Relating Creep Testing to Rutting of Asphalt Concrete Mixes, HR-311, Part 2, 1991

The Iowa Department of Transportation began creep and resilient modulus testing of asphalt concrete mixtures in 1989. Part 1 of this research reported in January 1990 was a laboratory study of hot mix asphalt (HMA) mixtures made with O, 30, 60, 85 and 100% crushed gravel, crushed limestone and crushed quartzite combined with uncrushed sand and gravel. Creep test results from Marshall specimens related well to the percent of crushed particles and the perceived resistance to rutting. The objective of this research, part 2, was to determine if there was a meaningful correlation between pavement rut depth and the resilient modulus or the creep resistance factor. Four and six inch diameter cores were drilled from rutted primary and interstate pavements and interstate pavements with design changes intended to resist rutting. The top 2 1/2 inches of each core, most of which was surface course, was used for creep and resilient modulus testing. There is a good correlation between the resilient modulus of four and six inch diameter cores. Creep resistance factors of four and six inch diameter cores also correlated well. There is a poor correlation between resilient modulus and the creep resistance factor. The rut depth per million 18,000 pound equivalent single axle loadings (ESAL) for these pavements did not correlate well with either the resilient modulus or the creep resistance factor.

Investigation of High Density Polyethylene Pipe for Highway Applications, HR-373, Phase 1, 1996

In the past, culvert pipes were made only of corrugated metal or reinforced concrete. In recent years, several manufacturers have made pipe of lightweight plastic - for example, high density polyethylene (HDPE) - which is considered to be viscoelastic in its structural behavior. It appears that there are several highway applications in which HDPE pipe would be an economically favorable alternative. However, the newness of plastic pipe requires the evaluation of its performance, integrity, and durability; A review of the Iowa Department of Transportation Standard Specifications for Highway and Bridge Construction reveals limited information on the use of plastic pipe for state projects. The objective of this study was to review and evaluate the use of HDPE pipe in roadway applications. Structural performance, soil-structure interaction, and the sensitivity of the pipe to installation was investigated. Comprehensive computerized literature searches were undertaken to define the state-of-the-art in the design and use of HDPE pipe in highway applications. A questionnaire was developed and sent to all Iowa county engineers to learn of their use of HDPE pipe. Responses indicated that the majority of county engineers were aware of the product but were not confident in its ability to perform as well as conventional materials. Counties currently using HDPE pipe in general only use it in driveway crossings. Originally, we intended to survey states as to their usage of HDPE pipe. However, a few weeks after initiation of the project, it was learned that the Tennessee DOT was in the process of making a similar survey of state DOT's. Results of the Tennessee survey of states have been obtained and included in this report. In an effort to develop more confidence in the pipe's performance parameters, this research included laboratory tests to determine the ring and flexural stiffness of HDPE pipe provided by various manufacturers. Parallel plate tests verified all specimens were in compliance with ASTM specifications. Flexural testing revealed that pipe profile had a significant effect on the longitudinal stiffness and that strength could not be accurately predicted on the basis of diameter alone. Realizing that the soil around a buried HDPE pipe contributes to the pipe stiffness, the research team completed a limited series of tests on buried 3 ft-diameter HDPE pipe. The tests simulated the effects of truck wheel loads above the pipe and were conducted with two feet of cover. These tests indicated that the type and quality of backfill significantly influences the performance of HDPE pipe. The tests revealed that the soil envelope does significantly affect the performance of HDPE pipe in situ, and after a certain point, no additional strength is realized by increasing the quality of the backfill.

