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This study was conducted with the aim to chemically remove the cement paste attached to the aggregate surface using acidic substances. Sulfuric and hydrochloric acids were used as the acidic substances, and after analyzing the quality characteristics of the aggregates following the acid treatment, a mortar test was performed using the aggregates. The results showed that the acidtreated recycled aggregates were superior to the original aggregates and the recycled aggregates that were manufactured using natural water in terms of density, absorption ratio and solid volume percentage. Based on this, it was determined that acid treatment was effective in improving the quality of recycled fine aggregates. In addition, the results of reviewing the strength characteristics of the mortar obtained using the acid-treated aggregates showed that the residue substances remaining in the recycled fine aggregates after reacting with the cement paste had a negative impact on the concrete strength. Based on this, it was determined that in case of improving the quality of recycled aggregates by acid treatment, there needs to be strict management of the products of the reaction with the acid in order for the aggregates to be used in structural construction.

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Despite its excellent physical and mechanical properties, polymer concrete has not been widely used owing to its much higher unit price than conventional portland cement concrete. To ensure the economic efficiency of polymer concrete, it is utmost important to reduce the use of polymer binder, which occupies most of the production cost of polymer concrete. Based on the experimental investigations, replacing filler (calcium carbonate) and fine aggregate (river sand) with fly ash and rapid-cooled steel slag (RCSS), which are spherical materials obtainable from industrial by-products, was found to be effective for improving the strength characteristics and durability as well as the cost efficiency of polymer concrete. The product developed in this study successfully reduced the demand for polymer binder by 21.3% compared to the conventional product, which in turn saved the total material costs by 18.5%. Although the use of RCSS showed performance degradation at an elevated temperature condition, considering typical temperature ranges that actual concrete infrastructures experience, it is expected that the polymer concrete using fly ash and RCSS will provide high-level performances as construction and repair materials.