Evaluation of Cement Stabilization of a Road Base Material in Conjunction with Full-Depth Reclamation in Huaquillas, Ecuador Dario David Batioja A selected project submitted to the faculty of Brigham Young University in partial fulfillment of the requirements for the degree of Master of Science W. Spencer Guthrie Mitsuru Saito Grant G. Schultz Department of Civil and Environmental Engineering Brigham Young University August 2011 Copyright 2011 Dario David Batioja All Rights Reserved
GRADUATE COMMITTEE APPROVAL of a project submitted by Dario David Batioja The project of Dario David Batioja is acceptable in its final form, including (1) its format, citations, and bibliographical style are consistent and acceptable and fulfill department style requirements; (2) its illustrative materials including figures, tables, and charts are in place; and (3) the final manuscript is satisfactory and ready for submission. This project has been read by each member of the following graduate committee and by majority vote has been found to be satisfactory. Date W. Spencer Guthrie, Chair Date Mitsuru Saito Date Grant G. Schultz Accepted for the Department of Civil and Environmental Engineering Date Grant G. Schultz Graduate Coordinator
ABSTRACT Evaluation of Cement Stabilization of a Road Base Material in Conjunction with Full-Depth Reclamation in Huaquillas, Ecuador Dario David Batioja Department of Civil and Environmental Engineering Master of Science The primary purposes of this research were to classify the pavement materials sampled from a failed road in Huaquillas, Ecuador, investigate the optimum cement content required to stabilize a blend of the moisture-susceptible base material and recycled asphalt pavement (RAP),and recommend a flexible pavement design adequate for the conditions at the site.the laboratory procedures consisted of material classifications, sulfate concentration tests, compaction tests, California bearing ratio (CBR) tests, unconfined compressive strength (UCS) tests, and tube suction tests (TSTs). The RAP, base, subbase, and subgrade materials tested in this research were sampled by the municipality personnel of Huaquillas, Ecuador, and shipped to the Brigham Young University Highway Materials Laboratory for evaluation. The studied road has one paved lane in each direction, and the existing pavement structure consists of 4.0 in. of asphalt on 6.0 in. of base on 15 in. of granular subbase. The sulfate concentrations for the base, subbase, and subgrade were all below the maximum threshold of 3000 ppm, indicating that the introduction of cement to these materials should not cause sulfate swelling problems. The base, subbase, and subgrade materialshad average CBR values of 31, 18, and 12, respectively. The RAP-base blend treated with 2.0, 4.0 and 6.0 percent cement had average 7-day UCS values of 233, 417, and 624 psi, respectively. Additionally, the base and subbase had average final dielectric values of 18.1 and 27.4, respectively, in the TST. On the other hand, after the 10-day soak, the RAP-base blend treated with 2.0, 4.0, and 6.0 percent cement had average final dielectric values of 5.3, 5.2, and 5.4, respectively, indicating that cement treatment helps the materials improve to a non-moisturesusceptible condition. Pavement reconstruction using full-depth reclamation (FDR) in conjunction with cement stabilization is recommended for this project. Based on the results of the UCS tests and TSTs performed in this research, a cement content of 4.0 percent is recommended for stabilizing the 50:50 ratio of RAP to base evaluated in this research. Two alternative pavement configurations were designed, both of which involve FDR. Design A specifies 4.5 in. of new HMA overlying 8.0 in. of CTB and 17 in. of granular subbase, and design B specifies 4.0 in. of new HMA over 9.0 in. of CTB and 16 in. of granular subbase. Both pavement designs provide adequate protection to each layer and should provide satisfactory performance for this site in Huaquillas, Ecuador. Keywords: full-depth reclamation, pavement rehabilitation, pavement design, pavement reconstruction, cement stabilization, ecuador, cement treated base, moisture susceptibility.
ACKNOWLEDGEMENTS I express gratitude to my graduate advisor, Dr. W. Spencer Guthrie, not only for his constant guidance and advice throughout this research project but also for teaching me important engineering and writing skills that will help me during the course of my life. I thank the entire faculty at the Department of Civil and Environmental Engineering for having shared their knowledge and professional experience with me. I especially acknowledge Dr. Mitsuru Saito and Dr. Grant G. Schultz for their willingness to be part of my graduate committee and for the time they spent to review this report and give valuable feedback. I thank my parents for their support and, most importantly, for teaching me the great value of education. I thank my beautiful wife, Lucia, for her support, understanding, and help during all these years. Finally, I acknowledge the public works personnel of the City of Huaquillas, Ecuador, for sampling and providing the materials for this investigation.
