Lederle, Rita E.

This research investigated the effects of incorporating recycled concrete aggregate (RCA) at low replacement levels on the properties of concrete. Four different RCA sources were used, each with different aggregate properties. For each source, replacement levels of 5, 10, and 15% were tested and compared to a control group, which had no RCA. Of the four RCA sources investigated, three had similar levels of absorption capacity and percent fines, while one source had higher levels of both properties. RCA replaced virgin aggregate of a similar gradation and replacement was on the basis of volume. Fresh and hardened concrete properties were tested, including air content, super air meter (SAM) number, slump, workability via the box test, compressive strength, flexural strength, elastic modulus, Poisson’s ratio, coefficient of thermal expansion, surface resistivity, freeze-thaw durability, and unrestrained shrinkage. Digital image correlation was used to visualize strain fields during compression testing. A statistical analysis was conducted to determine if any observed differences in hardened properties between the test mixes and the control group were statistically significant. This research found that using up to 15% of an RCA with reasonable values of absorption capacity and percent fines would not negatively impact most concrete properties. It also provided an outline for future research to develop a specification to define what constitutes reasonable values of RCA properties for future use.

The report describes the construction and design of composite pavements as a viable design strategy to use an asphalt concrete (AC) wearing course as the insulating material and a Portland cement concrete (PCC) structural layer as the load-carrying material. These pavements are intended for areas with heavy trucks and problem soils to increase the service life and minimize maintenance. The project focused specifically on thermally insulated concrete pavements (TICPs) (that is, composite thin AC overlays of new or structurally sound existing PCC pavements) and developed design and construction guidelines for TICPs. Specific research objectives include determining behavior of the layers of the TICP system, understanding life-cycle costs and the feasibility of TICPs, and incorporating the results into design and construction guidelines. Both construction and design guidelines are considered in light of the construction and performance of TICP test sections at the Minnesota Road Research project (MnROAD).

This project assesses the mechanisms and methods to assess built-in curling of jointed plain concrete pavements. Through the use of literature review or previous work, material, geometric, restraint, curing and local ambient relative humidity were found to be factors affecting both construction curl and drying shrinkage, leading to built-in curl of concrete slabs. Through the extensive use of a finite element program, an artificial neural network (ANN) was developed to backcalculate the built-in curl of an in-service concrete slab using falling-weight deflectometer testing for a variety of parameters. This ANN was used to evaluate existing concrete test cells at the MnROAD facility. In addition to non-destructive evaluations, significant studies into surface profiling of these same test cells was conducted to evaluate the most accurate and simplified method for evaluating built-in curl. While the nondestructive ANN method evaluates the interaction of the concrete slab with the underlying layers, the surface profiling method does not directly reflect this interaction, but instead gives an understand of the slab's curvature at the surface. Comparisons between these methods as well as between numerous different surface profiling methods were conducted.