Characterizing Lime- and Cement-Treated Soil with the PM Device at a Full-Scale Pavement Test Track

A Roadware ARAN inertial profiler was used to calculate the International Roughness Index (IRI) for the Auburn University National Center for Asphalt Technology (NCAT) test track tangent sections as well as three paving projects in Michigan. IRI values were calculated for short intervals [4.6 to 7.6 meters (15 to 25 feet)] rather than for the traditional 160 meters (0.1 mile). These short intervals were able to identify easily localized anomalies in the pavement smoothness due to changes in the construction activities. They were also useful in evaluating relationships between IRI and mix variables in the short NCAT test track test sections [60 meters (200 feet)]. IRI repeatability (standard deviation for three replicates) immediately after onstruction was found to be 0.063 m/km (3.99 inches/mile) in the right wheel path for mixes at the test track. The left wheel path tended to have higher and more variable IRI values. This was attributed to the left laser path being close to potentially segregated mix at the edges of the screed extension. The IRI variability increased with traffic. Using this nitial estimate of variability, some statistically significant differences due to mix variables such as aggregate source and/or binder grade can be seen. Results from the test track indicate that the finer mixes tended to have IRI values that ncrease slightly as density increases. This suggests that working the fine mixes to obtain higher densities results in a higher initial roughness.This observation was also generally seen in the data from the Michigan field projects. IRI values decreased significantly within 6 months of trafficking for the majority of the mixes at the test track. This suggests that traffic can have a smoothing affect on the pavement for up to 6 months after the start of trafficking. All results from this research were based on the construction of test track sections. These results should be verified on actual paving projects.

The National Center for Asphalt Technology (NCAT) Test Track has generated valuable information related to the installation of gauges, methodology for data collection and data analysis. However, information regarding the effect of pavement instrumentation on in situ properties is nonexistent. The objective of this study was to evaluate the effect of pavement strain gauges on the in situ density. In 2009, during construction of two test sections it was necessary to remove and replace the bottom lift since quality control targets were not met. Prior to removal, cores were taken in the gauge array and outside the array so that a two-sample T-test could be conducted for each section, respectively. The results showed that there were no significant differences between air void content and consequently no negative effect caused by the presence of pavement instrumentation. Additional density testing was conducted in and around the gauge array in these two test sections after completion of the surface layer. The data indicated no difference in measured density resulting from the presence of embedded instrumentation.

Pavement temperature is an important factor of the urban heat island (UHI) effect and it also plays an important role in pavement design. The objective of this study was to compare the pavement temperatures and heat absorbed for nine different pavement sections placed during construction of Phase IV at the National Center for Asphalt Technology (NCAT) Test Track. Temperature probes were installed in each section to measure temperatures at the top, middle and bottom of the asphalt concrete (AC) and three inches into the underlying aggregate base layer. Temperatures were recorded on an hourly basis over a one month period from August to September 2009. Results indicated that an increase in density may also increase pavement temperatures and stored energy. Additionally, changing components or the structure of the asphalt mixture may change its thermophysical properties as well as the amount of energy the pavement is able to store.

Mechanistic–empirical pavement design relies on empirical transfer functions to convert stresses and strains (from mechanistic analyses) to an allowable number of load repetitions until an acceptable limit of damage occurs. One method of determining transfer function for bottom-up fatigue cracking is to perform laboratory fatigue tests on the mixture or a range of potential mixtures intended for the pavement. Previous research estimated that shift factors on the order of 4 to 100 are needed to relate laboratory and field performance. There are a number of potential explanations for these shift factors, such as rest periods and healing. The structural test sections at the National Center for Asphalt Technology (NCAT) Test Track provided an opportunity to determine shift factors between transfer functions developed from laboratory beam fatigue tests and from the Guide for Mechanistic–Empirical Design of New and Rehabilitated Pavement Structures (MEPDG) and field performance. Strains input into the beam fatigue transfer function were measured using embedded pavement strain gauges and calculated using layered-elastic theory (PerRoad). The MEPDG was used to calculate strains for its transfer function. Fatigue shift factors were calculated for four of the structural sections from the 2003 NCAT Test Track. The fatigue shift factors determined using the measured strains ranged from 4.2 to 75.8. The fatigue shift factors determined with PerRoad ranged from 6.7 to 19.2. The fatigue equations developed from the laboratory testing were not used in the MEPDG; the NCHRP 1-37A-calibrated fatigue models were used. On the basis of these analyses, the MEPDG fatigue model reasonably predicts observed cracking.

