This article presents the results of a study dealing with the utilization of sludge water from a concrete plant as a partial replacement for mixing water in the production of cement composites. The replacement of mixing water with sludge water from a concrete plant was carried out in the amounts of 20% and 50%. The following tests were carried out in order to determine the effect of the replacement of mixing water with sludge water from a concrete plant on the physical and mechanical properties of the cement composites: cement mortar consistency, beginning and end of setting, strength characteristics (compressive strength and flexural strength), and thermal properties. The measured values of the strength characteristics of the test specimens after 28 days of age confirm the possibility of replacing mixing water with sludge water from a concrete plant without significantly reducing the compressive and flexural strength.

This paper presents the results of research dealing with the use of recycled waste sludge water from a concrete plant (CP) as partial or complete replacement of mixing water in cement mixtures. The need to recycle waste sludge water generated as a by-product (waste sludge water) during the production of fresh concrete in the concrete plant results from the environmental and economic problems associated with the operation of the concrete plant. Mixing water was replaced with recycled waste sludge water in the amount of 25%, 50%, 75%, and 100%. In order to determine the effect of partial or complete replacement of mixing water with waste sludge water from the concrete plant in the production of cement composites, laboratory tests of waste sludge water were carried out to determine whether the waste sludge water complies with the requirements for mixing water defined in CSN EN 1008. The tests also determined the properties of fresh cement mortar and hardened cement composites. These were tests of the beginning and end of cement mortar setting, and the strength characteristics (flexural strength, compressive strength). The results of these tests show that it is possible to replace the mixing water by waste sludge water from the concrete plant in the amount of up to 25% without significantly affecting the tested properties, in comparison with the formula containing pure mixing water.

This paper presents the results of a research dealing with the testing of the properties of wastewater forming during the production of concrete mixture in a concrete plant. The test results are compared with the limit values of concrete mixing water according to ČSN EN 1008 in order to use this waste water as a partial replacement of mixing water during the production of concrete.

This article presents the results of a research dealing with the effect of CO ₂ on cement composites prepared on the basis of waste sludge water from the concrete plant. The designed formulas R1 and R3 use waste sludge water from the concrete plant as a partial or complete replacement of mixing water in the production of cement composites. The mixing water was replaced by waste sludge water in the amounts of 25%, 50%, 75% and 100%. Laboratory tests that are defined in ČSN EN 1008 standard were performed in order to determine the effect of partial or complete replacement of mixing water. The test specimens were further subjected to the effect of CO ₂ in the Lamart laboratory chamber, where the effect of CO ₂ was simulated for the period 50 years. Subsequently, the cement composites were tested for their strength characteristics (tensile flexural strength, compressive strength) and subjected to a mineralogical analysis. The results show that the effect of CO ₂ will reduce the strength characteristics of the composite compared to the comparative samples.

This article presents the results of a research dealing with the use of waste water from concrete industry as a possible substitution of mixing water during the production of cement composites. This experimental research involved the preparation of two recipes of cement composites, named R1 and R3. Mixing water in these recipes was replaced with waste water from a concrete plant in the amount of 25, 50, 75 and 100%. Samples of recycled waste water, which were tested for the content of sulphates, chlorides and alkali according to ČSN EN 1008, were taken in order to determine the properties of waste water from a concrete plant. The prepared test specimens were tested for frost resistance after 100 freezing cycles according to ČSN 73 1322. The results of the frost resistance test showed that the required value of the frost resistance coefficient of 0.75 according to ČSN 73 1322 was achieved only in case of recipe R1 based on Portland cement CEM I 52.5R and 75 and 100% substitution of the mixing water with recycled water from a concrete plant.