Heavy Agricultural Loads on Pavements and Bridges, HR-1073, 1999

During the harvest season in Iowa, it is common to have single axle loads on secondary roads and bridges that are excessive (typical examples are grain carts) and well beyond normal load limits. Even though these excessive loads occur only during a short time of the year, they may do significant damage to pavements and bridges. In addition, the safety of some bridges may be compromised because of the excessive loads, and sometimes there may be little indication to the users that damage may be imminent. At this time there are no Iowa laws regulating axle loads allowed for agricultural equipment. This study looks at the potential problems this may cause on secondary roads and timber stringer bridges. Both highway pavement and timber bridges are evaluated in this report. A section (panel) of Iowa PCC paved county road was chosen to study the effects of heavy agricultural loads on pavements. Instrumentation was applied to the panel and a heavily loaded grain cart was rolled across. The collected data were analyzed for any indication of excessive stresses of the concrete. The second study, concerning excessive loads on timber stringer bridges, was conducted in the laboratory. Four bridge sections were constructed and tested. Two of the sections contained five stringers and two sections had three stringers. Timber for the bridges came from a dismantled bridge, and deck panels were cut from new stock. All timber was treated with creosote. A hydraulic load was applied at the deck mid-span using a foot print representing a tire from a typical grain cart. Force was applied until failure of the system resulted. The collected data were evaluated to provide indications of load distribution and for comparison with expected wheel loads for a typical heavily loaded single axle grain cart. Results of the pavement tests showed that the potential of over-stressing the pavement is a possibility. Even though most of the tension stress levels recorded were below the rupture strength of the concrete, there were a few instances where the indicated tension stress level exceeded the concrete rupture strength. Results of the bridge tests showed that when the static ultimate load capacity of the timber stringer bridge sections was reached, there was sudden loss of capacity. Prior to reaching this ultimate capacity, the load sharing between the stringers was very uniform. The failure was characterized by loss of flexural capacity of the stringers. In all tests, the ultimate test load exceeded the wheel load that would be applied by an 875 bushel single axle grain cart.

Investigation of High Performance Concrete Pavement, MLR-05-01, 2006

The Iowa DOT has been using blended cements in ternary mixes since 1999. Use of these supplementary cementitious materials gives concrete with higher strengths and much lower permeability. Use of these materials has been incorporated for use in High Performance Concrete (HPC) decks to achieve lower permeability and thus long term performance. Since we have been using these materials in paving, it would be informative to determine what concrete pavement properties are enhanced as related to high performance concrete. The air void system was excellent at a spacing factor of 0.0047 in (0.120 mm). AVA spacing factor results are much higher than the hardened air void analysis. Although only 3 samples were tested between the image analysis air content and the RapidAir457, there is pretty good agreement between those test methods. Air void analysis indicates that excessive vibration was not required to place the concrete. Vibration was well within the specification limits with an average of 6683 vpm’s with a standard deviation of 461. Overall ride of the project was very good. The average smoothness for the project was 2.1 in/mile (33.8 mm/km). The International Roughness Index (IRI) was 81 in/mi (1.29 m/km). The compressive strength was 6260 psi (43.2 MPa) at 28 days and 6830 (47.1 MPa) at 56 days. The modulus of rupture by third point loading (MOR-TPL) tested at 28 days was 660 psi (4.55 MPa). The AASHTO T277 rapid chloride permeability results at 28 days using the Virginia cure method correlate fairly well with the 56 and 90 day results with standard curing. The Virginia cure method 28 day results were 2475 coulombs and the standard cure 56 and 90 day test results were 2180 and 2118, respectively.

Early Strengths of Class F, C, and B Portland Cement Concrete, MLR-87-07, 1987

Fast track concrete has proven to be successful in obtaining high early strengths. This benefit does not come without cost. Type III cement and insulation blankets to accelerate the cure add to its expense when compared to conventional paving. This research was intended to determine the increase in time required to obtain opening strength when a fast track mix utilized conventional Type I cement and also used a conventional cure. Standard concrete mixes also were tested to determine the acceleration of strength gain when cured with insulation blankets. The goal was to determine mixes and procedures which would result in a range of opening times. This would allow the most economical design for a particular project and tailor it to that projects time restraint. Three mixes were tested: Class F, Class C, and Class B. Each mix was tested with one section being cured with insulation blankets and another section without. All used Type I cement. Iowa Department of Transportation specifications required 500 psi of flexural strength before a pavement can be opened to traffic. The Class F mix with Type I cement and using insulation blankets reached that strength in approximately 36 hours, the Class C mix using the blankets in approximately 48 hours, and the Class F mix without covers in about 60 hours. (Note: Class F concrete pavement is opened at 400 psi minimum and Class F bonded overlay pavement at 350 psi.) The results showed a significant improvement in early strength gain by the use of insulation blankets. The Type I cement could be used in mixes intended for early opening with sacrifices in time when compared to fast track but are still much sooner than conventional pavement. It appears a range of design alternatives is possible using Type I cement both with and without insulating blankets.

