The Effects of TiO2 in the Performance of Mortar

Titanium dioxide (TiO2) is a material that contains photocatalysic which acts as self-cleansing agents on a material surface. In the application of TiO2 in the civil engineering construction, it can be mixed with the fresh mortar known as TiO2 mortar. Hence, a study on the characteristic strength of the TiO2 mortar needs to be carried out. Moreover, the optimum dosage levels of the TiO2 in the mortar can be determined. The characteristics of the TiO2 were identified based on the compressive strength and flexural strength at 3, 7, 21 and 28 days. A total of five sets of specimens with different dosage levels were prepared and compared with the control specimen.


Introduction
Titanium Dioxide (TiO 2 ) has received considerable attention in recent years as coating for concrete pavement [1,2]. The photocatalytic process of TiO 2 can be used as trap agent to absorb organic and inorganic air. It gives a promising benefit such as reduce the environmental impacts such as acidification, eutrophication, criteria air pollutants and smog formation. It is also practical for self-cleaning [3] and air-purifying concrete pavement [4]. For other material, the effect of TiO 2 on properties of polyethylene nano composites [5], self-cleaning glass [6] and as coating on residential window glass [7] have also been investigated. Effectiveness of TiO 2 in the perspective of environmental friendly building materials such as in the aspect of coating, cement, concrete, wallpaper, glass, porcelain and PVC profile has been investigated by Chen and Xu [8]. They found that, TiO 2 has excellent performance in improving human environment and facilitate the effectiveness of human health to achieve environmental protection. It also has great benefit in improving air quality inside a building [9]. A study on TiO 2 photocatalytic concrete for air purification with different percentage by weight with respect to the binder has been conducted by Husken et al. [10]. The effects of TiO 2 nanoparticles on flexural damage of self-compacting concrete (SCC) have been studied by Nazari and Riahi [11]. In their study, the TiO 2 nanoparticles has been replaced in concrete instead of cement with 4 % weight of SCC and it was found that the replacement of more than 4 % weight of SCC reduced the flexural strength of the SCC. In the production of building materials, the TiO 2 functions as an additive that significantly reduces the consumption of resources such as traditional energy. It is because TiO 2 particles crystallize in three forms, anatase, rutile, and brookite [12]. Anatase is a meta-stable that transforms into rutile at high temperature [13] and has photocatalyst semiconductor in environmental purification [14]. Since the TiO 2 contains an agent which acts as self-cleansing due to photocataclysic composition, it is useful in civil engineering construction. It can be used as a self-cleaning material in order to maintain the surface condition of the structure especially on reinforced concrete structure which is highly exposed to aggressive environment. The application of TiO 2 in such structure can be implemented by a generic study of its performance such as inclusion of TiO 2 in the mortar and concrete. However, the reviews on the inclusion of TiO 2 in both materials are still limited. In this paper, only the mixture of TiO 2 and fresh mortar at various dosage levels is presented. In the present study, only the compressive strength and the flexural strength were identified at 3, 7, 21 and 28 days of harden TiO 2 mortar specimens. The results were then compared with the control specimen and the strength effectiveness of the TiO 2 mortar specimens was identified.

Experimental Programme
The physical properties of the TiO 2 are solid state (powder), slightly odour and white colour. The chemical properties of the TiO 2 are density of 4.05 g/cm 3 and 1800 0 c melting point. In the preparation of the TiO 2 mortar, the mortar was designed for different proportions by weight of water: cement: fine aggregate and it was 0.5: 1: 3, respectively. Then, 5 % of silica fume based on cement weight was added to the mortar mix to improve the workability of the mortar. Table 1 shows the dosage levels of the TiO 2 used in the mortar mix. For control specimen, no TiO 2 and silica fume were added to the mortar mix. Two sizes of TiO 2 mortar were prepared, 100 mm x 100 mm x 100 mm cubes and 40 mm x 40 mm x 160 mm prisms for compressive strength and flexural strength, respectively. A total of 72 cubes size 100 mm x 100 mm x 100 mm were prepared for the compressive strength at 3, 7, 21 and 28 days. Meanwhile, for flexural strength test, a total of 72 prisms with the size of 40 mm x 40 mm x 160 mm were tested at the age of 3, 7, 21 and 28 days. The fresh mix of the control specimen and TiO 2 mortar is presented in Fig. 1. For each dosage level and age of test for both tests, three cubes were prepared. Then, the results were averaged.  Fig. 2a, it is also a) b)

