Recycling of waste materials plays a significant role in waste management strategies, but the interactive properties of recycled aggregates in concrete have been considered by only a few researchers. The experimental study reported in this paper focused on the effects of recycled concrete aggregate (RCA) and waste glass (WG) on the properties of concrete. The response surface methodology was used to optimise and model the results of tests for compressive strength, tensile strength, slump, water absorption, electrical resistivity and hardened unit weight. The effective variables of the experiment were RCA (0–65%) as coarse aggregate replacement and WG (0–40%) as fine aggregate replacement. The results obtained indicate that high volumes of waste materials could be used in concrete without a significant reduction in the mechanical and durability (namely water absorption and electrical resistivity) properties of the concrete. Moreover, when WG was substituted in the mixture, the water absorption, electrical resistivity and workability of the concrete improved and the use of RCA had a significant influence on the mechanical properties of the concrete. Based on statistical analysis, all the proposed models were adequate, with coefficients of determination above 0·95. The optimum condition in which all response targets performed properly was found to be 17% of RCA and 35% of WG.

No abstract

Background and purpose: Excessive amount of heavy metals in industrial wastewater is a seriously crucial issue and requires efficient methods to be introduced and dealt with. Meanwhile, steel making plants as productive units in every country release large amounts of fluid into surface and underground sources. Typically, this wastewater contains heavy metals in minor amounts, while this amount could cause severe damages to the living organisms. Materials and methods: In this study, removing iron, manganese, zinc and total dissolved solid in a typical wastewater resulted from steel making plant was considered using reverse osmosis (RO) and nanofiltration (NF) membranes. At first, different pH values and operating pressures were applied to the wastewater. Then, these parameters were evaluated for a wastewater only containing iron to compare the interaction of other elements in iron removal. Results:The results indicated that RO and NF membranes could successfully treat industrial wastewater containing several heavy metals with high concentrations of Fe, Zn and Mn, especially at optimum pH and pressure. Moreover, the interaction of other heavy metals and components in the influent decreased the efficiency of RO but improved the NF efficiency to remove iron. To have a better image, a formula was proposed for each method to represent the influence of the parameters on removal rates. Finally, cost estimation for both procedures showed that RO was not economicallytechnically efficient in comparison with NF. Conclusion: NF showed an acceptable performance with high water flow which made it more suitable for industries. At the end, the relative cost analysis showed that even if the initial price of NF is high, the energy consumption and total cost of RO will be higher.