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Abstract: |
The manufacturing of cement is blamed to contribute between 5 and 7% of total CO2 emission into atmosphere worldwide. The building materials sector is the third largest CO2 emitting industry in the world. Countries across the globe under the umbrella of intergovernmental panel on climate change (IPCC) have recently come to a consensus on reducing the greenhouse gases and in particular CO2 emission. Therefore, it is utmost important for construction industry to reduce the consumption of cement in concrete and cement based construction materials. On the other hand, to meet the power demands, coal-burning power stations worldwide have been producing colossal quantities of fly ash as a by-product. Most of them are sent for land filling which cause air and underground water pollutions. The presence of high silica and alumina contents make it a suitable pozzolanic material for concrete, which contributes to the improvement of properties of concrete. This paper presents experimental results on chloride induced corrosion and related durability properties such as chloride permeability, water sorptivity, chloride diffusion and porosity of ordinary concrete and high volume fly ash (HVFA) concretes containing nano silica (NS) and nano calcium carbonate (NC) particles as partial replacement of cement. The NS and NC are used as 2% and 1%, respectively by wt. of cement in the above concretes. Results show that the addition of NS and NC significantly improved the corrosion resistance of ordinary concrete and HVFA concretes in terms of lower corrosion currents, lower steel loss and longer time require creating corrosion induced crack. Sorptivity, chloride diffusivity and chloride permeability of above concretes also reduced significantly due to the addition of NS and NC, which correlate well with the corrosion tests. The addition of NS and NC also significantly reduced the capillary pores and gel pores of above concretes and also shifted the pore concentration towards the medium capillary pores. Thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) analysis of above concretes also confirms the reduction of calcium hydroxide (CH) in the concretes containing nano particles, thus the formation of additional calcium-silicate-hydrate (CSH) gel in the system.
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