# A Study on the Applicability of Waste Glass Wool and Waste Mineral Wool as Fiber Reinforcement
## 4 Results and Discussion
### Freezing and Thawing Resistance of Waste Fiber-Reinforced Concrete  
Concrete is a structural material constructed under various environments and is directly exposed to various environmental conditions such as rainfall, heat waves, and snowfall. In particular, in the case of a cold region, a phenomenon in which moisture due to rainfall penetrates into the concrete and freezes may occur. At this time, moisture inside the concrete is frozen and expands to about 9%, and accordingly, expansion pressure is applied to the concrete [47]. Continuous application of expansion pressure to concrete can cause cracks and, in severe cases, lead to defects such as destruction of concrete. Various types of fibers, such as steel fiber, artificial fiber, and glass fiber, are widely used as reinforcing materials that can be an alternative to securing durability such as freezing-thawing resistance of concrete through many research cases [48]. This experiment was conducted to evaluate whether the freezing-thawing resistance, one of parameter of concrete durability evaluation, can be improved by the addition of waste fiber wool. Figures 15 and 16 show the results of the measurement of relative dynamic modulus of elasticity by cycle of freezing-thawing according to the addition rate of waste glass wool and waste mineral  
Figure 12: Compressive strength test results at 90 days. wool. Most of the waste glass wool-added specimens in Figure 15 showed high resistance to freezing-thawing compared to reference concrete. For reference concrete, the relative modulus of elasticity dropped below 60% in 210 cycles, while in waste glass wool-added specimens subjected to the same cycle, it was found to be 62 (0.5%), 66 (1.0%), and 66% (2.0%), respectively. It was confirmed that the addition of waste glass wool affects the improvement of the freezing-thawing resistance of concrete, and this effect is because the waste glass wool dispersed in concrete shares the expansion pressure with freezing pressure to delay the generation of cracks and prevent the cement paste from being separated. Figure 16 is the result of measuring the relative modulus of elasticity for the waste mineral wool-added specimens, and it was found that the relative modulus of elasticity was higher up to the initial 120 cycles compared to the reference concrete. However, after 150 cycles, specimens with 0.5% and 1.0% added waste mineral wool decreased sharply to 71 (0.5%) and 66% (1.0%), respectively, particularly in specimens with 0.5% added waste mineral wool that were destroyed in 180 cycles as it can be shown in the Figure 16. The 1.0% addition specimen showed a relative modulus of elasticity of 58% in the same cycles, which did not meet the criteria. When 210 cycles of freezing-thawing were applied, the relative dynamic modulus of elasticity of reference concrete fell below the criterion, but the 2.0% waste mineral wool-added specimen maintained above the criterion at 64%, and it was confirmed that it fell below the standard in 240 cycles to 54%. This means that in the case of waste mineral wool, unlike waste glass wool, the appropriate fiber addition rate required to improve the durability in terms of freezing-thawing resistance is high. Figures 17 and 18 shows the weight retention rate of specimens to the application of freezing-thawing cycles by type of waste fiber and addition rate. As a result of the measurement, it showed a similar tendency to the result of the relative dynamic modulus of elasticity. Until the initial 150 cycles, both specimens to which two types of waste fiber wool are added had a weight loss due to freezing-thawing less than reference concrete, but after 150 cycles, the weight retention rate was decreased sharply in specimens with low addition rate of waste fibers. In the case of waste mineral wool, like the relative dynamic modulus of elasticity, the weight retention rate was 83% in the specimen to which 1.0% was added which was 4% lower than 87% of the reference concrete.