Mingjiang Tao

Effects of Warm-Mix Asphalt Additives on Workability and Mechanical Properties of Reclaimed Asphalt Pavement Material

The soaring cost of liquid asphalt binder and anticipated stricter environmental regulations have driven highway agencies to maximize the amount of reclaimed asphalt pavement (RAP) used for pavement construction. However, because of already aged and stiffened asphalt binder in RAP, the use of high percentages of RAP in hot-mix asphalt (HMA) presents many challenges. Problems with workability and compactability during construction need to be resolved first. This study investigated the feasibility of using 100% RAP HMA as a base course with warm-mix asphalt (WMA) additives (Sasobit H8 or Advera zeolite) at a lower temperature (125°C). Mix samples (control set with 100% RAP; a set with 100% RAP plus Sasobit H8 at 1.5%, 2.0%, and 5.0%; and a set with 100% RAP plus Advera zeolite at 0.3%, 0.5%, and 0.7%) were compacted with 50 gyrations. Their workability, bulk specific gravity, indirect tensile strength at 0°C, and moduli at 0°C, 26.7°C, and 50°C were determined. The effects of different amounts of WMA additives were compared. The results showed that workability of the 100% RAP HMA improved with the addition of Sasobit H8 or Advera zeolite at temperatures as low as 110°C. At temperatures less than 80°C, the addition of Sasobit H8 or Advera zeolite tended to stiffen the mix, as also reflected in increased seismic moduli and indirect tensile strength. Seismic modulus of the mixes was also found to be dependent on bulk specific gravity. The addition of Sasobit H8 proportionally increased bulk specific gravity of the mixes. The effect of amounts of Advera zeolite on bulk specific gravity was less well defined. It seemed that stiff asphalt binder in the RAP also affected compaction by preventing asphalt foam from fully forming, as it would when Advera zeolite was mixed with a virgin asphalt binder.

Development of a methodology and a tool for the assessment of vulnerability of roadways to flood-induced damage

Proper assessment of flooded pavement is very critical for reducing the risk and ensuring the safety of construction crews, department of transportation personnel and the public. The objective of this paper is to present a rational procedure for the assessment of vulnerability of asphalt pavements to flood-induced damage. A system dynamics-based methodology was developed to determine the critical time (Tcritical) for full saturation of the unbound base and for failure of the bound surface layer. The methodology and the web-based simulation tool presented here will help the users to identify potentially vulnerable stretches of highway prior to flooding and either take action to improve them or monitor them closely to obtain preflood conditions which can be compared against post-flood conditions to detect deterioration; it will help them decide whether emergency and non-emergency vehicles can be allowed during and immediately after flooding, and in planning post-flooding investigative actions.

Practical Method to Understand the Effect of Aggregate Drying on the Moisture Content of Hot-Mix Asphalt

The drying of aggregates is a critical step in obtaining moisture-free hotmix asphalt (HMA). The drying depends on many factors, which include the absorption and the moisture content of the aggregates as well as the drying temperature and time. The effect of drying of the aggregates on the moisture content of the resultant HMA needs to be understood so that adequate drying can be carried out for mixes, such as warm-mix asphalt (WMA), which are produced at lower than conventional temperatures. The objectives of this study were (a) to develop a laboratory method to produce HMA samples with various moisture contents that mimic insufficient drying of aggregates in a drum mixer and (b) to develop a nondestructive laboratory testing procedure to determine moisture content of compacted HMA samples. Aggregates with relatively high and low absorption rates were selected. A practical method was developed to mimic the retention of aggregate moisture in HMA in the laboratory. Good correlation was obtained between drying time and moisture-content loss for the aggregates of high and low water absorption. An experiment with heat transfer and a simulation with a finite element method confirmed the presence of moisture and its significant effect on the thermal conductivity of the mixes, which provided a nondestructive approach to determine moisture content of compacted HMA samples.

Investigation of Moisture Susceptibility of Warm-Mix Asphalt Mixes Through Laboratory Mechanical Testing

Moisture can lead to serious damage and failures in hot-mix asphalt concrete pavements. This is an even greater concern for warm-mix asphalt because the much lower production temperatures may not completely dry the aggregates. In this Maine Department of Transportation study, the use of fracture energy parameters was evaluated to determine the influence of incomplete drying of mixes on their mechanical properties. Fracture energy–based parameters [energy ratio (ER); ratio of energy ratio (RER)] were determined from the following testing of mixes with fully and partially dried aggregates, some of which were subjected to moisture conditioning: resilient modulus, creep compliance, and indirect tensile strength (ITS) at 5°C. The results indicate that (a) resilient modulus, creep compliance, and ITS were all affected by the presence of moisture in mixes; (b) the trend and the degree of influence of moisture for different mechanical parameters were different; (c) the moisture conditioning process caused larger decreases in modulus and ITS values than did incomplete drying of aggregates; however, the same moisture conditioning process caused much larger decreases in modulus and ITS in mixes prepared with incompletely dried aggregates than did the counterparts prepared with fully dried aggregates; and (d) fracture energy–based parameters (ER and RER) appeared to be more-distinctive moisture effect and damage indicators than are the other parameters.

