Keywords

Fly ash, TiO2 nanoparticles, TGA, Hydration, Isothermal calorimetry, Strength

Abstract

Incorporation of fly ash in cementitious systems containing ordinary portland cement (OPC) increases their long-term strength and durability. However, replacement of cement by fly ash also reduces the heat of hydration of such systems and reduces early-age strength development. The reduced rate of strength development can increase the risk of durability problems, e.g. scaling, in cases when young concrete is exposed to low temperatures and deicing chemicals. This study investigated the potential of nano-titanium dioxide (nano-TiO2) particles to modify the hydration kinetics of fly ash pastes and compressive strength development of corresponding mortars cured under low (4°C) and standard (23°C) temperatures. The kinetics of the hydration study was performed on paste specimens using the thermogravimetric analysis (TGA) and isothermal calorimetry (IC) methods. The mortar specimens used for compressive strength testing were prepared using the same w/cm values and the same types of binders as those used to prepare the paste specimens. It was found that although the addition of nano-TiO2 accelerated the hydration rate of all pastes, that treatment was, however, more effective in the fly ash pastes than in the ordinary portland cement (OPC) pastes, especially for the cases of low temperature curing. These findings were confirmed by the results of strength testing as the specimens experiencing accelerated rates of hydration were also found to be stronger.

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The Effects of Curing Temperature on the Hydration Kinetics of Plain and Fly Ash Pastes and Compressive Strength of Corresponding Mortars with and without nano-TiO2 Addition.

Incorporation of fly ash in cementitious systems containing ordinary portland cement (OPC) increases their long-term strength and durability. However, replacement of cement by fly ash also reduces the heat of hydration of such systems and reduces early-age strength development. The reduced rate of strength development can increase the risk of durability problems, e.g. scaling, in cases when young concrete is exposed to low temperatures and deicing chemicals. This study investigated the potential of nano-titanium dioxide (nano-TiO2) particles to modify the hydration kinetics of fly ash pastes and compressive strength development of corresponding mortars cured under low (4°C) and standard (23°C) temperatures. The kinetics of the hydration study was performed on paste specimens using the thermogravimetric analysis (TGA) and isothermal calorimetry (IC) methods. The mortar specimens used for compressive strength testing were prepared using the same w/cm values and the same types of binders as those used to prepare the paste specimens. It was found that although the addition of nano-TiO2 accelerated the hydration rate of all pastes, that treatment was, however, more effective in the fly ash pastes than in the ordinary portland cement (OPC) pastes, especially for the cases of low temperature curing. These findings were confirmed by the results of strength testing as the specimens experiencing accelerated rates of hydration were also found to be stronger.