Australian Society For Concrete Pavements - ASCP … Papers/Paper 02... · Australian Society for...

Australian Society for Concrete Pavements

4th Concrete Pavements Conference

Factors Influencing CRCP Performance in Texas

Moon Won1, P.E., Ph.D. and Pangil Choi2, Ph.D.

1Professor and 2Senior Research Associate

Texas Tech University, USA

ABSTRACT

As of 2016, there are 21,799 lane kilometres of continuously reinforced concrete pavement

(CRCP) managed by the Texas Department of Transportation (TxDOT). CRCP is a premium

pavement type, with a higher initial construction cost than jointed plain concrete pavement

(JPCP), primarily due to the material and installation cost of steel reinforcement. In Texas,

the long-term performance of CRCP has been far superior to that of JPCP. Based on the

performance histories of the two Portland cement concrete (PCC) pavement types in Texas,

in 2001, TxDOT made it a policy to utilize CRCP when a rigid pavement is selected for

projects.

Over the years, CRCPs designed and built in accordance with TxDOT’s design standards

and specifications have provided overall excellent performance; however, some premature

distresses have been observed in CRCP. Since CRCP is more expensive than JPCP, and is

placed where heavy truck traffic volume is high, minimizing premature distresses and thus

eliminating the need for lane closures for any maintenance work is of prime importance to

TxDOT. To achieve the goal of developing near zero-maintenance CRCP, TxDOT has

initiated a number of research studies and forensic evaluations, with a primary goal of

identifying the mechanisms of premature distresses and developing design standards and

construction/materials specifications that would result in minimizing premature distresses

and extending CRCP pavement life.

ASCP 4th Concrete Pavements Conference 2

Factors Influencing CRCP Performance in Texas, Won

The major findings from those studies and investigations included; (1) structural distresses in

CRCP are rare in Texas where tied-concrete shoulders and stabilized bases were utilized,

(2) most, if not all, of the distresses are due to deficiencies in quality control for materials and

construction, (3) many of what appear to be full-depth failures are actually partial-depth

failures, (4) transverse crack spacing does not appear to have significant effects on long-

term performance, (5) concrete properties, especially the coefficient of thermal expansion

(CTE), have significant effects on major spalling development, and (6) the use of lower

amounts of longitudinal steel than the generally accepted 0.6 % resulted in poor

performance.

Based on these findings, TxDOT revised its CRCP design standards in 2013 and

construction/material specifications in 2014. The implementation of those design standards

and specifications is expected to further enhance long-term CRCP performance in Texas.



Introduction

In Texas, various types of Portland cement concrete (PCC) pavement have been used. They

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

(JRCP), continuously reinforced concrete pavement (CRCP), precast concrete pavement

and cast-in-place prestressed concrete pavement. The last two types were built as test

sections for research and implementation projects. In general, the performance of JRCP was

not as good as JPCP or CRCP, therefore TxDOT discontinued the use of this pavement

type. Accordingly, only JPCP and CRCP are now utilized in Texas. Figure 1 illustrates the

lane kilometres of JPCP and CRCP managed by TxDOT from 2006 to 2016. It shows that

the usage of CRCP has increased while that of JPCP has steadily decreased.

Figure 1 Lane kilometres of PCC pavement managed by TxDOT

The reason for this trend is that, in 2001 TxDOT made it a policy to utilize CRCP when a

rigid pavement is selected for projects, and since then most of the PCC pavements built in

Texas, if not all, were CRCP. TxDOT districts are allowed to use JPCP in certain locations or



with the approval from the administration. The TxDOT policy of exclusive use of CRCP was

based on the overall poor performance of JPCP and the excellent performance of CRCP.

Figure 2 shows the percentage of lane miles with distress scores of 80 or above for various

pavement types for the last 4 years (TxDOT PMIS, 2016). CRCP has the highest

percentage, while JPCP has the lowest.

Figure 2 Percentage of lane miles with distress score of 80 or above

Figure 3 Percentage of lane miles with ride score of 3.0 or above

Figure 3 illustrates the percentage of lane miles with a ride score of 3.0 or above for various

pavement types for the last 4 years, which clearly indicates the superior ride quality of CRCP



to other pavement types, better than that of asphalt concrete pavement. It also indicates the

poor ride quality of JCPC.

