Experimental and numerical investigation of the performance of geopolymer piles with recycled concrete aggregate

In recent years, attention has been paid to carrying out environmentally friendly processes and sustainability in all business sectors. Accordingly, environmentally friendly production and sustainability are becoming more important gradually in civil engineering. Therefore, designing environmentally friendly (green) single pile and piled raft systems will contribute to sustainability in geotechnical engineering, which is a branch of civil engineering. For this purpose, the behavior of single pile and piled raft systems with recycled concrete aggregate (RCA) and geopolymer binder was examined within the scope of this thesis. In the first phase of the thesis; geopolymer mortars with RCA (RGM) were prepared using class F fly ash (FA), silica fume (SF) and ground granulated blast furnace slag (GGBFS) as precursor materials (PM), RCA as aggregate and mixture of sodium silicate (SS, Na2SiO3) and sodium hydroxide (SH, NaOH) as activator solution (AS). Strength, durability and workability properties of these mortars were examined. Effects of SF/PM, GGBFS/PM, SS/SH, NaOH molarity, AS/PM and RCA/PM variables on compressive strength, flexural strength, initial setting time and flow values were determined by a definitive screening design (DSD) consisting of 13 mixtures. Four variables that are most effective on mortar performance were selected and a design consisting of 27 mixtures were prepared with the central composite design (CCD), which is a response surface method (RSM). For CCD mixtures, compressive and flexural strengths, initial setting time and flow values of specimens cured for 7 and 28 days under ambient conditions were determined. In addition, the durability was evaluated by determining the mass losses, compressive and flexural strengths of the specimens cured for 28 days at ambient conditions after being kept in magnesium sulfate (MgSO4) and sodium chloride (NaCl) solutions for certain periods. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were performed on the selected samples based on the test results. The optimum RGM design was determined based on the criteria of strength, durability, workability, and setting time. In the second phase of the thesis, the behavior of single pile and piled raft systems produced with the optimum RGM determined in the first phase was investigated under vertical loading. Firstly, the load-settlement behavior of single piles produced with GGH, the axial loads in the piles, and the stress distribution in the soil were determined under vertical loading. To investigate the behavior of piled raft foundations, a Taguchi L9 design was created where pile length (Lp) / pile diameter (Dp), distance between pile axes (sp), relative density of sand soil (Drsand), and number of piles (Np) are variables. For the piled raft systems produced according to this design, load-settlement behavior of the piled raft, axial loads on the piles, pile-raft load sharing, and stress distribution in the soil were determined under vertical loading. Loading was performed in a small-scale model experimental setup. The results of numerical analysis based on the finite element method were compared with experimental data. The contribution to sustainability and the acquisition of scientific data by using RGM in single piles and piled raft systems make this thesis original. Thus, the behavior of alternative single pile and pile raft systems, which can provide solutions for adverse environmental conditions (sulfate-containing soil, sulfate water, and saline water) encountered in geotechnical applications, was presented. Furthermore, for single piles and piled raft systems, which still exhibit gaps in the existing literature, the behavior of the piles and the piled raft under vertical loading, together with the stresses developed in the soil, were examined in detail.