Volumetric Analysis-Based Comparison between Superpave and Marshall Mix Design Procedures

Volumetric Analysis-Based Comparison between Superpave and Marshall Mix Design Procedures By Dr. Ghazi G. Al-Khateeb 1 Prof. Taisir S. Khedaywi 2 Prof. Turki I. Obaidat 3 Abstract This research intended to compare the Superpave asphalt mixture design procedures with the Marshall asphalt mixture design method. The comparison was based on several issues including evaluation of materials prior to mixture design, the design asphalt content, and the relationship between mixture design and pavement performance. Limestone aggregate and asphalt binder having a penetration grade 60/70 (performance grade PG 64) were used to prepare the asphalt mixtures. One aggregate gradation conforming to both Superpave and Marshall criteria was used. Limestone aggregate-asphalt mixtures were prepared using the Superpave mixture design procedures and using the Marshall mixture design method to achieve the objectives of this study. The evaluation process of the limestone aggregate covered the Superpave aggregate tests including: coarse aggregate angularity (CAA), flat and elongated (F&E) particles, fine aggregate angularity (FAA), and sand equivalent (SE) test, as well as the Superpave asphalt binder tests including: rotational viscosity (RV), dynamic shear rheometer (DSR), and rolling thin-film oven (RTFO) test. Results of the study showed that the design asphalt content (DAC) obtained using the Superpave mixture design procedure was 5.4 percent and the optimum asphalt content (OAC) obtained using the Marshall mixture design method was 5.6 percent when taking the optimum at 4.0-percent air voids; however, when taking the OAC as the average of: the asphalt content at the maximum stability, the asphalt content at the maximum unit weight, and the asphalt content at 4.0-percent air voids, the OAC was determined as 5.4 percent, which was similar to the DAC obtained using the Superpave mixture design 1 Assistant Professor of Civil Engineering, Jordan University of Science and Technology, Irbid 22110 Jordan, Tel.: +962-2-720-1000 Ext. 22129 or 22198, Cell.: +962-79-659-9507, e-mail: ggalkhateeb@just.edu.jo, homepage: www.just.edu.jo/ggalkhateeb. 2 Professor of Civil Engineering, Jordan University of Science and Technology, Irbid 22110 Jordan, Tel.: +962-2-720-1000 Ext. 22143, Cell.: +962-79-558-8657, e-mail: khedaywi@just.edu.jo. 3 Professor of Civil Engineering, Jordan University of Science and Technology, Irbid 22110 Jordan, e-mail: turk957@just.edu.jo. 1

procedure. In the former case, the design asphalt content from the Superpave design procedure was lower than that obtained from the Marshall design method. Consequently, asphalt mixtures designed using the Superpave design procedures would be less rutting susceptible than Marshall mixtures and probably have less bleeding. Background SUperior PERforming asphalt PAVEments (SUPERPAVE) is the outcome of the asphalt research portion of the 1987-1992, $150 million Strategic Highway Research Program (SHRP) in the United States. In the Superpave system, new asphalt binder tests and specifications, new aggregate tests and criteria, and novel mix design procedure were developed. In addition, simplified performance testing for asphalt mixtures were adopted. Superpave asphalt mixtures are hypothesized to have superior performance over Marshall-designed asphalt mixtures. Several research studies have been conducted to compare Superpave and Marshall asphalt mixtures in terms of volumetric properties and performance. In this study, a volumetric-based comparison between Superpave and Marshall asphalt mixtures was conducted. In the following paragraphs, a summary of results for previous studies is presented. Habib et al. (1) compared the Superpave and Marshall mix designs for lowvolume roads and paved shoulders in term of volumetric properties; the project site was Kansas Route 177 in northeast Kansas. Three different locally available aggregates were selected: crushed limestone and coarse and fine river sands. For material selection, three different aggregates were combined to design the aggregate structure in this study. It was found in their study that the Superpave mix design for low-volume roads/shoulders resulted in lower estimated asphalt content compared to the Marshall method, and therefore, Superpave mixtures will be more economical than Marshall mixtures for these applications due to the lower asphalt content. Musselman et al. (2) presented Florida s early experience about the Superpave field implementation in the state of Florida. In their study, a review of the major Supeprave projects in different counties of Florida was conducted. It was concluded in the study that compaction of coarse-graded Superpave mixes is (as expected) significantly more difficult than the compaction of fine-graded Marshall mixes. It was also found that coarse-graded Superpave mixes required a higher level of density to reduce the water permeability to a level that was comparable with existing fine-graded Marshall pavements. This level appeared to equate to an in-place air void content of 6-7 percent. This was notably lower than that required for existing Marshall mixes. Based on the findings of this study, the Florida Department of Transportation (FDOT) made several changes to the existing Superpave specifications. Xie and Watson (3) compacted five aggregates in three Nominal Maximum Aggregate Size (NMAS) by Marshall Hammer and Superpave Gyratory Compactor (SGC). The relationship between aggregate breakdown and influencing factors including compaction effort, Los Angeles (LA) abrasion, and flat and elongated (F and E) particles 2

