LOAD-DEFORMATION BEHAVIOR OF SELF-COMPACTING GEOPOLYMER CONCRETE FILLED STEEL TUBES UNDER AXIAL LOADING

Abstract

In this thesis load-deformation behavior of the self-compacting geopolymer concrete (SCGC) filled composite columns was investigated. To achieve the aim of the study, the experimental study was designed as a two-stage program. The first one is the determination of proper mix proportions for geopolymer concrete to attain self-compatibility criteria conforming to EFNARC with a proper mechanical property. For this purpose, three types of coarse aggregate with three different grades were used for SCGC. The effect of aggregate type and size on the fresh and hardened properties of produced SCGCs was investigated. Two different base materials, blast furnace slag and fly ash, were used to produce self-compacting geopolymer concrete. Fresh properties were tested as per EFNARC requirements. A total of eighteen mixtures were produced. Compressive strength developments were investigated at ages 7 days, 14 days, 28 days, and 90 days. The second stage covers an experimental study regarding composite columns filled with self-compacting geopolymer concrete of the highest mechanical properties. To achieve this, concrete-filled steel tubes (CFST) were produced. The deformation performance of the produced composite columns and the load-carrying capacity were investigated. The research involved fabricating sixteen specimens of CFST with two length-todiameter (L/D) ratios (short and long), four different tube diameters, and two different wall thicknesses. Self-compacting geopolymer concrete with a compressive strength of 45 MPa was used to ensure optimal compaction. The specimens were then subjected to axial load tests to examine their load-deformation characteristics, ultimate strength, shortening curves, and failure modes. The ultimate loading capacity of the columns was compared with two design codes, the American code ANSI/AISC 360-16 and European specifications for composite structural design for steel structures EC4. The test results show that the ultimate loading capacity increased with increasing the tube thickness; overall, the code provisions accurately predicted the capacity of the columns. The factors of L/D and relative slenderness are crucial and directly influence the behavior of CFST. However, the D/t ratio proved to have no significant effect on the column's behavior.