Date of Award
Doctor of Philosophy
Civil, Construction, and Environmental Engineering
Civil Engineering ( Geotechnical Engineering)
Although good-quality (i.e., stiff and durable) natural aggregates have been widely used to construct structurally adequate base layers in flexible pavements, the cost of these aggregates has been increasing due to high demand, loss of natural sources, and federal/local restrictions regarding their production. Recycled concrete aggregate (RCA) and recycled asphalt pavement (RAP) materials are two alternative materials that are commonly used to replace good-quality natural aggregates used in base layers. Such use of recycled aggregates is promising because base layers constructed with these aggregates [such layers are referred to as recycled aggregate base (RAB) layers] have the potential to perform better than natural aggregate base layers.In addition, the use of large stones, containing a significant number of particles larger than 25 mm, in subbase layers [such layers are referred to as large stone subbase (LSSB) layers] has become popular in recent years to improve pavement sustainability. Large stones generally go through less crushing operations than conventional-size natural aggregates (these can be considered aggregates that generally contain particles finer than 25 mm), so energy consumption can be reduced by using large stones in pavement systems. LSSB layers placed over weak subgrade layers can provide stable working platforms for pavement construction. Although a significant number of studies have investigated different RCA materials, there is still a lack of information about the effect of gradation on the engineering properties of these materials and the performance of RAB layers constructed with such materials. There is limited information in the literature regarding the engineering properties of mixtures of RCA and RAP materials and the performance of RAB layers constructed with such mixtures. Furthermore, there is also a lack of practice about optimizing RAB layer thicknesses based on rutting predictions using the mechanistic-empirical (ME) design procedure. In addition, although recycled aggregates are prone to exhibiting greater mechanical degradation than natural aggregates due to their physical properties, there are not many reliable and accurate models to estimate such characteristics of recycled aggregates. Laboratory tests cannot be easily performed on large stones due to the size limitations of existing laboratory equipment, so there is limited knowledge of large stones in the literature. While the most convenient method for evaluating the engineering properties of large stones is to conduct field testing on full-scale pavement systems built with LSSB layers, there is still limited information about the characteristics of LSSB layers used as structural elements in pavements. To fill the gaps in the literature and evaluate the use of alternative materials in pavement foundation layers, three different RCA materials with different gradations, two different blends of RCA and RAP materials, a natural aggregate (control material), and a large stone were used in this research. Laboratory characterizations of the recycled and natural aggregates were made, and models were developed to estimate the mechanical degradation characteristics of these aggregates. Several full-scale test cells were constructed in two groups at a pavement test facility. In the first group of cells, three of the recycled aggregates were used to construct RAB layers. In this group, a natural aggregate base layer was also constructed and used as a control layer. In the second group of cells, the large stone was used to construct LSSB layers with two different thicknesses. Two of the recycled aggregates were used to construct RAB layers overlying the LSSB layers. In addition, several geosynthetics were placed beneath the thinner LSSB layers. Construction monitoring was performed, and a series of field tests were conducted to evaluate the performance of the constructed RAB, natural aggregate base, and LSSB layers. Changes in soil and air temperatures over time were also assessed to better evaluate the performance of these layers under different environmental conditions. Overall, in the laboratory, the recycled aggregates exhibited higher stiffness, less permanent deformation, and higher permeability than the natural aggregate. It was concluded that gradation significantly affected the performance (i.e., stiffness and rutting characteristics) of the RAB layers constructed using the RCA materials. In the laboratory, the RCA materials exhibited higher stiffness, less permanent deformation, and higher permeability than the blend of RCA and RAP materials. Similarly, in the field, the RAB layers constructed using the RCA materials performed better than that constructed using the blend of RCA and RAP materials. It was concluded based on the observations that the RAB layers could be thinner than the natural aggregate base layer to obtain equivalent (or similar) structural capacity. Therefore, the thicknesses of the RAB layers were optimized using the ME design method. While the recycled aggregates showed better performance than the natural aggregate in terms of stiffness, permanent deformation, and permeability, the recycled aggregates experienced considerable mechanical degradation compared to the natural aggregate, showing that special attention needs to be paid to their use. With respect to the LSSB layers, it was concluded that the construction of the thinner LSSB layers was problematic overall. Construction monitoring showed that using geosynthetics beneath the thinner LSSB layers improved the workability of the subgrade soil and the constructability of the LSSB layers. Field test results showed that the thicker LSSB layers provided better structural support than the thinner LSSB layers to the pavement system.
Haluk Sinan Coban
Coban, Haluk Sinan, "Evaluation of the use of alternative materials in pavement foundation layers" (2020). Graduate Theses and Dissertations. 18295.
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