Evaluation and Mix Design of Cement-Treated Base Materials with High RAP Content Paper Number 11-2742 2011 Annual TRB Meeting Deren Yuan Research Engineer Center for Transportation Infrastructure Systems The University of Texas at El Paso 500 W. University Ave., El Paso, Texas 79968 Tel: (915)-747-5474, Email: [email protected]Soheil Nazarian Professor and Director of Center for Transportation Infrastructure Systems The University of Texas at El Paso 500 W. University Ave., El Paso, Texas 79968 Tel: (915)-747-6911, Email: [email protected]Laureano R. Hoyos Associate Professor Department of Civil Engineering The University of Texas at Arlington Arlington, Texas 76019 Tel: (817)-272-3879, Email: [email protected]Anand J. Puppala Professor Department of Civil Engineering The University of Texas at Arlington Arlington, Texas 76019 Tel: (817)-272-3879, Email: [email protected]Item Number Words Abstract 1 250 Text 3850 Table 1 250 Figure 12 3000 Total 7350 TRB 2011 Annual Meeting Paper revised from original submittal.
Transcript
Evaluation and Mix Design of Cement-Treated Base Materials with High RAP Content
PROPERTIES OF RAP 56 RAP properties are governed by the milling and crushing operation, as well as by the 57
characteristics of the aggregate, binder and age from which the RAP is obtained. Since the 58
quality of virgin aggregate used in asphalt concrete usually exceeds the requirements for granular 59
aggregate used in base courses, there are generally no durability concerns regarding the use of 60
RAP in base courses. The main properties of RAP considered here are the gradation, asphalt 61
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Yuan et al. Paper No. 11-2742 3
content and sand equivalency value. Sieve analysis, asphalt content test, and sand equivalency 62
test were performed on each of the six randomly sampled RAP materials from each stockpile. 63
The particle size distribution of milled RAP is determined by the characteristics of the 64
milling unit, speed of and temperature during milling operation and the original HMA gradation 65
and binder content. Figure 1a shows the average gradation curves of the RAP from the six 66
stockpiles obtained through dry sieving. For comparison, typical range of particle size 67
distribution of RAP reported by FHWA (6) and the upper-lower limits for Grade 1 (high quality) 68
base materials specified by TxDOT are also shown in this figure. The lack of aggregates passing 69
No. 40 sieve is evident, similar to the findings in a previous study in Texas (7). A significant 70
portion of coarse aggregates visually consisted of a conglomerate of finer particles. Wet sieving 71
was not deemed effective in breaking down these aggregates because of the gluing action of the 72
binder. The differences in the average gradations among all six RAP materials are not very 73
significant with the largest variation of about 15% occurring around No. 4 sieve. The coefficient 74
of variation among the results from the six samples of each RAP stockpile increased as particle 75
size decreased from less 1% for aggregates retained on 1 in. sieve to about 50% for particles 76
passing No. 200 sieve. 77
Asphalt contents of RAP were determined by using NCAT ignition oven method. The 78
RAP samples from each of the six locations within a stockpile were divided into the following 79
three bins: 80
Bin 1: particles retained on 0.5 in. sieve 81
Bin 2: particles passing 0.5 in.-sieve and retained on No. 4 sieve 82
Bin 3: materials passing No. 4 sieve 83
The asphalt contents by bin and by weighted average for all RAP materials are shown in Figure 84
1b. The lowest asphalt contents were usually observed for Bin 2. The unusually high asphalt 85
content in Lubbock RAP can be attributed to a significant amount of recycled surface treatment 86
that manifested as disk-shape aggregates. 87
Average sand equivalency values (ASTM D 2419) for six samples of each stockpile 88
varied from 50% to 91%. The standard variation among individual stockpiles varied from 1.7% 89
to 5.6%. The high sand equivalency values can be attributed to the asphalt binders coating finer 90
aggregates. 91
92
LABORATORY EVALUATION OF RAP MIXES 93 Since the main goal of this study is to examine the feasibility of using mixes with high RAP 94