The superior performance of CRCP over other pavement types in Texas is the result of

continuous efforts made by TxDOT. Over the years, TxDOT has sponsored a number of

research studies on CRCP behaviour and performance, with the objectives of obtaining

optimum CRCP performance by improving design standards and specifications. This also

resulted in a better understanding of CRCP behaviour under various loading conditions, as

well as the mechanisms of various distress types in CRCP. In addition, a long-term CRCP

performance study was conducted, which spanned from 2005 to 2013 (Choi, et al, 2014).

This study evaluated the field performance of CRCP throughout Texas, and investigated

detailed structural responses of CRCP. The findings from this study indicated that most of

the CRCP distresses in Texas were not related to structural deficiency of the pavement

system; rather, they were due to poor quality control issues in materials selection and/or

construction. Also discovered were (1) punchout distress, which is considered the only

distress type caused by a structural deficiency of CRCP, is not always a full-depth distress,

(2) there was a poor correlation between transverse crack spacing and punchout distress,

(3) most of the severe spalling problems were due to the use of coarse aggregate with a

high coefficient of thermal expansion (CTE), and (4) the amount of longitudinal steel plays a

role in CRCP performance.

To improve long-term CRCP performance, it is of a great importance to understand correct

mechanisms of CRCP distresses, which requires an accurate understanding of CRCP

behaviour and interactions between steel and concrete under environmental and wheel

loading. This paper presents the findings made from various research studies conducted in

Texas on CRCP behaviour and important factors on CRCP performance. This paper also

discusses technical implications in terms of what needs to be done in design, materials

selection and construction practices to further enhance CRCP performance.



CRCP Behaviour under Environmental and Wheel Loading

Portland cement concrete undergoes volume changes when subjected to temperature and

moisture variations. In PCC pavement, these volume changes are accommodated in two

different ways. In JPCP, means are provided so that concrete volume changes are least

restrained. Those means include smooth dowels and a short joint spacing. Accordingly,

curling stresses in concrete are minimized. On the other hand, in CRCP, concrete volume

changes are severely restrained by longitudinal reinforcement, which causes larger curling

and warping stresses and results in numerous transverse cracks. In JPCP, transverse

cracks are considered as a distress, while in CRCP they are not.

Currently, punchout is considered the only distress type caused by a structural deficiency of

CRCP systems. All the other distresses, such as spalling, are considered functional

distresses. Accordingly, the objectives of structural designs of CRCP are to limit the number

of punchout distress at the end of the design period to an acceptable level. In most CRCP

design procedures, prediction of punchout is made by estimating concrete stresses in the

transverse direction at the top of the slab and resulting fatigue life of concrete due to wheel

loading applications and environmental loading (ARA, 2003). In the development of those

design procedures, the following assumptions were made:

(1) Crack widths vary almost linearly with crack spacing, i.e., the larger the crack

spacing, the greater the crack width.

(2) Transverse cracks go through the slab depth.

(3) Crack width increases over time due to continued drying shrinkage.

(4) LTE at transverse cracks vary with crack widths (and crack spacing), i.e., the larger

the crack widths or crack spacing, the lower the LTE, and vice versa.

With the above assumptions, an ‘optimum transverse crack spacing’ concept was

developed. To minimize the punchout distress, the AASHTO Guide for Design of Pavement



Structures (AASHTO, 1993) recommends crack spacing between 1.1-m and 2.4-m. The

minimum value of 1.1-m was derived from the assumption that, if a transverse crack spacing

is smaller than this value, wheel load stress in the transverse direction will be large and

critical, which could cause longitudinal cracks between two closely spaced transverse

cracks, resulting in punchout. The maximum value of 2.4-m was set to minimize the potential

for spalling, which is derived from the above assumption (1). In other words, larger crack

widths could increase the potential for spalling.

The relationship between crack spacing and crack width was investigated, which is

illustrated in Figure 4 (Suh et al, 1992 and Nam, 2005). Figure 4-(a) shows a somewhat

inverse relationship between crack spacing and crack width, which is contradictory to the

above assumption (1). In Figure 4-(b), there is no correlation in Austin (04) or Cleveland (04)

projects, while a loose correlation is observed in the Baytown (03) project.

