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1 0 0 0 REVISED PAPER #- QUANTIFYING EFFECTS OF PARTICLE SHAPE AND TYPE AND AMOUNT OF FINES ON UNBOUND AGGREGATE PERFORMANCE THROUGH CONTROLLED GRADATION Submitted for the th Annual Meeting DVD of the Transportation Research Board Washington, DC, January 0 by Debakanta Mishra Graduate Research Assistant Ph: (0) - / dmishra@illinois.edu Dr. Erol Tutumluer Professor Paul F. Kent Endowed Faculty Scholar (Corresponding Author) / Ph: () - tutumlue@illinois.edu / (Fax: --) Department of Civil and Environmental Engineering University of Illinois at Urbana-Champaign 0 North Mathews, Urbana, IL 0 and Dr. Abbas A. Butt - President Engineering and Research International, Inc. 0 Regency Drive East, Savoy, IL Ph: () - / (Fax: --) eri@erikuab.com Word Count:, words + Figures (*0) + Tables (*0) =, November 00 TRB 0 Annual Meeting CD-ROM

2 Mishra, Tutumluer and Butt Quantifying Effects of Particle Shape and Type and Amount of Fines on Unbound Aggregate Performance through Controlled Gradation Debakanta Mishra Graduate Research Assistant Erol Tutumluer Professor University of Illinois at Urbana-Champaign Abbas A. Butt Engineering and Research International, Inc. ABSTRACT Construction of a pavement working platform is often needed on soft, unstable soils to provide sufficient stability and adequate immediate support for equipment mobility and paving operations without developing excessive rutting. Standard specifications may often allow the use of a wide range of aggregate materials for subgrade applications regardless of aggregate properties. The aggregate type and quality are important factors for determining the required treatment/replacement thickness. This paper describes laboratory findings from an ongoing research study at the University of Illinois aimed at evaluating aggregate cover thickness requirements on soft subgrade through characterizing strength and deformation behavior of crushed limestone and dolomite and uncrushed gravel, commonly used in Illinois for subgrade replacement and subbase. The initial laboratory phase consisted of moisture-density, unsoaked CBR, imaging based aggregate shape characterization, and shear strength tests based on a comprehensive experimental test matrix which considered both plastic and non-plastic fines (passing No. 00 sieve or 0.0 mm) blended in the engineered gradations at %, %, %, and % target fines contents. From the test results, the most important property at low fines contents (less than %) was the aggregate type governed by the angularity, i.e. crushed or uncrushed, and the amount of voids in the aggregate matrix. The uncrushed gravel more quickly filled the voids at lower fine percentages thus making gravel less tolerable to negative effects of increasing fines. When plastic fines (plasticity index or PI of or higher) were included, the amount of fines had a drastic effect on aggregate performance. Key Words: Unbound Aggregates, Pavement Working Platform, Aggregate Shape, Type of Fines, Fines Content, Moisture-Density, Shear Strength TRB 0 Annual Meeting CD-ROM

