subbase applications

Accepted Manuscript Strength Characteristics of Crushed Gravel and Limestone Aggregates with up to 12% Plastic Fines Evaluated for Pavement Base/Subbase Applications Abdolreza Osouli, Rabindra Chaulagai, Erol Tutumluer, Heather Shoup PII: DOI: Reference:

S2214-3912(18)30056-4 https://doi.org/10.1016/j.trgeo.2018.10.004 TRGEO 205

To appear in:

Transportation Geotechnics

Received Date: Revised Date: Accepted Date:

19 March 2018 10 October 2018 11 October 2018

Please cite this article as: A. Osouli, R. Chaulagai, E. Tutumluer, H. Shoup, Strength Characteristics of Crushed Gravel and Limestone Aggregates with up to 12% Plastic Fines Evaluated for Pavement Base/Subbase Applications, Transportation Geotechnics (2018), doi: https://doi.org/10.1016/j.trgeo.2018.10.004

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Strength Characteristics of Crushed Gravel and Limestone Aggregates with up to 12% Plastic Fines Evaluated for Pavement Base/Subbase Applications Abdolreza Osouli1, Rabindra Chaulagai2, Erol Tutumluer3, Heather Shoup4 1

Corresponding Author, Associate Professor, Southern Illinois University Edwardsville, 62026, Edwardsville, IL, USA 2 Research Assistant, Southern Illinois University Edwardsville, 62026, Edwardsville IL, USA 3 Professor, Paul F. Kent Endowed Faculty Scholar, Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 205 N Mathews, Urbana, IL 61801, USA 4 Central Office Geotechnical Engineer, Illinois Department of Transportation, Springfield, IL 62764, USA

ABSTRACT Performance period or life span of a flexible pavement is dependent upon the load carrying capacity of its base and subbase layers. Pavement strength characteristics influenced by material properties of these foundation layers are of utmost importance in the pavement design. In this experimental study, the goal was to adequately define the limits of different unbound aggregate properties influencing the strength of unbound aggregate. Material type, gradation, maximum particle size, fines content, dust ratio and plasticity index were among the different properties studied. Dust ratio is defined as the ratio of material passing the No. 200 sieve (i.e. fines content) to material passing the No. 40 sieve. As for the aggregate materials, crushed limestone and crushed gravel, commonly used in Illinois in base/subbase applications, were considered. Illinois dense graded base specifications allow aggregate materials with a maximum particle size of 25 mm for the CA 6 specification and 50 mm maximum particle size for the CA 2 aggregate. Plasticity index, fines content, and dust ratio ranged from 5% to 13%, 5% to 12%, and 0.4 to 1.0, respectively. California Bearing Ratio (CBR) and staged triaxial tests were performed to characterize the material strength. Higher strength values were obtained for the CA 6 aggregates with 25-mm maximum particle size compared to the aggregates tested for CA 2 specification. Considering typical property ranges, a dust ratio of 1.0 was found to be a viable option in some cases for base/subbase applications providing an acceptable soaked strength for both crushed limestone and crushed gravel. However, for both material types, the combination of a dust ratio of 0.4 and a fines content of 12% posed a severe negative effect on aggregate strength. Keywords: Aggregate, Strength, Dust Ratio, Fines Content, Gradation, Maximum Particle Size, Plasticity Index 1

1. INTRODUCTION Base and subbase layers are the main load bearing layers of a flexible pavement system. These layers may serve as a working platform and ultimately provide structural stability to an asphalt pavement surface course. The load distribution in base/subbase is provided by a dense graded unbound aggregate matrix, which distributes the wheel load on a larger area on top of subgrade. Performance and durability of these unbound aggregate layers is attributed to different index properties such as gradation, maximum particle size, aggregate particle shape, texture and angularity, moisture content, fines content (material passing the No. 200 sieve), dust ratio and plasticity index (PI). Dust ratio (DR) is defined as the ratio of material passing the No. 200 sieve (i.e., 0.075 mm) to material passing the No. 40 sieve (i.e., 0.425 mm). Gradation is the distribution of particle sizes contributed by the maximum particle size, fines content and dust ratio. Gradation plays a significant role in determining the packing order of the particles and load carrying capacity of unbound aggregate layers, and it affects aggregate shear strength, stiffness and permanent deformation characteristics (Bilodeau et al., 2007 and 2008; Tutumluer et al., 2009; Salam et al., 2018). While dense graded aggregates are commonly used in the construction of flexible pavements to achieve the maximum dry density and therefore the highest attainable strength (Kamal et al., 1993; Dawson et al., 1996; and Bennert et al., 2005), the maximum particle size and fines content can severely influence the unbound aggregate base strength and performance (Gray, 1962; Faiz, 1971; Yoder and Witczak, 1975; Jorenby and Hicks, 1986; Barksdale and Itani, 1989; Itani, 1990; Kamal et al., 1993; Kolisoja, 1997; Lekarp et al., 2000a; Osouli et al., 2016; Chaulagai et al., 2017; Osouli et. al., 2017a). Fines content in this paper refers to material finer than 0.075 mm (i.e., passing the No. 200 sieve). Barksdale and Itani (1989) found a 60% decrease in the stiffness of a granitic gneiss aggregate for base applications when fines content increased from 0% to 10%. The aggregate strength can also decrease with additional fines content. For example, Gandara et al. (2005) found more than 40% reduction in aggregate strength of dolomite aggregate when fines content was increased from 5% to 17%. A number of studies focused on optimal fines content values, which ranged from 7% to 11% (Gray, 1962; Ahlberg et al., 1969; Tutumluer et al., 2000). However, these studies did not consider the dust ratio interaction with material type, maximum particle size, PI and gradation. In fact, there are not many studies available in the literature to report on the influence of dust ratio. There is one out of very few studies that reported on the 2

importance of material passing the No. 200 sieve in relation to material passing the No. 30 sieve (Yoder and Witczak 1975), which they labeled as the “dust ratio.” They observed 5% and 11% reductions in the triaxial strength value of gravels with a 25 mm maximum particle size at 7.5% and 10% fines contents, respectively, when the dust ratio was increased from 0.3 to 0.5. However, the strength value increased by more than 10% when the dust ratio was increased from 0.5 to 1.0 at both fines contents. It was concluded that skip grading (i.e., dust ratio of 1) might in fact be beneficial. Also, their study, which was only limited to gravel aggregates, showed a minimal effect of dust ratio on strength at low fines content, i.e., 5% (Yoder and Witczak, 1975). Aggregate particle angularity (i.e. crushed vs uncrushed), moisture content and compaction properties also influence the strength and deformation of aggregates. Angular materials provide better interlock between particles and hence undergo much less permanent deformation after proper shakedown when compared to rounded aggregates or gravel (Lekarp et al., 2000b). Angularity increases the number of contact points between particles, therefore, results in better load distribution (Hicks and Monismith, 1971; Allen and Thompson, 1974; Thom, 1988; Thom and Brown, 1988; Barksdale and Itani, 1989). In terms of moisture content, aggregates compacted on the dry side of optimum develop capillary suction between the particles and this provides higher strength. Excessive moisture on the other hand causes lubrication among the particles and decreases the effective stress and aggregate strength (Tutumluer, 2013; Osouli et al., 2017a). Also, high moisture content in the presence of fines may result in lowering internal friction and breaking sharp edges of the angular particles, which ultimately accelerates the rutting process. It is worth mentioning that: 1) Coronado et al. (2011) has discovered that the higher suction developed with the increase in fines content from 7% to 29% resulted in higher resilient modulus values at any given vertical stress levels; 2) Coronado et al. (2016) has noted that in aggregates with high fines content, the resilient modulus is higher when the moisture content is smaller because of the increase in the capillary forces in the menisci formed among grains; and 3) the effect of fines content and moisture content on deformational characteristics of aggregates are linked (Jing 2017) and it is expected these factors will have similar effects on strength characteristics of aggregates. In addition, in the field, the base and subbase layers may be compacted at moisture contents other than the optimum. Therefore, it is critically important to identify the strength characteristics of aggregates in relation to an applicable range of field moisture contents.

