# Pore Structure Degradation of Different Cement
## 4 Results and Discussion
### Mercury Intrusion Porosimetry
This could be indicative of the damage causedby this attack, which entails a progressive dissolution of Portlandite and decomposition of C-S-H phases [31], as well as the formation of expansive products [27; 32; 33], which can cause microcracking of the pore network of the material, reducing its refinement (increasing the proportion of higher pores) and making it more accessible to aggressive substances. In relation to the ethyl silicate specimens (as occurred with the control mortars), the volume of pores with diameters greater than 100 nm slightly altered between the samples exposed to the acid attack and those hardened in the optimal condition. Nevertheless, for specimens in which this solution was applied, pores with diameters lower than 100 nm showed an increase in volume in contact with the aggressive medium. The rise of total porosity obtained for the ethyl silicate mortars exposed to the attack could thus be due to that increase in volume of pores with sizes \(<\)100 nm. It can, therefore, be noted that the pore structure of samples with ethyl silicate became more refined after 90 days of exposure to the sulphuric acid attack, compared to those without, despite being more porous. The global increase in intrusion volume, and consequently in total porosity, for the ethyl silicate exposed to the sulphuric acid condition shows the harmful effects of the attack [2; 4]. In addition, the rise in volume of finer pores are also indicative of this attack, and represents a part of the pore network in which the attacksdevelops at the studied exposure age. As has been explained, ethyl silicate reacts with the material to which it is applied, producing pozzolanic solid phases [18]. In the initial steps of the sulphuric acid attack, these pozzolanic products react with the aggressive ions, leading to the formation of ettringite and gypsum [4; 5] which progressively fill the pores, reducing their sizes. This takes place in part of the microstructure of ethyl silicate samples, as suggested by the pore size distributions obtained (see Figure 2). In further stages of the attack, once all the pores are completely filled, and with a continuous formation of expansive products, it is expected that the degradation of the microstructure of the material is complete [34]. Their behaviourof the zinc stearate specimens with regards to pore size distributions is relatively similar to that observed for the control mortar samples, although with higher values of global intrusion volume and total porosity. The volume of pores with diameters higher than 100 nm wasfound to be very similar for the zinc stearate specimens exposed to the acid attack than for those that were not subject to the attack. On the contrary, for the samples exposed to the acid attack, a reduction in volume of pores lower than 100 nm was observed. Therefore, the acid attack produced a higher proportion of greater pores in the zinc stearate mortars, limitingthe refinement of their microstructure [2; 4]. Regarding mortars with nanosilica, minute changes were observed in pore size distribution, when the results obtained for specimens exposed to the optimal condition and the acid attack are compared. The main variations were a slight decrease in the volume of pores \(<\)10 nm and a small rise in the volume of pores with diameters in the range of 10-100 nm. In view of this result, it seems that the microstructural effects of the sulphuric acid attack were still emerging at the studied age for nanosilica mortars, particularly with regards to the accuracy and limitations of the mercury intrusion porosimetry technique used to study this type of attack [34; 35; 36]. Finally, if the different studied mortars exposed to the acid attack are compared, it is important to emphasise that those with ethyl silicate, zinc stearate, and nanosilica showed a more refined microstructure, with higher proportion of smaller pores (diameters lower than 100 nm) compared to the control mortars, despite their greater global intrusion volume and total porosity.