Isaac L. Howard

Rutting and moisture damage resistance of high reclaimed asphalt pavement warm mixed asphalt: loaded wheel tracking vs. conventional methods

An increased potential for moisture damage and rutting has been the two main problems with warm mixed asphalt (WMA) implementation. The use of high reclaimed asphalt pavement (RAP) contents (25% or more) in WMA may alleviate these problems. At present, susceptibility to the moisture damage and rutting are usually tested for independently; however, these distress mechanisms can be linked for in-service pavements. An enhanced loaded wheel tracking test performed on dry and wet specimens, the PURWheel, is investigated in this paper to evaluate the interaction of traffic and moisture. The PURWheel is also compared with conventional rutting and moisture damage tests. PURWheel results are used to evaluate the performance of 25% and 50% RAP–WMA. Rutting and moisture susceptibility of the high RAP–WMA was comparable with current practice low RAP content hot mixed asphalt.

Merits of reclaimed asphalt pavement-dominated warm mixed flexible pavement base layers

Use of reclaimed asphalt pavement (RAP) has increased considerably over the past few years; approximately 85% of the RAP available is used within either hot mix asphalt (HMA) or warm mix asphalt (WMA). Within this time frame a number of research efforts have been performed, but most efforts have focused on RAP contents of 50% or less. This paper describes a laboratory effort that studied WMA with RAP contents of 50–100% in the areas of rutting, moisture damage, durability, cracking, and mixing uniformity. Lack of a RAP surplus coupled with performance data presented in this paper indicates that mixtures with more than 50% RAP do not, for most applications, add value to the highway system in present day. WMA with 50% RAP for use as an underlying (or base) pavement layer performed adequately in all performance areas investigated, durability and cracking included.

Alternative Geotextile Tube Fill Materials for Marine Applications

This paper focuses on using alternative materials for filling geotextile tubes for selected marine and shoreline applications. High moisture content fine grained materials are often prevalent at remote construction sites that use geotextile tubes. In some cases, containment of these sediments is the geotextile tubes purpose, making them a waste material of sorts. Sand is used in the overwhelming majority of geotextile tube applications (dewatering is a notable exception), and this paper does not aim to replace sand except for some applications where fine grained soils at the project site could be stabilized with cementitious material and used as fill. Four case studies are presented as examples of using cementitious stabilized fine grained soils in place of sand. Shear strength test data of cementitious stabilized fine grained soil is presented and compared to sand fill in terms of strength and economy. Results of the investigation were favorable to stabilized fill.

Thermal Cracking Potential of High RAP-WMA Evaluated with Bending Beam Rheometer Mixture Beam Test

In recent years, increasing cost of the raw materials for asphalt paving has generated interest in using greater quantities of reclaimed asphalt pavement (RAP). During the same period, development of warm-mix asphalt (WMA) technology has allowed use of lower production temperatures that can reduce the amount of short-term aging of the virgin binder. The reduction in short-term aging can be beneficial in reducing problems associated with increased binder stiffness that are normally encountered when using high percentages of RAP in a mixture. This paper presents the results of an investigation that compared the low-temperature performance of WMA with a high RAP content to the performance of mixtures produced in accordance with current practice, which limits the content of RAP in the mixture to 15 % or less. Comparisons were made through a combination of mixture testing with the bending beam rheometer (BBR) and thermal cracking analysis of the BBR data. Emphasis was placed on mixture performance when the mixture is used on the surface of highway pavements. Test results from over 1000 beam specimens tested in the BBR are presented, and the results indicate that low-temperature performance of WMA containing 25 % RAP is likely to be comparable to performance of surface mixtures produced in accordance with current practice. The test results also indicate WMA containing 50 % RAP may be more susceptible to thermal cracking than surface course mixtures produced by the current practice.

Full-Scale Instrumented Testing and Three-Dimensional Modeling of Airfield Matting Systems

Matting systems are used for temporary applications on soft soils to reduce ground pressure exerted by aircraft, heavy equipment, vehicles, and construction material. They have been used for military airfields, construction platforms, and similar applications. Previous evaluation studies of matting systems have typically consisted of full-scale testing, with only a limited amount of numerical modeling found in the literature. This paper presents results of full-scale accelerated testing of 21 test sections encompassing five matting systems, five soil-support conditions, and two aircraft loadings. One of the soil-support conditions was instrumented and tested in conjunction with three matting systems and one aircraft loading. Three-dimensional finite-element modeling was performed on the instrumented sections using the measured test data for calibration. Good matches of measured soil stresses were obtained with the model for two of the mats, whereas the model underpredicted stresses in the third mat. Modeling of the type performed in this paper was capable of correctly ranking the performance of the matting systems modeled relative to the full-scale test results.

