Abstract
Surface protection has been accepted as an effective way to improve the durability of concrete. In this study, nanosilica (NS) was used to improve the impermeability of cement-fly ash system and this kind of material was expected to be applied as surface protection material (SPM) for concrete. Binders composed of 70% cement and 30% fly ash (FA) were designed and nanosilica (NS, 0–4% of the binder) was added. Pore structure of the paste samples was evaluated by MIP and the fractal dimension of the pore structure was also discussed. Hydrates were investigated by XRD, SEM, and TG; the microstructure of hydrates was analyzed with SEM-EDS. The results showed that in the C-FA-NS system, NS accelerated the whole hydration of the cement-FA system. Cement hydration was accelerated by adding NS, and probably, the pozzolanic reaction of FA was slightly hastened because NS not only consumed calcium hydroxide by the pozzolanic reaction to induce the cement hydration but also acted as nucleation seed to induce the formation of C-S-H gel. NS obviously refined the pore structure, increased the complexity of the pore structure, and improved the microstructure, thereby significantly improving the impermeability of the cement-FA system. This kind of materials would be expected to be used as SPM; the interface performance between SPM and matrix, such as shrinkage and bond strength, and how to cast it onto the surface of matrix should be carefully considered.
Highlights
Concrete has been widely employed in civil constructions in the past decades, and the main reason is due to its excellent performance, especially long life serving [1, 2]
Reinforced-concrete structures inevitably suffer from damages in harsh environment, such as in the presence of chloride ions, carbon dioxide, and sulphate, resulting in shortening its life [3,4,5,6]. e generally accepted reason for those is that concrete is a porous material with microstructural defect, and the harmful ions could penetrate the surface into the inside of concrete structure and cause corrosion, leading to crack [7, 8]
Sulphate was able to penetrate the surface into the inside and react with hydrates to produce ettringite or gypsum, associating with a volume expansion. e mechanical performance could be deteriorated, and under load, the cracks occurred; thereafter, sulphate ions were easier to go into the inside of concrete structure along the cracks and the more serious corrosion would happen [9,10,11]
Summary
Concrete has been widely employed in civil constructions in the past decades, and the main reason is due to its excellent performance, especially long life serving [1, 2]. Advances in Civil Engineering behind the enhanced impermeability was that the chemicals could go through the capillary and form an inorganic hydrophobic film along the capillary as a result of reacting with hydration products; the other was that these hydrates in the capillary structure would block the transportation of water and gas [21]. Another kind of SPM was coated as a layer on the surface of the matrix. Hydrates were evaluated with XRD, TG-DSC, NMR, and SEM. e findings would expect to be useful for the design of surface protection materials
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