Accelerated pavement testing (APT) applies intensive traffic loading for the purpose of observing long-term performance of pavements in a short time. The testing is beneficial for researchers as a timely and valuable data resource. As Mechanistic-Empirical (M-E) pavement design approaches emerge as a favorable alternative to traditional empirical approaches, there is a need for conducting calibration of the performance models in the M-E design framework. Data from APT testing may be considered advantageous for calibration due to research-grade accuracy conducted over shorter time intervals, but even so, M-E calibration is still time-consuming because many combinations of the respective calibration coefficients need to be evaluated against observed performance from pavement sections. The current version of the AASHTOWare™ Pavement ME Design software, though serving as a powerful pavement design and analysis tool, is not necessarily conducive to calibration studies as many interactions are needed by the user to populate the software with trial calibration coefficients and extract performance predictions after simulations have been completed. This study proposes using automation to facilitate calibration studies whereby the repetitive manual operations required by the software are recorded and built into a macro that greatly reduces the required human interactions. The software automation is demonstrated through a calibration study conducted at the National Center for Asphalt Technology (NCAT) Test Track that examined fatigue cracking calibration. The efficiency of the automated approach is compared against conducting calibration requiring human interaction with the software.

This study, for the first time, explores the possibility of reducing the lime consumption demand for stabilizing a high plasticity clay soil using xanthan gum (XG). A total of 24 different mix-designs, covering three lime-to-soil contents and five XG-to-water concentrations, were tested for standard Proctor compaction and unconfined compressive strength (UCS) to assess the individual and combined stabilization effects of lime and XG over time. The UCS of the compacted soil–XG blends exhibited ‘rise–fall’ responses with increasing XG concentration, peaking at 1.5% XG, with all cases mobilizing higher UCS values than the unamended soil. Moreover, extending the curing duration (1–28 days) led to notable further improvements in the UCS. Although the soil–XG mix-designs were unable to reproduce the 28-day UCS values of soil–lime blends, they were able to replicate or outperform early-age (≤ 7 days of curing) lime stabilization outcomes attained with up to 9% lime. All soil–lime–XG samples followed ‘fall–rise–fall’ UCS trends with increasing XG concentration, with 1.5% XG persisting as the optimum concentration. For the test soil examined, the application of 1.5% XG (applied as the mixing/compaction liquid) in conjunction with lime effectively reduced the 28-day lime consumption demand by at least 50% (e.g., UCS of sample with 3% lime + 1.5% XG > UCS of sample with 6% lime). The optimum soil–XG and soil–lime–XG mix-designs were also investigated for their long-term UCS performance; the beneficial effects of XG stabilization, with and without lime, were strongly preserved over time, with the 28-day UCS for all cases exhibiting notable further improvements after 365 days.

Cement-bentonite (CB) mixtures, compacted soil-lime (SL), and compacted soil-lime-fly-ash (SLFA) mixtures are frequently used materials in environmental engineering. The properties of these materials change over time due to chemical reactions between the binder, soil, and/or water. The acceptance criteria for these materials are usually defined by specific property values, such as permeability, stiffness, and shear strength, measured at certain curing times. The small-strain shear modulus, G0, can be non-destructively measured using the Bender Element method. The present paper illustrates the trend of G0 in CB, SL, and SLFA mixtures over curing time until 60–90 days. In addition, the hydraulic conductivity, k, was also measured. Three different CB mixtures, one SL mixture, and one SLFA mixture were examined. It was observed that the G0 for the CB mixtures increased as the curing time progressed, while the k decreased noticeably. The ratio of cement to water in CBs seemed to play a key role in determining the G0, while other factors, like the use of additives, also significantly affected the k. For SL and SLFA mixtures, the G0 was found to rise with curing time, showing a pattern reflecting the advancement of pozzolanic reactions between the soil and binders, and the permeability correspondingly decreased within one order of magnitude.

Effects of freeze-thaw cycles on mechanical properties of polypropylene Fiber and cement stabilized clay

Freeze-thaw performance of a cement-treated expansive soil

Experimental investigation on expansion characteristics and strength of carbonating reactive magnesia solidified clay

This paper presents unconfined compressive strength (UCS) test results of cement-treated soil cured under different curing conditions. During curing in water at different temperatures (21.1°C and 45.0°C), the samples for short-term curing were demolded at different times and then placed into the water again to continue the curing. UCS tests were conducted on all the short-term curing samples after an entire curing time of 28 days. On the other hand, for long-term curing, some samples were demolded at seven days and exposed to the water for further curing, while the other samples were sealed by a plastic mold during the entire curing period without any exposure to the water. The entire curing times for the long-term curing were between 100 and 400 days. The UCS test results showed that for the short-term curing, a sample demolded later and exposed to water for a short period was stronger than the sample exposed to water early. This trend was more evident at a high temperature (45.0°C), but the differences in the strength were small. For the long-term curing, a sample cured in the mold at room temperature (21.1°C) for the entire curing time had a higher UCS than the sample demolded at seven days and exposed to water for further curing, while there was no demolding effect at 45.0°C. The test results implied that a cement-treated soil sample cured in the mold can have a higher strength than a soil-cement column for the wet method of deep mixing that is exposed to materials around the column depending on curing conditions.