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Common standard tests and state specifications used for quality control on aggregates often have mismatches due to lack of comprehensive and comparative study findings for identifying effects of aforementioned factors on the strength characteristics of unbound aggregates. This paper investigates the interactions of aggregate strength characteristics with those of aggregate gradation, material type, fines content, dust ratio and plasticity index and also proposes aggregate strength zones for pavement base and subbase applications. Typical values of fines content, dust ratio and plasticity index were varied in this study to determine their effects on the California Bearing Ratio (CBR) of aggregates within an applicable range of + 1.5% variation of Optimum Moisture Content (OMC). Two dense graded aggregate gradations utilized in this study, as adopted by Illinois Department of Transportation (DOT) coarse aggregate specifications of CA 6 and CA 2, were very similar to Gradations A and C of American Society for Testing and Materials (ASTM) D1241 with maximum particle sizes of 25 and 50 mm, respectively. Additionally, staged triaxial tests were performed on selected samples to compare and verify the findings with the soaked CBR results. 2. CONSTRUCTION PRACTICES OF TRANSPORTATION AGENCIES Majority of flexible pavements are constructed with unbound aggregate base and subbase layers (Tutumluer, 2013). However, to achieve adequate strength and long service life from these layers, the properties of aggregates should be controlled. Table 1 summarizes the limit of different index properties defined by state DOTs in the United States and national standards such as ASTM D 1241 and American Association of State Highway and Transportation Officials (AASHTO) M147 for base and subbase construction. ASTM and AASHTO standards recommend fines content to be less than 15% and 20%, respectively, with a maximum particle size of 50 mm or less for unbound aggregate layers. Typical ranges of index properties used by state agencies in the US and Canada for dense graded aggregates in base and subbase application were surveyed by Tutumluer (2013). Accordingly, (1) large aggregates with maximum particle sizes up to 100 mm and 150 mm are currently utilized by several DOTs for base and subbase layers, respectively; (2) fines contents used in unbound aggregate base layers range from 5% to 20% while for subbase layers they range from 6% to 34%; (3) PI values are less than or equal to 15% for both the base and subbase unbound layers; and (4) a deviation of up to 5% from OMC is also allowed by DOTs during pavement construction in the field. 4

3. TEST PROGRAM Samples of crushed gravel and limestone aggregates were prepared at four to five different moisture contents to establish the moisture density relationships following the standard Proctor compaction test procedure of AASHTO T99. On every compacted specimen, a CBR test was also performed under soaked condition to represent severe moisture conditioning following AASHTO T193. Therefore, soaked CBR results of all engineered samples were obtained for a range of moisture contents, which covered OMC + 1.5%. It is worthwhile to note that 20% of samples were retested to validate the results. For further analyses, a series of staged undrained triaxial tests were also performed to be discussed in detail in later sections. For the laboratory investigation, samples from crushed limestone were engineered with Illinois CA 6 and CA 2 gradation, while samples from crushed gravel were engineered with CA 6 gradation only. These gradations will be discussed in next section. To study the influence of fines content on soaked strength, typical low to high amount of fines content (i.e., 5%, 8% and 12%) were considered. This fines content range of Illinois Standard Specification (IDOT, 2016) studied herein is also within the ASTM and AASHTO standard limits, however, there are some European standards that allow use of fines content up to 30% (Coronado et al. 2016). Similarly, dust ratios of 0.4, 0.6 and 1 were taken into account when considering the proportion of fines content to material smaller than sand sizes materials in a sample. Dust ratio values for this study were defined in accordance with the ASTM, AASHTO and the Illinois Standard Specification (IDOT 2016), which recommends less than 0.6 for base and subbase layers application. However, to determine the impact of higher DR or skip grading on crushed gravel and limestone aggregates, a greater value (i.e., DR of 1) was also considered. Plasticity index requirements by DOTs and national standards (see Table 1) typically list maximum PI values from 4% to 9% for unbound aggregates. Therefore, PI values of 5% and 9% were also considered in this study. It is important to note that, in order to achieve these targeted PIs of 5 % and 9 %, liquid limit values are also limited to being less than 25% as an additional requirement of national standards (ASTM D 1241, AASHTO M147) and several state DOT specifications. Although, the PI more than 9% is not typically allowed in US, the use of aggregates with PIs up to 16% has been reported in some European standards (Coronado et al. 2018). Therefore, a material with the LL of 30% and PI of 13% was also engineered to evaluate the impact of higher LL and PI on the strength characteristics of unbound aggregates. To properly control and achieve the desired 5

plasticity indices, nonplastic fines of limestone and gravel materials were carefully blended with highly plastic bentonite, kaolinite, ball clay and other minerals. For each blend, the nonplastic fines of limestone and gravel materials consisted more than 70% of the blend and many replicate Atterberg Limit tests were conducted to ensure the accuracy. Fig 1 shows a laboratory test matrix developed to characterize the effect of index properties on base and subbase unbound aggregates. For better illustrations, crushed limestone samples with CA 6 and CA 2 gradations are referred to as C-CA 6 and C-CA 2 respectively, while crushed gravel samples are represented as G-CA 6 herein. 4. GRADATION Dense graded aggregate with a maximum particle size of 25 mm is commonly referred to in Illinois as the CA 6 gradation which is also comparable to typical Gradation C of ASTM D1241. Dense graded aggregate with a 50 mm maximum particle size is referred to in Illinois as the CA 2 gradation which is comparable to Gradation A of ASTM D1241. Fig 2a and Fig 2b show the targeted CA 6 and CA 2 gradations, respectively. Washing and dry sieving of aggregates were carried out to achieve these target gradations. For particles larger than 1.18 mm (i.e., sieve No. 16), the maximum density packing approach commonly referred to as the Talbot equation (Equation 1) was used to develop the target gradations (Talbot and Frank, 1923): Equation (1) where p is the percentage of the particles that passes through the sieve. The sieve size opening is represented by d, D is the maximum particle size of aggregate and n is called shape factor of gradation curve. The n value of close to 0.5 was recommended for achieving higher density (Thom and Brown, 1988). For this research, the n value used was 0.5 for the CA 6 gradation and 0.45 for the CA 2 gradation to achieve higher density and be within the upper and lower limits of targeted gradations. Coarse particles were corrected for both CA 2 and CA 6 gradation in accordance with AASHTO T224. The percentage passing through the No. 40 sieve was determined for different configurations by multiplying the targeted dust ratio with the targeted fines content values.

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Samples with CA 2 gradation and a combination of 12% fines content and a dust ratio of 0.4 was logically impossible to develop. For samples to fall within the CA 2 gradation limits, the percentage passing through No. 40 sieve had to be greater than the percent passing through No. 16 sieve. Therefore, C-CA 2 samples with 12% fines and DR of 0.4 (i.e., samples A, D and G) were not prepared (see Figure 1). Void ratio that is controlled in compaction depends primarily on gradation or particle size distribution and aggregate particle shape, texture and angularity. Using specific gravity values from 2.60 to 2.70 for graded aggregates and maximum dry densities obtained from the standard Proctor tests, the void ratio ranges of the test samples were estimated (see Table 2). Regardless of fines content and dust ratio, samples with a maximum particle size of 50 mm (i.e., CA 2 gradation) had a greater range of void ratio compared to the aggregate samples with a 25 mm maximum particle size (i.e., CA 6 gradation). Moreover, as the amount of fines content was increased from 5% to 12%, the range of the void ratio decreased as expected. It should be noted that the gravel-to-sand (G/S) ratio, defined as the percentage of gravel to sand based on definitions of Unified Soil Classification System (USCS) (ASTM D 2487-11), ranges from 1.5 to 1.8 and 2.2 to 2.8 for the utilized CA 6 and CA 2 gradations, respectively, as the fines content increased from 5% to 12%. 5. DRY DENSITY Fig 3 shows the dry densities obtained at optimum moisture contents (OMCs) of aggregate samples prepared with 5%, 8% and 12% fines content. Generally, for both the CA 2 and CA 6 gradations, OMCs of aggregate samples with 12% fines were in the range of 5.8% to 9.4% while for samples prepared and tested with 5% fines, the OMC varied from 8.5% to 11%. The reason for higher OMC at 5% FC is because of the presence of higher air voids in samples with 5% FC compared to 12% FC, which requires more water to expel air during compaction process. In Fig 3a, for samples with 5% fines content, due to the presence of larger voids, the dry densities obtained at OMCs of all C-CA 2 samples were up to 12% and 6% lower than G-CA 6 and C-CA 6 samples, respectively. However, dry densities of C-CA 6 and G-CA 6 were more comparable to each other. Dry density at OMC for G-CA 6, C-CA 6 and C-CA 2 samples ranged from 2.0 to 2.2 g/cm3. In general, in all samples with 5% fines content, dry density decreased with an increase in dust ratio. At higher DR, there is less sand particles (particles passing the No. 7