content were investigated. The influence of aggregate breakdown on volumetric properties was also investigated. The aggregate breakdown by the Marshall hammer was found to be significantly higher than the breakdown by the SGC. LA abrasion was found to have a strong relationship with aggregate breakdown, and also directly related to the Voids in Mineral Aggregate (VMA) of stone matrix asphalt (SMA) mixtures. F and E content had a moderate relationship with aggregate breakdown, but had relatively little effect on VMA. Swami, Mehta and Bose (4) compared the design of asphalt concrete by Superpave and Marshall method of mix design for Indian conditions and studied the properties of Superpave mixes at different angles and different numbers of gyrations. They found that Superpave mixes fulfilled all the criteria for easy and good construction at lesser binder content than the Marshall mixes (4.4 percent versus 5.3 percent). It was also found that Superpave mixes are least affected by water. Zaniewski and Kanneganti (5), in a study performed for West Virginia Division of Highways in cooperation with the US Department of Transportation-Federal Highway Administration, conducted a comparison between a 19 mm Superpave and Base II Marshall mixes in West Virginia. The Marshall and Superpave methods were compared by preparing similar mix design with each method. The mix designs from each method were cross-compared with the conclusion that mixes developed under one method met the criteria of the other method. The asphalt contents of Superpave mix designs were higher than Marshall mix design for the same traffic level. The Marshall mix design method provided a 4.9 percent optimum asphalt content, while the Superpave mix design method provided a 5.1 percent design asphalt binder content. In addition, the Asphalt Pavement Analyzer (APA) was used to evaluate rutting performance of gyratory compacted samples in the laboratory. The statistical analysis of rut depth results indicated there was not enough evidence to conclude there was a significant difference between the Marshall and Superpave mix design methods. Asi (6) conducted a study to find the adoptability of Superpave mixtures specifications to the Hashemite Kingdom of Jordan specific materials, traffic, and environmental conditions. A comparison study was carried out to use local materials to design the asphalt mixtures using both Marshall and Superpave mixtures. Design procedures in addition to performance of both mixtures were evaluated. One of the conclusions of the study was that the Superpave design procedure provided lower asphalt content than that predicted by Marshall design procedure. Lee, Amirkhanian, and Kown (7) evaluated the volumetric properties of crumb rubber modifier (CRM) asphalt mixtures as a function of four different compaction temperatures using two compaction methods: the Superpave gyratory compaction and the Marshall compaction and suggested a range of compaction temperatures to satisfy the properties required in the mix design. They also used a control binder (PG 64-22) and SBS-modified binder (PG 76-22) for comparison purposes. It was found that the optimum asphalt contents of the control and SBS-modified asphalt mixtures from the Marshall method were 0.6-0.7 percent higher than those from the Superpave method. 3

However, there was little difference in optimum asphalt contents of the CRM mixtures between the Superpave and Marshall methods. From the Superpave mix design method, the optimum asphalt contents of the CRM mixtures were approximately 1.5 percent higher than the control mixture, depending on the CRM content used. The CRM mixtures also showed high air void contents at low compaction temperature; especially the mixtures compacted with the Superpave gyratory compactor. The change of air void contents of the CRM mixtures with compaction temperature was relatively smaller in the Marshall compactor. Objectives of the Study The main objectives of the study are: 1. To design asphalt mixtures using two different methods: the Marshall mix design method and the Superpave mix design procedure, using limestone aggregate in Jordan. 2. To Compare between the two mix design procedures in terms of volumetric properties. Design of Asphalt Mixtures Using Marshall and Superpave Methods A laboratory testing matrix to design asphalt mixtures using the two methods was established. A limestone aggregate from Al-Husun quarry in the northern part of Jordan and a 60/70-penetration grade asphalt binder from Jordan petroleum refinery were used to prepare the asphalt mixtures. Marshall Mix Design Method Aggregate Gradation and Proportioning Sieve analysis of the four stockpiles received from the quarry was conducted in the laboratory as shown in Table 1. Proportioning of the stockpiles based on the results of the sieve analysis was done to obtain a target aggregate gradation according to the Marshall gradation criteria. The selected gradation conformed to both criteria of Marshall and Superpave. Design of Asphalt Mixtures The Marshall test method following the procedures described in the Asphalt Institute (AI) manual (MS-2) (8) was used to design the asphalt mixtures and to determine the optimum asphalt content (OAC). Marshall asphalt mixtures for each aggregate gradation were prepared using the blended limestone aggregates. The asphalt mixture samples were compacted using 75 blows per each side in a cylindrical mold of 100-mm diameter using the Marshall hammer. For each asphalt binder content, three test 4

