2004) 1167–1172

Anonymous., IRC : 58 – 2002, “Guidelines For The Design Of Plain Jointed Rigid Pavements For Highways” India Road Congress, New Delhi.

ACI Committee 226. 1987b. Silica fume in concrete: Preliminary report. ACI Materials Journal March-April: 158-66.

E Kohler, R Alvarado, “Coefficient of Thermal Expansion of Concrete Pavements”, University of California Pavement Research Centre, April 2007

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THANK YOUTHANK YOU

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