40 sieve and retaining on the No. 200 sieve) which resulted in higher air voids between coarse aggregate and fine aggregate particles (See Table 2). In fact the higher DR resulted in a more gap-graded material. Therefore, dry density was lower at higher DR. Fig 3b shows the dry densities at OMCs of samples prepared and tested with 8% fines content. Similar to the case with 5% fines content, lower dry densities were achieved for all C-CA 2 samples when compared to the samples with CA 6 samples. Dry density at OMC for G-CA 6, CCA 6 and C-CA 2 samples ranged from 2.1 to 2.3 g/cm3 showing a higher dry density at OMC compared to the samples prepared and tested at 5% fines content. Fig 3c presents dry density at OMC values of engineered samples prepared and tested with 12% fines content. Dry densities of C-CA 2 samples were up to 9% and 6% lower than C-CA 6 and G-CA 6 samples, respectively. For all samples with CA 6 gradation, samples with a dust ratio of 0.6 had greater dry density at OMC value than samples with a dust ratio of 0.4. Dry density at OMC for G-CA 6, C-CA 6 and C-CA 2 samples ranged from 2.18 to 2.25 g/cm3, 2.14 to 2.32 g/cm3 and 2.07 to 2.20 g/cm3, respectively. In general, (1) a higher dry density was obtained with a higher fines content; (2) in lower fines content (i.e., 5% and 8%) samples, a lower dry density was generally observed with an increase in dust ratios; and (3) the dry densities of C-CA 2 samples were found to be lower than those of the C-CA 6 and G-CA 6 samples regardless of fines content.

6. AGGREGATE PROPERTY EFFECTS ON STRENGTH Fig 4, Fig 5 and Fig 6 show the soaked CBR of samples prepared and tested with 5%, 8% and 12% fines content, respectively. The tip of the arrow in the figures indicates the magnitude of the soaked CBR at OMC + 1.5%. The arrows to the left and right of the symbols represent the change in CBR at OMC+1.5% and OMC-1.5% compared to CBR at OMC, respectively. Upward and downward arrow represents the increase and decrease of soaked CBR values, respectively, relative to the strength at OMC. Fig 4 presents soaked CBR strength characteristics at 5% fines content for crushed limestone and crushed gravel. Soaked CBR values at OMC for engineered samples G-CA 6, C-CA 6 and C-CA 2 for all engineered samples were at least 45%, 55% and 32%, respectively. Overall, soaked 8

strength values of crushed gravel (i.e., G-CA 6) samples with low PI were higher than crushed limestone samples, but for PIs of 9% or 13%, they were less. This observation might be due to differences in mineralogy of these materials. It should also be mentioned that the CBR only evaluates the static behavior of the aggregate and it is a possibility that aggregates with a high strength provide less resistance under cyclic loading. Overall, the strength characteristics of crushed limestone samples with larger voids (i.e., C-CA 2) were the least among all. In general, for crushed limestone samples with both small and large voids at 5% fines, an increase in dust ratio from 0.4 to 0.6 within each PI level slightly increased soaked CBR at OMC values. However, further increase of DR from 0.6 to 1.0 had a negative effect and soaked CBR at OMC decreased where reductions were up to 35% for C-CA 2 samples and up to 15% for C-CA 6 samples. For crushed gravel samples, a clear trend of increasing or decreasing soaked CBR strength was not observed with respect to DR. The reduction in strength with an increase in PI and in each DR was only obvious for crushed gravel samples and crushed limestone samples with larger voids (i.e., C-CA 2). The reductions in soaked CBR at OMC for crushed gravel (except Sample G) and C-CA 2 samples were up to 35% and 16%, respectively, when PI was increased from 5% to 13%. Crushed limestone and crushed gravel samples engineered with 9% PI were the most sensitive to moisture content variations as soaked CBR values at OMC could be up to 40% different than the ones at OMC+/-1.5%. Fig 5 shows the soaked CBR strengths of all engineered samples prepared and tested with 8% fines content. Soaked CBR values at OMC of G-CA 6, C-CA 6 and C-CA 2 were at least 45%, 44% and 39%, respectively. Within the same PI level, an increase in dust ratio from 0.4 to 1.0 increased the soaked CBR at OMC of crushed gravel for up to 31%. However, for crushed limestone samples, increasing dust ratio from 0.4 to 1 within the same PI level did not indicate a clear trend on soaked strength fluctuation within the OMC+/-1.5% except for crushed limestone samples with larger voids and low PI (i.e., 5%). A general decreasing trend of soaked CBR within OMC+/-1.5% with an increase in PI from 5% to 13% was observed for both crushed limestone and crushed gravel samples. Fig 6 illustrates the soaked strengths of crushed limestone and crushed gravel samples prepared and tested with 12% fines content. Due to the anomaly in gradation noted earlier, C-CA 2 samples with dust ratio 0.4 were impossible; therefore, Fig 6 does not contain C-CA 2 samples 9

with dust ratio 0.4. For samples with high fines content (i.e., 12 %), a low dust ratio of 0.4 resulted in soaked CBR values at OMC of less than 30% for both crushed gravel samples (except Sample A) and crushed limestone samples. Within the same PI level, when dust ratio was increased from 0.4 to 1.0, the soaked CBR values at OMC of crushed gravel (i.e., G-CA 6) and crushed limestone with less voids (i.e., C-CA 6) increased at least by 23%. However, for crushed limestone samples with large voids, the soaked CBRs at OMC decreased up to 53% by an increase of DR from 0.6 to 1. With an increase in PI from 5% to 13%, soaked CBR values at OMC for G-CA 6, C-CA6 and C-CA 2 (except Sample B) decreased by and up to 83%, 17% and 38%, respectively. A more significant strength sensitivity to moisture content was observed for samples with fines content of 12% and DR of 0.6 and 1.0. It is concluded that within the same fines content level, the strength of crushed gravel samples prepared and tested with 5%, 8% and 12% fines content typically increases within the same PI level when dust ratio increases from 0.4 to 1.0. With a few exceptions, the strength values for crushed limestone samples with smaller voids (i.e., C-CA 6) and larger voids (i.e. C-CA 2) increase when DR increases from 0.4 to 0.6 and decrease with the increase in DR from 0.6 to 1.0. Finally, at all fines content, the increase in PI level in samples with the same DR resulted in less strength except for crushed limestone samples with less voids (i.e., 5% fines content), in which case the PI effect on strength was negligible. The moisture sensitivity of CBR results was significantly observed for samples with high fines content.

7. SOAKED STRENGTH ZONES FOR DEVELOPED CONFIGURATIONS Fig 7 demonstrates the range of average soaked CBR values for all the developed samples with CA 6 and CA 2 gradations regardless of their PI. The average soaked CBRs were obtained using CBRs at OMC, OMC + 0.75% and OMC + 1.5%. Fig 7 depicts the average soaked CBR values with dust ratios of 0.4, 0.6 and 1 for various fines contents. Three different strength zones have been defined to generalize the results obtained from each sample (Chaulagai et al., 2017; Osouli et al., 2017b). An average soaked CBR value of less than 40% was considered in a “Low” strength zone. Average soaked CBR values ranging from 40 to 55% were considered in a “Medium” strength zone, and finally, samples with average soaked CBRs greater than 55% were considered in a “High” strength zone. 10

