Baoshan Huang

Louisiana experience with crumb rubber-modified hot-mix asphalt pavement

A comparative study of laboratory and field performance of several applications of crumb rubber-modified (CRM) hot-mix asphalt in Louisiana is presented. Eight CRM asphalt pavement sections were constructed by eight different CRM processes or applications. These eight CRM sections were built at five state highway projects. A control section with conventional asphalt mixture was constructed at each project to compare with the performance of pavement sections built with CRM asphalt mixtures. To evaluate the mixture characteristics of the CRM and conventional mixes, laboratory tests of Marshall stability and flow, indirect tensile strength and strain, and indirect tensile resilient modulus were conducted on field compacted Marshall specimens. Comparisons of the field performances of the pavements were achieved through roadway core air void analysis, rut-depth measurement, international roughness index, pavement structure numbers measured through the Dynaflect (dynamic deflection determination) system, and visual inspections of cracks. The results indicated that the conventional mixtures exhibited higher laboratory strength characteristics than the CRM mixtures. The pavement sections constructed with CRM asphalt mixtures showed overall better performance indices (rut depth, fatigue cracks, and international roughness index numbers) than the corresponding control sections after 5 to 7 years of traffic.

Influence of Asphalt Tack Coat Materials on Interface Shear Strength

Asphalt tack coat is a light application of asphalt, usually asphalt diluted with water. It is used to ensure a bond between the surface being paved and the overlying course. Normally, hot asphalt cements, emulsified asphalts, or cutback asphalts are used as tack coats. The objective of this study was to evaluate the practice of using tack coats through controlled laboratory simple shear tests and determine the optimum application rate. The influence of tack coat types, application rates, and test temperatures on the interface shear strength was examined. Four emulsions (CRS 2P, SS-1, CSS-1, and SS-1h) and two asphalt binders (PG 64-22 and PG 76-22M) were selected as tack coat materials. The residual application rates considered were 0.00 (0.00), 0.09 (0.02), 0.23 (0.05), 0.45 (0.1), and 0.9 (0.2) L/m2 (gal/yd2). A simple shear test was performed to determine the shear strength at the interface at two test temperatures, 25°C (77°F) and 55°C (131°F). The results indicated that CRS-2P emulsion was the best tack coat type and 0.09 L/m2 (0.02 gal/yd2) was the optimum application rate at which a maximum interface shear strength was measured for both test temperatures.

Multivariate random-parameters zero-inflated negative binomial regression model: An application to estimate crash frequencies at intersections

Crash data are collected through police reports and integrated with road inventory data for further analysis. Integrated police reports and inventory data yield correlated multivariate data for roadway entities (e.g., segments or intersections). Analysis of such data reveals important relationships that can help focus on high-risk situations and coming up with safety countermeasures. To understand relationships between crash frequencies and associated variables, while taking full advantage of the available data, multivariate random-parameters models are appropriate since they can simultaneously consider the correlation among the specific crash types and account for unobserved heterogeneity. However, a key issue that arises with correlated multivariate data is the number of crash-free samples increases, as crash counts have many categories. In this paper, we describe a multivariate random-parameters zero-inflated negative binomial (MRZINB) regression model for jointly modeling crash counts. The full Bayesian method is employed to estimate the model parameters. Crash frequencies at urban signalized intersections in Tennessee are analyzed. The paper investigates the performance of MZINB and MRZINB regression models in establishing the relationship between crash frequencies, pavement conditions, traffic factors, and geometric design features of roadway intersections. Compared to the MZINB model, the MRZINB model identifies additional statistically significant factors and provides better goodness of fit in developing the relationships. The empirical results show that MRZINB model possesses most of the desirable statistical properties in terms of its ability to accommodate unobserved heterogeneity and excess zero counts in correlated data. Notably, in the random-parameters MZINB model, the estimated parameters vary significantly across intersections for different crash types.

Laboratory Investigation of Cracking Resistance of Hot-Mix Asphalt Field Mixtures Containing Screened Reclaimed Asphalt Pavement

This paper presents the results from a laboratory study in which hot-mix asphalt (HMA) mixtures with No. 4 sieve screened reclaimed asphalt pavement (RAP) were characterized for their cracking resistance through laboratory performance testing. A typical surface mixture commonly used in the state of Tennessee was evaluated at 0, 10, 20, and 30% RAP contents. Two types of aggregate (limestone and gravel) and three types of asphalt binders (PG 64-22, PG 70-22, and PG 76-22) were used in this study. Mixture cracking resistance was evaluated through Superpave indirect tension (IDT), beam fatigue, and semicircular bending (SCB) tests. The results from this study indicated that the inclusion of RAP generally increased stiffness and indirect tensile strength; however, it generally compromised cracking resistance for the mixtures studied. Mixture properties changed significantly at 30% RAP content as compared to those with 10 and 20% RAP. Field projects validated the findings from the laboratory study.

