**6. Conclusions**

usually depends upon the composition of the host cement-based composite. On the other

strate. However, much more insight is needed from engineering design and modeling point of view, for successful application of the laboratory-scale techniques to large-scale operation. Questionless, there exist some beneficial effects on the environment derived from inclusion of TiO<sup>2</sup> nanoparticles to cement production. But on its own, cement is a highly efficient material in terms of energy consumption and welfare that generates; therefore we should aim to respect

to the cement to develop a sufficiently efficient photocatalytic activity. Many works reported in literature ensure that the minimum fraction of nanoparticles to be added to cement in order to obtain a minimum photocatalytic activity must exceed 1% by mass of cement [16]. In fact, the photocatalytic properties begin to be significant from the eco-efficient point of view when the percentage of nanoparticles included in cement is close to 3%. This percentage not only provides photocatalytic activity to the material, but also favors the development of hydration products, leading to improvements of up to 62% in mechanical properties for long ages [17].

physical methods, such as sol-gel, using different precursors based on titanium oxides, such as titanium tetrabutoxide and titanium tetraisopropoxide (TTIP). These methods have proven to be suitable for the formation of spherical nanoparticles with controlled particle size. In addition, the so obtained nanostructured material features high specific area, which is an

At the end of the synthesis procedure, the nanoparticles can be kept in liquid medium or be subjected to a calcination process in order to increase their crystallinity and achieve a particulate system. Regardless, the most appropriate way to include the nanostructured TiO<sup>2</sup>

cement matrix is found to be adding it directly to the hydration water. Thus, the nanoparticles will directly occupy the capillary pores that remain as the water is consumed due to the formation of products. In addition, the aqueous environment around the nanoparticles is guaranteed.

Another key factor when preparing photocatalytic cement with adequate structural characteristics is the correct choice of manufacturing parameters for the cement mixture. Many researchers have used white cement to prepare their photocatalytic mixtures. The choice of white cement basically supports esthetic reasons, since from its preparation, it already seems a "clean" material and therefore more conducive to integration in a pollutant-free environment. In any case, other types of cement are also valid to form the cementitious matrix in which the nanoparticles are going to be housed. The requirement is so that the matrix must be properly hydrated and provide an adequate porous structure. In this sense, the water-cement

its identity in attempting to develop a more sustainable material.

essential requirement to obtain adequate rates of photocatalysis.

**5.2. Suitable fabrication parameters of the cementitious matrix**

**5.1. Optimal content and inclusion method of nano-TiO<sup>2</sup>**

Initially, we focused on the optimum weight fraction of TiO<sup>2</sup>

Regarding the preparation method, the TiO<sup>2</sup>

ratio plays an extremely important factor.

photocatalyst can be used either as freestanding particulate or as coating on a sub-

 **in cement**

nanoparticles can be synthesized by chemical-

nanoparticles that should be added

in the

hand, TiO<sup>2</sup>

58 Cement Based Materials

This chapter concludes that the singularities and the qualities of the hydrated cement microstructure enhance the photocatalytic processes, driven by titanium dioxide, to create environment-friendly cement. We have exposed the microstructural characteristics of cement and those aspects that make possible the promotion of photocatalytic activity. The cement porosity and the nanostructure of the C-S-H have been identified as surface modificators of nano-TiO<sup>2</sup> providing charge reservoir sites which promote the interfacial charge transfer mechanism. Cement microstructure can therefore effectively mediate in TiO<sup>2</sup> photocatalytic performance. Suggested directions have been provided for the preparation of photocatalytic mixtures, taking into account both the suitable content of nano-TiO<sup>2</sup> as well as the formulation of the cementitious material, according to the most recent trends reported. This framework is also a starting point for future studies that seek to improve the photocatalytic response of titanium dioxide inserted in the cement matrix as well as to provide implications for the application of photocatalytic cement technology in the construction materials industry.