Fig 7a show the ranges of average soaked CBRs for samples with a dust ratio of 0.4 (i.e., Sample A, D, and G) at 5%, 8% and 12% fines contents. The upper and lower bounds of average soaked CBR of G-CA 6, C-CA 6 and C-CA 2 decreased with an increase in fines content. The upper limits of average soaked CBR strengths of crushed limestone and gravel with CA 6 gradation at 5% fines content were 63% and 70%, respectively. However, with an increase in fines content from 5% to 12%, the maximum soaked CBR values decreased to 23% and 46% for C-CA 6 and G-CA 6 samples, respectively. The soaked CBRs of CA 6 samples with lower dust ratios and higher fines contents were limited to Low and Medium strength zones. One of the main reasons for lower average soaked CBRs is the excessive amount of fines which filled the voids between coarse grained particles and restricting grain to grain contact (Yoder and Witczak, 1975). Similarly, the fines were just filling the voids between the coarse-grained particles, and not supporting the applied load (Thevanayagam et al. 2000). It can be concluded that regardless of material type, for aggregate gradations with a dust ratio of 0.4, the use of 12% fines might be not as appropriate as other configurations for construction of pavement base and subbase layers. The upper limit of average soaked strengths of C-CA 6 and C-CA 2 decreased from 63% to 57% and from 60% to 55%, respectively, when fines content was increased from 5% to 8%. Overall, the range between upper and lower boundaries of average soaked CBR for crushed limestone with less voids (i.e., C-CA 6) was smaller than the one for crushed gravel or crushed limestone with larger voids. This indicates that C-CA 6 strength behavior is more reliable, and the strength has less volatility with respect to moisture content variation than others. Fig 7b shows the ranges of average soaked CBR for samples with a dust ratio of 0.6 (Sample B, E and H) at different percentages of fines content. A decreasing trend of average soaked strength was observed with increasing fines content for crushed gravel and crushed limestone with less voids. For crushed limestone with higher voids, the increase in fines content increases the upper limit of average soaked CBR strength. The lower bound of average soaked CBR strengths that were obtained from G-CA 6 and C-CA 6 samples were at least 35% and 46%, respectively, which shows a higher strength than samples prepared with DR of 0.4 (see Fig 7a). The average soaked CBR values of all C-CA 6 and G-CA 6 samples, except a few samples of crushed gravel that had 12% fines content, were in the Medium and High designated strength zones. Interestingly, the strengths of the C-CA 2 limestone samples were also within the Medium and High strength zone and the average soaked CBRs were greater than 39%. In general, CA 6 11

crushed limestone showed a narrower range between upper and lower bound of average CBR strength, therefore, it is less sensitive to soaking level than the crushed gravel or crushed limestone with larger voids. It is concluded that for aggregates with DR of 0.6, the strength is in acceptable ranges for base and subbase applications even with common variations in material type, fines content, plasticity index, and maximum particle size. Fig 7c characterizes the soaked strengths of all samples with DR of 1.0 (i.e., samples C, F and I). Note that samples with DR of 1.0 do not contain any sand size material in between the No. 40 and No. 200 sieve sizes. This implies that all voids between the coarse-grained particles are filled with minus No. 200 fines only. It is also noteworthy to reiterate that the DR of 1.0 is not within acceptable limits of the ASTM and AASHTO standard specifications. However, the average soaked CBR values of all crushed gravel samples were in the high strength zone and greater than 55%. Generally, all crushed limestone samples were in Medium to High strength zones except crushed limestone samples with larger voids (i.e., C-CA 2) that had low fines content of 5%. As the fines content increased from 5% to 12%, the soaked CBR also increased. This behavior was opposite to what was observed for aggregates with DR of 0.4 and 0.6. Overall, it is concluded that aggregates with a DR of 1.0 may also be viable options for base and subbase applications with the variation of fines content from 5% to 12% and plasticity index from 5% to 13%.

8. STAGED TRIAXIAL TESTS Staged triaxial tests were performed on selected samples, i.e., B-5, F-5, B-12, and F-12 (see Fig 1) from crushed limestone and gravel materials. These selected samples allowed to evaluate strength and stiffness at 5% and 12% fines contents, 5% and 9% PI, and 0.6 and 1.0 DR. In pavement construction, usually higher plasticity index of greater than 9.0 is not desired. For this reason, samples with PI of less than or equal to 9.0 were selected for staged triaxial test. Also, samples with DR of 0.6 (i.e., within the limit of standards) and 1.0 (i.e., beyond the limit of standards) allow us to study the effect of DR on unbound aggregate which has rarely been studied in the past. Cylindrical samples with 30.4-cm height and 15.2-cm diameter were tested at three confining pressures of 35 kPa, 69 kPa and 103 kPa. At each stage, deviatoric stress was increased until the peak stress was obtained. Then, deviatoric stress was removed, and confining pressure was increased to its corresponding value in the next stage followed by shearing. 12

Samples were prepared at optimum moisture contents and sheared under a loading rate of 1% strain per minute according to ASTM D2850. It is important to mention that drainage lines were closed at all stages of the triaxial test. Strain, height and cross section corrections were applied for different stages. Fig 8, Fig 9 and Fig 10 show the stress-strain plots of crushed limestone CA 6, crushed limestone CA 2 and crushed gavel samples, respectively.

Similarly, Table 3

summarizes the result obtained from triaxial test for all tested materials. As shown in Fig 8a, a higher confining pressure generally resulted in a higher maximum deviatoric stress and higher stiffness for the crushed limestone samples with CA 6 gradation at 5% fines content. Tutumluer et al. (2009) also found a similar result on CA 6 crushed limestone samples. The strains at failure for both B-5 and F-5 samples were greater than 7% at 35 kPa confining pressure, while at higher confining pressures of 69 kPa and 103 kPa, the strain at failure ranged from 3.8 to 4.3%. The initial moduli of these tests for the elastic portion response of samples in small strains were also calculated for each stage of triaxial testing. The moduli of both samples at lower confining pressure of 35 kPa were about 135 kPa and it increased with an increase in confining pressure to about 365 kPa in the second and third stages of the test. Moreover, the secant friction angles of 61, 55, and 52 degrees were determined for both samples at 35, 69 and 103 kPa confining pressures, respectively (see Table 3). These results were in agreement with findings of others in the literature on crushed dolomitic limestone (Saeed et. al 2001). They also show that with an increase in confining pressure, secant friction angles are reduced (Terzaghi et al. 1996). Triaxial and CBR tests can reveal strength of material with different mechanism of loading and confinement. For completeness the trend of CBR results and triaxial tests are discussed. The CBR strengths at OMC of B-5 and F-5 were 69% and 55%, respectively. There is a higher difference in soaked CBR values of B-5 and F-5 compared to the difference of their secant friction angles. This can be attributed to the fact that a rigid mold used in CBR tests provides a higher confining pressure and the CBR mechanism of loading is also different than triaxial test mechanism. Fig 8b presents the triaxial test results for crushed limestone samples with CA 6 gradation and 12% fines content. The strains at failure for B-12 were 4.7%, 3.2% and 2.4% at 35, 69 and 103 kPa confining pressures, respectively, while for F-12 sample, they were more than B-12 values with differences being up to 3% at 35 kPa and 0.8% at 69 and 103 kPa confining pressures. The 13

moduli of B-12 were 125, 336 and 455 kPa at the first, second and third stages of the triaxial test, respectively. These moduli of B-12 were greater than the moduli of F-12 by 19, 68 and 146 kPa at those consecutive stages. Secant friction angles for the sample of B-12 were about 58, 54 and 51 degrees and for the sample of F-12 about 60, 54 and 50 degrees at first, second and third stages of triaxial test, respectively. The CBR strengths at OMC for B-12 and F-12 samples were 80% and 71%, respectively. Even though, there were differences in CBR strengths, the secant friction angles of B-12 and F-12 samples from the triaxial tests were very close. These differences in secant friction angles and CBR strengths can be attributed to the differences in loading mechanism. CBR is a penetration shearing index test and load is applied in the center of the sample in a limited diameter confined mold, while in a triaxial test, the load is applied through a top plate on the complete sample diameter and horizontal deformation or bulging is not restricted but rather linked to an applied confining pressure, which describes more of a fundamental constitutive behavior. The increase in fines content from 5% to 12% resulted in the soaked CBR values at OMC to increase from 69% to 80% and from 55 to 71% for samples B and F, respectively. However, the secant friction angles of the B and F samples decreased up to 5% and 4%, respectively, with a similar increase in fines content. It is worth noting that one of the main reasons for lower secant friction angles at 12% fines content is that coarse particles float at higher fines content limiting load transfer among the coarse particles (Kolisoja 1997). Fig 9a shows the variations of deviatoric stress with the mobilized strain for crushed limestone samples with 5% fines content and larger voids (i.e., C-CA 2). Deviator stresses at failure of B-5 samples were slightly higher than F-5 samples at all stages. The strains at failure of these samples were in the range of 2.9% to 4.3% for B and F samples. The B-5 sample had greater stiffnesses compared to F-5. The modulus values of B-5 and F-5 were very similar and about 350 kPa at first, second and third stages of triaxial test. The secant friction angles of B-5 and F-5 were 58, 51, 48 degrees and 57, 51 and 47 degrees at 35, 69 and 103 kPa confining pressures, respectively (see Table 3). The soaked CBR strengths at OMC of B-5 and F-5 were 67% and 54%, respectively. There is a difference of 13% in soaked CBR values of B-5 and F-5 when compared to the difference of their secant friction angles, which can be attributed to the rigid