A number of reasons present themselves for the discrepancy between the above

assumption (1) and the field observations as shown in Figures 4-(a) and 4-(b). One reason

is that not all transverse cracks occur at the same time. Those that occur at early ages will

experience more drying shrinkage with time, resulting in larger crack widths. On the other

hand, those cracks that occur at later ages will have quite small crack widths because the

drying shrinkage of concrete that occurred up to that point of cracking must have been

absorbed by the creep of concrete. Another reason for the poor correlation between crack

spacing and width might be that restraints on concrete volume changes by longitudinal steel

are limited to about 305 mm from transverse cracks, even though this distance might vary

depending on the environmental loading. Steel strains were evaluated in longitudinal steel

as shown in Figure 5-(a) (Nam, 2005).



Figure 4-(a) Crack spacing vs crack width in Houston

Figure 4-(b) Crack spacing vs crack width in Baytown, Cleveland and Austin



Figure 5-(a) Testing plan for steel strain measurements

Steel strain gages were installed at 0-mm, 152 mm, 305 mm, 457 mm, and 610 mm from the

induced transverse crack. Figure 5-(b) illustrates the steel strains at different distances from

a transverse crack. It shows that steel strains remain almost zero beyond 305 mm from the

transverse crack, which means that concrete stresses beyond 305-mm from a transverse

crack are nearly uniform. This indicates that concrete volume changes contributing to crack

widths at the steel depth are limited to about 305 mm from a transverse crack by bond

slippage. The contribution of the concrete beyond this point to crack width is minimal. In

other words, as long as crack spacing is larger than 61 cm, the effect of crack spacing on

crack width will be negligible. Based on the poor correlations observed in the field between

crack spacing and crack width and the restraints by longitudinal steel on concrete volume

changes being limited to about 305 mm from transverse cracks, the validity of the

assumption (1) is questionable. It should be noted that spalling has not been observed in



CRCP with limestone coarse aggregate regardless of how large a crack spacing is. It

appears unreasonable to place a limit on a maximum crack spacing.

Figure 5-(b) Steel strain variations at different distances from a transverse crack

In CRCP, temperature and moisture variations in concrete slabs are largest near the

concrete surface, and decrease further down the slab depth. Since transverse cracks in

CRCP occur in order to relieve excessive concrete stress due to temperature and moisture

variations and due to the existence of longitudinal reinforcement, transverse cracks normally

do not go through the slab depth and are quite often limited to the top half of the slab. Figure

6-(a) shows a transverse crack with a large crack width on the surface. The concrete slab

was cut longitudinally for widening, and Figure 6-(b) illustrates that the crack did not go

through the whole slab; rather it stopped midway between the concrete surface and the

longitudinal steel. This pavement on US 290 in Houston was placed in 1977, and this crack

maintained its integrity for over 30 years. It is true that transverse cracks could go through

the slab depth if slab support is not adequate, or if the concrete slab thickness and/or

longitudinal reinforcement is deficient. However, in Texas, base layers are required to be

stabilized with either cement or asphalt, and slab thickness and longitudinal steel amount are

quite adequate. Accordingly, most of the transverse cracks in CRCP in Texas are partial-

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depth cracks, and as will be discussed later, LTE values in all the transverse cracks

evaluated were quite high.

Figure 6-(a) Large crack width on the surface Figure 6-(b) Crack stopped above steel

It has been assumed that crack width in CRCP increases over time, resulting in reduced LTE

at transverse cracks and ultimately contributing to punchout. However, as discussed above,

even in CRCP sections as old as 33 years, transverse cracks were kept tight. To evaluate

variations in crack widths over time, vibrating wire strain gages (VWSG) were installed in a

CRCP construction project. The pavement structure consisted of 279-mm CRCP over 102-

mm asphalt stabilized base on top of a flexible base. VWSGs were installed at the top,

middle, and bottom of the concrete slab. A transverse crack was induced at the location of

the vibrating wire gages. Crack widths were calculated by the product of strains recorded in

VWSG and gage length. In this calculation, tensile strains in concrete due to stresses within

the gage length of VWSG were ignored. In other words, the crack widths estimated by this

method might slightly over-predict actual crack widths. Figure 7 shows the crack widths

values at mid-depth over about a three-year-period. It illustrates that crack widths vary

almost linearly with concrete temperatures. It also illustrates that crack widths decreased

over time, which is contradictory to the above assumption (3). Redistribution of concrete

stresses and displacements in CRCP as more cracks form as well as continued creep and



stress relaxation in concrete are considered the mechanisms of the reduction of crack widths

over time.

