## 3 Literature Review
### DK with Slag (GGBS and EAFS)
The authors explained that the reacted particles of DK act as synergetic agent filling the pores, which reduces the formation of microcracks in the matrix, thus preventing the penetration of chloride and sulphate ions. This contributed to the overall durability enhancement. The above findings confirm DK as a viable precursor in AAC. However, its performance is highly dependent on the nature of the co-precursor, alkali concentration, and curing conditions. In MK-based systems, DK contributes positively to strength development up to an optimum dosage, likely due to its high amorphous silica content, which promotes the formation of N-A-S-H-type geopolymer networks. The optimal mechanical performance observed in DK-MK blends (30-40%) suggests the formation of a compact and well-connected gel matrix. At this ratio, MK provides sufficient reactive alumina to balance the Si/Al ratio, while DK contributes additional amorphous silica. SEM and EDX analyses from [27] confirm that DK-MK precursor systems result in a homogeneous and dense matrix at moderate DK contents, characterised by well-developed binding gels and low porosity. Alkali concentration is another key factor: low dosages lead to incomplete precursor dissolution, whereas excessive alkali may destabilise the gel structure. Strength gains and reduced porosity were consistently reported at moderate activator levels. In slag-based systems, DK showed beneficial effects when added at 25-30%, likely due to its filler role and contribution to gel development. However, higher DK contents appear to disrupt the Ca/Si balance necessary for robust C-(A)-S-H formation, leading to strength loss and delayed setting. Based on DTA, FTIR, and SEM, study [26] demonstrated that excessive untreated DK resulted in increased porosity and lower C-S-H/C-(A)-S-H gel development. Conversely, thermal activation (FDK) improved the performance of DK at lower dosages (e.g., 10%), enhancing strength and hydration, likely due to increased silica reactivity. Similarly, in EAFS-based binders, moderate DK additions improved matrix densification and durability, presumably through secondary gel formation and refined pore structures, a behaviour also observed in SCM systems. The compatibility of DK with co-precursors therefore depends strongly on precursor chemistry: [27] highlighted the importance of achieving balanced Na\({}_{2}\)O/Al\({}_{2}\)O\({}_{3}\) and SiO\({}_{2}\)/Al\({}_{2}\)O\({}_{3}\) ratios in DK-MK-slag blends to optimise strength and densification, while [26] found that excessive DK in calcium-rich matrices compromised C-S-H/C-(A)-S-H development. This indicates that DK performs more favourably in low-calcium systems (e.g., MK or WTS), where its silica integrates into aluminosilicate networks. In high-calcium systems such as GGBS or EAFS, its use must be more controlled, either by limiting dosage or using thermal pretreatment. Overall, these findings highlight the need to balance reactive silica and calcium availability while tailoring activation regimes, ensuring efficient precursor dissolution and gel formation. DK is more compatible with low-calcium aluminosilicate systems, where excess silica promotes N-A-S-H formation, rather than in calcium-rich systems, where unreacted silica may interfere with C-(A)-S-H unless DK is carefully dosed or pretreated.