Multivariate statistical techniques were used to determine the feasibility of quantifying segregation in hot-mix asphalt pavements. Data obtained by using visual ratings of segregation, nuclear density gauge readings, and laboratory tests at nine field sites as reported by the National Center for Asphalt Technology were analyzed. Data were screened, before multi variate statistical analyses were performed, to develop relationships among segregation level, change in key mixture properties (air voids, asphalt content, and percent passing various sieves), and change in mixture density. The results revealed that segregation level could not be accurately identified by visual ratings and that multivariate statistics based on actual measured properties were appropriate for evaluating segregation level. Laboratory-prepared samples were made to assess the accuracy of the model developed in the study. The verification results indicated that the model could predict segregation level of these samples with accuracy. From the analysis of the models, it was concluded that a change in mixture density could predict segregation. This allows screening of segregated pavement sections on the basis of numerical field measurements instead of reliance on subjective visual observations. Given the promising results from this work, further studies on segregation models based on density measurements are suggested.

This paper discusses the strength characteristics of cement-treated soil cured at extremely low temperatures ranging from 5°C to −20°C. To examine how extremely low curing temperatures affect the strength of cement-treated soil, a field study of cement stabilisation executed in the severe winter of Hokkaido, Japan, is presented in the first part of this paper. This study reveals that extremely low air temperatures prevented the shallow part of the cement-treated ground at the site from solidifying sufficiently. Then the influence of extremely low curing temperatures on the strength characteristics of cement-treated soil is discussed, based on the results of laboratory cement mixing and other tests. It is found that cement-treated soils cured at lower temperatures (−20°C, −5°C, 0°C and 5°C) have lower unconfined compressive strengths (UCSs) than that cured at 20°C (a standard curing temperature according to the Japanese Geotechnical Society Standard). Cement-treated soils cured at −5 and −20°C showed almost no gain in UCS. For cement-treated soils cured at 0°C or above, the UCS increased with an increase in maturity. Finally, based on the above experimental results, points to be noted in the construction of cement stabilisation in winter in cold regions are proposed.

The effects of rate of strain on strength and deformation characteristics of soil–lime were investigated. Five strain rates (0.1, 0.8, 2.0, 4.0 and 7.0 %/min), five lime contents (0, 3, 6, 9 and 12 %) by dry soil weight and three cell pressures (100, 200 and 340 kN/m2) were carried. Triaxial tests, under unconsolidated condition, were used to study the effect of strain rate on strength and initial modulus of elasticity of soil and soil–lime mixture after two curing periods 7 and 21 days, respectively. A total of 405 triaxial specimens have been tested, where 225 specimens have been tested with first curing period (7 days). The testing program includes nine specimens for each strain rate, and each lime content was carried out, including natural soil with zero lime content. Another set of triaxial tests with a total of 180 specimens for the second curing period (21 days) was prepared at optimum moisture content, and the corresponding maximum dry density was also tested. The effects of strain rate and curing period on each of stress–strain behavior, type of failure, deviator stress at failure, cohesion and angle of internal friction and initial modulus of elasticity were studied thoroughly for the natural soil as well as soil–lime mixtures. For natural soil, the test results showed that the undrained shear strength, the initial modulus of elasticity and the cohesion increase significantly as the strain rate increase, while for soil–lime mixture at different curing periods, the undrained shear strength, initial modulus of elasticity and the cohesion increases to a maximum and then decreases as the strain rate and lime content increase. Also, the same variables and angle of internal friction increase with increasing curing period.

The Mississippi corridor of Interstate 269 (I-269) is located in northwest Mississippi and construction of this corridor encompassed approximately 27 miles of new Interstate. This study documents I-269 as a case study of the chemically stabilized soil pavement layers. The evaluation comprises pre-construction activities (material selection, mixture design, pavement design, contract information), construction activities (processes, specifications, as-built quality), and an assessment of three cement stabilized base sections. Detailed assessment included on-site specimen preparation using the plastic mold compaction device (PM Device), core drilling, and subsequent laboratory testing for density, unconfined compressive strength, and elastic modulus. This project was able to document and quantify density variability within current Proctor and nuclear gauge practices to the point where there was noticeable agency and contractor risk. Variability is known to exist in large construction projects, but quantifiable measurements over a large project, as presented in this paper, are more valuable than general expectations for basing future decisions. This paper provides evidence that a construction quality control program where nuclear gauge and Proctor compaction practices are interconnected with mechanical property measurements taken on specimens fabricated with the PM Device is worth considering for implementation. The PM Device fared well for construction, mixture design, and pavement design activities when benchmarked relative to the density, strength, and modulus of the several dozen cores taken and assessed from I-269.