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Construction and Performance Evaluation of Thin Roller Compacted Concrete under Accelerated Pavement Testing

Word Count: 7,551 (Manuscript: 4,051; 3 Tables and 11 Figures: 1,750)

Zhong Wu, Ph.D., P.E.

Associate Professor, Research

Accelerated Pavement Research Program Manager

Louisiana Transportation Research Center

4101 Gourrier Avenue, Baton Rouge, LA 70808

(225) 767-9163

[email protected]

Moinul I. Mahdi

Research Assistant


Louisiana State University


(225) 614-8874

[email protected]

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Wu, Xiao, Zhang and Yang

Tyson Rupnow

Senior Concrete Pavement Research Engineer



(225) 767-9148

[email protected]

Paper Prepared for Publication and Presentation at the

2015 Annual Meeting of the Transportation Research Board

July, 2014

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mailto:[email protected]

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ABSTRACT

Roller Compacted Concrete (RCC) has drawn a great deal of attention from many state highway agencies in recent years due to its outstanding compressive strength, simple and cost-effective construction method and comparable-to-asphalt material costs. The objective of this study was to evaluate the constructability, structural performance and load carrying capacity of thin RCC-surfaced pavement structures through accelerated pavement testing (APT). Six full-scale RCC pavement test sections, each of 71.7 ft long and 13 ft wide, were constructed using normal pavement construction procedures. The test sections include three RCC thicknesses (4 in., 6 in., and 8 in.) and two base types: an 8.5-in. soil cement base and a 12-in. cement treated soil base. A heavy vehicle load simulation device named ATLaS30 was used in the APT testing. This paper mainly focuses on the APT experimental design, construction of RCC test sections, in situ non-destructive testing, pavement modeling and APT results from an 8-in. RCC-surfaced pavement test section.

Keywords: Roller compacted concrete, construction, APT, pavement performance, non-destructive testing

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INTRODUCTION

Roller compacted concrete (RCC) is a zero-slump concrete mixture placed with modified asphalt paving equipment and compacted by vibratory rollers (1). RCC is an economical, fast construction and durable candidate for many pavement applications. Properly designed RCC mixes can achieve outstanding compressive strengths similar to those of conventional concrete. Due to its relatively coarse surface, RCC has traditionally been used for pavements carrying heavy loads in low-speed areas, such as parking, storage areas, port, airport service areas, intermodal and military facilities (1). With improved paving and compaction methods as well as surface texturing techniques, recent applications of RCC are found for interstate highway shoulders, city streets, and other highways (2-4). As asphalt prices continuously soared up, the use of RCC has been significantly increased for last decade, especially in private and non-military public uses (1). Studies found that the at-present cost per square yard for RCC is about 84-89 percent of the cost of multiple-lifted asphalt layers (1, 5-6). In addition, the maintenance costs of RCC pavements have been reportedly very low (7).

The proven outstanding compressive strengths of RCC pavement, combined with its simple and cost-effective construction method and high placement speed, have created a great deal of interests from many states and local transportation agencies. Louisiana has many thousands of miles of low to medium volume roadways currently used by a significant large amount of heavy trucks from shale gas industries, logging and agricultural activities. A typical low- or medium- volume roadway in Louisiana consists of a 3.5-in. to 7-in. asphalt concrete layer over a soil cement or cement-treated soil base. The Louisiana Department of Transportation and Development (LADOTD) has great interest in finding out if a thin RCC layer (usually 4 ~ 6 in.) is suitable to be used as a cost-effective alternative to the current practice of asphalt concrete surfacing for those roadways with heavy truck trafficking. Portland Cement Association (PCA) in 2005 published a computer program called RCC-Pave for the thickness design of RCC industrial pavements (8). However, the RCC-Pave is only suited for the design of thick RCC pavements with a minimum RCC thickness greater than 8-in. (1). While a structural design guide for thin RCC pavements is currently not available, the constructability and performance of thin RCC pavements are also generally unknown.

