This study investigates the effects of the use of two different types of recycled aggregates with known characteristics as backfill materials in newly built cantilever reinforced concrete retaining walls on the seismic performance of the walls. The physical properties of the recycled aggregates used as backfill materials were determined using aggregate tests. Subsequently, analytical studies for the reinforced concrete retaining walls containing recycled aggregates in the amounts of 25%, 50%, 75%, and 100% were performed under seismic and static loads and the results were compared with those obtained for the retaining walls containing 100% natural aggregate as the backfill material. The experimental and analytical studies showed that the internal friction angles and effective ground acceleration coefficients significantly affected the overturning moment and total active pressure values of the retaining walls. The results led to the conclusion that recycled aggregates can be partially or completely used as the backfill material in retaining walls. Moreover, the current conventional calculation methods for design and analysis were proven valid for the reinforced concrete retaining walls containing recycled aggregates as backfill materials.

Recently, the demand for environmentally friendly products has been increasing worldwide. In this study, the improvement of cohesive soil with a biopolymer material (Guar Gum), which is a type of additive and organic, environmentally friendly, is investigated. For this purpose, various laboratory tests have been conducted on the biopolymer-added soils, including the compaction test, the Atterberg limits test, and the unconfined compressive strength test. The samples for tests have been prepared that the biopolymer has been mixed with the soil in three different proportions to determine the optimum mixing ratio. Also, in the biopolymer-added soils, some samples have been cured at varying times to determine the effect of curing periods on their strength. For comparison, the tests performed on improved soils have been also carried out on the untreated cohesive soil. For a comprehensive evaluation, scanning electron microscopy analyses (SEM analyses) was carried out on some samples. On the other hand, X-ray fluorescence analysis (XRF analysis) was performed to have an idea about the composition of the cohesive soil. Consequently, the biopolymer additive material has improved the geotechnical properties of the cohesive soil in all mixing ratios and curing times. Moreover, the optimum mixing ratio has been obtained at 1% according to the results of tests.

Many researchers suggest using construction and demolition materials (C&D) in engineering applications rather than virgin aggregates (VA). However, the engineering properties of C&D tend to be poorer than those of VA. This study presents the results of plate loading tests performed on unpaved roads with C&D, reinforced by different types of geosynthetics on the soft subgrade. As part of these tests, the effects of some geosynthetic parameters such as (a) the embedment depth, (b) the height and pocket opening of the geocell, (c) the embedment depths and number of geogrids, (d) the distance between geogrids and (e) the stiffness of the geotextile on the bearing capacity of the unpaved road were investigated. Moreover, the same plate loading test was also conducted on an unpaved road built with VA. As a result of this study, although the performance of C&D was determined to be lower than that of VA, it was concluded that C&D performed well enough to be used as an alternative to VA on unpaved roads. Furthermore, with a very small number of geosynthetics, it was determined that C&D could have a better performance than VA.

In this study, the usability of construction and demolition waste (CDW) aggregates as filling when stabilized with alkaline activator solution (AAS) and blast furnace slag (BFS) was investigated. The initial stage of this study involved determining the engineering properties of CDW by laboratory experiments. In the next stage, modified Proctor tests were performed to investigate the compaction behavior of CDW, to which 5% to 30% BFS was added with water or AAS. In the following stage, California bearing ratio experiments were performed to determine the mixture specimen with the highest strength. In the final stage, a weak soil layer was created in a test tank, and fillings of different thicknesses were built on it using CDW with and without additives in the determined optimum mixing ratio. Then, plate-loading tests were conducted using a model foundation to evaluate the load–deformation behavior of the fillings. The study’s results indicated that adding BFS with water or AAS to CDW increased strength. Furthermore, the addition of 20% BFS yielded the highest strength value, and the CDW aggregates with the added BFS increased the ultimate bearing capacity by up to 4.72 times compared to those without the additive.