Use of Portland Cement and Polymer Fibers to Stabilize Very High Moisture Content Fine-Grained Soils

Very high moisture content fine-grained soils are plentiful in wetlands, river basins, and after floods. They can be problematic and require disposal facilities to be constructed in some instances. Any means of handling or re-using these materials is potentially appealing. Using chemical stabilization (e.g., Portland cement) can enhance strength, but the resulting product can be brittle. Adding polymer fibers as a secondary stabilizer can add noticeable ductility while offering at least some strength and stiffness benefits. Two fiber types and Portland cement were mixed into three soils with varying properties at elevated moisture content and tested for shear strength via: (1) unconfined compression (UC), and (2) with hand-held gages. Fiber-reinforced and non-fiber-reinforced specimens were compared in terms of shear strength, elastic modulus, and ductility. Fiber addition, in general, increased shear strength, and the level of increase was affected by soil organic content. Ductility was considerably improved by fiber addition. Correlations were developed by soil type so that conservative elastic modulus values could be calculated from shear strength, and it was observed that fibers increased elastic moduli values.

Emergency paving using hot-mixed asphalt incorporating warm mix technology

This paper presents results of a study on hot-mixed and warm-compacted asphalt incorporating warm mix technologies for use in emergency construction following a natural disaster. Case studies were first reviewed to investigate feasibility of the concept. Next, an overall emergency paving framework was developed, complemented by a two-component laboratory investigation. Component one developed a series of short-term ageing protocols for use in preparation of test specimens; component two evaluated those specimens for compactability and rut resistance. Results indicated that (1) material could be hauled up to 6 h and still be effectively used in emergency paving, (2) the two warm mix additives studied improved compactability of hot-mixed and warm-compacted asphalt and (3) rut resistance was acceptable for emergency applications. A discussion on the post natural disaster permanent residual value of the hot-mixed and warm-compacted material is also provided.

Improving Concrete Sustainability and Performance with Use of Portland–Limestone Cement Synergies

The increased use of portland–limestone cements (PLCs) in the United States is anticipated in response to a new provision that has been added to blended cement specifications for PLCs containing up to 15% limestone. Published research has documented the performance synergies of cementitious mixtures with finely ground limestone (which has particle sizes generally smaller than cement particle sizes), especially in combination with certain supplementary cementitious materials (SCMs). Time of setting and strength development benefits are reported, generally in proportion to limestone fineness. It appears possible to fully develop the potential for these performance synergies in mill-ground PLCs, in which limestone comprises the majority of the finest particles. This study further investigated performance trends observed in concrete with PLC using separately proportioned, commercially ground limestone and ordinary portland cement, as well as cement mill–ground PLC samples. The influences of variables such as SCM type and limestone fineness were evaluated with laboratory paste mixtures. Set acceleration increased with limestone fineness for all combinations, including mixtures without SCMs. Strength improvements were clearly evident with all SCMs, more significantly with Class C ash and slag cement than with Class F ash. All strength trends improved as limestone fineness was increased. Consistently enhanced setting and strength performance appear achievable with PLCs. Optimizing particle fineness will be a key factor in achieving these benefits. As performance contributions of SCMs in combination with PLCs may exceed those of similar mixtures with traditional ordinary portland cements, SCM use can be maximized and related sustainability impacts further extended.

Haul Time Effects on Unmodified, Foamed, and Additive-Modified Binders Used in Hot-Mix Asphalt

In recent years, warm technologies have made enormous changes to the flexible pavement industry in a variety of ways. Warm-mix asphalt is the most recognizable warm technology product, although other advantages are associated with better compaction over a wide range of temperatures and have made long-haul distances appealing for some applications. This paper focuses on using warm-mix technology at traditional hot-mix production temperatures for the purpose of facilitating long haul distances. The primary objective of this study was to investigate how binder-related properties change with haul time when material was mixed at hot-mix temperatures. A secondary objective was to determine if any behavioral differences were present between asphalt binders with no additive, foamed asphalt binders, and asphalt binders with a chemical additive. Plant-mixed asphalt was used for the investigation. The overall conclusion of the research was that haul times of 1 to 8 h produced no major differences in aging for a given binder type or between binder types. Subtle differences were observed between binder types in some instances (e.g., low-temperature properties were slightly better for mixes using warm-mix technologies).

Evaluation of the Cantabro Durability Test for Dense Graded Asphalt

The Cantabro durability test is typically used for open graded asphalt mixtures and has seen little use with dense graded mixtures. This paper presents durability data from the Cantabro test for a number of dense graded mixes meeting current low Reclaimed Asphalt Pavement (RAP) specifications with the goal of evaluating the test method for use with dense graded mixtures. The purpose is to assist with developing a baseline of durability performance of current low RAP dense graded mixtures for future comparison to dense graded mixtures with elevated RAP contents. Eight mixtures were tested for this paper; the focus was on low RAP content mixture types commonly used in Mississippi, especially those used for rehabilitation applications. Data from mixes with of a variety of aggregate types, gradations, and binder grades are presented. Test data from laboratory-mixed laboratory-compacted, plant-mixed field-sampled laboratory-compacted, and plant-mixed quality control specimens are included. The effects of changes in binder content on durability results are investigated for 0% RAP mixtures. Overall, results were found to be repeatable and the Cantabro durability test was found to be a candidate for future comparison of dense graded mixture durability performance of conventional mixes to high RAP content mixes.