Cob is an earthen building material comprised of sand, clay, straw, and water used for millennia to construct dwellings. Although cob construction largely died out during the nineteenth century, it is experiencing a revival in England and the Pacific Northwest of the United States. Little scientific research has investigated the engineering properties of cob, knowledge of which is important for modern-day design practices and code requirements. Researchers at Oregon State University investigated six different Oregon cob mixtures using a series of standard soils and concrete tests adapted for this material. The objectives were to characterize the constituents, to establish estimates for the magnitude of, and degree of variability in, the mixture properties, and to develop correlations between the engineering properties and mixture composition. Results indicated low to moderate variation in basic mixture properties (i.e., unit weight, moisture content, and sand equivalent), moderate variation in strength properties, and high variation in the elastic modulus. Several reasonable correlations were found between shrinkage, compressive strength, elastic modulus, and sand equivalent and between flexural strength and fiber tensile strength.
Since 1984, the Oregon State Highway Division has constructed 724 km (450 centerline miles) of cold in-place recycled pavements. During this period, an intensive study was undertaken by the Oregon Department of Transportation (ODOT) and Oregon State University (OSU) with the following purposes: 1. To develop an improved mix design procedure for cold in-place recycled pavements. 2. To evaluate the structural contribution of cold in-place recycled pavements. 3. To develop improved guidelines and specifications for the construction of cold in-place recycled pavements. This paper summarizes the development of a mix design process and describes the early procedures used and their limitations. The first section of the paper describes the recycling process used during the 1984–1988 period. The second part of the paper describes the evolution of the mix design process used during this period. It describes the steps needed to estimate the emulsion content from properties such as RAP gradation, residual asphalt content, and asphalt properties (penetration and viscosity). Also described are the mix design criteria developed to date (stability, modulus, etc.). The third part describes the expected ranges in strength properties (stability, modulus, etc.) for cold recycled mixes. The last part of the paper presents significant conclusions from the work performed to date as well as recommendations for further study.
Sponsoring Agency Code Supplementary Notes AbstractThe Oregon Department of Transportation (ODOT) Pavement Services Unit is in the process of implementing a new pavement design procedure being developed under the sponsorship of the American Association of State Highway and Transportation Officials. Fatigue cracking is a key distress mechanism that is predicted as part of the overall process using a theoretical model calibrated to empirical data. Tensile strain at the underside of the hot-mix asphalt pavement layers induced by truck axle loads is, in turn, a key input into the fatigue cracking model. In the new design procedure tensile strain is predicted utilizing a layered elastic analysis model.The principal objective of the project was to obtain key information to be used to assess the validity of the predicted tensile strain via layered elastic analysis. This involved collecting data from an existing test site along Interstate 5 just north of Albany, Oregon and installing and collecting data from instruments at a new test site along US 97 in Redmond, Oregon.This report documents the progress made toward achieving the principal objective of the study during the contract period
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