The National Road Research Alliance (NRRA) is hosting “Improve Material Inputs into Mechanistic Design Properties for Reclaimed HMA Roadways” on November 16 at 10 a.m. CST, presented by Bora Cetin, Michigan State University.
The NRRA’s monthly seminar highlights research topics that will make an impact on the work done here in the state of Minnesota and around the country.
In the mechanistic pavement design approach (AASHTO, 2008), pavement performance is evaluated based on mechanistically determined critical stresses, strains, temperatures, and moisture levels that are in turn the inputs to empirical prediction models for specific pavement distresses such as rutting, fatigue cracking, thermal cracking, and roughness for flexible pavements and cracking, faulting, and roughness for rigid pavements. Accurate characterization of the traffic, climate, and material input parameters is therefore important to ensure that the theoretical computation of pavement stresses, strains, temperatures, and moisture levels are accurate at the critical locations within the system. Local calibration is desirable to improve the accuracy of the empirical distress model predictions for a particular state or region. Depending on the desired level of accuracy of input parameter, three levels of input are provided from Level 1 (highest level of accuracy) to level 3 (lowest level of accuracy). Depending on the criticality of the project and the available resources, the designer has the flexibility to choose any one of the input levels for the design as well as use a mix of levels.
The material parameters required for pavement foundation materials including unbound granular materials, subgrade, and bedrock may be classified in one of three major groups: (1) pavement response model material inputs, (2) Enhanced Integrated Climatic Model (EICM) material inputs, and (3) other material inputs. Pavement response model materials input required are resilient modulus, Mr, and Poisson’s ratio, μ used for quantifying the stress dependent stiffness of unbound materials under moving wheel loads. Material parameters associated with EICM are those parameters that are required and used by the EICM models to predict the temperature and moisture conditions within a pavement system. These inputs include Atterberg limits, gradation, and saturated hydraulic conductivity. The “other” category of material properties constitute those associated with special properties required for the design solution. An example of this category is the coefficient of lateral pressure.
While there is a rich database nationwide about Mr and California Bearing Ratio (CBR)/Unconfined Compressive Strength (UCS) of subgrade and conventional unbound granular aggregates, there is no stiffness/strength/gradation/hydraulic conductivity database for reclaimed hot mix asphalt (HMA) materials-reclaimed asphalt pavement (RAP) material and recycled concrete aggregate (RCA) used as a base/subbase layer in pavement systems. The main goal of this project is to collect these data from the National Road Research Alliance (NRRA) member states and the literature. In addition, the list of field and laboratory tests that had been conducted to use in mechanistic pavement design along with the construction specification will be summarized. Moreover, it will be determined whether any data exist that evaluate the impact of any specific characteristics and/or mix design of RAP on the stiffness and strength of pavement systems in short- and long-term. The research team will also conduct some preliminary sensitivity analyses with AASHTOWare Software by using the collected data to determine the most sensitive parameter that may impact the pavement performance predictions in use of RAP as a base/subbase material.
The proposed study will help to establish a database for RAP and RCA material characteristics including resilient modulus (Mr), CBR/UCS, gradations along with construction specifications. Thus, this would lead to more consistent material input and specifications between NRRA agencies. Once a database of material characteristics is established, the cost involved in acquiring and testing field samples for new design is reduced/refined. The outcome of this research in the form of a pavement design specification could be immediately implemented by the department of transportations (DOTs) of states participating in NRRA.
The overall research methodology is proposed by a highly-qualified team with expertise in pavement systems and geotechnical engineering and pavement engineering at Michigan State University (MSU) and the Recycled Materials Research Center (RMRC). The methodology primarily involves collecting and summarizing Mr, CBR/UCS, and gradation data for RAPs tested by NRRA state members. Construction specifications, literature, and design methods for building and design pavement foundation layers with RAP from NRRA member states will also be investigated. In addition, preliminary sensitivity analyses with the pavement AASHTOWare Pavement ME Design software will be conducted via use of RAP data collected. Based on the results of this study it will be determined whether more detailed laboratory and field tests will be necessary to enhance the database.
The proposed team has been working on MnDOT data and NRRA states for years and very familiar with the process. This project contains four tasks: (1) initial memorandum on expected research benefits and potential implementation steps, (2) collection of data from NRRA member states and literature, (3) sensitivity analyses, and (4) final report.