# Alkali-silica Reaction Elimination Potential of High-Performance Concrete Containing Glass Powder
## 4 Discussion
### Alkali-silica Expansion
Figure 4: Summarized results of dependence of ASR expansion on time according to the TP137. Figure 3: Summarized results of the dependence of the ASR expansion on time according to the ASTM C1260 standard. According to [PERSON] et al. (2018), there is no relationship between the amount of glass that is used and the expansion that is caused by ASR. At the same time, he claims that metakaolin, fly ash, or silica fume can also affect the ASR expansion. In this work, in the proposed mixtures of the type GPP HPC 50 and GPP HPC 100, microsilica was removed from the composition of the mixture. In the first pilot test, cracks formed during the setting of the concrete. The mixture was subsequently optimized, and one of the steps in the new mix was the omitting of silica fume. Therefore, this work confirms the assumption of a possible negative effect of silica fume on ASR. But, of course, it depends on the chemical properties of the material ([PERSON] et al., 2018). In an alkaline environment, the surface of Si-OH groups of siliceous materials ionizes, thereby acquiring a multiple negative charge. Among the most important aspects of the environment are pH values and the content of NaCl, BaCl\({}_{2}\), or other neutral salts. As the concentration of these salts and pH increase, the intensity of the negative charge increases. In an alkaline environment with such a high ionic charge, hydroxyl ions OH\({}^{-}\) are also released, entering deeper into the material, and penetrate the center of the material. When OH\({}^{-}\) penetration slows down, the ASR rate also slows down. However, the source of ions does not have to be the only solution that is used ([PERSON] et al., 2018). If there are enough calcium ions in the solution, the so-called C-S-H gel is formed, which causes cracks in concrete. Changes in the pH occur when the calcium ions Ca\({}^{2+}\) or SiO\({}_{2}\) in the solution come into contact ([PERSON] et al., 2018). This advanced form of ASR was recognized for one reference sample, although the values that were measured during the experiment indicated higher length changes for the SGP HPC 100 mixture (values measured according to TP137). The reason may be precisely the higher content of Si in SF and SGP. Based on the testing of GP samples, it is not possible to estimate in advance how they will behave as a replacement component in the HPC mixture. Therefore, it is advisable to experimentally verify this behavior repeatedly of both GP and HPC and analyze the possibility of dependence and its possible nature. In the aggressive conditions that are specific for both experiments that were performed (ASTM C1260 and TP137), it is possible that sudden fluctuations after the standard test period are caused by the extended expansion horizon. These were the SGP HPC 50 and SGP  
Figure 5: Microstructure after ASR testing. (a) GGP HPC 100, (b) REF HPC. HPC 100 mixtures according to ASTM C1260 that experienced expansion between 14 and 28 days (Figure 3). However, according to TP137 (Figure 4), a very continuous increase was observed throughout the experiment with SGP HPC 100, and it may be an inappropriate material to be used as a substitute for SF, leading to dangerous expansion that is caused by ASR. However, the directions for further research may vary--apart from the standard option of long-term research (which was carried out by [PERSON] et al. [20]). In recent years, other directions have appeared, namely numerical calculations of the expansion that is caused by ASR that were presented mainly by [PERSON] et al. [35; 36].