This report documents recommendations for the design and construction of 

portland cement concrete (KC) pavements. The recommendalions were derived 

from the analysis of Long-Term Pavement Performance (LTHP) data. 

The positive outcomes of this study are the recommendations for improving 

PCC pavement design and the development of prediction models to be used in 

pavement design and management. Most of the performance models developed 

are mechanistic-based, and this is expected to provide expanded capabilities for 

considering the effects of load- and climate-related stresses on PC@ pavement 

performance, The development of mechanistic-based mo els agrees with current 

trends of upgrading the pavement design and evaluation process through the 

use of mechanistic-based design. methods. 

This rep? is important to everyone who designs, constructs, and manages 

pavements. 

earners, P, E, 

This document is disseminated under the sponsorship of the Department of 

Thnsportation in the interest of information exchange. The United States 

Government assumes no liability for its contents or use thereof. This report does 

not constitute a standard, specification, or regulation. 

The United States Government does not endorse products or manufacturers. 

Trade and marwfacturers names appear in this report only because they are 

essential to the object of the document. 
1. Report No. 

FHWA-RD-98-052 

2. Government Accesslon No. 

Technical Report Documentation Page 

3. Recipient’s Catalog No. 

I 

4. Title and Subtitle 

DESIGN AND CONSTRUCTION OF PCC PAVEMENTS 

Volume I: S ummary of Design Features and Construction 

Practices That Influence Performance of Pavements 

5. Report Date 

April 1998 

I 7. Author(s) 

6. Performlng Organization Code 

8. Performlng Organization Report No. 

E. B. Owusu-Antwi, L. Titus-Glover, M. I. Darter 

9. Performlng Organization Name and Address 

ERES Consultants, Inc. 

505 W. University Avenue 

Champaign, IL 61820-3915 

10. Work Unlt No. (TRAIS) 

Il. Contract or Grant No. 

DTFH61-94-C-00218 

13. Type of Report and Period Covered 

12. Sponsorlng Agency Name and Address 

Office of Engineering R&D 

Federal Highway Administration 

6300 Georgetown Pike 

McLean, Virginia 22101-2296 

15. Supplementary Notes 

Final Report 

14. Sponsorlng Agency Code 

FHWA Contracting Officer’s Technical Representative: Cheryl Allen Richter, P.E., HNR30 

16. Abstract 

A study has been conducted to evaluate and analyze portland cement concrete (PCC) pavements in order to develop 

recommendations for the design and construction of long-lived concrete pavements. It involved a detailed evaluation 

and analysis of the PCC pavement data in the Long-Term Pavement Performance (LTPP) database using a variety of 

means to determine the beneficial effects of design features and construction practices on long-term performance. 

Emphasis was placed on identifying those specific design features that can be included during design to improve the 

performance of PCC pavements under various combinations of environmental and traffic loading conditions, and for 

different subgrade support conditions. The study focused on the development of practical recommendations that can 

be easily implemented by highway agencies to increase pavement life. 

This volume provides a concise summary of the results that were obtained from the study. It includes an overview of 

the engineering and statistical analyses that were conducted and presents results that can be used by State highway 

agencies to obtain high-performance PCC pavements. Implementation of the recommendations will increase the 

reliability of PCC pavements. 

This report is the first in a series of three volumes from the study. The other volumes are as follows: 

FHWA No. Vol No. Short Tiile 

FHWA-RD-98-053 II Design Features and Construction Practices that Influence Performance of 

PCC Pavements 

FHWA-RD-98-054 Ill Improved PCC Performance Models 

117. Key Words 1 18. Dlstrlbutlon Statement I 

Concrete pavement, design, construction, performance, 

distress, design guidelines, construction guidelines, 

life cycle cost 

No restrictions. This document is available to the 

public through the National Technical Information 

Service, Springfield, Virginia 22161. 

19. Security Classlf. (of thls report) 

I 

20. Security Classlf. (of thls page) 21. No of Pages 22. Pdce 

I 

I Unclassified 

Form DOT F 1700.7 (E-72) 

I 

Unclassified 

I 

92 

I I 

Reproduction of completed page authorized 
APPROXIMATE CONVERSIONS TO SI UNITS 

Symbol When You Know Multiply By To Find Symbol 

in 

ft 

Yd 

mi 

in2 

fF 

Y@ 

ac 

miz 

fl 01 

gal 

ftj 

Y@ 

NOTE: 

02 

lb 

T 

fc 

fl 

Ibf 

Ibf/W 

LENGTH 

inches 

feet 

yards 

miles 

25.4 

0.305 

0.914 

1.61 

AREA 

millimeters 

meters 

meters 

kilometers 

square inches 

square feet 

square yards 

acres 

square miles 

645.2 

0.093 

0.836 

0.405 

2.59 

VOLUME 

square millimeters 

square meters 

square meters 

hectares 

square kilometers 

fluid ounces 29.57 milliliters 

gallons 3.785 liters 

cubic feet 0.028 cubic meters 

cubic yards 0.765 cubic meters 

Volumes greater than 1000 I shall be shown in m3. 

MASS 

ounces 28.35 grams 

pounds 0.454 kilograms 

short tons (2006 lb) 0.907 megagrams 

(or “metric ton”) 

TEMPERATURE (exact) 

Fahrenheit 5(F-32)/9 Celcius 

temperature or (F-32)/1.8 temperature 

ILLUMINATION 

footcandles 10.76 Iux 

foot-Lamtxxts 3.426 candela/m* 

FORCE and PRESSURE or STRESS 

poundforce 

poundforce per 

square inch 

4.45 

6.89 

newtons 

kilopascals 

mm 

m 

rrn 

mm2 

m2 

m2 

ha 

km2 

mL 

L 

m3 

m3 

“C 

lx 

cd/m2 

N 

kPa 

SI is the symbol for the International System of Units. Appropriate 

rounding should be made to comply with Section 4 of ASTM E380. 

APPROXIMATE CONVERSIONS FROM SI UNITS 

Symbol When You Know Multiply By To Find Symbol 

mm 

m 

kmm 

mm2 

m2 

m2 

ha 

km2 

mL 

L 

m3 

m3 

N 

kPa 

LENGTH 

millimeters 

meters 

meters 

kilometers 

0.039 

3.28 

1.09 

0.621 

AREA 

square millimeters 

square meters 

square meters 

hectares 

square kilometers 

0.0016 

10.764 

1.195 

2.47 

0.386 

VOLUME 

milliliters 

liters 

cubic meters 

cubic meters 

0.034 

0.264 

35.71 

1.307 

MASS 

grams 

kilograms 

0.035 

2.202 

inches 

feet 

yards 

miles 

square inches 

square feet 

square yards 

aaes 

square miles 

fluid ounces 

gallons 

cubic feet 

cubic yards 

ounces 

in 

ft 

yd 

mi 

in2 

fP 

Y# 

ac 

mi2 

fl 02 

gal 

fP 

Y@ 

02 

lb 

megagrams 1.103 short tons (2000 lb) T 

(or “metric ton”) 

TEMPERATURE (exact) 

Celcius 

temperature 

1.8C + 32 

ILLUMINATION 

Fahrenheit 

temperature 

“F 

Iux 0.0929 foot-candles fc 

candela/m2 0.2919 foot-Lamberts fl 

FORCE and PRESSURE or STRESS 

newtons 

kilopascals 

0.225 

0.145 

poundforce 

poundforce per 

square inch 

Ibf 

IbWin2 

(Revised September 1993) 
TABLE OF CONTENTS 

Chauter Page 

1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

Overview ................................................. . 

Background ............................................... . 

ScopeofReport ........................................... 

. 

2 EFFECT OF SITE CONDITIONS ON KC 

PERFORMANCE . . . e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 

Introduction ............................................. .5 

Traffic Loading ........................................... .5 

Influence of Climate on Pavement Performance ............. .12 

Influence of Subgrade Support on Pavement Performance ... .14 

Summary of Site Condition ............................... .23 

3 RECOMMENDATIONS FOR SELECTING DESIGN 

FEATURES OF CONCRETE PAVEMENTS . . . , . . . . . . . . . .31 

Introduction ........................................... ..3 1 

Design Features That Affect PCC Pavement Performance .... .31 

JPCP Faulting ........................................... .33 

JPCP Transverse Joint Spalling ............................ .38 

JPCP Transverse Cracking ................................ .40 

JPCPCornerBreaks ..................................... ..4 2 

JPCP Roughness ......................................... .42 

JRCP Transverse Joint Spalling ........................... .47 

JRCP Roughness ......................................... .47 

CRCPRoughness ....................................... ..4 9 

Summary .............................................. ..5 1 

. . . 

111 
TABLE OF CONTENTS (Continued) 

Chanter Page 

4 RECOMMENDATIONS FOR CONSTRUCTION OF 

KC PAVEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59 

Introduction ........................................... ..5 9 

Effect of Construction Practices on Joint Faulting ............ .62 

Effect of Construction Practices on KC Transverse Cracking . .62 

Effect of Construction Practices on Roughness .............. .62 

Summary .............................................. ..6 3 

5 APPLICATIONS OF DISTRESS PERFORMANCE 

MODELS . . . . . . . . . . e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65 

Introduction . . . . . . . . . I . s . e . . . . s . . . . . . . . . . . . . . . . . . . . . . . . . .65 

Faulting of JPCP (Models Provided in Chapter 4, Volume III) .65 

Transverse Joint Spalling for JPCP and JRCP (Models 

Provided in Chapter 5, Volume III) . . . . . . . . . . . . . . . . . . . . . . . .66 

Transverse Cracking for JPCP (Models Provided in 

Chapter 6, Volume III) . . . . . . . 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . .68 

Corner Breaks for JPCI? (Models Provided in Chapter 6, 

VolumeIII) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...69 

Roughness for JPCP, JRCP, and CRCP (Models Provided 

in Chapter 7, Volume III) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70 

Suitability of Prediction Models . . . . . . . . . . . . . . . . . . . . . . . . . . . .72 

Examples of Application of Performance Models . . . . . . . . . . . . .72 

Checking the Design of New Pavements with Prediction 

Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...72 

Comparing Cost-Ef.fectiveness of Alternative Design . . . . . . . . .75 

Summary . . . . . ...* D a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...79 

