This report presents information on the characterization of cementitiously stabilized layers and the properties that influence pavement performance. It also contains recommended performance-related procedures for characterizing these layers and performance-prediction models for incorporation into the mechanistic–empirical pavement analysis methods. Individual chapters highlight pavement distresses of hot-mix asphalt pavements and concrete pavements, laboratory tests and model development, and model calibration. The material contained in the report will be of immediate interest to state materials, pavement, and construction engineers and others involved in the different aspects of pavement design and construction.

Characterization of Cementitiously Stabilized Layers for Use in Pavement Design and Analysis

The suitability of the current resilient modulus test protocol (NCHRP 1-28A) for its application to unsaturated soils was assessed. Modifications to the stress state conditions of the protocol are necessary due to the axis-translation needed during the test when measuring matrix suction. This study presents the modulus of unbound materials resulting from tests performed under unsaturated soil conditions. Two different materials were tested. The base material was tested under drained and undrained boundary conditions, while the subgrade was tested under drained boundary condition. The results allowed for the enhancement of the Universal Model for resilient modulus prediction by incorporating suction as a stress state. This model predicts the resilient response of unbound materials as a function of external stress state and matrix suction levels and therefore, it is independent of moisture variation.

Resilient modulus for unsaturated unbound materials

This study aims at developing an accurate and efficient methodology to estimate the resilient modulus of unbound aggregates. First, a new resilient modulus model is proposed to incorporate the moisture dependence of the resilient modulus in addition to the stress dependence in existing models. Second, prediction models are developed to conveniently and accurately determine the coefficients in the proposed model. In order to characterize the moisture dependence of unbound aggregates, the degree of saturation and the matric suction parameter are added into the proposed model. The soil-water characteristic curve (SWCC) is used to determine the matric suction value at any given moisture content. The moisture dependence of the model is validated for selected materials with different moisture contents. In order to develop prediction models for the coefficients in the proposed model, laboratory experiments and multiple regression analysis are conducted on 20 different base course materials. The laborator...

Estimation of Resilient Modulus of Unbound Aggregates Using Performance-Related Base Course Properties

Soft clays are widely distributed in Missouri, United States. Due to their relatively low strength and high compressibility, subgrade construction in soft clays has encountered many difficulties. In recent practice, the use of fly ash (FA) along with lime to tackle soft subgrade problems has shown promising results. The effectiveness of Class C FA and lime kiln dust (LKD) in clay subgrade stabilization is examined in this research. Scanning electron microscopic (SEM) analysis, proctor compaction tests, unconfined compression tests, and resilient modulus tests were carried out on the FA and LKD modified soil mixtures. Test specimens were prepared at optimum water content and tested at various curing periods. The test specimens were reconstituted by static compression. Test results revealed that the addition of Class C FA could increase the dry unit weight of the FA treated soil, enhance the unconfined compressive strength, and improve the resilient modulus. Regression equations were developed to co...

Chemically Stabilized Soft Clays for Road-Base Construction

The present study deals with the revision of the current model in the Mechanistic-Empirical Pavement Design Guide (MEPDG) used to predict the environmental factor for unfrozen unbound materials (FU), which is used to adjust the resilient response of soils resulting from seasonal changes. A large database with data from the existing literature and studies at Arizona State University was developed to evaluate the model. The results suggest that the environmental factor is underestimated for fine-grained materials with high plasticity under dry (arid) conditions. However, insufficient data were available to enhance the FU models for wetter conditions. Three fundamental factors that may have impacts on the FU values were evaluated in this study: stress state, compaction energy (soil density), and soil type. The stress state was found to have little to no impact on the predictions of FU. But density changes and soil type were found to be important. The potential for soil index properties to be predictive varia...