OBJECTIVES AND SCOPE

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The objective of this study was to evaluate the constructability, structural performance and load carrying capacity of thin RCC-surfaced pavement structures through the accelerated pavement testing (APT).

The scope of this paper focuses on the following: the APT experimental design, construction of RCC test sections, in situ non-destructive testing, pavement modeling and APT results from an 8-in. RCC-surfaced pavement test section.

APT EXPERIMENTAL DESIGN

RCC Pavement Test Sections

Six RCC pavement test sections were constructed at the Louisiana Pavement Research Facility (PRF) site in Port Allen, Louisiana, using normal highway construction equipment and procedures. Figure 1 presents the plan view and pavement layer thickness configurations of the six test sections. Each section was about 13 ft. wide and 71.5 ft. long. As shown in Figure 1, the pavement structures for sections 1-3 generally consist of a RCC surface layer (4 to 8 in. thick), a 12-in. cement treated base layer and a natural subgrade, whereas, sections 4-6 include a RCC surface layer (4 to 8 in. thick), an 8.5-in. soil cement base layer, a 10-in cement treated subgrade layer and a natural subgrade. LADOTD requires that all high-volume pavement design include a treated subgrade layer between the base layer and natural subgrade. The 10-in. cement treated subgrade layer is designed for this purpose. Overall, sections 1-3 are designed to determine if a thin RCC surface layer can be used as a cost-effective alternative in lieu of asphalt concrete surfacing for low-volume roads having significantly heavy truck traffic; whereas, sections 4-6 are designed to study the RCC surfacing for high-volume road applications.

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FIGURE 1 Pavement Structures of ALF Test Lanes

Materials

Roller Compacted Concrete

Figure 2 shows the design gradation and corresponding mix quantities obtained during the RCC mix design of this study. In general, a well-graded aggregate blend using #67 limestone and manufactured sand was selected with a Type I Portland cement of 11.4% and optimum moisture content of 6.5%. More details of RCC mix design may be found elsewhere (9).

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FIGURE 2 Mix Quantities and Gradation for RCC Pavement Sections

Base and Subgrade Soils

A silty-clay embankment soil was used in both soil cement and cement treated soil layers as well as the treated subgrade. This soil consisted of 47.7 percent silt and 30 percent clay. The liquid limit and the plastic index were 32- and 14- percent, respectively. Based on the AASHTO soil classification, it was classified as an A-6 soil. According the LADOTD’s roadway design specification, the minimum 7-day unconfined compressive strength for treated subgrade, cement treated base and soil cement base would be 100, 150 and 300 psi, respectively. To meet the specifications, the cement treated soil base layer used in sections 1-3 contained 6 percent cement by volume, whereas, 8 percent by volume of cement was applied in the soil cement base layer on sections 4-6. Meanwhile, 4 percent cement by volume was used for the 10-in. treated subgrade layer on sections 4-6.

Instrumentation

Figure 3 shows the instrumentation plan of this experiment. Each test section was instrumented with three earth pressure cells (Geokon 3500), two H-type asphalt strain gages (Tokyo Sokki KM-100HAS), and two concrete strain gages (Tokyo Sokki PML-60), which were placed at various locations and layer interfaces. Several moisture sensors (TDR CS 616) and thermocouples (T 108-L) from campbell sceintific were also placed to monitor the pavement temperature and subgrade moisture variation. The purpose of the instrumentation is to measure

Mix Quantities

Max Dry Density (pcf) 146.0

Max Wet Density (pcf) 155.5

Optimum % Moisture 6.5

Coarse Aggregate Absorption % 0.2

Fine Aggregate Absorption % 2.1

% Cemetitious 11.4

% Cement 11.4

%Fly Ash 0.0

Target Coarse Aggregate % 45.0

Target Fine Aggregate % 55.0

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the direct pavement responses under the wheel and environmental loading and to provide information for characterization and evaluation of the relative damage evolution of RCC pavements.

