# Effect of Super Retarder on Recycled Water and Concrete Properties of Waste Slurry in Mixing Plant
## 4 Results
### Effect of Compounding Super Retarder on Concrete Properties  
ACS+PBTCA and ACS+SDP-90, which have good retarding effect under compound mixing conditions, were selected, and the compounding ratios of the two groups of super retarding agents were changed respectively to study their effects on the working performance and compressive strength of concrete. The results of working performance test are shown in Tables 3 and 4, and the results of compressive strength test are shown in Figures 4 and 5.  
As shown in Table 3, compared to the reference group, the slump and extensibility of concrete exhibited a pattern of initial increase followed by decrease as the ratio of PBTCA to ACS increased. When PBTCA:ACS reached 1:20, there was no loss of 1 h slump and the loss of 1 h extensibility was 15 mm. Concrete has good workability in this condition.  
Table 4 shows the effect of SDP-90 compounded with ACS at different ratios and added to waste slurry recycling water on the slump, extension, 1 h slump and 1 h extension of concrete at 1.5% admixture. As can be seen from Table 4, with the increase of the ratio of PBTCA to ACS, the slump and extensibility of concrete showed a decreasing trend. When SDP-90:ACS was 1:20, the 1 h slump loss was the smallest, only 5 mm; at this time, the extension loss was 85 mm. Compared with the reference group, when using the compound super retarder of SDP-90 and ACS, the 1 h slump loss of concrete were all significantly reduced, but the 1 h extension loss were all larger.  
As can be seen from Figure 4, after mixing the compound super retarder of PBTCA and ACS, the waste slurry recycled water did not adversely affect the compressive strength of concrete in both low and high ratios, but improved the 7 days and 28 days compressive strengths. When PBTCA:ACS was 1:20, the 7 days compressive strength was increased by 3.5 MPa and the 28 days compressive strength was increased by 3.0 MPa; when PBTCA:ACS was 1:30, the 7 days compressive strength was increased by 2.2 MPa and the 28 days compressive strength was increased by 5.5 MPa. As can be seen from Figure 5, after admixing the compounded super retarding agent of SDP-90 and ACS, the waste slurry recycled water has little effect on the compressive strength of concrete, but the overall  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**PBTCA:ACS**} & \multirow{2}{*}{**Slump/mm**} & \multirow{2}{*}{**Extensibility/mm**} & \multirow{2}{*}{**1 h Slump/mm**} & **1 h** \\  & & & & **Extensibility/mm** \\ \hline blank & 235 & 590 & 210 & 435 \\
1:10 & 260 & 640 & 235 & 470 \\
1:20 & 255 & 635 & 240 & 550 \\
1:30 & 250 & 630 & 240 & 525 \\
1:40 & 245 & 620 & 240 & 560 \\
1:50 & 240 & 610 & 230 & 465 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Effect of SDP-90 and ACS at different ratios on the workability of concrete.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**PBTCA:ACS**} & \multirow{2}{*}{**Slump/mm**} & \multirow{2}{*}{**Extensibility/mm**} & \multirow{2}{*}{**1 h Slump/mm**} & **1 h** \\  & & & & **Extensibility/mm** \\ \hline blank & 235 & 590 & 210 & 435 \\
1:10 & 245 & 615 & 210 & 450 \\
1:20 & 240 & 630 & 245 & 615 \\
1:30 & 235 & 605 & 215 & 510 \\
1:40 & 235 & 595 & 240 & 545 \\
1:50 & 240 & 590 & 220 & 430 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Effect of PBTCA and ACS at different ratios on the workability of concrete.  
trend is decreasing, and when SDP-90:ACS is 1:10 and 1:20, the phenomenon of water secretion occurs.  
In summary, although either PBTCA or SDP-90 compounded with ACS can effectively retard the setting time of waste slurry recycled water, the effect of waste slurry recycled water on the working and mechanical properties of concrete is minimized when using the super retarding additive compounded with PBTCA and ACS, and it can increase the 7 days and 28 days compressive strengths of concrete when PBTCA:ACS is 1:20.