Evaluation of the Baladi Indirect Tensile Apparatus, MLR-89-08, 1990

Dr. Gilbert Y. Baladi of Michigan State University has developed a new device intended for reliable determination of asphalt concrete mechanical properties such as Poisson's ratio, resilient modulus, and indirect tensile strength. The device is the result of an effort to improve upon procedures and equipment currently available for evaluation of mechanical properties. A duplicate of this device was fabricated in the Iowa Department of Transportation, Materials Lab Machine Shop in 1989. This report details the results of an evaluation of the effectiveness of the device in testing Marshall specimens for indirect tensile strength as compared to results obtained with standard equipment described in AASHTO T-283. Conclusions of the report are: l. Results obtained with the Baladi device average 6 to 8 percent higher than those obtained with the standard device. 2. The standard device exhibited a slightly greater degree of precision than did the Baladi device. 3. The Baladi device is easier and quicker to use than the standard apparatus. 4. It may be possible to estimate indirect tensile strength from the stability/flow ratio by dividing by factors of 1.8 and 1.5 for 50 blow and 75 blow mixes respectively.

Evaluation of Long-Term Field Performance of Cold In-Place Recycled Roads: Field and Laboratory Testing, TR-502, 2007

Cold in-place recycling (CIR) has become an attractive method for rehabilitating asphalt roads that have good subgrade support and are suffering distress related to non-structural aging and cracking of the pavement layer. Although CIR is widely used, its use could be expanded if its performance were more predictable. Transportation officials have observed roads that were recycled under similar circumstances perform very differently for no clear reason. Moreover, a rational mix design has not yet been developed, design assumptions regarding the structural support of the CIR layer remain empirical and conservative, and there is no clear understanding of the cause-effect relationships between the choices made during the design/construction process and the resulting performance. The objective of this project is to investigate these relationships, especially concerning the age of the recycled pavement, cumulative traffic volume, support conditions, aged engineering properties of the CIR materials, and road performance. Twenty-four CIR asphalt roads constructed in Iowa from 1986 to 2004 were studied: 18 were selected from a sample of roads studied in a previous research project (HR-392), and 6 were selected from newer CIR projects constructed after 1999. This report describes the results of comprehensive field and laboratory testing for these CIR asphalt roads. The results indicate that the modulus of the CIR layer and the air voids of the CIR asphalt binder were the most important factors affecting CIR pavement performance for high-traffic roads. For low-traffic roads, the wet indirect tensile strength significantly affected pavement performance. The results of this research can help identify changes that should be made with regard to design, material selection, and construction in order to improve the performance and cost-effectiveness of future recycled roads.

Case Study of Seasonal Variation in the Subgrade and Subbase Layers of Highway US 20, TR-516, 2008

Seasonal variations in ground temperature and moisture content influence the load carrying capacity of pavement subgrade layers. To improve pavement performance, pavement design guidelines require knowledge of environmental factors and subgrade stiffness relationships. As part of this study, in-ground instrumentation was installed in the pavement foundation layers of a newly constructed section along US Highway 20 near Fort Dodge, Iowa, to monitor the seasonal variations in temperature, frost depth, groundwater levels, and moisture regime. Dynamic cone penetrometer (DCP), nuclear gauge, and Clegg hammer tests were performed at 64 test points in a 6-ft x 6-ft grid pattern to characterize the subgrade stiffness properties (i.e., resilient modulus) prior to paving. The purpose of this paper is to present the field instrumentation results and the observed changes in soil properties due to seasonal environmental effects.