Figure 7 Variations in crack width over time

Figure 8 compares actual crack width measurements with predicted crack width values from

a theoretical model (Kohler, 2005). Dr. Kohler used accurate input values for the

mechanistic-empirical model developed for MEPDG. It shows that actual crack widths are

much smaller than predicted values. In general, the difference in terms of ratio of actual to

predicted crack width values gets larger with time, which appears to support the information

in Figure 7. This also indicates that the theoretical model in the MEPDG for the estimation of

crack widths severely over-predicts crack width.

Deterioration in LTE has been cited as the most critical process of punchout development in

CRCP (ARA, 2003). To evaluate LTE conditions in Texas, two test sections with 305-m long

in each section were selected at 27 CRCP projects. In each test section, a total of 24 slab

segments – 4 each of small, medium, and large crack spacing – were selected for each test

section. The crack spacing for small spaced cracks is 60 to 90-cm, for medium spaced

cracks 120 to 180-cm and for large spaced cracks 210 to 300-cm.



Figure 8 Comparisons of crack widths from mechanistic model with actual values

To evaluate the behaviour of a transverse crack with a specific crack spacing, two slab

segments with comparable spacing at both sides of the crack were selected. Falling weight

deflectometer (FWD) drops were made at the mid-slab of the upstream section, at the

upstream of the crack, at the downstream of the crack and at the mid-slab of the

downstream section for each crack. In order to determine the effect of temperature on the

average slab deflection as well as the LTE of the transverse cracks, FWD testing was

conducted twice a year for all the sections, once in the summer and once in the winter for all

the test sections. The age of the pavements varied from 7 years to 43 years when the

evaluations were completed, and the slab thicknesses were from 15.2-cm to 38.0-cm.

Accordingly, the inference space for the LTE evaluations was quite large, encompassing

CRCP projects with small to large thicknesses and from relatively young and quite old.

Figure 9 illustrates the effects of crack spacing and concrete temperature on LTE in all the

sections evaluated in this study. Blue columns show LTE values for small crack spacing, red

for medium, green for large crack spacing and pink at transverse construction joints. Quite

high LTE values were obtained regardless of time of testing (temperature effect) and crack

spacing. These high levels of LTE values are supported by the information in Figures 6



through 8, which is that crack widths in CRCP are maintained quite small if CRCP was built

with adequate longitudinal steel, slab thickness and base support.

Figure 9 Effect of concrete temperature and crack spacing on LTE

Figure 10 shows the results of LTE evaluations conducted for LTPP (Tayabji, et al, 1999). It

shows 96 percent of LTE values were larger than 90 % LTE.

In Figure 10, larger crack spacing resulted in greater LTE values, which is contradictory to

the above assumption (4). It is clear that if CRCP is built with adequate designs (slab

thickness, amount of longitudinal steel and base support), the punchout mechanism

advocated in the concrete pavement research community (increased crack width over time

leading to lower LTE and punchout) is not applicable in Texas. It appears that researchers

over the years adopted distress mechanisms in JPCP in modelling punchout distress in

CRCP. It should be recognized, however, that punchout does take place in Texas, and the

next section discusses the mechanisms and factors involved.



Figure 10 Effect of crack spacing on LTE

Punchout Mechanisms in CRCP and Factors Involved

Punchout distresses observed in Texas have common denominators. They are (1) CRCP

with asphalt shoulder, (2) evidence of pumping, (3) heavy truck traffic, and (4) the use of a

non-stabilized base. Figures 11-(a) and 11-(b) illustrate typical punchouts observed. The

distress in Figure 11-(a) shows slab segmentation under the wheel path. This pavement of

20.3-cm CRCP, which was built in the early 1960s, is a connector between Loop 610 to IH-

10 west in Houston. It is interesting to note that the edge of the pavement in the distressed

area preserves its shape, which strongly indicates the cause of this distress is poor slab

support at a localized area. It is also observed that there is a longitudinal crack in the middle

of the outside lane, and transverse cracks in the inside half of the outside lane appear to be

quite tight. Accordingly, this distress does not appear to be related to deteriorations of

transverse cracks. Rather, repeated wheel loading applications for 50 years on the small

location of deteriorated base support resulted in this distress. Figure 11-(b) shows a distress

type that resembles a traditional punchout.



