s Chapter 2 - Highway Concrete Technology Development and Testing Volume Iv:Field Evaluation of SHRP C-206 Test Sites (Early Opening of Full-Depth Pavement Repairs), July 2006 - FHWA-RD-02-085
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Publication Number: FHWA-RD-02-085
Date: July 2006

Chapter 2

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DESCRIPTION OF FIELD SECTIONS

The Georgia site consists of three test sections located on eastbound U.S. Interstate 20 (I-20), near Augusta, GA, between mileposts 189 and 192. The existing pavement at this site is 230-millimeter (mm) jointed plain concrete pavement (JPCP) with 9-meter (m) joint spacing. The two-way annual average daily traffic (ADT) at this location was 25,750, with 19.5 percent trucks. The average truck factor during the time of field testing was 1.37.

The materials tested at this site include Georgia Department of Transportation’s 4-hour (h) mix (GADOT), Fast Track I (FT I), and Very-High-Early-Strength (VES). The mix designs for these materials are given in table 1. GADOT has extensive experience with fast-track full-depth repairs, and the SHRP C-206 repairs were included as a part of an on-going repair project. FT I is a 12- to 24-hr opening PCC mix developed by the Iowa DOT (Grove, Jones, and Bharil, 1993). VES is a 4-hr h opening PCC mix that utilizes a nonchloride accelerator (calcium nitrite) developed under SHRP C-205.

Table 1. Mix design for the materials used at the Georgia site (Whiting et al., 1994).
Mix Component
(per cubic yard (yd3))
GADOT FT I VES
Cement type Type I Type III Type III
Cement, pound (lb) 752 740 870
Fine aggregate, lb 1,025 1,320 825
Coarse aggregate, lb 1,805 1,420 1,720
Water, lb 285 262 335
Water reducer, ounce (oz) 44.0
Accelerator (DSA), gallon (gal) 6.0
Accelerator (CaCl2), gal 1.6
High-range water reducer, oz 43.5
Air entraining agent, oz 9.8 12.0 43.5
w/c ratio 0.38 0.35 0.39
Nominal opening time 4 hr 12 to 24 hr 4 hr

1 yd3 = 0.7645 m3; 1 lb = 0.4535 kg; 1 gal = 3.78 liter (L);
1 oz = 29.57 millileter (mL)

w/c = water to cement ratio

The Georgia sections were placed between about 10 p.m. and 2 a.m. and opened to traffic at 6 a.m. At this site, a typical day’s work started at 6:30 p.m. with the closing of the work area to traffic. Concrete removal started as soon as enough of the work area was blocked off, and concrete placement typically started at 10 p.m. (Whiting et al., 1994).

Table 2 provides a summary of Georgia sections, including the strength at opening for each repair and calculated fatigue damage due to early opening. Fatigue damage due to early opening was defined as the damage incurred within the first 14 days of service in this project, based on typical curing time and the strength at the opening time for conventional projects. Fatigue damage was calculated on an hourly basis for the first 3 days, then on a daily basis for the remaining 11 days.

Table 2. Summary of Georgia sections.
Repair Number Repair Size, Ft Age at Opening
Hour, Days
Strength at Opening, Psi Early Opening Damage*
fc' Modulus of
Rupture
Section 1, GADOT
1-1 8 7.8 2,250 365 0.001
1-3 8 7.2 2,050 350 0.001
1-4 8 7.1 2,050 350 0.001
1-5 8 6.8 1,950 340 0.001
1-6 8 6.8 1,950 340 0.001
1-7 15 6.6 1,900 330 0.038
1-8 15 7.8 2,250 365 0.036
1-9 8 7.7 2,250 360 0.001
1-10 8 7.5 2,150 360 0.001
1-11 15 6.3 1,800 320 0.040
1-12 8 6.0 1,700 310 0.002
1-13 8 5.9 1,650 305 0.003
1-14 15 5.7 1,550 295 0.047
1-15 8 5.7 1,550 295 0.003
1-16 16 5.2 1,350 270 0.057
1-17 15 4.8 1,200 245 0.059
1-18 15 4.8 1,200 245 0.059
1-19 15 4.3 1,000 200 0.067
1-20 15 4.0 900 170 0.103
Section 2, FT I
2-3A 7 8.8 1,300 250 0.006
2-4 10 8.5 1,300 245 0.011
2-5 6 8.3 1,250 245 0.003
2-6 12 8.3 1,250 245 0.048
2-7 10 8.3 1,250 245 0.011
2-8 10 8.1 1,250 240 0.011
2-9 10 7.8 1,200 230 0.012
2-10 10 7.8 1,200 230 0.012
2-11 10 7.6 1,150 230 0.012
2-12 6 7.5 1,150 225 0.004
2-13 11 7.5 1,150 225 0.027
2-14 6 7.3 1,100 220 0.004
2-15 6 7.2 1,100 215 0.005
2-16 6 7.1 1,100 215 0.005
2-17 6 6.8 1,000 205 0.006
2-18 7 6.8 1,000 205 0.012
Section 3, VES
3-2 12 6.7 2,600 365 0.003
3-3 12 6.3 2,500 360 0.003
3-4 12 6.0 2,450 350 0.003
3-5 12 5.8 2,350 335 0.003
3-6 8 5.6 2,350 335 0.001
3-7 12 5.5 2,200 320 0.003
3-8 8 5.2 2,100 305 0.001
3-9 8 4.9 2,050 300 0.001
3-10 12 4.8 2,000 295 0.004
3-11 12 4.6 1,950 290 0.004
3-12 8 4.3 1,800 270 0.002
3-13 8 4.3 1,800 270 0.002
3-14 12 4.2 1,700 260 0.014
3-15 9 4.1 1,650 255 0.005
3-16 12 3.8 1,550 230 0.015
3-17 8 3.7 1,500 225 0.008
3-18 8 3.7 1,500 225 0.008
3-19 8 2.8 1,050 165 0.073
3-20 8 2.7 1,000 155 0.122