contents, only mixes containing 100%, 75% and 50% RAP were utilized. For mixes with 75% 95
and 50% RAP, both virgin and recycled base materials, when available, were added to the RAP. 96
Four levels of cement content, 0%, 2%, 4% and 6%, by dry weight were used for all 97
mixes except for 100% RAP. Stable specimens could not be made from the untreated (0% 98
cement) mixes of 100% RAP. As listed in Table 1, since six RAP materials and eight granular 99
base materials were used in this study, there are 18 (3 x 6) mixes for 100% RAP, 32 (4 x 8) 100
mixes for 75% RAP and 32 (4 x 8) mixes for 50% RAP. 101
102
Evaluation Protocol and Methodology 103 Achievement of a specified strength/stiffness does not always ensure the durability of chemically 104
stabilized mixes. To develop a realistic mix design procedure for RAP mixes, a number of 105
parameters were considered. Some of these parameters were necessary for a comprehensive 106
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Yuan et al. Paper No. 11-2742 4
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a) Average Gradations of RAP 130 131
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b) Asphalt Content by Bin and by Weighted Average 149
Figure 1. Characteristics of RAP Materials Used in This Study 150
0
10
20
30
40
50
60
70
80
90
100
0.010.1110100
Sieve Size, mm
Pe
rce
nt
Pa
ss
ing
Typical FHWA Range Limits of TxDOT Grade 1
Childress El PasoFt. Worth Lubbock
Pharr Waco
#4 #40 #200
9.4
4.7 4.7
11.0
3.94.6
3.85.3
3.4
5.7
3.14.3
7.45.8 5.8
8.8
6.5 6.7
6.5
5.34.7
7.9
4.85.2
0
2
4
6
8
10
12
14
Childress El Paso Ft. Worth Lubbock Pharr Waco
RAP Source
As
ph
alt
Co
nte
nt,
%
Bin 1: > 0.5"Bin 2: 0.5" > but > 0.187" (No. 4)
Bin 3: < 0.187" (No. 4)Weighted Average
TRB 2011 Annual Meeting Paper revised from original submittal.
Yuan et al. Paper No. 11-2742 5
evaluation but may not lend themselves to the day-to-day mix design and operation for most 151
state highway agencies. These parameters and their related tests are briefly described below. 152
153
Gradation. The RAP aggregates consisting of crushed rock or gravel covered by asphalt binder 154
exhibit mechanical properties that may be much different from the aggregates in typical granular 155
base materials. As will be seen later, the strength and stiffness of a compacted cement-treated 156
RAP mixes are mainly determined by the gradation of the mix and the cement hydration rather 157
than the properties and shape of aggregate (especially for mixes with high RAP content. 158
159
Moisture-Density Characteristics. Based on this study, the optimum moisture contents (OMC) 160
and maximum dry densities (MDD) can be determined in a simplified manner. For each RAP 161
content, moisture-density curves were developed for the mixes with 0% and 6% cement contents. 162
The OMC and MDD values for mixes with 2% and 4% cement contents were estimated through 163
linear interpolation of the OMC and MDD values obtained from the mixes with 0% and 6% 164
cement contents. This was deemed justified since the variations in these two parameters between 165
0% and 6% cement contents are reasonably small. 166
167
Strength. Unconfined compressive strength (UCS, ASTM D 1633 or Tex-120-E) has been used 168
by many highway agencies in their mix design for cement-stabilized base layers as the only 169
quantitative requirement for engineering properties. A target 7-day UCS in the range of 200 psi 170
to 600 psi or more is currently adopted by different highway agencies. A minimum 7-day UCS 171
of 300 psi is used as the main criterion for cement content selection in this study, since this value 172
is used recommended by TxDOT. Requirements for other parameters such as modulus, moisture 173
susceptibility and long-term durability are established on the basis of this UCS requirement. 174
The indirect tensile strength (ITS, ASTM D 6931) could be a primary parameter for 175
evaluation and qualification of asphalt emulsion-treated or dual-stabilized (asphalts emulsion 176
plus calcium-based additive) base mixes including those containing RAP up to 80% (8). To 177
study the significance of this parameter for cement-treated RAP mixes, ITS tests were performed 178