Performance Evaluation of Concrete Pavement Granular Subbase - Pavement Surface Condition Evaluation, TR-554, 2008

This research project covered a wide range of activities that allowed researchers to understand the relationship between stability, pavement distress, and recycled portland cement concrete (RPCC) subbase aggregate materials. Detailed laboratory and field tests, including pavement distress surveys, were conducted at 26 sites in Iowa. Findings show that specific gravities of RPCC are lower than those of crushed limestone. RPCC aggregate material varies from poorly or well-graded sand to gravel. A modified Micro-Deval test procedure showed that abrasion losses of virgin aggregate materials were within the maximum Micro-Deval abrasion loss of 30% recommended by ASTM D6028-06. Micro-Deval abrasion loss of RPCC aggregate materials, however, was much higher than that of virgin materials and exceeded 30% loss. Modulus of elasticity of RPCC subbase materials is high but variable. RPCC subbase layers normally have low permeability. The pavement surfaces for both virgin and RPCC subbase across Iowa were evaluated to fulfill the objectives of this study related to field evaluation. Visual distress surveys were conducted to gather the detailed current pavement condition information including the type, extent, and severity of the pavement distresses. The historical pavement condition information for the surveyed field sections was extracted from the Iowa DOT's Pavement Management Information System (PMIS). The current surface condition of existing field pavements with RPCC subbase was compared with the virgin aggregate subbase sections using two different approaches. The changes in pavement condition indices (PCI and IRI) with time for both types of pavements (subbases) were compared.

Evaluation of Hot Mix Asphalt Moisture Sensitivity Using the Nottingham Asphalt Test Equipment, TR-555, 2010

Pavements are subjected to different stresses during their design lives. A properly designed pavement will perform adequately during its design life, and the distresses will not exceed the allowable limits; however, there are several factors that can lead to premature pavement failure. One such factor is moisture sensitivity. AASHTO T 283 is the standard test used in the moisture susceptibility evaluation of asphalt mixtures, but the results of the test are not very representative of the expected behavior of asphalt mixtures. The dynamic modulus test measures a fundamental property of the mixture. The results of the dynamic modulus test can be used directly in the Mechanistic-Empirical Pavement Design Guide (MEPDG) and are considered a very good representation of the expected field performance of the mixture. Further research is still needed to study how the dynamic modulus results are affected by moisture. The flow number test was studied in previous research as a candidate test for moisture-susceptibility evaluation, but the results of that research were not favorable. This research has four main objectives. The first objective of this research is to evaluate the usefulness of the dynamic modulus and flow number tests in moisture-susceptibility evaluation. The second objective is to compare the results to those achieved using the AASHTO T 283 test. The third objective is to study the effect of different methods of sample conditioning and testing conditions. The fourth objective of the research is to study the variability in the test results.

Biofuel Co-Product Uses for Pavement Geo-Materials Stabilization, TR-582, 2010

The production and use of biofuels has increased in the present context of sustainable development. Biofuel production from plant biomass produces not only biofuel or ethanol but also co-products containing lignin, modified lignin, and lignin derivatives. This research investigated the utilization of lignin-containing biofuel co-products (BCPs) in pavement soil stabilization as a new application area. Laboratory tests were conducted to evaluate the performance and the moisture susceptibility of two types of BCP-treated soil samples compared to the performance of untreated and traditional stabilizer-treated (fly ash) soil samples. The two types of BCPs investigated were (1) a liquid type with higher lignin content (co-product A) and (b) a powder type with lower lignin content (co-product B). Various additive combinations (co-product A and fly ash, co-products A and B, etc.) were also evaluated as alternatives to stand-alone co-products. Test results indicate that BCPs are effective in stabilizing the Iowa Class 10 soil classified as CL or A-6(8) and have excellent resistance to moisture degradation. Strengths and moisture resistance in comparison to traditional additives (fly ash) could be obtained through the use of combined additives (co-product A + fly ash; co-product A + co-product B). Utilizing BCPs as a soil stabilizer appears to be one of the many viable answers to the profitability of the bio-based products and the bioenergy business. Future research is needed to evaluate the freeze-thaw durability and for resilient modulus characterization of BCP-modified layers for a variety of pavement subgrade and base soil types. In addition, the long-term performance of these BCPs should be evaluated under actual field conditions and traffic loadings. Innovative uses of BCP in pavement-related applications could not only provide additional revenue streams to improve the economics of biorefineries, but could also serve to establish green road infrastructures.

