1

Assignment 1-201720182

1. A two lane interstate expressways of jointed reinforce concrete pavement

(JRCP) with average daily traffic (ADT) 40 000 (both ways), is to be design

according to PCA method. The pavement will be built on cement stabilized

subbase with a design life of 20 years. The percentage of trucks was found to

be 13% with yearly rates of 4% in traffic growth. The pavement is to be designed

with tied Portland concrete shoulder. The modulus of subgrade reaction is 80

MPa/m and the concrete modulus of rupture is 4.0 MPa. Use the load frequency

distribution data given in Table 1.1. Check the adequacy of 210 mm concrete

slab thickness and discuss your findings. Please state clearly your assumptions.

Use all the charts and tables given.

(15 marks)

Table 1.1 Load frequency distribution

Single Axles

Axle Load (kN) Axles per 1000 trucks

133 0.58

125 1.35

115 2.77

107 5.92

98 9.83

88 21.67

Tandem Axles

Axle Load (kN) Axles per 1000 trucks

231 1.96

213 3.94

195 11.48

178 34.27

160 81.42

142 85.54

2

Table 1.2 Load safety factor

Road classification Load safety factor

Interstate Pavements 1.2

Highways and arterials streets 1.1

Roads , low volume streets 1.0

Figure 1.1 Percentage of trucks in right lane of a multilane divided highway

3

Table 1.3 Yearly rates of traffic growth and corresponding projection factors

Yearly rate of traffic

growth %

Projection factor, 20 years Projection factor, 40 years

1 1.1 1.2

1 ½ 1.2 1.3

2 1.2 1.5

2 ½ 1.

3

1.6

3 1.3 1.8

3 ½ 1.4 2.0

4 1.5 2.2

4 ½ 1.6 2.4

5 1.6 2.7

5 ½ 1.7 2.9

6 1.8 3.2

4

Table 1.4 Equivalent stress- with concrete shoulder (Single Axle/Tandem Axle)

5

Table 1.5 Erosions factors- doweled joints, concrete shoulder ( Single Axle/Tandem

Axle)

6

Figure 1.2 Fatigue analysis- allowable load repetitions based on stress ratio factor

(with and without concrete shoulder)

7

Figure 1.3 Erosion analysis – allowable load repetitions based on erosion factor

(with concrete shoulder)

8

9

2. A continuous reinforced concrete pavement (CRCP) has been designed with a

trial thickness of 250mm. It was designed with a dowel joints and asphalt

shoulder on top of 100mm unstabilized subbase. Based on PCA method,

percentage of fatigue analysis and erosion analysis was found to be 108% and

95% respectively. Please summarize the output of the design .Suggest what are

the steps that can be done in order to improve the results.

(8 marks)

3. A concrete pavement is designed to last 20 years. During the first year, the

estimated two- way equivalent single –axle applications are 300,000. And the

expected annual growth rate is 4%. The design reliability is 90%, and the overall

standard deviation is 0.4. The loss of serviceability is 1.7.

The pavement is to be laid on a granular subbase material. Using the standard

laboratory tests on 28-day specimens, the average compressive strength is 6000

psi, and the average modulus of rupture for third-point loadings is 550 psi.

The drainage is considered to be poor, and the pavement is expected to be

subjected to moisture levels approaching saturation 20% of the time. The

pavement is to be designed with jointed reinforced concrete with dowels and

untied asphalt shoulders. The effective modulus of subgrade reaction (corrected

for loss of support) k= 180 pci.

` Determine the design thickness by the AASHTO method. Use the tables, charts

and formulas given.

Ec= 57, 000 (f’c)0.5

T= [ (1+r)n – 1 ] × T1

r

T1= traffic volume during the first year

r = rate of growth expressed as a fraction

n= design period (years)

(12 marks)

10

Table 3.1 Recommended Load –Transfer Coefficients for Various

Pavement Type and Design Conditions

Shoulder Asphalt Tied PCC

Load trasnfer device Yes No Yes No

Pavemet type

1. Plain and

jointed

reinforced

3.2 3.8-4.4 2.5-3.1 3.6-4.2

2. Continuously

reinforced

concrete

pavement

2.9-3.2 N/A 2.3-2.9 N/A

Table 3.2 Recommended Values of Drainage Coefficient, Cd for

Rigid Pavement Design

Quality of

Drainage

Percent of Time Pavement Structure is

Exposed to Moisture Levels Approaching

Saturation

Less

Than 1%

1-5% 5-25% Greater

25%

Excellent 1.25-1.20 1.20-1.15 1.15-1.10 1.10

Good 1.20-1.15 1.15-1.10 1.10-1.00 1.00

Fair 1.15-1.10 1.10-1.00 1.00-0.90 0.90

Poor 1.10-1.00 1.10-0.90 0.90-0.80 0.80

Very Poor 1.00-0.90 0.90-0.80 0.80-0.70 0.70

11

Design chart for rigid pavement based on using mean values for each input variable (segment 1)

12

Design chart for rigid pavements based on using mean values for each input variables (segment 2)