Study On The Synergistic Effect And Mechanism Between Nano-SiO₂ And Concrete Admixture

Due to various reasons leading to the long-term deterioration of the concrete structure in the using environment, eventually which making concrete durability failure. The use of mineral admixtures not only can reduce the cost of production, improve the working performance of concrete, but also can improve the durability of concrete. Mineral admixtures?such as Fly Ash or Blast Furnace Slag? are generally larger in size and lower in activity, so that the early strength of concrete is low, while the nano SiO₂ has smaller size and higher activity, so it can improve the compactness of concrete on the micro scale. Therefore, it is very important to study nano SiO₂ and mineral admixtures synergistic effect to improve the durability and the service life of the concrete.The synergistic effect of nano SiO₂ and mineral admixture is studied, the influence of nano SiO₂ with mineral admixture synergistic effect on the cement based materials was discussed. By means of the compressive strength, hydration heat, pozzolanic activity, non-evaporation water content and pore structure analysis, this paper will elucidate the positive and negative effects of nano SiO₂ and mineral admixture, in order to make best use of the advantages and bypass the disadvantages and to make rational use of nano SiO₂ and mineral admixture.After a lot of experiments and research, the main conclusions are as follows:?1? Different dispersion methods have different influence on the mechanical properties and working properties. Through the analysis of laser particle size analysis and compressive strength can concluded that: When the ultrasonic power is 50 W, the combination of naphthalene series water reducing agent, the dispersion effect of nano SiO₂ is the best. At this time, the dosage of nano SiO₂ is 3%, the compressive strength of 28 d is 56.82 MPa, which is improved by 10.67%.?2?The mechanical properties of the cement mortar can be improved by the interaction of nano SiO₂ with slag or fly ash, especially the early strength. The compressive strength of the slag is increased with the increase of the fineness of slag after adding 3% nano SiO₂ in different fineness slag. With incorporation of 810m2/kg BFS and 3% NS, the highest compressive strength?62.94MPa? and highest percentage?19.17%? of strength increases of mortars were got than the corresponding reference slag mortars in the 28 d ages. In the same way, with incorporation of 540m2/kg FA and 3% NS, the highest compressive strength?51.53MPa? and highest percentage?8.89%? of strength increases of mortars were got than the corresponding reference slag mortars in the 28 d ages.?3? Through the analysis of the early hydration heat, pozzolanic activity and non-evaporation water content, nano SiO₂ will ahead the hydration accelerated period of cement, BFS and FA, increase the early hydration products of mineral admixture of the same age, improve the content of the early non evaporable water. Through the analysis of pozzolanic activity and non-evaporation water content, the effect of nano SiO₂ on mineral admixture dosage is larger than fineness. With the increase of the dosage of mineral admixtures, the increased amount of the hydration product by nano SiO₂ decreased gradually. Through the pozzolanic activity analysis, nano SiO₂ can induce the hydration of mineral admixtures and generate C-S-H gel in advance.?4? Through the analysis of microstructure, the total porosity of cement mortar can be reduced by the synergistic effect of nano SiO₂ with FA or BFS. With 30% BFS, porosity decreased from 21.15% to 20.51%, and with the addition of nano SiO₂, the porosity was reduced to 16.41%; With the incorporation of 30% fly ash and 3% nano SiO₂, the porosity was reduced to 18.51%. After adding 3% nano SiO₂, the less harmful hole is transformed into harmless pore, the pore size distribution is improved obviously, and the synergistic effect of the mineral admixture and nano SiO₂ on the scale is reached.