Qinwu Xu

Modelling linear viscoelastic properties of asphalt concrete by the Huet–Sayegh model

In order to seek an appropriate mechanical model to describe the complex modulus and characterise the linear viscoelastic property of asphalt concrete, the Huet–Sayegh model was studied in this research. Laboratory tests of complex modulus were conducted on 20 different mixtures. Several mechanical models (Maxwell, Kelvin, generalised Maxwell, generalised Kelvin and Huet–Sayegh) and the mathematical model of sigmoidal function were applied to establish master curves of dynamic moduli. Results indicate that the Huet–Sayegh model can describe complex modulus more accurately using fewer numbers of parameters compared with other mechanical models.

Measurement and Evaluation of Asphalt Concrete Thermal Expansion and Contraction

Thermal expansion and contraction (TE/TC) of asphalt concrete (AC) play a significant role in both the thermal fatigue and low-temperature cracking of AC pavements. This paper discusses a test method and procedure developed to determine the AC coefficients of thermal expansion and contraction (CTE and CTC, respectively). Cylindrical specimens were subjected to temperature variations in an environmental chamber and specimen deformations were measured using extensometers. Temperature was applied in the range of −5°C to 40°C during both expansion and contraction phases. A specimen made from ceramic with very low CTE/CTC was also tested so that the influence of the self TE/TC of extensometers could be accounted for, and therefore, the measured deformation of an AC specimen was properly adjusted. A finite element (FE) model was developed to simulate the thermal stresses and strains inside the specimen, and to provide means for reliable computation of CTE/CTC. For this FE model, required AC viscoelastic properties were determined from the dynamic modulus test. The CTE/CTC of AC were then determined by using the calibrated deformation-temperature relationship. The standard aluminum and rubber specimens were also tested for TE/TC within a temperature range to validate the developed test method and computation approach. It was found that the CTE/CTC of AC were nonlinear and temperature dependent. The CTE/CTC determined for the aluminum and rubber specimens were found to be close to the standard values, therefore, validating the proposed approach for determination of CTE/CTC of AC.

Improving Quality Control of Hot-Mix Asphalt Paving with Intelligent Compaction Technology

This paper answers whether existing intelligent compaction (IC) technology can be used in a practical way to improve the quality control (QC) process for hot-mix asphalt (HMA) paving projects. Specifically, the paper investigates the use and the benefits of IC technology for tandem drum vibratory rollers used to construct HMA materials. There is a need to improve QC practices for most typical HMA paving operations. This paper identifies and discusses major shortcomings in conventional compaction equipment and current QC practices. The use of IC technology can address these shortcomings and provide innovative QC tools to contractors and agencies. The paper is based on the findings of the Intelligent Compaction Pooled Fund (ICPF) project that included 16 field demonstration projects in 12 participating states. The ICPF projects were actual highway construction projects in which various pavement materials were placed and compacted with both conventional compaction equipment and rollers that were equipped with IC technology from various suppliers. Eight of the projects included placement and compaction of HMA materials. On these projects, IC was used for only a portion of the project. A case study of the Wisconsin project illustrates the benefits that could have been obtained if IC technology and specifications had been used for the entire project from beginning to end.

Moisture Transport Model for Enhancing FHWA HIPERPAV Predictions

A portland cement concrete pavement (PCCP) moisture model and associated program are developed for enhancing the FHWA HIPERPAV software predictions. This model predicts PCCP moisture transport and moisture loss to the environment due to drying and self-desiccation. The former is simulated in terms of Ficks second law; the second part is based on Oh and Chas model. The one-dimensional Crank–Nicolson finite difference method is used to build the mathematical algorithm for solution. FORTRAN coding is developed to program this computational procedure and incorporate the moisture model into the HIPERPAV software. The moisture model has been partially validated with other researchers’ experimental data. Results showed reasonable agreement between predictions and measurements. A sensitivity analysis shows that parameters such as the diffusivity coefficient, surface emissivity, and curing method affect moisture variations, especially at positions close to the surface and the bottom of the slab. Future research will focus on simulations of PCCP critical stresses and distresses with this enhanced moisture model.

A Sensing-Information-Statistics Integrated Model to Predict Asphalt Material Density With Intelligent Compaction System

Intelligent compaction (IC) is an innovative technology that has been used in road and earthwork construction. However, the current IC technology is unable to measure material density directly as the acceptance criteria by owner agencies. To tackle this issue, the authors have developed a sensing-information-statistics integrated model to predict asphalt material density for 100% coverage of construction area. Instrumented with the satellite navigation system, accelerometer, and infrared sensors, IC rollers measure mechanical responses of roller drums and material temperature in real time. With these measurements, panel data models-including both the multivariate linear and nonlinear models-were developed to predict asphalt material density. A reasoning model was proposed to estimate idiosyncratic errors due to uncertainty of measurements. An information management software was developed to analyze IC measurements with univariate statistics and geo-statistical models. Statistical models were implemented and validated with data collected from four paving projects in the US. Results indicate that the multivariate nonlinear panel data model can predict asphalt material density at the project level for 100% coverage of the construction zone within reasonable accuracy. Therefore, this model may serve as an enhanced quality control and acceptance tool for asphalt pavement construction to improve consistency and uniformity and long-term performances.

Use of Slab Curvature and ProVAL to Identify the Cause of Premature Distresses

It has been argued that dynamic traffic loading due to the presence of a nonflat pavement shape may result in accelerated deterioration of the pavement because of higher stresses in the slab from restrained curling–warping movement. Slab curvature, though imperceptible to the naked eye, usually develops on the riding surfaces of the individual slab segments after construction. Select case studies on high- and low-altitude Bolivian concrete highways illustrate the magnitude of curvatures that are generated. The Butterworth high-pass and spectral density analysis tools in the ProVAL software are used to identify the pavement slab curvature in these projects. A mechanistic analysis is used to ascertain the causes of the observed longitudinal cracking. By resorting to a newly developed curvature index, the second-generation curvature index, the equivalent temperature gradient that corresponds to the fitted curvature was included in a finite element method analysis to determine stresses in the slabs. It is concluded that the curved shape of the slabs resulting from permanent curling–warping coupled with traffic loading is inducing excessive stresses and causing the observed cracking distress in one of the evaluated highways.

Evaluation of Time of Set for Concrete Mix in Cold Weather with HIPERPAV Wisconsin Model

The major objective of this research was to evaluate time of set (TOS) predictions with the HIPERPAV Wisconsin software for cold weather concrete paving when Class C fly ash is used. The effects of Class C fly ash on the hydration properties and TOS of paving concrete were investigated on State Highway 95 near Alma Center, Wisconsin. Researchers teamed with the National Concrete Pavement Technology Center of Iowa State University to select the highway project and to conduct field testing, isothermal, and semi-adiabatic calorimetry for that project. The project data and experimental information were used to compare measured TOS with that predicted by the HIPERPAV Wisconsin software. The TOS computed with the HIPERPAV model was compared with the TOS obtained by the ASTM C403 test method and the thermal TOS computed by the derivatives method from isothermal test data. It was concluded that the HIPERPAV model may overestimate TOS predictions for Class C fly ash and alternative solutions to solve this problem were recommended.