PSI - Issue 70

Siddesh K N et al. / Procedia Structural Integrity 70 (2025) 231–238

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3.1. Cube Testing results The compression test results for cubes at 7 days and 28 days of curing, as presented in fig 5, reveal significant trends in the compressive strength of concrete with varying percentages of aluminum dross (Al Dross) as a replacement for cement. The following inferences and justifications can be drawn from the results: 7-Day Compressive Strength (Fig 5): From fig 5, 7 days test results , it is observed that At 0% Al Dross (control mix), compressive strength ranges between 12.00 and 12.89 kN/mm², consistent with M20 concrete at early age. With increasing Al Dross content, strength decreases significantly. At 5% replacement, it drops to 10.22 – 11.56 kN/mm², and at 10%, it further reduces to 6.67 – 7.78 kN/mm². Beyond 10%, the decline is sharp, with values as low as 0.89 – 1.33 kN/mm² at 25% and 30% replacement. This reduction is due to the slower pozzolanic activity of Al Dross and dilution of cement, limiting calcium hydroxide availability, essential for strength development. From fig 5, 28 days test results, it is observed that At 0% Al Dross, strength ranges from 25.33 to 31.56 kN/mm². At 5% replacement, it increases slightly to 31.56 – 33.78 kN/mm², indicating enhanced long-term strength. At 10%, it remains comparable (22.67 – 30.22 kN/mm²). However, beyond 10%, strength reduces drastically, reaching 1.78 – 2.67 kN/mm² at 30%. The slight improvement at 5% is attributed to Al Dross's pozzolanic reaction forming additional cementitious products like calcium aluminate hydrates. At higher levels, excessive cement dilution and impurities hinder strength gain. The optimal replacement level lies between 5% and 10%, where 28-day strength is maintained or slightly improved, and early strength remains acceptable. Beyond 10%, both early and long-term strengths decline, making higher replacements unsuitable for structural applications.

Fig. 5. Comparison of compressive strength with respect to no of curing days.

3.2. Beam Testing results The flexural test results for beams with varying percentages of aluminum dross (Al Dross) replacement (0% – 5%) reveal clear trends in load-deflection behavior under two-point loading (Fig. 6). The control beam shows gradual deflection with increasing load, reaching 146 kN at failure and a maximum deflection of 3.75 mm. The smooth load deflection curve indicates ductile behavior typical of reinforced concrete without additives. These beams outperform the control, especially at 1% and 2% replacement, achieving maximum loads of 151 kN and 147 kN, respectively. At 3%, the load slightly reduces to 132 kN. The improved performance is due to the pozzolanic activity of Al Dross, which forms additional cementitious compounds (e.g., calcium aluminate hydrates), enhancing the bond between concrete and reinforcement. These beams show reduced deflection at the same load levels, indicating higher stiffness and improved ductility with visible cracking and gradual failure. The densified matrix due to pozzolanic reaction increases resistance to deformation and cracking. These beams exhibit lower maximum loads (116 kN and 112 kN)