*Miner’s fatigue damage.

1 m = 3.28 ft;
1 megapascal (MPa) = 145.04 pounds per square inch (psi)

PERFORMANCE OF GEORGIA SECTIONS

In general, the Georgia sections provided excellent performance. After 6 years of service, the only patches that developed any distresses were the 4.6-m repairs in the GADOT section and one 2.4-m repair in the same section. Faulting was minimal (less than 1 mm) and remained unchanged (within measurement error) throughout the monitoring period, although the LTE was somewhat less than that found in new pavements with an effective load transfer design. A summary of joint performance data is given in table 3; detailed data are given in appendix B. The Georgia sections also did not exhibit any material-related distresses.

ANALYSIS OF CRACKING IN GADOT SECTION

The cracking of the longer (4.6-m) repairs in the GADOT section is consistent with expectations. The Georgia sections were placed at night and opened to traffic at 6 a.m. At the time of concrete hardening, there was no difference in the temperature between the top and bottom of the PCC slab. Thus, the repair slabs were built flat with no built-in temperature gradients. Although an excessive built-in negative temperature gradient is undesirable because it contributes to top-down cracking, a moderate amount of built-in negative curling is beneficial because it moderates the effects of high daytime temperature gradients (Yu et al., 1998). Without any built-in curling, the 4.6-m repair length is excessive for a 230-mm repair slab. Differential shrinkage does provide equivalent built-in temperature of about –2.2 °C (28.04 °F), but that is not enough to counter sufficiently the effects of high daytime temperature gradients.

Table 3. Summary of joint performance of Georgia sections.
Section Faulting, inch* Average LTE, percent
1994 1995 1996 1997 1998 1992 1996
GA DOT 0.04 0.01 0.01 0.01 0.01 73 75
FT I 0.04 0.03 0.03 0.03 0.03 77 72
VES 0.04 0.01 0.01 0.00 0.03 77 80

*Average absolute faulting.

1 in = 25.4 mm

The cracking problem was analyzed using the fatigue calculation procedure and model developed by Yu and colleagues (1998). The traffic data needed for the fatigue analysis are shown in figure 1. The traffic on I-20 through the project site is relatively high. The annual traffic is about 1.1 million equivalent single axles (ESALs) in the design lane.

This project did not include a material-testing program; therefore, certain assumptions had to be made regarding long-term strength development of the GADOT mix. Under SHRP C-206, extensive laboratory testing of repair materials was conducted to develop correlation relationships for maturity and pulse-velocity methods of determining in-place material properties (Whiting et al., 1994). Those tests showed that for the GADOT mix, the 90-day compressive strength is about 9 percent greater than the 28-day strength. Also under SHRP C-206, cores were retrieved from the test sections during a 2-month evaluation and tested for strength. Figure 2 summarizes the available information on Georgia site materials.

Figure 1. Estimated traffic on Georgia site.

This figure is a graph showing traffic data needed for the fatigue analysis. Years, from 1991 to 2002, is graphed on the horizontal axis. Cumulative traffic, in million E S A Ls, is graphed on the vertical axis from zero to 14. Two-way average daily traffic equals 25,750 in 1992, 19.5 percent truck. Average truck factor equals 1.37. The annual growth in E S A Ls is 3 percent. The line begins in 1992 at zero million E S A Ls and increases in a straight line to 12 million in 2001

Figure 2 shows lower strength for cores retrieved at 2 months, but this is likely caused by damage during coring or shipping of the cores and testing variability. Extensive material testing was conducted under task C of this project for VES and HES mixes, and the results of those tests showed that the long-term (5-yr) strength of those mixes is up to 18 percent greater than the 28-day strength. A comparison of early-age (up to 90 days) strength-gain characteristics of these mixes suggests that the long-term strength-gain characteristics of the GADOT mix should be similar to those of VES and HES. Based on this assumption, figure 3 was developed to show the long-term strength development of the GADOT mix.

Figure 2. Available material strength data for the Georgia sections.

