Seawater desalination has the potential to reliably produce enough potable water to support large populations located near the coasts. This process results in the production of a hypersaline waste by-product known as reject brine. Reject brine generally has significantly higher total dissolved solids (> 30,000 ppm) compared to seawater (> 15,000 ppm). In many locations, this reject brine is dumped back into the ocean, and this has potentially detrimental effects on water quality and marine life. It is hypothesized that using the reject brine as a portion of the total mixing water for casting concrete would be significantly beneficial for the economy and environment. This study was carried out to investigate whether simulated reject brine could potentially be used to manufacture cementitious materials. The effects of different concentrations of simulated reject brine on hydration kinetics, strength and drying shrinkage of cement paste and mortar were investigated. Cement paste and mortars were prepared with water-to-cement ratio 0.45 and mixed with simulated reject brine, tap water, and diluted reject brine (an equal mass mixture of reject brine and tap water). The results showed that the reject brine causes an acceleration of the early cement hydration and strength, however, this effect is negligible at later ages. The reject brine caused a drastic increase in the shrinkage. The differences between the results obtained using reject brine and diluted reject brine were generally insignificant. While these results are preliminary, they suggest that reject brine may be used to make unreinforced concrete or concrete reinforced with non-corrosive materials, provided shrinkage may be mitigated.

Authors: Nima Hosseinzadeh, Prannoy Suraneni