Highway Concrete Technology Development and Testing Volume I: Field Evaluation of SHRP C-202 Test Sites (Hpc)

Chapter 4

INTRODUCTION

This site consists of two eastbound lanes of State Route 58 eastbound in Boron, CA, as well as an overhead structure carrying State Route 58 over a rail spur immediately before the test section. The individual test sites and test results are described in the following sections.

BORON OVERHEAD

The Boron overhead, Bridge No. 50-353R 9-KER-58-R141.5, consists of two parallel structures carrying State Route 58 over the rail spur leading to the U.S. Borax mine in Boron, CA. Each structure consists of a three-span continuous bridge with no expansion joints. Each bridge has two traffic lanes and a shoulder. The bridge beams were cast integrally with the deck slab. The entire deck appears to be undergoing significant ASR, as manifested by widespread visible map cracking. The deck surface was treated with a methacrylate (HMWM) in 1995, into which a coarse, rounded sand was broadcast. Figure 35 shows a photograph of the deck surface.

Figure 35. Treated section on Boron overhead structure over State Route 58 looking east (Boron, CA).

Pavement Sections

The following information was excerpted from the CTL report (Stark to Surdahl letter, dated October 8, 1997):

This pavement section is located on State Route 58 between Barstow and Mojave near Boron on the Kern-San Bernardino county line in California. The pavement of interest was built between 1971 and 1974 as part of a four-lane divided section with 20.32-cm (8-inch) portland cement concrete slip-formed onto 10.16 to 15.24 cm (4 to 6 inches) of cement-treated base. The concrete was made using low-alkali cement (less than 0.60 percent equivalent to Na₂O) and natural sand and gravel from a source in Barstow. In the early to middle 1980s, observations of this and several other concrete structures containing aggregate from the same source revealed deleterious ASR. In 1991, SHRP discussion with CALTRANS [California Department of Transportation] personnel revealed major surface cracking had been observed in the State Route 58 pavement. In 1988, a high molecular weight methacrylate (HMWM) had been applied to the pavement wearing surface in selected westbound sections near Boron to minimize cracking development and improve and prolong traffic service life, particularly with truck loading. A side effect would be to minimize any effects of deleterious ASR. In 1991, cores were taken as part of the SHRP program to confirm the occurrence of ASR and estimate the depth of penetration of the HMWM into the pavement concrete.

Observations

As noted in SHRP-C-343, six full-depth 10.16-cm (4-inch) diameter cores were taken from the experimental pavement section of Route 58, and sawed and finely lapped in the longitudinal direction for microscopic examination. The examinations confirmed that deleterious ASR had developed in the pavement concrete, and that the reactive aggregate constituents were cryptocrystalline volcanics of rhyolite to andesite composition. These were evidenced by reaction rims on aggregate particles, microcracks in the concrete, and ASR gel in cracks and voids. The examinations revealed that the applied HMWM penetrated and filled surface cracks to maximum depths of 51 to 62 mm (2 to 2.25 inch). Also, HMWM was found to have penetrated and filled cracks as little as 0.05 m (0.002 in) wide.

Status of Test Sections

For a period of years since 1988 when HMWM was applied, improved performance was noted, compared with sections with no treatment. For more than 5 years, only minor additional surface cracking appeared, while more severe surface cracks continued to develop along transverse joints, and adjacent to other random cracks in untreated sections. Also, numerous small surface spalls continued to develop in the untreated sections but not in the treated sections.

By 1995, 7 years after application of HMWM on State Route 58, it became apparent to CALTRANS that pavement performance both with and without the treatment reached a state of deterioration that required full-surface overlay. In 1996, this asphalt overlay was completed. However, CALTRANS agreed to retain a short section of exposed pavement with HMWM. This is presently the only section still available for visual inspection.

The test section described herein consists of two lanes of U.S. Route 52. Figures 36 and 37 show different views of the test pavement site, and figure 38 shows a plan of the test sections. The original test sections consisted of control 1, methacrylate 1, and methacrylate 2, all of which are located in the travel lane (number 2). Sections methacrylate 1 and methacrylate 2 were treated with a single coat of methacrylate into which a sand was broadcast. In 1995, three test sections in the passing lane (number 1); control 2, control 3, and methacrylate 3 were added alongside the existing test areas in the travel lane (number 2) by CALTRANS to evaluate the effect of traffic loading on the ASR damage. The Boron Overhead section was also added at this time. Lane 1 does not have the extreme damage present at the joints that lane 2 had. A coat of methacrylate was applied to the methacrylate 3 section in 1995, at the same time the bridge deck was treated. At that time, a second coat of methacrylate was added to section methacrylate 2 in the travel lane. Also, in 1995, the pavement on either side of the test section was overlayed with asphaltic concrete. The asphalt overlays were placed to reduce the maintenance liability of the large length of exposed ASR pavement adjacent to the test sections.

