# Durability of High Volume Glass Powder Self-Compacting Concrete
## 3 Results
### Chloride Diffusion Coefficient  
The apparent chloride diffusion measured at the curing ages of 28, 90, 180, 365 and 545 days for control mixes and 30% glass powder SCC mixes are shown in Figure 13, while the results for the different levels of glass replacement are provide in Figure 14. The GP concrete showed the highest chloride diffusion coefficient among all mixes. The fly ash and glass powder mixes showed lower diffusion coefficient than GP at 28 days and continued to decrease with curing age. [PERSON] and [PERSON] (2017) [36] reported a reduction of 90% in the chloride diffusion coefficient for 30% glass powder incorporated concrete as compared to GP control. The denser microstructure accompanied with refined pores and lower connectivity contribute to the reduce diffusivity. [PERSON] and [PERSON] (2015) [28] also reported a reduction in chloride penetrability with increase in glass powder content in concrete. The time-dependent changes in diffusion coefficient due to continued hydration is often represented by diffusion decay index (m) or ageing factor. Taking 28 days diffusion coefficient as reference, the diffusion decay coefficient was calculated at the ages 90, 180, 365 and 545 using the following equation:  
\[\frac{D_{t}}{D_{ref}}=\left(\frac{t_{ref}}{t}\right)^{m}\]  
where \(D_{t}\) (m\({}^{2}\)/s) is the diffusion coefficient at time t (days), \(D_{ref}\) (m\({}^{2}\)/s) is the diffusion coefficient at \(t_{ref}\) 28 days. Figure 13: Chloride diffusion coefficient of SCC mixes at 30% cement replacement at different ages. The average diffusion decay index across all ages for different mixes are given in Table 5. The diffusion decay index values of glass powder mixes are larger than those for the fly ash mixes. The decay index of 40G30% and 20G40% are similar to FAF30% indicating glass powder could bring similar changes in the pore structure that restricts the movement of chloride ions even with coarser particle size and higher replacement level. The higher ageing factor values for glass SCC mixes could improve the service life of structure subjected to chloride-induced corrosion. A good correlation was observed between chloride diffusion coefficient and electrical resistivity (Figure 15). From the results, it can be inferred that electrical resistivity provides a reasonable estimate of the diffusion coefficient value, which is easier to perform and much faster. As with the strength vs. permeability comparison, the chloride diffusion coefficient vs. resistivity relationship is most accurate when evaluating similar mix deign compositions. Where prequalification of mixes for use in marine construction applications is conducted based on bulk chloride diffusion testing, the resistivity testing may provide a good indication of individual batch performance for SCC containing glass powder. Figure 14: Chloride diffusion coefficient of SCC mixes containing glass powder with 20μm particle size at different replacement levels. \begin{table}
\begin{tabular}{c c} \hline \hline
**Mix** & **Diffusion Decay Index \(m\)** \\ \hline
**GP** & 0.16 \\
**FAF30\%** & 0.38 \\
**FAC30\%** & 0.34 \\
**10G30\%** & 0.47 \\
**20G20\%** & 0.56 \\
**20G30\%** & 0.42 \\
**20G40\%** & 0.32 \\
**40G30\%** & 0.34 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Diffusion decay index for different SCC mixes. The results from chloride diffusion coefficient and the time dependent decay coefficient \"\(m\)\" were in good agreement with the previous durability index tests of porosity, permeability and resistivity, such that there was a decrease in measured performance with an increase in the glass particle size and replacement level. The replacement of 20% glass powder resulted in the lowest chloride diffusion coefficient even below that of the finer glass powder at 30% replacement levels. Some percentage of glass powder is clearly necessary to refine the pore structure of the concrete, but additions beyond 20% appear to be less effective.