Performance and microstructure of red-mud-blended concrete under different aqueous environments

The effects of aqueous environments on the performances of red-mud-blended concretes (RMCs) were evaluated by measuring their compressive strength, water absorption, and porosity. The pH value, electrical conductivity, and heavy metal concentrations of the immersion solutions were measured to determine the effects of RMCs on the aqueous solutions. The hydration products and microstructures of RMCs were analyzed to determine the effect mechanisms. The results showed that the addition of red mud to concretes increases the apparent porosity and water absorption and decreases the compressive strength. Acidic environments exhibited the most significant effect on the performances of RMCs. In a neutral environment, C-S-H gel generation and a high Si/Ca ratio resulted in enhanced corrosion resistance for the RMC with 35 % red mud, and its compressive strength decreased by 15.07 % after 28 d of immersion. The pH value and electrical conductivity showed a rapid increase, indicating the leaching of soluble alkalis and a large number of ions during soaking. The electrical conductivity showed a rapid increase with the immersion time within 60 d, indicating the leaching out of a large number of ions. The heavy metal concentration and pH value were within the range specified by Chinese standard (DZ/T 0290-2015), which provides many references for evaluating the interaction between RMCs and the aqueous environment.