TABLE OF CONTENTS LIST OF TABLES... vii LIST OF FIGURES... ix 1 Introduction... 1 1.1 Problem Statement... 1 1.2 Scope... 3 1.3 Outline of the Report... 3 2 Background... 5 2.1 Overview... 5 2.2 Water-Related Damage Mechanisms... 5 2.3 Cement Stabilization with Full-Depth Reclamation... 6 2.4 Summary... 8 3 Procedures... 9 3.1 Overview... 9 3.2 Material Classifications... 10 3.3 Sulfate Concentration Tests... 11 3.4 Compaction Tests... 12 3.5 California Bearing Ratio Tests... 13 3.6 Unconfined Compressive Strength Tests... 15 3.7 Tube Suction Tests... 16 3.8 Pavement Designs... 18 3.9 Summary... 22 4 Results... 23 4.1 Overview... 23 4.2 Material Classifications... 23 v
4.3 Sulfate Concentration Tests... 25 4.4 Compaction Tests... 25 4.5 California Bearing Ratio Tests... 26 4.6 Unconfined Compressive Strength Tests... 27 4.7 Tube Suction Tests... 27 4.8 Pavement Designs... 28 4.8 Summary... 30 5 Conclusion... 33 5.1 Summary... 33 5.2 Findings... 34 5.3 Recommendations... 35 REFERENCES... 37 vi
LIST OF TABLES Table 4.1 Particle-Size Distributions... 23 Table 4.2 Atterberg Limits... 24 Table 4.3 Soil Classifications... 25 Table 4.4 Sulfate Concentration Test Results... 25 Table 4.5 Compaction Test Results... 26 Table 4.6 CBR Test Results... 26 Table 4.7 UCS Test Results... 27 Table 4.8 TST Results... 28 Table 4.9 Pavement Design Input Values... 29 vii
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LIST OF FIGURES Figure 3.1 Existing pavement condition at location 1... 9 Figure 3.2 Existing pavement condition at location 2... 10 Figure 3.3 Mechanical compactor... 12 Figure 3.4 Specimen in CBR test... 14 Figure 3.5 Specimen after CBR test... 15 Figure 3.6 Specimen in UCS test... 16 Figure 3.7 Specimens in TST... 18 Figure 4.1 Particle-size distributions from washed sieve analyses... 24 Figure 4.2 Proposed pavement design A... 31 Figure 4.3 Proposed pavement design B... 31 ix
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1 Introduction 1.1 Problem Statement The reconstruction of failed roadways and highways has become a priority for many coastal public works agencies in Ecuador. Each year these organizations need to repair or totally reconstruct hundreds of miles of asphalt pavement after the rainy season. In Ecuador many coastal cities and towns experience harsh wet seasons that last many months. Due to this climatic condition, pavementsmust be designed to withstand the negative effects of moisture. As water enters the pavement structure, the durability of the aggregate base materials can be negatively affected (1). Excavating and replacing failed materials and resurfacing using overlays are the techniques most often used by Ecuadorian city officials to rehabilitate failed pavements. However, these techniques are not always the most cost-effective and have not proven successful in preventing the recurrence of pavement failures. Instead, full-depth reclamation (FDR) is a more suitable alternative for addressing recurring problems caused by moisture-susceptible base materials in the coastal pavements of Ecuador. FDR has increased in popularity recently as a method of rehabilitating deteriorated roadways in America (2, 3). In the FDR process, the asphalt layer and some of the native granular base material are recycled to create a new base material (2, 3, 4). Cement stabilization is often used in conjunction with FDR when the base material does not exhibit adequate strength or durability (4). In this case, the reclaimed asphalt pavement (RAP) and the base material are blended together with cement and water and then compacted to produce a stronger and more 1
durable material that, when designed and constructed properly, resists moisture-related damage (2, 5). The use of FDR offers specific advantages over the use of other asphalt pavement rehabilitation techniques. Significant economic savings can be achieved because,in the FDR process, many materials are reused that would otherwise have had to be hauled out and discarded. Thus, expenses associated with transportation and with the purchase of new materials are reduced (6). In addition, the amount of material that might otherwise have been sent to a landfill is substantially reduced (7). For these reasons, an understanding of FDR and cement stabilization processes is becoming more important for pavement engineers and transportation officials in developing countries such as Ecuador. These methods provide new and technically sound alternatives for reconstruction of failed pavements.fdr and cement stabilization are techniques well known in America, where they have been investigated for many years; however, their implementation in some developing countries is limited due primarily to a lack of education on these topics by pavement engineers in those regions. Therefore, to assist engineers in Ecuador in learning more about FDR and cement stabilization through a demonstration project, this project was conceived. The primary purposes of this research were to classify the pavement materials sampled from a failed road in Huaquillas, Ecuador, determine the optimum cement content required to stabilize a blend of the moisture-susceptible base material and RAP,and provide flexible pavement design recommendations adequate for the conditions at the site. 2
1.2 Scope The pavement materials studied in this investigation were sampled by the municipality personnel of Huaquillas, Ecuador, and shipped to the Brigham Young University (BYU) Highway Materials Laboratory for evaluation. For this research, RAP, aggregate base, subbase, and subgrade materials were tested. A RAP content of 50 percent by mass and cement contents of 2.0, 4.0, and 6.0 percent were used in the experimental design, with three replicates of each treatment being evaluated. Test procedures included material classification followed by sulfate concentration tests, compaction tests, California bearing ratio (CBR) tests, unconfined compressive strength (UCS) tests, and tube suction tests (TSTs). Once all of the laboratory evaluations were completed, pavement design recommendations were developed for this project. 1.3 Outline of the Report This report contains five chapters. Chapter 1 presents the objectives and scope of this investigation. Chapter 2 reviews some background information about water-related damage mechanisms and the use of FDR in conjunction with cement stabilization. Chapter 3 describes the experimental methodology that was used in this research. Chapter 4 provides the laboratory test results and presents recommendedpavement designs. Finally, Chapter 5 provides a summary of the work and presents important findings and recommendations. 3
