Effect of the addition of nanoparticles of CaCO3 and different water-to-powder ratios on the physicochemical properties of white Portland cement.

The addition of calcium carbonate nanoparticles (nano-CaCO3 ) accelerates the hydration of Portland cement improving its mechanical properties. Conversely, nano-CaCO3 addition leads to reduction in the water required during initial PC hydration. Therefore, the use of a correct water-to-powder ratio is fundamental for manipulating this hydraulic cement. This study evaluated the effect of nano-CaCO3 addition and different water-to-powder ratios on the physicochemical properties of white Portland cement (WPC). WPC was associated to different concentrations of nano-CaCO3 , and the following experimental groups were created: G1a (no nano-CaCO3 ); G2a (0.5% nano-CaCO3 ), G3a (1% nano-CaCO3 ), G4a (2% nano-CaCO3 ), and G5a (5% nano-CaCO3 ). The setting-time (ST), compressive strength (CS), dimensional change (DC), solubility (S), and pH were assessed (24 hr and 30 days). Next, WPC + 5% nano-CaCO3 was manipulated varying the water-to-powder ratio: G1b (WPC/0.33 ml); G2b (WPC/nano-CaCO3 /0.33 ml); G3b (WPC/0.29 ml); G4b (WPC/nano-CaCO3 /0.29 ml); G5b (WPC/0.26 ml); and G6b (WPC/nano-CaCO3 /0.26 ml). The tests were repeated. The data analysis (2-way ANOVA and Tukey test, α = 5%) demonstrated that ST was shorter for samples containing nano-CaCO3 (p < .05). Reduction in CS was observed for all groups at 30 days, except G5a, G2b, and G6b (p < .05). DC and S had no statistical difference among groups (p > .05) independently of nano-CaCO3 water-to-powder ratio. After 30 days, there was significant reduction in pH for G3a and G6b (p < .05). The different concentrations of nano-CaCO3 and water-to-powder ratios affected the physicochemical properties of WPC, especially the setting-time and compressive strength.