3 Mishra, Tutumluer and Butt INTRODUCTION Construction of a working platform plays an important role in pavement construction in Illinois as the local soils are relatively soft (). For any type of pavement to be constructed on an unprepared soft grade, the subgrade must be sufficiently stable to: (i) prevent excessive rutting and shoving during construction, (ii) provide good support for placement and compaction of paving layers, and (iii) limit permanent deformation buildup during pavement service life. The working platform provides such an aggregate cover to facilitate paving operations without developing excessive rutting under the construction equipment and allows for the compaction of overlying pavement layers. The Illinois Department of Transportation (IDOT) Subgrade Stability Manual (SSM) recommends required thickness values for aggregate cover based on the Immediate Bearing Value (IBV) of the subgrade (). IBV is a measure of soil strength obtained by conducting the standard bearing ratio test, commonly known as the California Bearing Ratio (CBR) according to AASHTO T, on molded soil samples immediately after compaction (without soaking). For untreated soils with IBV values less than.0, subgrade removal and aggregate replacement for cover is one of the most commonly used options for treating soft, unstable soils (). However, the remedial thickness determined by the IBV does not differentiate between various aggregate properties when recommending aggregate thickness. Further, IDOT s standard specifications allow the use of a wide range of aggregate materials for subgrade applications regardless of aggregate properties. The aggregate type and quality are important factors for determining the required treatment/ replacement thickness. Depending on the location of a subgrade soil project, various locally available aggregates may be used to replace unsuitable soil. For example, dense-graded aggregates with high fines (minus No. 00 sieve size or 0.0 mm) contents and/or excessive Plasticity Index (PI) values may exhibit increased or high moisture sensitivity effect on their performance in subgrade applications. A comprehensive evaluation of the effects of aggregate properties, such as aggregate type or angularity, fines content, PI, and moisture-density on the strength and deformation characteristics is needed to develop end-performance related linkages between aggregate cover thickness and aggregate properties. Such an evaluation can ultimately economize the use of aggregate materials in working platform applications by either reducing thickness or avoiding failures due to poor quality aggregate cover performances. This paper presents preliminary laboratory findings from an ongoing research study at the University of Illinois aimed at evaluating aggregate cover thickness requirements on soft subgrade. The overall objective was to develop an experimental test matrix to quantify both individual and combined effects of different aggregate properties on aggregate performance as indicated by the strength, stiffness, and deformation behavior of three aggregate materials, crushed limestone and dolomite and uncrushed gravel commonly used in Illinois for subgrade replacement and subbase. The approach used for developing the test matrix is described first by emphasizing the importance of controlling aggregate gradation in such a parametric study. Aggregate particle shape, texture and angularity properties are quantified through imaging based indices. Then, the effects of aggregate shape characteristics, as well as type and amount of fines on aggregate strength and deformation behavior are investigated from the moisture-density, unsoaked CBR, and triaxial shear strength test results. Critical combinations of test matrix variables having the most drastic effects on aggregate performance are highlighted. DEVELOPMENT OF TEST MATRIX The laboratory testing efforts in this research study were designed such that researchers could assess the relative importance of different test matrix variables affecting aggregate behavior. An experimental test matrix was developed for the three most commonly used aggregate types in the state of Illinois: uncrushed gravel and crushed limestone and dolomite. The primary objective was to establish ranges for major aggregate properties that primarily influence strength, modulus, and deformation behavior of TRB 0 Annual Meeting CD-ROM

4 Mishra, Tutumluer and Butt 0 aggregates thus govern the behavior of aggregate layers in any pavement system. These aggregate properties include: [] fines content (defined in this study, as amount of material passing sieve No. 00 or 0.0 mm), [] Plasticity Index (PI) of fines, [] particle shape (flatness and elongation), angularity and surface texture, and [] moisture content and dry density (compaction) properties. For studying the effects of fines on aggregate behavior, laboratory specimens were tested at four different fines contents, established at %, %, % and % material by weight passing No. 00 sieve. These values were selected to encompass entire ranges of fines contents mostly allowed by state agencies. To distinguish between different types of fines, the plasticity index (PI), determined by measuring the Atterberg limits of the material passing No. 0 sieve size, was taken as the indicative parameter. Two different fine types (non-plastic and plastic with a PI in the range of -% obtained by adding refinery clay to non-plastic fines) were used to evaluate the effect of plasticity of fines on aggregate behavior. Each sample was tested at three different moisture contents: optimum moisture content (w opt ), dry of optimum (0% of w opt ), and wet of optimum (% of w opt ) following the standard Proctor procedure (AASHTO T). Importance of Controlling Gradation Before conducting any parametric study on the aggregate properties affecting behavior, it was important to control the gradations consistently among the different materials tested. Differences in aggregate gradations can lead to significantly different behavior for the same aggregate type. A controlled particle size distribution would therefore help to attribute the observed change in behavior to the effect of varied aggregate property (e.g., fines percentage, plasticity of fines, etc.). Figure shows the engineered aggregate gradation curves developed for the different target fines contents. To blend test samples according to the engineered gradations, sieving and size separation of the aggregates was undertaken first. Approximately tons of each aggregate material received were processed through sieving for amounts retained on individual sieve sizes and collecting them into different barrels. The test samples were then blended for the target gradation and fines content following the engineering gradation curves in Figure Cumulative Percent Passing % Fines % Fines % Fines % Fines % Fines Particle Size (mm) FIGURE Engineered Aggregate Gradations for Different Fines Contents TRB 0 Annual Meeting CD-ROM