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2 Background 2.1 Overview Roadways play a significant role in the national economic system in Ecuador. These roadways interconnect large cities, provinces, and small rural villages. Millions of field workers and commuters travel on them to deliver their harvests and other goods to city markets. Because Ecuador is a tropical country that experiences severe rainy seasons, moisture-related pavement damage has become a significant problem for the Ecuadorian economy, especially in coastal areas. FDR in conjunction with cement stabilization can be an appropriate alternative for solving the problems caused by the moisture-susceptible road base materials commonly utilized in pavement construction along the coast of Ecuador. The following sections discusspavement damage caused by water ingress in base materials and detail the use of cement stabilization in conjunction with FDR. 2.2 Water-Related Damage Mechanisms Moisture intrusion is a significant problem that affects pavement structures in regions that receive large amounts of precipitation. Water can enter a pavement system not only through the pavement surface, but also through subsurface flow from a high water table or through lateral infiltration (1). Water that infiltrates the base and subbase layers of a pavement system causes negatives effects on the mechanical properties of these materials (1). Accumulations of free or unbound water weaken base materials, reducing their shear strength and stiffness. Additionally, 5
under traffic loading, high hydrodynamic pressures can be generated in affected materials, leading to pumping of fine particles from the base and subbaselayers, which further reduces the bearing capacity of the entire pavement structure (1). The moisture susceptibility of soil and aggregate materials is related to their suction potential. Aggregate and soil materials characterized by high suction potentials are highly susceptible to water damage. When available, water will be readily absorbed and retained by these materials, leading to diminished structural properties over time and potentially to premature failure of the pavement (8). 2.3 Cement Stabilization with Full-Depth Reclamation Soil stabilization is the process of mixing a stabilization agent with a soil or aggregate material to improve the strength and/or durability of the material. Stabilization should be considered when these properties of a material are insufficient for expected traffic loads and/or environmental conditions. Stabilization agents include additives such as portland cement, lime, fly ash, and asphalt emulsions (3, 5). The choice of stabilizing agent depends on several factors, including the composition of the soil or aggregate and the in-situ service conditions (3). A sufficient amount of the selected stabilizer, usually 2 to 6 percent by dry weight of soil or aggregate, should be added to achieve recommended material improvements, but additions of excessive amounts of stabilizer should be avoided; for example, the addition of too much cement can increase the tendency of the base to exhibit shrinkage cracking (7, 9, 10). The optimum stabilizer content can be established by examining the strength and durability of the treated base in specific laboratory tests. While the CBR test is very commonly used to assess the strength of untreated materials, the UCS test andtst are recommended by 6
many agencies to establish the proper amount of stabilizer for material treatment (8). For cement treatment, which is one of the most common forms of stabilization used when FDR is specified (11), the Texas Transportation Institute suggests a target UCS of between 300 and 400 psi after 7 days of curing and a dielectric value in the TST of less than 10 to achieve adequate strength and durability, respectively (8). At this level of stabilization, treated materials are expected to exhibit adequate resistance to water ingress and moisture-induced structural deterioration even in wet conditions. When cement stabilization is specified in conjunction with FDR on a pavement rehabilitation project, the optimum cement content should be determined in the laboratory for the ratio of RAP to base material expected in the field (7, 9). Separate sampling of these materials in the field allows for convenient blending in the laboratory at specified ratios of RAP to base of interest to the pavement engineer. Appropriate ratios can be determined from consideration of the existing asphalt and base layer thicknesses and the type of pulverization and compaction equipment available for a given project. In addition, when cement stabilization is being evaluated, the sulfate concentration of the in-situ materials must be considered. When aggregate materials treated with calcium-based stabilizers contain high concentrations of sulfate and/or sulfide, they can experience swelling problems due to chemical reactions with these minerals (12). A sulfate concentration below 3000 ppm has been recommended as acceptable to prevent sulfate swelling problems in soil materials treated with calcium-based stabilizers (12). 7
2.4 Summary Because Ecuador is a tropical country that experiences severe rainy seasons, moisturerelated pavement damage has become a significant problem for the Ecuadorian economy, especially in coastal areas. Moisture intrusion is a significant problem that affects pavement structures in regions that receive large amounts of precipitation. Furthermore, accumulations of free or unbound water weaken base materials, reducing their shear strength and stiffness.when available, water will be readily absorbed and retained by these materials, leading to diminished structural properties over time and potentially to premature failure of the pavement. However, soil stabilization in conjunction with FDR can provide cost-effectiveoptionsforsolvingthe problems caused by moisture intrusion in the coastal pavements of Ecuador. Soil stabilization is the process of mixing a stabilization agent with a soil or aggregate material to improve the strength and/or durability of the material. Stabilization should be considered when these properties of a material are insufficient for expected traffic loads and/or environmental conditions. When cement stabilization is specified in conjunction with FDR on a pavement rehabilitation project, the optimum cement content should be determined in the laboratory for the ratio of RAP to base material expected in the field. Additionally, when cement stabilization is being evaluated, the sulfate concentration of the in-situ materials must be considered. 8