on specimens prepared from all mixes. Each specimen for ITS testing is 6 in. in diameter and 179
about 4.5 in. in height. 180
181
Modulus. Moduli of specimens were measured through the resilient modulus (RM, AASHTO T 182
307) test and the free-free resonant column (FFRC, ASTM C 215) test. RM test is widely 183
accepted since it attempts to simulate vehicular loading conditions on pavement structures even 184
though the test is time consuming, complicated and less accurate, in particular, for stabilized 185
materials. As part of a comprehensive evaluation program in this study, RM tests were limited to 186
those mixes with the optimum cement contents and are not presented here due to space 187
limitation. 188
The FFRC test is nondestructive, rapid, reliable and easy to perform for stabilized 189
materials. The principle of the FFRC method is based on the determination of the fundamental 190
resonant frequencies of vibration of a cylindrical specimen. From the longitudinal frequency, 191
Young’s modulus (called FFRC modulus here) of the specimen can be calculated. Over the years, 192 the test setup and data reduction of this method have been significantly simplified and enhanced for 193 day-to-day use (Figure 2 and draft Tex-148-E). FFRC tests were performed on all UCS specimens 194
to see the feasibility for establishing the relationships between the FFRC modulus (instead of 195
RM) and the strength parameters from the standard tests. 196
197
TRB 2011 Annual Meeting Paper revised from original submittal.
Yuan et al. Paper No. 11-2742 6
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a) FFRC Test Setup b) Records from a FFRC Test 211
Figure 2. Free-Free Resonant Column (FFRC) Test 212 213
Moisture Susceptibility. Moisture susceptibility represents the potential of a soil to lose 214
strength/stiffness by absorbing water under capillary conditions. Moisture susceptibility is 215
particularly of major concern with the RAP blends in pavement base courses due to potential for 216
stripping. This parameter was evaluated by using tube-suction test (TST, 9). Outputs from TST 217
on a moisture-conditioned specimen include the retained strength, retained modulus and 218
dielectric constant. The retained strength is here defined as a ratio of the UCS measured after 2-219
day oven (140o F) cure and 8-day capillary soaking to the standard 7-day UCS (ASTM D 1633 220
or Tex-120-E). The current acceptance criterion for retained strength is 80%. It may be 221
reasonable to propose the same number for the retained ITS and FFRC modulus. 222
223 Long Term Durability. This parameter was studied by following the procedure of ASTM D 224
559. The procedure involves a cyclic wet-dry process that simulates rainfall events in a 225
reasonably short time period. The test was carried out by immersing samples in water at room 226
temperature for 5 hrs and then oven-drying at 160º F for 48 hrs to complete one cycle. This 227
process was repeated for up to 14 cycles. Figure 3a shows the setup of wetting-drying process. 228
After removal from the oven, the specimen was subjected to volume change and moisture 229
content measurements. After 3, 7, and 14 cycles, the specimens were subjected to UCS tests. The 230
results obtained provide adequate information whether the cement treated RAP materials are 231
durable or fail prematurely. This test was applied to those mixes with the optimum cement 232
contents. 233
234
Leachate. Due to the coarse nature of RAP materials, cement-treated RAP mixes should be 235
studied for any possible leaching of cement stabilizer due to moisture flow. Figure 3b shows the 236
apparatus for leachate test (10). The test utilizes flexible wall molds housing specimens. The 237
specimens were first cured in a moisture room for 7 days before subjecting to leachate testing. 238
This test was applied to those mixes with the optimum cement contents. Leachate was collected 239
after 3, 5, 7, 11, and 14 cycles of leaching, while the UCS tests were conducted at the end of 14 240
cycles of leaching. The leachate collected was tested for pH value change and the amount of 241
calcium present after the corresponding cycles. Results were analyzed to address the loss of 242
cement due to leaching. 243
TRB 2011 Annual Meeting Paper revised from original submittal.