6 CONCLUSIONS AND RECOMMENDATIONS . . . . . . . . .81 

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83 

iv 
Figure 

LIST OF FIGURES 

Pace 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

JPCP joint faulting versus traffic loadings, showing the effect of 

different dowel diameter ...................................... .7 

Percent slabs with transverse cracking versus traffic loadings, 

showing the effect of different KC slab thickness ................ .8 

Percent slabs with corner breaks versus traffic loadings, showing 

the effect of different PCC slab thicknesses ...................... .9 

Plot of roughness versus traffic loadings, showing the effect of 

different dowel diameters ..................................... 10 

Plot of JRCP roughness versus traffic loadings, showing the 

effect of edgedrains ........................................... 11 

CRCP roughness versus traffic loadings, showing the effect of 

longitudinal steel content .................................... .13 

Effect of annual number of wet days on JPCP faulting ............ .16 

Effect of annual number of wet days on JPCP transverse cracking . . 17 

Effect of climate (freeze or nonfreeze) on IRI of JPCP ............. .18 

Effect of mean annual precipitation on IRI of JRCP ............... .19 

Effect of climate (dry, wet, freeze, nonfreeze) on IRI of CRCP ..... .20 

Effect of annual number of days with temperature above 32 “C 

onIRIofCRCP ............................................ ..2 1 

Effect of modulus of subgrade reaction on faulting for JPCP ...... .24 

Effect of subgrade type (fine or coarse) on IRI for JPCP ........... .25 

Effect of subgrade type on IRI for JRCP ........................ .26 

Effect of modulus of subgrade reaction on IRI for CRCP .......... .27 

Influence of dowels on JPCP faulting .......................... .34 

Influence of slab thickness on JPCP faulting ..................... .36 

Influence of base type on JPCP faulting ........................ .37 

Plot of percent JPCP spalling versus traffic for the different joint 

sealant materials evaluated ................................... .39 

Influence of KC slab thickness on JPCP transverse cracking ...... .41 

Percent slabs with corner breaks versus cumulative ESAL’s for 

different slab thicknesses ..................................... .43 

Plot of percent slabs with corner breaks versus cumulative 

ESAL’s for different KC slab joint spacing ..................... .44 

Influence of dowel diameter on JPCP roughness ................. .46 

Influence of joint sealant type on JRCP transverse joint spalling ... .48 

Influence of design longitudinal steel content on CRCP roughness . .50 

V 
LIST OF FIGURES (Continued) 

Figure Page 

27 Schematic diagram of pavement design practice with emphasis 

on cost-effectiveness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76 

vi 
LIST OF TABLES 

Table 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

Page 

Summary of the effect of climate-related variables on pavement 

distress ................................................... ..15 

Summary of the effect of subgrade support variables on pavement 

distress ................................................... ..2 2 

Effect of key pavement design features on JPCP transverse joint 

faulting ................................................... ..5 2 

Effect of key JPCP design features on transverse joint spalling ..... .53 

Effect of key pavement design features on JPCP transverse 

cracking .................................................. ..5 4 

Effect of key JPCP design features on corner breaks .............. .54 

Effect of key pavement design features on JPCP roughness ....... .55 

Effect of key JRCP design features on transverse joint spalling .... .56 

Effect of key pavement design features on JRCP roughness ....... .56 

Effect of key pavement design features on CRCP roughness ...... .57 

Summary of construction practices on pavement performance .... .60 

Summary of variables required for estimating faulting ........... .66 

Summary of variables required for predicting JPCP joint spalling .. .67 

Summary of variables required for predicting JRCP joint spalling .. .68 

Summary of variables required for estimating transverse cracking . .69 

Summary of variables required for estimating corner breaks ...... .70 

Summary of variables required for predicting IRI for the three 

pavement types (JPCP, JRCP, and CRCP) ....................... .71 

Suggested critical values for key performance indicators ......... .73 

Comparison of cost-effectiveness of two alternative pavement 

designs ................................................... ..7 8 

vii 
LIST OF ACRONYMS AND ABBREVIATIONS 

AC 

ANOVA 

cci 

CRCP 

Dowdia 

D32 

E PCC 

ESAL 

FI 

Ftcyc 

FWD 

GPS 

h KC 

IRI 

JPCP 

JRCP 

JTSP 

k 

LTPP 

PCC 

TEMP 

Wtdys 

asphalt concrete 

analysis of variance 

drainage coefficient 

continuously reinforced concrete pavement 

dowel diameter 

average annual number of days with temperature below 32 “C 

elastic modulus of KC slab 

equivalent single axle load 

freezing index 

average annual number of air freeze-thaw cycles 

falling weight deflectometer 

general pavement studies 

PCC slab thickness 

international roughness index 

jointed plain concrete pavement 

jointed reinforced concrete pavement 

joint spacing or KC slab length 

modulus of subgrade reaction 

Long-Term Pavement Performance 

portland cement concrete 

temperature 

average annual number of wet days 

1.. 

Vlll 
1. INTRODUCTION 

Overview 

Several variables influence the long-term performance of portland cement 

concrete (KC) pavements. They can be classified into the site conditions at the 

location of the pavement, the design features that are incorporated into the 

pavement, and the construction practices that are followed to build the 

pavement. The site conditions include traffic loading, climate, and the support 

provided by the subgrade. Examples of the design features that influence 

performance include layer thicknesses, joint spacing, joint and load transfer 

design, reinforcement design, and subdrainage. Factors related to construction 

that can also have a significant influence on the performance of KC pavements 

include mix design; method of paving; method of dowel installation; method of 

finishing, texturing, and curing; and the method used to form joints. 

For designers to provide long-lasting PCC pavements, practical 

recommendations on these design features and construction practices are 

required. While there are several examples of pavements that have lasted for 

over 40 years, there have also been instances where KC pavements have only 

lasted a fraction of their design lives. Typical reasons for such premature 

failures of KC pavements include inadequate characterization of site conditions 

and the use of inappropriate inputs in the design process. Also, there are several 

examples of instances where the required design features have not been used for 

particular pavements; for example, not providing dowels for heavily trafficked 

PCC pavements has led to excessive faulting. Other reasons include deficient 

design features and poor construction practices. 

Therefore, to build high-performance concrete pavements that will last a long 

time, designers need to understand clearly the influence of all these factors on 

long-term performance. Based on this understanding, the design features and 

construction practices that can promote good performance throughout the design 

life of the pavement can then be selected to construct high-performance concrete 

pavements. The primary objective of this study was to evaluate in-service KC 

pavements from the Long-Term Pavement Performance (LTPP) study to 

quantify the influence of the site condition factors on long-term performance and 

to determine the beneficial effects of design features and construction practices. 

This report provides information on the design features and construction 

practices that have been identified as influencing KC pavement performance. It 

also provides recommendations on the design features and construction 

1 
practices that can be used by pavement design engineers to improve long-term 

performance. 

Background 

To develop improved recommendations for the design and construction of 

high-performance concrete pavements, a study was conducted that had the 

following two specific objectives: 

l Examine and analyze the rigid pavement LTPP data to determine design, 

site, and construction variables that influence the long-term performance 

of KC pavements. 

l Develop specific recommendations that can be implemented in design 

and construction to improve long-term performance. 

These objectives were accomplished through extensive analysis of jointed 

plain concrete pavement (JPCP), jointed reinforced concrete pavement (JRCP), 

and continuously reinforced concrete pavement (CRCP) included in the LTPP 

General Pavement Studies (GPS) database in a two-part study. First, there was a 

comprehensive engineering and statistical evaluation of the in-service KC 

pavements in the LTPP database to evaluate the effect of traffic loading, climate, 

subgrade support, and pavement design features on some of the key distress 

types: transverse joint faulting, transverse cracking, and roughness. Similarly, 

there was an evaluation of the effect of construction practices on the occurrence 

and progression of these key distress types. Details of the results of that part of 

the study are presented in volume II of this report. 

Second, using the best tools currently available, improved mechanistic-based 

prediction models were developed for joint faulting, joint spalling, roughness, 

transverse cracking, and corner breaks (JPCP). The models were used in 

sensitivity analyses to quantify the influence of site conditions and to identify 

the effects of design features on PCC pavement performance. Volume III of this 

report provides detailed results on that part of the study. This volume of the 

report contains a summary of the findings and recommendations from the 

overall study presented in an easy-to-reference format. It is not intended to 

provide all the detailed information contained in volumes II and III; however, 

this volume highlights the important findings of the study. 
Scope of Report 

This volume of the report consists of six chapters. Chapter 2, which follows 

this introductory chapter, provides information that quantifies the effect of the 

site conditions-traffic loading, climate, and subgrade support-on long-term 

pavement performance. Information in this chapter was obtained from volume 

II and III of this report. Chapter 3 is a summary of findings from volumes II and 

III of this report and provides guidance and recommendations for selecting 

design features that will improve long-term pavement performance. 

Recommendations for construction practices are discussed in chapter 4. The 

information presented in chapter 4 is from volume II of this report. 

Chapter 5 presents a summary of the design and site variables required as 

input for the improved distress and roughness prediction models that were 

developed as part of this study and presented in volume III. The effect of these 

variables on distress and examples of the models’ application are also provided. 

Chapter 6 concludes this report. Although the report covers the three 

conventional KC pavement types (JPCP, JRCP, and CRCP), emphasis is placed 

on JPCP. 

3 

2. EFFECT OF SITE CONDITIONS ON KC PERFORMANCE 

Introduction 

Being able to effectively and accurately account for the effect of site 

conditions on KC pavements is a very important part of pavement design. 

Assessing or quantifying the influence of traffic loading, climate, and subgrade 

support on performance is the first priority in pavement design, since this 

information is required in order to identify the design features that should be 

incorporated in the pavement to promote long life. A key part of this study was 

to evaluate the effect of traffic loading, climate, and subgrade support, both 

separately and together, on the occurrence and progression of the common 

distress types in PCC pavements using the LTPP data. This evaluation provided 

several results that should be of use to practicing pavement engineers. The key 

distress types that were evaluated are as follows: 

l JPCP 

Joint faulting 

Transverse joint spalling 

Transverse cracking 

Corner breaks 

Roughness 

. JRCP 

Transverse joint spalling 

Roughness 

. CRCP 

Roughness 

A comprehensive evaluation of the effect of several site-related variables on 

distress and roughness is presented in volumes II and III of this report. This 

chapter summarizes the key observations and recommendations that resulted 

from the evaluation. 

Traffic Loading 

Repeated traffic loading is the main source of the stresses, strains, and 

deformations within the pavement structure that leads to the development of 

distresses and roughness. Vehicles with different gross weights, axle types, and 

axle weight distributions can be converted into a standard measure to generally 

5 
characterize traffic loading for design. The cumulative 80-kN equivalent single 

axle load (ESAL) is the standard traffic loading designation that is used in most 

design procedures. (I) Therefore, the effect of cumulative 80-kN ESAL’s on the 

key KC pavement distress types was investigated in this study. Set out below 

is a summary of the results obtained on the effect of cumulative ESAL’s on JPCP 

JRCP, and CRCP performance as determined from the LTPP database. 