3 Procedures 3.1 Overview The RAP, base, subbase, and subgrade materials tested in this research were sampled by the municipality personnel of Huaquillas, Ecuador, and shipped to the BYU Highway Materials Laboratory for evaluation. The studied road has one paved lane in each direction, and the existing pavement structure consists of 4.0 in. of asphalt on 6.0 in. of base on 15 in. of granular subbase.figures 3.1 and 3.2 show the existing pavementcondition at two different locations. Figure 3.1 Existing pavement condition at location 1. 9
Figure 3.2 Existing pavement condition at location 2. The laboratory procedures consisted of material classifications, sulfate concentration tests, compaction tests, CBR tests, UCS tests, and TSTs as described in the following sections. Pavement design recommendations were developed after the laboratory testing was completed. 3.2 Material Classifications Material classifications included dry and washed sieve analyses and determination of Atterberg limits for the RAP, base, subbase, and subgrade. The dry sieve analyses were performed in general accordance with American Society for Testing and Materials (ASTM) D422 (Standard Test Method for Particle-Size Analysis of Soils). A large tray shaker was used to separate each material over the 1/2-in., 3/8-in., No. 4, No. 8, No. 16, No. 30, and No. 50 sieves, and a 12-in.-diameter sieve shaker was used to separate materials passing the No. 50 sieve over the No. 100 and No. 200 sieves. Each bulk material was sieved in its entirety in 10
preparation for further testing. This procedure enabled the fabrication of specimens having the same gradations as the bulk material. Washed sieve analyses were performed in general accordance with ASTM C117 (Standard Test Method for Materials Finer than 75-um (No. 200) Sieve in Mineral Aggregates by Washing) to determine the particle-size distribution of each material. Atterberg limits were determined following ASTM D4318 (Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils). Results from the washed sieve analyses and Atterberg limits tests were used to classify each material according to American Association of State Highway Transportation Officials (AASHTO)M145 (Standard Specification for Classification of Soils and Soil-Aggregate Mixtures for Highway Construction Purposes) and ASTM 2487 (Standard Classification of Soils for Engineering Purposes, Unified Soil Classification System). 3.3 Sulfate Concentration Tests Sulfate concentration testing was performed to determine whether cement stabilization would be a viable option for this project. For the base, subbase, and subgrade materials, 0.220-lb samples finer than the No. 40 sieve were prepared in proportions representing the bulk gradation and sent to the BYU Soil and Plant Analysis Laboratory for determination of the sulfate concentrations in accordance with ASTM C1580 (Standard Test Method for Water-Soluble Sulfate in Soil). The results of this testing were compared to the maximum recommended threshold of 3000 ppm to prevent sulfate swelling problems in soil materials treated with calcium-based stabilizers (12). 11
3.4 Compaction Tests Following separation, classification, and sulfate concentration testing of the materials, the compaction characteristics of each of the materials were investigated. Untreated specimens of base, subbase, and subgrade were prepared to determine the optimum moisture content (OMC) and maximum dry density (MDD) of each material. Compaction of the specimens was carried out in general accordance with ASTM D698 Method B (Standard Test Methods for Laboratory Compaction Characteristics of Soils Using Standard Effort (12,400 ft-lbf/ft 3 (600 kn-m/m 3 )) using the compaction device shown in Figure 3.3. All the specimens were compacted into a 4.0- in.-diameter mold to atarget height of 4.6 in. The standard Proctor test requires compaction of the specimens in three lifts of 25 blows per lift with a 5.5-lb hammer dropped from a height of 12 in. In order to improve mechanical interlock between lifts, the surfaces of the first two lifts were scarified prior to placement and compaction of the next lift in each case. Figure 3.3 Mechanical compactor. 12
Additionally, a finishing tool was used to level the surface of each specimen after compaction of the last lift. In addition to testing of the neat untreated materials, testing of a cement-treated RAP-base blend was also performed. In this research, a 50:50 ratio of RAP to base by mass was specified. The specimens were prepared in accordance with laboratory procedures specified by the Portland Cement Association (PCA) (13). The coarse fraction of each specimen, or the fraction retained on the No. 4 sieve, was weighed out separately and soaked in the compaction water for 24 hours prior to compaction. The fine fraction, or the fraction passing the No. 4 sieve, was weighed out and mixed in a dry state with the amount of cement specified for the given specimen. The cement required for each specimen was calculated as a percentage of the total dry weight of the RAP-base blend. Immediately before compaction, the fine fraction and selected amount of cement were added to the coarse fraction and compaction water and then mixed thoroughly. For compaction of specimens at different cement contents, the water required was adjusted by adding or subtracting0.25 percentage pointsto or from the previously determined OMC for every 1.0 percent cement above or below the cement content already tested; MDD values for RAP-base blends treated at different cement contents were not determined. 3.5 California Bearing Ratio Tests The CBR test was used to characterize the strength of the untreated base, subbase and subgrade materials as needed for the pavement design. This test was performed according to ASTM D1883 (Standard Test Method for CBR (California Bearing Ratio) of Laboratory- Compacted Soils), except that the specimens were tested at OMC instead of being soaked for a period of time before testing. A total of nine specimens, three specimens of each material, were 13
