Journal of Materials in Civil Engineering

Adhesion between asphalt binder and aggregate in a dry state as well as in the presence of water is critical to the performance and durability of asphalt mixtures. According to the literature, distress mechanisms in asphalt mixtures such as rutting, fatigue cracking, and moisture-induced damage are correlated to the nature and quality of adhesion between asphalt binder and aggregate. Surface free energy components of aggregates and asphalt binders can be used to compute the work of adhesion between the two materials in a dry condition as well as the thermodynamic potential of water to displace the asphalt binder from the surface of the aggregate. This paper presents a methodology to estimate the surface free energy components of aggregates using the microcalorimeter. The microcalorimeter is a relatively fast and simple alternative tool to estimate surface free energy components of aggregates compared to other techniques such as the gas adsorption method. In addition to surface energy measurement, the application of the microcalorimeter to directly measure the total energy of adhesion between the asphalt binder and the aggregate at mixing temperatures and the hydrophilicity of different aggregates at ambient temperatures is also demonstrated. Both of these properties influence the performance of asphalt mixtures in dry conditions and in the presence of water.

Mesoscale constitutive models of frost-damaged concrete are developed in this study through numerical simulation using a two-dimensional rigid body spring model (RBSM). The aim of the simulation is to predict the macrobehavior of frost-damaged concrete subjected to mechanical loading. The models also clarify the difference in failure behavior of concrete with and without frost damage. Zero strength elements and the concept of mesoscale plastic tensile strain are introduced into the normal RBSM springs to consider the experimentally observed cracking and plastic deformation caused by frost damage. The difference in the effect of frost damage on compression and tension behavior as found in the experiments is clearly predicted. Finally, analysis of a notched beam subjected to bending after different degrees of frost damage is carried out. The resulting load-deflection curves agree well with those obtained in the experiments. These good correlations confirm the applicability of the mesoscale model for predicting the macrobehavior of frost-damaged concrete.

Accurate prediction of the fatigue life of asphalt mixtures is a difficult task due to the complex nature of materials behavior under various loading and environmental conditions. This study explores the utilization of an artificial neural network (ANN) in predicting the fatigue life of rubberized asphalt concrete mixtures containing reclaimed asphalt pavement (RAP). Over 190 fatigue beams were made with two different rubber types (ambient and cryogenic), two different RAP sources, four rubber contents (0, 5, 10, and 15%), and tested at two different testing temperatures of 5 and $20°\mathrm{C}$ . The data were organized into nine or 10 independent variables covering the material engineering properties of the fatigue beams and one dependent variable, the ultimate fatigue life of the modified mixtures. The traditional statistical method was also used to predict the fatigue life of these mixtures. The results of this study showed that the ANN techniques are more effective in predicting the fatigue life of the modified mixtures tested in this study than the traditional statistical-based prediction models.

This research work investigates approaches for computing the average asphalt film thickness in asphalt mixtures and examines whether the in-place asphalt film thickness has a rational relationship with the performance of hot-mix asphalt mixtures. Two methods for calculating the aggregate surface areas, the surface area factor and index methods, are discussed in this research and the analytical results show that both the fine aggregate particles and aggregate shapes significantly affect the calculation and should be taken into consideration to obtain greater accuracy for the surface area. A computation method is proposed and significantly improves the current conventional method for the asphalt film thickness calculation by incorporating shape factors and flat surface factors for all sieve sizes. Field performance data from MnROAD and rutting data from laboratory fabricated mixtures, including both coarse and fine gradations, were analyzed to investigate the asphalt film thickness and corresponding performance of asphalt mixtures. Both the field data and laboratory experimental results show that the asphalt film thickness is a significant factor affecting the rutting performance for asphalt mixtures. However, more research work is needed to investigate the relationship between the asphalt film thickness and the other performance parameters of asphalt mixtures, such as fatigue cracking, before a film thickness specification can be proposed.