Influence of Traffic Loading; on TPCP 

Repeated traffic loading contributes greatly to faulting, transverse cracking, 

corner breaks, and roughness. This finding is in agreement with the results of 

past studies.(2, 3, 4g 5z 6, Fi gures 1 through 4 illustrate the effect of increasing traffic 

load applications (ESAL’s) on faulting, transverse cracking, corner breaks, and 

roughness, respectively. The plots are from prediction models developed with 

the LTPP data. A summary of the input variables for the models is presented in 

chapter 5 of this volume, and the actual models are presented and discussed in 

greater detail in volume III of this report. 

Figure 1 illustrates that as the cumulative load applications increase, JPCP 

faulting increases rapidly in the beginning and then levels off. As shown by the 

figure and discussed in detail in the next chapter, design features such as dowels 

can be used to reduce the influence of traffic loading on faulting of JPCP. 

Similarly, figure 2 illustrates the effect of cumulative ESAL’s on transverse 

cracking of JPCP. As shown, increasing the PCC slab thickness is one way to 

reduce the effect of traffic loading. Figures 3 and 4, respectively, illustrate the 

influence of traffic loading on corner breaks and roughness. Once again, traffic 

loading clearly increases the severity of corner breaks and roughness. However, 

design features can be used to minimize the negative effect of traffic loading on 

pavement performance. Increasing pavement thickness will reduce corner 

breaks, and the use of dowels will reduce roughness of JPCP. 

Influence of Traffic Loadinp on JRCP 

Figure 5 shows the effect of traffic loading on JRCP roughness. Increased 

traffic loadings increase the rate and occurrence of distress, and this is 

manifested as increased roughness. A key JRCP distress type that greatly affects 

roughness is joint faulting. Also, deterioration of transverse cracks in JRCP with 

repeated heavy loads contributes to roughness. Traffic loading, like other site 

conditions, usually cannot be influenced by the pavement designer. Therefore, 

distress and roughness developed as a result of increased traffic loading can be 

minimized only through the selection of design features and construction 

6 
rt + c 

7 
0 10 20 30 

ESAL’s (millions) 

Figure 2. Percent slabs with transverse cracking versus traffic loadings, 

showing the effect of different KC slab thickness. 
9 
0 5 10 15 20 25 

ESAL’s (millions) 

- 

E pcc = 31,000 kPa 

wtdys = 120 

ftcyc = 70 

D32 = 50 

-- 

Figure 4. Plot of roughness versus traffic loadings, showing the effect of 

different dowel diameters. 
, I 
practices that limit the occurrence of distress and roughness. The figure also 

shows that design features such as the provision of edgedrains can be used to 

minimize the effect of traffic loading on roughness. 

Influence of Traffic Loading: on CRCP 

Figure 6 shows the effect of traffic loading on CRCP roughness. The plot is 

derived from prediction models developed as part of this LTPP study to predict 

distress and roughness. The figure shows that increasing traffic loading 

increases the roughness of CRCP. This is due to the development of different 

distresses that occur as a result of increased traffic loading, such as 

punchouts. c7f 8, 

Punchouts and pumping are the key distress types in CRCP that are 

influenced by traffic loading. Traffic loading can also contribute to an increase 

in crack widths that eventually leads to steel rupture. Punchouts occur when two 

closely spaced cracks are present that cannot adequately transfer load by 

aggregate interlock, and the piece of pavement between the cracks acts as a 

“beam.” With repeated traffic loading, a longitudinal crack will form in the 

cantilever beam within 0.6 to 1.2 m of the longitudinal edge joint of the 

pavement. Further traffic loading will cause rupture of the reinforcement and 

will cause the piece of pavement between the longitudinal joint and crack to 

break down further. 

Any design feature that leads to reduced crack width will minimize 

punchouts. Past studies have shown that increasing the design steel content of 

CRCP reduces the severity of the distress and, therefore, roughness.@,9) Results 

from the sensitivity analysis of the CRCP roughness model developed as part of 

this study and illustrated in figure 6 show that steel content is one of the key 

design features that influences roughness. A comprehensive analysis of the effect 

of design features on roughness is presented in chapter 3 of this volume. 

Influence of Climate on Pavement Performance 

The effects of climate on pavement performance were investigated 

thoroughly as part of this study. The investigation consisted of both statistical 

analyses, such as analysis of variance and discriminant analysis, and mechanistic 

analysis used as the basis for estimating damage in model development and 

calibration. The primary climate variables identified as influencing pavement 

performance were classified as follows: 

12 
13 
l Moisture Variables 

Climatic region (wet, dry) 

Annual number of wet days/annual mean precipitation 

l Temperature Variables 

Climatic region (freeze or nonfreeze) 

Annual number of freeze-thaw cycles 

Annual mean temperature 

Average annual number of days with temperature above 32 “C 

The effects of the key climate-related variables on distress and roughness are 

summarized in table 1. Table 1 shows that an increase in air temperature or the 

temperature gradient within the KC slab increases the occurrence of joint 

spalling for both JPCP and JRCP. Also, JPCP located in climates with high 

annual freeze-thaw cycles and JRCP located in climates with high freezing index 

values tend to have an increased occurrence of spalling. 

Figures 7 to 12 show the effects of several climate-related variables on the 

pavement distress types investigated as part of this LTPP study. Figure 7 

illustrates the effect of wet days on JPCI? faulting. The figure shows that an 

increase in the number of wet days increases the amount of faulting. Figure 8 

illustrates the effect of annual number of wet days on transverse cracking. An 

increase in the annual number of wet days generally weakens the subgrade 

support or increases erosion and loss of support of a JPCP and results in higher 

deflections and increased transverse cracking. Figure 9 illustrates the effect of 

temperature (nonfreeze or freeze) on JPCP roughness. The figure shows that 

pavements located in the freeze climates experience more roughness than those 

in nonfreeze climates. Figure 10 illustrates the effect of precipitation on JRCP 

roughness; increasing precipitation increases the occurrence of moisture-related 

distresses and therefore increases roughness. Figures 11 and 12 illustrate the 

effect of the climate region (nonfreeze, freeze, wet, dry) and the annual number 

of days with temperature above 32 “C on CRCP roughness. Freeze climates 

appear to greatly affect the development of roughness of CRCP. 

Influence of Subgrade Support on Pavement Performance 

Table 2 summarizes the effect of subgrade support on distress formation. The 

modulus of subgrade reaction was backcalculated from FWD deflections and 

converted to a static value. Figures 13 to 16 also show the effect of subgrade type 

14 
Table 1. Summary of the effect of climate-related variables on pavement distress. 

Influence on distress formation (J = increases distress) 

Climate variable Classification 

Faulting Transverse Joint Transverse Corner Roughness 

Spalling cracking Breaks 

JPCP JPCP JRCP JPCP JPCP JPCP JRCP CRCP 

Climate (moisture) Wet J J J 

hual number of wet days Increasing J 

Average annual Increasing J J J J 

precipitation 

Climate (temperature) Freeze J J 

Average annual Increasing J J J 

freeze-thaw cycles 

Freezing index Increasing J 

Annual average temp. and Increasing J J J J J J 

temperature gradient 

Days with temperature Increasing J 

above 32 “C 
0 

+ wtdys=80 

--m- wtdys=130 

-A- wtdys=180 

I I 1 I I 

0 5 10 15 20 25 30 

ESAL’s (millions) 

h,,, = 225 mm 

Dowel diameter = 0 

Joint spacing = 6.1 m 

Base type = erodible 

Cd = 1.0 

Figure 7. Effect of annual number of wet days on JPCP faulting. 
c 

17 
0 

18 
1 

19 
20 
21 
I 

1 

I- I 

I 

: 

I 

I 

22 
and support on distress and roughness. Table 2 shows that increasing the 

modulus of subgrade reaction reduces JPCP faulting but increases transverse 

cracking. Increased subgrade support also reduced the occurrence of joint 

spalling in both JPCP and JRCP. Figure 13 shows that an increased modulus of 

subgrade reaction decreased faulting. Also, JPCP and JRCP constructed over fine 

subgrade material experience more faulting, transverse cracking, and roughness. 

Figures 14,15, and 16 also show that pavements constructed over coarsegrained subgrade material or material with higher modulus of subgrade reaction 

decrease roughness in JPCP, JRCP, and CRCP. The trends shown by the 

sensitivity plots are in agreement with the results from the statistical analysis 

presented in table 2. 

Natural subgrades with a high fine material content are more susceptible to 

pumping and faulting, especially when located in wet environments. Several 

design features can be used to limit the negative effect of inadequate subgrade 

support or soil type on pavement performance. (lo) Some of the design features 

are as follows: 

l Treating the subgrade with lime or portland cement. 

l Using a base course (treated or untreated). 

The LTPP study shows that flexible base material such as an asphalt-treated base 

reduces both faulting and transverse cracking. Cement-treated (with sufficient 

cement content) and lean concrete bases are nonerodible and also reduce the 

occurrence of pumping and faulting; however, the use of very stiff bases (not 

bonded to the slab) results in increased transverse cracking. The LTPP study also 

showed that pavements constructed directly over the subgrade (treated or 

untreated) generally perform worse than those with a base course. 

Summary of Site Condition 

The LTPP data analysis results summarized in tables 1 and 2, and the 

sensitivity analysis plots from distress and roughness prediction models 

developed as part of this study, show the importance of considering traffic, 

climate, and subgrade support in the pavement design process. These site 

conditions, in most cases, cannot be controlled by the designer. However, the 

negative influences of adverse site conditions on pavement performance can be 

minimized by the selection of appropriate design features. Some of the design 

features identified in this study to minimize the most common distresses for 

JPCP are the provision of dowels, use of nonerodible base material, stronger 

23 
1 

0 

24 
FI = 277 deg. C Days 

Dowel diameter = 25.4 mm 

Climate = freeze 

0 5 10 15 20 25 

ESAL’s (millions) 

Figure 14. Effect of subgrade type (fine or coarse) on IRI for JPCI?. 
I I 

26 
1 

0 5 10 15 20 25 30 

ESAL’s (millions) 

Figure 16. Effect of modulus of subgrade reaction on IRI for CRCP. 
base/subbase material, and the use of thicker PCC slabs. The use of these design 

features to minimize distress and roughness is discussed in greater detail in the 

next chapter. The site conditions that most adversely affect performance are 

summarized as follows: 

JPCP Faulting 

l Increased traffic loading results in increased faulting. 

l JPCP located in wet climates with greater than 140 wet days per annum 

or precipitation greater than 1 m/yr experience a higher degree of 

faulting than JPCP located in drier climatic regions. 

l JPCP constructed over natural subgrade material classified as fine-grained 

experience a higher degree of faulting than JPCP located in regions with 

coarse subgrades or subgrades with less fine material content. 

