# Experimental Study on a Prediction Model of the Shrinkage and Creep of Recycled Aggregate Concrete
## 1 Introduction  
The recycling of construction waste (RCW) refers to the crushing of construction waste to obtain different types of products and reuse them as resources. An important product of RCW is recycled aggregate, which itself is attached to old mortar that is difficult to peel due to the limitation of crushing technology. Therefore, it can be approximated that recycled aggregate is a two-phase material composed of the old mortar and the natural aggregate wrapped therewith. Recycled aggregate concrete (RAC) refers to recycled aggregate, which is made by crushing and classifying waste concrete and mixing according to a certain proportion, and partially or completely replacing the natural aggregate to make new concrete referred to as RAC [1]. RAC not only digests waste concrete and solves the problem of a serious shortage of natural resources, but also meets the requirements of existing specificationsunder reasonable design. It is a green building material worthy of promotion. At present, domestic and foreign countries have given eager attention and long-term exploration of RAC, especially towards the shrinkage and creep of the concrete, which can cause structural deterioration and safety problems. Based on a number of research reports on concrete shrinkage and creep [2; 3; 4], the effects of concrete shrinkage and creep mainly include the increase of beam deflection and the reduction of structural bearing capacity. In addition, the shrinkage and creep of the concrete can also cause prestressing loss of the prestressed members and secondary internal forces that create the structure. In the local area of the concrete, due to the shrinkage of internal stress, it is easy for problems such as cracks on the outer surface of the member to be created. In view of the fact that RAC has properties close to that of ordinary concrete [5; 6; 7; 8; 9; 10; 11; 12], the structural adverse effects caused by shrinkage and creep are similar or even more serious than in natural concrete. Therefore, the research on the shrinkage and creep of RAC has an irreplaceable significance. Many scholars have conducted relevant research on the importance of the shrinkage and creep of RAC. [PERSON] et al. [13] studied the shrinkage and creep tests of RAC with different substitution rates. The results show that with the increase of the replacement rate of recycled aggregates, the shrinkage and creep deformation of RAC increases. However, there is a lack of in-depth exploration of the impact of factors. [PERSON] et al. [14] conducted experimental research on the creep behavior of RAC with different water-cement ratios of base concrete. The results show that the creep properties of recycled base concrete with a low water-cement ratio are significantly affected by recycled coarse aggregate (RCA), and the establishment of a prediction model for the creep of recycled base concrete needs to consider the influence of the water-cement ratio. However, the effects of different recycled aggregate-attached mortars on shrinkage and creep have not been deeply considered. [PERSON] et al. [15] studied the shrinkage and creep of RAC based on three factors: curing condition, loading age, and axial stress level. The experimental results show that the corresponding average ratios of the shrinkage strain of RAC of a 50% and 100% substitution rate are 1.21 and 1.71, compared to ordinary concrete. [PERSON] et al. [16] devoted himself to the study of the effect of old adhesive mortar on the creep of RAC. Based on the experimental data, it is proposed that the RAC with a 100% substitution rate develops more rapidly and the amplitude is 1.6 times larger than that of traditional concrete. [PERSON] et al. [17] explored the effect of recycled aggregates from Portuguese construction and demolition waste on the shrinkage and creep properties of concrete. The results showed that the creep coefficient of the 12 recycled aggregates tested at 91 days was 0.22 to 1.63.