Sieve Size (in.) Table 1: Sieve Analysis of Aggregate Stockpiles and Proportioning Sieve Size (mm) Stockpile #1 Stockpile #2 % Passing Stockpile #3 Combined Gradation Limits 1 25 100.0 100.0 100.0 100.0 100 3/4 19 99.8 100.0 100.0 100.0 100 1/2 12.5 59.5 98.3 100.0 93.0 80-100 3/8 9.5 35.0 100.0 76.0 70-90 No. 4 4.75 76.2 56.0 50-70 No. 8 2.36 58.5 43.0 35-50 No. 16 1.18 46.2 34.0 No. 30 0.6 35.4 26.0 18-29 No. 50 0.3 24.5 18.0 13-23 No. 100 0.15 16.2 12.0 8-16 No. 200 0.075 5.8 4.0 4-10 specimens were prepared. Marshall compacted specimens were tested for bulk specific gravity (G sb ), stability, and flow. The theoretical maximum specific gravity (G mm ) was also determined for loose asphalt mixtures for each asphalt binder content and gradation following the test procedures described in AASHTO T 209 (9). The test results and the volumetric properties for asphalt mixtures are summarized in Table 2. The volumetric properties included the voids in total mixture (VTM), the voids in mineral aggregate (VMA), and the voids filled with asphalt (VFA). Asphalt Binder Content, % Table 2: Test Results for Marshall Mix Design Unit Weight (kg/m 3 ) Stability (N) Flow (0.25 mm) VTM (%) VMA (%) VFA (%) 4.5 2,318.3 13,785 6.0 5.8 13.1 56.2 5.0 2,333.1 14,667 6.3 4.4 13.1 66.4 5.5 2,351.1 14,896 12.7 2.9 12.8 77.2 6.0 2,337.9 13,818 14.0 2.8 13.8 80.1 5

The optimum asphalt content was calculated in this study following the procedure described in the AI MS-2 manual. In other words, the optimum asphalt content was determined as the average of: (1) the asphalt binder content at the maximum stability, (2) the asphalt binder content at the maximum density, and (3) the asphalt binder content at 4 percent air voids. The Marshall mix design parameters at the optimum asphalt content are shown in Table 3 below: Table 3: Marshall Mix Design Parameters Parameter Value Specifications OAC, % 5.1 NA Stability, N 14,866 > 8,006 Flow (0.25 mm) 8.7 8-14 VTM, % 4.0 3-5 VMA, % 14.1 14.0 VFA, % 71.7 65-75 Superpave Mix Design for Asphalt Mixtures The Superpave mix design was carried out in the laboratory according to the test procedures described in the AI SP-2 manual (10) following the steps: (1) material selection, (2) selection of design aggregate structure, (3) selection of design binder content, (4) evaluation of moisture sensitivity. The Superpave gyratory compactor (SGC) was used to compact the prepared asphalt mixtures in accordance with AASHTO T 312 (11) test method. Material Selection The materials used for the Superpave mix design included: limestone aggregate (three stockpiles) from Al-Husun quarry in the northern part of Jordan, asphalt binder of 60/70 penetration grade from Jordan Petroleum Refinery. Selection of Design Aggregate Structure The selection of the design aggregate structure involved the following steps: (1) establishing trial blends, (2) compacting specimens, (3) evaluating trial blends, and (4) selecting design aggregate structure. Three trial blends were established having proportions of aggregate as follows: 6

Table 4: Proportions of Aggregates for Trial Blends Blends Proportions of Aggregate, % Stockpile #1 Stockpile #2 Stockpile #3 Trial Blend #1 20.0 10.0 70.0 Trial Blend #2 18.0 9.0 73.0 Trial Blend #3 10.0 10.0 80.0 The combined aggregate gradations for the three trial blends are plotted on the 0.45 power chart shown in Figure 1 along with the Superpave specifications for aggregate gradation. After establishing the trial blends, specimens were compacted using the SGC to evaluate the trial blends. 100.0 90.0 80.0 70.0 Trial Blend #1 Trial Blend #2 Trial Blend #3 % Passing 60.0 50.0 40.0 30.0 20.0 10.0 0.0 0.0750.150.30.6 1.18 2.36 4.75 9.5 12.5 19.0 Sieve Size (mm) Figure 1: Aggregate Gradations for the Three Trial Blends plotted on 0.45 Power Chart. 7