JPCP Transverse Joint Spalling 

l Increased traffic loading results in increased transverse joint spalling. 

l JPCP experience higher levels of spalling with increasing age. 

l JPCP located in regions with higher annual freeze-thaw cycles experience 

more spalling. 

l JPCP located in regions with higher temperature gradients within the 

KC slab on higher climatic temperatures in general experience a higher 

degree of spalling. 

l JPCP located over strong subgrade material generally experience less 

spalling. 

JPCP Transverse Cracking 

l Increased traffic loading results in increased transverse cracking. 

l JPCP located in wet climates are more likely to crack transversely at the 

slab midsection than JPCP located in drier climatic regions. 

l JPCP located in climates with mean temperature > 10 “C are more likely to 

crack than JPCP located in colder climatic regions. 

l JPCI? located on a stiff subgrade material (natural or treated) (k value > 38 

kPa/mm) experience a higher degree of transverse cracking than JPCP 

located in regions with a softer subgrade soil. 

JPCP Corner Breaks 

l Increased traffic loading results in increased corner breaks. 

28 
l JPCP experience higher levels of corner breaks with increasing age. 

l JPCP located in regions with higher annual freeze-thaw cycles experience 

more corner breaks. 

JPCP Roughness 

l Increased traffic loading results in increased roughness. 

l JPCP located in wet climates experience more roughness than JPCP 

located in drier climatic regions. 

l JPCP located in areas with mean temperature > 10 “C in general 

experience more roughness than JPCP located in colder climatic regions. 

JRCP Transverse Joint Spalling 

l Increased traffic loading results in increased transverse joint spalling. 

l JRCP experience higher levels of spalling with increasing age. 

l JRCP located in regions with higher annual freezing index experience 

more spalling. 

l JRCP located in regions with higher temperature gradients within the 

KC slab on higher climatic temperatures in general experience a higher 

degree of spalling. 

l JRCP located over strong subgrade material generally experience less 

spalling. 

JRCP Roughness 

l Increased traffic loading results in increased roughness. 

l JRCP located in climates with precipitation greater than 1 m/yr 

experience more roughness than JRCP located in other climatic regions. 

l JRCP located in nonfreeze climates (mean temperature > 10 “C) experience 

more roughness than JRCP located in colder climatic regions. 

l JRCP constructed over natural subgrade material classified as “fine” 

experience more roughness than JRCP located in regions with coarse 

subgrades or subgrades with less fine soil content. 

CRCP Roughness 

l Increased traffic loading results in increased roughness. 

l CRCP located in nonfreeze environments (mean temperature > 10 “C) 

experience much less roughness than CRCP located in other climatic 

regions. 

29 
These results will help in selecting appropriate design features given the specific 

traffic, subgrade, and climate site conditions. 

30 
3. RECOMMENDATIONS FOR SELECTING DESIGN FEATURES 

OF CONCRETE PAVEMENTS 

Introduction 

This chapter provides recommendations for selecting pavement design 

features that will improve concrete pavement performance. The 

recommendations are based on results obtained from an evaluation of the LTPI? 

database. The LTPP database was evaluated using both statistical and 

mechanistic analysis. The statistical analysis involved the use of basic techniques 

such as univariate and bivariate plots and more advanced concepts such as 

analysis of variance (ANOVA) and discriminant analysis. A comprehensive 

mechanistic analysis of the processes of distress development was also made. 

This resulted in the development of several mechanistic-empirical models for 

predicting pavement distress, such as transverse joint faulting, transverse 

cracking, corner breaks, transverse joint spalling, and roughness. Detailed 

results from these analyses are presented in volumes II and III of this report. 

This chapter presents a summary of the results and can be used as guidance for 

selecting pavement design features. 

Design Features That Affect KC Pavement Performance 

The requirements for sound PCC pavement design include the following: 

l Full consideration of site conditions, including uniform foundation 

support for the pavement, traffic, and climate. 

l Selection of design features such as adequate slab thickness, quality 

concrete, widened lanes, joint spacing, joint load transfer (JPCP and 

JRCP), reinforcement (JRCP and CRCP), and others that will provide a 

smooth, long-lasting pavement. 

The following design features were identified as those that affect distress 

formation and, therefore, long-term performance of KC pavements: 

0 JPCP Joint Faulting 

Radius of relative stiffness of the pavement/subgrade 

Load transfer or dowels 

KC slab thickness 

Base type (treated or untreated) and modulus 

31 
Skewed joints 

Subdrainage 

l JPCP Transverse Joint Spalling 

Joint sealant characteristics 

PCC slab thickness 

PCC slab elastic modulus 

l JPCI? Transverse Cracking 

Load transfer or dowels 

KC slab thickness 

KC elastic modulus 

Modulus of rupture of the PCC slab 

Base type (treated or untreated) 

l JPCP Corner Breaks 

KC slab thickness and elastic modulus 

Joint spacing 

Subdrainage 

JPCP Roughness 

Base type 

KC slab thickness and modulus 

Subdrainage 

Edge support (widened lane, flexible or rigid shoulder) 

Load transfer or dowels 

JRCP Transverse Joint Spalling 

Joint sealant characteristics 

PCC slab thickness and elastic modulus 

JRCP Roughness 

PCC slab thickness 

Joint spacing 

Subdrainage 

32 
0 CRCP Roughness 

PCC slab thickness 

PCC slab steel content 

Subdrainage 

Base type 

Detailed summaries of the effects of these design features on PCC pavement 

performance are presented in the next sections. 

JPCP Faulting 

Effect of Radius of Relative Stiffness 

JPCP pavements with a higher radius of relative stiffness experience less 

faulting. Results show that JPCI? with radius of relative stiffness greater than 

1.15 m experience little or no faulting. Pavements with a high radius of relative 

stiffness values have lower deflections and experience less pumping and 

faulting. This is in agreement with the results of several past studies and 

mechanistic analysis. (*j 6, 

The radius of relative stiffness of a pavement is dependent on several design 

variables, namely modulus of subgrade reaction, KC modulus, PCC thickness 

(very strong effect), and PCC Poisson’s ratio. The values of these design 

variables should be selected to maximize the radius of relative stiffness to reduce 

the potential for faulting. 

Effect of Load Transfer (Dowels) 

The data analysis results show that doweled JPCP experience less faulting 

than undoweled JPCP. Load transfer provided at joints and cracks of concrete 

pavements has an enormous influence on the occurrence of faulting. Good load 

transfer from installed load transfer devices reduces the high slab deflections at 

the joint, reducing the potential for pumping and faulting. This improves the 

performance of concrete pavements. Therefore, it is good practice to provide 

load transfer for all JPCP that will carry heavy truck traffic. The characteristics of 

the dowel that influence load transfer are the diameter, length, and spacing. 

Whether the dowel is coated is also another important consideration in design. 

Typically, round steel bars between 25.4 and 38 mm diameter, 450 mm long, and 

spaced at 300-mm centers have been used as dowels. Figure 17 illustrates the 

effect of different dowel diameters on predicted faulting. 

33 
+ Dowel diameter=38.1 mm 

I i I 

I I 

I I I 

0 5 10 15 20 25 30 

ESAL’s (millions) 

Figure 17. Influence of dowels on JPCP faulting. 
Figure 17 clearly shows that dowels (of a minimum size of 25.4 mm) greatly 

decrease faulting of jointed concrete pavements. Increasing the dowel diameter 

further reduces faulting to a level that is acceptable from a ride quality aspect. 

. feet of KC Slab Thickness 

Pavements with thicker PCC slabs experience less faulting. Thicker KC slabs 

reduce the deflections at the slab edges and corners, and hence, reduce pumping 

and faulting. The effect of PCC slab thickness on the predicted faulting is 

illustrated in figure 18. Increasing PCC slab thickness increases the stiffness of 

the concrete pavement. Increasing pavement stiffness results in a reduction in 

deflections at the joints, and this is believed to be responsible for the decrease in 

faulting. 

Effect of Base Type and M,odulus 

JPCP pavements with treated bases (asphalt or portland cement) experience 

less faulting than pavements with untreated bases. This is because the most 

common mechanism for erosion and faulting is possible only if the top of the 

base material is saturated and is erodible. Most treated bases are less erodible 

and, therefore, have a reduced potential for pumping. The influence of the type 

of base, shown in figure 19, was investigated using sensitivity plots of the 

faulting model developed. The plots show that there is a tremendous reduction 

in faulting for pavements constructed using a nonerodible base, such as lean 

concrete, portland cement-treated, and asphaltvtreated bases. 

Also, pavements with a higher base modulus generally experience less 

faulting because an increase in base modulus results in less erosion’and 

deflections at the PCC slab joints. Results presented in volume II of this report 

show that JPCP with higher base modulus values experience the least amount of 

faulting. 

Rffect of Skewed Joints 

Transverse joints can be either skewed or square. Skewness can range up to 

about 0.6 to 0.9 m per lane width. The analysis shows that JPCF with skewed 

joints experience less faulting than those with square joints. The use of skewed 

joints is a means of reducing the magnitude of deflections at a joint. Deflections 

are reduced because wheels of the same axle strike the joints at different times, 

reducing the load the axle imparts on one side of the joint. 

35 
M cv r-i 0 

36 
! 

rI I 

37 
Effrzetzrf Subdrain@ 

The provision of positive drainage in the LTPP pavements generally reduced 

the occurrence of moisture-related distresses, such as pumping and faulting. 

Adequate drainage reduces the amount of free water within the pavement 

structure and reduces the potential for erosion and pumping of the underlying 

pdtiement materials. The provision of drainage is most necessary for JPCP 

Mated in wet climatic regions, where moisture-related distresses are common. 

$I?3 YiMkisvCkse Joint Spallirkg 

Effect uf Joint Sealant Character& 

The influence of sealants on joint spalling is illustrated by the sensitivity plot 

shown in figure 20. In all cases, the worst condition was for joints without any 

sealants (presumably filled up with incompressibles); The magnitude of the 

difference between the pavements with and without sealants is an indication of 

the importance of sealing joints. For those pavements with sealed joints, there is 

also an appreciable effect of the type of sealant used and the amount of spalling 

that occurs. Preformed sealants are far better at reducing joint spsilling than the 

other types of sealants. The performance of the other types of sealants is 

comparable. 

