## 4 Conclusions  
This paper presents the results of an experimental research of the possibility of an effective use of recycled waste sludge water from CPs. Waste sludge water is mostly a product of agitation truck rinsing. The aim of the research was to understand the properties of the waste sludge water from the CP plant in order to assess the possibility of its use as mixing water in the production of cement composites. Based on the presented results of the experimental research, we can draw the following conclusions:  
* The replacement of pure mixing water with waste sludge water from the CP in the amounts of 25%, 50%, 75%, and 100% is possible, because the properties of the waste sludge water from the CP meet the limit requirements for mixing water stipulated in CSN EN 1008 (see Table 1).
* The replacement of mixing water with 25%, 50%, 75%, and 100% of waste sludge water from the CP affects the consistency of the fresh concrete mixture when using CEM I 52.5R and CEM II/B-LL 32.5R as the binder. The higher the replacement, the lower the diffusion value and there is also a negative impact on the workability of the fresh cement mixture.
* Replacing the mixing waste sludge water with 25%, 50%, 75%, and 100% of water from the concrete plant will accelerate the initial setting time and shorten the final setting time of the mixture when using CEM I 52.5R and CEM II/B-LL 32.5R as the binder. Another factor affecting mortar workability may be the increased chloride content in waste sludge water from the concrete plant, which may accelerate the initial setting time as indicated in [21]. This phenomenon can be suppressed by the addition of a suitable plasticizer or superplasticizer.
* Replacement of mixing water with, in the amounts of 25%, 50%, 75%, and 100%, waste sludge water from the concrete plant when using Portland cement CEM I 52.5R (Formula R1):
* Does not significantly reduce flexural strength after 28 and 90 days of age.
* Causes a decrease in compressive strength after 28 days (maximum by 12.5%), but after 90 days, there is an increase in strength (maximum by 18%) compared to a comparative formula without waste sludge water from the CP.
* In terms of the results of the strength characteristics, 75% replacement of pure mixing water with waste sludge water from the CP shows the best results.  
Figure 8: Compressive strength of formula R3 with 25%, 50%, 75% and 100% of mixing water replaced with waste sludge water from the CP.  
Replacement of mixing water with waste sludge water from the CP in the amounts of 25%, 50%, 75%, and 100% while using Portland CEM II/B-LL 32.5R mixed cement (Formula R3): 1. Increases the flexural strength after 28 days for 25% and 75% replacement of pure mixing water with waste sludge water from the CP, and the same trend is seen in case of flexural strength after 90 days. 2. Increases the compressive strength after 28 days for 25% and 75% replacement of pure mixing water with waste sludge water from the CP. After 90 days, the compressive strength of all mixing water replacements with waste sludge water from the CP will be increased. 3. The research results show that despite the acceleration of the hydration process at the initial setting time, this process continues after 90 days and increases the strength of the tested samples. 4. In terms of the results of the strength characteristics, 75% replacement of pure mixing water with waste sludge water from the CP shows the best results.  
[PERSON] and [PERSON] conceived and designed the experiments; [PERSON] performed the experiments. [PERSON], [PERSON] and [PERSON] analyzed the data; [PERSON], [PERSON], [PERSON] contributed reagents/materials/analysis tools. [PERSON], [PERSON], [PERSON] and [PERSON] wrote the paper.  
This research was funded by VSB-TUO, Faculty of Mining and Geology--grants numbers SP2018/12, SP2019/29; Moravian-Silesian Region--grant number RRC/10/2018; The Ministry of Education, Youth and Sports--National Sustainability Program I--grant number LO1406.  
The authors declare no conflict of interest.