Nam Tran

Coefficient of Thermal Expansion of Concrete Materials: Characterization to Support Implementation of the Mechanistic–Empirical Pavement Design Guide

The new Mechanistic-Empirical Pavement Design Guide (MEPDG) requires the coefficient of thermal expansion (CTE) of concrete materials as a direct input to determine critical pavement distresses. The CTE can be determined using AASHTO TP 60. For this study, a CTE measuring device in compliance with AASHTO TP 60 was acquired. Three replicate specimens were prepared for each of 24 concrete and cement paste mixtures and tested at 7 and 28 days. The range of CTE determined in this study was in agreement with the range of values reported by other studies, and the variability of test results was favorably comparable. Analysis of variance and sensitivity analyses were performed to evaluate the influence of mixture properties on the CTE and the effect on pavement performance predictions of using Level 1- and 3-CTE inputs. It was concluded that the type of coarse aggregate used in portland cement concrete (PCC) mixtures significantly influenced the CTE and pavement performance predictions. The proportion of coarse aggregates in the PCC mixture could significantly affect the CTE depending on the types of aggregates used in the mixture. In addition, recommendations for Level-3 CTE input can be used for PCC mixtures with limestones and sandstones. However, CTE recommendations for PCC mixtures with gravels were not available for comparisons. It is recommended that a future CTE testing program for supporting implementation of the MEPDG include primary local aggregate types and that CTE recommendations for Level-3 CTE input in the design software be updated to include more aggregate types, especially gravels.

Evaluation of Long-Lasting Perpetual Asphalt Pavement with Life-Cycle Cost Analysis

In 2006, the Oklahoma Department of Transportation sponsored work at the pavement test track of the National Center for Asphalt Technology to compare the performance of two sections that had been designed to determine the necessary thickness for perpetual pavement. One section (Section N9) was designed to be a perpetual pavement at 14 in. thick. The other section (Section N8), at 10 in. thick (according to the AASHTO 1993 design guide), was used to test performance and to identify the thickness needed for perpetual pavement. This paper presents a life-cycle cost analysis for quantifying the benefits of a perpetual pavement section compared with the long-term cost of the thinner section. The life-cycle cost analysis was conducted with RealCost 2.5, which was available through FHWA, and included a determination of quantitative estimates of construction schedule, work zone user costs, and agency costs for initial construction and rehabilitation activities. The perpetual pavement section was found to have had a lower life-cycle cost than the conventional pavement section and to have provided better service to highway users. For better planning of future preservation studies, the estimated present serviceability rating as a function of the international roughness index for two designs (perpetual and nonperpetual) was evaluated. The findings of surface measurements for both sections demonstrate a clear difference between perpetual and conventional pavement serviceability for a given level of roughness and accumulated traffic. These results are also useful for assessing the improvement of conventional pavement after rehabilitation treatments.

Short-Term Laboratory Conditioning of Asphalt Mixtures

This report develops procedures and associated criteria for laboratory conditioning of asphalt mixtures to simulate short-term aging. The report presents proposed changes to the American Association of State Highway and Transportation Officials (AASHTO) R 30, Mixture Conditioning of Hot-Mix Asphalt (HMA), and a proposed AASHTO practice for conducting plant aging studies. The report will be of immediate interest to materials engineers in state highway agencies and the construction industry with responsibility for design and production of hot and warm mix asphalt.

Long-term ageing of asphalt mixtures

Ageing of asphalt mixtures occurs during production and construction and continues throughout the service life of the pavement. Although this topic has been studied extensively, recent changes in asphalt mixture components, production parameters, and plant design have raised a need for a comprehensive evaluation that considers the impacts of climate, aggregate type, recycled materials, WMA technology, plant type, and production temperature. In this study, field cores were acquired from seven field projects at construction and several months afterwards, and raw materials were also collected for fabricating laboratory specimens that were long-term oven aged (LTOA) in accordance with selected protocols. The resilient modulus and Hamburg wheel tracking tests were conducted on both specimen types to evaluate the evolution of mixture stiffness and rutting resistance with ageing. The concepts of cumulative degree days and mixture property ratio were proposed to quantify field ageing and its effect on mixture properties. Test results indicated that the LTOA protocols of two weeks at 140°F (60°C) and five days at 185°F (85°C) produced mixtures with equivalent in-service field ageing of 7–12 months and 12–23 months, respectively, depending on climate. Finally, among the factors investigated in the study, WMA technology, recycled materials, and aggregate absorption exhibited a significant effect on the long-term ageing characteristics of asphalt mixtures, while production temperature and plant type had no effect.