Effect.of PCC Slab. Thickness 

The analysis shows that increasing PCC slab thickness reduces the tensile 

stresses generated around the upper part of a joint, where spalling occurs. The 

sensitivity analysis presented in volume III of this report shows that increasing 

slab thickness reduces tensile stresses generated around the joints considerably. 

Such a reduction in stress is significant because the occurrence of spalls is related 

to excessive tensile stresses around pavement joints. Increasing slab thickness, 

thereforei is beneficial and reduces the occurrence of spalling. 

Increasing the PCC slab elastic modulus generally increases the tensile 

strength of the pavement and decreases the potential for spalling. This was 

observed from the finite element analysis conducted as part of this study and 

presented in volume III of this report. 

38 
--+-Asphalt 

--c Preformed 

+ Silicone 

* Other 

- 9% - None or N/A 

0 10 20 30 

ESAL’s (millions) 

Relative humidity = 67 

percent 

Temperature range = 14 OC 

h PCC=225mm 

E pcc=30,000 MFa 

Figure 20. Plot of percent JPCP spalling versus traffic for the different joint 

sealant materials evaluated. 
JPCP Corner Breaks 

Effect of PCC Thickness and Elastic Modulus 

Figure 22 is a plot of percent slabs with corner breaks versus cumulative 

ESAL’s for different slab thicknesses. The plot shows that there is a rapid 

increase in the amount of corner breaks in a pavement as the slab thickness 

decreases. As PCC slab thickness decreases, the tensile stresses generated within 

the pavement increases, resulting in corner breaks. Also, it will take longer for a 

microcrack to propagate from the bottom to the top of a KC slab as the slab 

thickness increases. This observation adds to the benefits derived from 

increasing PCC slab thickness. 

An increase in KC elastic modulus generally increases pavement strength 

and decreases the occurrence of corner breaks. 

Effect of Joint Spacing 

Figure 23 is a plot of percent slabs with corner breaks versus cumulative 

ESAL’s for different PCC slab joint spacing. The plot shows that there is an 

increase in the amount of corner breaks in a pavement as the joint spacing 

increases. This is in agreement with engineering principles and previous 

research results.(*/ 4t “1 

Effect of Subdrainape 

The provision of positive drainage in the LTPP pavements generally reduced 

the occurrence of moisture-related distresses, such as pumping. Adequate 

drainage reduces the amount of free water within the pavement structure and 

reduces the potential for erosion and pumping of the underlying pavement 

materials that results in loss of support of the KC slab and, hence, corner 

breaks. 

JPCP Roughness 

Effect of Base Tvne 

Base type (treated or untreated) shows no significant influence on JPCP 

roughness. However, further evaluation of the data seems to indicate that the 

stiffer the base, the less the roughness experienced. This was found to be true for 

42 
8o i- -.-_____ __---~--.--.-- ~ 

ESAL’s (millions) 

30 

Joint spacing = 6.1 m 

E pcc = 30,000 kPa 

Cd = 1 

Ftcyc = 70 

_~-_____~- 

Figure 22. Percent slabs with corner breaks versus cumulative ESAL’s for 

different slab thicknesses. 
0 10 20 30 

ESAL’s (millions) 

Figure 23. Plot of percent slabs with corner breaks versus cumulative ESAL’s 

for different PCC slab joint spacing. 
thinner pavements (< 250 mm), as well as for thicker pavements (> 250 mm). 

Pavements with stiffer bases or foundations are stronger and experience less 

deflections for a given traffic loading. Therefore, such pavements may be less 

susceptible to distress and roughness development in general. 

Effect of PCC Thickness and Modulus 

The analysis shows that pavements with thicker KC slabs (> 250 mm) have 

more roughness than those with thinner PCC slabs. This may be because thicker 

pavements are generally more difficult to construct. Consequently, they may be 

built rougher than thinner sections and remain rougher throughout the 

pavement’s design life. The LTPP data show that JPCP with higher PCC 

modulus exhibit lower roughness. The KC modulus correlates positively with 

flexural strength and thus lower fatigue damage and cracking and, therefore, 

less roughness. 

Effect of Subdrainage 

The provision of positive subdrainage to a JPCP generally reduces roughness. 

Improved subdrainage reduces the amount of faulting and transverse cracking. 

Reducing the occurrence and severity of distress reduces roughness. 

Effect of Edee Sunport 

Jointed concrete pavements with KC tied shoulders or widened lanes tend 

to experience less distress and, hence, less roughness. The edge support 

increases load transfer at the joints and increases the rigidity of the slab. This 

reduces the critical bending stresses and deflections at the midsection and joints 

of the slabs when subjected to wheel loads. 

Effect of Load Transfer (Dowels\ 

JPCP pavements with dowels are smoother than those without dowels. 

Dowels provide load transfer across the joints of adjacent slabs. Load transfer 

reduces deflections and faulting at the joints, and also transverse cracking. This 

results in lower roughness. Figure 24 shows a plot of ESAL’s versus roughness 

for different dowel diameters. The plot was developed from a JPCP roughness 

prediction model developed as part of this study. According to the plot, 

increased dowel diameter reduces roughness. The model clearly shows the 

importance of using dowels and also shows that increasing the dowel diameter 

reduces the progression of roughness. 

45 
3 

1- 

-+-Dowel diameter = 0 

+ Dowel diameter = 25.4 mm 

+ Dowel diameter = 38.1 mm 

I I 

I I I I 

0 5 10 15 20 25 

ESAL’s (millions) 

Figure 24. Influence of dowel diameter on JPCP roughness. 

FI = 277 deg. C Days 

Climate = freeze 

Subgrade type = coarse 
JRCP Transverse Joint Spalling 

Effect of Toint Sealant Characteristics 

The effect of the different types of sealants on joint spalling of JRCP was not 

much different from that observed for the JF’CP model. Figure 25 illustrates the 

influence of the different joint sealant conditions. For JRCP, unsealed joints were 

also found to spa11 more, and the type of sealant used has an influence on 

spalling. However, silicone sealants and not preformed sealants seem to provide 

the best protection against spalling, followed by preformed sealants. Joints with 

rubberized asphalt sealants do not perform as well and seem not to be much 

better than unsealed joints. 

Effect of PCC Slab Thickness and Elastic Modulus 

The effect of both KC slab thickness and elastic modulus on JRCP joint 

spalling is similar to that for JPCP. The effects for JPCP discussed in detail in the 

preceding sections are therefore applicable to JRCP. 

JRCP Roughness 

Effect of KC Thickness 

The LTPP database shows significant roughness values for JPCP with PCC 

thickness less than 225 mm and those greater than 300 mm. JRCP with thin PCC 

slabs have a reduced load-carrying capability and are more susceptible to 

distress and roughness. Also, JRCP with KC thickness greater than 300 mm 

experience more roughness because of difficulties with constructing thicker 

JRCP sections. A previous study found that the thicker JRCP were indeed 

constructed rougher than thinner JRCP.(13) 

Effect of Joint Snacing 

JRCP with joint spacing greater than 13.7 m tend to experience more 

roughness than those with shorter joint spacing. Horizontal slab movement due 

to temperature changes and vertical deflections from curling increase for JRCP 

with longer joint spacing (greater than 13.7 m). Also, JRCP with longer joint 

spacing may develop more deteriorated transverse cracks. Reducing joint 

spacing will enhance JRCP performance. 

47 
40 

--t- Preformed 

--+---Rubberized asphalt 

- -L - Silicone 

---st- Asphalt 

- No joint sealant 

0 10 20 30 

ESAL’s (millions) 

FI = 360 deg. C Days 

k-value = 41 kPa/mm 

E pee = 30,000 MPa 

hPcc = 200 mm 

Figure 25. Influence of joint sealant type on JRCP transverse joint spalling. 
Effect of Subdrainaee 

The provision of positive subdrainage to a JRCP generally reduces distress 

and roughness. Improved subdrainage (primarily through edgedrains and 

granular embankments) reduces the amount of water within the pavement 

structure, thereby reducing the potential for weakening and pumping of the 

underlying pavement materials. The comparative effect of different drainage 

facilities such as edgedrains and permeable bases was not analyzed due to 

insufficient data; however, the provision of drainage is recommended for 

enhanced JRCP performance. 

CRCP Roughness 

Effect of PCC Thickness 

The analysis shows that pavements with thicker KC slabs (> 250 mm) have 

more roughness than those with thinner KC slabs. This is similar to the trend 

observed for JPCP. The reasons for this are most likely similar and may be 

because thicker pavements are generally more difficult to construct. 

Consequently, they may be built rougher than thinner sections and remain 

rougher throughout the pavement’s design life. 

Effect of DesiPn Steel Content 

CRCP with increased steel content has lower IRI, as illustrated in figure 26. 

This result is reasonable and is in agreement with recent observations in Belgium 

and the U.S. that indicate that higher steel contents for CRCP are beneficial, as 

they keep the cracks that form tight. (‘J lo) Although the higher steel contents 

induce more cracking in CRCP, as long as they are kept tight this does not 

appear to cause a problem. 

Effect of Subdrainaee 

The provision of positive subdrainage to a CRCP generally reduces 

roughness. Adequate subdrainage reduces the amount of water within the 

pavement structure, thereby reducing the potential for pumping and weakening 

of the underlying pavement materials. 

49 
0 5 10 15 20 25 30 

ESAL’s (millions) 

Figure 26. Influence of design longitudinal steel content on CRCP roughness. 

Steel content = 0.7% 

Steel spacing = 0.45 m 

k-value = 41 kPa/mm 

D32 = 40 
Effect of Base Type 

An increase in base thickness and the use of treated bases result in less 

roughness for CRCP. This agrees with both empirical and mechanistic analyses 

from past studies, which show that a stronger pavement structure generally 

experiences less distress and, therefore, less roughness. 

Summary 

The design features that influence concrete pavement performance are 

summarized in tables 3 through 10. The tables show the effect of the design 

features on the different pavement and distress types analyzed. These should 

serve as guidance for selecting design features when designing KC pavements. 

51 
Table 3. Effect of key pavement design features on JPCP transverse joint faulting. 

Key design feature 

Radius of relative stiffness 

Effect on JPCP joint faulting 

Increasing the radius of relative stiffness significantly reduces the progression of 

faulting. 