FIGURE 3 Instrumentation Plan

CONSTRUCTION OF RCC TEST SECTIONS

The test lane construction for the project was carried out with the assistance from industry partners in the concrete fields using normal highway construction procedures (10). The construction of the subgrade and base course layers was begun by removing the existing test lanes used in a previous experiment at PRF. The contractor used a Roadtech roto-milling machine to reclaim the existing asphalt pavement. After removing the existing pavements, additional amounts of the subgrade soil (A-6) were added to construct the proposed subgrade layers (Figure 1). Note that a rate of 4 percent of cement by volume was used to treat the cement treated subgrade layers in sections 4, 5 and 6. A Caterpillar RM 500 stabilizer was used to process the cement treatment at the plan depth of 10 inches. Initial compaction was accomplished by the CP 563 E vibratory sheep foot drum roller, and graded using a CAT motor

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grader. Final grade was accomplished using a Komatsu D-21P finishing dozer followed by a CAT PS-150C multi-wheel rubber tire roller. A Troxler Nuclear Density gauge was used to measure the field density and moisture right after the construction. In general, the average field proctor density and moisture content for the cement-treated subgrade were 104.5 and 16 percent, respectively, whereas, for the existing subgrade, the two measurements were 111.3 and 15 percent, respectively. Subsequently, water was spread on top of the finished subgrade layer for curing. Three PVC pipes were placed at an equal distance to take out all the instrumentation wires through the pipes. Precautions were taken not to damage any wire or PVC pipes during the construction process.

Same procedure was followed for the base layers construction except that a 6-percent cement by volume was spread for the 12-in. cement treated layer on sections 1, 2 & 3 and an 8-percent cement by volume was applied for the 8.5-in. soil cement layer on sections 4, 5 & 6 to achieve a minimum 7-day UCS of 150 and 300 psi, respectively. Both the base layers were compacted to achieve a 95 percent of the maximum dry density.

All RCC layers of test sections were constructed within a day using a set of specialized asphalt paving and RCC mixing equipment. As shown in Figure 4, the RCC placement involves a number of steps: RCC production, transportation and placement, compaction, jointing, and curing. For the production of RCC, a Rapidmix 400C horizontal twin shaft pugmill was used. It consists of one or two aggregate feeders, a cement silo and feeder, a main feeder belt, a water supply system, a pugmill mixer, a discharge belt, and a gob hopper at the end of the discharge belt. The pugmill offers a number of advantages, such as rapid mobilization (takes 2-3 hours from travel mode to fully operational mode), self-contained with its own power source, reduced transportation time for fresh concrete, high production rate (50 to 300 yd3/hr) and an efficient mixing system (11;12). During the startup operation, the pugmill was calibrated and batching of RCC was monitored to fulfill the specification in accordance with ASTM C94. The RCC mix was then transported to the jobsite in dump trucks. Precautions were taken to avoid excessive moisture loss during transportation.

Before placing the RCC on the actual pavement sections, a 200-ft long trial section was constructed on top of an existing roadway at the PRF site to validate the design, rolling pattern and method of construction using the same construction equipment. A Rollcon high density paver was used to place the RCC over the prepared base layer to achieve high initial density and smoother surface. A CAT CB-64 vibratory steel drum roller was then used to compact the RCC layer. Nuclear density gage was used to check the moisture and density right after the paver and after the compaction using vibratory roller. The density ranges between 94-96 % of the target

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density right behind the paver and increased to 97-98% after compaction. Note that not all density measurements satisfied the target density value of 98%, but all test sections achieved 96.5% or greater density after the construction.

All RCC layers were placed in single lift and no construction joints were formed. Precautions were taken not to damage any instrumentation wire or PVC pipes during the placement. During the construction, transverse saw-cut joints were created on each RCC test section to minimize or prevent possible randomly-generated shrinkage cracking. Saw-cutting began after RCC was hard enough to withstand spalling damage during sawing operations. The saw-cut joints were typically spaced at 20-ft, 15-ft and 10-ft. interval for the 8 in., 6 in. and 4 in. RCC layers respectively, with the corresponding joint depths of 1.5 in., 1.0 in., and 0.5 in. Finally, a white pigmented water base concrete curing compound conforming to ASTM C309 was sprayed on the finished RCC surfaces for curing.

