Evaluation of Curing Effects on Cold In-Place Recycled (CIR) Materials

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Date Created
2022
Report Number
2022-11
Description
Most cold In-place recycled (CIR) construction uses asphalt emulsion or foamed asphalt with or without active fillers as a stabilizing agent. To ensure the CIR layer gains appreciable stiffness and strength to support traffic, the stabilizing agents have to undergo curing (to dry additional moisture). If traffic is allowed on the CIR layer before sufficient strength and structural capacity is gained, premature damage will occur. Lack of a fast and reliable procedure to determine the extent of in-situ curing significantly increases the risk of such damage. Current construction specifications rely on empirically based time recommendations to ensure sufficient curing. Current empirical time estimates do not account for material variations, climatic inputs and construction process differences. This research uses a combination of in-situ testing of actual CIR construction projects and supplementary laboratory tests to develop a model for pavement engineers and practitioners to reliably predict the recommended time (as a function of mechanical property) for placing of overlay on CIR layers. The prediction model incorporates the critical factors that influence curing in CIR including stabilizer type and amount, presence of active filler, initial moisture content, in-situ density and curing temperature. Due to the large number of possible model variables and their interactive effects, rigorous regression analysis is conducted to determine the most significant variables. The model provides an option of defining sufficient curing based on criticality of the project. The major outcome of this research is a user-friendly spreadsheet-based tool with pre-programmed curing model predictive equations.

Pothole Prevention and Innovative Repair

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Date Created
2018
Report Number
2018-14
Description
Pothole repairs continue to be a major maintenance problem for many highway agencies. There is a critical need for finding long-lasting; cost-effective materials and construction technologies for repairing potholes. This research effort investigates critical components associated with pothole formation and pothole repair and proposes solutions to reduce the occurrence of potholes and increase the durability of pothole repairs. The components include investigating and documenting pavement preservation activities; experimental work on traditional repair materials as well as innovative materials and technologies for pothole repairs; stress analysis of pothole repairs to identify whether certain geometric configurations are more beneficial than others; evaluating cost analyses to determine the effectiveness of various repair methods. A number of conclusions and recommendations were made. Potholes are mainly caused by the delayed response to timely fixing common pavement distresses. The state of Minnesota has a number of preservation strategies that are available and have been successfully used. Recommendations are made to improve these strategies using documents made available as part of new Every Day Counts; EDC-4; initiative. Currently; there are no required specifications for patching materials. Mechanical testing can be used to select patching materials based on the estimated durability of the pothole repair; such as short-; medium-; and long-term. A number of new materials and technologies are available for more durable solutions for winter pothole repairs; however; they require additional heat source and are more expensive.

Investigation of Performance Requirements of Full-Depth Reclamation Stabilization

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Date Created
2016
Report Number
2016-09
Description
This research investigates the relationship between the mechanical properties of SFDR and the final performance of the rehabilitated pavements. The study involves two computational tools (MEPDG and MnPAVE) for the simulation of the long-term rutting behavior of pavements containing SFDR layers. Based on the simulations of three existing MnROAD cells, it is shown that for MEPDG the SFDR layer is best modeled as a bounded asphalt layer. To further investigate the applicability of MEPDG, a series of laboratory experiments are performed on cores taken from several sites constructed with different stabilizers including engineered emulsion, foamed asphalt with cement and CSS-1 with cement. The experiments include IDT creep and tension, semi-circular bending, dynamic modulus and disc compact tension tests. The measured mechanical properties are inputted into MEPDG to predict the rutting performance of these sites and it is shown that the simulated rut depth agrees well with the site measurement. However, it is found that MEPDG may suffer a convergence issue for some ranges of the values of the mechanical properties of SFDR. Due to this limitation, MnPAVE was used as an alternative. It was shown that the results simulated by MnPAVE are consistent with those obtained by MEDPG. A parametric study was performed on the three sites constructed with SFDR to determine the relationship between the long-term reliability of the rut performance and the mechanical properties of the SFDR.