The original concrete to be used for the production of recycled aggregate is basically composed of the original aggregate and the original mortar, and, if the original aggregate has sound properties, the quality of the recycled aggregate depends on the property of the original mortar to a large extent. In addition, it is said that the degree of deterioration in the quality of the recycled fine aggregate is larger than that of the recycled coarse aggregate. Therefore, when the recycled fine aggregate or the concrete prepared using it is applied to the structural concrete, it becomes imperative to make a proper estimation of the effects of the properties of the original mortar as to their qualities prior to setting various mix design conditions. From this point of view, this paper presents a series of experiments which analyze recycled fine aggregate and recycled aggregate concrete as given below. 1. 12 types of original concrete were prepared using 3 types of original aggregate having different strengths, shapes and surface characteristics, and changing the water-cement ratio of the original mortar in 4 levels of 35%, 45%, 55% and 65%, respectively. Then, 16 types ofrecycled fine aggregate were made by manufacturing the prepared original concrete using 2 types of crushing methods. 2. The amounts of the original mortar contained in 16 types of recycled fine aggregate were estimated, and the tests on their various physical properties were carried out to clarify the relationship between them. 3. From among the above-mentioned 16 types of recycled fine aggregate, 6 types, which were made using the same type of original aggregate and the original mortar of different strengths, and by different methods to crush the original concrete, were selected. Using these 6 types of recycled fine aggregate, 48 types of recycled concrete having a different replacement ratio of recycled fine aggregate and a different water-cement ratio of concrete were produced to investigate the effects of the amount of the original mortar contained in each recycled fine aggregate and its properties on the quality of the recycled aggregate concrete. Much valuable information regarding useful results pertaining to the mix design of the recycled aggregate concrete to be produced using the recycled fine aggregate was obtained through these experiments and the analysis described above.