14

mold in CBR tests which imposes a boundary condition and interferes with a fully mobilized plane of shearing resistance. Fig 9b presents the triaxial test results of crushed limestone samples with 12% fines content and larger voids (i.e., C-CA 2). In general, higher maximum deviator stresses were found in B-12 samples compared to those in F-12 samples. Both B-12 and F-12 samples had strains at failure greater than 6.8% at lower confining pressure and 2.8% to 3.8% at higher confining pressures. The moduli of both B-12 and F-12 samples were about 115, 460 and 660 kPa at 35, 69 and 103 kPa confining pressures, respectively. Finally, secant friction angles decreased with increasing confining pressure. Particularly, secant friction angles of B-12 were 59, 54 and 51 degrees and F12 were 58, 53 and 49 degrees at first, second and third stages of the triaxial test. The CBR strengths at OMC for B-12 and F-12 samples were 77% and 43%, respectively. Even though, there was a difference of 34% in CBR strengths of these samples, the secant friction angle of F12 from the triaxial tests was less than B-12 by 1 degree at lower confining pressure and 2 degrees at higher confining pressure. These differences in secant friction angle and CBR can be attributed to the differences in loading mechanism and confinement realized in CBR and triaxial tests. The increase in fines content from 5% to 12% resulted in soaked CBR values at OMC to increase from 67% to 77% for B samples and a decrease from 54 to 43% for F samples. However, the secant friction angles of B and F samples increased up to 6%, when fines content increased from 5% to 12%. In general, CA 6 crushed limestone samples performed better by providing higher deviator stresses at failure and secant friction angles compared to CA 2 crushed limestone samples. The secant friction angle of B and F samples with CA 6 gradation were greater up to 9% and 10%, respectively, when compared with CA 2 gradation samples. The soaked CBR values of B and F samples with CA 6 gradation were greater than those samples prepared with CA 2 gradation at fines contents of both 5% and 12% and the difference was as high as 28% (see Section 6). Fig 10a present the stress-strain results of B-5 and F-5 crushed gravel samples. Samples of B-5 showed distinctly higher deviatoric stresses compared to F-5 samples at all confining pressures. Strains at failure for B samples ranged from 3.2% to 3.8% while F samples ranged from 3.1% to 5.5% at various confining pressures. The moduli of B-5 samples ranged from 420 to 540 kPa 15

while F-5 samples had moduli ranging from 120 to 380 kPa. The secant friction angles of B-5 samples were 56, 51 and 49 degrees at first, second and third stages of triaxial test, which are about 3 degrees higher than the ones for F-5 samples at similar confining pressures (See Table 3). The soaked CBR strengths at OMC of B-5 and F-5 samples were 81% and 62%, respectively. There is a larger difference in soaked CBR values of B-5 and F-5 compared to the difference of their secant friction angles. This is because of a more severe loading mechanism of punching shear empirical index test represented by CBR in a limited rigid mold when compared to more fundamental stress states applied and proper shearing due to deviator stress applied on the full specimen cross-section in triaxial tests. Fig 10b presents the triaxial results of crushed gravel samples with 12% fines content. Deviatoric stresses at failure of B-12 samples were greater than F-12 samples tested at 35 and 69 kPa confining pressures, while at the high confining pressure of 103 kPa, the deviatoric stress for B12 was slightly less. The strains at failure for both B-12 and F-12 samples were 4.6% and 5.6%, respectively, at the low confining pressure of 35 kPa. However, at higher confining pressures of 69 and 103 kPa, the strains at failure for both samples were limited to 2.9%. The moduli of B-12 samples ranged from 430 to 640 kPa while the moduli of F-12 samples ranged from 350 to 690 kPa. Moreover, the secant friction angles of B-12 sample was 54, 49 and 47 degrees while F-12 sample was about 54, 49 and 48 degrees at first, second and third stages of the triaxial test, respectively. It is worthwhile to note that secant friction angles of B-12 and F-12 samples for crushed gravel are less than the ones for crushed limestone. The CBR strengths at OMC for B-12 and F-12 samples were 89% and 85%, respectively. Differences in CBR strengths of these crushed gravel samples were relatively less compared to other tested samples of crushed limestone, and the secant friction angles of B-12 and F-12 samples were almost equal. The increase in fines content from 5% to 12% resulted in the soaked CBR values at OMC to increase from 81% to 89% and 62% to 85% for B and F samples, respectively. With an increase of fines content from 5% to 12%, the secant friction angle of B samples decreased up to 4% and while that of F samples increased up to 4%. Both CBR and triaxial tests show that the F samples with 12% fines had higher strength than F samples with 5% fine content. In general, CA 6 crushed limestone provided higher secant friction angles compared to CA 6 crushed gravel. The secant friction angles of B samples of CA 6 crushed limestone was greater 16

by about 9%, 9%, and 8% compared to the similar samples of crushed gravel at the first, second and third stages of triaxial tests, respectively. Thompson and Smith (1989) also showed using CA 6 gradation, the crushed stone had higher strength than crushed gravel. However, soaked CBR values of B and F samples of CA 6 crushed limestone were about 10% less than those of CA 6 crushed gravel samples at fines contents of both 5% and 12%. Summarizing the results of staged triaxial tests conducted on both crushed limestone and crushed gravel aggregates, B samples had better strength and stiffness characteristics compared to F samples prepared and tested with 5% and 12% fines contents. When fines content was increased from 5% to 12%, the stiffness of CA 6 crushed limestone decreased up to 27%. However, such stiffness increases were in excess of 16% and 31% for CA 6 crushed gravel and CA 2 crushed limestone, respectively, for a similar increase in fines content from 5% to 12%. Likewise, the crushed limestone specimen stiffness decreased by up to 43% with a change in gradation from CA 2 to CA 6 with maximum particle size going down from 50 mm (i.e., C-CA 2) to 25 mm (i.e., C-CA 6). Thom (1988) also found that for crushed dolomitic limestone samples, the stiffness decreased up to 25% with a reduction in maximum particle size from 30 mm to 3 mm. 9. CONCLUSIONS This research aimed to determine the influences of individual aggregate properties affecting the strength characteristics of aggregates used as base/subbase material in pavements. The dry densities of unbound aggregate with CA 6 and CA 2 gradations were the largest at higher fines content of 12%. However, maximum dry densities achieved from all crushed limestone CA 2 samples were less than both limestone and gravel CA 6 samples at any levels of fines content. At 5% and 12% fines contents, the strength values of crushed limestone samples in CA 6 and CA 2 gradations typically increase within the same PI level when dust ratio increases from 0.4 to 0.6 and decreases thereafter. However, at 8% fines content, the effect of DR is opposite compared to results obtained at 5% and 12% fines contents for the crushed limestone CA 6 gradation and insignificant for the crushed limestone CA 2 gradation. In case of the crushed gravel, soaked strengths increased gradually with increasing DR at all PIs and all levels of fines content. Similarly, the increase in PI decreased the soaked strength of engineered samples. Also, it is important to mention that the sample with 12% fines content and a DR of 0.4 had a significantly

17

lower soaked CBR values for all materials and gradations. Therefore, these samples, which are in the allowable limits of typical standards for base/subbase layer applications, are not appropriate. Findings from this study were used to propose Low, Medium and High aggregate strength zones. With common variations in material properties, strength characteristics of unbound aggregates with DR of 0.6 were found to be in an acceptable range for base and subbase applications. Furthermore, the CA 6 gradations of both the crushed limestone and crushed gravel samples with DR of 1.0 have a potential to be considered for roadway construction since the static strength of all samples were found to be in Medium and High strength zones; however, their performance trends under cyclic loading need to be further investigated. Moreover, the results from staged triaxial tests showed higher strengths for CA 6 crushed limestone samples compared to CA 6 crushed gravel and CA 2 crushed limestone samples at 5% and 12% FC. Similarly, CA 2 crushed limestone performed better compared to CA 6 crushed gravel at 5% and 12% FC. Regarding stiffness characteristics of the tested samples, when FC was increased from 5% to 12%, moduli of C-CA 6 samples decreased up to 27% while it increased in excess of 31% and 16% for C-CA 2 and G-CA 6 samples respectively.