Load transfer or dowels JPCI? with dowels of at least 25.4 mm in diameter can reduce faulting by at least one - 

half. The larger the dowel diameter, the more the reduction in faulting for any given 

set of site conditions and design features. 

PCC slab thickness 

Base type/modulus 

Thicker JPCP exhibit significantly less faulting than thinner slabs. 

A nonerodible base (e.g., lean concrete) appreciably decreases faulting in comparison 

to erodible bases, such as untreated aggregates. 

Skewed joints 

Subdrainage (Drainage 

coefficient, C,) 

Pavements with skewed joints fault less than those with square joints. However, 

skewed joints with dowels are not recommended. Dowels can control faulting 

without skewing the joints. 

Increasing the drainage coefficient by improving subdrainage (edgedrains and 

granular embankment), thus reducing the extent of pavement saturation for long 

periods, reduces faulting. 
Table 4. Effect of key JPCP design features on transverse joint spalling. 

Design feature 

Joint sealant 

characteristics 

KC slab thickness 

PCC slab elastic modulus 

Effect on JPCP joint spalling 

In general, pavements with sealants experience less spalling than those 

without. Among the different sealants, preformed sealants perform best in 

terms of reduction in joint spalling. Also, stiffer sealants cause more 

spalling. 

Pavements with thicker KC slabs experience less spalling in general. 

Stiffer KC slabs (i.e., higher elastic modulus) experience less spalling 

because of the increased strength of the pavements. 
Table 5. Effect of key pavement design features on JPCP transverse cracking. 

Key design feature 

Load transfer or dowels 

Effect on JPCP transverse cracking 

Pavements with dowels experience less transverse cracking. Load transfer reduces 

bending moments and stresses throughout the KC slab and particularly at the top 

of the PCC slab. The reduction of stresses and strains at this location lowers the 

possibility of top-down cracking. 

KC slab thickness and 

elastic modulus 

Modulus of rupture 

Base type 

JPCP with thicker slabs (likely higher flexural strength) experience less transverse 

cracking. JPCP with a stiffer PCC slab exhibit less transverse cracking. 

JPCP with increased modulus of rupture values exhibit less transverse cracking. 

Pavements with treated bases generally experience less transverse cracking; 

however, cement-treated and lean concrete bases are susceptible to transverse 

cracking. The use of flexible (AC-treated) bases considerably reduces the 

occurrence of transverse cracking. 

Table 6. Effect of key JPCP design features on corner breaks. 

Design feature Effect on TPCP corner breaks II 

Joint spacing Longer joint spacing will increase the occurrence of corner breaks. 

PCC slab thickness and Thicker slabs experience less corner breaks. Stiffer PCC slabs experience less 

elastic modulus corner breaks. 

II Subdrainage II A higher drainage coefficient will reduce the occurrence of corner breaks. II 
Table 7. Effect of key pavement design features on JPCP roughness. 

Key design feature 

Base type 

Effect on JPCP roughness 

Pavements with treated bases generally experience less roughness; 

however, cement-treated and lean concrete bases are more susceptible to 

transverse cracking. 

KC slab thickness and 

modulus 

Thicker PCC slabs tend to be rougher. This is because thicker KC slabs are 

often constructed rougher than thinner slabs, and the high initial 

roughness is maintained throughout the pavement life. 

Subdrainage (Drainage 

coefficient, C,) 

Edge support 

Increasing the drainage coefficient by improving positive subdrainage 

reduces moisture-related distresses such as faulting and, hence, roughness. 

Pavements with tied PCC shoulders or widened lanes experience less 

roughness. This is because tied shoulders and widened lanes provide 

additional load transfer at the joints and between the JPCP and concrete 

shoulder, reducing stresses and deflections and, therefore, load-related 

distresses and roughness. 

Load transfer or dowels Use of dowels in JPCP pavements reduces roughness. Increasing the 

dowel diameter reduces faulting, further reducing roughness. 
Table 8. Effect of key JRCP design features on transverse joint spalling. 

Design feature 

Joint sealant 

characteristics 

Effect on JRCP joint spalling 

In general, pavements with sealants experience less spalling than those 

without. Among the different sealants, silicone sealants perform best in 

terms of reduction in joint spalling. 

II KC slab thickness II Pavements with thicker KC slabs experience less spalling in general. 

/I KC slab elastic modulus II 

Stiffer PCC slabs (i.e., higher elastic modulus) experience less spalling 

because of the increased strength of the pavements. 

Table 9. Effect of key pavement design features on JRCP roughness. 

Kev design feature Effect on JRCP roughness 

KC slab thickness 

Joint spacing 

Subdrainage 

Thicker JRCP slabs have increased roughness. This is because thicker KC 

slabs are often constructed rougher than thinner slabs, and the high initial 

roughness is maintained throughout the pavement’s life. 

Pavements with longer joint spacing experience more roughness. 

The provision of positive drainage for JRCP will reduce the progression of 

moisture-related distresses and, therefore, roughness. 
Table 10. Effect of key pavement design features on CRCP roughness. 

Key design feature 1 Effect on CRCP roughness 

KC slab thickness Thicker CRCP slabs increase the progression of roughness. This is because 

thicker slabs are often constructed rougher than thinner slabs, and the high 

initial roughness is maintained throughout the pavement life. 

CRCP with a higher steel content exhibit less roughness. 

CRCP with edgedrains exhibit less roughness. 

Base type II CRCP with treated bases generally experience less roughness. 

4. RECOMMENDATIONS FOR CONSTRUCTION OF KC 

PAVEMENTS 

Introduction 

The construction of PCC pavement demands careful coordination between 

the construction practices that must be followed at different stages. These 

construction practices can be grouped into two phases: (1) practices required to 

prepare the existing subgrade to an acceptable condition ready for placement of 

the base and PCC slab and (2) paving operations, formation of joints, and 

smoothness considerations. Both phases play a critical role in the overall 

performance of PCC pavements. The LTPP database has a number of data 

elements that can be used to quantify and evaluate the effect of pavement 

construction practices on performance. A summary of the data elements is 

presented below and was used as the basis for evaluating the effects of 

construction practices on performance. Note that due to the extreme complexity 

of construction, these findings should be considered tentative until confirmed by 

further studies. 

l Curing method. 

l Texture method. 

l Dowel placement method. 

l Joint forming method. 

This chapter summarizes results from the evaluation of the effect of 

construction practices on pavement performance presented in volume II of this 

report. The influence of construction practices on the development of the 

following three distress/performance indicators was evaluated: 

l Transverse joint faulting. 

l Transverse cracking. 

l Roughness (IRI). 

Brief descriptions of the effect of these construction practices on pavement 

performance and distress formation are provided in the next few sections. 

The effect of construction practices on pavement performance is presented in 

table 11. The information presented is the result of an analysis of the LTPP 

database to determine the effect of construction practices on distress. 

59 
Construction Classification Effect on distress type Average Remarks 

practice ranking* J = better 

JPCP JPCP Roughness performance 

faulting cracking 

Dowel placement Others 3 X X 3 

method 

Mechanically installed 2 X X 2 

Replaced in baskets 1 X X 1 J 

Joint forming Sawed 2 X X 2 

method 

Plastic insert 1 X X 1 J 

Coarse aggregate less than 1800 kg/m3 X 2 X 2 

C Nontent of concrete 

mixture greater than 1800 kg/m3 X 1 X 1 J 

_.- . . ,-A. l . 1 . . P r .1 < . , --- 5 ltankmg or 1 rmplres better perrormance tor tne respective pavement and distress type. 

Table 11. Summary of construction practices on pavement performance. 
Table 11. Summary of construction practices on pavement performance (cont’d). 

Construction 

practice 

Classification Effect on distress type and ranking Average 

Faulting Cracking Roughness 

ranking 

Fine aggregate less than 1300 kg/m3 X 1 X 1 

content of concrete 

mixture greater than 1300 kg/m3 X 2 X 2 

Concrete curing I membrane I X I X 

method polythene 

burlap 

t 

X X 1.5 1.5 

X X 1.5 1.5 

Concrete texture 

method 

astroturf X X 6 6 

others X X 5 5 

broom 

tine 

X X 4 4 

X X 3 2 

burlap drag 

grooved float 

X X 2 2 

X X 1 2 

Remarks 

J = better 

performance 

J 

J 

J 

J 

J 

J 
Effect of Construction Practices on Joint Faulting 

Effect of Dowel Placement Method 

The LTPP data evaluated show that pavements with dowels preplaced in 

baskets experience less faulting than pavements with dowels placed 

mechanically. The cause of this result is unknown but may be related to the 

better alignment and stability obtained because of the care taken by workmen in 

placing the dowels manually. However, in recent times, improved dowel 

placement equipment has been developed, and this may have improved the 

performance of pavements with mechanically installed dowels. 

Effect of Taint Forming Method 

The LTPP data evaluated show that pavements with joints formed with 

plastic inserts experience less faulting than those with joints formed by sawing. 

The reason for this needs to be investigated further. 

Effect of Construction Practices on PCC Transverse Cracking 

Effect of Coarse and Fine Aeg;reeate Content 

PCC pavements with more coarse aggregates (greater than 1800 kg/m3) and 

less fines (less than 1300 kg/m3) experience less transverse cracking than those 

with less coarse aggregates and more fine aggregates. This is expected because 

concrete materials with a high content of coarse material generally are stronger 

and more durable. They have a higher resistance to fracture and cracking. 

Effect of Construction Practices on Roughness 

Effect of Curing 

PCC pavements cured with burlap and polyethylene have significantly less 

roughness than those cured with a membrane. Effective curing is the best way to 

avoid early age cracking and disintegration of the concrete slab due to excessive 

stresses resulting from temperature and shrinkage. The early age cracks usually 

grow with age and traffic load applications into transverse cracks, corner breaks, 

and spalling, which all increase roughness. Therefore, using burlap or 

polyethylene should be considered to minimize future distresses and roughness. 

62 
Effect of Concrete Texture Method 

The mode of finishing the KC pavement slab surface has a great influence 

on roughness. Previous studies have shown that pavements built with a high 

initial roughness mostly stay rougher than those built smoother. The LTPP data 

show that pavements that were textured with astroturf and brooms exhibit 

higher roughness; pavements finished with the grooved float and burlap drag 

had lower roughness. 

Summary 

These findings should be considered tentative. Further study is needed for 

confirmation. 

Faulting 

The construction features that influence faulting were found to be related to 

the pavement joint or the strength of the concrete. Data analysis results show 

that the joint forming method, dowel placement method, and load transfer 

mechanism all influence faulting. Using dowels preplaced in baskets and joints 

formed using proper plastic inserts appeared to reduce faulting. 

