# Sulfuric Acid Resistance of CNT-Cementitious Composites
## 2 Experimental Programs
### Experimental Methods  
The compressive and flexural strengths were measured. To identify resistance to sulfuric acid, the specimens were immersed in 5% or 10% sulfuric acid solution ([PERSON] et al., 2006 [55]; [PERSON] et al., 2010 [56]; [PERSON] et al., 2018 [57]), and the weight change ratio, compressive strength change ratio, and electrical resistance change rate were observed. In addition, the porosity before and after the damage for 28 days caused by the sulfuric acid solution and its characteristics were analyzed based on MIP and SEM images. To evaluate the chemical resistance of CNT cement mortar, three cylindrical specimens per test with a diameter of 100 mm and a height of 200 mm were made and stored for 24 h at a temperature of 20 \(\pm\) 1 \({}^{\circ}\)C with humidity of 60 \(\pm\) 1% and demolded in accordance with KS L ISO 679 [54]. Then, the specimens were cured in a water tank at 20 \(\pm\) 1 \({}^{\circ}\)C for 28 days, dried for 24 h at a temperature of 80 \(\pm\) 1 \({}^{\circ}\)C, and then immersed in 5% or 10% sulfuric acid solutions for 28 days according to JSTM C 7401 [58], as shown in Figure 2a. The position of the immersed specimens was rotated every 12 h, because when their surface was attached, it may influence deterioration. Changes in electrical resistance, weight change ratio, and compressive strengths were measured at 3, 7, and 28 days of immersion where the compressive strength change ratio (\(F_{c}\)) and weight change ratio (\(W_{c}\)) are determined by Equations (1) and (2). \[F_{c}=\left(\frac{F_{s}-F_{ini}}{F_{ini}}\right)\times 100 \tag{1}\]  
\[W_{c}=\left(\frac{W_{s}-W_{ini}}{W_{ini}}\right)\times 100 \tag{2}\]  
where \(F_{s}\) is the compressive strength after damage by sulfuric acid (MPa), \(F_{ini}\) is the initial compressive strength after 28 days of water curing (MPa), \(W_{s}\) is the weight of the specimen after damage by sulfuric acid (g), and \(W_{ini}\) is the initial weight of the specimen after 28 days of water curing (g). Figure 2: Immersion in sulfuric acid solution. In accordance with KS L ISO 679 [53], a rectangular parallelepiped specimen with dimensions of 40 \(\times\) 40 \(\times\) 160 mm was fabricated, demolded after 24 h, and cured in water maintained at 20 \(\pm\) 1 \({}^{\circ}\)C. The compressive and flexural strength tests of the CNT cement mortar were performed. The same specimen with dimensions of 40 \(\times\) 40 \(\times\) 160 mm was used for measuring the electrical resistance of CNT cement mortar and its electrical resistance after damage by a sulfuric acid solution, and copper plates were inserted at both ends of the specimen (see Figure 3). Before the test, it was confirmed that the copper plates were not damaged by treatment with sulfuric acid for 28 days. The electrical resistance was measured in a 2-probe method using the data acquisition system DAQ970A with the program BenchVue) as presented in Figure 4. In addition, each measurement was made after drying for 24 h at a temperature of 80 \(\pm\) 1 \({}^{\circ}\)C in a dryer because of the results of previous research ([PERSON], 2009 [59]) showing that the moisture content affects the conductivity of cement mortar. Figure 3: Dimension of rectangular parallelepiped specimen of cement mortar for electrical resistance test: (**a**) side view and front view; (**b**) plan view. To measure pore size distribution before and after the 28-day immersion of CNT cement mortar in a sulfuric acid solution, about 2 g of the sample immersed for 28 days was collected from the same location on the top end of the surface of the specimen (see Figure 5), because the most damaged area was the surface. The upper part of the samples damaged by sulfuric acid attack was first cut with a cutter to about 20 mm in size and then crushed with a small hammer for the SEM tests. In addition, MIP was utilized as an analytical technique using Autopore V 9600 (Figure 6) and was also used as damage identification due to crushing during the collection process of the composites.