Determination of Trial (Initial) Binder Content for Trial Blends The effective specific gravity (G se ), volume of binder absorbed (V ba ) and volume of effective binder (V be ) were computed for each trial blend, and further they were used to calculate the trial asphalt binder content for each trial blend. The trial (initial) asphalt binder content (P bi ) were as follows: For trial blend #1 P bi = 5.11 %, For trial blend #2 P bi = 5.09%, For trial blend #3 P bi = 5.04%. A 5.0 percent initial binder content was used for all three trial blends. Evaluation of Trial Blends Two samples were compacted at the trial (initial) binder content for each trial blend using the Superpave gyratory compactor (SGC). Aggregate and asphalt were heated and mixed at the mixing temperature determined for this asphalt binder (156-163 C) and then compacted at the compaction temperature determined for this asphalt binder (146-152 C). The SGC is used to compact asphalt mixture samples at a vertical pressure of 600 kpa, external angle of gyration of 1.25, and rate of gyration of 30 rpm. The number of gyrations N ini, N des, and N max were selected as 8, 109, and 174 that corresponded to an average design high air temperature of less than 39 C and traffic loading of 10-<30 million design ESALs. The initial number of gyrations (N ini ) is used in Superpave to estimate the compactability of the asphalt mixture, while the maximum number of gyrations (N max ) is used to compact the test specimens and represents the traffic loading at the end of the service life of the asphalt pavement. N ini and N max are functions of N des as shown in the following equations: LogN = 0. 45 (1) ini LogN des LogN max = 1. 10LogN des (2) Using the gyratory data (number of gyrations versus specimen height), the estimated bulk specific gravity (G mb-estimated ), the correction factor (CF), the corrected bulk specific gravity (G mb-corrected ), the percentage of G mm, and the percentage of air voids (V a ) using the following equations: G W V mb mix mb estimated = (3) γ w 8

2 πd hx Vmix = 4 (4) Gmb measured CF = G (5) G G mb mb estimated A measured = (6) B C mb corrected = ) ( CF G (7) G mb estimated mb corrected % Gmm corrected = (8) Gmm V = 100 % (9) a G mm Where: W mb = weight of asphalt mixture, d = diameter of mold (150 mm), h x = height of specimen during compaction, G mb-measured = measured bulk specific gravity of compacted specimen, A = weight of dry compacted specimen, B = weight of saturated surface dry (SSD) specimen, and C = weight of submerged specimen. The measured bulk specific gravity is determined using the procedure described in standard test method AASHTO T 166 (12). The values of the volumetric properties at N des : V a, VMA, VFA, and DP and %G mm at N ini, %G mm at N des, and %G mm at N max are all computed using the following formulas: V = 100 % (10) a G mm at N des % Gmm N Gmm P des s % VMA = 100 Gsb (11) VMA Va VFA = 100 VMA (12) P = (13) 0. 075 DP P be 9

Where: G mm = theoretical maximum specific gravity of the asphalt mixture, P s = percentage of aggregate, G sb = specific gravity of aggregate, P 0.075 = passing No. 200 (0.075 mm) sieve, percent, P be = effective asphalt binder content (percent) calculated from the following formula: Pba Pbe = Pb Ps 100 Where: (14) P ba = absorbed asphalt binder content (percent) computed from the following formula: P G G se sb ba = 100 Gb (15) GsbGse Where: G se = effective specific gravity of the aggregate in the asphalt mixture computed from the following formula: G P mm b se = (16) Pmm Pb G mm P G b Where: P mm = maximum percentage of the asphalt mixture (100 %), P b = percentage of asphalt binder, and G b = specific gravity of asphalt binder. Table 5 shows the compaction (densification) data and calculations for one sample for trial blend #2. The values of the volumetric and compaction properties for the three trial blends are summarized in Table 6 below. An estimated binder content (P b-estimated ) from these data was determined for each trial blend to achieve 4 percent air voids using the following equation: P [.4( Va b estimated = Pbi 4 Where: 0 )] (17) P bi = initial (trial) binder content, and V a = percent air voids at N des. 10

N Table 5: Compaction Data for Trial Blend #2-Specimen #2 Height (mm) Volume (cm 3 ) G mb Estimated CF G mb Corrected % G mm V a (%) 1 135.7 2398.0 1.975 2.004 82.0 18.0 5 129.2 2283.2 2.074 2.105 86.1 13.9 8 126.8 2240.7 2.113 2.145 87.7 12.3 10 125.6 2219.5 2.133 2.165 88.6 11.4 15 123.7 2186.0 2.166 2.198 89.9 10.1 20 122.3 2161.2 2.191 2.224 90.9 9.1 25 121.3 2143.5 2.209 2.242 91.7 8.3 50 118.7 2097.6 2.257 2.291 93.7 6.3 100 116.9 2065.8 2.292 2.326 95.1 4.9 1.01493 109 116.7 2062.3 2.296 2.330 95.3 4.7 110 116.7 2062.3 2.296 2.330 95.3 4.7 120 116.5 2058.7 2.300 2.334 95.5 4.5 130 116.4 2057.0 2.302 2.336 95.6 4.4 140 116.2 2053.4 2.306 2.340 95.7 4.3 150 116.1 2051.7 2.308 2.342 95.8 4.2 160 116.0 2049.9 2.310 2.344 95.9 4.1 170 115.9 2048.1 2.312 2.346 96.0 4.0 174 115.9 2048.1 2.312 G mb-measured = 2.331 2.346 96.0 4.0 Table 6: Volumetric and Mix Compaction Properties for Trial Blends Trial Blend Blend #1 Blend #2 Blend #3 Initial Binder Content (%) V a (%) VMA (%) VFA (%) DP %G mm at N ini %G mm at N des %G mm at N max 5.0 5.8 13.5 57.5 0.8 84.6 94.5 96.6 5.0 4.9 14.5 66.0 1.0 87.3 95.1 95.9 5.0 5.3 13.0 57.4 1.2 87.8 94.8 95.4 Criteria --- 4.0 14.0 65-75 0.6-1.2 89 96.0 98 11

