# Experimental Study on Preparation and Characteristics of Concrete Modified by Construction Waste
###### Abstract
Due to the old hardened mortar in recycled aggregates, more interface transition zones are introduced, and the distribution of interface transition zones between recycled aggregates varies due to the different content of hardened mortar, resulting in more complex structures and affecting the mechanical properties of cement-based recycled materials. Research by [PERSON] et al. [31] has shown that there is a difference in strength between recycled concrete aggregates and natural aggregates, and the average strength of concrete prepared with recycled aggregates is slightly higher than that of natural aggregates. Therefore, the preparation of recycled aggregates from waste concrete is feasible. [PERSON] [32] also indicates that the strength of recycled aggregate concrete is directly proportional to the improvement in the quality of recycled aggregate. [PERSON] et al. [33] pointed out that compared to using recycled aggregates to prepare cement-based recycled materials, the mechanical properties of concrete prepared with natural aggregates are significantly lower in the latter. And it is believed that the main reason for this phenomenon is the stone damage caused by the preparation process of recycled aggregates and the hardened mortar attached to the surface. [PERSON] et al. [33; 34; 35; 36] found that there is a significant difference in the water absorption and strength properties of recycled aggregates compared to natural aggregates, mainly manifested in the high water absorption rate, high crushing value, and low apparent density of recycled aggregates. The water absorption rate of recycled aggregate is about four times higher than that of natural coarse aggregate, and the crushing index is also 23.85% higher than that of natural coarse aggregate. [PERSON] et al. [37; 38; 39] studied recycled coarse aggregate concrete and found that the physical and mechanical indicators of recycled coarse aggregate recycled concrete were lower than those of ordinary concrete. However, it is feasible to prepare concrete with lower strength, If high-strength concrete is prepared, it needs to be achieved through the addition ratio and modification effect of recycled aggregates. In summary, existing research has mainly focused on the study of recycled concrete with a single recycled aggregate. Compared to natural aggregates, due to the adhesion of waste mortar on the surface of recycled aggregates and the distribution of numerous micro cracks on the surface and inside, the water absorption rate of recycled aggregates increases and the strength decreases, becoming a key factor limiting the promotion and application of recycled aggregates. In order to more stably control the quality of recycled aggregates and improve their applicability, it is necessary to carry out low-cost surface modification treatment on recycled aggregates. At present, most urban buildings in China are in the form of concrete structures, and the construction waste generated is mainly waste concrete. The recycling and utilization of waste concrete is very important. There are some studies on the preparation of recycled low strength concrete from waste concrete, but there is relatively little research on the surface modification of recycled coarse aggregates from waste concrete, and there is a lack of relevant mix design. Due to the high content of mortar on the surface of recycled fine aggregate, the crushed recycled fine aggregate has more cracks and pores than the recycled coarse aggregate, and the higher water absorption rate is more unfavorable for the preparation of recycled rubber sand. Therefore, conducting mix proportion research on waste concrete is of great significance. In order to design the mix ratio of different types of recycled coarse aggregate concrete, recycled coarse aggregate of waste concrete is used to replace natural aggregate.