Fly ash and bottom ash are coal combustion by-products (CCBPs) that are generated in large quantities throughout the world. It is often economical to dispose ash as mixtures rather than separately; that notwithstanding, only a few studies have been performed to investigate the behavior of fly and bottom ash mixtures, particularly those with high contents of fly ash. Also, there is very limited data available in the literature on the field performance of structures constructed using ash mixtures. This paper describes the construction and the instrumentation of a demonstration embankment built with an ash mixture (60:40 by weight of fly ash:bottom ash) on State Road 641, Terre Haute, Ind. Monitoring of the demonstration embankment was conducted for a period of $1\text{year}$ from the start of construction of the embankment. The settlement of the embankment stabilized approximately $5\text{months}$ after the end of its construction. According to horizontal inclinometer readings, the differential settlement at the top of the embankment is about $5\mathrm{mm}$ . Results from field quality control tests performed during construction of the demonstration embankment and monitoring data from vertical and horizontal inclinometers and settlement plates indicate that the ash mixture investigated can be considered an acceptable embankment construction material.

As part of the validation effort to evaluate the consistency of a new cold in-place recycling using foamed asphalt (CIR–foam) mix design process for the Iowa Department of Transportation, the dynamic modulus and repeated load tests were conducted to evaluate the performance characteristics of CIR–foam mixtures over a wide range of loading and temperature conditions. The main objective of this research is to study the impacts of the foamed asphalt contents and reclaimed asphalt pavement (RAP) material characteristics on dynamic modulus and flow number. Dynamic modulus and repeated load tests were conducted on CIR–foam mixtures with RAP materials collected from seven different CIR project sites located throughout Iowa. Dynamic modulus values of the RAP materials varied depending on the sources and foamed asphalt contents. Coarse RAP materials with a small amount of residual asphalt content exhibited a higher modulus value at $4.4°\mathrm{C}$ but exhibited a lower dynamic modulus value at $37.8°\mathrm{C}$ than fine RAP materials with a large amount of residual asphalt content. Flow numbers were varied significantly depending on their RAP sources and foamed asphalt contents. Fine RAP materials with a hard residual asphalt binder exhibited a higher flow number than coarse RAP materials with a soft residual binder. The relative rankings of RAP materials in terms of the flow number did not change when the foamed asphalt was increased from 1.0 to 3.0%, which supports the repeated load test being consistent in evaluating a rutting potential of RAP materials.

Various models have been developed over the past several decades to predict the dynamic modulus $\mid E^{*}\mid$ of hot-mix asphalt (HMA) based on regression analysis of laboratory measurements. The models most widely used in the asphalt community today are the Witczak 1999 and 2006 predictive models. Although the overall predictive accuracies for these existing models as reported by their developers are quite high, the models generally tend to overemphasize the influence of temperature and understate the influence of other mixture characteristics. Model accuracy also tends to fall off at the low and high temperature extremes. Recently, researchers at Iowa State Univ. have developed a novel approach for predicting HMA $\mid E^{*}\mid$ using an artificial neural network (ANN) methodology. This paper discusses the accuracy and robustness of the various predictive models (Witczak 1999 and 2006 and ANN-based models) for estimating the HMA $\mid E^{*}\mid$ inputs needed for the new mechanistic-empirical pavement design guide. The ANN-based $\mid E^{*}\mid$ models using the same input variables exhibit significantly better overall prediction accuracy, better local accuracy at high and low temperature extremes, less prediction bias, and better balance between temperature and mixture influences than do their regression-based counterparts. As a consequence, the ANN models as a group are better able to rank mixtures in the same order as measured $\mid E^{*}\mid$ for fixed (e.g., project-specific) environmental and design traffic conditions. The ANN models as a group also produced the best agreement between predicted rutting and alligator cracking computed using predicted versus measured $\mid E^{*}\mid$ values for a typical pavement scenario.

The alkali-aggregate reaction (AAR) has been detected in the spillway driftway of the Furnas Hydroelectric Power Plant, Brazil, which was built in 1963. To investigate the properties of this concrete, several cores were drilled in the affected structure and ultrasonic tests in association with mechanical tests were conducted. This paper presents the results of the following properties: splitting tensile strength, compressive strength, modulus of elasticity, and ultrasonic pulse velocity. For the ultrasonic tests, initial in situ determinations were performed on the driftway concrete surface under different exposure conditions before actual coring took place. The concrete cores drilled from the same location were tested by direct ultrasonic method before determining their mechanical properties. The ultrasonic results showed that the pulse velocity is sensitive to different degrees of deterioration due to AAR and correlates with the modulus of elasticity of the concretes investigated. Furthermore, the modulus of elasticity was the main property affected by AAR.