Figure 36. Photograph showing part of Boron, CA, test site, M2, Station 250.

Figure 37. Photograph showing part of Boron, CA, test site, M3, Station 160.

Figure 38. Plan view of Boron, CA, test site.

MAP CRACKING

All the sections making up the Boron, CA, test site had map cracking over 100 percent of their area in 1998. Most of the map cracking was of low severity, but there was some medium and high severity also. Figure 39 shows an example of high-severity map cracking. Figure 40 shows a close-up view of typical map cracking at the Boron site. Figures 41 through 44 show the amount of each level of severity as a percentage of the total area for each section for all 5 years of the study. In the travel lane, control section 1 (C1) had more severe map cracking than the methacrylate sections (M1 and M2). The cracking was less severe in M2 than in M1. It appears that the second application of methacrylate to section M2 in 1995 has helped reduce cracking. In the passing lane, methacrylate section 3 (M3) is performing better than control section 3 (C3). Overall, the passing lane sections are performing better than the travel lane sections. A description of the map cracking in each section is as follows:

• Control 1—the map cracking in this section progressed from more than 90 percent low severity and the remainder medium in 1994, to about 70 percent low severity and 15 percent each for medium and high severity in 1998.
• Methacrylate 1—the map cracking in 1998 in this section was less severe than C1, with just over 80 percent low severity and 20 percent medium severity.
• Methacrylate 2—the map cracking in 1998 was less than in section M1. There was also some redirection in the severity levels after the second application of methacrylate in 1995. The level in 1998 was 90 percent low severity and 10 percent medium severity. The deterioration increased only slightly during the four years of study.
• Control 3—the map cracking of 1998 in this section is at about the same level of severity as M2 in 1998, but the rate of increase in deterioration appears to be greater in C3 than in M2.
• Methacrylate 3—this section has the least severe map cracking of all the sections. Approximately 95 percent of the section is low severity and 5 percent is medium severity. The amount of medium-severity distress has increased only slightly during the 4 years of study.

Figure 39. Example of high-severity map cracking (Boron, CA).

Figure 40. Close-up photograph showing typical map cracking (Boron, CA).

Figure 41. Map cracking as a percentage for each level of severity (Boron, CA, 1995).

Figure 42. Map cracking as a percentage for each level of severity (Boron, CA, 1996).

Figure 43. Map cracking as a percentage for each level of severity (Boron, CA, 1997).

Figure 44. Map cracking as a percentage for each level of severity (Boron, CA, 1998).

JOINT DISTRESS

The widespread map cracking in the test sections made exact crack recording impossible. Therefore, only the large, clearly visible cracks were noted. The transverse joints were all completely distressed, with cracks and spalled areas occurring over the entire length of the joints. Figure 45 shows a photograph with an example of medium-severity joint distress. Figure 46 shows an example of high-severity joint distress. According to the LTPP criteria for rating joint distress, the entire length of each joint was rated at the highest severity level if at least 10 percent of the joint length had the higher severity distress.

Figure 45. Photograph showing medium-severity joint distress (Boron, CA).

Figure 46. Photograph showing an example of high-severity joint distress (Boron, CA).

Figures 47 through 50 are a series of graphs illustrating the amount and severity of joint distress for each section. There is also a series of graphs showing the actual lengths of distress at each level in figures 51 through 54. Both series compare all sections for each year. The 1998 observations of the joint distress for individual sections are as follows:

• Control 1—the severity of joint distress in section C1 had increased from almost entirely low severity in 1994 to mostly high severity in 1998. This was the worst section of the five. At least 10 percent of the length of almost all joints in this section had at least some high-severity joint distress. The graph of actual length of each distress condition (figure 54) indicates that for 1998 most of the length was of medium severity.
• Methacrylate 1—the methacrylate-1 section was the second worst section after C1. It had deteriorated from almost all low-severity distress in 1994 to 75 percent medium and 25 percent high in 1998. The rating system used showed no joints of low severity, while the graph of actual lengths of distressed joint indicates there were some areas of low-severity distress.
• Methacrylate 2—the methacrylate-2, with the second application of methacrylate, appeared to be performing better than the M1 section, which only had one application. This section was the best in the travel lane and second overall to the M3 section. The rating scheme rules imply that almost all the joint length was of medium-severity distress with a small amount of high-severity distress. The actual joint lengths show about one-third low severity, two-thirds medium, and a very small amount of high severity.
• Control 3—section control 3 has a rating of medium severity over the full joint length using the 10 percent rating scheme, but the true lengths show a small amount of low severity. Section C3 in the passing lane is much better than the control C1 in the travel lane.
• Methacrylate 3—the joint distress in section M3 appears to be more severe than that of C3 when using the 10 percent rule. Using this rule, C3 is performing better than M3 with C3 having all medium severity and M3 having mostly medium-, some high-, and a very small amount of low-severity distress. The actual length of each severity shows M3 has about two-thirds of its joint length rated as low severity, one-third medium severity, and a very small amount of high severity. If the actual length of each severity is used for comparison, M3 is performing much better than C3.