Yuan et al. Paper No. 11-2742 7
244
a) Wetting b) Drying 245
a) Setup for Wetting/Drying Process 246
247
b) Apparatus for Leachate Test 248
249
Figure 3. Test Setups for Long-Term Durability and Leachate Tests 250 251
TRB 2011 Annual Meeting Paper revised from original submittal.
Yuan et al. Paper No. 11-2742 8
Presentation and Discussion of Results 252
Moisture-Density Characteristics 253 Figure 4a shows the variations in OMC and MDD with different RAP contents for the untreated 254
mixes containing virgin base materials. In general, both OMC and MDD decrease as RAP 255
content increases except for OMC with Ft. Worth mixes. Figure 4b compares the OMC and 256
MDD for mixes of 100% RAP without and with 6% cement. The OMC and MDD of all mixes 257
are greater with 6% cement than those without treatment. The average differences are about 258
1.2% for OMC and 3.5 pcf for MDD. These two numbers may have significance for roadway 259
maintenance and minor rehabilitation projects as well as quality assurance if only the moisture-260
density curve is developed for untreated mixes in the laboratory. 261
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a) Variations of OMC and MDD of Untreated Mixes with RAP Content 275
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b) OMC and MDD of 100% RAP Mixes without Treatment and Treated with 6% Cement 290 291
Figure 4. Moisture-Density Characteristics of RAP Mixes 292
293
Effect of Asphalt Content 294 As shown in Figure 2b, the asphalt contents of RAP materials collected from the six stockpiles 295
cover a quite large range from 4.7% to 7.9%. The effects of asphalt content on strength and 296
6.6
6.1
4.8
7.2 7
.7
7.6
6.5
5.8
5.2
6.6 7
.2
6.9
5.4
5.2
6.0 6.4
5.2
6.2
0
2
4
6
8
10
12
CHR ELP FTW LBB PHR WAC
Material Source
OM
C, %
50% RAP 75% RAP 100% RAP
13
3.2
13
1.8
12
5.6
12
8.8
11
9.8
11
7.3
12
5.5
121
.7
12
4.8
11
9.6
11
6.3
12
3.2
116
.0
115
.9 121
.7
119
.3
10
8.5
13
0.0
100
110
120
130
140
150
CHR ELP FTW LBB PHR WAC
Material Source
MD
D, p
cf
50% RAP 75% RAP 100% RAP
5.4 5.26.0
6.4
5.2
6.26.5 6.47.1
8.2
6.3
7.2
0
2
4
6
8
10
12
CHR ELP FTW LBB PHR WAC
RAP Source
OM
C, %
0% Cement 6% CementOMC
123
.2
118
.0
11
6.9
11
9.7
119
.3
11
1.5
12
6.7
120
.8
12
2.3
12
2.9
12
2.4
11
5.3
90
100
110
120
130
140
150
CHR ELP FTW LBB PHR WAC
RAP Source
MD
D, p
cf
0% Cement 6% CementMDD
TRB 2011 Annual Meeting Paper revised from original submittal.
Yuan et al. Paper No. 11-2742 9
modulus for all mixes with 100% RAP are shown in Figure 5. Strength and modulus are perhaps 297
independent of asphalt content for different levels of cement treatment, even for the RAP from 298
Lubbock stockpile with 7.9% asphalt content. 299
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Figure 5. Variations of UCS with Asphalt Content in Mixes of 100% RAP 337
338
Effect of Fine-Grained Aggregate 339 The lack of particles passing No. 40 sieve is apparent in all RAP materials collected as shown in 340
Figure 1. In particular, the fines contents (particles passing No. 200 sieve) are about 1% or less. 341
This occurs because the fines in RAP manifest themselves as larger particle sizes in the presence 342
0
50
100
150
200
250
300
3 4 5 6 7 8 9
Asphalt Content, %
UC
S, p
si
2% Cement
150
0
100
200
300
400
500
600
3 4 5 6 7 8 9
Asphalt Content, %
UC
S, p
si
4% Cement
290
0
200
400
600
800
3 4 5 6 7 8 9Asphalt Content, %
UC
S, p
si
6% Cement
440
TRB 2011 Annual Meeting Paper revised from original submittal.
