## 2 Description of Experimental Program  
### Materials and Mixture Design  
In this study, the Type I Ordinary Portland cement (OPC) was used to build the specimens. The chemical composition of the Type I OPC is shown in Table 1. C\({}_{3}\)S and C\({}_{2}\)S were the main components, and the weight percentages, _w/w_, of the C\({}_{3}\)S and C\({}_{2}\)S were 54.0% and 21.0%, respectively. In this study, three different pozzolanic materials were selected to investigate carbonation resistance of pozzolan blended concrete materials, as shown in Table 2. The chemical compositions used in this study were analyzed using X-ray fluorescence spectrometry (XRF); the results are also presented in Table 2, which shows that the silica fume and nanosilica were primarily composed of amorphous silica. The weight percentages of SiO\({}_{2}\) in the silica fume and nanosilica were 97.38% and 98.82%, respectively. For the fly ash, the weight percentage of SiO\({}_{2}\) was 61.18%, which is approximately 36-37% lower than that of the silica fume and nanosilica. The particle size of the pozzolanic material is the important parameter affecting the pozzolanic reaction. Thus, the particle sizes of the fly ash, silica fume, and nanosilica used in this study were analyzed. The mean particle sizes of the fly ash, silica fume, and nanosilica were 4, 0.9, and 0.2 um, respectively. The nanosilica mean particle size was the smallest among the pozzolanic materials used in this study, being 20 and 4.5 times smaller than fly ash and silica fume, respectively. \begin{table}
\begin{tabular}{c c} \hline
**Chemical Composition** & _w/w (\%)_ \\ \hline C\({}_{3}\)S & 54.0 \\ C\({}_{2}\)S & 21.0 \\ C\({}_{3}\)A & 11.0 \\ C\({}_{4}\)AF & 9.0 \\ \hline \end{tabular}
\end{table} 
Table 1: The chemical compositions of Type I Ordinary Portland cement (OPC). It is well known that carbonation rate is highly affected by the porosity of surface, permeability, the types and amount of cement and cementitious materials, and several mechanical properties of concrete. To investigate the effects of pozzolanic materials, the influence of mechanical properties has to be excluded at a given water-to-cemenentitious ratio by precisely adjusting the replacement ratio of cement by fly ash, silica fume, and nanosilica. Thus, in this study, the pozzolanic materials were used only to increase the carbonation resistance. Thus, the target compressive strength for all specimens was set uniformly as 50 MPa. For this, the concrete mixtures shown in Table 3 were prepared. The OPC was the reference specimen without any pozzolanic material. FA15 represents the specimen with 15 wt.% of the cement replaced with fly ash. SF35 and NS20 were the specimens with 3.5 wt.% and 2.0 wt.% of the cement replaced by silica fume and nanosilica, respectively. It should be noted that a liquid-state nanosilica with 50% liquid fraction was used in this study. Thus, 1 wt.% of nanosilica was included in the NS20 specimen. The water to binder ratio, W/B, was set as 0.362 for all specimens. The same amount of water-reducing chemical admixture was used in all specimens. The amount of sand and gravel used for each specimen is also presented in Table 3.  
For each mixture design, 60 cylindrical specimens (\(\mathcal{O}100\times 200\) mm) were prepared for evaluating the mechanical properties: 30, 18, and 12 specimens were used for the test of compressive strength, modulus of elasticity, and splitting tensile strength, respectively. In the case of the compressive strength, measured values from six specimens were averaged. For modulus of elasticity, and splitting tensile strength, at least four measured values were averaged. Three prism specimens (\(100\times 100\times 400\) mm\({}^{3}\)) for each mixture were casted to assess the carbonation resistance of pozzolan blended concretes.