*2.1. Materials*

The test materials were selected from PC32.5R ordinary Portland cement, natural coarse aggregate, RCA, natural fine aggregate, ordinary fine sand, and urban tap water. The RCA was provided by Shaanxi Science and Technology Environmental Protection Co., Ltd. (Xi'an, China), and its physical properties are shown in Table 1.


**Table 1.** Physical properties of recycled coarse aggregate (RCA) and natural coarse aggregate (NCA).

#### *2.2. Mix Proportion Design*

According to JGJ55-2011 [26] "Ordinary concrete mix design rules", the mixing ratio of natural aggregate concrete (NAC) was calculated. The mixing ratio of RAC was replaced by equal mass. The natural coarse aggregate in ordinary concrete was replaced by RCA. Considering that the water absorption of the RCA is higher than that of the natural coarse aggregate, a certain amount of additional water was added, which was 3.83% of the mass of the RCA. The concrete slump of each component during mixing is about 90 mm. The proportions of each group and the compressive strength of the concrete cubes are shown in Table 2.



Note: Group I was the water–cement ratio (*w*/*c*) = 0.527 sample; Group II was the water–cement ratio = 0.4 sample. The additional water was calculated to take 3.83% of the weight of the recycled coarse aggregate under consideration of the water absorption rate of the recycled coarse aggregate.