5 Mishra, Tutumluer and Butt Sample Blending and Effect of Fines Sticking To Coarse Particles After separating individual aggregate sizes into separate barrels, the next step was to blend the aggregates as per the engineered gradations, and to check the target vs. achieved gradation through wet sieving of the samples. The wet sieving results showed that the actual fines content of a sample was always higher than the target fines content during blending. This difference in achieved vs. target fines content was attributed to the significant amount of fines that remained stuck to the surfaces of larger particles during dry sieving and contributed towards the total fines content determined by wet sieve analysis. These fines could influence considerably the aggregate behavior, and therefore, had to be accounted for while preparing test samples. Table lists the target vs. actual fines contents determined through wet sieving. TABLE Target and Achieved Fines Contents Actual Fines Content (%) Target Fines Content (%) (based on wet sieving) (through dry blending of different sizes) Limestone Uncrushed Gravel Dolomite Table indicates that even a sample blended targeting 0% fines (no material passing No. 00 sieve) contains.% fines in the case of limestone, and.% fines for uncrushed gravel. However, the dolomite sample, (received as already washed) contained less than % fines. The limestone and uncrushed gravel stockpiles were received directly from the quarry and hence had significant amount of fines sticking to larger particles. An interesting observation for both limestone and gravel, the achieved fines were consistently about.%-% higher than the target fines. Therefore, it was decided to blend these samples targeting 0%, %, % and % fines, so that the actual fine contents would be in the order of %, %, %, %, respectively. Dolomite samples (which had negligible fines sticking to larger particles) were blended targeting %, %, %, and % actual fines. CHARACTERIZING AGGREGATE SHAPE, TEXTURE AND ANGULARITY Aggregate particle shape, texture and angularity have been found to affect the performance of aggregate layers (both bound as well as unbound) in pavement structures. Unbound aggregate layers having crushed particles have consistently performed superior compared to those with uncrushed particles. Allen () and Barksdale and Itani () investigated the effects of surface characteristics of unbound aggregates and found that angular materials resisted permanent deformation better than rounded particles because of improved particle interlock and higher angle of shear resistance between particles. Barksdale and Itani () also concluded that blade shaped crushed particles were slightly more susceptible to rutting than other types of crushed aggregate and that cube-shaped, rounded river gravel with smooth surfaces was more susceptible than crushed aggregates. More recently, Rao et al. () studied the impact of imaging based aggregate angularity index variations on the friction angle of different aggregate types and reported an improvement in aggregate performance when the percentage of crushed particles increased. An increase in the proportion of crushed particles beyond 0% increased the friction angle significantly, indicating higher resistance to permanent deformation accumulation. Knowing the effect of aggregate type (in terms of quantifiable measures of angularity and surface texture) on field performance for the subgrade replacement/subbase application would enable TRB 0 Annual Meeting CD-ROM