Yuan et al. Paper No. 11-2742 10
of asphalt binder. As shown in Figure 6, the higher the fines content is, the higher the UCS 343
seems to be. Similar effects were also found for ITS and FFEC modulus. 344
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Figure 6. Effect of Percent Aggregates Passing No. 40 Sieve on UCS for 100% RAP Mixes 363
364 The fines contents (particles passing No. 200 sieve) of the granular base materials 365
collected for this study are significantly higher (from 1% to 6%). Thus, for mixes with different 366
RAP contents, the total finer contents in these mixes are different. Figure 7 shows an example of 367
the positive impact of fines content on the UCS for El Paso materials. Again, similar effects were 368
also found for ITS and FFRC modulus. Of course, other material properties may also affect the 369
strength and modulus of a cement-treated mix. However, the effect of materials passing No. 40 370
sieve on strength and stiffness seems to be significant for cement-treated RAP mixes 371
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Figure 7. Effect of Fines Content on UCS 388
0
200
400
600
800
1000
1200
0% 2% 4% 6%
Cement Content
UC
S, p
si
100% RAP (0.3% Fines)
75% RAP (1.5% Fines)
50% RAP (2.7% Fines)
0
100
200
300
400
500
5%
(WAC)
6%
(ELP)
7%
(FTW)
11%
(LBB)
11%
(CHR)
12%
(PHR)
Aggregates Passing No. 40 Sieve in RAP
UC
S, p
si
2% Cement
4% Cement
TRB 2011 Annual Meeting Paper revised from original submittal.
Yuan et al. Paper No. 11-2742 11
Effect of Coarser Aggregate 389 Figure 8 shows the gradation curves of RAP, recycled base and virgin base collected 390
from Pharr stockpiles. The gradations of the two bases are very different except for the particles 391
passing No. 100 sieve. However, with 2% cement treatment, the two mixes, 50% RAP plus 50% 392
recycled base and 50% RAP plus 50% virgin base, provide quite similar strength and modulus 393
values. That is, 396 psi vs. 359 psi for UCS, 51 psi vs. 46 psi for ITS, and 1350 ksi vs. 1233 ksi 394
for FFRC modulus. This example indicates that the particle size distribution of coarse aggregate 395
has a lesser role on strength and modulus of cement-treated RAP mixes. The significance of this 396
phenomenon is that under cement treatment more RAP resources can be used in base course 397
applications. 398
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Figure 8. Gradations of RAP, Recycled Base and Virgin Base 418 419
Moisture Susceptibility 420 The average retained UCS, ITS and FFRC moduli for all mixes involved in tube suction tests are 421
shown in Figure 9. The bar on each value corresponds to ± 1 standard deviation. All three 422
parameters meet or closely meet the requirement of 80% retained values. The smaller retained 423
ITS can be attributed to the shorter specimen heights relative to those used for the UCS and 424
modulus tests (about 4.5 in. vs. 8 in.), and thus the moisture due to capillary has more effect on 425
the properties of ITS specimens. The longer error bars for the retained ITS can be attributed to 426
the uncertainty in indirect tensile testing. Dielectric constant measurement was applied to all 427
specimens involved in the moisture susceptibility study. All dielectric values were significantly 428
less than 10 (a recommended value by TxDOT draft Tex-144-E). Thus, dielectric constant 429
seems to have less meaning for cement-treated materials. 430
431
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433
0
10
20
30
40
50
60
70
80
90
100
0.010.1110100
Sieve Size, mm
Pe
rce
nt
Pa
ss
ing
TxDOT Limits for Grade1
RAP
Recycled Base
Virgin Base
#4 #40 #200
TRB 2011 Annual Meeting Paper revised from original submittal.
