In recent years, blended cement—cement into which additional constituents are mixed—has been widely produced with the aim of reducing environmental impact. According to JIS (Japanese Industrial Standard) R5211, blast furnace cement mixed with Blast Furnace Slag (BFS) is classified into three types according to the mixing ratio of BFS: Type A (from 5 to 30%), Type B (from 30 to 60%), and Type C (from 60 to 70%). Type B blast furnace cements mixed with 40–45% BFS are popular blast furnace cements. For quality control of blast furnace cement, quantitative analysis of BFS is normally performed by the Rietveld refinement combined with a standard material because BFS is an amorphous component. In this example, BFS in blast furnace cement was quantified by Rietveld refinement using the reference intensity ratio (RIR) without a standard material. The RIR value of the amorphous component was calculated from a simulated blast furnace cement with known content.