# High-Durability Concrete Using Eco-Friendly Slag-Pozzolanic Cements and Recycled Aggregate
## 3 Concrete Properties Using Slag-Pozzolanic Cement
### Durability Aspects: Frost and Permeability of CEM V Concretes  
The negative effect of supplementary cementitious additives concerning frost resistance is well known, e.g., [59, 60]. In this case, frost resistance could not be laboratory-confirmed during frost-testing,  
Figure 8: Concrete compressive strength using different cement types at 2, 28, and 90 days of water curing (each value as mean value of 3 individual tests).  
Figure 9: Modulus of elasticity (static) using different cement types at 2, 28, and 90 days of water curing (each value as mean value of 3 individual tests).  
either. Testing was performed under intensified conditions without adding artificially entrained air additionally to the air content shown in Table 6. Frost resistance was evaluated indirectly via reduction in the bending flexural strength after 50 frost-thawing cycles in demineralized water. One frost-thawing cycle takes 24 h, whereby the temperature is lowered from the initial temperature of 20 \({}^{\circ}\)C to \(-\)20 \({}^{\circ}\)C within 12 h, then kept at \(-\)20 \({}^{\circ}\)C for 4 h and subsequently raised again to the initial temperature within 8 h. Temperature measurement is performed in the center of the concrete test specimen. Frost testing was performed after a period of 90 days of water curing at 150 x 150 x 600 mm samples. The results are illustrated in Figure 10: Bending flexural strength decreases strongly after frost impact, declining to a level between approx. 45 and 17% in the case of (1) CEM V/A (S-V) 32.5 R to less than 10%, indicating structural damage of the test specimen.  
Additional optimization of pore structure (porosity is reduced by the additives) and mixing design (high contents of additives increase the demand of water) will be necessary to improve frost resistance of the tested admixtures to prevent structural degradation of the concrete. An opportunity was used to build a concrete test track (washing station for trucks; Figure 11a,b) in a concrete factory in Austria in an alpine region (+815 m above the Adriatic Sea) using cement type (1) CEM V/A (S-V) 32.5 R. The concrete track itself is a horizontal structure experiencing a lot of water impact and mechanical exposure to truck tires. In winter, the input of chlorides by the truck tires is also most likely.  
Figure 11: Test track construction using (1) CEM V/A (S-V) 32.5 R using a cement content of 400 kg/m\({}^{3}\) and a water-binder ratio of 0.45 during (**a**) concreting work and (**b**) after finishing the construction.  
Figure 10: Bending flexural strength without and with frost impact evaluated after 90 days of water curing (each value as mean value of 3 individual tests).  
Considering the results from Figure 10, the mixture was adapted as the following: Cement content was increased to 400 kg/m\({}^{3}\), water-binder ratio was 0.45, and plastifying admixture was added to reach a flow consistency of F3 to F4 according to [57], additionally using an air-entraining admixture to reach 5% of air content. The practical realization went well and the concrete structure showed no sign of damage after winter 2019/2020, imposing at least 25 frost-thawing-cycles, implying the frost resistance of the applied concrete mixture.  
Permeability of the various concrete mixtures was tested via water pressure impact. Pressure testing was conducted for concrete cubes after 90 days of water curing at 20 \(\pm\) 1 \({}^{\circ}\)C and at atmospheric pressure according to [61]. Pressure testing was done at a water pressure of 500 kPa for the duration of 72 h. Afterward, the maximum depth of penetration was measured in millimeters. Water penetration depths for the different concrete mixtures with different CEM V-cements are illustrated in Figure 12.  
As evident from Figure 8, water penetration lies in the range of 16 to 23 mm, whereby the water penetration was reduced by using the slag-pozzolanic cements. Especially, cement type (4) CEM V/B (S-P) 32.5 N shows a strongly reduced water penetration.