## 3 Test Results and Analysis  
### Compressive Strength  
Compressive strength is often regarded as an important indicator of CLSM quality. Figures 2 and 3 present the relationship of the desulfurization slag content (DS) and curing time (\(t\)) on the compressive strength of a CLSM. Figure 2 shows the compressive strength of the CLSM, indicating that the DS replacement is between 0% and 50%, the compressive strength at the age of one day is 0.2-1.3 MPa, and the compressive strength value of the test group with the DS substitution amount of 10% to 50% is lower than the control group's compressive strength value between 0.9 MPa and 2 MPa. The seven-day compressive strength reduction is between 2.0 MPa and 5.5 MPa; the 28-day compressive strength reduction is between 2.7 MPa and 7.2 MPa. The compressive strength of the CLSM increases with age. If the curing age is from seven days to 28 days, the percentage of the compressive strength of each DS replacement ratio increases by 21.1-85.7%. The 28-day compressive strength of all test specimens did not exceed 9 MPa, which was in-line with the majority of the CLSM regulations in Taiwan; the growth of the compressive strength after 28 days of age was relatively flat, with each substitution group increasing by 5.3% to 10%; if the maximum substitution amount was at 50%, there was no growth in the compressive strength from 56 to 91 days of age.  
Figure 1: Test equipment. (**a**) Compressive strength-testing machine. (**b**) Four-pole resistance-measuring instrument.  
Figure 3 shows the compressive strength development of the CLSM. At 28 days of age, the average amount of the DS replacement is increased by 10%, the compressive strength is reduced by 0.9 MPa, and the age is 28 days to 91 days. The compressive strength of each group of DS is not much different from that of the control group, and the strength reduction range is between 2.6 MPa and 4.9 MPa (36.1-63.6%). The test results show that the compressive strength increases with the increasing curing age but decreases as the DS replacement increases. When the replacement ratio of the DS is less than 20%, the compressive strength decreases rapidly with the replacement of the DS. However, when the replacement ratio of DS is between 20% and 50%, the reduction in the compressive strength value does not change much at any curing age.  
Figure 3: The relationship between the DS content and compressive strength of the CLSM.  
Figure 2: The relationship between the curing age and compressive strength of the controllable low-strength materials (CLSM). DS: desulfurization slag and w/b: water-binder ratio.  
It can be seen from the above that the compressive strength of the CLSM is inversely related to the substitution amount of industrial by-product DS. The more the substitution amount, the lower the compressive strength. The possible reason is that the CLSM is a high water-binder ratio material, although it improves workability. Relatively, the compressive strength is also reduced, and the particle size of the desulfurized slag is smaller than that of the fine aggregate, which is also a cause of low strength, which causes the bond formed during the coagulation to be weak and, therefore, cannot provide strength.