Abstract
Titanium dioxide (TiO2) is an excellent photocatalytic material that imparts biocidal, self-cleaning and smog-abating functionalities when added to cement-based materials. The presence of TiO2 influences the hydration process of cement and the development of its internal structure. In this article, the hydration process and development of a pore network of cement pastes containing different ratios of TiO2 were studied using two noninvasive techniques (ultrasonic and NMR). Ultrasonic results show that the addition of TiO2 enhances the mechanical properties of cement paste during early-age hydration, while an opposite behavior is observed at later hydration stages. Calorimetry and NMR spin–lattice relaxation time T1 results indicated an enhancement of the early hydration reaction. Two pore size distributions were identified to evolve separately from each other during hydration: small gel pores exhibiting short T1 values and large capillary pores with long T1 values. During early hydration times, TiO2 is shown to accelerate the formation of cement gel and reduce capillary porosity. At late hydration times, TiO2 appears to hamper hydration, presumably by hindering the transfer of water molecules to access unhydrated cement grains. The percolation thresholds were calculated from both NMR and ultrasonic data with a good agreement between both results.
Highlights
Titanium dioxide (TiO2 ) has been studied for potential applications, notably as a white pigment and in hydrolysis [1] and electricity production [2], as well as an additive in construction materials for its sterilizing, deodorizing and antifouling properties [3,4,5,6,7,8].TiO2 integrated into construction materials effectively decomposes or deactivates volatile organic compounds, removing bacteria and other harmful agents
Water is trapped inside capillary pores (3–50 nm) and microcracks of the hydrating cement pastes, with considerably higher relaxation times (~5–10 ms) [48,49], albeit lower compared to bulk water (~2 s)
Note that the w/c ratio is the same for all mixtures. These calorimetry data show that the peak heights were increased with the addition of the inert
Summary
Titanium dioxide (TiO2 ) has been studied for potential applications, notably as a white pigment and in hydrolysis [1] and electricity production [2], as well as an additive in construction materials (cement, concrete, tiles and windows) for its sterilizing, deodorizing and antifouling properties [3,4,5,6,7,8]. The most widely used technique to study the porosity and hydration of cement pastes is proton (1 H) NMR relaxometry [20,21,22,23] In this method, the molecular motion and chemical and physical environments of water molecules are probed continuously by measuring the 1 H nuclear-spin–lattice and spin–spin relaxation times of hydrogen nuclei. The effect of adding TiO2 in cement hydration and hardening, as well as the effect on the mechanical properties at late hydration times, are not fully clarified This is considerably important for the development of new construction materials that incorporate TiO2 for its sterilizing effects but less likely for its photocatalytic properties where a more practical approach would be the application of coatings to the exterior surface of the structures. These measurements monitor the dynamics of water molecules confined in cement pores and their interaction with the pore surface
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