Yuan et al. Paper No. 11-2742 12
Figure 9. Average Retained Strengths and Modulus 434 435
Long Term Durability and Leachate 436 Figure 10 presents the results from wet-dry tests on the mixes of Childress and Ft. Worth 437
materials to assess the long-term durability of different mixes. Term “original” in the figure 438
stands for the UCS measured on specimens subjected to the 7-day standard cure. All three Ft. 439
Worth mixes exhibit high retained UCS strengths even after 14 cycles of wetting-drying. The 440
retained strengths of mixes from Childress exhibit different patterns and the retained strength of 441
the mix of 100% RAP decreases significantly. The adequate strength of a RAP mix from 442
standard cure may not always ensure its long-term durability even though the wet-dry testing 443
simulates an extreme situation of moisture damage. Results from leachate tests indicate that the 444
loss or leaching of cement for most treated mixes is not significant (less than 50 ppm in terms of 445
calcium ion concentration), and pH values almost keep constant after 14 leaching cycles. Rich 446
limestone in granular base materials may have an impact on leachate testing. 447
448
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460
461
Figure 10. Variation of UCS with the Number of Wetting-Drying Cycles 462
0
20
40
60
80
100
120
140
100% RAP 75% RAP 50% RAP
Mix
Reta
ined
Str
en
gth
/ M
od
ulu
s, %
UCS ITS FFRC Modulus
0
100
200
300
400
500
600
700
100% RAP
(4% Cement)
75% RAP
(4% Cement)
50% RAP
(2% Cement)
Nnumber of Wet-Dry Cycles
UC
S, p
si
Oginal
3 Cycles7 Cycles
14 Cycles
a) Childress
0
100
200
300
400
500
600
700
100% RAP
(4% Cement)
75% RAP
(4% Cement)
50% RAP
(2% Cement)
Nnumber of Wet-Dry Cycles
UC
S, p
si
Oginal
3 Cycles7 Cycles
14 Cycles
b) Ft. Worth
TRB 2011 Annual Meeting Paper revised from original submittal.
Yuan et al. Paper No. 11-2742 13
Strength and Modulus vs. Cement Content and RAP Content 463 The UCS, ITS and FFRC modulus values for all mixes with different cement contents and 464
different RAP contents are summarized in Figure 11. Once again, the error bars corresponds to ± 465
one standard deviation. The effects of cement content and RAP content on strength and modulus 466
are evident. The large standard deviations can be attributed to the variability in RAP and 467
granular base materials from different sources. The larger variations for ITS may also be 468
attributed to the mechanism of indirect tensile testing. 469
Figure 11. Variations of Average UCS, ITS and FFRC Modulus with Cement Content 470
471
MODELS FOR MIX DESIGN 472 One of the main objectives of this study is to provide an easy way to determine the optimum 473
cement content for cement-treated RAP mixes. As shown in Figure 12, linear relationships 474
represent well the dependence of average UCS, ITS and FFRC modulus values on cement 475
content for all mixes involved in this study. The results shown Figure 12 indicate that for a 300-476
psi UCS, the optimum cement contents are about 4%, 3% and 2% for mixes with 100% RAP, 477
75% RAP and 50% RAP, respectively. Also, corresponding to a 300-psi UCS, the ITS would be 478
about 40 psi and FFRC modulus about 1000 ksi. In addition, in terms of per 1% cement, the 479
average rates of increase in UCS (the slopes of the lines) are 73 psi for 100% RAP content, 115 480
psi for 75% RAP content, and 145 psi for 50% RAP content. Since the relationships were 481
developed based on the RAP and granular base materials from only six stockpiles in Texas, they 482
need to be refined when a larger database becomes available. The large standard deviation 483
reelected as error bars in Figure 11 clearly indicates that the typical cement contents proposed 484
here should be validated through laboratory testing for a given mix before they can be used in 485
construction. 486
0
300
600
900
1200
0% 2% 4% 6%
Cement Content
UC
S,
psi
100% RAP
75% RAP
50% RAP
0
500
1000
1500
2000
2500
0% 2% 4% 6%
Cement Content
FF
RC
Mo
du
lus,
ksi 100% RAP
75% RAP
50% RAP
0
20
40
60
80
100
120
140
0% 2% 4% 6%
Cement Content
ITS
, p
si
100% RAP
75% RAP
50% RAP
TRB 2011 Annual Meeting Paper revised from original submittal.
