Sustainable concrete made with wastewater from different stages of filtration

Reusing natural resources in concrete to create sustainable and environmentally friendly structures becomes more important as the demand for concrete increases annually and as the population grows. Among available resources, wastewater can be an alternative, although its use in concrete needs to be fully explored. In this feasibility study, the micro and macrostructural characteristics of concrete made with wastewater at three different levels of filtration were investigated and the results were compared to the control batch made with potable water. A series of compression tests at six different ages of 1, 7, 14, 28, 56, and 90 days along with water absorption tests, isothermal calorimetry tests, and SEM/EDS tests were performed in this research. The relations between compressive strength and age were determined for different specimens. Results showed that the change in the compressive strength of specimens made with wastewater compared with the control batch was less than 7 % on average. It was shown that the lowest and the highest values of water absorption were for the least and most considered filtration levels of the wastewater. The isothermal calorimetry tests revealed a difference of about 4 % at the heat flow's main exothermic peak between the specimens. Furthermore, isothermal calorimetry and water absorption tests showed a correlation between hydration and water absorption. The SEM tests showed that the specimens made with the least filtration level of wastewater had a denser structure with fewer pores. Results of the compression tests, water absorption experiments and microstructural properties are shown to be consistent with the SEM findings. In general, this study demonstrates that wastewater can be a sustainable alternative to potable water for concrete construction. No significant differences were observed between the test results of specimens made with wastewater and those made with potable water.