6 Mishra, Tutumluer and Butt practitioners to optimize the required aggregate cover thickness. Therefore, the three aggregate types studied in this research project were first tested for particle shape, texture and angularity characteristics. The use of a validated image analysis system, the University of Illinois Aggregate Image Analyzer (UIAIA), was pursued to quantify aggregate shape (flatness and elongation), angularity and surface texture characteristics. More information about the capabilities and operating principles of UIAIA can be found elsewhere (,,). Approximately 0 particles were selected from each aggregate type and analyzed using the UIAIA through three replicate tests. The shape and angularity indices calculated were: Flat and Elongated (F&E) ratio (), angularity index (AI) (), and surface texture (ST) index (). The AI and ST indices have, in the past, been directly linked to shear strength and permanent deformation behavior of aggregates to compare the contributions of crushed vs uncrushed particles (). All the particles selected for image analyses belonged to barrels corresponding to material retained on No. (. mm) and No. (. mm) sieves, as UIAIA results tend to be more accurate for coarse aggregates. Figure shows aggregate AI values graphed with percentage by weight of particles for the limestone and gravel. For lower AI values (in degrees), the uncrushed gravel particles have much higher percentages than those for the crushed limestone (see Figure ). However, as the AI values increase, the percentages of limestone particles dominate. 0 Percentage Particles by Weight (%) 0 Crushed Limestone Uncrushed Gravel 0 Below Above 0 0 Angularity Index (AI) FIGURE Comparisons of Angularity Index (AI) Values for the Limestone and Gravel Materials TABLE lists the average particle shape, texture and angularity characteristics for the three aggregate types studied, measured in terms quantifiable imaging based shape indices using the UIAIA. Note that higher AI and ST values indicate more angular and rougher surface textured aggregates, i.e., the crushed dolomite and limestone particles. The uncrushed gravel particles are closer to spherical shapes with the lowest flatness and elongation ratios by weight among the three aggregate types. Table also lists typical AI and ST index values for uncrushed gravel and crushed limestone, identified from samples of different coarse aggregate materials studied in a nationwide research study (). It should be noted that the imaging based shape indices determined in the current study appropriately fall within the typical ranges determined in the previous study. TRB 0 Annual Meeting CD-ROM

7 Mishra, Tutumluer and Butt TABLE Average Values of F&E Ratio, ST and AI Indices for the Three Aggregate Types Average Values Angularity Index (AI) Measured Typical Range* Surface Texture (ST) Index Measured Typical Range* Flat and Elongated Ratio (by Weight) Measured Uncrushed Gravel Dolomite N/A. N/A. Limestone * Typical values identified from different coarse aggregate materials in a recent pool fund study () MOISTURE-DENSITY TESTS The objective of compaction is to improve the engineering properties of the soil mass; by compaction soil strength can be increased, bearing capacity of pavement layers can be improved, and undesirable volume changes, for example, caused by frost action, swelling and shrinkage, may be controlled (). Density is used in pavement construction as a quality control measure to help determine the compaction level of the constructed layers. Generally, increasing the density of a granular material makes the aggregate layer stiffer and reduces the magnitude of the resilient and permanent deformation response to static and dynamic loads (). As most construction specifications for unbound aggregate layers are designed referencing the maximum dry density and optimum moisture content values as determined from Proctor (standard or modified) testing of laboratory samples, it was important to first study the moisture-density characteristics of the aggregate materials. Optimum moisture content (w opt or OMC) was taken as the basis for studying the effect of moisture content variation on aggregate performance. Moreover, the compaction curves were also used to determine target density values while preparing samples on the dry or wet side of OMC. Compaction tests were conducted following the standard Proctor method specified in ASTM D (AASHTO T-). IBV or unsoaked CBR tests were also performed on the same Proctor specimens by following ASTM D procedure (without soaking specimens) to provide expedited shear strength index test results from the moisture-density test specimens. Any change in unsoaked CBR results with moisture content was studied at different fines contents to determine the strength variation trends of each material with moisture content. Detailed discussion on the moisture-density and IBV test results are presented elsewhere (). Primary trends observed in moisture-density behavior as well as unsoaked CBR values are analyzed in this paper in relation to the effects of particles shape characteristics and type and amount of fines. Note that the legends provided in figures showing both compaction and CBR results represent the actual fines contents of the samples from washed sieve analyses. Effect of Non-plastic Fines Figure presents the dolomite standard Proctor and unsoaked CBR test results conducted on samples prepared by adding different percentages of non-plastic fines. The upper part of Figure shows the moisture-density behavior of dolomite samples with non-plastic fines, whereas the lower part shows the unsoaked CBR values for each of the Proctor samples. Typically, the maximum dry density values increase as the percentage of fines in the sample increases, with the highest maximum dry density obtained at a fines content of.%. As the addition of fines gradually fills the voids, the aggregate matrix continues to become denser thus making.% sample the densest. The dependence of unsoaked TRB 0 Annual Meeting CD-ROM