The corresponding volumetric properties at the estimated binder content for each trial blends were also computed using the following equations: estimated initial [ C( Va % VMA = % VMA + 4 )] (18) % VMA estimated 4.0 % VFA = estimated 100 (19) % VMAestimated ( V ) % Gmm estimated at N max = % Gmm trial at N max 4 a (20) mm estimated at Nini = % Gmm trial at Nini 4 ( V ) % G (21) a P = (22) 0. 075 DR P be Where: P be G G se sb = Pb estimated Ps Gb GseG (23) sb The estimated binder content and the corresponding volumetric properties for the three trial blends are shown in Table 7 below: Table 7: Estimated Binder Content and Volumetric Properties for Trial Blends Trial Blend Estimated Binder Content (%) VMA (%) VFA (%) DP %G mm at N ini %G mm at N max Blend #1 5.5 13.4 70.1 0.97 88.3 96.6 Blend #2 5.3 14.1 71.6 0.94 85.6 96.9 Blend #3 5.5 13.2 69.7 1.14 88.4 96.4 Criteria 14.0 65-75 0.6-1.2 89 98 Based on the results in Table 8, trial blend #2 meets the Superpave design criteria, and therefore, it was selected as the design aggregate structure in the Superpave mix design. 12

Selection of Design Binder Content After selecting the design aggregate structure (trial blend #2), two specimens were compacted at each of the binder contents: 4.5, 5.0, 5.5, and 6.0 % using the SGC set at the required vertical pressure, angle of gyration, and rate of gyration (600 kpa, 1.25, and 30 rpm, respectively). The compaction (densification) curves for the four binder contents are shown in Figure 2. Tables 8 through 11 also show the compaction data and calculations for the selected trial blend at the four binder contents, respectively. 100.0 95.0 4.5 % 5.0 % 5.5 % 6.0 % % Gmm 90.0 85.0 80.0 1 10 100 1000 Number of Gyrations, N Figure 2: Compaction (Densification) Curves for the Four Binder Contents 13

N Table 8: Compaction Data for Trial Blend #2-Specimen #1a, 4.5 percent Height (mm) Volume (cm 3 ) G mb Estimated CF G mb Corrected % G mm V a (%) 1 131.3 2320.3 2.008 2.032 82.5 17.5 5 125.9 2224.8 2.094 2.119 86.0 14.0 8 124.0 2191.3 2.126 2.151 87.3 12.7 10 123.1 2175.4 2.142 2.167 88.0 12.0 15 121.6 2148.8 2.168 2.194 89.1 10.9 20 120.5 2129.4 2.188 2.214 89.9 10.1 25 119.7 2115.3 2.203 2.229 90.5 9.5 50 117.4 2074.6 2.246 2.272 92.3 7.7 100 115.4 2039.3 2.285 2.312 93.9 6.1 1.01183 109 115.2 2035.8 2.289 2.316 94.0 6.0 110 115.1 2034.0 2.291 2.318 94.1 5.9 120 114.9 2030.5 2.295 2.322 94.3 5.7 130 114.7 2026.9 2.299 2.326 94.4 5.6 140 114.5 2023.4 2.303 2.330 94.6 5.4 150 114.3 2019.8 2.307 2.334 94.8 5.2 160 114.2 2018.1 2.309 2.336 94.8 5.2 170 114.0 2014.5 2.313 2.340 95.0 5.0 174 114.0 2014.5 2.313 G mb-measured = 2.340, G mm = 2.463 2.340 95.0 5.0 14

N Table 9: Compaction Data for Trial Blend #2-Specimen #1a, 5.0 percent Height (mm) Volume (cm 3 ) G mb Estimated CF G mb Corrected % G mm V a (%) 1 135.4 2392.7 1.990 2.020 82.6 17.4 5 129.4 2286.7 2.082 2.113 86.4 13.6 8 127.3 2249.6 2.116 2.148 87.9 12.1 10 126.3 2231.9 2.133 2.165 88.6 11.4 15 124.5 2200.1 2.164 2.197 89.8 10.2 20 123.3 2178.9 2.185 2.218 90.7 9.3 25 122.3 2161.2 2.203 2.236 91.5 8.5 50 119.7 2115.3 2.251 2.285 93.4 6.6 100 117.5 2076.4 2.293 2.327 95.2 4.8 1.01504 109 117.3 2072.9 2.297 2.331 95.4 4.6 110 117.3 2072.9 2.297 2.331 95.4 4.6 120 117.1 2069.3 2.301 2.335 95.5 4.5 130 116.9 2065.8 2.305 2.339 95.7 4.3 140 116.7 2062.3 2.309 2.343 95.8 4.2 150 116.5 2058.7 2.313 2.347 96.0 4.0 160 116.4 2057.0 2.315 2.349 96.1 3.9 170 116.2 2053.4 2.319 2.353 96.3 3.7 174 116.2 2053.4 2.319 G mb-measured = 2.353, G mm = 2.445 2.353 96.3 3.7 15