Highway Applications for Rammed Aggregate Piers in Iowa Soils, TR-443, 2003

This report describes a study to evaluate Geopier® soil reinforcement technology in transportation construction. Three projects requiring settlement control were chosen for evaluation—an embankment foundation, a box culvert, and a bridge approach fill. For each project, construction observations, in situ soil testing, laboratory material characterization, and performance monitoring were carried out. For the embankment foundation project, Geopier elements were installed within and around an abutment footprint for the new I-35 overpass at the US Highway 5/Interstate 35 interchange in Des Moines, Iowa. Although the main focus of this investigation was to evaluate embankment foundation reinforcement using Geopier elements, a stone column reinforced soil provided an opportunity to compare systems. In situ testing included cone penetration tests (CPTs), pressuremeter tests (PMTs), Ko stepped blade tests, and borehole shear tests (BSTs), as well as laboratory material testing. Comparative stiffness and densities of Geopier elements and stone columns were evaluated based on full-scale modulus load tests and standard penetration tests. Vibrating wire settlement cells and total stress cells were installed to monitor settlement and stress concentration on the reinforcing elements and matrix soil. Settlement plates were also monitored by conventional optical survey methods. Results show that the Geopier system and the stone columns performed their intended functions. The second project involved settlement monitoring of a 4.2 m wide x 3.6 m high x 50 m long box culvert constructed beneath a bridge on Iowa Highway 191 south of Neola, Iowa. Geopier elements were installed to reduce total and differential settlement while ensuring the stability of the existing bridge pier foundations. Benefits of the box culvert and embankment fill included (1) ease of future roadway expansion and (2) continual service of the roadway throughout construction. Site investigations consisted of in situ testing including CPTs, PMTs, BSTs, and dilatometer tests. Consolidated drained triaxial compression tests, unconsolidated undrained triaxial compression test, oedometer tests, and Atterberg limit tests were conducted to define strength and consolidation parameters and soil index properties for classification. Vibrating wire settlement cells, total stress cells, and piezometers were installed for continuous monitoring during and after box culvert construction and fill placement. This project was successful at controlling settlement of the box culvert and preventing downdrag of the bridge foundations, but could have been enhanced by reducing the length of Geopier elements at the ends of the box culvert. This would have increased localized settlement while reducing overall differential settlement. The third project involved settlement monitoring of bridge approach fill sections reinforced with Geopier elements. Thirty Geopier elements, spaced 1.8 m apart in six rows of varying length, were installed on both sides of a new bridge on US Highway 18/218 near Charles City, Iowa. Based on the results of this project, it was determined that future applications of Geopier soil reinforcement should consider extending the elements deeper into the embankment foundation fill, not just the fill itself.

Laboratory Performance Evaluation of CIR-Emulsion and its Comparison Against CIR-Foam Test Results from Phase 2, TR-474, 2009