8 Mishra, Tutumluer and Butt CBR (see lower part of Figure ) with moisture content is erratic at low fines contents (i.e.,.% and.%). However, at higher fines contents, the CBR values decrease rapidly with increases in moisture. The rate of decrease in the CBR value with moisture is higher at higher fines contents. A similar trend was observed for limestone samples (); the density of limestone samples increased as the fines content increased with the highest density achieved at a fines content of.%. Generally, the limestone samples experienced erratic CBR with moisture changes at low fines contents. However, as the fines content increased, a rapid fall in CBR value with increase in moisture content was noticeable. FIGURE : Effect of Non-plastic Fines on Dolomite Aggregates Figure shows a similar plot for uncrushed gravel samples blended with different percentages of non-plastic fines. Initially, as the fines content is increased from.% to.%, the maximum dry TRB 0 Annual Meeting CD-ROM

9 Mishra, Tutumluer and Butt density also increases. However, as the fines content is further increased to.%, the maximum dry density value decreases. This can be explained by considering the packing characteristics of crushed and uncrushed aggregates. The uncrushed gravel matrix, comprised of rounded aggregate particles, has a lower amount of total voids as compared to that of crushed limestone or dolomite sample. As the fines content is increased beyond a certain point, all the voids in the uncrushed gravel matrix get filled and the coarse particles start to float in the matrix. This results in a reduction in the dry density, as the specific gravity of the fines is lower than that of the coarse particles. It should be noted that for limestone samples even the presence of.% fines did not completely fill the voids. Similar to the case of dolomite, the unsoaked CBR relationship of gravel with moisture content is erratic at low fines contents. However, as the fines content increases, there is a rapid decrease in CBR with increasing moisture content. FIGURE Effect of Non-plastic Fines on Uncrushed Gravel TRB 0 Annual Meeting CD-ROM

10 Mishra, Tutumluer and Butt Effect of Plastic Fines To study the effect of plastic fines on aggregate behavior, test samples were prepared at different percentages of plastic fines. The plastic fines used in the study had plasticity index (PI) values in the range of % to %. Figure shows more drastic effects of plastic fines on the behavior of dolomite samples. The moisture-density behavior exhibits a pattern similar the case of non-plastic fines. The attained maximum dry densities increase with fines content increasing from.% to.%. However, the lower part of Figure clearly captures the different influences of plastic and non-plastic fines. Unlike in the case of non-plastic fines, the unsoaked CBR value decreases rapidly with increasing moisture content, even at a fines content of.%. Moreover, it should be noted that the CBR values for samples with plastic fines are appreciably lower than those with non-plastic fines, even at the same moisture contents. FIGURE Effect of Plastic Fines on Dolomite TRB 0 Annual Meeting CD-ROM

