Syed Asif Imran

Dynamical model of asphalt-roller interaction during compaction

Proper and uniform compaction during construction is of utmost importance for the long term performance of asphalt pavement. Variations in the conditions of freshly laid pavements require adjustment of the compaction effort in order to obtain uniform and adequate density. One of the goals of on-going research in Intelligent Compaction (IC) is the development of adaptive feedback control mechanism to adjust the compaction effort according to the field and pavement conditions. Such feedback control systems require a good understanding of compaction dynamics. In this study, a dynamical model is developed to study the interaction between a moving vibratory roller and the underlying asphalt pavement during compaction. The asphalt pavement is represented as a lumped element model with visco-elastic-plastic properties. A procedure is presented to estimate the parameters of this model from standard tests on asphalt mix conducted in the laboratory. The combined roller-pavement dynamical model is used to replicate field compaction of an asphalt pavement using a vibratory roller. Numerical simulation results indicate good agreement with results observed during compaction of pavements in the field. Comparison between the simulation results and the results collected from the actual pavement construction job show that the model could be used as a mathematical basis for the development of advanced compaction methods.

Transient response of a vibratory roller during compaction

Compaction is the last, but possibly the most important, phase that an asphalt pavement goes through during construction. Adequate compaction is necessary for the long term performance of an asphalt pavement. Inadequate/improper compaction is one of the leading causes of early deterioration and failure of these pavements. Current quality control procedures also depend on destructive testing to ascertain the quality and thereby contribute to the early failure of the pavements. Non-destructive Intelligent Compaction (IC) techniques have been introduced to control the quality of construction of these pavements, but with limited success. Currently available IC systems display real-time measurements that are indicative of the pavement quality. However, these measurements are not adequately correlated with any measurements obtained from the finished pavement. One of the reasons for the poor accuracy is the lack of adequate modeling and mathematical analysis in the design of IC systems. These systems are typically built using heuristic data and are not amenable to mathematical analysis. In this paper, the dynamics of the vibratory compactor is studied and the effect of system parameters like the thickness of the pavement, type of asphalt mix, etc., on the response characteristics is determined. These measurements are then used to analyze the transient response of a vibratory roller during compaction. The response characteristics provide an insight into the requirements for feedback control and can be used as a starting point for improving the performance of IC systems.

Quality control of subgrade soil using intelligent compaction

Intelligent Compaction (IC) of subgrade soil has been proposed to continuously monitor the stiffness of subgrade during its compaction. Modern IC rollers are vibratory compactors equipped with (1) an onboard measuring system capable of estimating the stiffness of the pavement material being compacted, (2) Global Positioning System (GPS) sensor to precisely locate the roller, and (3) an integrated mapping and reporting system. Using IC, the roller operator is able to evaluate the entire subgrade and address deficiencies encountered during compaction. Continuous monitoring of quality during construction can help build better quality and long-lasting pavements. However, most of the commercially available IC rollers report stiffness in terms of Original Equipment Manufacturer (OEM) specified indicator, known as Intelligent Compaction Measurement Value (ICMV). Although useful, additional tests are required to establish the correlation between these ICMV values and the resilient modulus of subgrade (Mr). Since the mechanistic design of the pavement is performed using Mr, it is important to know if the design Mr is achieved on the entire subgrade during compaction. This paper presents a systematic procedure for monitoring the level of compaction of subgrade in real time using intelligent compaction (IC). Specifically, the Intelligent Compaction Analyzer (ICA) developed at the University of Oklahoma was used for estimating the modulus of the subgrade. Results from two demonstration studies show that the ICA is able to estimate subgrade modulus with an accuracy that is acceptable for quality control activities during the construction of pavements.

A 2 Dimensional Dynamical Model of Asphalt-roller Interaction during Vibratory Compaction

The quality and longevity of an asphalt pavement is influenced by several factors including, the design of the mix and environmental factors at the time of compaction. These factors are difficult to control during the construction process and often result in inadequate compaction of the pavement. Intelligent Compaction (IC) technologies address this issue by providing continuous real-time estimation of the compaction level achieved during construction. This information can then be used to address quality issues during construction and improve the overall quality of the pavement. One of the goals of IC is the dynamic adjustment of the compaction effort of the vibratory roller in order to achieve uniform density and stiffness of the pavement. However, complex dynamics of the compaction process and lack of computationally tractable dynamical models hamper the development of such controllers of vibratory rollers. In this study, the interaction between the vibratory roller and the underlying pavement is studied. A two-dimensional lumped element model that can replicate the compaction in the field is developed and its parameters are determined using the visco-elastic plastic properties and the shear deformation properties of the asphalt mix. Numerical simulation results show that the model is capable of capturing the coupled vibration dynamics of the asphalt-roller system in both the vertical and longitudinal direction. Comparison of numerical studies with the field compaction data also indicates that the model can be helpful in the development of control algorithms to improve the quality of pavements during their construction.

Intelligent Compaction of Stabilized Subgrade of Flexible Pavement

The long-term performance of a flexible pavement largely depends on the compaction level achieved in different layers during construction. Traditionally, the compaction level of the subgrade is monitored through spot checking of moisture content and dry density at some discrete points. However, this type of quality control work does not cover the entire pavement and may leave under-compacted areas. These under-compacted areas could likely lead to early failure of the pavement structure. Therefore, it is necessary to develop a real-time compaction monitoring tool that can provide an accurate measurement of the compaction level of the entire pavement. Such measurements could be used to identify and remediate under- compacted areas and provide adequate support to asphalt layers constructed on top of the prepared subgrade. The application of the Intelligent Compaction Analyzer (ICA) for real-time monitoring of compaction of a stabilized subgrade is addressed in this paper. Four case studies demonstrating the successful application of the ICA are included. The compaction level of the stabilized subgrade was monitored in terms of ICA density and modulus. In each case study, it was found that ICA could estimate the compaction level with a reasonable accuracy. It was also found that the ICA modulus and nuclear density gauge (NDG) measured density exhibits a good correlation with R 2 equal to 0.73.