Xiang Shu

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.

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.

Characterizing Rheological Properties of Binder and Blending Efficiency of Asphalt Paving Mixtures Containing RAS through GPC

AbstractUse of recycled asphalt shingles (RAS) into asphalt mixture has become more popular in asphalt paving industry due to dwindling natural resources and potential economic benefits. However, one critical question arises as to how much of aged asphalt binder in RAS can be effectively blended with virgin binder during mixing and construction. This paper presents a laboratory study in which gel permeation chromatography (GPC) was used to determine the blending efficiency of RAS. A correlation was first established between percentages of large molecules (LMS) obtained from GPC and rheological properties of RAS binders. Then the relationship was used to estimate the blending efficiency of RAS binders. The effects of aggregate size, RAS content, and mixing time on blending efficiency were evaluated. The test results show that the percentage of LMS was highly correlated with the complex shear modulus (G*) of asphalt binder. Increasing mixing time led to a better blending of RAS mixture. Aggregate size did n...

Effects of mineral fillers on hot-mix asphalt laboratory-measured properties

It is well recognized that mineral fillers play an important role in the properties of mastics and hot-mix asphalt (HMA) mixtures. Better understanding of the effects of fillers on the properties of mastics and HMA mixtures is crucial to good mix design and high performance of HMA mixtures. This paper presents a laboratory investigation into the effects of different fillers on some properties of asphalt mastics and HMA mixtures. Three filler types and four filler contents were used to obtain the master curves of mastics and to characterize the stiffening effect of filler in mastics. The effects of filler on the characteristics of HMA mixtures were also investigated. The properties of HMA mixtures evaluated include optimum asphalt cement (AC) content, indirect tensile (IDT) strength, toughness index (TI), tensile strength ratio (TSR) and asphalt pavement analyzer (APA) rut depth. The results suggested that fillers had significant influence on the properties of HMA mixtures. With the increase of filler content, some properties of HMA improved while others decreased. Filler content for mix design should be determined based on the overall performance of HMA mixtures.

Investigation into Laboratory Abrasion Test Methods for Pervious Concrete

Portland cement pervious concrete (PCPC) has been increasingly used in concrete pavements during recent years. In addition to strength and permeability, abrasion durability is another important property of PCPC. In this study, three laboratory abrasion test methods were investigated for their potential capability of evaluating the abrasion and raveling resistance of PCPC. The three tests are the Cantabro test, the loaded wheel abrasion test, and the surface abrasion test. To evaluate the three test methods, eight PCPC mixtures containing different sizes of coarse aggregates and additives were tested. The comparison of the three abrasion tests indicates that all three tests were fairly effective in differentiating between the PCPC mixtures. However, the results from the Cantabro test may not reflect the abrasion resistance of the mixtures because the failure of the specimens was caused by impact rather than abrasion. With studded wheels and increased wheel load, the loaded wheel abrasion test exhibited best sensitivity and sufficient repeatability. The surface abrasion test successfully differentiated the control mix from other mixtures, but failed to differentiate between the mixtures containing latex and/or fiber, which may be attributed to the unfavorably low weight loss values from this test.

Air-Void Distribution Analysis of Asphalt Mixture Using Discrete Element Method

Heterogeneous air void distribution is a common phenomenon in asphalt mixtures and is intimately related to the behavior of the asphalt mixture. Air void distribution within an asphalt mixture specimen is related to several factors, such as compaction effort, method of compaction (equipment), and aggregate gradation. In this study, virtual digital specimens generated by an open source discrete element method (DEM) program were utilized to investigate the effect of compaction factors on air void distribution. The compaction processes of a Superpave gyratory compactor (SGC) and a vibratory compactor were simulated by DEM. Effects of aggregate gradation, specimen height, mold size, mold shape, and compaction method on the inhomogeneous distributions of air voids were studied through statistical analyses. The results from DEM simulation were in good agreements with laboratory test results as well as those found in the literature. This research demonstrated that DEM simulation could be a potentially helpful tool for analyzing asphalt mix compaction and selecting appropriate aggregates for asphalt mix design.

COMPARISON OF SEMI-CIRCULAR BENDING AND INDIRECT TENSILE STRENGTH TESTS FOR HMA MIXTURES

This paper presents the comparison between the result s of the Semi-Circular Bending (SCB) test and that of the Indirect Tensile (IDT) tes t in characterizing the tensile strength of hot-mix asphalt (HMA) mixtures. Analytical and numerical simulations were employed to interpret the experimental results. IDT test, a standard test method of AASHTO and ASTM, is adopted by most state highway agencies. Despite its broad usage and many advantages, the permanent deformation under the loading strips is undesirable and in some cases unbearable for the evaluation of the cracking potential of asphalt mixes. SCB test could significantly reduce the load ing stripinduced permanent deformation and thus is more suitable IDT for evaluating tensile properties of HMA mixtures. The results from this study indicated that SCB and IDT test were fully comparable and convertible.