# Effect of Super Retarder on Recycled Water and Concrete Properties of Waste Slurry in Mixing Plant
## 4 Results
### Microanalysis  
The super retarder PBTCA and ACS were selected with a fixed ratio of 1:20, and XRD, DTG, TG and other microscopic tests were used to study their effects on the hydration of cement in waste slurry recycled water at different ages. The dosages were 0.5%, 1.5% and 2.0% (external mixing method), and the concentration of waste slurry recycled water was 10%. Study of the types and amounts of hydration products at different ages using XRD:  
Figure 6 shows the effect of different dosages of ACS+PBTCA on the type and amount of cement hydration products in 10% concentration of waste slurry recycled water as characterized by XRD. As can be seen from Figure 6, the types of crystalline phases in the hydration products did not change at all ages after doping with ACS+PBTCA. The calcium alumina peak intensities of blank and ACS+PBTCA doped specimens with different amounts of ACS+PBTCA were similar for the specimens with ages of 1 day, 3 days and 7 days, and the calcium hydroxide peak intensities of ACS+PBTCA doped specimens with ages of 1 day and 3 days were lower than those of the blank specimens; The calcium hydroxide peak intensity of the 0.5% ACS+PBTCA doped specimen at the age of 7 days is higher than that of the blank specimen, and the calcium hydroxide peak intensity of the remaining two doped ACS+PBTCA specimens is similar, and both are lower than that of the blank group and the 0.5% ACS+PBTCA doped specimen group. Figure 4: Effect of PBTCA and ACS at different ratios on the compressive strength of concrete. Figure 5: Effect of SDP-90 and ACS at different ratios on the compressive strength of concrete. After adding ACS and PBTCA compound super retarder, it reacts with Ca(OH)\({}_{2}\) on the surface of the generated clinker phase to form \"insoluble\" calcium phosphate, which hinders normal hydration and slows down the setting time of waste slurry recycled water. At the same time, after adding the compound super retarder, the content of C\({}_{3}\)S is obviously increased, so it is favorable to the compressive strength. Study on the types and amounts of hydration products at different ages using DTG:  
Four components were selected for the test, one group was a blank group and the remaining three groups were control groups with ACS+PBTCA. The concentration of recycled water was 10%. Thermogravimetric tests were performed on the four cement pastes separately. The changes in hydration products of the four pastes were analyzed at different hydration times. Figure 7 shows the effect of different dosages of ACS+PBTCA on cement paste in recycled water as characterized by DTG. As shown in Figure 7, ACS+PBTCA does not cause new hydration products to appear in the cement paste. The more obvious characteristic peaks in the figure are the dehydration and heat absorption peak of free water or water of crystallization inside the decomposition of calcite near 100 \({}^{\circ}\)C, the CH decomposition peak near 430 \({}^{\circ}\)C and the CaCO\({}_{3}\) decomposition peak near 700 \({}^{\circ}\)C, in which CaCO\({}_{3}\) mainly comes from the raw materials in the cement, and a small amount of carbonation will occur in the cement during the storage process. It can be seen that, with the advance of hydration time, the DTG curves of cement slurry and blank cement slurry in recycled water with 10% concentration of waste slurry doped with different amounts of ACS+PBTCA gradually converge, indicating that doping  
Figure 6: XRD of blank and ACS+PBTCA doped specimens at different ages. (**a**) 1 day, (**b**) 3 days, (**c**) 7 days. Figure 7: DTG of blank and ACS+PBTCA doped specimens at different ages. (**a**) 1 day, (**b**) 3 days, (**c**) 7 days. of ACS+PBTCA affects the rate of generation of hydration products, but does not have an effect on the type of cement hydration products. Study of the types and amounts of hydration products at different ages using TG:  
Figure 8 shows the effect of different dosages of ACS+PBTCA on cement paste in 10% concentration of waste slurry recycled water as characterized by TG.