ABSTRACT An investigation into the use of metakaolin (MK) and fly ash (FA) as partial cement replacements in concrete was conducted to enhance the sustainability of the construction industry. The MK and FA were incorporated into the concrete mix design by weight, replacing a portion of the portland cement content. The replacement percentages varied in two sets: 5%, 7.5%, 10%, 12.5%, and 15% for MK; and 5%, 10%, 15%, 20%, and 25% for FA. Workability of the fresh concrete was evaluated using the slump cone test to identify the optimal replacement level. Subsequently, the mechanical properties of the hardened concrete were investigated using compressive strength (CS), split tensile strength (STS), flexural strength (FS), modulus of elasticity (MoE). The results revealed that incorporating MK improved the mechanical properties: CS increased by 12.06%, STS by 16.84%, and FS by 15.42% compared to the control mix. In comparison, FA substitution resulted in a slightly lower increase: CS by 9.72%, STS by 12.84%, and FS by 8.57%. The study concluded that MK exhibited a superior performance in enhancing the strength properties of concrete compared to FA. Additionally, linear regression analysis was employed to establish correlations between the experimentally determined strength properties and the mix design parameters. This analysis demonstrated a strong correlation between the predicted and experimental values, making it a valuable tool for future concrete mix design optimization. (MK (FA industry weight content sets 5 5% 75 7 7.5% 10 10% 125 12 12.5% 15 20 20% 25 level Subsequently CS, , (CS) STS, (STS) FS, (FS) MoE. MoE . (MoE) 1206 06 12.06% 1684 16 84 16.84% 1542 42 15.42 comparison increase 972 9 72 9.72% 1284 12.84% 857 8 57 8.57% Additionally parameters values optimization 7.5 1 12.5 2 (CS (STS (FS (MoE 120 0 12.06 168 16.84 154 4 15.4 97 9.72 128 12.84 85 8.57 7. 12. 12.0 16.8 15. 9.7 12.8 8.5 16. 9. 8.

ABSTRACT Currently, fully encased composite columns (FECCs) and high-strength concrete (HSC) are widely used in the construction industry to build durable structures. Specifically, HSC is primarily employed in high-rise buildings, highway bridges, and tunnels. This study examined eight FECC specimens with 200 mm × 250 mm × 1000 mm dimensions. Four FEC columns were considered control specimens, while the remaining four were cast with the optimum content of 0.60% Steel Fibre (SF). These specimens were fabricated with two different lateral reinforcement spacing: 100 mm and 80 mm. All specimens were tested under axial loading using a 500 T capacity frame. The main objective of this study was to evaluate the axial load-carrying capacity, axial load-deformation behaviour, ductility, stiffness, energy absorption capacity, and mode of failure of all FECC specimens. Adding 0.6% steel fibre and reduced lateral reinforcement spacing enhanced the specimens axial load-carrying capacity, ductility, and energy absorption capacity. The steel fibre was crucial in preventing concrete cover spalling and cracks on the specimens. Experimental test results for the FECC specimens were compared to various codes, including IS: 456 – 2000, JGJ 138-2016, and EN 1994-1-1. The present results were compared to previously published data and evaluated using the same codes. According to the experimental and analytical findings, the prediction results from JGJ 138-2016 and EN 1994-1-1 were highly correlated with the experimental results. EN 1994-1-1 is recommended for developing two proposed methods, which were also compared to the experimental test results. These proposed methods demonstrated good agreement with the experimental outcomes, with mean values of 1.08 and 1.06, standard deviations of 0.04, and coefficients of variation of 3.54% and 3.53% for proposed methods 1 and 2, respectively. Currently FECCs (FECCs highstrength high strength (HSC structures Specifically highrise rise buildings bridges tunnels 20 25 dimensions 060 0 60 0.60 SF. SF . (SF) 10 8 50 frame loadcarrying load carrying loaddeformation deformation behaviour ductility stiffness 06 6 0.6 codes IS 45 2000 1382016, 1382016 138 2016, 2016 199411. 199411 1994 1. findings 138-201 1994-1- outcomes 108 08 1.0 106 1.06 004 04 0.04 354 3 54 3.54 353 53 3.53 2 respectively (SF 5 0. 4 138201 13 201 19941 199 138-20 1994-1 00 0.0 35 3.5 13820 19 138-2 1994- 3. 1382 138-