# Experimental Study on Preparation and Characteristics of Concrete Modified by Construction Waste
###### Abstract  
With the advancement of urbanization construction, the proportion of construction waste to the total urban waste continues to increase, especially waste concrete. The treatment and reuse of waste concrete is a major trend that poses enormous pressure on environmental protection. This article focuses on the problems in the preparation of recycled aggregates from waste concrete, which has important practical value. This article presents a new type of recycled concrete prepared through surface modification of recycled coarse aggregate and design experiments to change the replacement rate of coarse aggregate. The physical properties of recycled coarse aggregate, workability of fresh concrete, and mechanical properties of recycled concrete are analyzed. The research results indicate the following: (1) Through surface modification, recycled concrete can improve the workability of fresh concrete at a fixed water cement ratio, which can meet the requirements of mixing, transportation, and pouring of fresh concrete. (2) By modifying the surface of recycled aggregates, the strong water absorption performance of recycled aggregates caused by old mortar and surface defects has been reduced. And the modification effect of recycled aggregate improves the hydration process of recycled concrete, making the surface structure dense and further enhancing the strength of recycled concrete. (3) The compressive strength of recycled concrete specifications from construction waste shows a decreasing trend with the increase in coat aggregate replacement rate. The final ratio is as follows: modular dose of 12%, modification time of 90 min, and 20% recycled aggregate content. recycled high-strength concrete; construction waste; concrete strength; optimized content +
Footnote †: journal: Applied  
on the mechanical properties and other aspects of recycled concrete [18; 19; 20; 21; 22; 23; 24; 25].The production of recycled concrete using waste concrete coarse aggregate as variables of substitution rate and water cement ratio shows that the higher the substitution rate, the more unfavorable the mechanical and working properties of recycled concrete. The higher the strength of the original waste concrete, the better the mechanical properties of recycled concrete. However, it was not taken into account that recycled coarse aggregates have a rough and porous surface and complex properties compared to natural coarse aggregates, which increases the water absorption rate of recycled aggregates. [PERSON] et al. [26] conducted uniaxial compression dynamic mechanical performance tests using recycled coarse aggregates from waste concrete instead of natural coarse aggregates, indicating that recycled concrete has good deformation characteristics, this study demonstrates the possibility of using recycled coarse aggregate to prepare concrete. [PERSON] et al. [27] applied recycled coarse aggregate from waste concrete to steel-concrete components, indicating that steel pipes have a good restraining effect on recycled concrete, as well as good bearing capacity and ductility. [PERSON] et al. [28] research has observed that due to the cement hydration reaction, waste concrete has a high porosity and water absorption. [PERSON] [29] have shown that the microstructure of cement-based recycled materials is much more complex than that of ordinary concrete. They believe that the interface transition zone containing a large number of micro pores and cracks seriously affects the ultimate strength of cement-based recycled materials. The authors attribute this to the increased consumption of water by pores and cracks, which reduces the amount of water involved in hydration reactions. [PERSON] [30] research found that the main reason affecting the performance of recycled aggregates is the presence of a certain amount of old hardened mortar in the recycled aggregates. The various properties of old hardened mortar are weaker than those of stone, which leads to weaker comprehensive performance of recycled aggregates compared to natural aggregates.