compacted at OMC in a 6-in.-diameter steel mold to a height of 4.6 in. using standard Proctor effort and then subjected tothe testing. The loading configuration employed in the CBR testing is shown in Figure 3.4. A surcharge weight was placed on the surface of the specimen, and a piston having a crosssectional area of 3 in. 2 penetrated the specimen surface at a rate of 0.05 in./minute through a hole in the overburden weight. The load at each 0.1-in. penetration depth interval up to 0.5-in. was recorded, and the computed stress was divided by a standardized stress value for each depth interval. The maximum ratio was multiplied by 100 and reported as the CBR for the material (1); higher values indicate stronger materials. Figure 3.5 shows the hole in the surface of a specimen after CBR testing. Figure 3.4 Specimen in CBR test. 14
Figure 3.5 Specimen after CBR test. 3.6 Unconfined Compressive Strength Tests The UCS test was used to evaluate the strength of therap-base blend treated with three different cement concentrations and was performed according to ASTM D1633 (Standard Test Method for Compressive Strength of Molded Soil-Cement Cylinders), Method A. Trial cement concentrations were determined from material classifications according to PCA recommendations (13). Three specimens were prepared at each cement content in the same manner previously described for compaction testing and then compacted at OMC using standard Proctor effort in a 4.0-in.-diameter steel mold to a height of 4.6 in. The specimens were then immediately extruded and placed in a fog room for curing at 100 percent relative humidity for a period of 7 days. Consistent with PCA protocols (13), the specimens were thensoaked under water for 4 hours immediately prior to being capped with gypsum and subsequently tested in compression at a rate of 0.05 in./minute as depicted in Figure 3.6. The peak load measured during 15
Figure 3.6 Specimen in UCS test. testing was recorded and divided by the cross-sectional area of the specimen to determine the UCS in each case. 3.7 Tube Suction Tests The TST was used to evaluate the moisture susceptibility of the untreated base andsubbasematerials and that of the RAP-base blend treated at the three different cement concentrations; the moisture susceptibility of the subgrade was not evaluated in this research.three specimens of each material, for a total of 15 specimens, were prepared and tested in accordance with the Texas Department of Transportation Test Method Tex-144-E, with the variation, consistent with previous research at BYU (7), that each specimen was compacted in a 4-in.-diameter mold to a target height of 4.6 in. instead of in a 6-in.-diameter mold to a height of 16
8 in. All of the specimens were compacted at OMC using standard Proctor effort into plastic molds pre-drilled with four 1/16-in.-diameter holes in the bottom of each mold, with one hole in each quadrant, and additional holes about 1/4 in. from the bottom of the mold and spaced about 1/2 in. apart around the base of the mold. After compaction, the untreated specimens were then dried, still in their molds, in an oven at 140 o F for 72 hours. The treated specimens, also still in their molds, were cured for 7 days in a fog room before also being dried at 140 o F for 72 hours. Following the drying stage, the initial weights and surface dielectric values of the specimens were measured. Dielectric values were measured at six locations on the surface of each specimen, one in the center and the remaining five around the perimeter. The specimens were then placed in a 0.5-in.-deep water bath inside an ice chest for a 10-day capillary soaking period; the lid of the ice chest was closed except during testing to minimize evaporation of the water bath. The surface dielectric values of each specimen were then measured daily for 10 consecutive days as shown in Figure 3.7. In the analyses of these data, the lowest and the highest dielectric values were discarded, and the remaining four measurements were averaged. The evaluation of moisture susceptibility in the TST is based on the mean surface dielectric value measured at the conclusion of the test, where higher dielectric values indicate higher amounts of unbound water at the specimen surface and therefore greater moisture susceptibility; considerable amounts of unbound water will rise in the specimen if the material has high suction potential and permeability (14). Materials with a final dielectric value in the TST of less than 10 are classified as non-moisture-susceptible, those with a dielectric value between 10 and 16 are classified as marginally moisture- 17
Figure 3.7 Specimens in TST. susceptible, and those with a dielectric value greater than 16 are classified as moisturesusceptible (14). 3.8 Pavement Designs The AASHTO flexible pavement design procedure was used to design a pavement structure adequate for the site conditions. In this process, inputs were required for several design variables, including design life, serviceability loss, reliability, traffic characteristics, and material properties. While design life, serviceability loss, and reliability are often specified based on the roadway importance, traffic characteristics and material properties must be computed. Traffic characteristics are among the most important pavement design inputs. In the AASHTO pavement design procedure, the expected traffic loads over the design life of the pavement areequated to a number of equivalent single-axle loads (ESALs) on which the pavement design can then be based. Equation 6-1 gives the equation for calculating total ESALs for design (1): 18