Yuan et al. Paper No. 11-2742 14
487
488
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518
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524
525
526
527
528
529
530
Figure 12. Relationships between Average UCS, ITS and FFRC Modulus and 531
Cement Content 532
R2 = 0.9992
R2 = 1R
2 = 0.9995
0
300
600
900
1200
0 1 2 3 4 5 6
Cement Content, %
UC
S, p
si
100% RAP
75% RAP
50% RAP
300 psi
R2 = 0.9999
R2 = 0.9963
R2 = 0.9976
0
20
40
60
80
100
120
140
0 1 2 3 4 5 6
Cement Content, %
IDT
S, p
si
100% RAP
75% RAP
50% RAP
R2 = 0.9896
R2 = 0.9728R
2 = 0.9357
0
500
1000
1500
2000
2500
0 1 2 3 4 5 6
Cement Content, %
FF
RC
Mo
du
lus
, k
si 100% RAP
75% RAP
50% RAP
TRB 2011 Annual Meeting Paper revised from original submittal.
Yuan et al. Paper No. 11-2742 15
CONCLUSIONS 533 Eighty untreated and cement-treated mixes consisting of the RAP from 6 stockpiles and the 534
granular materials from 8 stockpiles in Texas were evaluated to develop a realistic mix design 535
procedure for high-RAP-content mixes used in roadway base course construction. The results 536
from the study can be concluded as follows: 537
538
• The RAP content in a mix strongly impacts strength, modulus and durability of the mix. 539
• For a UCS of 300-psi, the average optimum cement contents are about 4%, 3% and 2% for 540
mixes of 100% RAP, 75% RAP and 50% RAP, respectively. 541
• The results from UCS, ITS and FFRC modulus tests are quite consistent. Corresponding to a 542
300-psi UCS, ITS and FFRC modulus are about 40 psi and 1000 ksi, respectively. 543
• For the mixes that meet the 300-psi UCS requirement, the average retained UCS, ITS and 544
FFRC modulus from tube suction tests meet or closely meet the recommended value of 80% , 545
and the average retained UCS values from wet-dry testing are similar. 546
• Dielectric values are significantly less than 10 for all cement-treated RAP mixes. 547
• Percentage of particles passing No. 40 sieve in general, and passing No. 200 sieve in 548
particular, in a RAP mix significantly impact its strength and modulus. Since the lack of 549
these particles in Texas RAP is common, RAP mixed with granular base (including recycled 550
base) materials with higher fines content can improve the quality of the mixes. 551
• Asphalt content in RAP does not seem to have a considerable impact on strength and 552
modulus of cement-treated RAP mixes. 553
• Particle size distribution of coarse aggregate only has a minor impact on strength and 554
modulus of cement-treated RAP mixes. 555
556
ACKNOWLEDGEMENTS 557 The authors wish to gratefully acknowledge the financial support and guidance of the Texas 558
Department of Transportation. Special thank you is extended to Dr. Jimmy Si of TxDOT for 559
directing this project. 560
561
REFERENCES 562
1. Recycling of Asphalt Pavement. Missouri Asphalt Pavement Association (MAPA), 2007, 563
