Abstract
Abstract Filling and nucleation are the mechanisms of modifying cement paste with nanomaterials, as investigated by previous studies, and are difficult to reflect the different effects of nanomaterials, especially on the changes of cement clinker and hydration products in the cement hydration process. In this study, the mechanisms of modifying cement paste with nano-calcium carbonate (NC), nano-graphene oxide (NG), nano-silica (NS), and nano-titanium dioxide (NT) were investigated by determining the mechanical properties of cement paste treated with nanomaterials and analysing the changes in the cement clinker (tricalcium silicate and dicalcium silicate), hydration products (portlandite and ettringite), and microstructure through many micro-test methods. The results indicate that the incorporation of nanomaterials could improve the early strength of cement paste specimens due to more consumption of cement clinker. Meanwhile, different nanomaterials promote the formation of different hydration products at early ages. C–A–S–H gel, flower-like ettringite, and C–S–H seeds are widely distributed in the cement paste with the incorporation of NC, NG, and NS, respectively. NT exhibits insignificant nucleation effect and has inhibitory effect on portlandite precipitation. This study provides key insights into the mechanism of nanomaterials from the perspective of cement hydration, which may promote the further research and application of nanomaterials in the cement and concrete industries.
Highlights
When the particle size of a material is reduced to the range of 1–100 nm, the resulting nanoparticles exhibit novel physical and chemical properties
The results indicate that the incorporation of NS, nano-calcium carbonate (NC), and nano-graphene oxide (NG) could improve the early compressive strength of the cement paste specimens at 1, 3, and 7 days
Excessive incorporation of nano-titanium dioxide (NT) will cause its uneven distribution in the cement paste, enrichment, or agglomeration in some areas, which will cause the decrease of mechanical properties
Summary
When the particle size of a material is reduced to the range of 1–100 nm, the resulting nanoparticles exhibit novel physical and chemical properties. The differences in the structure of the nanomaterials relative to that of the macromaterial are that the former have a large specific surface area, and the state of their surface atoms is closer to the gaseous state, forming neither long-range nor short-range amorphous layers, while the atoms inside the nanoparticles may be in an orderly arrangement. In the last few years, an increasing number of scientists have devoted themselves to studying nanomaterials, including the application of nanomaterials to cementbased material reinforcement, and have achieved fruitful results in the preparation, property modification, and application of nanomaterials [3]. It has been proven that NS can effectively improve the workability, strength, and durability of cement-based materials, and the reinforcing effect of NS
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