Optimizing the content of nano-SiO2, nano-TiO2 and nano-CaCO3 in Portland cement paste by response surface methodology

Nano materials have become an important means of modifying cement-based materials. The excessive content of nano materials often causes some problems. Therefore, optimizing the content of nano materials in Portland cement paste appear to be particularly important. This paper mainly studies the effects of nano-SiO2 (NS), nano-TiO2 (NT) and nano-CaCO3 (NC) on the early hydration and mechanical properties of Portland cement at small dosages, and optimizes the dosage of the three nano materials by response surface methodology (RSM). The results show that the addition of nano materials can greatly promote the hydration and improve the early compressive strength of Portland cement. When the addition amount is small, the three nano materials have the best effect when added together. Compared with the blank sample, the compressive strength of 1 day, 3 days and 7 days are increased by 52.54%, 53.76% and 61.09%, respectively. In addition, adding NT, NC and NS together to Portland cement can produce more hydration products, increase the rate of hydration, optimize pore structure and reduce the total porosity from 23.2% to 16.8%. Moreover, with three nano materials adding together, the response surface can predict that when the content of NS, NT and NC are 0.86 wt%, 2.75 wt% and 0.14 wt%, respectively, it will have the best hydration promotion effect of Portland cement and it's compressive strength can reach 83 MPa at 7 days.