(a) Rapidmix 400-C Pugmill (b) Transportation

(c) Placement of RCC (d) Compaction

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(e) Saw-Cutting Joints (f) Curing

FIGURE 4 RCC Construction

IN SITU MEASUREMENTS

RCC Strengths and Surface Characteristics

As shown in Figure 5, cylindrical samples and saw-cutting beams of RCC were prepared on site during and after the construction for the laboratory strength tests. Several field cylinder cores were also taken from different sections after the construction. The overall compressive strength at 28 days was found exceeding 5,000 psi with an average flexural strength of 661 psi for the RCC mixtures used in the test sections. It should be pointed out that all the cylindrical samples and field cores achieved the adequate strength requirements for this experiment. However, the overall compressive strength for lane 1 (including sections 1-3) was found approximately 10 percent lower than that of lane 2 (including sections 4-6). This could be due to a high paving/construction speed used on lane 1, which subsequently was reduced when paving on lane 2. Higher paving speed could have resulted in a lower density and strength for lane 1 than those for lane 2. More details on the strength test results may be referred to elsewhere (9).

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FIGURE 5 In-Situ Testing and Sample Fabrication

As also shown in Figure 5, a suite of in situ tests were performed on RCC surfaces after the construction, including sand patching, Dynamic Friction Tester (DFT), walking profiler and falling weight deflectometer (FWD). The sand patch test was used to determine the average macrotexture depth (MTD) of the finished RCC surfaces, whereas, a Dynamic Friction Tester (DFT) was used to measure the corresponding pavement surface friction. In addition, an ARRB Walking Profiler G2 was used to measure the centerline profilers of the finished RCC surfaces. A software named “ProVAL” was used to convert a measured longitudinal profile into the International Roughness Index (IRI) number for each RCC pavement section tested (13).

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The DFT and sand patching test results are presented in Table 1. The DFT20 value shown in the table represents the DFT measured friction number at 20 km/h, which is often used as an indicator for surface micro-texture of a pavement (14). In general, the measured DFT20 values of RCC test sections ranged from 0.22 to 0.42, which are in a similar range as those measured on the top of different asphalt mixes (14). On the other hand, the measured MTD values varied from 0.36 to 0.99 that are also similar to those of asphalt concrete surfaces (14). Overall, it is felt that RCC pavement surfaces should have a similar surface friction characteristic as asphalt concrete surfaces, in terms of both micro- and macro- textures.

Table 1 Sand Patching and DFT Test Results

Section DFT20 MTD (mm)

Section 1 0.3 0.99

Section 2 0.4 0.72

Section 3 0.22 0.89

Section 4 0.3 0.36

Section 5 0.42 0.39

Section 6 0.28 0.43

Figure 6 presents the surface texture photos for each RCC test section constructed as well as the corresponding predicted IRI values. As shown in Figure 6, the three sections on lane 1 (sections 1-3) appeared much rougher than those sections on lane 2 (sections 4-6). The IRI results indicate that all sections on lane 1 have an IRI number greater than 300 in/mile, whereas, sections on lane 2 have an IRI number less than 200 in/mile with a lowest IRI of 120 in/mile achieved in section 5. The rough RCC surfaces of lane 1 may be partially attribute to the high paving speed used in the construction. While diamond grinding or a thin asphalt overlay on top of the RCC pavement would overcome the rough surface issue, on the other hand, it is suggested that a finer aggregate gradation be used to achieve a smoother surface for RCC-surfaced pavements. More discussion on the gradation and surface smoothness of RCC sections may be referred to elsewhere (9).