N Table 10: Compaction Data for Trial Blend #2-Specimen #1a, 5.5 percent Height (mm) Volume (cm 3 ) G mb Estimated CF G mb Corrected % G mm V a (%) 1 134.9 2383.9 2.003 2.022 83.3 16.7 5 128.5 2270.8 2.103 2.122 87.4 12.6 8 126.2 2230.1 2.141 2.161 89.0 11.0 10 125.1 2210.7 2.160 2.180 89.8 10.2 15 123.1 2175.4 2.195 2.215 91.3 8.7 20 121.8 2152.4 2.218 2.239 92.3 7.7 25 120.9 2136.5 2.235 2.256 92.9 7.1 50 118.3 2090.5 2.284 2.305 95.0 5.0 100 116.3 2055.2 2.323 2.345 96.6 3.4 1.00930 109 116.1 2051.7 2.327 2.349 96.8 3.2 110 116.1 2051.7 2.327 2.349 96.8 3.2 120 115.9 2048.1 2.331 2.353 97.0 3.0 130 115.7 2044.6 2.335 2.357 97.1 2.9 140 115.6 2042.8 2.337 2.359 97.2 2.8 150 115.5 2041.1 2.339 2.361 97.3 2.7 160 115.3 2037.5 2.344 2.365 97.5 2.5 170 115.3 2037.5 2.344 2.365 97.5 2.5 174 115.2 2035.8 2.346 G mb-measured = 2.367, G mm = 2.427 2.367 97.5 2.5 16

N Table 11: Compaction Data for Trial Blend #2-Specimen #1a, 6.0 percent Height (mm) Volume (cm 3 ) G mb Estimated CF G mb Corrected % G mm V a (%) 1 132.9 2348.5 2.050 2.070 85.9 14.1 5 126.3 2231.9 2.157 2.178 90.4 9.6 8 123.9 2189.5 2.199 2.220 92.1 7.9 10 122.7 2168.3 2.220 2.242 93.0 7.0 15 120.9 2136.5 2.253 2.275 94.4 5.6 20 119.8 2117.0 2.274 2.296 95.3 4.7 25 119.1 2104.7 2.287 2.309 95.8 4.2 50 117.8 2081.7 2.313 2.335 96.9 3.1 100 117.2 2071.1 2.324 2.347 97.4 2.6 1.00967 109 117.2 2071.1 2.324 2.347 97.4 2.6 110 117.2 2071.1 2.324 2.347 97.4 2.6 120 117.1 2069.3 2.326 2.349 97.5 2.5 130 117.1 2069.3 2.326 2.349 97.5 2.5 140 117.0 2067.6 2.328 2.351 97.5 2.5 150 117.0 2067.6 2.328 2.351 97.5 2.5 160 117.0 2067.6 2.328 2.351 97.5 2.5 170 116.9 2065.8 2.330 2.353 97.6 2.4 174 116.9 2065.8 2.330 G mb-measured = 2.353, G mm = 2.410 2.353 97.6 2.4 The volumetric properties at N des (V a, VMA, VFA, and DP) and %G mm at N ini, %G mm at N des, and %G mm at N max for the trial blend at the four binder contents are summarized in Table 12 below. In Superpave, the design binder content is established at 4 percent air voids. Figures 3 through 9 show the relationship between the asphalt binder content (P b ) and each of the volumetric and mix compaction properties: air voids (V a ) at N des, VMA, VFA, DP, %G mm at N ini, %G mm at N des, and %G mm at N max for the selected design aggregate structure (trial blend #2). The design binder content was determined from Figure 3 at 4.0-percent air voids as 5.4 percent. Table 13 shows the volumetric properties corresponding to the design binder content (5.4 percent) for the design aggregate structure (trial blend #2) along with the corresponding Superpave criteria for a traffic level of 10-<30 million ESALs and nominal maximum aggregate size (NMAS) of 12.5 mm. 17

