# Pore Structure Degradation of Different Cement
## 4 Results and Discussion
### Mercury Intrusion Porosimetry
The results of mercury (Hg) retained after the end of the porosimetry test at 90 days of exposure to the optimal (\"no attack\") and sulphuric acid aggressive (\"attack\") conditions are compiled in Table 4. This parameter provides qualitative information on the evolution of the microstructure [37; 38]--its tortuosity and the progressive closure of pores. For the mortars and conditions studied in this research, the values of Hg retained had a similar order of magnitude. For the control mortars, this parameter was higher for those subjected to the sulphuric acid attack, compared to those exposed to the optimal condition. This result could be related to the damage caused in the pore network by the acid attack. As has been explained before, degradation of the microstructure due to this attack [4; 29; 39] results in the formation of microcracks. This microcracking phenomenon modifies the internal surface of the pores, increasing this surface [40] and consequently the tortuosity of the pore network. This result is in line with the loss of microstructure refinement observed in the control mortars with the attack (discussed earlier). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Control**} & \multicolumn{2}{c}{**Ethyl Silicate**} & \multicolumn{2}{c}{**Zinc Stearate**} & \multicolumn{2}{c}{**Nanosilica**} \\ \hline  & **No Attack** & **Attack** & **No Attack** & **Attack** & **No Attack** & **Attack** & **No Attack** & **Attack** \\ \hline \(<\)10 nm & 0.0002 & 0.0019 & 0.0011 & 0.0024 & 0.0028 & 0.0033 & 0.0019 & 0.0008 \\
10–100 nm & 0.0141 & 0.0083 & 0.0138 & 0.0206 & 0.0273 & 0.0176 & 0.0091 & 0.0113 \\
100 nm–1 \(\upmu\)m & 0.0243 & 0.0211 & 0.0259 & 0.0266 & 0.0253 & 0.0235 & 0.0262 & 0.0253 \\
10–100 \(\upmu\)m & 0.0024 & 0.0021 & 0.0011 & 0.0004 & 0.0032 & 0.0021 & 0.0009 & 0.0016 \\
10 \(\upmu\)m–0.1 mm & 0.0015 & 0.0024 & 0.0009 & 0.0014 & 0.0009 & 0.0008 & 0.0012 & 0.0021 \\ \(>\)0.1 mm & 0.0008 & 0.0004 & 0.0013 & 0.0003 & 0.0010 & 0.0006 & 0.0009 & 0.0010 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Volume (mL/g) of each pore interval for the studied samples. Figure 2: Pore size distribution of the studied mortars at 90-day exposure. The samples referred to as “no attack” are those that were hardened in a non-aggressive environment and the specimens labelled as “attack” are those that were exposed to sulphuric acid. For the ethyl silicate mortars, a reduction in the retained Hg was noted when subjected to the acid attack, as compared those exposed to the optimal condition. An increase in pore refinement of this type of mortar, subjected to attack by the acid, was observed, with a high percentage of finer pores. This is in agreement with the decrease of Hg reduction under the same conditions and can be explained in relation to the silting of the pores by the formation of ettringite and gypsum, whichare produced by a reaction of the pozzolanic products (caused by the sprayed ethyl silicate) with the aggressive ions [4; 5]. This process closes the microstructure, reducing its tortuosity, at least until they are filled (when the microcracking phenomenon is predominant). In relation to zinc stearate mortars, the Hg retained was found to be slightly higher for samples exposed to the acid attack than for those in contact with the non-aggressive environment. This result is in line with the lower microstructure refinement shown by zinc stearate mortars subject to the acid attack. As was with control mortars, this could be due to the formation of microcracks [29; 41; 42], which increase the pore surface [40], resulting in a higher tortuosity of the microstructure. Regarding the nanosilica mortars, those exposed to the acid attack showed slightly lower retained Hg, compared to those stored in conditions that do not have aggressive substances. This result is in line with the total porosity and pore size distribution obtained for these additions. This lower value is indicative of a possible process of pore silting, which could reduce tortuositydue to closure of the microstructure.