Main Ingredient Of Cement | Main Component Of Cement Cement is primarily composed of lime (Cao), silica (SiO2), alumina (Al2O3), and iron oxide (Fe2O3). These ingredients react in a clinker production process to form specific compounds that are essential for cement's binding properties. The percentages of these ingredients can vary slightly, but generally, lime makes up 60-65%, silica 19-25%, alumina 3-8%, and iron oxide 1-3%