Experimental investigation of the usability of recycled concrete aggregate in road superstructure

In developed countries, the use of recycled concrete aggregate (RCA) from construction and demolition wastes in granular road base (GRB) and granular road sub-base layer (GRSB) has become widespread in order to consciously use natural resources and contribute to sustainability. In our country, RCAs do not find use in GRB and GRSB. The most important reason for this is that there are no regulatory rules and conditions regarding the use of RCAs in road superstructures in the Highway Technical Specification (2013) (HTS). It is of great importance that the use of RCA which will emerge from the ongoing urban transformation practices that will continue for many years to come, will contribute to sustainability. For this purpose, in this thesis, the usability of RCAs in GRB and GRSB was investigated together with crushed aggregate (CA) and natural aggregate (NA). The RCAs were obtained from the debris of 3 buildings with different concrete strengths. A series of laboratory tests have been conducted on pure forms of the RCAs, CA, NA and mixtures of the RCAs with NA and CA at 25% - 50% - 75% ratios respectively. As a result of the laboratory tests for 23 different designs consisting of mixtures and pure materials, suitable designs were determined according to the requirements in HTS (2013) of GRB and GRSB materials. According to this, RCAs, which are found to be sufficient to be used in GRB and GRSB in terms of strength and hydraulic properties, were found to be insufficient at some points in terms of their durability characteristics. However, it was observed that a large part of these negative properties disappeared in the mixture designs. After laboratory tests, image analyzes were performed. For this purpose, Scanning electron microscopy (SEM) and fractal dimension analyzes were performed for pure form of the materials. SEM analysis was carried out for 1 - 7 - 28 days cured samples in order to investigate the effect of secondary cementation in RCAs. But secondary cementation was not observed. By using fractal dimension analysis, roughness and angularity of the materials were investigated. It was found that the high fractal dimension value had a positive effect on the strength characteristics and the fractal dimensions of RCAs were high. Flexible pavement designs were made for the pure state of RCA which was determined to be the most suitable for use in GRB and GRSB, 50% of the same RCA mixed with CA. and the use of pure CA. In these designs, superstructure thicknesses were determined in GRB in case of using selected materials. After the thickness determination, the cost analysis was performed for a 1 km long flexible pavement to be constructed according to these thicknesses. In this case, although the GRB thickness is less if pure CA is used, it was determined that pavement design with RCA is more economical because of the high transportation cost of CA and the high cost of preparation CA in quarry. As a result, it was determined that RCAs can be used in the GRB of flexible superstructure, because they have sufficient strength in spite of some negative durability properties, they are economical and their negativity in terms of durability can be greatly reduced when mixed with traditional aggregate. Therefore, the use of these materials in our country should be urgently encouraged. Thus, RCA, which emerged as waste in urban transformation applications, will have a very important contribution in ensuring the economic sustainability of road superstructure construction activities.