Magdy Abdelrahman

Enhancing the performance of crumb rubber-modified binders through varying the interaction conditions

Traditional crumb rubber-modified (CRM) binders produced with coarse particles according to the McDonald method, the wet process, raise engineering as well as environmental concerns for their suitability in Superpave applications. This paper investigates the possibility of producing high-performance terminal blending CRM binders suitable for Superpave applications through the wet process. This paper re-examines the asphalt–rubber interaction mechanism and focuses on controlling the swelling of crumb rubber particles through varying the interaction conditions. This study considers parameters such as time, temperature, shearing speed and the addition of polymer modifiers to enhance the binder performance properties to meet the requirements of Superpave mixes. Rubber-modified terminal blends are very different from the McDonald-type binders and so are the conditions required for each binder type. The binder properties of interest are those related to performance and compatibility.

Controlling Performance of Crumb Rubber-Modified Binders Through Addition of Polymer Modifiers

The use of tire rubber as a modifier to enhance the properties of asphalt mixes through the wet process has proved to be a successful procedure, but full control of the properties of crumb rubber-modified binders has been a challenge. The literature indicates a wide variation on adding rubber to asphalt and that the degree of success of rubber modification in AC mixes depends on several factors, the majority of which relate to the method of mixing, storing, and transporting and to construction technologies. Understanding the nature of the interaction process between asphalt cement and crumb rubber-modifier (CRM) helps explain the development of binder properties. This paper covers the wet process, a relatively different technology in the application of CRM in asphalt with virgin polymers used to control and enhance the performance properties of CRM binders. The paper provides some clear insights into the mechanisms by which the interaction, with and without the existence of polymer modifiers, takes place....

Sensitivity of Untreated Reclaimed Asphalt Pavement to Moisture, Density, and Freeze Thaw

The objective of the research was to assess the structural capacity of reclaimed asphalt pavement (RAP) as a base layer and to investigate the effect of RAP content, moisture content (MC), freeze-thaw (F-T) conditioning, and dry density (DD) on the resilient modulus of untreated RAP as a base layer. The resilient modulus test was conducted in the laboratory for specimens containing different ratios of RAP and aggregate. All samples containing RAP had higher resilient modulus and lower permanent deformation compared to virgin aggregate. Resilient modulus of RAP decreased as the MC increased. At low MCs there was no clear effect of MC on permanent deformation. However, as moisture increased to the wet side of the optimum MC curve, loss of stability was clear. F-T conditioning did not have a negative impact on the stiffness of RAP; this was explained by the low ability of RAP/aggregate blends to hold moisture. DD effect on the resilient modulus was dependent on the level of MC, but developed models showed th...

Contractor Performance Evaluation for the Best Value of Superpave Projects

The best-value (BV) procurement process uses other key factors as well as bid price in the evaluation and selection of the best-performing contractor for the job. Contract time, lane rental, warranty, and quality of delivered product are examples of the key factors that indicate the contractor-expected performance. Literature on best value shows a need for analyzing the past performance of the contractor in similar jobs as an indicator of his/her qualification trend. This paper addresses this issue and proposes a methodology to incorporate quality of delivered product in the BV procurement system of asphalt construction. The paper uses past quality control (QC) testing results and utilizes Monte Carlo simulation to estimate the probability that the contractor gets full payment as an indication of qualification trend. The QC data were obtained from the Nebraska Department of Roads for a number of Superpave pavement projects. The results show the possibility of assigning a quality score for the contractor based on the past performance. This paper contributes to the current practice of best value with a new approach of employing QC as part of the selection process.

Integration of Mechanistic-Empirical Pavement Design Guide Distresses with Local Performance Indices

The pavement management system (PMS) is the organizational entity within a state highway agency responsible for the condition of the pavement network. Visual distress surveys are typically combined into an index to provide an overall measure of performance. Decision makers use these familiar indices in a number of facets. A recent survey suggests every state highway agency has implemented or plans to implement the Mechanistic–Empirical Pavement Design Guide (MEPDG). As they do so, maintaining the role these local indices play is critical for upholding the systems continuity. However, using the MEPDG output directly in calculating performance indices becomes problematic because local distresses and MEPDG distresses are not always congruent. Therefore, there is a need to develop procedures for calculating local performance indices with locally calibrated MEPDG output. Doing so will allow interchangeable use of both while preserving the role of the local indices. The Nebraska Department of Roads (NDOR) PMS serves as a model case. NDOR employs three indices in network-level PMS analyses for flexible pavements. MEPDG flexible distress models were calibrated by using local agency data and input into the existing index functions. This paper explores how the current measures of network condition used in decision making can coexist with the new design methodology. This connection allows mechanistic–empirical analyses of fund allocation, needs estimations, performance modeling, planning, and remaining service life. In addition, local indices can provide much more meaningful failure criteria in the MEPDG to local designers. Practical methods for index calculations are introduced. Detailed guidance for local calibration is also presented.