Evaluation of foamed warm mix asphalt with reclaimed asphalt pavement: field and laboratory experiments

Warm mix asphalt (WMA) technology and reclaimed asphalt pavement (RAP) materials have been increasingly used in asphalt paving mixtures due to environmental and cost benefits. Combining WMA and RAP offers more economic and environmental benefits compared to using either alone. To evaluate the combined effect of WMA and RAP, two WMA mixtures with 20% and 30% RAP were produced using water-injection plant foaming, and they were compared with two comparable hot-mix asphalt (HMA) mixtures with 20% and 30% RAP. The four mixtures were paved on I-70 near Eagle, Colorado in May 2013. Laboratory performance properties of plant-produced mixes and field performance of the four test sections after 13, 25, 38 months were evaluated. The research results showed that the effect of water foaming WMA and RAP was not significant on the laboratory performance properties, construction quality and field performance. Thus, water-injection plant foaming WMA could be used to produce WMA mixtures with 20% and 30% RAP at a lower production temperature. These sections will continue to be monitored to evaluate their long-term performance and compare with the laboratory test results.

Effect of rejuvenator on performance characteristics of high RAP mixture

As more reclaimed asphalt pavement (RAP) is utilised in asphalt mixtures, there are increasing concerns about the potential negative effect of the aged RAP binder on the field performance, especially cracking resistance, of the high RAP mixtures. To address the concerns, there have been increasing interests in utilising rejuvenators to improve the cracking performance of high RAP mixtures. The objective of this study was to determine the benefits of using a new rejuvenator made from renewable sources in asphalt mixtures with high RAP contents. The study was conducted by determining and comparing the laboratory performance properties of three mixtures and the binders extracted from the mixes. The three mixtures evaluated in this study included two 50% RAP mixtures (RAP binder ratiou2009=u20090.55) with and without the rejuvenator and a comparable virgin mix. Results of this study suggested that the new rejuvenator was effective in improving both the intermediate and low-temperature cracking performance characteristics of the 50% RAP mix close to those of the virgin mix at the short-term laboratory ageing condition without affecting its rutting and stripping resistance. It is recommended that a field study of this rejuvenator be conducted to further evaluate its effect on the long-term field performance of high RAP mixes.

Evaluation of moderate and high RAP mixtures at laboratory and pavement scales

Abstract The use of reclaimed asphalt pavement (RAP) to replace the virgin materials in asphalt mixtures can result in significant cost savings and provide environmental benefits. As part of the national efforts to support the increasing use of RAP without adversely affecting the long-term performance of asphalt mixtures, a field evaluation of six asphalt mixtures containing moderate and high RAP contents has been conducted on six test sections at the National Center for Asphalt Technology Pavement Test Track since the third research cycle started in 2006. The objective of this study was to present the latest field and laboratory evaluation results of these six RAP mixtures. The field performance evaluated included rutting, roughness, surface texture and cracking. Sections W4 and W3 were constructed with 20% RAP mixes using PG 67-22 and PG 76-22 base binders, respectively. The four other sections, W5, E5, E6 and E7, were paved with 45% RAP mixtures using four different base binder options, consisting of PG 52-28, PG 67-22, PG 76-22 and PG 76-22 + 1.5% Sasobit. The results of this study show that moderate (20%) and high (45%) RAP contents can be used to produce asphalt mixtures that provide good performance, and a softer base binder can be used to improve the performance of a high RAP mixture. In addition, the creep strain rate determined in the indirect tensile test at 10 °C closely matched the field performance ranking – the mix with a higher creep strain rate exhibited more cracking in the field. The difference between the laboratory and field rank order discussed in this study may be affected by the different laboratory and field specimens and testing conditions, illustrating challenges when one uses smaller scale specimens and/or tests to simulate the performance and results of much larger scale pavement sections.