(6-1) where: = average daily traffic at the start of the design period = fractionof trucks in the ADT = truck factor (number of ESALs per truck) growth factor directional distribution factor lane distribution factor design period, years Material properties required for pavement design include the modulus, structural layer coefficients, and drainage coefficients for each layer. For this project, the modulus and structural layer coefficients were determined from the results of CBR and UCS tests using standard AASHTO correlation charts designed for this purpose(1). The drainage coefficients were specified based on an assessment of the drainage characteristics of the site given by city personnel. In the AASHTO flexible pavement design procedure, a structural number (SN) required to protect each subsurface layer is computed using Equation 6-2 (1): 19
( ) [ ] ( ) (6-2) where: = number of ESALs normal deviate for a given reliability standard deviation structural number serviceability loss effective roadbed resilient modulus The relationship between the SN required to protect a given layer and the properties of the layers available to protect that layer is shown in Equation 6-3 (1): SN = a 1 D 1 + a 2 D 2 m 2 + a 3 D 3 m 3 (6-3) where: structural number a 1, a 2,anda 3 = layercoefficients of the asphalt, base, and subbaselayers, respectively D 1, D 2, and D 3 = thicknesses of the asphalt, base, and subbase layers, respectively m 2 and m 3 = drainage coefficients ofthe base and subbase layers, respectively 20
Based on Equation 6.3, the following Equations 6-4 to 6-6 can be derived for determination of individual layer thicknesses in the AASHTO design procedure (1): (6-4) where: = thickness of the asphalt layer =structural number required to protect the base layer = structural layer coefficient of the asphalt layer (6-5) where: = thicknesses of the asphalt and base layers, respectively = structural number required to protect the subbase layer = structural layer coefficients of the asphalt and base layers, respectively = drainage coefficient for the base layer (6-6) where: 21
D 1, D 2, and D 3 = thicknesses of the asphalt, base, and subbase layers, respectively = structural number required to protect the subgrade a 1, a 2, and a 3 layer coefficients for the asphalt, base, and subbase layers, respectively and = drainage coefficients for the base and subbaselayers, respectively 3.9 Summary The laboratory procedures consisted of material classifications, sulfate concentration tests, compaction tests, CBR tests, UCS tests, and TSTs. Material classifications included dry and washed sieve analyses and determination of Atterberg limits for the RAP, base, subbase, and subgrade. After material classifications were complete, sulfate concentration testing was performed to determine whether cement stabilization would be a viable option for this project. Compaction tests were then performed on untreated specimens of base, subbase, and subgrade to determine the OMCand MDD of each material. Next, CBR testing was conductedto characterize the strength of the untreated base, subbase and subgrade materials as needed for the pavement design. UCS tests were then performed to evaluate the strength of therap-base blend treated with three different cement concentrations. Finally, TSTs were performed to assess the moisture susceptibility of the cement-treated and untreated base and subbase materials. Pavement design recommendations were developed after the laboratory testing was completed. 22
4 Results 4.1 Overview Results from the material classifications, sulfate concentration tests, compaction tests, CBR tests, UCS tests, and TSTs are presented in the following sections. Pavement design recommendations are given after the laboratory test results are discussed. 4.2 Material Classifications The material classifications included dry and washed sieve analyses and determination of Atterberg limits. Table 4.1 shows the dry and washed particle-size distributions for the pavement materials, including RAP, base, subbase, and subgrade,and Figure 4.1 presents the washed gradations in graphical form. Table 4.2 shows the liquid and plastic limits and the plasticity index for the base, subbase, and subgrade materials. Results from the washed sieve analysis and the Atterberg limitstesting were used to classify each material according to the AASHTOand Unified Soil Classification System (USCS) methods. Table 4.3 presents the classification for each pavement material under both systems. 23
Percent Finer (%) Table 4.1 Particle-Size Distributions Percent Passing (%) Sieve Size RAP Base Subbase Subgrade Dry Washed Dry Washed Dry Washed Dry Washed 1/2 in. 77.2 76.6 93.9 93.7 94.7 95.2 96.2 97.4 3/8 in. 61.9 59.5 90.2 89.5 91.4 90.4 92.7 96.6 No. 4 41.6 41.1 81.8 81.6 80.4 83.7 79.7 91.2 No. 8 30.6 29.8 72.8 72.8 65.4 75.1 62.8 81.2 No. 16 21.5 22.0 56.0 57.1 45.0 62.1 43.4 71.9 No. 30 12.7 14.5 29.6 37.5 22.4 45.1 21.2 58.1 No. 50 6.0 8.6 15.7 24.6 7.0 34.7 8.5 54.2 No. 100 2.3 4.3 6.4 17.3 2.7 29.8 3.0 49.9 No. 200 0.7 3.0 3.2 14.0 1.2 25.7 0.5 47.3 100 90 80 70 60 50 40 30 20 10 0 1.000 0.100 0.010 Grain Size (in.) RAP Base Subbase Subgrade 0.001 Figure 4.1 Particle-size distributions from washed sieve analyses. Table 4.2 Atterberg Limits Material Plastic Limit (%) Liquid Limit (%) Plasticity Index RAP Non-Plastic Non-Plastic Non-Plastic Base 19 22 3 Subbase 17 35 18 Subgrade 19 33 14 24
Table 4.3 Soil Classifications Material Soil Classifications AASHTO USCS RAP A-1-a GW (Well-graded gravel with sand) Base A-2-4 SM (Silty sand with gravel) Subbase A-2-6 SC (Clayey sand with gravel) Subgrade A-6 SC (Clayey sand) 4.3 Sulfate Concentration Tests Table 4.4 presents the results of the sulfate concentration testing performed on the base, subbase, and subgrade materials. The sulfate concentrations were all below the maximum threshold of 3000 ppm, indicating that the introduction of cement to these materials should not cause sulfate swelling problems. Table 4.4 Sulfate Concentration Test Results Material Sulfate Concentration (ppm) Base 133 Subbase 1345 Subgrade 312 4.4 Compaction Tests The OMC and MDD values associated with each untreated material are shown in Table 4.5. Compactioncharacteristics for the RAP-base blend treated with different cement concentrations are also presented in Table 4.5. Hyphens are given in the table for MDD values that were not computed in this research. The variations in OMC and MDD values are consistent with the variations in fines contents observed among the tested materials. 25