Table 12: Volumetric and Mix Compaction Properties for Trial Blend #2 at the Four Binder Contents P b (%) V a (%) VMA (%) VFA (%) DP % G mm at N ini = 8 % G mm at N des = 109 % G mm at N max = 174 4.5 6.5 14.8 56.1 1.1 86.1 93.5 94.5 5.0 4.9 14.5 66.0 1.0 87.3 95.1 95.9 5.5 3.7 14.5 74.3 0.9 88.8 96.3 96.9 6.0 3.2 15.1 79.0 0.8 91.3 96.8 97.0 8.0 6.0 V a (%) 4.0 2.0 y = 1.095x 2-13.711x + 46.06 R 2 = 0.9995 0.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 P b (%) Figure 3: Asphalt Binder Content versus Air Voids for the Design Aggregate Structure (Trial Blend #2). 18

18.0 VMA (%) 16.0 14.0 y = 0.9797x 2-10.131x + 40.599 R 2 = 0.9952 12.0 10.0 0.0 2.0 4.0 6.0 8.0 P b (%) Figure 4: Asphalt Binder Content versus VMA for the Design Aggregate Structure. 90.0 80.0 VFA (%) 70.0 60.0 y = -5.2829x 2 + 70.863x - 155.91 R 2 = 0.9993 50.0 0.0 2.0 4.0 6.0 8.0 P b (%) Figure 5: Asphalt Binder Content versus VFA for the Design Aggregate Structure. 19

2.0 1.5 DP 1.0 0.5 y = 0.0501x 2-0.7401x + 3.4224 R 2 = 1 0.0 0.0 2.0 4.0 6.0 8.0 P b (%) Figure 6: Asphalt Binder Content versus DP for the Design Aggregate Structure. 100.0 95.0 % Gmm at N ini 90.0 85.0 y = 1.2763x 2-9.957x + 105.09 R 2 = 0.9988 80.0 0.0 2.0 4.0 6.0 8.0 P b (%) Figure 7: Asphalt Binder Content versus %G mm @ N ini for the Design Aggregate Structure. 20

100.0 % Gmm at Ndes 95.0 y = -1.095x 2 + 13.711x + 53.94 R 2 = 0.9995 90.0 0.0 2.0 4.0 6.0 8.0 P b (%) Figure 8: Asphalt Binder Content versus %G mm @ N des for the Design Aggregate Structure. 100.0 % Gmm at Nmax 95.0 y = -1.2597x 2 + 14.936x + 52.769 R 2 = 0.9982 90.0 2.0 4.0 6.0 8.0 P b (%) Figure 9: Asphalt Binder Content versus %G mm @ N max for the Design Aggregate Structure. 21

Table 13: Volumetric and Mix Compaction Properties for the Design Aggregate Structure Corresponding to Design Binder Content (5.4 percent). Design P b (%) Design V a (%) VMA (%) VFA (%) DP % G mm at N ini = 8 % G mm at N des = 109 % G mm at N max = 174 5.4 4.0 14.4 72.4 0.9 88.4 96.0 96.7 Criteria 4.0 >14.0 65-75 0.6-1.2 <89 96.0 <98 Retained Stability and Moisture Sensitivity Retained stability test of Marshall specimens was conducted to investigate the effect of moisture on Marshall asphalt mixtures. Marshall specimens were placed in water bath at 60 C for 24 hours before tested for Marshall stability. The ratio of the average stability of the conditioned specimens to the average stability of unconditioned (dry) specimens is the retained stability. The retained stability for Marshall specimens was 83% higher than the Marshall specification of 75% (Ref.). On the other hand, moisture sensitivity test was conducted on cut Superpave specimens (150 mm diameter 50 mm thickness) to find out the effect of moisture on Superpave asphalt mixtures. Superpave specimens were soaked in water bath maintained at 60 C for 24 hours and then at 25 C for 2 hours. Afterwards, the conditioned (soaked) specimens were tested for indirect tensile strength (diametric loading). The moisture sensitivity is the ratio of the average indirect tensile strength of the conditioned specimens to the average strength of unconditioned specimens. The moisture sensitivity for Superpave specimens was 92% higher than the Superpave specification of 80% (Ref.). Thus, Superpave asphalt mixtures were found to be less affected by moisture compared to Marshall asphalt mixtures. Marshall Versus Superpave Mix Design Method In this study, the comparison between Marshall and Superpave mix design methods was done exclusively to see the difference in design binder content for asphalt mixtures designed using these two methods. Consequently, volumetric analysis was conducted for the test data obtained from both methods. The optimum asphalt content obtained using the Marshall mix design method was determined as 5.6 percent at 4.0 percent design air voids, but when taking into consideration the asphalt content at maximum stability and that at maximum unit weight, the optimum asphalt content represented by the average of the three values came out as 5.4 percent, which is the same design binder content obtained from the Superpave mix design method at 4.0 percent air voids; i.e. 5.4 percent. 22