Figure 11-(a) Slab segmentation Figure 11-(b) Typical punchout

This section of 20.3-cm CRCP is in IH-35 W in Dallas, which was completed in 1966.

Evidence of minor pumping is observed. Also, deteriorated transverse cracks are observed

within the distressed area. However, transverse cracks in the inside half of the outside lane

are in good condition. The deteriorated transverse cracks within the distressed area are not

the cause of the distress; rather, they are the result of the distress, which was caused by

other factors than lower LTE at transverse cracks. The half-moon shape of the concrete

crack indicates that the slab has been pushed down by repeated wheel loading applications,

and during that process, transverse cracks deteriorated and two longitudinal cracks

developed between two adjacent transverse cracks. The two distresses shown in Figure 11

appear different; however, the underlying cause appears to be identical, which is a poor slab

support. Figure 12-(a) shows the initial stage of punchout distress, and in order to identify

the cause of this distress, deflection testing with FWD was conducted at a 3-m interval. This

pavement section, 20.3-cm CRCP on asphalt stabilized base on IH-45 in Dallas was

completed in 1975. When the evaluation was made, the pavement was already 35 years old.

The testing results are shown in Figure 12-(b), which illustrates poor slab support at the

location of the distress. LTE values were evaluated at two transverse cracks (LTE 3-1 and

LTE 3-2 in the Figure 12-(a)) and the values were near 100 percent. Dynamic cone



penetrometer testing was also conducted, and average back-calculated modulus values at

locations of no distress was 1,730 MPa, while the value at the middle of initial punchout area

was 1,261 MPa, which clearly explains the mechanism of this distress.

Figure 12-(a) Initial stage of punchout Figure 12-(b) Deflections along PO area

Figure 13 shows a different distress type in CRCP in Texas. This pavement, consisting of

22.9-cm CRCP slab on 10.2-cm asphalt concrete pavement + 30.5-cm reworked base +

20.3-cm lime treated subgrade, was placed in 2002 on IH-35 in Cotulla.

Figure 13 CRCP distress due to heavy wheel loading applications



The distress shown in Figure 13 is different from a traditional punchout, since no evidence of

edge pumping or slab depression is observed. Forensic investigations were conducted and

the concrete segmentation was confined at the top half of the slab. The bottom concrete was

solid. Since there were no distresses in the inside lane, it was postulated that this distress

was related to heavy wheel loading applications. Traffic data on this section was obtained

from the weigh-in-motion (WIM) station located in this section. Figures 14-(a) and 14-(b)

illustrate single and tandem axle truck traffic applications in 2007 and 2011, respectively. In

Texas, the legal weight limit of single axle load is 20-kips (89 kilo-newton) and that for

tandem axle load is 34-kips (151 kilo-newton).

Figure 14-(a) Single axle load distribution Figure 14-(b) Tandem axle load distribution

Figures 14-(a) and 14-(b) show the applications of weights that far exceeded legal weight

limits. Structural responses of CRCP on the application of overweight axles were

investigated by analysing CRCP systems with a 3-dimensional finite element program as a

part of the development of the mechanistic-empirical CRCP design program for TxDOT (Ha,

et al, 2012). Figure 15 illustrates the analysis results for 40 kilo-newton wheel loading

application near a transverse crack. Maximum principal stresses at the top or bottom of

concrete slabs near transverse cracks are much smaller than those in the concrete

surrounding longitudinal steel. It is also interesting to note that crack stiffness does not have

substantial effects of wheel load stress at the top or bottom of the slab, while principal

stresses in concrete around longitudinal steel are affected. The analysis results imply that



the interactions between longitudinal steel and surrounding concrete are significant, resulting

in large concrete stresses near longitudinal steel, and if excessive, the large concrete

stresses could cause cracks near longitudinal steel in the form of horizontal cracking and

ultimately segmentation of concrete slab as shown in Figure 13. Lately, CRCP distresses as

shown in Figure 13 were more frequently observed in Texas than in the past. Applications of

illegally overweight trucks are considered as a cause for those distresses. A new technology

called fracking has been implemented in Texas to extract oil and natural gas that previously

were locked away in shale and other tight-rock formations. This technology requires

enormous amounts of water and other materials, and hauling them to the job site

economically appears to be responsible for the applications of illegal overweight trucks. The

distress type shown in Figure 13 is relatively new, and increasing slab thickness/changing

the depth of the longitudinal steel could provide a solution to this problem.

