Pozzolanic Effects of Meta-Halloysite and Micro-Silica on Mechanical Strength and Durability of Concrete

To determine the effects of meta-halloysite and micro-silica pozzolans on mechanical strength and durability of concrete, 8 mix designs with two water/cementitious (W/C) ratios of 0.40 and 0.45 were performed. The ordinary Portland cement (OPC) was replaced by incorporations of 10 and 20% of metahalloysite, and 7% of micro-silica. Samples were cured until the ages of 14, 28 and 90 days. Results imply that the combination of meta-halloysite and micro-silica for both W/C ratios particularly in the case of the lower ratio (0.40) when the sample contains 10% meta-halloysite, leads to a significant increase (89%) in the compressive strength of mixes (from 25.3 to 47.7 MPa). Also, the highest flextural strength (6.18 MPa) resulted in the lower W/C ratio (0.40). It is noteworthy that increases in W/C ratios for all mixes don’t lead to remarkable decreases in flextural strengths. Notably, the ultrasonic velocity (UV) for all mixes in the lower W/C ratio (0.40) shows a considerable increase particularly in 10% meta-halloysite compared with control samples. The findings above are all indications of better improvement of concrete strengths by natural pozzolan (meta-halloysite).