Transverse Cracking 

The main construction-related factor that seems to influence the occurrence of 

transverse cracking was the amount of coarse aggregate in the concrete mix. The 

greater this variable, the lower the amount of transverse cracking. 

Rouphness 

The most influential construction feature on roughness is the method of 

finishing. Specifications to control the method of finishing will therefore be 

beneficial and will reduce the current levels of roughness experienced on 

pavements. The three texture methods showing the lowest roughness were 

grooved float, burlap drag, and tining. Other LTPP studies showed that initial 

smoothness was extremely important to future smoothness of the pavement.(r3) 

63 

5. APPLICATION OF DISTRESS PERFORMANCE MODELS 

Introduction 

Important products obtained from this study are the performance prediction 

models that can be used to determine whether a given pavement design will 

meet certain performance criteria. Mechanistic-empirical models are 

recommended because they more realistically consider the mechanism of 

distress formation. The critical checks recommended for concrete pavements 

include the following: 

l Faulting for doweled and nondoweled JPCP. 

l Transverse joint spalling for JPCP and JRCP. 

l Transverse cracking of JPCP. 

l Corner breaks for JPCP. 

l Roughness for JPCP, JRCP, CRCP. 

Each of the models should be used to predict distress over the design period 

for the applicable PCC pavement design, and the results should be checked 

against the performance criteria of the agency. The models can also be used for 

analysis of the cost effectiveness of design alternatives. A summary of the 

variables required as input for models developed as part of this study and 

examples of the models’ applications are presented in this chapter. This chapter 

presents examples of how the models developed were tested and used to 

determine their suitability. The methods of model formulation, calibration, and 

limitations identified in the model development process are discussed fully in 

volume III of this report. 

Faulting of JPCP (Models Provided in Chapter 4, Volume III) 

Faulting of JPCP is the most critical distress related to ride quality. A faulting 

model was developed as part of this study with data available from the GPS 3 

pavement sections in the LTPP database and is recommended for checking 

design. A summary of the input variables required for use in the model 

developed is presented in table 12. The actual faulting model and procedure for 

calculating faulting using that model are given in volume III of this report. 

65 
Table 12. Summary of variables required for estimating faulting. 

Dependent variable Independent variables Effect on joint faulting* 

Cumulative number of 80-kN + 

axle wheel load applications 

KC elastic modulus, kPa 

Transverse joint 

faulting, mm 

PCC thickness, mm 

Modulus of subgrade 

reaction, kPa/mm 

Dowel diameter, mm 

Drainage coefficient 

Annual number of wet days + 

BASE, Base, or subbase type, 

O=erodible l=nonerodible 

* Positive indicates that an increase in this variable results in an increase in 

faulting. 

Transverse Joint Spalling for JPCP and JRCP (Models Provided in Chapter 5, 

Volume III) 

The mechanism of spalling is yet to be fully understood. However, spalling 

is believed to be caused by several interacting mechanisms, including stresses 

imposed by both traffic and environmental forces, as well as inadequate quality 

control during construction. Although traffic may have some effect on spalling, 

environmental factors constitute the largest contributor to development of the 

distress. Two models were developed as part of this study for estimating the 

percentage of transverse joints with spalling (all severities) for JPCP and JRCP, 

and they are recommended for design checking. A summary of the input 

variables required for use in the models is presented in tables 13 and 14. The 

actual spalling models and the procedure for calculating the percent joints with 

spalling for a given pavement section are given in volume III of this report. 

66 
Table 13. Summary of variables required for predicting JPCP joint spalling. 

‘redicted variable Dependent variables Effect on joint spalling / 

Cumulative number of 80-kN + 

axle wheel load applications 

Joint spacing, m + 

PCC coefficient of thermal + 

PCP transverse 

expansion 

Dint spalling Thermal gradient within the + 

percent of joints PCC slab 

palled) PCC drying shrinkage strain + 

Subbase friction factor + 

Depth of sealant, mm + 

Modulus of sealant or + 

incompressibles, kPa/mm 

KC elastic modulus, kPa 

PCC thickness, mm 

Modulus of subgrade 

reaction, kPa/mm 

Pavement age in years + 

Average daily temperature + 

range, “C 

Average daily relative 

humidity range for the 

1 month of construction 

Average -annual freeze-thaw : + 

cycles 

. __ _ . . . . indicates that an increase in this variable results in an increase in joint 

spalling. 

67 
Table 14. Summary of variables required for predicting JRCP joint spalling. 

Predicted Dependent variables Effect on joint 

variable spalling 

Cumulative number of 80-kN axle + 

wheel load applications 

Joint spacing, m + 

KC coefficient of thermal expansion + 

JRCP transverse Thermal gradient within the KC slab + 

joint spalling 

(percent of joints PCC drying shrinkage strain + 

spalled) Subbase friction factor + 

Depth of sealant, mm + 

Modulus of sealant or incompressibles, + 

kPa/mm 

KC elastic modulus, kl?a 

PCC thickness, mm 

Modulus of subgrade reaction, 

kPa/mm 

Pavement age in years 

Average annual freezing index, “C 

days 

+ 

+ 

* Positive indicates that an increase in this variable results in an increase in joint 

spalling. 

Transverse Cracking for JPCP (Models Provided in Chapter 6, Volume III) 

Transverse cracks are a major cause of structural failure of JPCP. They 

develop from the repeated application of heavy axle loads and as the slab 

responds to drying shrinkage, thermal curling, and thermal contractions. 

Medium- and high-severity transverse cracks in JPCP cause increased roughness 

and user discomfort, and trigger the need for rehabilitation. A model was 

developed as part of this study for estimating the percentage of slabs with 

68 
transverse cracks (all severities), and it is recommended for design checking. A 

summary of the input variables required for use in the model developed is 

presented in table 15. The actual transverse cracking model and the procedure 

for calculating the percent slabs with transverse cracking for a given pavement 

section are given in volume III of this report. 

Corner Breaks for JPCP (Models Provided in Chapter 6, Volume III) 

Corner breaks also are a major cause of structural failure in JPCP. They 

develop as the slab corners are subjected to repeated application of heavy axle 

loads. KC slabs with inadequate load transfer or weak underlying material are 

susceptible to corner breaks. Corner breaks in JPCP cause increased roughness, 

user discomfort, and trigger the need for rehabilitation. A model was developed 

as part of this study for estimating the percentage of slabs with corner breaks (all 

severities), and it is recommended for design checking. A summary of the input 

variables required for use in the model developed is presented in table 16. The 

actual corner breaks model and the procedure for calculating the percent slabs 

with corner breaks for a given pavement section are given in volume III of this 

report. 

Table 15. Summary of variables required for estimating transverse cracking. 

Dependent 

variable 

Transverse 

cracking (percent 

of slabs cracked) 

Independent variables 

Cumulative number of SO-kN 

axle wheel load applications 

PCC elastic modulus, kPa 

Effect on transverse 

cracking* 

+ 

I PCC thickness, mm 

Pavement age in years 

Average annual number of 

freeze-thaw cycles 

Annual number of wet days I + 

Average annual number of days + 

with temperature above 32 “C 

* Positive indicates that an increase in this variable results in an increase in 

transverse cracking. 

69 
Table 16. Summary of variables required for estimating corner breaks. 

Dependent variable Independent variables Effect on corner breaks” 

Cumulative number of + 

80-kN axle wheel load 

applications 

Corner breaks (percent 

of slabs cracked) 

Average annual number 

of freeze-thaw cvcles 

+ 

* Yositive indicates that an increase in this variable results in an increase in 

corner breaks. 

Roughness for JPCP, JRCP, and CRCP (Models Provided in Chapter 7, 

Volume III) 

Roughness is the irregularity of the pavement surface. In general, road users 

consider roughness the most important criterion when deciding on the state or 

condition of a road. Rough roads lead to user discomfort, increased travel times, 

and higher vehicle operating costs that can lead to millions of dollars in losses to 

the general economy. Although the structural performance of a pavement is 

most important to highway designers, the complaints generated by rough roads 

often contribute to a large part of the rehabilitation decisions made by State 

highway agencies. Three models were developed as part of this study for 

estimating roughness for JPCP, JRCP, and CRCP, and they are recommended for 

design checking. A summary of the input variables required for use in the 

roughness models developed is presented in table 17. The actual roughness 

models are given in volume III of this report. 

70 
Table 17. Summary of variables required for predicting IRI for the three 

pavement types (JPCP, JRCP, and CRCP). 

Predicted Dependent variables Effect on 

variable roughness* 

Cumulative number of 80-kN axle wheel load applications + 

Dowel diameter, mm 

Elastic modulus of KC slab, kPa + 

Pavement age since construction, in years + 

‘PCP IRI 

:m/km) Freezing index in degree days (“F days) + 

FREEZE (pavements located in climates with average mean temperature + 

less than 12.75 “C) 

[RCP IRI 

(m/km) 

CRCP IRI 

(m/km) 

Subgrade type l=coarse-grained, O=fine-grained 

Average annual number of wet days 

Cumulative number of 80-kN axle wheel load applications 

Percent steel per area for KC slab 

Presence of edgedrain, 1 = edgedrain, 0 = no edgedrains 

Pavement age since construction, in years 

Average annual precipitation, in mm 

Subgrade type l=coarse-grained, O=fine-grained 

Cumulative number of BO-kN axle wheel load applications 

Percent steel per area for PCC slab 

Pavement age since construction, in years 

Average annual number of days with temperature above 32 “C 

DRY (pavements located in climates with average precipitation less than 0.6 

4 

FREEZE (pavements located in climates with average mean temperature 

less than 12.75 “C) 

+ 

Modulus of subgrade reaction, kPa/mm 

indicates that an increase in this variable results in an increase in 

roughness. 

71 
Suitability of Prediction Models 

The models presented in this chapter have all been checked using both 

diagnostic statistics and sensitivity analyses to determine their suitability. In all 

cases, the models were found to be in agreement with sound engineering 

principles and judgment. These models can therefore be used for checking new 

pavement design. Detailed procedures for using these models and discussions 

on their limitations are presented in volume III of this report. 

Examples of Application of Performance Models 

The assessment of PCC pavement performance and failure is based on critical 

levels of the common distresses that occur. The distress and roughness 

prediction equations developed under this study may be used for a variety of 

applications. Examples of possible applications are as follows: 

l Evaluation of a pavement design obtained through a standard procedure. 

l Evaluation of the cost-effectiveness of designs. 

The application of these models can be best explained by using examples. 

