## 3 Literature Review
### DK with Slag (GGBS and EAFS)  
The literature search identified four studies where DK was used as a precursor together with a slag. Two of these incorporated DK with GGBS in AAC mortars. The first study [27] investigated GGBS-DK precursor systems with varying proportions of DK ranging from 0% to 60%; it also used four different concentrations of alkali activators (sodium hydroxide, NaOH and sodium silicate, Na\({}_{2}\)SiO\({}_{3}\)). The results indicated that the maximum compressive strength achieved was 18.4 MPa at 40% DK content--considerably lower than the strength typically attainable with GGBS alone [6,9]. Additionally, the study also reported a drop in flowability and water absorption with increasing DK percentages. Microstructural analysis and morphology scans revealed the formation of C-S-H gel and geopolymer phases. Notably, incorporating up to 25% DK with the GGBS contributed to the development of a more intensified and homogeneous geopolymer matrix, characterised by the coexistence of amorphous N-A-S-H and C-(A)-S-H gels. However, further increase in the DK content beyond 25% led to greater structural heterogeneity, which therefore reduced the overall effectiveness of the geopolymerisation reaction [27]. In another study [26], GGBS was investigated with two different types of DKs: original DK (untreated) and a thermally modified DK subjected to an elevated temperature treatment of 1000 \({}^{\circ}\)C (FDK). Both DK types were used as GGBS replacement at percentages of 10%, 20%, and 30% to produce slag pastes. The results showed that the replacement of slag with DK caused a substantial reduction in compressive strength at 28 days, dropping from 42 MPa for the DK free mix to 26 MPa for the 10% DK sample. The strength degradation which occurred with the inclusion of 10% DK exceeded 60% of the 0% DK mix strength. Moreover, it also prolonged the initial setting time (from 58 min for DK free mix to 92 min) and increased the total porosity (from 23% to 35%). Conversely, the replacement of GGBS by 10% FDK (thermally treated DK) improved the compressive strength at 28 days by 9.5%, reaching 46 MPa. In addition, the setting time almost remained the same as the DK free mix, and the porosity was improved by about 3%. However, higher FDK percentages also showed an adverse effect on the compressive strength, setting time, and total porosity. These effects are likely attributed to the high silica content of DK, which comes at the expense of available calcium in the slag. Furthermore, the poor performance of the matrix with more DK or FDK in the system was attributed generally to the excess of Na\({}_{2}\)O in the matrix (which comes from the activator) and the higher silica content, both of which delayed the condensation process and reduced the slag dissolution [26]. Two other studies [5; 48], proceeded with the partial replacements of electric arc furnace slag (EAFS) by DK in AAC systems. In [5], four percentages of DK (10%, 20%, 30%, and 50%) were used as EAFS replacement to produce geopolymer pastes. Results of compressive strength at 90 days showed an increase in compressive strength with 30% DK replacement from 17.6 MPa (0% DK) to 22.9 MPa. Incorporation of DK in excess of 30% caused a dramatic reduction in compressive strength. An extensive material analysis study was performed (XRD, TGA/DTG, SEM-EDS), which showed that DK considerably improved the formation of gels such as CSH, CASH, and N(C)ASH, which are characteristic of alkali activation. This was attributed to the high content of reactive silica and the high reactivity of alumina present in DK. An extended study on DK and EAFS by the same research team showed better durability in terms of fire resistance of the same mixes [48]. The reported compressive strength at 1000 \({}^{\circ}\)C for the 30% DK mix increased to 44.7 MPa, indicating thermal stability. The same study also reported a good durability of this mix against seawater with a compressive strength improvement of about 3 MPa after 180 days of immersion in seawater.