10. ACKNOWLEDGEMENTS This publication is based on the results of R27-157, Plasticity Requirement of Aggregate Used in Based and Sub-base. ICT R27-157 was conducted in cooperation with the Illinois Center for Transportation; the Illinois Department of Transportation, Office of Program Development, and the US Department of Transportation, Federal Highway Administration. The authors would like to acknowledge the members of IDOT Technical Review Panel (TRP) for their useful advice at different stages of this research. The contents of this paper reflect the views of the authors only. 11. REFERENCES 1.

AASHTO M 147-65. Standard Specification for Materials for Aggregate and Soilaggregate Subbase, Base, and Surface Courses. American Association of State Highway and Transportation Officials, Washington D.C 2008.

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2.

3. 4.

5.

6. 7.

8.

9. 10.

11. 12. 13. 14.

15.

16.

17.

AASHTO T99. Standard Method of Test for Moisture-Density Relations of Soils Using a 2.5-kg (5.5-lb) Rammer and a 305-mm (12-in.) Drop. American Association of State Highway and Transportation Officials, Washington D.C 2017. AASHTO T193. Standard Method of Test for The California Bearing Ratio. American Association of State Highway and Transportation Officials, Washington D.C 2013. AASHTO T224. Standard Method of Test for Correction for Coarse Particles in the Soil Compaction Test. American Association of State Highway and Transportation Officials, Washington D.C 2010. Ahlberg, H.L., Barenberg, E.J., and Bartholomew, C. L. Physical Properties of Illinois Aggregates Affecting Load Bearing Strength and Performance. A & H Engineering & Testing Corporation, Champaign, Illinois 1966. Allen, J.J. and Thompson, M.R. Resilient Response of Granular Materials Subjected to Time Dependent Lateral Stresses. Transportation Research Record 1974 (1-13). ASTM Standard D 1241 – 00. Standard Specification for Materials for Soil- Aggregate Subbase, Base, and Surface Courses, ASTM International, West Conshohocken, Pennsylvania 2000. ASTM Standard D 2850 – 15. Standard Test Method for Unconsolidated-Undrained Triaxial Compression Test on Cohesive Soils, ASTM International, West Conshohocken, Pennsylvania 2015. Barksdale, R.D. and Itani S.Y. Influence of Aggregate Shape on Base Behavior. Transportation Research Record 1989; 173–182. Barksdale, R.D., S.F. Brown, and F. Chan. NCHRP Report 315: Potential Benefits of Geosynthetics in Flexible Pavements. Transportation Research Board, Washington D.C 1989. Bennert, T., & Maher, A. The Development of a Performance Specification for Granular Base and Subbase Material, Trenton 2005. Bilodeau, J. P., Doré, G., & Pierre, P. Erosion susceptibility of granular pavement materials. International Journal of Pavement Engineering 2007; 8(1): 5566. Bilodeau, J. P., Dore, G., & Pierre, P. Gradation influence on frost susceptibility of base granular materials. International Journal of Pavement Engineering 2008; 9(6): 397411. Chaulagai, R., Osouli, A., Salam, S., Tutumluer, E., Beshears, S., Shoup, H., & Bay, M. Maximum Particle Size, Fines Content and Dust Ratio Influencing Behavior of Base and Subbase Coarse Aggregates. Transportation Research Record, 2017; 2026. Coronado, O., Caicedo, B., Taibi, S., Correia, A.G., Fleureau, J.M. A Macro Geomechancial Approach to Rank Non-standard Unbound Granular Materials for Pavements. Engineering Geology 2011, 119, 64-73. Coronado, O., Caicedo, B., Taibi, S., Correia, A.G., Souli, H., Fleureau, J.M. Effect of Water Content on the Resilient Behavior of Non-standard Unbound Granular Materials. Transportation Geotechnics 2016, 7, 29-39. Dawson, A. R., N. H. Thom and J. L. Paute. Mechanical Characterstics of Unbound Granular Materials as a Function of Condition. Proceedings of European Symposium Euroflex, A.A. Balkema, Rotterdam 1996; 3544.

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18. Faiz, A. The Effect of Skip-Grading on Stability of Soil-Aggregate Mixtures. Ph.D, Purdue University 1971. 19. Gandara, J. A., Kancherla, A., Alvarado, G., Nazarian, S., & Scullion, T. Materials, Specifications, and Construction Techniques for High Performance Flexible Bases. Center for Transportation Infrastructure System, El Paso 2005. 20. Gray, J.E. Characteristics of Graded Base Course Aggregates Determined by Triaxial Tests. Engineering Research Bulletin No. 12, National Crushed Stone Association 1962. 21. Hicks, R.G. and Monismith, C.L. Factors Influencing the Resilient Response of Granular Materials. Highway Research Record 1971; 15-31. 22. Illinois Department of Transportation (IDOT). Standard Specifications for Road and Bridge Construction, Springfield, Illinois 2016. 23. Itani, Samir Youssef. Behavior of Base Materials Containing Large Sized Particles. Ph.D, Georgia Institute of Technology 1990. 24. Jing, P. Experimental Study and Modelling of the Elastoplastic Behaviour of Unbound Granular Materials under Large Number of Cyclic Loadings at Various Initial Hydric States. PhD Thesis. University of Strasbourg. 211 pages. 25. Jorenby, B.N. and Hicks R.G. Base Course Contamination Limits. Transportation Research Record 1986; 86–101. 26. Kamal, M. A., Dawson, A. R., Farouki, O. T., Hughes, D. A. B., & Sha’at, A. A. Field and laboratory evaluation of the mechanical behavior of unbound granular materials in pavements. Transportation Research Record 1993; 8897. 27. Kolisoja, P. Resilient Deformation Characteristics of Granular Materials. Ph.D, Tampere University of Technology, Tampere 1997. 28. Lekarp, F., Isacsson U., and Dawson A. State of the Art. I: Resilient Response of Unbound Aggregates. Journal of Transportation Engineering 2000a; 126(1): 66–75. 29. Lekarp, F, Isacsson U. and Dawson A. Permanent Strain Response of Unbound Aggregates. Journal of Transportation and Engineering 2000b; 76-83. 30. Missouri Department of Transportation (MODOT). Missouri Standard Specification for Highway Construction 2016. 31. Oklahoma Department of Transportation (OKDOT). Oklahoma Standard Specifications for Highway Construction 2009. 32. Osouli A., Salam S, Tutumluer E. Effect of plasticity index and dust ratio on moisturedensity and strength characteristics of aggregates. Transportation Geotechnics 2016; 69 – 79. 33. Osouli, A., Salam, S., Othmanawny, G., Tutumluer, E., Beshears, S., Shoup, H., & Eck, M. Results of Soaked and Unsoaked California Bearing Rate Tests on Unbound Aggregates with Varying Amounts of Fines and Dust Ratios. Transportation Research Record 2017a; 13-19. 34. Osouli A., Salam S, Tutumluer E., Shoup H. Fines inclusion in a crushed limestone unbound aggregate base course material with 25.4-mm maximum particle size. Transportation Geotechnics, 2017b; 96-108.