This finding differed from some of the research studies found in the literature. For instance, Habib et al. (1) found in their study that Superpave mix design for low-volume roads/shoulders resulted in lower estimated asphalt content compared to the Marshall method. Swami et al. (4) found in their study that Superpave mixes fulfilled all the criteria for easy and good construction at lesser binder content than the Marshall mixes (4.4 percent versus 5.3 percent). In addition, Asi (7) concluded that the Superpave design procedure provided lower asphalt content than that predicted by Marshall design procedure, and Lee et al. (8) found in their study that the optimum asphalt contents of the control and SBS-modified asphalt mixtures from the Marshall method were 0.6-0.7 percent higher than those from the Superpave method. On the other hand, the finding of this study agreed with the findings of Zaniewski and Kanneganti (5) who found in their study that the asphalt contents of Superpave mix designs were higher than those of the Marshall mix design for the same traffic level. In conclusion, it seems that the differences in the design asphalt binder content between the Marshall and Superpave mix design methods are function of aggregate gradation. Since the same aggregate gradation was used in this study for the Marshall mix design method and for the Superpave mix design method that met the criteria of both methods, the design asphalt binder contents obtained from both methods did not differ much and the difference was statistically insignificant. Conclusions Based on the analysis and results of this study, the following conclusions are drawn: 1. The optimum asphalt binder content obtained using the Marshall mix design method was found to be similar to the design asphalt binder content using the Superpave mix design procedure (5.4 percent). 2. It seems that if the same aggregate gradation (conformed to both Marshall and Superpave aggregate criteria) was used in the mix design, the design asphalt binder contents from the two methods would be similar or very close. 3. Reviewing the different studies in the literature and from the results of this study, it could be concluded that the differences in the design asphalt binder content between the Marshall and Superpave methods is a function of aggregate gradation used in the mix design. 4. The Superpave system provided estimation for the dust ratio in the mixture, while the Marshall mix design method did not provide any estimation of such ratio. 5. The Superpave system investigated the compactability and tenderness of the mixture through the estimation of the % G mm at N ini, while the Marshall mix design method had no check on the compactability of the mixture at early stages of service. 23

References 1. A. Habib, M. Hossain, R. Kaldate, and G. A. Fager, Comparison of Superpave and Marshall Mixtures for Low-Volume Roads /Shoulders, The Transportation Research Board (TRB) 77 th Annual Meeting, CD-Rom, Transportation Research Board (TRB), National Research Council, Washington, D.C., USA, 1998. 2. James A. Musselman, Superpave Field Implementation: Florida s Early Experience, The Transportation Research Board (TRB) 77 th Annual Meeting, CD-Rom, Transportation Research Board (TRB), National Research Council, Washington, D.C., USA, 1998. 3. H. Xie and D. Watson, Lab Study on Degradation of Stone Matrix Asphalt (SMA) Mixtures, The Transportation Research Board (TRB) 83 rd Annual Meeting, CD-Rom, Transportation Research Board (TRB), National Research Council, Washington, D.C., USA, 2004. 4. B. L. Swami Y. A. Mehta and S. Bose, A Comparison of Marshall and Superpave Desing for Materials Sourced in India. The International Journal of Pavement Engineering (IJPE), Vol. 5 (3), September 2004, pp. 163 173. 5. J. P. Zaniewski and V. Kanneganti, Comparison of 19mm Superpave and Marshall Base II Mixes in West Virginia, Final Report, Prepared for the West Virginia Department of Transportation, Division of Highways, in cooperation with the US Department of Transportation, Federal Highway Administration, June 2003. 6. I. M. Asi, Performance evaluation of SUPERPAVE and Marshall asphalt mix designs to suite Jordan climatic and traffic conditions, Construction and Building Materials Journal (CBMJ), Vol. 21, 2007, pp. 1732 1740. 7. S-J Lee, S. N. Amirkhanian, S-Z Kwon, The effects of Compaction Temperature on CRM Mixtures made with the SGC and the Marshall Compactor, Construction and Building Materials Journal (CBMJ), Vol. 22, 2008, pp. 1122 1128. 8. The Asphalt Institute (AI) Manual Series No. 2 (MS-2), Mix Design Methods for Asphalt Concrete and Other Hot-Mix Types, 1996. 9. AASHTO T 209, Theoretical Maximum Specific Gravity of Bituminous Mixtures. Standard Specifications for Transportation Materials and Methods of Sampling and Testing, Part II-Tests, Twentieth Edition, 2000. 10. The Asphalt Institute (AI) Handbook SP-2, Superpave Mix Design, 1996. 11. AASHTO T 312, Preparing and Determining the Density of Hot-Mix Asphalt (HMA) Specimens by means of the Superpave Gyratory Compactor. Standard 24

Specifications for Transportation Materials and Methods of Sampling and Testing, Modified-Method A, 2008. 12. AASHTO T 166, Bulk Specific Gravity of Compacted Bituminous Mixtures Using Saturated Surface-Dry Specimens. Standard Specifications for Transportation Materials and Methods of Sampling and Testing, Part II-Tests, Twentieth Edition, 2000. 25