11 Mishra, Tutumluer and Butt The findings outlined here support the common observation that plastic fines deteriorate aggregate performance significantly. Moreover, the rapid fall in CBR value on the wet side of OMC highlights the drastic reduction in the overall material quality caused by the combined action of plastic fines and moisture. Therefore, the type of fines needs to be paid significant attention when determining limits for the maximum amount of fines allowed in any aggregate layer. Specifying one limit for both non-plastic and plastic fines may lead to poor performance, particularly in cases where plastic fines are introduced with high moisture contents. Figure shows the effect of plastic fines on gravel samples. The moisture density curves exhibit similar trends to those observed with non-plastic fines (maximum dry density falls at very high fines contents). However, the CBR-moisture content relationship exhibits a stronger impact of plastic fines on the aggregate strength characteristics, as already discussed for limestone. Comparing Effects of Plastic and Non-Plastic Fines To compare and better evaluate the effect of fine type and amount of fines on aggregate strength, the unsoaked CBR values of the three aggregate types at the optimum moisture content were graphed with the different percentages of fines (see Figure ). Figure clearly shows that for all the three aggregate types, CBR values for samples with plastic fines are lower than those with non-plastic fines, at high fines contents. For limestone and dolomite samples, the same trend was observed even at low fines contents. However, the effect of plastic fines on gravel is not as pronounced at low fines contents. Comparing Effects of Crushed and Uncrushed Aggregates Figure clearly illustrates the contribution of particle shape on the CBR behavior. For the same fines percentage, the crushed stones (limestone and dolomite) exhibit higher unsoaked CBR values when compared to uncrushed gravel. This observation can be directly correlated to the ST and AI values listed in Table. Limestone and dolomite, both comprised of crushed particles with a rough surface texture, demonstrate better particle to particle contact in the aggregate skeleton. The better interlock manifests itself into higher CBR values, which can be used as an indicator of the shearing resistance of the material. This also reinforces the common observation that crushed aggregate particles perform better in pavement systems compared to uncrushed particles as far as shear related failure is concerned. Interestingly, limestone surpasses dolomite in CBR values attained beyond a fines content of % (see Figure ). Note that this can possibly be explained by the slightly higher AI and ST indices for limestone when compared to those of dolomite (see Table ). For limestone, higher angularity also brings higher voids and greater tolerance to accommodate increased amounts of fines beyond % without compromising aggregate to aggregate contact, which may be essential for maintaining high CBR values. RAPID SHEAR STRENGTH TESTS To better evaluate effects of different aggregate properties on the shear strength behavior, triaxial shear strength tests were also conducted on the aggregate samples. The test procedure followed was the University of Illinois rapid shear strength test. Compared to the conventional triaxial shear tests, rapid shear tests punch the loading ram into a 0-mm high specimen at a very high loading rate of mm/second causing.% deformation. Due to the high loading rate, this test gives slightly higher peak stresses as compared to results from the conventional shear strength tests. However, rapid shear tests are believed to better simulate any possible failure condition of an in-service pavement layer under the dynamic application of a moving wheel load (,). Three different samples were tested at confining pressures of.,.0, and. kpa to determine the shear strength properties of the aggregate materials. TRB 0 Annual Meeting CD-ROM

12 Mishra, Tutumluer and Butt The maximum deviator stress at failure or the peak deviator stress value was compared to evaluate strength properties of the different aggregate samples. It was decided to average the peak deviator stresses corresponding to the three confining pressures for each material tested. This way, instead of using friction angles or cohesion intercepts, which may not be consistent when individually compared, the average peak deviator stress (maximum stress at failure) values could be used to consistently compare strength characteristics and draw conclusions regarding the effects of material type, amount of fines, type of fines, and moisture content on aggregate shear strength. Significant trends observed in the strength behavior of the three aggregate materials are reported in this section. FIGURE Effect of Plastic Fines on Gravel TRB 0 Annual Meeting CD-ROM

13 Mishra, Tutumluer and Butt Table compares the average peak deviator stress values of the dolomite samples containing nonplastic fines with those containing plastic fines both tested at optimum moisture contents. As listed in Table, the samples with plastic fines have a tendency to steadily decrease the average peak deviator stresses at failure when fines content is increased, whereas, an increase in non-plastic fines generally result in higher average peak deviator stresses except between % to % fines content where the shear strength did change considerably. These results are similar to the Unsoaked CBR results presented earlier. It should be noted that for dolomite samples with non-plastic fines, even the unsoaked CBR value did not change significantly as the fines contents were changed from % to % (the value changed from to ). Moreover, at very low fines contents, there is no significant difference between the peak deviator stresses for samples containing non-plastic fines, as compared to those with plastic fines. However, as the fines content increases beyond %, the average peak deviator stress values for the samples containing plastic fines become significantly lower than those with non-plastic fines. These results are in perfect agreement with the permanent deformation results reported from this study elsewhere (). Therefore, the effect of fines plasticity on shear strength or permanent deformation is not very pronounced at low fines contents (around %). 0 0 Gravel : Nonplastic Gravel: Plasic Limestone: Nonplastic Limestone: Plastic Dolomite: Nonplastic Dolomite: Plastic Unsoaked CBR (IBV) % Fines FIGURE Variations of Unsoaked CBR (IBV) with Fines Content at w opt for all the aggregates Table compares the average peak deviator stresses for the gravel and dolomite samples, both containing non-plastic fines and tested on the dry side of optimum moisture conditions. Note that the crushed dolomite samples have consistently higher strength values when compared to the uncrushed gravel samples (similar to the results for Unsoaked CBR). The differences may become even more pronounced as the fines percentage varies; at % fines dolomite becomes almost twice as strong. Therefore, as far as shear strength is concerned, which represents complete failure and destruction of the aggregate matrix, aggregate type (i.e., crushed or uncrushed and the size of the void space) plays the most important role, particularly at low fines contents. Therefore, for layers with low fines contents, aggregate behavior is primarily governed by aggregate angularity (in terms of crushed or uncrushed). However, as the amount of fines is increased, the type of fines tends to play a dominant role in governing aggregate TRB 0 Annual Meeting CD-ROM