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found that the compressive strength of TiO 2 mortar is lesser than control specimen. The inclusion of TiO 2 in mortar increased the porosity of the mortar and hence reduces the strength of the mortar. In overall, it indicates that the inclusion of TiO 2 did not increase the compressive strength of the mortar especially at the optimum age of 28 days. However, the compressive strength of TiO 2 mortar for specimen TDM 2 at the age of 21 days increases more than the control specimen. The compressive strength effectiveness of the TiO 2 mortar is presented in Fig. 2b. It indicates that the TDM 2 which contains the inclusion of 0.30 % TiO 2 produced more strength effectiveness than the other specimens which have different inclusion of TiO 2 dosage levels at early age of 3 to 21 days. However, the strength effectiveness reduced to 3.3 N/mm 2 when it reached 28 days. It indicates that the optimum inclusion of TiO 2 in mortar is 0.30 %. If higher percentage of TiO2 is used, it reduced the strength of its combination. The compressive strength effectiveness can be used to determine the difference in the strength between the control specimen and the mortar with the inclusion of TiO 2 . From the Fig. 2b, the TDM 5 has lower compressive strength effectiveness compared to other specimens. In overall, the compressive strength effectiveness of TiO 2 mortar increases when it reaches the age of 21 days. However, it reduces when reaches to optimum age of 28 days. Although the TiO 2 seemingly did not increase the performance of the mortar in terms of its compressive strength, at the age 21 days, the inclusion of TiO 2 at low dosage level such as 0.28 % and 0.30 % TiO 2 in the mortar is found to increase when compared to the control specimen. This depicts that it is still practical to be used if the inclusion of other material in the composition of the mortar can be made. At the same time, the TiO 2 role as self-cleaning agent in the composition can still be maintained. It can be depicted in Fig. 3 that the surface of the TiO 2 mortar cube is brighter or cleaner than the control cube. Hence, the inclusion of TiO 2 in the mortar composition can be used as decorative materials. Applied Mechanics and Materials Vols. 773-774 increased to 7.40 N/mm 2 when reached the optimum age of 28 days. It indicates that the harden TiO 2 mortar prism specimen when subjected to three point loading increases the flexural strength as the age of the specimen increases. However, the inclusion of the TiO 2 in the mortar mix is found to reduce the flexural strength as the dosage level of the TiO 2 increases. It can be depicted that in Fig.  4a where at optimum age of 28 days, the flexural strength of TDM 1 (0.28 % TiO 2 ), TDM 2 (0.30 % TiO 2 ), TDM 3 (0.32 % TiO 2 ), TDM 4 (0.34 % TiO 2 ) and TDM 5 (0.36 % TiO 2 ) were 7.40 N/mm 2 , 6.94 N/mm 2 , 5.90 N/mm 2 , 5.16 N/mm 2 and 4.18 N/mm 2 , respectively. It seemingly indicates that the higher the inclusion of TiO 2 in the mortar mix did not improve the performance of the flexural strength. The flexural strength effectiveness of the TiO 2 mortar at various dosage levels is depicted in Fig. 4b. It indicates that the inclusion of 0.28 % TiO 2 and 0.30 % TiO 2 designated as TDM 1 and TDM 2 have better strength effectiveness than the other prisms that has other inclusion of TiO 2 . It can be seen especially at the optimum age of the prisms. In overall, the flexural strength effectiveness of TiO 2 is lesser than the compressive strength effectiveness as discussed in preceding section. However, it is confirmed that 0.3 % of TiO 2 is the optimum dosage level can be used to improve the strength of the mortar.  5 shows the failure of the prism specimens when subjected to monotonic load where the specimens fail almost halves for control specimen and TiO 2 mortar specimen. From the observation of the appearance of the surface of the specimens, it is found that the specimens of TiO 2 mortar are brighter than control prisms. It is due to the composition of photocataclysic in the TiO 2 which affect to the surface of the specimen. Although the flexural strength of the TiO 2 mortar is lesser than control specimen, this study is useful. It is because the review on the application of TiO 2 in the civil engineering construction is still limited. Hence, this study can be used as a milestone or reference to other researchers who are interested in the application of TiO 2 in the mortar.

Conclusion
In overall, the comparison between TiO 2 mortar specimen and control specimen indicates that the strength of control specimen is higher than TiO 2 mortar. Hence, the inclusion of TiO 2 did not a) b) a) b)

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increase the performance of mortar such as compressive strength and flexural strength. Although the strength of the TiO 2 is lesser than control specimen, this study is vital as the inclusion of TiO 2 in the mortar can be used for the structure appearance where it gains brighter feature of the structure's surface. It can be concluded that the optimum dosage level that can be used to improve the strength of the mortar is 0.3 % of TiO 2 . For future research, the TiO 2 mortar will be applied in the reinforced concrete structure to investigate the performance of the surface that relates to the self-cleaning structure.