Example 1 uses prediction models to check and evaluate a new pavement 

design. Example 2 uses prediction models to evaluate the cost-effectiveness of 

alternative pavement designs. 

Checking the Design of New Pavements with Prediction Models 

The inputs to each of the prediction models must be obtained first. If the 

predicted distress at the end of the initial performance period exceeds some 

defined critical level, the pavement design will be considered inadequate, and 

modifications to certain design inputs may be appropriate. Some suggested 

critical distress levels used in the examples presented in this chapter are given in 

table 18. An example application of using the models for checking concrete 

pavement design is as follows: 

72 
Table 18. Suggested critical values for key performance indicators. 

II Performance indicator I JPCP 

(I Joint faulting I 3.05 mm 

Transverse cracking 30 percent 

JRCP 

6.1 mm 

30 deteriorated transverse 

cracks/km 

10 percent 

25 percent of joints 

2.7 m/km 

Examnle 1 

Pavement desien features 

Pavement type = 

Modulus of subgrade 

reaction, k = 

Joint spacing = 

Standard lane slab width = 

Joint sealant type = 

Drainage coefficient = 

KC elastic modulus = 

KC thickness = 

Dowel diameter = 

Base type = 

Sealant depth = 

JPCP without dowels 

20.4 kPa/mm 

6.1 m 

3.65 m 

Silicone joint sealant (modulus = 99,425 kPa/mm) 

0.7 (poor) 

24,150 MPa 

200 mm 

0 mm (no dowels) 

erodible (untreated aggregate) 

50.8 mm 

Climatic variables 

Wet climate, precipitation = 1.016 m/yr 

Freezing Index, FI = 278 degree days (cold climate) 

Annual air freeze-thaw cycles = 70 

Temperature range = 6.66 “C 

Annual number of wet days = 50 ( precipitation > 12.7 mm) 

Relative humidity = 60 percent 

Days with temperature 

above 32 “C = 40 

73 
Performance variables 

Performance period = 20 yrs 

ESAL applications = 20 million 

Evaluation of DesiPn 

Iteration No. 1 - Initial pavement design 

Predicted mean transverse joint faulting 

Predicted mean transverse joint spalling 

Percent slabs with transverse cracking 

Percent slabs with corner breaks 

Predicted IRI 

= 4.6 mm (high) 

= 42.8 percent (high) 

= 42.51 percent (high) 

= 20.3 percent (high) 

= 2.4 m/km (rough) 

The design is not adequate because the levels of all five distresses are above 

acceptable or too close to the acceptable values to ensure an adequate safety 

factor. Some design features should be modified to obtain more acceptable levels 

of distress. 

Iteration No. 2 - The following inputs are used in the next iteration: 

Drainage coefficient C, = 1.2 (permeable treated base with edge drain) 

Base type = Nonerodible 

Dowel diameter = 25.4 mm 

Depth of sealant = 12.7mm 

Elastic modulus of KC = 31,000 MPa 

KC thickness = 300 mm 

The revised design results in the following projected distress levels after 20 years 

and with 20 million ESAL applications: 

Predicted faulting = 0.75 mm 

Predicted spalling = 38 percent 

Slabs with transverse cracking = 28.5 percent 

Slabs with corner breaks = 3.46 percent 

Predicted IRI = 2.18 mm/km 

The levels of the distresses are reduced considerably in all cases (refer to 

iteration 1) and, based upon the results of this final iteration, the revised design 

is acceptable, with the exception of transverse cracking, which will require a 

74 
thicker slab (e.g., 350 mm). The acceptability of the distress levels is based on the 

values in table 17, which presents recommendations for critical levels of 

pavement distress at which some form of rehabilitation is required. The critical 

distress levels are subjective and depend on the performance standards of the 

State highway agency in question or the local experience of the design and 

maintenance engineer. The evaluation of this design illustrates the use of distress 

and roughness equations and shows that distress and roughness models are very 

important tools in pavement design and evaluation. 

Comparing Cost-Effectiveness of Alternative Designs 

Good management of pavements can provide several benefits for highway 

agencies at both the network and project levels. Foremost among these benefits is 

the selection of more cost-effective design alternatives. Whether new 

construction, rehabilitation, or maintenance is concerned, an evaluation of costeffectiveness can help management achieve the best possible performance value 

for the public dollar. 

At the project level, detailed consideration is given to alternative designs, 

construction, maintenance, or rehabilitation activities for a particular roadway 

section or project within the overall program. By comparing the costs and 

benefits among alternative designs, an optimum strategy is identified that will 

provide the desired benefits and service levels at the least total cost over the 

analysis period. Figure 27 presents a flow chart of a procedure for selecting 

alternative designs based on performance models. The pavement that is most 

cost-effective is selected. The process of selecting the most cost-effective 

pavement design is explained with the following example. 

Examule 2 

Pavement design features for DesiPn Alternative 1 

Pavement type = JPCP 

Subgrade modulus, k = 54.33 kPa/mm 

Joint spacing = 4.6 m 

Joint sealant type = silicone joint sealant 

Drainage coefficient = 1.1 

KC elastic modulus = 31,000 MPa 

PCC thickness = 300 mm 

75 
Time 

(Age) 

Materials 

Environment 

Traffic and Loading 

r 

MODELS OF 

- PAVEMENT STRUCTURE . DESIGN 

INCL. ENGR. FACTORS CONSTRAINTS 

BEHAVIOR 

1 

DISTRESS 

1 

PERFORMANCE 

NO -- 

LIFE CYCLE 

(Meets Constraints?1 

YES 

RELIABILITY 

COST 

DIRECT 

INDIRECT 

ECONOMIC 

EVALUATION 

t 

OPTIMIZATION 

(List by minimum cost at specified level of reliability) 

1 

SELECT FINAL DESIGN BUDGET 

, 

1 

J 

r 1 

DATA PMS 

BANK + INFORMATION 

SYSTEM 

II FEEDBACK\ 

Figure 27. Schematic diagram of pavement design practice with 

emphasis on cost-effectiveness.(*4) 

76 
Climatic variables 

Wet climate precipitation 

Annual number of wet days 

Freezing index 

Annual number of air 

freeze-thaw cycles 

= 1.3 m/yr 

= 50 

= 555 degree days below freezing 

= 75 

c Pavement 

Pavement type = JPCP 

Granular base, k = 20.4 kPa/mm 

Joint spacing = 9.15 m 

Joint sealant type = silicone joint sealant 

Drainage coefficient = 0.65 

KC elastic modulus = 24,150 MPa 

PCC thickness = 200 mm 

(The climate variables remain the same) 

Performance variables 

Performance period = Determined based on critical distress values in table 10 

Maximum IRI = 2.7m/km 

Maximum faulting = 3.05 mm 

Maximum spalling = 40 percent of joints with low, medium, and high severity 

Transverse cracking = 50 percent 

Corner breaks = 50 percent 

A comparison of the two design alternatives is given in table 19. The percent cost 

and life as calculated are as follows: 

Percent Cost = lOO* Cost of Alternative 1 _ 1 

Cost of Alternative 2 

Percent Life = 100 * ESAL’s 1 - 1 

ESAL’s 2 

(1) 

(2) 

77 
If the percent increase in life is greater than the percent increase in cost, then 

Design Alternative 1 is more cost-effective. However, if the percent increase in 

life is less than the percent increase in cost, then the design alternative is not 

more cost-effective. 

It is obvious from the analysis presented in table 19 that alternative 1 is more 

cost-effective. Performance equations are used in this manner on a routine basis 

by design engineers to evaluate different pavement design alternatives and 

strategies. 

Table 19. Comparison of cost-effectiveness of two alternate pavement designs. 

Faulting (ESAL’s/millions to reach 

critical) 

Spalling (ESAL’s/millions to reach 

critical) 

Transverse cracking (ESAL’s/millions 

to reach critical) 

Corner breaks (ESAL’s/millions to 

reach critical) 

IRI (ESAL’s/millions to reach critical) 

Cost of design 

Lifespan of design (ESAL’s) 

Percent cost 

Percent life 

More cost-effective design 

Alternate Design 1 Alternate Design 2 

30 + 7 

23.6 20.5 

20 12 

30 26 

23 19 

$2.0 million $1.6 million 

20”106 T106 

124 percent 

185 percent 

J 1 

78 
Summary 

This chapter has presented two different ways performance models are used. 

The models were used in the evaluation of pavements designed using standard 

design procedures and in selecting between alternative pavement designs. They 

indicate the wide variety of ways in which performance models can be 

used. However, these models must be used with care and not extend beyond the 

inference space for which they were developed. 

79 

6. CONCLUSIONS AND RECOMMENDATIONS 

The following conclusions and recommendations are made based on the 

findings of this project: 

There are three major site conditions that a pavement designer must deal 

with: traffic loadings, subgrade support, and climate. Each of these site 

conditions was found to be significant in the performance of PCC 

pavements. 

There are several critical design features that must be fully considered in 

the design process. These design features include transverse joint load 

transfer system, base type (erodible or nonerodible), provision of 

subdrainage, joint spacing for JPCI? and JRCP, widened slab, shoulders, 

and reinforcement for JRCP and CRCP. Findings regarding the effect of 

each of these design features on performance have been provided for 

consideration in the design and construction process. 

Commonly used pavement design procedures and other standards for 

highways are often adequate; however, the independent checking for 

critical distress types will minimize the potential for distress and early 

failure. 

The distress and roughness prediction models developed as part of this 

study are effective tools for use in design evaluation, pavement 

management, and for evaluating the cost-effectiveness of alternative 

pavement designs. 

The construction features that influence faulting were found to be related 

to the pavement joint or the strength of the concrete, namely, joint 

forming method and dowel placement method. Using dowels in 

preplaced baskets and joints formed using proper plastic inserts showed 

reduced faulting; however, newer technology may have improved on the 

process of joint construction. 

The main construction-related factor that influences the occurrence of 

transverse cracking is the amount of coarse aggregate in the concrete mix. 

The greater this variable, the lower the amount of transverse cracking. 

81 
l The construction feature most influential on roughness was the method of 

finishing. Specifications to control the method of finishing will therefore 

be beneficial and will reduce the current levels of roughness experienced 

on pavements. The three texture methods that result in the lowest 

roughness are grooved float, burlap drag, and tining. Past research has 

shown that initial roughness is critical to future roughness, but this was 

not examined in the present study. 

l Important products obtained from this study are performance prediction 

models that can be used for pavement design evaluation and the 

assessment of the cost-effectiveness of alternative designs, as well as 

recommendations on the selection of design features for PCC pavements. 

82 
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