14 Mishra, Tutumluer and Butt behavior. High amounts of plastic fines, when combined with high moisture contents, will no doubt result in the worst combination. TABLE Type of Fines Influencing the Failure Peak Deviator Stress of Dolomite at w opt Fines Content (%) Dolomite Average Peak Deviator Stress (psi) Tested at w opt Non-Plastic Fines Plastic Fines TABLE Aggregate Type Influencing the Average Peak Deviator Stress at 0% of w opt Non-plastic Fines Content (%) Average Peak Deviator Stress (psi) 0 Gravel Dolomite SUMMARY AND CONCLUSIONS This paper presented findings from an ongoing research study aimed at investigating effects of different aggregate properties, such as particle shape and angularity, types and amounts of fines, and moisture content, affecting the behavior of highway construction aggregates commonly used for subgrade replacement and subbase in the state of Illinois. The initial laboratory phase of the study presented in this paper considered both plastic and non-plastic fines (passing No. 00 sieve or 0.0 mm) blended in the engineered gradations of three crushed and uncrushed aggregate materials, i.e., limestone, dolomite and uncrushed gravel commonly found in Illinois, at %, %, %, and % target fines content. The laboratory test results presented comprised of standard Proctor moisture-density, unsoaked CBR, imaging based aggregate shape characterization, and rapid shear strength tests according to a comprehensive experimental test matrix. From the imaging based particle shape, texture and angularity characterizations and the triaxial tests, it appears that the most important parameter at low fines contents is the aggregate type governing the angularity, i.e. crushed or uncrushed particles. Unless all voids in aggregate matrix are completely filled with fines, particle angularity typically governs the shear strength. The second most important parameter that affected aggregate behavior was the plasticity of fines. Especially for plastic fines (plasticity index to ), the amount of fines had a drastic effect on aggregate performance. High amounts of plastic fines (in excess of % by weight) at wet of optimum moisture conditions were found TRB 0 Annual Meeting CD-ROM