Enhanced Model for Resilient Response of Soils Resulting from Seasonal Changes as Implemented in "Mechanistic–Empirical Pavement Design Guide"

The resilient modulus of the materials used in various pavement layers has been used extensively as an important material property in structural design of pavement. The state of stress and moisture content of cohesive soils have been observed to exert significant effects on the measured resilient modulus. Since the moisture content in the cohesive subgrade soils underneath the pavement undergoes seasonal changes due to infiltration of precipitations and since characterization of moisture and stress dependent resilient modulus of cohesive soils is a demanding and tedious task, there is a practical need for a predictive equation for the resilient modulus as a function of stress states and moisture content. This paper presents a new predictive equation for the resilient modulus of cohesive soils using the concept of soil suction. The accuracy of the proposed model is validated against experimental data of A-4 and A-6 soils conducted by the writers as well as by other data available in the literature. The proposed model provides advantages over the existing predictive equations by reducing the number of tests and soil specimens needed for determining the regression coefficients in the equation. The proposed predictive equation compares well with the empirical equation in the new mechanistic empirical pavement design guide (MEPDG) in predicting the effect of moisture content variation on the resilient modulus. The proposed model provides an advantage over the MEPDG empirical equation in taking into account the effects of both the stress state and moisture content on the resilient modulus of cohesive soils.

Predicting Moisture-Dependent Resilient Modulus of Cohesive Soils Using Soil Suction Concept

Effect of glass fiber on the properties of expansive soil and its utilization as subgrade reinforcement in pavement applications

Integrated assessment of free draining base and subbase materials under flexible pavement

A research program was conducted to study the behavior of different drainable base and subbase materials used by the Ohio Department of Transportation (ODOT). Two construction sites were chosen from this program to be built with different base course materials. Site I (ATB-90-19.56) consisted of ODOT 306 cement-treated, ODOT 308 asphalt-treated, and ODOT 304 sections. Site II (ATB-90-0.00) consisted of 307-NJ, 307-IA, 307-CE, ODOT 306 cement-treated, ODOT 304, and ODOT 308 asphalt-treated sections. Time domain reflectometry (TDR) probes were installed in subgrade and unbound subbase layers to provide continuous monitoring of the moisture variation in the pavement system. The laboratory calibration for TDR probes resulted in the development of suitable calibration coefficients for the studied materials and more accurate conversion of TDR field measurements to the in situ water content. The monitored moisture content variation was used to determine the drainage efficiency of different drainable base materia...

Field Monitoring of Moisture Variations Under Flexible Pavement

The current study aims to examine the potential use of recycled polyethylene terephthalate (RPET) plastic waste as a modifier for asphalt binder. Plastic bottles were collected, shredded, cleaned, melted, ground, then sieved. An asphalt binder with a penetration grade of 60/70 was used. The RPET plastic waste was blended with 60/70 penetration grade asphalt binder at five percentages (0, 5, 10, 15, and 20 %, by weight of asphalt binder) using a high shear mixer. To study the physical and mechanical properties of RPET-modified asphalt binders, both traditional and Super pave tests were conducted. The test results showed that by incorporating RPET into asphalt binder, the ductility and penetration values decreased, whereas the softening point and viscosity of asphalt binder increased. Furthermore, the rutting performance of RPET-modified asphalt binder, as presented by the rutting parameter (G*/sinδ), was enhanced by increasing the amount of RPET plastic waste at all testing temperatures. The high-temperature performance grade of asphalt binder was raised by one grade (from 64°C to 70°C) by adding 15% and 20% of RPET plastic waste. On the other hand, the low-temperature performance of asphalt binder, as presented by creep stiffness and m-value, was negatively affected by adding RPET. The low-temperature performance grade of asphalt binder was dropped by one grade (from −22°C to −16°C) by adding RPET plastic waste at percentages of 15 % and 20 %. Moreover, the fatigue cracking performance of asphalt binder, as presented by the fatigue parameter (G*.sinδ), was slightly reduced by adding RPET to the asphalt binder but remained lower than the acceptable Super pave limit (≤ 5000 kPa).

Samer R Rabab'ah

Papers

Predicting Moisture-Dependent Resilient Modulus of Cohesive Soils Using Soil Suction Concept

Effect of glass fiber on the properties of expansive soil and its utilization as subgrade reinforcement in pavement applications

Integrated assessment of free draining base and subbase materials under flexible pavement

Field Monitoring of Moisture Variations Under Flexible Pavement

The potential use of recycled polyethylene terephthalate (RPET) plastic waste in asphalt binder