Table 4.5 Compaction Test Results Material Optimum Moisture Maximum Dry Content (%) Density (lb/ft 3 ) Base 7.6 131.3 Subbase 8.9 123.4 Subgrade 9.2 114.4 RAP-Base Blend Treated with 2% Cement 6.9 - RAP-Base Blend Treated with 4% Cement 7.4 134.3 RAP-Base Blend Treated with 6% Cement 7.9-4.5 California Bearing Ratio Tests Table 4.6 presents the CBR test results for the materials tested in this research. The base, subbase, and subgrade materials had average CBR values of 31, 18, and 12, respectively. These values are comparatively low; for example, local cities in the state of Utah specify a CBR of 70 for road base (15). Table 4.6 CBR Test Results Material Base Subbase Subgrade California Bearing Specimen Ratio 1 31 2 29 3 34 1 18 2 17 3 19 1 12 2 11 3 12 26
4.6 Unconfined Compressive Strength Tests Table 4.7 presents the 7-day UCS test results. The RAP-base blend treated with 2.0, 4.0 and 6.0 percent cement had average 7-day UCS values of 233, 417, and 624 psi, respectively. Given the target of 300 to 400 psi, 4.0 percent cement is recommended for stabilizing the 50:50 ratio of RAP to base evaluated in this research. Table 4.7 UCS Test Results Cement Content (%) 2 4 6 Unconfined Compressive Specimen Strength (psi) 1 264 2 251 3 184 1 387 2 448 3 415 1 657 2 592 3 623 4.7 Tube Suction Tests Table 4.8 presents the final dielectric values measured in the TST. The base and subbase had average final dielectric values of 18.1 and 27.4, respectively, indicating that both materials are moisture-susceptible. In fact,water reached the surface of all the subbase specimens in less than 24 hoursof capillary soaking and was visible at the surface of the untreated base specimens after a few days of soaking. On the other hand, after the 10-day soak, the RAP-baseblend treated with 2.0, 4.0, and 6.0 percent cement had average final dielectric values of 5.3, 5.2, and 5.4, respectively, indicating that cement treatment improves the material to a non-moisturesusceptible condition. 27
Material Base Subbase Table 4.8 TST Results RAP-Base Blend Treated with 2.0% Cement RAP-Base Blend Treated with 4.0% Cement RAP-Base Blend Treated with 6.0% Cement Specimen Dielectric Values 1 18.1 2 18.2 3 18.2 1 30.8 2 26.1 3 26.2 1 5.4 2 5.4 3 5.2 1 4.8 2 5.5 3 5.2 1 5.9 2 5.3 3 4.9 4.8 Pavement Designs Table 4.9 gives the values of various inputs used in the AASHTO flexible pavement design procedure employed in this research. The average daily traffic, percentage of trucks, and truck factor were estimated from traffic counts provided by public works personnel in Huaquillas, Ecuador, and values for the directional and lane distribution factors were assigned after reviewing the characteristics of the roadway. The structural layer coefficients were determined from standard AASHTO correlation charts using the CBR and 7-day UCS test results obtained in this research. The assigned design reliability was based on the classification of the investigated roadway, and the values for serviceability loss and standard deviation were estimated based on the type of construction. 28
Table 4.9 Pavement Design Input Values Description Traffic Characteristics Average Daily Traffic, ADT 0 Design Life (years) Directional Distribution Factor Estimated Growth Rate (%) Total Growth Factor Lane Distribution Factor Percent Trucks Truck Factor Total Number of ESALs Material Characteristics Modulus Values (psi) Asphalt Cement Concrete Cement-Treated Base Granular Subbase Clayey Sand Subgrade Structural Layer Coefficients, a i Asphalt Cement Concrete, a 1 Cement-Treated Base, a 2 Granular Subbase, a 3 Clayey Sand Subgrade Drainage Coefficients, m i Cement-Treated Base, m 2 Granular Subbase, m 3 Other Characteristics Level of Reliability (%) Design Serviceability Loss Overall Standard Deviation Value 4,500 20 0.50 5.0 33.06 1.0 0.12 0.30 977,419-600,000 10,000 8,000 0.40 0.16 0.07-1.0 1.0 85 2.0 0.45 Based on the pavement design inputs presented in Table 4.9,two alternative pavement configurations were designed, both of which involve FDR and a similar ratio of RAP to base as that investigated in this research. For either design, the existing asphalt layer will need to be pulverized and mixed with a certain thickness of the existing base layer. As previously 29
explained in Chapter 3, the existing pavement structure consists of 4.0 in. of asphalt on 6.0 in. of base on 15 in. of granular subbase. For design A presented in Figure 4.2, the full 4.0 in. of asphalt should be pulverized and mixed with 4.0 in. of the existing base and 4.0 percent cement to create an8.0-in. cement-treated base (CTB). A new 4.5-in. layer of hot mix asphalt (HMA) should then be placed on the new CTB. For design B presented in Figure 4.3, the full 4.0 in. of asphalt should be pulverized and mixed with 5.0 in. of the existing base and 4.0 percent cement to createan 9.0-in. CTB. A new 4.0-in. layer of HMA should then be placed on the new CTB. In both designs A and B, the 2.0 or 1.0 in. of remaining base not included in the CTBis treated as subbaseand added to the entire undisturbed 15 in. of subbase to create a 17.0 or 16.0 in. of subbase, respectively. Both pavement designs provide adequate protection to each layer and should provide satisfactory performance for this site in Huaquillas, Ecuador. 4.8 Summary The results consisted of material classifications, sulfate concentration tests, compaction tests, CBR tests, UCS tests, and TSTs. Pavement design recommendations were developed after the laboratory testing was completed. The RAP material was classified as A-1-a and as wellgraded gravel with sand (GW) in the AASHTO and USCS methods, respectively, and corresponding classifications for the base material were determined to be A-2-4 and silty sand with gravel (SM). In the USCS, the subbase was classified as clayey sand with gravel (SC), while the subgrade was classified as clayey sand (SC). In the AASHTO method, the subbase and subgrade materials were categorized as A-2-6 and A-6, respectively. 30
Figure 4.2 Proposed pavement designa. Figure 4.3 Proposed pavement designb. 31
