Exploring the Synergistic Effects of Microsilica, Nanosilica, and Multiwalled Carbon Nanotubes in Cementitious Composites Using the Random Forest Method

This study investigates the synergistic effects between microsilica (MS), nanosilica (NS), and carbon nanotubes (CNTs) in cement-based composites. Two water-to-binder (W/B) ratios, 0.42 and 0.50, were selected. Mortar samples were prepared with plain cement as a reference, along with mixtures containing MS, NS, or CNT individually, as well as their binary and ternary combinations. Uniaxial compressive and three-point bending tests at 7, 28, and 90 days, and sorptivity tests at 28 and 90 days were performed. Scanning electron microscopy images were taken to investigate the microstructural morphologies. In evaluating the synergistic effects of MS, NS, and CNT combinations on the specified properties, the importance ratios of the parameters on the results were determined using the random forest (RF) method. The highest compressive and flexural strength (CS and FS), as well as the lowest sorptivity, were obtained from the ternary mixtures at both W/B ratios. In ternary mixtures, the 28- and 90-day results at both W/B ratios showed a 15% increase in CS and a 40% increase in FS at 28 days for a W/B ratio of 0.42. Sorptivity, on the other hand, decreased by approximately 60% and 40%, respectively, in the mixtures with a W/B ratio of 0.50 and 0.42. The importance ratios of MS, NS, and CNT, as determined for CS and sorptivity results, significantly increased both in binary and ternary mixtures compared to their individual use, highlighting a strong synergistic effect. In the FS results, however, the importance ratios of all the considered parameters demonstrated a significant influence, whether used individually or combined.