Combined Model Framework for Asphalt Pavement Condition Determination After Flooding

Flooding of pavements often causes damage that is invisible on the surface. A way to predict the condition of a pavement after flooding will be useful for agencies to make rational decisions about the need for closing a road to traffic or opening it up for cleaning and recovery work. In this study, the problem of flooded pavement assessment was formulated as a combination of hydraulic and structural analyses. A model was developed; it consisted of results from unsaturated hydraulic and layered elastic structural analyses. An interactive simulation was developed from the model and was made available on the web to users in the public domain. Simulations with the model showed significant impacts when subgrade layer moduli were below 50 MPa and layer thickness was less than 200 mm for the hot-mix asphalt (HMA) and less than 600 mm for the base. Axle loads exceeding 80 kN exacerbated damages and hazardous conditions. The time to reach conditions that will not lead to damage or failure within a short period of time depends on both the pavement conditions and the load magnitude. On the basis of thickness of surface HMA layer and soil subgrade moduli, restrictions of traffic could be placed on flooded pavements.

Impact of Flooding on Roadways

Flooding can cause extensive damages in roadways, particularly in those with granular base layers and thin asphalt mix surface layers. The objective of this paper is to present a summary of work conducted on the evaluation of the impact of flooding on pavements. Research shows that flood-induced damage occurs through various ways—weakening and washing away of granular base and soil subgrade layers, washing away of thin surface layers such as seals, and through erosion of subsurface materials near flowing water. Dislocation of concrete slabs due to washing away of subgrade soils during flooding has also been noted. Several models and frameworks have been developed to predict change in structural and surface properties such as roughness due to the impact of flooding. A number of models relating resilient modulus of soil to saturation and matric suction have been proposed. Researches have use both finite difference and finite element models to simulate flow of water through pavements. It has been confirmed that flow under unsaturated conditions is the dominant drainage mechanism in pavements. The role of base course material properties, trench backfill material, and drainage systems has been found to be crucial for drainage. The importance of considering the soil water characteristic curve information and an understanding of change in hydraulic conductivity for different saturation conditions has been emphasized.

A framework for the assessment of contribution of base layer performance towards resilience of flexible pavement to flooding

ABSTRACT Flood-induced moisture damage of flexible pavements is a serious concern for many road authorities. Reports from several studies confirm the significant structural damage that is caused by flooding on pavements. In general, there is a consensus to design and construct roads that are resistant to flooding. Simultaneously, the concept of resilience has gained popularity – frameworks and specifics are being developed to make civil infrastructure components resilient to natural and manmade disasters. This study provides a framework for quantitatively assessing the resilience of flexible pavements to flooding. The different interlinked steps consist of utilising unsaturated flow through the different layers to estimate drainage, interpretation of the results in terms of stiffness of the relevant layers, estimation of the impact of the change in stiffness on the overall structural condition of the pavement and then translating that change to a resilience index. The paper provides an illustrative example of such an estimation of resilience for a pavement. The results demonstrate the need for providing base course materials with appropriate gradation to ensure adequate hydraulic conductivity, and/or thicker surface layer, to avoid a reduction in service quality and loss of resilience for an extended period of time, in flood-prone areas. Abbreviations: CBR: California bearing ratio; D60: diameter corresponding to 60% passing in results of sieve analysis; FE: finite element; FWD: falling weight deflectometer; HMA: hot-mix asphalt; k eff: effective hydraulic conductivity; k sat: saturated hydraulic conductivity; MEPDG: mechanistic empirical pavement design guide; M R: resilient modulus; M Ropt: optimum resilient modulus; Q (t); Q: quality; R L: loss of resilience; R: Resilience; S Saturation; SNCratiof: post and pre-flood modified structural numbers (SNCs); SWCC: soil–water characteristic curve; wPI: percentage passing No. 200 sieve × plasticity index.

Laboratory Comparison of Rejuvenated 50% Reclaimed Asphalt Pavement Hot-Mix Asphalt with Conventional 20% RAP Mix

The Maine Department of Transportation (DOT) currently allows 20% reclaimed asphalt pavement (RAP) in base and intermediate courses. To help the Maine DOT decide whether RAP could be increased to 50%, this study evaluated the critical laboratory properties of hot-mix asphalt with 50% RAP materials and rejuvenator. The scope of work consisted of preparing 20% and 50% RAP mixes with and without rejuvenators and testing compacted specimens for their volumetric properties, moduli, indirect tensile strength, moisture susceptibility, and low- and intermediate-temperature cracking potential. Two rejuvenators were used: (a) generic waste vegetable oil and (b) proprietary, commercially available rejuvenator. Virgin binder, extracted RAP binder, and extracted binder from recycled mixes were tested for continuous performance grading. The results showed that rejuvenators improved the properties of high RAP mixes, and the performance of rejuvenated 50% RAP mixes was equal to that of the currently allowed 20% RAP mixes. Results from semicircular bending tests were used to evaluate and quantify the effect of rejuvenators on mixes with high RAP content. Field trials of 50% RAP mixes were recommended as a result of the study.