## 4 The Compressive Strength and Resistivity Prediction Model of the CLSM  
### The Prediction Model of Compressive Strength  
In the design of controlling low-strength DS, its compressive strength is essential. The 28-day compressive strength is usually regarded as the design strength. To ensure this power, we must wait for a long time--that is, 28 days [16]. Thus, if it is possible to prove a later compressive strength prediction model based on early strength, it will be very helpful for the application of the material and its subsequent evaluation. Many studies have been conducted to predict and analyze the compressive  
Figure 6: Logarithmic regression relationship between the surface resistivity and compressive strength with various DS ratios of the CLSM. Figure 7: Linear regression relationship between the surface resistivity and compressive strength with various DS ratios of the CLSM. strength of concrete or cement mortar at 28 days or other days based on early strength [14; 15; 16; 17; 18], but few people have raised the compressive strength prediction models of CLSMs containing desulfurized slag. [PERSON] et al. (2003) [17] proposed a series of models to predict the compressive strength of cement samples after a series of cement mortar test results. The prediction model can predict the compressive strength results of seven days and 28 days according to the compressive strength within 24 h. The model considers six variables, but up to 17 variables can be considered. If more variables are considered, the prediction accuracy will be higher. [PERSON] et al. (2012) [16] was based on the seven-day test results, and [PERSON] and [PERSON] (2010) [24] established a 28-day compressive strength prediction analysis based on the three-day test results. The results of the study show that if some aggregate substitutes (including fly ash, slag, and waste glass) are added, the compressive strength will increase with the curing time, but this increase becomes stable over time. [PERSON] et al. 's (2014 and 2017) [14; 23] previous studies used a hyperbolic function to simulate the relationship between the compressive strength of liquid-crystal display (LCD) waste glass concrete and curing time. Thus, the relationship between compressive strength and curing age were discussed in this study under the condition of a fixed water-cement ratio (w/b = 1.5) and the replacement rate of desulfurized slag instead of fine aggregate gradually changing from DS = 0% to DS = 50%. The final test results showed the same trend as past studies [14; 15; 16; 17; 18]. There is a nonlinear relationship between the compressive strength and the increase in curing time. The increasing trend of the compressive strength will gradually decrease with age and will tend to be horizontal. The CLSM is cured at room temperature. Under the condition of changing the desulphurization slag substitution rate (DS), the relationship between the compressive strength and curing age within 28 days can be expressed as a hyperbolic function, where \(f^{\prime}_{c}\), is the compressive strength of any curing age, \(f^{\prime}_{c,28}\) is the compressive strength of 28 days of curing age, as shown in Figure 8.  
In the prediction model of the curing age and compressive strength based on the strength test results, we will use the compressive strength at 28 days as the normalization basis, combined with the hyperbolic function, to obtain the predictive model of the controlled low-strength DS material. The compressive strength equation is shown in Equation (1), where \(f^{\prime}_{c}\) refers to the compressive strength at any curing age, \(f^{\prime}_{c,28}\) refers to the compressive strength at the age of 28 days, \(t\) refers to the curing  
Figure 8: Hyperbolic function relationship of the compressive strength and surface resistivity with various DS contents of the CLSM. age (1 to 91 days), DS refers to the replacement rate of desulfurization slag, \(a\) and \(b\) are the hyperbolic function coefficients of the compressive strength prediction analysis based on the DS content.