This study used liquefied red mud (RM) sludge, an aluminum industry by-product, as a construction material. Accordingly, various methods were examined that used the fabricated liquefied red mud (LRM) as an admixture for concrete, and the mechanical properties of concrete were then evaluated according to the cement type and the amount of LRM. The LRM mixing methods (replacement and addition) were compared, and the slump and compressive strengths of concrete were evaluated for each method. To examine the mechanical properties according to the cement type and the amount of LRM, two types of cement (ordinary Portland cement and slag cement (SC)) were used, and 20 and 40 wt% LRM (with respect to the cement weight) were added. The mechanical properties of the stress–strain curve (SSC), compressive strength, peak strain, and elastic modulus were quantified. When the slump and compressive strength of concrete were considered based on the experimental results, the addition LRM mixing method was recommended as the appropriate method for LRM. As the addition of LRM increased, the mechanical properties of concrete degraded. However, when SC was used, the mechanical properties did not significantly change when different amounts of LRM were added (up to 20%). In addition, the SSC of LRM concrete could be approximated based on the use of the relationship of the compressive strength and peak strain according to the cement type and the amount of LRM.
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