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1 2 3 4 5 6 Avg.0

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IRI

(in/m

ile)

(a) (b)

FIGURE 6 (a) Predicted IRI Results; (b) Surface Texture of RCC sections

FWD Results

A Dynatest 8002 FWD was used in this experiment with nine sensors spaced at 0”, 8”, 12”, 18”, 24”, 36”, 48”, 60” and 72”from the center of the load plate. Four FWD load levels: 9,000-, 12,000-, 15,000- and 25,000- lb were used on the finished surfaces of RCC test sections to determine the surface deflections and the results were used for the backcalculation of pavement layer moduli. ELMOD 6 was used in the backcalculation and the results are presented in Figure 7 (15).

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Figure 7 FWD Backcalculated Moduli of RCC Test Sections

As expected, the backcaluated moduli of RCC layers in sections 1-3 are generally lower than those in sections 4-6, which is consistent with the compressive strength test results obtained in the laboratory. The soil cement layers with 8 percent of cement content are stiffer in terms of the backcalucated moduli than the cement treated soil layers of 6 percent cement content. The backcalcuated subgrade moduli are also found higher for those sections on lane 2 due to the 10-in. cement-treated subgrade, Figure 7.

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ACCELERATED PAVEMENT TESTING

A heavy vehicle load simulation device - ATLaS30 was used for the accelerated loading of RCC test sections in this experiment. The ATLaS 30 device is 65-ft long, 7 ft. high and 10 ft. wide, constructed around two parallel steel I-beams. The ATLaS wheel assembly models one half of a single axle and is designed to apply a dual-tire load up to 30,000 lbs by hydraulic cylinders. With a computer-controlled loading system, the weight and movement of traffic is simulated repetitively over a 40-ft long loading area in bi-directional mode at a top speed of 6 mi/hr. By increasing the magnitude of load and running the device for 24 hours a day, it is possible to condense 20 years of loading into a period of only one month.

Figure 8 The ATLaS 30 Device

Pre-Loading Fatigue Analysis of RCC Test Sections

A pre-loading fatigue analysis of RCC test sections was conducted using the finite element (FE) program, KENSLAB (16). As shown in Figure 9, each RCC test section was modelled as a two-layer system-RCC over a solid foundation in KENSLAB. First, based on the FWD backcalcuation results a modulus value of 4,000 ksi was chosen for all RCC layers to represent

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an overall average modulus of this material in a field condition. Second, based on the results of elastic analysis using KENSLAB a set of modulus values of 30 ksi and 38 ksi were selected to model a solid foundation layer for sections 1-3 and sections 4-6, respectively. As presented in Table 2, when those selected modulus values were applied in the elastic analysis under a FWD load, the predicted surface deflections matched fairly well with those measured deflections under different FWD loads, except the FWD load of 9000-lb.

RCC pavements have engineering properties similar to those of conventional Portland cement concrete (PCC) pavements. Thus, RCC pavement design methods usually employ the same basic strategy as PCC pavements: keeping the pavements flexural stress and fatigue damage caused by wheel loads within the allowable limits (1).

Proposed FEA Model

Solid Foundation

E= 30 ksi

4”- 8” RCC

Subgrade

12” Cement Treated Base

4”- 8” RCC

Section 1, 2 & 3

Proposed FEA Model

Solid Foundation

E= 38 ksi

4”- 8” RCC

10” Treated Subgrade

Subgrade

8.5” Soil Cement

4”- 8” RCC

Section 4, 5 & 6

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Figure 9 RCC Pavement Structures used in Finite Element Analysis

Table 2 Comparison of Predicted and Measured FWD Deflections

Sect

ions FWD

Load

Measured Deflection

D0 ( in)

Predicted Deflectio

n (in)

Measured/Predicted

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Load

Measured Deflection

D0 (in)

Predicted Deflection

(in)

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ion

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9kip 0.0037 0.00041 >1.0

12 kip 0.0049 0.00582 0.8 12 kip 0.0048 0.00493 1.0

15 kip 0.0062 0.00629 1.0 15 kip 0.006 0.00532 1.1

25 kip 0.01 0.01193 0.8 25 kip 0.0098 0.01009 1.0

Sect

ion

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Sect

ion

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12 kip 0.00752 0.00752 1.0 12 kip 0.00625 0.00636 1.0