Analytical modeling and experimental study of tensile strength of asphalt concrete composite at low temperatures

In this study, analytical modeling of the tensile strength of hot-mix asphalt (HMA) mixtures at low temperatures was developed. To do this, HMA mixtures were treated as a two-phase composite material with aggregates (coarse and fine) dispersed in an asphalt mastic matrix. A two-phase composite model, which was similar to Papanicolaou and Bakoss [J. Reinforced Plast. Compos. 11 (1992) 104] model with a particle embedded in an infinite matrix, was proposed. Unlike Papanicolaou and Bakoss model, an axial stress was introduced to the fiber end to consider the load transferred from the asphalt mastic the aggregate. Efforts were also made to consider the effect of aggregate gradation, asphalt mastic degradation, and interfacial damage between the aggregates and asphalt mastic matrix on the tensile strength of the HMA mixtures. Experimental investigations were conducted to validate the developed theoretical relations. A reasonable agreement was found between the predicted tensile strength and the experimental results at low temperatures. Parameters affecting the tensile strength of asphalt mixtures were discussed based on the calculated results.

Regression Model for Resilient Modulus of Subgrade Soils

Subgrade soil is an important part in both flexible and rigid pavement structures. AASHTO recommends the use of bulk stress and deviatoric stress models to characterize granular and cohesive soils, respectively. However, these models oversimplify the fundamental behavior of subgrade soils. Being proposed is the use of an octahedral stress-state model to characterize the resilient modulus of different soils. Eight different soils representing major soil types in Louisiana were selected to validate the model and to calibrate the model parameters. Additional analysis was then performed to develop correlations between the model parameters and other soil properties. Three types of correlation were produced: (a) model parameter with soil properties, (b) model parameters with California bearing ratio, and (c) model parameters with unconfined compressive strength. Statistical analysis indicated that the correlation between model parameter and soil properties yielded the best results.

Laboratory Performance Evaluation of Warm-Mix Asphalt Containing High Percentages of Reclaimed Asphalt Pavement

This study evaluated the rutting resistance, moisture susceptibility, and fatigue resistance of warm-mix asphalt (WMA) mixtures containing high percentages of reclaimed asphalt pavement (RAP) through laboratory performance tests. The WMA mixtures were plant produced with a foaming technology commonly used in the United States. RAP content ranged from 0% up to 50%. Laboratory performance tests included the asphalt pavement analyzer rutting test, the Hamburg wheel-tracking test, the tensile strength ratio test, the Superpave® indirect tension test, and the beam fatigue test. For comparison purposes, hot-mix asphalt mixtures containing 0% and 30% RAP were also evaluated and compared with WMA. The laboratory test results indicated that WMA mixtures with high percentages of RAP exhibited higher resistance to rutting, better resistance to moisture damage, and better fatigue performance.

Laboratory Evaluation of Abrasion Resistance of Portland Cement Pervious Concrete

High porosity with interconnected voids between aggregate particles is the primary characteristic of portland cement pervious concrete (PCPC), which, however, causes a significant decrease in its strength and abrasion resistance. In this study, latex and fiber were added to improve the abrasion resistance of PCPC mixtures. Laboratory tests were conducted to evaluate the performance of latex-modified pervious concrete with a particular focus on abrasion resistance. Test results show that adding latex desirably improved strength and abrasion resistance of PCPC, whereas fiber did not show a significant effect on the mechanical properties of PCPC. In addition, the asphalt pavement analyzer (APA) abrasion test was found to be feasible for evaluating the abrasion resistance of pervious concrete.

Predicting Dynamic Modulus of Asphalt Mixtures with Differential Method

ABSTRACT Dynamic modulus (/E*/) is one of the fundamental engineering properties of asphalt mixtures and has been selected as a basic material property input in the new American Association of State Highway and Transportation Officials (AASHTO) Mechanicstic-Empirical (M-E) Design Guide. The M-E design guide either requires the direct laboratory testing for/E*/values or recommends using the Witczak model to estimate/E*/values. While laboratory testing is costly and time-consuming to conduct, the Witczak model is a purely empirical regression model in nature. Micromechanics approach provides another possible access to obtaining/E*/values. In this paper, the differential method was employed to predict the dynamic modulus and phase angle of asphalt mixtures. The predictive models were formulated from the differential method. The major characteristics of asphalt mixtures (viscoelastic effect, aggregate gradation, and air voids) were taken into account in the predicting procedures. Laboratory experiments were conducted to evaluate the developed predictive models. The results show that the predicted E*values from some predictive models were favourably close to the measured data, which confirmed the potential applicability of these models to asphalt mixtures.

Laboratory Evaluation of Moisture Susceptibility of Hot-Mix Asphalt Containing Cementitious Fillers

Moisture-induced damage has long been recognized as one of the major concerns for asphalt pavements. To mitigate potential moisture damage, one general method is to add mineral antistripping additives or liquid antistripping agents into hot-mix asphalt (HMA) mixtures. In this study, a comparative laboratory experiment was conducted to investigate the effectiveness of cementitious fillers on moisture susceptibility of HMA mixtures. Five types of cementitious fillers were considered: fly ash, cement kiln dust, and three types of hydrated lime with different finenesses. The laboratory performance of HMA mixtures subjected to moisture conditioning was evaluated through the following tests: dynamic modulus test; superpave indirect tensile tests; and tensile strength ratio test. The test results indicate that the cementitious fillers were generally effective in reducing the moisture susceptibility of HMA mixtures. The finer the hydrated lime particle, the more resistant the asphalt mixtures. In addition, dynamic shear rheometer test was conducted on asphalt mastics to explore the stiffening effect of different cementitious fillers.