Influence of raw greywater on compressive strength of concrete

Raw greywater, as an alternative water source, was used in concrete production with an aim to save the freshwater sources. Therefore, the variations of compressive strength, the most important and impact causing property of the concrete as regards to its quality and service, were assessed. Greywater was collected from a household where blackwater and greywater were separately disposed of. Total 162-cylinder specimens were cast by using the collected greywater and freshwater (municipally supplied tap water). The specimens were tested for compressive strength after 7, 14 and 28 days of curing. The investigation was carried out considering several experimental conditions: difference in the quality of water in the casting phase, curing phase and casting-curing phase and, also in types of coarse aggregates. A total of 28 water quality parameters (physical, chemical and biological) were tested for both greywater and freshwater. Some tests (turbidity, salinity, solids, organic matter, ammonium, nitrate, phosphate, calcium, magnesium, potassium, sodium, and zinc) exhibited higher (about 2 to as high as 1800 times) and a few others (dissolved oxygen, chloride and iron) showed lower values (about 5 to 8 times) for greywater in comparison to freshwater were decreased. The compressive strength of concrete decreased by about 20 % when greywater was used in the casting-curing phase. Whereas, this reduction was found to be only up to 4 % when greywater was used in the casting phase. Raw greywater could be used in concrete for some specified structures considering its lower strengths as found in this study. But in such cases, the impact of the greywater on other important characteristics of concrete and the consequent changes in the phase-structural parameters of the material also need to be clarified through further research.