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35. Saeed, A., J.W. Hall, Jr., and W. Barker. NCHRP Report 453: Performance-Related Tests of Aggregates for Use in Unbound Pavement Layers, Transportation Research Board, National Research Council, Washington, D.C 2001. 36. Salam, S., Osouli, A., Tutumluer E. Crushed Limestone Aggregate Strength Influenced by Gradation, Fines Content and Dust Ratio. Journal of Transportation Engineering, Part B, 2018. 37. South Carolina Department of Transportation (SCDOT). Standard Specifications for Highway Construction 2007. 38. Terzaghi K., Peck R.B., Mesri G. Soil Mechanics in Engineering Practice, John Wiley & Sons, Inc; 1996. 39. Thom, N. H., & Brown, S. F. The effect of grading and density on the mechanical properties of a crushed dolomitic limestone. Australian Road Research Board (ARRB) Conference, 14th, Australian Road Research Board (ARRB), Canberra 1988; 94-100 . 40. Thom, N.H. Design of Road Foundations. Ph.D Dissertation. Nottingham, United Kingdom: University of Nottingham; 1988. 41. Thevanayagam S., Fiorillo M., and Liang J. Effect of Non-Plastic Fines on Undrained Cyclic Strength of Silty Sands. Geo-Denver, Colorado 2000. 42. Thompson M.R., Smith K.L. Repeated Triaxial Characterization of Granular Bases. Transportation Research Record 1990; 7-17 43. Tutumluer, E. Practices for Unbound Aggregate Pavement Layers. NCHRP Synthesis 445, Transportation Research Board, Washington, DC 2013. 44. Tutumluer, E., D. Mishra, and A. Butt,. Characterization of Illinois Aggregates for Subgrade Replacement and Subbase. Final Report, Illinois Center for Transportation (ICT) R27-1 Project, University of Illinois, Urbana–Champaign 2009. 45. Tutumluer, E., & Seyhan, U. Effects of fines content on the anisotropic response and characterization of unbound aggregate bases. In Proceeding of the 5th Symposium of Unbound Aggregates in Roads (UNBAR5), A.A. Balkema, Rotterdam 2000; 153-160. 46. Virginia Department of Transportation (VDOT). Road and Bridge Specifications 2016. 47. Washington State Department of Transportation (WSDOT). Standard Specifications for Road, Bridge and Municipal Construction 2014. 48. Yoder, E. J. and Witczak M.W. Principles of Pavement Design, John Wiley & Sons, Inc; 1975. 49. Yoder, E. J. Principles of Pavement Design, John Wiley and Sons, Inc; 1959.

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Vitae Dr. Abdolreza Osouli, Ph.D., P.E., is an assistant professor in the Department of Civil Engineering at SIUE and is a registered professional engineer in Missouri. He received his PhD in geotechnical engineering from University of Illinois at Urbana-Champaign. He has been active in research and education for over nine years. His research focuses include geotechnical engineering, soil and rock mechanics, and scour prediction. Dr. Osouli has served as an investigator on over 10 research projects funded by various funded agencies. He is currently serving as PI on a research project related to quality aggregates used as base and subbase material.

Rabindra Chaulagai, is a recent MS graduate of Southern Illinois University and served as research Assistant in this research project. He has received his Bachelor in civil engineering from Kathmandu University. He is currently working as Geotechnical Engineer with Marino Engineering Associates, Inc. His research interests include aggregate quality, mining engineering, and slope stability.

Erol Tutumluer, Ph.D., is a Professor and Paul F. Kent Endowed Faculty Scholar in the Department of Civil and Environmental Engineering at the University of Illinois at UrbanaChampaign (UIUC). Dr. Tutumluer has research interests in testing and modeling of pavement and railroad track geo-materials, i.e., soils and base/ballast aggregates, size and shape 22

characterization of aggregates using imaging and laser techniques, use of geosynthetics in transportation facilities, modeling of particulate media using discrete and finite element methods, neural network modeling, and mechanistic based pavement and railroad track design. Dr. Tutumluer has served as an investigator on over 60 research projects with grants received from Federal agencies including FHWA, FAA, FRA, US Army Corps of Engineers, NCHRP (served as co-PI on 4-30 and 4-34 projects) and NSF; state agencies including single grants from Illinois, Indiana and Minnesota DOTs and pool-funded research contributions from 5 other state DOTs; and private/industry such as IFAI, ICAR, AAR, BNSF, BASF, Caterpillar, Inc. and Tensar International, Inc.

Ms. Heather Shoup is the Central Office Geotechnical Engineer for the Illinois Department of Transportation. She participates on several research panels with the Illinois Center for Transportation and NCHRP. Ms. Shoup holds B.S. and M.S. degrees in Civil Engineering from South Dakota School of Mines & Technology with emphasis in Geotechnical Engineering. As the IDOT Central Geotechnical Engineer, she coordinates and provides technical support to the 9 Districts and oversees the Central Soils and Soils Instrumentation Laboratories. Ms. Shoup responsibilities include development and maintenance of the IDOT Geotechnical Manual, Subgrade Stability Manual, STTP S-33 Soil Field Testing and Inspection Course Manual, as well as several other forms, specifications, and test procedures pertaining to soils used by the Department.

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Table 1. National Standard and State Agency Requirements for Index Properties Standard Specification Maximum particle Plasticity Dust Ratio Maximum or State DOT Spec. size (mm) Index (%) (DR) allowable fines content (%) ASTM D1241-00 50 mm <4 <0.6 15% (2000) AASHTO M147-6550 mm <6 <0.66 20% 08 (2008) Illinois2 75 mm <6 or 4 or 91 13% Missouri 38 mm <6 15% Montana 50 mm 10% max ≤ 0.66 8% Oklahoma 75 mm <6 <2/3 12% South Carolina 50 mm 6 %max. 20% Virginia 50 mm <6 12% Washington 2/3 of the depth of ≤ 0.66 10% the layer being placed 1 2

In case of crushed gravel, stone or slag, lower plastic material with PI <6 can be used. When DR < 0.6, PI requirements are waived.

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Table 2. Ranges of Void Ratio for CA 6 and CA 2 Crushed Limestone Gradations Fines content Dust ratio Void ratio range for Void ratio range CA 6 gradation (%) for CA 2 gradation (%) 0.4 23-27 24-28 5% 0.6 22-27 26-30 1 28-33 29-34 0.4 20-25 21-26 8% 0.6 19-24 21-26 1 22-27 23-28 0.4 21-26 NA1 12% 0.6 17-21 20-25 1 20-24 23-28 1 NA = not available

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CA 6 Crushed Gravel

CA 2 Crushed Limestone

CA 6 Crushed Limestone

Table 3. Summary of Triaxial Test Results on Crushed Limestone and Crushed Gravel Plasticity Confining Failure Failure Friction Dust Modulus Material Index Sample Pressure Stress Strain Angle Ratio (kPa) (%) (kpa) (kpa) (%) (Degree) 35 487 7.3 137 61 5 0.6 B-5 69 622 3.9 366 55 103 761 3.8 411 52 35 482 7.6 141 61 9 1.0 F-5 69 620 4.3 365 55 103 756 4.2 384 52 35 392 4.7 125 58 5 0.6 B-12 69 574 3.2 336 54 103 706 2.4 455 51 35 442 7.7 105 60 9 1.0 F-12 69 581 4.0 268 54 103 669 3.2 309 50 35 372 4.1 357 58 5 0.6 B-5 69 488 3.2 353 51 103 587 3.3 393 48 35 360 3.6 348 57 9 1.0 F-5 69 467 2.9 343 51 103 566 4.3 378 47 35 419 7.4 116 59 5 0.6 B-12 69 577 2.8 463 54 103 699 2.9 656 51 35 396 6.9 111 58 9 1.0 F-12 69 560 3.1 458 53 103 651 3.8 652 49 35 339 3.8 494 56 5 0.6 B-5 69 493 3.3 416 51 103 618 3.2 537 49 35 279 5.5 122 53 9 1.0 F-5 69 417 3.1 311 49 103 532 3.6 382 46 35 300 4.6 431 54 5 0.6 B-12 69 432 2.3 636 49 103 559 2.6 639 47 35 290 5.6 351 54 9 1.0 F-12 69 422 2.5 580 49 103 590 2.9 688 48

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5%

Fines Content = 5%

9%

13 %

CA 6/CA 2 Gradation

Crushed Limestone/Gravel

5%

Fines Content = 8%

9%

13 %

5%

Fines Content = 12%

9%

13 %

0.4

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1

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H-12

1 I-12 x e l nd io y I t Rat abe t i L c s e sti Du ampl Pla S

Fig 1. Test program of engineered samples

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No. 200

No. 4

(a) 100

U.S. Standard Sieve Sizes CA6 Upper Limit

90

CA6 Lower Limit G-CA 6-5-A,D,G

70

G-CA 6-5-B,E,H

60

G-CA 6-5-C,F,I

50

G-CA 6-8-A,D,G

40

G-CA 6-8-B,E,H

30

G-CA 6-8-C,F,I

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G-CA 6-12-A,D,G G-CA 6-12-B,E,H

