# A Study on the Properties of Recycled Aggregate Concrete and Its Production Facilities
## 1 Introduction  
In the latter part of the 1980s, Korea constructed large-scale housing developments, as well as new cities for building pleasant residential environments and resolving housing issues. Thereafter, during the 2010s, with the drastic increase of old housing that caused re-development and re-construction to become increasingly active, the production of construction waste materials increased yearly. According to the nationwide waste material volume of 2016, which was reported by the Korea Environment Corporation in 2017. The volume of construction waste materials has been on the rise every year (as shown in Figure 1), with the highest value reaching up to approximately 48%. From the figure, the ratio of waste concrete was 62.8% and the waste asphalt concrete was 17.9%, illustrating that the recycling of waste concrete has become an urgent matter [1]. In accordance with the provision of Article 35 of the Construction Waste Recycling Promotion Act, the government established the Recycled Aggregate Quality Standard for promoting the recycling of waste materials from construction, to recommend a more diversified and broadened facilitation of waste concrete. Therefore, in terms of applying recycled aggregate for concrete, there have been a significant number of studies that have been conducted at home and abroad, and recently, there have been active studies on the addition of diversified mixed materials to the recycled aggregate concrete or the mixed use of natural aggregate, to provide recycled aggregate concrete with capabilities equivalent to that of ordinary concrete [2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14]. However, recycled aggregate for use in concrete has not been widelyemployed in Korea, as the aggregates are of poor quality; they have a high absorption rate and low density, therefore, are mostly used for filling the ground. The recycled aggregates are not used in structural buildings as their quality fluctuation is severe. It might only be used in buildings if the cement paste on the surface of the recycled aggregate is removed, but the removal of impurities and fine aggregates is also very important. Previous research, has studied the removal of cement paste on the surface of recycled aggregates but there have been no research on the development of impurities and the aggregate fine powder removal facilities. Therefore, the main purpose of this study was to develop and verify facilities, to activate recycled aggregate for concrete. Theoretically, there exists a technology that improves the quality of recycled aggregate by adding wind speed to the impact method, which removes the impurities. Previous studies that have pursued the improvement of the quality of recycled aggregates, have mostly been conducted on the removal of surface cement paste, and the removal methods were typified by impact, chemical, and heating methods. [PERSON] and [PERSON] reported that the impact strength increased as the number of impacts increased, and that the compressive strength of the recycled aggregate concrete decreased [15]. [PERSON] and [PERSON] have reported a technique of removing the cement paste on the surface of the recycled aggregate, by heating and fracturing [16]. [PERSON], [PERSON], [PERSON], and [PERSON], as a study of chemical methods, focused on the technique of removing the cement paste adhered to the recycled aggregate, with hydrochloric acid solution [17; 18; 19; 20]. [PERSON] also reported cement paste removal with sulfuric acid solution [12]. However, the heating and fracturing and chemical methods have not been utilized due to its spatial and temporal constraints. In order to promote the use of recycled aggregates, the Korean government has presented a new standard of use with an expanded scope that requires the use of recycled fine aggregate, from the existing recycled coarse aggregate. This standard was in accordance with the laws and regulations of the quality standard of the recycled aggregate.