## 4 Discussion  
The main advantages and disadvantages of the proposed model in this paper are as follows:  
First, one of the advantages of the proposed model is that this paper uses the experimental results of the cumulative hydration heat of the first 7 days to calibrate the cement hydration model parameters B, C, kr, and De\({}_{0}\) and the eggshell powder nucleation effect parameter nu. These parameters do not change with the change in the experimental mix ratio. When researchers use other mix ratios to conduct experiments, the model proposed by us can automatically calculate the experimental results corresponding to the new mix ratio, such as hydration heat, microscopic hydration products, compressive strength, and surface electrical resistivity. Therefore, the proposed model can greatly reduce the cost of the experiment and save the time of the experiment.  
Figure 6: Evaluation of strength and surface electrical resistivity using hydration heat. (**a**) Relation between hydration heat and strength. (**b**) Relation between hydration heat and surface electrical resistivity.  
Second, the second advantage of this paper is that the hydration model proposed in this paper covers multiple levels of prediction. The macro level includes the development of compressive strength and the development of surface electrical resistivity. The strength prediction results are helpful for construction management and structural design, and the surface electrical resistivity results are helpful for the evaluation of steel corrosion rate. The micro level includes hydration heat and the formation of hydration products. The prediction of hydration heat helps to evaluate the early temperature cracking of hardening concrete, and the formation of hydration products helps to estimate the mechanics and durability of concrete from the micro level. The authors believe that these multi-level evaluation models are helpful for the material design of eggshell powder hybrid concrete and promote the recycling of eggshell powder.  
Third, the main disadvantage of the proposed model is that compared with other models, this paper does not consider the chemical reaction of eggshell powder [28]. The chemical reaction of eggshell powder can refine the pores and improve the durability [29; 30]. When the aluminum content of the binder is relatively high, the reaction between the calcium carbonate in the eggshell powder and the aluminum phase in the binder can generate more carbo-aluminate. In future research, more experimental studies on the chemical reaction of eggshell powder should be carried out. After obtaining a large number of experimental results, the chemical reaction effect and pore refinement effect of eggshell powder should be considered in the hydration model.  
Fourth, another major disadvantage of the proposed model is that the input parameters of the model are obtained by calibration of the experimental results of cumulative hydration heat. Some researchers may not have the experimental conditions for cumulative hydration heat measurement. In this case, the researchers can collect the hydration degree of various types of cements through literature surveys, and the hydration model parameters B, C, kr, and De\({}_{0}\) corresponding to each type of cement can be obtained. Then, the relationship between the mineral composition of cement and the hydration model parameters is obtained through neural networks or other regression methods.