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G-CA 6-12-C,F,I

0 100

10

1

0.1

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No. 200

ASTM D2487 Classification

100

U.S. Standard Sieve Sizes CA2 Upper Limit

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CA2 Lower Limit

80

Percent Finer (%)

Percent Finer (%)

80

C-CA 2-5-A,D,G

70

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0 100

10

1 0.1 Particle Diameter (mm)

0.01

ASTM D2487 Classification

Fig 2. (a) CA 6 target gradations (b) CA 2 target gradations 28

Dry Density at OMC (g/cm3)

2.5

C-CA 6

a)

G-CA 6

C-CA 2

2.3 2.1 1.9 1.7

1.5

Dry Density at OMC (g/cm3)

A-5 2.5

B-5

C-5

D-5 E-5 F-5 Sample Label C-CA 6

b)

G-5

G-CA 6

H-5

I-5

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2.3 2.1 1.9 1.7 1.5

Dry Density at OMC (g/cm3)

A-8

2.5

c)

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D-8 E-8 F-8 Sample Label C-CA 6

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C-CA 2

2.3 2.1 1.9 1.7 1.5 A-12 B-12 C-12 D-12 E-12 F-12 G-12 H-12 I-12 Sample Label

Fig 3. Dry densities at OMC with (a) 5% fines content (b) 8% fines content and (c) 12% fines content

29

Fines Content = 5% 100

Soaked CBR (%)

90 80 70 60 50

PI = 5%

40 30 20 10 0 100

DR = 0.4 (A)

DR = 0.6 (B)

DR = 1.0 (C)

Soaked CBR (%)

90 80 70 60 50

PI = 9%

40 30 20 10 0 100

DR = 0.4 (D)

DR = 0.6 (E)

DR = 1.0 (F)

90

Soaked CBR (%)

80 70 60 50

PI = 13%

40 30 20 10 0

DR = 0.4 (G)

Symbol

Note

DR = 0.6 (H)

DR = 1.0 (I)

Legend Material and Gradation G-CA 6 (Crushed Gravel) C-CA 2 (Crushed Limestone) C-CA 6 (Crushed Limestone) Solid and hollow circular symbol represents soaked CBR at optimum moisture content. The arrows indicate the change in soaked CBR at OMC + 1.5%

Fig 4. Soaked CBR results of crushed limestone and gravel with 5% fines content 30

Fines Content = 8% 100

Soaked CBR (%)

90 80 70 60 50

PI = 5%

40 30 20 10 0 100

DR = 0.4 (A)

DR = 0.6 (B)

DR = 1.0 (C)

Soaked CBR (%)

90 80 70 60 50

PI = 9%

40 30 20 10 0 100

DR = 0.4 (D)

DR = 0.6 (E)

DR = 1.0 (F)

90

Soaked CBR (%)

80 70 60 50

PI = 13%

40 30 20 10 0

DR = 0.4 (G)

Symbol

Note

DR = 0.6 (H)

DR = 1.0 (I)

Legend Material and Gradation G-CA 6 (Crushed Gravel) C-CA 2 (Crushed Limestone) C-CA 6 (Crushed Limestone) Solid and hollow circular symbol represents soaked CBR at optimum moisture content. The arrows indicate the change in soaked CBR at OMC + 1.5%

Fig 5. Soaked CBR results of crushed limestone and gravel with 8% fines content 31

Fines Content = 12% 100

Soaked CBR (%)

90 80 70 60 50

PI = 5%

40 30 20 10 0 100

DR = 0.4 (A)

DR = 0.6 (B)

DR = 1.0 (C)

Soaked CBR (%)

90 80 70 60 50

PI = 9%

40 30 20 10 0 100

DR = 0.4 (D)

DR = 0.6 (E)

DR = 1.0 (F)

90

Soaked CBR (%)

80 70 60 50

PI = 13%

40 30 20 10 0

DR = 0.4 (G)

Symbol

Note

DR = 0.6 (H)

DR = 1.0 (I)

Legend Material and Gradation G-CA 6 (Crushed Gravel) C-CA 2 (Crushed Limestone) C-CA 6 (Crushed Limestone) Solid and hollow circular symbol represents soaked CBR at optimum moisture content. The arrows indicate the change in soaked CBR at OMC + 1.5%

Fig 6. Soaked CBR results of crushed limestone and gravel with 12% fines content 32

a) 0 10

Dust Ratio = 0.4 (A, D, G) 20 30 40 50 60 70 80 90 100 Medium

High

Low

Medium

High

12 % FC

12 % FC

8 % FC

8 % FC

5 % FC

5 % FC

Low

Dust Ratio = 0.6 (B, E, H) b) 0 10 20 30 40 50 60 70 80 90 100

Dust Ratio = 1 (C, F, I)

c) 0

10

20 30 40 50 60 70 80 90 100

LEGEND Low

Medium

High

C-CA 6 (Crushed Limestone)

5 % FC

G-CA 6 (Crushed Gravel) C-CA 2 (Crushed Limestone) Average CBR values at OMC and OMC +/- 1.5%

8 % FC

Zone boundary

12 % FC

FC = Fines Content Note: The lower and upper CBR boundaries for each test configuration show the minimum and maximum CBR values within OMC +/- 1.5%

Fig 7. Ranges of average soaked CBR for samples with (a) DR 0.4 (b) DR 0.6 (c) DR 1.0

33

800

a) 700

Deviator Stress (kPa)

600 500 400

C-CA 6-B-5 (35 kPa) 300

C-CA 6-B-5 (69 kPa) C-CA 6-B-5 ( 103 kPa)

200

C-CA 6-F-5 (35 kPa) 100

C-CA 6-F-5 (69 kPa) C-CA 6-F-5 (103 kPa)

0

0.0

2.0

4.0

6.0

8.0

10.0

Strain (%) 800

b) 700

Deviator Stress (kPa)

600 500 400 C-CA 6-12-B (35 kPa)

300

C-CA 6-12-B (69 kPa) C-CA 6-12-B (103 kPa)

200

C-CA 6-12-F (35 kPa) 100

C-CA 6-12-F (69 kPa)

C-CA 6-12-F (103 kPa)

0 0.0

2.0

4.0

6.0

8.0

10.0

Strain (%) Fig 8. Stress-strain results of C-CA 6 limestone (a) B-5 and F-5 samples with 5% fines (b) B-12 and F-12 samples with 12% fines (The numbers in the parentheses show confining pressures) 34

800

a) 700

Deviator Stress (kPa)

600 500 400

C-CA 2-5-B (35 kPa)

300

C-CA 2-5-B (69 kPa) C-CA 2-5-B (103 kPa)

200

C-CA 2-5-F (35 kPa) 100

C-CA 2-5-F (69 kPa) C-CA 2-5-F (103 kPa)

0 0.0

2.0

4.0

6.0

8.0

10.0

Strain (%) 800 700

b)

Deviator Stress (kPa)

600 500

400 C-CA 2-12-B (35 kPa) C-CA 2-12-B (69 kPa) C-CA 2-12-B (103 kPa) C-CA 2-12-F (35 kPa) C-CA 2-12-F (69 kPa) C-CA 2-12-F (103 kPa)

300 200 100 0 0.0

2.0

4.0

6.0

8.0

10.0

Strain (%) Fig 9. Stress-strain results of C-CA 2 limestone (a) B-5 and F-5 (b) B-12 and F-12 (The numbers in the parentheses show confining pressures)

35

800 (a)

Deviator Stress (kPa)

700 600 500 400 G-CA 6-B-5 (34.5 kPa G-CA 6-B-5 (69 kPa) G-CA 6-B-5 (103 kPa) G-CA 6-F-5 (35 kPa) G-CA 6-F-5 (69 kPa) G-CA 6-F-5 (103 kPa)

300 200

100 0

0.0

2.0

4.0

6.0

8.0

10.0

Strain (%) 800

G-CA 6-B-12 (35 kPa) G-CA 6-B-12 (69 kPa) G-CA 6- B-12 (103 kPa) G-CA 6-F-12 (35 kPa) G-CA 6-F-12 (69 kPa) G-CA 6-F-12 (103 kPa)

b) 700

Deviator Stress (kPa)

600 500 400 300 200 100 0 0.0

2.0

4.0

Strain (%)

6.0

8.0

10.0

Fig 10. Stress-strain results of G-CA 6 gravel (a) B-5 and F-5 (b) B-12 and F-12 (The numbers in the parentheses show confining pressures) 36