In this experimental study, tests were conducted to obtain the CaO/SiO₂ (C/S) molar ratio that minimizes the micropores of hardened concrete. To this end, the compressive strength, thermogravimetric analysis (TGA), and microporous structure of hardened concrete were investigated using concrete specimens made with silica fume and quartz powder under high-temperature/high-pressure conditions. The tests yielded the following results: (1) the highest compressive strength (200 MP) was exhibited in the C/S molar ratio range of 0.7–0.9, and lower compressive strength was exhibited in the C/S molar ratio ranges of ≤ 0.6 and ≥ 0.95; (2) the productivity of calcium silicate hydrate (C-S-H) tended to increase in proportion to the C/S molar ratio in all specimens; (3) the microstructure was measured using mercury intrusion porosimetry (MIP), and the maximum total porosity of specimens was calculated to be 10%. As the C/S molar ratio increased, the total porosity decreased, as did the pore diameter and threshold pore diameter. Thus, C/S molar ratio was found to be a major factor affecting the compressive strength and microporous structure of autoclave-cured cement and the optimal mechanical properties were exhibited in the C/S molar ratio of 0.8–0.9. However, the reactivity varies depending on the material used and curing conditions employed. Therefore, the hydration products obtained using the curing conditions need to be investigated further.

Electric arc furnace oxidizing slag (EAFOS) represents 80% of the electric arc furnace slag generated. Recently, EAFOS has been utilized as high value-added functional aggregate in a growing number of cases for the construction of air-cooling technology that turns EAFOS into fine aggregate-sized particles by spraying it into the air using high-pressure compressed air. Ladle furnace slag (LFS) is a product of the reduction process, accounting for approximately 20% of the steel slag enerated; however, LFS is predominantly landfilled without being utilized. This is mainly because LFS changes into sludge as it is turned into powder during water spray cooling. Therefore, in this study, spherical particles cooled at room temperature were fabricated as fine aggregates using LFS by applying atomization technology that uses high-pressure air in the molten state for the value-added utilization of LFS. Various experiments were performed to examine whether this aggregate can be used as a construction material. The experimental results showed that the air-cooled LFS (ALFS) fine aggregate generated from two different processes met the physical and chemical properties of the fine aggregate required for concrete despite its slightly lower spherical ratio compared to EAFOS aggregate. The volumetric stability experiment results also showed that ALFS fine aggregate is more stable than river sand and standard sand. In addition, the autoclave test results revealed that the mortar produced using ALFS fine aggregate was more stable for expansion than that of comparison groups. These results confirm the applicability of ALFS as an aggregate for construction. However, because the pop-out phenomenon caused by MgO was observed on the surface of some specimens, further research is required for improvement.