# Evaluation of the Performance of Previous Concrete Inspired by CO\({}_{2}\)-Curing Technology
## 3 Results and Discussion
### Concrete Degradation  
Figure 9 shows the weight and strength losses in the concrete samples at the end of acid storage. The average weight loss (and strength loss) in these samples was calculated to be 28% and 25% (and 53% and 47%) at the end of acid storage, respectively. These findings show the beneficial effect of carbonation on the resistance to calcium leaching of the pervious concrete matrix in aggressive chemicals. An acid attack on traditional concrete usually results in the dissolution of cement components, but the degradation of the aggregate depends on its mineralogy [57]. Hydroxyl ions contained in cement hydrates are neutralized by acid species (i.e., protons). Aluminum, iron, sulfur, and mainly calcium ions enter the pore solution and diffuse to the concrete surface. A highly porous degraded layer is formed consisting of hydrated silicates, and the rate of development of this layer is determined by the diffusion of acid species through the degraded layer to the reaction front and the acid reaction rate with the unaltered core concrete [58]. In this study, the CT image in Figure 9 reveals a significant removal of the cement binder from the porous concrete matrix due to the acid attack. A degraded layer surrounding the unaltered core concrete was not observed, but the presence of granite-derived crushed aggregates and their distribution were clearly seen as a result of the acid attack. A similar observation was observed in non-carbonated and carbonated samples. Although the ingredients are the same in the pervious concrete and traditional concrete, the physical characterization of degradation due to the acid attack was still different due to the formation of an interconnected pore structure.  
Figure 10 illustrates the SEM and XRD results that reveal the acid-degraded microstructure of the concrete samples. The CSH structure was completely decalcified, and only silica gel was left as a result of the exposure of the non-carbonated and carbonated samples to acid. The XRD result confirms the presence of porous silica gel in both the non-carbonated and carbonated samples. [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] [5] found a reduction in the compressive strength of cement paste samples caused by calcium leaching when the samples were carbonated for up to 16 h. These results were found to be contrasting when the carbonation period was prolonged. Limiting early carbonation exposure in cement paste samples can improve calcium leaching resistance by densifying the microstructure and producing stable  
Figure 9: Weight and strength losses in pervious concrete samples due to acid attack.  
CaCO\({}_{3}\)/silica gel. Severe CSH decalcification occurs in acid-exposed samples carbonated for a longer duration [5]. Two main factors that influence the long-term durability of pervious concrete mixes are porosity and compressive strength. [PERSON] et al. [59] found a strong correlation between porosity and the parameters that control long-term durability, and their findings report that lower porosity pervious concrete provided better resistance to extreme environments. [PERSON] et al. [60] found a reduction in the bond strength between aggregate particles due to cement degradation in pervious concrete samples exposed to aggressive aqueous species.