15 kip 0.00952 0.00811 1.2 15 kip 0.0079 0.00685 1.2

25 kip 0.0164 0.01527 1.1 25 kip 0.013 0.01288 1.0

Sect

ion

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Sect

ion

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9kip 0.0067 0.00071 >1.0

12 kip 0.0104 0.01063 1.0 12 kip 0.0086 0.00894 1.0

15 kip 0.0131 0.01141 1.2 15 kip 0.0107 0.00958 1.1

25 kip 0.0229 0.02117 1.1 25 kip 0.0184 0.01773 1.0

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In this study, the following two sets of fatigue damage model were used in the pre-loading fatigue analysis:

1. Fatigue Model developed by American Concrete Institute for PCC Pavements (17):

(a) when 0.45 < SR < 0.55, Nf = (4.2577/(SR-0.4325))3.268

(b) when SR ≥ 0.55, log Nf = 11.737 – 12.077 (SR)

2. Fatigue Model developed in RCC-Pave for RCC pavements (18):

(c) log Nf = 10.25476 – 11.1872 (SR)

where: Nf – the pavement fatigue life under a certain load category, or the allowable number of load repetitions;

SR – Critical flexural stress ratio, SR = ¿

The critical tensile stress at the bottom of RCC slabs was predicted using the finite element program of KENPAVE under different ATLaS dual tire loads, and the predicted fatigue lives of the six RCC test sections are presented in Table 3. In general, the analysis results indicate that the pavement fatigue lives predicted by the RCC fatigue model are significantly less than those predicted by the PCC model. However, to fail an 8-in. RCC test section both models predicted large numbers of allowable load repetitions, even under a 25-kip dual tire load, which simulates a 50-kip single axle load in reality. On the other hand, the predicted results also showed that only a few number of 20-kip dual tire passes would fail a 4-in. RCC pavement section. To find out the real performance of thin RCC pavements, the accelerated loading started on Section 4, the strongest 8-in. RCC pavement section in this study, Figure 1.

Table 3. Predicted Fatigue Lives (Number of Load Repetitions) of RCC Test Sections

Load (kips)

Fatigue Model

Section 1 Section 2 Section 3 Section 4 Section 5 Section 6

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(8” RCC) (6” RCC) (4” RCC) (8” RCC) (6” RCC) (4” RCC)

9PCC ∞ ∞ 136,000 ∞ ∞ 420,000

RCC 95 million 640,000 13,000 115 million 8 million 27,000

16PCC ∞ 12 millions 202 ∞ ∞ 765

RCC 6.5 million 124,000 33 9.3 million 220,000 113

20PCC ∞ 65,000 2 ∞ 145,000 6

RCC 960,000 7,000 0 1.5 million 12,250 1

22PCC ∞ 57,500 1 ∞ 92,000 1

RCC 650,000 4,500 0 1 million 9,300 0

25PCC ∞ 46,000 1 ∞ 12,250 1

RCC 168,000 600 0 284,000 1,500 0

Preliminary APT Results of Section 4

Based on the aforementioned fatigue analysis, an incremental loading sequence of the ATLaS 30 dual tire load was selected for the APT loading of section 4. Figure 10 presents the loading sequence and the corresponding predicted ESAL numbers. Note that under each selected load level, approximately 78,000 ATLaS 30 dual tire load passes were applied to the pavement.

0 100000 200000 300000 4000000

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25

30Loading Sequence

No. of Repetition (Thousands)

AT

LaS

Loa

d (k

ip)

9 kip

16 kip20 kip

22 kip25 kip

0 100000 200000 300000 4000000

2000000

4000000

6000000

8000000

10000000

12000000

No. of Repetition (Thousands)

Est

imat

ed E

SAL

(mill

ions

)

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Figure 10 Loading Sequence and Corresponding ESALs

The following are the summary of the APT loading results from section 4:

Neither visible nor measurable distresses could be obtained on this section at the end of 9-kip, 16-kip, 20-kip and 22-kip of ATLaS dual-tire loading. The measurements from a laser rutting profiler indicated that the permanent tire prints (i.e., the permanent tire marks) along the wheel-pass were generally less than 0.2 in.