This figure is a histogram showing lower strength for cores retrieved at 2 months and 28-day lab. Three sections, Georgia Department of Transportation parenthesis G A D O T end parenthesis mix, Fast Track 1 parenthesis F T 1 end parenthesis, and very early strength parenthesis V E S end parenthesis are graphed on the horizontal axis. Compressive strength, measured in poundforce per square inch parenthesis P S I end parenthesis is graphed on the vertical axis from zero to 7,000. For all three sections, the 28-day labs have higher results than the cores at 2 months. For the 28-day lab, G A D O T has 5,600 P S I, F T 1 has 5,700 P S I, and V E S has 6,500 P S I. For the cores at 2 months, G A D O T has 4,800 P S I, F T 1 has 4, 500 P S I, and V E S has 5,800 P S I.

1 megapascal (MPa) = 145.04 psi

Figure 3. Estimated strength development of GADOT mix.

This figure is a line graph showing long-term strength development of the G A D O T mix. The year is graphed on the horizontal axis from 1991 to 1999. Portland cement concrete parenthesis P C C end parenthesis modulus of rupture is graphed on the vertical axis from 640 P S I to 760 P S I. Starting in 1992 and 645 P S I, the strength increases to 710 P S I within a year. By 1994, the strength increases to 738 P S I. After 1994, the strength slowly increases steadily to 750 P S I in 1998.

1 MPa = 145.04 psi

The results of fatigue analysis are shown in figure 4, along with the observed slab cracking. The model was run with built-in curling of –2.2 °C (28.04 °F), which accounts for differential shrinkage. The effects of damage due to early opening are illustrated in figure 5. As shown in table B1 in appendix B, the amount of fatigue damage attributable to early opening was minimal (Miner’s damage of 0 to 0.07, except for 0.10 for the last patch). The damage due to early opening has the effect of shifting the time (or traffic) versus cracking curve upward, as illustrated in figure 5. However, for the Georgia sections, early opening to traffic had a negligible effect on the fatigue life of the repairs, even for the 4.6-m repairs. In fact, the last three 4.6-m repairs placed in the GADOT section (i.e., the repairs that were opened to traffic at the lowest strength) did not crack. For shorter repairs, the effects of early opening (and fatigue damage in general) are inconsequential.

Figure 4. Comparison of field performance of 4.6-m repairs in the GADOT section and predicted cracking using the rigid pavement performance/rehabilitation (RPPR) 1998 model (Yu et al., 1998).

This figure is a line graph. The year is graphed on the horizontal axis from 1991 to 2002. Percent of slab cracking is graphed on the vertical axis from zero to 100. The R P P R model begins in 1992 at 3 percent cracking. The model increases gradually to 65 percent in 2001. The field performance was repaired in 1992 where there was zero cracking, in 1994 and 1995 where there was 20 percent cracking, in 1996 at 30 percent cracking, and in 1997 and 1998 at 50 percent cracking. The performance increases each year.

Figure 5. Illustration of the effects of damage due to early opening.

This figure is a line graph showing the effects of damage due to early opening. Years are graphed on the horizontal axis from 1991 to 2002. The percent slab cracking is graphed on the vertical axis from zero to 80 percent. There are dual, parallel lines starting in 1992 at 5 and 6 percent cracking, respectively. The lines increase gradually to 65 and 66 percent in 2001. The space between the two lines represents the effects of damage due to early opening.

Figure 6 shows the effects of repair length and built-in curling on the fatigue performance of full-depth repairs. For bottom-up transverse cracking, the GADOT section represents the most adverse condition, because the repairs hardened with zero built-in temperature gradient.

However, even under this condition, the 3.7-m repairs have an expected fatigue life of 10 or more years; shorter repairs should have practically unlimited fatigue life. Figure 6 also shows that if moderate built-in curling were introduced, the fatigue life of the 4.6-m repairs would increase dramatically. In this example, a total effective built-in temperature gradient of –5 °C (23 °F) was used, including the effects of temperature and differential shrinkage. This is a typical magnitude of built-in curling for PCC pavements in wet-nonfreeze climates. In general, for daytime construction, excessive built-in curling is more of a problem than is an inadequate amount of built-in curling.

Figure 6. The effects of repair length and built-in curling on performance of full-depth repairs.

This figure is a line graph with 3 different lines, which are 15-foot repairs, 15-foot repairs with typical amount of built-in temperature gradient, and 12-foot repairs. Years are graphed on the horizontal axis from 1991 to 2002. Percent of slab cracking is graphed on the vertical axis from zero to 70 percent. All the lines begin in 1992. The 15-foot repairs line begins at 3 percent in 1992 and increases in a 45-degree angle to 65 percent in 2001. The 15-foot repair with typical amount of built-in temperature gradient line begins in 1992 with 1 percent cracking and increases gradually to 15 percent in 2001. The 12-foot repairs line begins in 1992 with 1 percent cracking and increases minimally to 5 percent in 2001. Figure 6 shows that if moderate built-in curling were introduced, the fatigue life of the 15-foot repairs would increase dramatically.

 

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