Figure 15 Concrete stresses at various depths near a transverse crack

Another type of distress observed in CRCP is shown in Figure 16. These distresses occur at

the transverse construction joints (TCJ). The frequency of this distress type is not high;

however, since distresses due to structural deficiency of CRCP system are quite rare in

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Texas, other than those due to poor slab support or illegal overweight truck applications, and

distresses in TCJ could occur at relatively early ages of pavement, TxDOT sponsored a

research study to identify the mechanisms of this distress type.

Figure 16 Distresses at transverse construction joints

Extensive evaluations of CRCP behaviour at TCJ, including stresses at longitudinal steel

and concrete strains and displacements at TCJ, indicated that the structural responses of

longitudinal steel and concrete were not excessive. Instead, the construction practices,

which includes dumping excess concrete mortar collected on the sides of the pavement into

TCJ or improper vibration in the morning side of the TCJ, were considered as a potential

cause for the distress.

Another significant distress type has been major spalling as shown in Figure 17. Major

problems with severe spalling include the degradation of ride quality, and potential safety

hazard. Severe spalling in CRCP was a major issue in Texas since the early 1980s. A

number of research studies were conducted over 30 years, and the last study was

conducted in 2011 and 2012, which revealed an excellent correlation between CTE of

coarse aggregate used and the potential for severe spalling (Ryu, et al, 2012). Sections with

severe spalling and no spalling were identified, and concrete material properties were

evaluated from cores taken from those sections. The concrete material properties evaluated



included modulus of elasticity and CTE. The correlation between concrete modulus and

severe spalling was not as good as that between CTE and severe spalling.

Figure 17 Severe spalling in CRCP in Texas CTE values of concrete from sections with no spalling problems were lower than 9.9

microstrains/°C, while those from sections with severe spalling problems were larger than

9.9 microstrains/°C. Based on the research finding, TxDOT included CTE as a requirement

for coarse aggregate property that should be met if the coarse aggregate would be used for

CRCP. In Texas, crushed limestone (LS) and siliceous river gravel (SRG) are the two major

coarse aggregate types used in PCC pavement construction. Crushed limestone is of

angular shape and has a rough surface texture, which is believed to provide better bonding

between the coarse aggregate and surrounding mortar. On the other hand, SRG is of round

shape and has quite a slick surface, which does not promote good interfacial bonding

between coarse aggregate and the surrounding mortar. Measurements of mechanical

properties of concretes made with those two coarse aggregate types reveal that concrete

with LS has lower modulus and CTE values than concrete containing SRG (Won, 2005). As

discussed earlier, in CRCP, concrete volume changes due to temperature and moisture

variations are severely restrained by longitudinal reinforcement, and larger CTE and

modulus values of concrete with SRG, along with lower interfacial bond strength, are

believed to be responsible for severe spalling distresses for CRCP containing SRG as a



coarse aggregate. It is interesting to note that spalling is not an issue in JPCP containing

SRG. It is because in JPCP, concrete volume changes due to temperature and moisture

variations are not restrained as much as in CRCP, and the resulting bond stresses at the

interfaces between coarse aggregates and surrounding mortar are kept to a minimum.

The role of longitudinal reinforcement in CRCP is to restrain concrete volume changes due

to temperature and moisture variations, which cause transverse cracks, and to keep

transverse cracks tight so that the continuity of the slab is provided. Accordingly, the amount

of longitudinal steel has effects on CRCP behaviour. Traditionally, the ratio of the steel

cross-sectional area to concrete area of 0.6 % to 0.7 % has been used. In 1989 and 1990,

TxDOT constructed test sections in 3 different projects to investigate the effects of

longitudinal steel amounts, coarse aggregate types, and concrete placement temperatures

on CRCP behaviour and performance (Suh, 1993). In Figure 18, the inside 2 lanes were built

with SRG as the coarse aggregate, while the concrete in the outside lane has LS as the

coarse aggregate. The marked difference in performance in terms of spalling is observed.

