## 3 Results and Discussion
### Compressive Strength and Drying Shrinkage of AASC
#### 3.1.3 Effect of Alkaline Activator  
In Sections 3.1.1 and 3.1.2, the experimental results indicated that the optimum water-to-slag and sand ratios were 0.35 and 0.64, respectively, in terms of high compressive strength and low drying shrinkage. Based on these ratios, the effects of silicate modulus and Na\({}_{2}\)O content of the alkaline activator on the compressive strength and drying shrinkage of AASC were determined as shown in Figure 8. On the whole, the compressive strength of the AASC increased as the curing time increased and decreased as the silicate modulus or Na\({}_{2}\)O content increased. The compressive strength was in the range of 39.2-48.8 MPa after 7 days. [PERSON] et al. [PERSON] et al. (2016) had also shown that the compressive strength of AAS paste decreased as the silicate modulus increased from 0.75 to 1.50 for Na\({}_{2}\)O contents of 6% and 8%, respectively. The same conclusion was obtained by [PERSON] et al. [PERSON] et al. (2016), who found that the compressive strength of AAS decreased as the Na\({}_{2}\)O content increased from 4% to 8% for the silicate modulus between 0 and 2.0. The compressive strength of AAS activated by water glass increased as the Na\({}_{2}\)O content increased from 6% to 8%, but it decreased when the Na\({}_{2}\)O content continued to increase up to 10% [PERSON] et al. (2016). However, the opposite conclusion has also been reached. Irrespective of being cured in air or in saturated limewater, the compressive strength of alkali-activated ladle furnace  
Figure 7: Effect of sand ratio on (**a**) compressive strength of AASC specimens; (**b**) drying shrinkage of AASC specimens. slag geopolymer was observed to increase as the alkali agent increased from 4% to 6% [42]. A higher Na\({}_{2}\)O content indicates a higher OH\({}^{-}\) concentration in the alkaline activator, which can accelerate slag dissolution and lead to the formation of larger quantities of reaction products [23]. However, an optimum OH\({}^{-}\) concentration in KOH or NaOH has been observed in relation to the compressive strength of slag-based inorganic polymers [26]. Excess OH\({}^{-}\) concentration can result in a decrease in final strength, mainly due to the fact that the additional OH\({}^{-}\) does not react with the raw materials. Instead, with a lower silicate modulus or higher Na\({}_{2}\)O content in the activator, the higher alkalinity solubilizes the water-impermeable layer on the surface of the slag particles [43], resulting in a faster rate of reaction and more rapid formation of reaction products. The drying shrinkage of AASC was observed to increase as the silicate modulus and Na\({}_{2}\)O content increased; thus, both a higher silicate modulus and Na\({}_{2}\)O content can result in higher drying shrinkage. When the Na\({}_{2}\)O content was 8%, the drying shrinkage of the AASC specimens after 28 days with silicate moduli of 1.4 and 1.6 were as much as 1.59 and 1.73 times greater, respectively, than the specimen with a silicate modulus of 1.2. A similar trend was reported in terms of drying shrinkage of AAS pastes at silicate moduli between 0.75 and 1.50 and Na\({}_{2}\)O contents between 4% and 8% [19]. The drying shrinkage of geopolymer concrete was also observed to increase as the sodium silicate to sodium hydroxide ratio increased from 1.5 to 2.5 [44]. Previous research has assumed that an increase in the portion of alkali agent helps to dissolve more of the Si and Al ions that participate in inorganic polymerization reactions, thus contributing to the observed increase in shrinkage over time [42]. It has also been observed that an increase in the portion of sodium oxide in blended alkali-activated binders results in a decrease in the measured shrinkage [45]. The pore structure of alkali-activated slag concrete is much finer and more complex [46], and this tightness of the pore structure may influence the degree of shrinkage.