Figure 47. Amount and severity of joint distress (Boron, CA, 1995).

Figure 48. Amount and severity of joint distress (Boron, CA, 1996).

Figure 49. Amount and severity of joint distress (Boron, CA, 1997).

Figure 50. Amount and severity of joint distress (Boron, CA, 1998).

Figure 51. True length of joint spalls at each level of severity (Boron, CA, 1995).

Figure 52. True length of joint spalls at each level of severity (Boron, CA, 1996).

Figure 53. True length of joint spalls at each level of severity (Boron, CA, 1997).

Figure 54. True length of joint spalls at each level of severity (Boron, CA, 1998).

In general, the sections in the travel lane had more severe joint distress than those sections in the passing lane. The control sections had the most severe joint distress in each lane relative to the treated areas. The second application of methacrylate to section M2 appeared to have helped, the severity of distress in M2 being less than that in section M1.

WHEELPATH DISTRESS

Visual surveys of the pavement sections were performed as previously done, with the wheelpath and centerline grading system changed to include sections with small, loose pieces in the high-severity (H) category. The wheelpaths and centerline were rated as follows:

• Low—no clear longitudinal cracking pattern developed.
• Medium—clear longitudinal cracking pattern developed with no spalls greater than 7.6 cm.
• High—clear longitudinal cracking pattern developed with spalls greater than 7.6 cm, or small, loose pieces.

Table 24 shows the number of slabs in each section at each level of severity for all years of the study. Some variability in the ratings occurred due to site lighting conditions and other inspection variations. In 1997, all the methacrylate-treated systems had a combination of low-and medium-severity cracking. There was little difference between section M2, which had the second application of methacrylate, and section M1, which only had one application. Both control sections had the most severe cracking with control section C1, which is in the No. 2 travel (truck) lane, having the most severe cracking. Section C1 had medium- and high-severity cracking while C3 had mostly medium severity with a small amount of low-severity cracking. In 1998, C1 still had the most severe cracking. The severity of cracking in all the other sections but M3 had increased. Sections M1 and M2 had medium-severity cracking over the wheelpaths of all slabs in 1998.

CENTERLINE DISTRESS

Table 25 shows the number of slabs in each section at each level of severity for all 5 years of the study for the centerline area of the sections. The same trend is evident here as in the wheelpath ratings. The ratings for all sections except M3 were more severe in 1998. Sections M1 and M2 were actually rated less severe than M3 in 1997, but in 1998 they were rated more severe then in previous years. The two control sections were rated the most severely distressed with C1 rated more severe than C3. Overall, the ratings in the centerline areas were much less severe than for the wheelpath areas.

ELASTIC MODULUS AND COMPRESSIVE STRENGTH

At least four cores were removed from each section, with many of the removed cores extracted in small, already fractured pieces. The cores were 1.22 and 1.83 m from the shoulder stripe to reflect wheelpath and centerline areas, respectively. The specific locations were chosen to avoid interfering with previous cores. If a core was retrieved in a broken or damaged condition, another core was taken approximately 0.61 m east of the original core at the same distance from the shoulder stripe.

The cores were tested to determine the compressive strength and elastic modulus of the concrete in both wet and dry conditions. The cores were tested in a dry as-received condition, then soaked in lime-saturated water for 2 weeks and retested. After the wet modulus tests were performed, the cores were tested to determine their compressive strength. The results of the dry modulus testing are shown in table 26. The results of the wet modulus testing are shown in table 27.

1 psi = 6.89 kPa

1 psi = 6.89 kPa

The results of the modulus testing show there is not much difference in modulus from one section to another. The wet and dry modulus values were generally similar. The one consistent trend is that the modulus for section M3 was the lowest in every year.

The wet lime-saturated compressive strength results are given in table 28. The compressive strength results show no significant difference between the sections. Generally, there has been a decrease in strength of each section over the test years.

The cores tested may represent a minimum strength or modulus for intact cores. If a core was taken and it fell apart as it was being removed, another core was drilled. This biases the results because only solid cores can be tested.