Figure 18 Effect of coarse aggregate type on spalling

Also, three different steel amounts (0.38 %, 0.50 % and 0.62 % with 19.1-mm bars) were

used. Additional section was built at 0.48 % with 22.2-mm bars. Figure 19 shows the



percentage of transverse cracks that experienced severe spalling. There is a reasonable

correlation between the amount of longitudinal steel and spalling ratio – the more

longitudinal steel, the lower the percentage of cracks that developed into spalling. It is

postulated that larger amounts of longitudinal steel restrain concrete volume changes more

effectively, resulting in higher concrete stresses, more cracks and less concrete strains at

transverse cracks, which caused fewer spalling. On the other hand, concrete strains become

larger at transverse cracks when smaller amounts of longitudinal steel are used, resulting in

a higher frequency of spalling.

Figure 19 Longitudinal steel amount and spalling



Acknowledgements:

The technical discussions made in this paper were possible thanks to a number of

researchers as well as TxDOT staff engineers. Special thanks are made to the late Dr. B.

Frank McCullough, my mentor and supervising professor. This study was conducted under a

research project (Development of Eco-Friendly Pavements to Minimize Greenhouse Gas

Emissions) funded by the Ministry of Land, Infrastructure and Transport (MOLIT) and the

Korea Agency for Infrastructure Technology Advancement (KAIA). The author would like to

thank the members of the research team, MOLIT and KAIA for their guidance and support

throughout the project.

References:

1. American Association of State Highway and Transportation Officials, AASHTO Guide

for Design of Pavement Structures, American Association of State Highway and

Transportation Officials, Washington, D.C., 1993

2. ARA, Inc., ERES Division, Guide for Mechanistic-Empirical Design of New and

Rehabilitated Pavement Structures,” Final Report, Appendix LL, Champaign, Illinois,

2003

3. Choi, P.G., Ryu, S.W., W. Zhou, S. Saraf, Yeon, J.H., and Won, M., Project Level

Performance Database for Rigid Pavements in Texas, II, Research Report FHWA/TX-

14-0-6274-2, Texas Tech University, Lubbock, Texas, 2013

4. Ha, S.J, Yeon, J.H., Cho, B.H., Jung, Y.S., Zollinger, D.G., Wimsatt, A., and Won, M.

Develop Mechanistic-Empirical Design for CRCP, Research Report FHWA/TX-11-0-

5832-1, Texas Tech University, Lubbock, Texas, 2011



5. Kohler, E.R., Experimental Mechanics of Crack Width in Full-Scale Sections of

Continuously Reinforced Concrete Pavements, Ph.D. Dissertation, University of Illinois,

Urbana Champaign, Illinois, 2005

6. Nam, J.H., Early-Age Behaviour of CRCP and Its Implications for Long-Term

Performance, Ph.D. Dissertation, The University of Texas at Austin, Austin, Texas, 2005

7. Ryu, S.W., Choi, P.G., Zhou, W., Saraf, S., Senadheera, S., Hu, J., Siddiqui, S., Fowler,

D., and Won, M. Optimizing Concrete Pavement Type Selection Based on Aggregate

Availability, Research Report FHWA/TX-12-0-6681-1, Texas Tech University, Lubbock,

Texas, 2012

8. Suh, Y.C., Hankins, K. & McCullough, B.F., Early-Age Behaviour of Continuously

Reinforced Concrete Pavement and Calibration of the Failure Prediction Model in the

CRCP-7 Program, Research Report 1244-3. Centre for Transportation Research, The

University of Texas at Austin, Austin, Texas, 1992

9. Tayabji, S.D., Selezneva, O, and Jiang Y.J, Preliminary Evaluation of LTPP

Continuously Reinforced Concrete (CRC) Pavement Test Section, Publication No

FHWA-RD-99-086, Federal Highway Administration, July 1999

10. Texas Department of Transportation, Condition of Texas Pavements – PMIS Annual

Report FY 2013 – 2016, Austin Texas, July 2016

11. Won, M. Improvements of Testing Procedures for Concrete Coefficient of Thermal

Expansion, Transportation Research Record 1919, Transportation Research Board,

National Research Council, Washington D.C., pp. 23-28., 2005

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