Comparison of Laboratory Cracking Test Results with Field Performance of Moderate and High RAP Content Surface Mixtures on the NCAT Test Track

In 2006, a group of experimental test sections was built on the National Center for Asphalt Technology Test Track to evaluate surface-layer mixtures containing 20 and 45 % Reclaimed Asphalt Pavement (RAP) with variations in the Superpave performance grade of the virgin binder. This paper discusses several laboratory tests that have been proposed as indicators of cracking susceptibility and how the results of these tests conducted on the mixtures used in the test sections compare with the observed cracking performance on the Test Track after five years. The cracking tests performed on the mixtures were the bending beam fatigue test, the Energy Ratio method developed at the University of Florida, the simplified viscoelastic continuum damage method developed at the North Carolina State University, and the Overlay Tester developed at the Texas Transportation Institute. On the track, the test sections performed very well, but exhibited a range of low-severity cracking, mostly near the edges of the wheelpaths. Cores were extracted to confirm that the cracks were limited to the surface layer. The field cracking performance indicates that the performance grade of virgin binder affects cracking resistance. The creep strain rate, measured as part of the Energy Ratio method, and the Overlay Tester results best matched the field performance of the test sections.

Adaptation and validation of stochastic limiting strain distribution and fatigue ratio concepts for perpetual pavement design

Traditional perpetual pavement thickness design is based, in part, on controlling strain levels at the bottom of the asphalt concrete layer below an endurance limit to prevent bottom-up fatigue cracking (FC). A field-based limiting strain threshold was developed from cumulative distributions of field-measured tensile strains in the 2003 and 2006 research cycles at the National Center for Asphalt Technology Pavement Test Track to understand the limiting strain necessary to control FC. Additionally, the fatigue ratio, the ratio of the nth percentile strain to the fatigue endurance limit, was developed. Both the tensile strain distributions and fatigue ratios showed a clear difference between sections that experienced bottom-up FC and those that did not. However, it is necessary to adapt these thresholds to strains predicted by perpetual pavement design tools. PerRoad, a stochastic perpetual pavement design programme, was used to predict strains for the same 2006 sections. Previously developed strain distrib...Traditional perpetual pavement thickness design is based, in part, on controlling strain levels at the bottom of the asphalt concrete layer below an endurance limit to prevent bottom-up fatigue cracking (FC). A field-based limiting strain threshold was developed from cumulative distributions of field-measured tensile strains in the 2003 and 2006 research cycles at the National Center for Asphalt Technology Pavement Test Track to understand the limiting strain necessary to control FC. Additionally, the fatigue ratio, the ratio of the nth percentile strain to the fatigue endurance limit, was developed. Both the tensile strain distributions and fatigue ratios showed a clear difference between sections that experienced bottom-up FC and those that did not. However, it is necessary to adapt these thresholds to strains predicted by perpetual pavement design tools. PerRoad, a stochastic perpetual pavement design programme, was used to predict strains for the same 2006 sections. Previously developed strain distributions and fatigue ratios were adjusted to reflect observed differences in predicted and measured strains. Cumulative distributions and fatigue ratios based on predicted strains for the 2009 research cycle validated the updated limiting strain distribution and maximum fatigue ratios for designing perpetual pavements to resist bottom-up FC.

Optimising water content in cold recycled foamed asphalt mixtures

During cold recycling, water is added to facilitate the dispersion of foamed asphalt in the mixture and to achieve uniform mixing and help compaction by providing sufficient lubrication. Too little water may cause difficulty in workability and compaction of the mixture, but too much water may extend the curing time and reduce density and strength. Therefore, the optimum water content (OWC) was considered as one of the most important factors in mix design procedures for cold recycling. Currently, mix design procedures for cold recycled foamed asphalt mixtures suggest adding water to the mixture at an optimum content to facilitate mixing and compaction. However, there is no standard method for determining the optimum total water content (OTWC) for cold recycling mixtures. Several empirical relationships were developed to determine the OTWC based on modified Proctor test results for Reclaimed Asphalt Pavement (RAP)/aggregate. However, the compaction effort in the modified Proctor test for RAP/aggregate may not match that for mixtures, which is compacted using the Superpave Gyratory Compactor (SGC) or Marshall hammer. A study is underway to improve the design method for cold recycled foamed asphalt mixtures with 100% RAP. The purpose of this paper is to optimise the design procedure by developing a new method to determine OTWC. SGC was used to compact RAP instead of the modified Proctor test to match the compaction effort recommended for foamed asphalt mixtures. A regression model was developed to calculate the OTWC for a mixture based on the determined OWC of the RAP, foamed asphalt content, and binder type as factors. The method for determining OTWC for a mixture was validated using six different mixtures and was found to correlate well with the measured OTWC, even though two of six mixtures had underestimated OTWC due to different binder source. Further comparisons with other two OTWC determining methods showed the mixtures at the proposed OTWC had improvement in indirect tensile strength.