Rational Best-Value Model Based on Expected Performance

The best-value procurement strategy is gaining the interest of federal and state agencies. The strategy increases the value added to a project for each dollar added. A new concept of best value, that is, a rational and flexible model based on expected performance, is presented. The models flexibility is obvious in the selection of parameters to be included in the contractor selection process and in the determination of their weights. The models rationality will be achieved through relating all awarded scores to the agencys expected performance. The establishment of the best-value model relies on the past record of the contractors work for the agency as an indicator of qualification trend. This research incorporates prequalification as a first-level screening technique in selecting top contractor bids in the best-value procurement and then applies a rational scoring system in the final selection. Selection of the most appropriate contractor with the best qualifications for a given project will be based on contractor best value. Data are collected from groups of experts in the Minnesota Department of Transportation and processed through the analytic hierarchy process to establish the parameter weights. Although this research assists departments of transportation in selecting the best contractor, the results are relevant to both academics and practitioners. The paper provides practitioners with a tool for ranking contractors based on best value and provides academics with selection parameters, a model to evaluate the best value, and a methodology for quantifying the qualitative effect of subjective factors.

Effectiveness of open-graded base layer on subgrade moisture regime and overall pavement performance

Rockcap (open-graded crushed aggregate with a nominal maximum size of 2.5 in.) base layer is commonly used in the construction of asphalt pavements in Idaho. The effectiveness of the rockcap layer on the subgrade moisture regime and the overall pavement performance were evaluated. Two pavement sites were selected in northern and southern regions of the state. At each site, two pavement sections that are identical and adjacent to each other were instrumented by temperature, frost, and moisture sensors using time domain reflectometry (TDR) probes. One was constructed by a well-graded 3/4-in. aggregate base, whereas the other was constructed by the rockcap base. Data collected over approximately 4 years included moisture, temperature, frost condition, climatic information, groundwater level, and deflections using a falling weight deflectometer for structural support evaluation. These data were analyzed to assess effects of the rockcap layer on the variation of moisture in the subgrade and on the overall structural capacity of the pavement system. Results showed that the rockcap layer helped reduce the subgrade moisture content in pavements with daylight ditch drains, and it showed an increase in subgrade moisture for sections where the rockcap was confined by native soil and did not continue to side drains. However, performance analysis showed that sections with rockcap layer were always stronger than sections with aggregate base, even when the subgrade moisture content under rockcap was greater. The predicted rutting life for pavement sections with rockcap base layers was approximately five times greater than for sections with aggregate base.

Incorporation of Property-based Testing in Coarse Aggregate Specifications for Pavement Applications

The demand for pavement facilities that can handle increasing loads escalates the need for high quality aggregate material. While once plentiful, quality aggregate sources are starting to diminish. When aggregates are eliminated locally by resource depletion as well as land development that prohibits mining, the cost of construction can rise significantly. The cost of transporting quality aggregate materials from other places that comply with specifications can be very expensive. Coarse aggregate specifications for pavement mixtures for many states are outdated, with some sections dating back to around the 1930s. Specifications do not reflect the current level of knowledge concerning testing methodologies of desirable aggregate properties for pavement applications, especially at the local and low volume level. There is a need to evaluate the quality of aggregates based on the suitability of property-based testing requirements. A better understanding of testing requirements used to evaluate material properties can lead to a better utilization of local aggregate materials and reduce the reliance on diminishing high quality sources. This study investigates what property-based testing requirements have been established in current specifications as well as new areas of testing that need to be developed. A questionnaire of professionals defined a set of testing requirements for different pavement applications, which were then compared to the currently specified testing requirements. The results concluded that gaps exist in how professionals define quality aggregate compared to what current specifications define as quality aggregate. This creates the need for the inclusion of more property-based testing that could better characterize aggregates based on pavement performance. This type of characterization could open up the possibility of utilizing local materials that are normally rejected for lower volume applications.