Study on cement mortar modified with co-calcined rice husk and red mud: mechanical and electromagnetic absorption performance

The use of co-calcined rice husk (RH) and red mud (RM) in cement mortar was investigated in this study. The effects of these additives on mechanical properties, electromagnetic shielding performance and environmental benefits were systematically analysed. The addition of calcined RH and RM notably improved the compressive strength of the cement mortar and exhibited strong electromagnetic wave absorption capabilities, particularly in the mid-frequency range. Under optimal conditions (5% dosage with RH and RM co-calcined at 800°C), the compressive strength increased by 3.03% at 7 days and by 8.33% at 28 days as compared with the control mortar. The material exhibited six absorption bandwidths spanning from low to high frequency, with the strongest absorption peak at 10.73 GHz, a reflection loss of −37.8 dB and an absorption bandwidth of 0.71 GHz (<−10 dB). Based on the principles of sustainable design, RH and RM, as agricultural and industrial wastes, were repurposed to develop a cement-based composite material that balances structural strength and electromagnetic absorption.