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Publication Number:  FHWA-HRT-12-068    Date:  December 2012
Publication Number: FHWA-HRT-12-068
Date: December 2012


Curl and Warp Analysis of The LTPP SPS-2 Site in Arizona


This report provides the results of profile and roughness analyses for the Long-Term Pavement Performance (LTPP) Specific Pavement Studies (SPS)-2 site in Arizona. The analyses emphasized the roles of curl and warp in the development of roughness. SPS-2 sites were established for the study of rigid pavement structural factors, including concrete slab thickness, concrete strength, base material, permeability, and lane width.(1) These test pavements were constructed on eastbound Interstate 10 from April 1993 through January 1994. The site includes 21 test sections and extends from milepost 106 to 109. Some properties of the sections are listed in table 1.

Table 1. Arizona SPS-2 Site Structural Factors.

Section Lane Width (ft) PCC Flexural Strength (psi) Layer Thickness
Layer Type
Layer 1 Layer 2 Layer 3 Layer 1 Layer 2 Layer 3
0213 14 550 8 6   PCC DGAB  
0214 12 900 8 6   PCC DGAB  
0215 12 550 11 6   PCC DGAB  
0216 14 900 11 6   PCC DGAB  
0217 14 550 8 6   PCC LCB  
0218 12 900 8 6   PCC LCB  
0219 12 550 11 6   PCC LCB  
0220 14 900 11 6   PCC LCB  
0221 14 550 8 4 4 PCC PATB DGAB
0222 12 900 8 4 4 PCC PATB DGAB
0223 12 550 11 4 4 PCC PATB DGAB
0224 14 900 11 4 4 PCC PATB DGAB
0260 8.5 4   AC DGAB  
0261 8.5 4   AC DGAB  
0262 14 550 8 6   PCC DGAB  
0263 14 550 8 4 4 PCC PBTB DGAB
0264 12 550 8.5 4 4 PCC PBTB DGAB
0265 12 550 8.5 6   PCC DGAB  
0266 14 550 12.5 4   PCC DGAB  
0267 14 550 11 4   PCC BTB  
0268 14 550 8 4   PCC BTB  

— Value unknown
Blank cell indicates that layer is not present in section
AC = Asphalt concrete
BTB = Bituminous-treated base
DGAB = Dense-graded aggregate base
LCB = Lean concrete base
PATB = Permeable asphalt-treated base
PCC = Portland cement concrete
PBTB = Permeable bituminous-treated base


Twelve sections, 0213–0224, were constructed as part of the standard SPS-2 experiment. These sections have the same design characteristics as the standard 12 sections that appear on several other SPS-2 sites within the LTPP study. They are all doweled jointed plain concrete pavements. This site also includes four undoweled sections with skewed joints, SPS-2A-type sections 0262–0265. Their doweled counterparts are 0213, 0221, 0223, and 0215, respectively. Three additional sections of doweled jointed plain concrete, 0266–0268, were included with specialized designs of interest to the Arizona Department of Transportation (ADOT). Asphalt concrete (AC) sections 0260 and 0261 were also included by ADOT.

This report seeks to characterize the surface roughness of these sections over time and link the observations to records of pavement distress and its development. Road profile measurements were collected on this site about once per year since the winter after it was opened to traffic. Profile data were also collected on section 0215 on 16 additional dates.

This study applied algorithms for estimating the level of curl and warp present in the pavement and its effect on surface roughness. The algorithms included slab-by-slab quantification of curl and warp throughout the monitoring history of the site. The analysis framework for this was established in a recent Federal Highway Administration (FHWA) study of seasonal and diurnal changes in jointed concrete pavement roughness.(2) This method applies Westergaard’s theory to establish the likely shape of a curled slab and a curve fitting algorithm to quantify the level of curling in each slab.

The study related aggregated measurements of curl and warp within each profile measurement to the International Roughness Index (IRI). The observed statistical relationship between changes in curl and warp and changes in IRI for a given section provided a way distinguish the long-term roughness caused by distress from short- and long-term changes in roughness associated with curl and warp. Estimates of curl and warp from the profiles also provide the opportunity to study underlying environmental causes, but that aspect was not explored in this study.

This study also analyzed the profiles in detail using profile analysis methods employed in the study of other SPS sites in Arizona. (See references 3–7.) These methods include calculating roughness index values, examining the spatial distribution of roughness within a section, viewing profiles with post-processing filters, and examining spectral properties. The study applied the traditional analysis methods to the AC sections (0260 and 0261) in an attempt to treat them as control sections for comparison to the portland cement concrete (PCC) sections.


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