At the beginning of the 25-kip loading, an overnight heavy rainfall (i.e., more than 3 in. of rain within a few hours) was received on the testing site, and a pumping action was observed through a saw-cut joint during the wheel loading. As shown in Figure 11, it is believed that, under such a heavy load of 25-kip and extremely wet condition, the joint, originally saw-cut to a depth of 1.5-in., has been cracked down to the bottom of the RCC layer and the pump-out materials were fine soil mixtures from underneath soil cement layer.

Approximately after 20,000 passes of the 25-kip loading, one longitudinal and one transverse cracks were noticed on the pavement surface. As shown in Figure 11, both cracks were hairline type, less than 0.1 in. wide and 2-3 ft long, and both of them were developed near from the joint of pumping. While the cracks seemed potentially related to the joint pumping action, however, without coring it is still different to tell if those cracks are from bottom-up or top-down.

The predicted total cumulative ESALs were approximately 10.9 millions. Based on the Miner’s damage law (19), more than 200% cumulative fatigue damage was predicted for the loading of section 4 when the RCC-Pave fatigue model was used. On the other hand, zero cumulative damage would be predicted if the PCC fatigue model was considered.

Instrumentation data has been collected for each load group at certain intervals. The instrumentation results will be further analyzed when results of other RCC test section will be obtained.

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Figure 11 Pumping of Fines and Visible Cracks on Section 4

SUMMERY AND CONCLUSION

Six thin RCC-surfaced pavement test sections were constructed for an APT experiment of LADOTD. The RCC layer thicknesses varied from 4 in. to 8 in. and two soil cement bases were considered for the RCC test sections. A set of specialized paving and RCC mixing equipment was used in the construction. A heavy vehicle load simulation device - ATLaS30 was used for the accelerated loading of RCC test sections. The following listed a few observations and conclusions drawn from this study:

The overall RCC compressive strength of lane 1 was approximately 10 percent lower than that of lane 2 due to a high paving/construction speed used on lane 1;

The predicted IRI on lane 1 were found more than 300 in/mile, whereas, lane 2 had an IRI number generally less than 200 in/mile with a lowest IRI value of 120 in/mile achieved in section 5. The extremely rough surface of lane 1 may be partially attribute to the high paving speed used. On the other hand, a finer aggregate gradation may be used to achieve a smoother surface for RCC-surfaced pavements.

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The pre-loading fatigue analysis indicated that the pavement fatigue lives predicted by the RCC-Pave fatigue model are significantly less than those predicted by the PCC model, especially under a large heave load. Both models predicted only a few number of 20-kip dual tire passes would fail a 4-in. RCC pavement section, which need to be validated using the APT results of this study.

The APT results from section 4 indicated that the distresses for RCC pavements include the longitudinal and transverse cracking, joint pumping and possible join faulting. More than 10.9 million of EASLs were applied on section 4. However, only a joint pump and two small cracks were observed. The failure criteria of RCC pavements under an APT loading need further investigation in order to predict true damage performance of RCC pavements. On the other hand, the 8 in. RCC section had performed better than expected. Both RCC-Pave and PCC fatigue models did not seem to fit for the prediction of fatigue damage of this section. After the completion of testing of all six RCC test sections, a new fatigue damage model is expected to be developed in this study for thin RCC-surfaced pavement as an option for both low- and high-volume pavement design in Louisiana

ACKNOWLEDGMENTS

This study was supported by the Louisiana Transportation Research Center and the Louisiana Department of Transportation and Development. The authors would like to express thanks to all those who provided valuable help in this study.

REFERENCES

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