Investigating the Technical Suitability of Gray Water in Concrete Production Based on Physical and Mechanical Properties

This research investigated the suitability of gray water as a non-conventional water source in the concrete production. The findings showed that both gray and tap water can be considered as mixing water, but based on water quality indicators for industry usage, gray water cannot be used without restrictions to build reinforced concrete structures due to its high corrosive ability. Gray water had no significant effect on the slump and setting time of the concrete. The compressive strength of concrete made with tap water increases from 7 days to 28 days, while gray water concrete, after an increasing trend from 7 days to 14 days, reached its lowest value at 28 days (28.1 MPa). This decrease is due to high TDS values and impurities, which can lead to a decrease in compressive strength. Gray water concrete showed a significant loss in tensile strength compared to tap water concrete after 28 days of curing. The P-wave velocity of the tap water concrete sample increased with the increase in curing time, while the gray water sample decreased by 13% in 28 days. Microscopic studies revealed the formation of carbonate halos around carbonate aggregates due to alkaline reactions in both tap and gray water concretes. The carbonate halo has developed to the inner parts of the aggregates in the gray water sample, indicating greater intensity of alkaline reactions. This means the long-term strength of the concrete will likely suffer a significant loss.