The sulfate concentrations were all below the maximum threshold of 3000 ppm, indicating that the introduction of cement to these materials should not cause sulfate swelling problems. The measured variation in OMC and MDD values is consistent with the variations in fines contents observed among the tested materials.the base, subbase, and subgrade materials had average CBR values of 31, 18, and 12, respectively. These values are comparatively low; for example, local cities in the state of Utah specify a CBR of 70 for road base. The RAP-base blend treated with 2.0, 4.0 and 6.0 percent cement had average 7-day UCS values of 233, 417, and 624 psi, respectively. Given the target of 300 to 400 psi, 4.0 percent cement is recommended for stabilizing the 50:50 ratio of RAP to base evaluated in this research. The base and subbase had average final dielectric values of 18.1 and 27.4, respectively. On the other hand, after the 10-day soak, the RAP-baseblend treated with 2.0, 4.0, and 6.0 percent cement had average final dielectric values of 5.3, 5.2, and 5.4, respectively, indicating that cement treatment improves the material to a non-moisture-susceptible condition. Pavement design recommendations were developed after the laboratory testing was completed. Based on the presented inputs, two alternative pavement configurations weredesigned, both of which involve FDR. Design A specifies 4.5 in. of new HMA overlying 8.0 in. of CTB and 17 in. of granular subbase. On the other hand, design B specifies 4.0 in. of new HMA over 9.0 in. of CTB and 16 in. of granular subbase. Both pavement designs provide adequate protection to each layer and should provide satisfactory performance for this site in Huaquillas, Ecuador. 32
5 Conclusion 5.1 Summary The primary purposes of this research were to classify the pavement materials sampled from a failed road in Huaquillas, Ecuador, determine the optimum cement content required to stabilize a blend of the moisture-susceptible base material and RAP,and provide flexible pavement designsrecommendations adequate for the conditions at the site. Because Ecuador is a tropical country that experiences severe rainy seasons, moisture-related pavement damage has become a significant problem for the Ecuadorian economy, especially in coastal areas. Due to this climatic condition, pavementsmust be designed to withstand the negative effects of moisture. FDR in conjunction with cement stabilization can be an appropriate alternative for minimizing the problems caused by the moisture-susceptible road base materials commonly utilized in pavement construction along the coast of Ecuador. The RAP, base, subbase, and subgrade materials tested in this research were sampled by the municipality personnel of Huaquillas, Ecuador, and shipped to the BYU Highway Materials Laboratory for evaluation. The studied road has one paved lane in each direction, and the existing pavement structure consists of 4.0 in. of asphalt on 6.0 in. of base on 15 in. of granular subbase. The laboratory procedures consisted of material classifications, sulfate concentration tests, compaction tests, CBR tests, UCS tests, and TSTs. Material classifications included dry and washed sieve analyses and determination of Atterberg limits for the RAP, base, subbase, and 33
subgrade. After material classifications were complete, sulfate concentration testing was performed to determine whether cement stabilization would be a viable option for this project. Compaction tests were then performed on untreated specimens of base, subbase, and subgrade to determine the OMCand MDD of each material. Next, CBR testing was conducted to characterize the strength of the untreated base, subbase and subgrade materials as needed for the pavement design. UCS tests were then performed to evaluate the strength of the RAP-base blend treated with three different cement concentrations. Finally, TSTs were performed to assess the moisture susceptibility of the cement-treated and untreated base and subbase materials. Pavement design recommendations were developed after the laboratory testing was completed. 5.2 Findings The RAP material was classified as A-1-a and as well-graded gravel with sand (GW) in the AASHTO and USCS methods, respectively, and corresponding classifications for the base material were determined to be A-2-4 and silty sand with gravel (SM). In the USCS, the subbase was classified as clayey sand with gravel (SC), while the subgrade was classified as clayey sand (SC). In the AASHTO method, the subbase and subgrade materials were categorized as A-2-6 and A-6, respectively. The sulfate concentrations for the base, subbase, and subgrade were 133, 1345, and 312 ppm, respectively. They were all below the maximum threshold of 3000 ppm, indicating that the introduction of cement to these materials should not cause sulfate swelling problems. The measured variation in OMC and MDD values is consistent with the variations in fines contents observed among the tested materials.the base, subbase, and subgrade materials had average CBR values of 31, 18, and 12, respectively. 34
The RAP-base blend treated with 2.0, 4.0 and 6.0 percent cement had average 7-day UCS values of 233, 417, and 624 psi, respectively. The base and subbase had average final dielectric values of 18.1 and 27.4, respectively, indicating that both materials are moisturesusceptible. On the other hand, after the 10-day soak, the RAP-base blend treated with 2.0, 4.0, and 6.0 percent cement had average final dielectric values of 5.3, 5.2, and 5.4, respectively, indicating that cement treatment helps the materials improve to a non-moisture-susceptible condition. 5.3 Recommendations Pavement reconstruction using FDR in conjunction with cement stabilization is recommended for this project. Based on the results of the UCS tests and TSTs performed in this research, a cement content of 4.0 percent is recommended for stabilizing the 50:50 ratio of RAP to base evaluated in this research. Based on the presented inputs, two alternative pavement configurations were designed, both of which involve FDR. Design A specifies 4.5 in. of new HMA overlying 8.0 in. of CTB and 17 in. of granular subbase. On the other hand, design B specifies 4.0 in. of new HMA over 9.0 in. of CTB and 16 in. of granular subbase. Both pavement designs provide adequate protection to each layer and should provide satisfactory performance for this site in Huaquillas, Ecuador. 35
36
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