RELATIVE HUMIDITY MEASUREMENTS

Relative humidity samples were removed from one or two locations in each section at various depth intervals, using a 38.1-mm-diameter bit and rotary hammer. The depth intervals and results of the relative humidity testing are shown in tables 29 through 33. Most of the relative humidity measurements were above 80 percent, especially below a depth of 10.2 cm. These results indicate that even though the pavement is located in a very dry climate, sufficient moisture is still present to sustain the ASR. The humidity results for the bridge were much lower than the pavement. This is encouraging and indicates that methacrylate treatment of bridge decks may be much more effective at slowing ASR than when treating pavements.

1 inch = 2.54 cm

1 inch = 2.54 cm

1 inch = 2.54 cm

1 inch = 2.54 cm

1 inch = 2.54 cm

PETROGRAPHIC EXAMINATION

Two cores from each section were examined petrographically to document the condition of the concrete. The cores were cut length-wise and polished. These sections were then soaked overnight and dried, and the entire lapped surface was traversed under a stereo microscope. Each lapped surface was divided into five or more traverse areas and examined at magnifications of 10 to 30 times. Because of their smaller diameters (6.99 cm (2.75 inches)), the Boron overhead bridge cores were divided into four traverses. All instances of cracks, alkali-silica gel, and deteriorated or reacted aggregate particles were counted. The petrographer’s notes for each year are included in appendix C. Table 34 gives a numerical summary of the findings for 1997 and 1998.

A summary description of the cores from each section follows:

• Boron overhead (bridges)—cores from 1997 and 1998 have shown moderately severe distress. This concrete is also poorly air-entrained. The top surface appeared moderately worn and partially coated with methacrylate.
• Control 1—the wearing surface of the cores for the past 3 years (1996, 1997, 1998) was moderately to severely worn with frequently exposed fine aggregate particles. All of these cores appeared to be air-entrained with approximately 5 percent entrained air. The condition of the cores was classified as moderately distressed in 1996 and severely distressed in 1997 and 1998. Observations indicated moderately frequent popouts over fine and coarse aggregates in the past 2 years. Microcracks, reacted particles, and gel locations are abundant and widespread within the concrete for all 3 years. Most, if not all, potentially reactive particles have reacted to some extent.
• Control 3—the cores from 1996, 1997, and 1998 were classified as severely distressed with extensive microcracking throughout the cores. Multiple generations of alkali-silica gel are abundant and ubiquitous. The top surface of the cores, from 1997 and 1998, was severely worn and had frequent exposed aggregate particles and worn popouts. The cores seemed to be well air-entrained with approximately 5 to 6 percent air content.
• Methacrylate 1—the surface of the cores taken in 1997 and 1998 were severely worn with frequently exposed fine aggregate particles. The cores were classified as moderately severely to severely distressed. There was an abundance of reacted particles, microcracks, and gel locations within the concrete matrix. All potentially reactive aggregate particles appeared to have reacted and some were deteriorated. The core from 1996 showed microcracks perpendicular to the wearing surface filled with resin. The cores appeared to be marginally air-entrained, with an estimated air content of 4 to 5 percent.
• Methacrylate 2—the wearing surface was severely worn. Aggregate particles were frequently exposed and polished. The cores were classified as moderately severe to severely distressed. The core from 1996 had a darkened area of the paste in the top 5 millimeters from the surface treatment. Distress was not prevalent in that area. The rest of that core and the cores from 1997 and 1998 had microcracks widespread throughout the core. Multiple generations of gel were generally ubiquitous and moderately abundant to abundant. The cores were marginally air-entrained, with an estimated air content of 4 percent.
• Methacrylate 3—the surface of the 1997 core was worn and partially coated. Occasional popouts over aggregates were evident. The core from 1998 had a severely worn surface with frequently exposed and polished aggregate particles. The cores were classified as moderately severely distressed. All potentially reactive particles appeared to have reacted to varying degrees. Multiple generations of gel were abundant.

SUMMARY OF BORON, CA TEST SITE

HMWM resin was topically applied to desert pavement sections with moderate to severe ASR distress. The methacrylate has extended the pavement life by filling cracks bonding the pieces of concrete and reducing spalling, especially near joints. The service life extension of one coat of HMWM appears to be about 3 to 5 years. Two coats of resin improved performance further. It is envisioned that periodic reapplication of HMWM would reduce future concrete spalling and continue to extend the pavement life.

HMWM resin was also applied to a bridge deck having low to moderate ASR distress. The resin had been effective in bonding and sealing almost all of the cracks. No new visible cracking was noted over the study period. The relative humidity in the deck concrete is moderately low and to a level that should slow ASR deterioration. Preliminary results are promising and continued monitoring of this structure is recommended.