Cement-based materials, is still the most consumed building materials in the world. Cement production is currently responsible for about 8% of the global CO2 emission. Low carbon is a major challenge for cementitious materials. From the perspective of technology, the rational utilization of supplementary cementitious materials and the improvement of durability, is two key methodologies to alleviate the low carbon problem which cementitious materials confront in the process of development.
Nanotechnology has shocked every corner of scientific research, of course, cement and concrete research area is no exception. Many kinds of nanoparticles have been used to modify cementitious, such as nano-silica, nano-alumia, graphene oxide, and so on. The collision between tradition and modernity motivate the new vitality of cement-based materials. For nanomaterials, they have superior performances, however, compared with cement, high price limits their extensive application in the industry. Therefore, the cross region between research value and application value seem more closed to reality. Nano-silica (NS), as one of most widely used nanomaterials as well as the lowest price, in cement and concrete area, combined the low-carbon problem background, its cross region focuses in two main directions: the first one is to utilize the early acceleration effect of NS to compensate the retardation effect of supplementary cementitious materials as kind of additive. The second one is to utilize NS as kind of surface-coated agents, to densify the surface areas of harden cementitious matrix resulting in the improvement of durability. The effect of NS is strongly dependent on its dispersion in the cementitious matrix, however, the effective dispersion of NS remains a big challenge.
Based on the background discussed above, to promote the dispersibility of NS and apply NS in a reasonable way, this paper carry out a series of studies from four main aspects: Firstly, to address the issue of the dispersion of NS, we synthesize a series of NS@PCE core-shell nano-particles, secondly, for enhancing the early acceleration effect, the relationship between the molecular structures of a series of NS@PCE and acceleration effect was studied. thirdly, for the surface-treatment application of NS, we studied the effects and mechanism of surface-treatment of cementitious with NS@PCE, which, fourthly, to enrich the mechanism of reducing water absorption performance, we adopted the molecular dynamics simulation, to study the interaction between water and C-S-H or C-S-H-PCE from the view of interface energy.
The main innovations of this paper are as follows:
(1) A conception, improving the dispersion of NS by core-shell structure, is first proposed in this area. A series of nano-silica-polycarboxylate acid copolymer core-shell nanoparticles have been synthesized by“grafting to”method. The feasibility that the formation of core-shell structure→dispersion enhanced→acceleration effect promoted, is verified.
(2) The influence of NS@PCE on the early hydration performance is studied. The relationship between the molecular structures of a series of NS@PCE and acceleration effect is elucidated by series of experimental methods, especially isothermal calorimetry.
(3) The application of NS@PCE as a kind of surface-treatment agent is explored. Combined the dispersion properties and pozzolanic reactivity of NS@PCE, a hypothesis is proposed to reveal the mechanism of surface-treatment process of nanoparticles.
(4) The interaction between water and C-S-H is studied by the molecular dynamics simulation method. In nanoscale, we uncover interaction mechanism between C-S-H with different calcium-silicon ratio or PCE modified C-S-H and water. From the perspective of interface, we revel the hydrophilic or hydrophobic of different interfaces, which enrich the surface-treatment mechanism of nanoparticles.
The research of this paper has the following enlightenment meaning for nano-modifying cement based materials research: firstly, the dispersion of nanoparticles can be improved by constructing the core-shell structure not limited to nano-silica, and PCE is the most potential polymer for shell structure. Secondly, the surface property of the nanomaterials plays a decisive role in their performance. we should put an end to “simple take” when nanoparticles used in this area, adjusting the surface properties of nanoparticles to make nanoparticles adapt to the cement system, is a smart way to magnify the value of nano. Thirdly, nanoparticles utilized as a kind of surface-treatment agent is a burgeoning research direction, should be and will be the prior development direction