Currently, no standard mix design procedure is available for CIR-emulsion in Iowa. The CIR-foam mix design process developed during the previous phase is applied for CIR-emulsion mixtures with varying emulsified asphalt contents. Dynamic modulus test, dynamic creep test, static creep test and raveling test were conducted to evaluate the short- and long-term performance of CIR-emulsion mixtures at various testing temperatures and loading conditions. A potential benefit of this research is a better understanding of CIR-emulsion material properties in comparison with those of CIR-foam material that would allow for the selection of the most appropriate CIR technology and the type and amount of the optimum stabilization material. Dynamic modulus, flow number and flow time of CIR-emulsion mixtures using CSS- 1h were generally higher than those of HFMS-2p. Flow number and flow time of CIR-emulsion using RAP materials from Story County was higher than those from Clayton County. Flow number and flow time of CIR-emulsion with 0.5% emulsified asphalt was higher than CIR-emulsion with 1.0% or 1.5%. Raveling loss of CIR-emulsion with 1.5% emulsified was significantly less than those with 0.5% and 1.0%. Test results in terms of dynamic modulus, flow number, flow time and raveling loss of CIR-foam mixtures are generally better than those of CIR-emulsion mixtures. Given the limited RAP sources used for this study, it is recommended that the CIR-emulsion mix design procedure should be validated against several RAP sources and emulsion types.

Examination of Curing Criteria for Cold In-Place Recycling, TR-553, 2008

Cold In-Place Recycling (CIR) has been used widely in rehabilitating the rural highways because it improves a long-term pavement performance. A CIR layer is normally covered by a hot mix asphalt (HMA) overlay in order to protect it from water ingress and traffic abrasion and obtain the required pavement structure and texture. Curing is the term currently used for the period of time that a CIR layer should remain exposed to drying conditions before an HMA overlay is placed. The industry standard for curing time is 10 days to 14 days or a maximum moisture content of 1.5 percent, which appear to be very conservative. When the exposed CIR layer is required to carry traffic for many weeks before the wearing surface is placed, it increases the risk of a premature failure in both CIR layer and overlay. This study was performed to explore technically sound ways to identify minimum in-place CIR properties necessary to permit placement of the HMA overlay. To represent the curing process of CIR pavement in the field construction, three different laboratory curing procedures were examined: 1) uncovered, 2) semi-covered and 3) covered specimens. The indirect tensile strength of specimens in all three curing conditions did not increase during an early stage of curing but increased during a later stage of curing usually when the moisture content falls below 1.5%. Dynamic modulus and flow number increased as curing time increased and moisture contents decreased. For the same curing time, CIR-foam specimens exhibited the higher tensile strength and less moisture content than CIR-emulsion. The laboratory test results concluded that the method of curing temperature and length of the curing period significantly affect the properties of the CIR mixtures. The moisture loss index was developed to predict the moisture condition in the field and, in the future, this index be calibrated with the measurements of temperature and moisture of a CIR layer in the field.

Examination of Curing Criteria for Cold In-Place Recycling Phase 2: Measuring Temperature, Moisture, Deflection and Distress from CIR Test Section, TR-590, 2009

The previous research performed laboratory experiments to measure the impacts of the curing on the indirect tensile strength of both CIR-foam and CIR-emulsion mixtures. However, a fundamental question was raised during the previous research regarding a relationship between the field moisture content and the laboratory moisture content. Therefore, during this research, both temperature and moisture conditions were measured in the field by embedding the sensors at a midpoint and a bottom of the CIR layer. The main objectives of the research are to: (1) measure the moisture levels throughout a CIR layer and (2) develop a moisture loss index to determine the optimum curing time of CIR layer before HMA overlay. To develop a set of moisture loss indices, the moisture contents and temperatures of CIR-foam and CIR-emulsion layers were monitored for five months. Based on the limited field experiment, the following conclusions are derived: 1. The moisture content of the CIR layer can be monitored accurately using the capacitance type moisture sensor. 2. The moisture loss index for CIR layers is a viable tool in determining the optimum timing for an overlay without measuring actual moisture contents. 3. The modulus back-calculated based on the deflection measured by FWD seemed to be in a good agreement with the stiffness measured by geo-gauge. 4. The geo-gauge should be considered for measuring the stiffness of CIR layer that can be used to determine the timing of an overlay. 5. The stiffness of CIR-foam layer increased as a curing time increased and it seemed to be more influenced by a temperature than moisture content. The developed sets of moisture loss indices based on the field measurements will help pavement engineers determine an optimum timing of an overlay without continually measuring moisture conditions in the field using a nuclear gauge.