15 Mishra, Tutumluer and Butt to quickly destruct the aggregate load transfer matrix thus resulting in drastic reductions in strength. Increasing the amount of fines, however, did not cause significant decreases in aggregate strength in the case of non-plastic fines. When selecting aggregate materials for the subgrade replacement and subbase application, careful attention should be given to particle shape as well as the types and amounts of fines. At low fines contents, the type of fines is not likely to play an important role. As a result, unbound aggregate layers constructed with crushed particles are likely to perform better than those having uncrushed gravel. However, as the amount of fines is increased, especially those fines plastic in nature may cause aggregate performance to deteriorate much faster than the influences observed by non-plastic fines. Therefore, high percentages of plastic fines combined with greater than optimum moisture contents should be avoided in order not to encounter excessive rutting and shoving of the pavement working platform under construction traffic. ACKNOWLEDGEMENTS AND DISCLAIMER This paper is based on the partial results of ICT R-, Characterization of Illinois Aggregates for Subgrade Replacement and Subbase research study. ICT R- project is conducted at the Illinois Center for Transportation (ICT) in cooperation with the Illinois Department of Transportation, Division of Highways, and the U.S. Department of Transportation, Federal Highway Administration. The contents of this paper reflect the views of the authors who are responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Illinois Department of Transportation or the Federal Highway Administration. This paper does not constitute a standard, specification, or regulation. REFERENCES. Illinois Department of Transportation IDOT. Subgrade Stability Manual. Bureau of Bridges and Structures, 00, p. ( stability manual.exe). Allen, J. The Effect of Non-Constant Lateral Pressures on the Resilient Response of Granular Materials. PhD. University of Illinois at Urbana-Champaign, Urbana, Illinois,.. Barksdale, R.D. and Itani, S.Y. "Influence of Aggregate Shape on Base Behavior." In Transportation Research Record: Journal of the Transporation Research Board, No., Transportation Research Board of the National Academics, Washington, D.C.,, pp -.. Rao, C., E. Tutumluer, and Kim, I.T. "Quantification of Coarse Aggregate Angularity Based on Image Analysis." In Transportation Research Record: Journal of the Transporation Research Board, No., Transportation Research Board of the National Academics, Washington, D.C., 00.. Rao, C. Determination of -D Image Analysis Techniques to Determine Shape and Size Properties of Coarse Aggregates. PhD Thesis. University of Illinois at Urbana-Champaign, Urbana, IL, 00.. Rao, C., E. Tutumluer, and Stefanski, J.A. "Flat and Elongated Ratios and Gradation of Coarse Aggregates Using a New Image Analyzer." ASTM Journal of Testing and Standard, Vol., No., 00, pp. -.. Tutumluer, E., C. Rao, and Stefanski, J.A. Video Image Analysis of Aggregates. Final Project Report, FHWA-IL-UI-, Civil Engineering Studies UILU-ENG-000-0, University of Illinois at Urbana-Champaign, Urbana, Illinois, Rao, C., T. Pan, and Tutumluer, E. "Determination of Coarse Aggregate Surface Texture Using Imaging Analysis." Proceedings of the th ASCE Engineering Mechanics Conference, University of Washington, Seattle, WA, 00. TRB 0 Annual Meeting CD-ROM

16 Mishra, Tutumluer and Butt 0. Tutumluer, E., T. Pan, and Carpenter, S.H. Investigation of Aggregate Shape Effects on Hot Mix Asphalt Performance Using an Image Analysis Approach. Final Technical Report, Pooled Fund Study TPF-(0), UILU-ENG-00-00, Federal Highway Administration Illinois Division, University of Illinois, Urbana, Illinois, 00.. Holtz, R.D. Compaction Concepts: Chapter, Guide to Earthwork Compaction, State of the Art Report Transportation Research Board, Washington D.C., 0.. Seyhan, U. Characterization of Anisotropic Granular Layer Behavior in Flexible Pavements. PhD Thesis. University of Illinois at Urbana-Champaign, Urbana, Illinois, 00.. Mishra, D., Tutumluer, E., and Butt, A.A., Types and Amounts of Fines Affecting Aggregate Behavior, Advances in Transportation Geotechnics, Proceedings Book of the st International Conference on Transportation Geotechnics and the th Unbound Aggregates in Roads Symposium (UNBAR), Nottingham, UK, August -, 00; Edited by E. Ellis, H.S. Yu, G. McDowell, A. Dawson, and N. Thom, 00, pp. -.. Thompson, M.R., and K. L. Smith. "Repeated Triaxial Characterization of Granular Bases." In Transportation Research Record: Journal of the Transporation Research Board, No., Transportation Research Board of the National Academics, Washington, D.C., 0.. Garg, N.,and M. R. Thompson. "Triaxial Characterization of Minnesota Road Research Project Granular Materials." In Transportation Research Record: Journal of the Transporation Research Board, No., Transportation Research Board of the National Academics, Washington, D.C.,.. Mishra, D., E. Tutumluer, A.A. Butt, and Kern, J. "Characterizing Aggregate Permanent Deformation Behavior based on Types and Amounts of Fines." Proceedings of the th International Conference on Bearing Capacity of Roads, Railways, and Airfields, University of Illinois at Urbana-Champaign, Champaign, Illinois, June -July, 00. TRB 0 Annual Meeting CD-ROM