High-Strength, Cement-Free Concrete of Flue Gas Desulfurization Gypsum-Based Non-Fired Brick

A high-strength, cement-free concrete, non-fired brick was prepared merely using waste flue gas desulfurization (FGD) gypsum, river sand, and water with a cost-effective technology. The processing procedures consisted of drying FGD gypsum, mixing the dried power with river sand, adding water, stirring, press-forming, spraying water, and naturally curing. The results revealed that the optimal content of FGD gypsum was as high as 75%, and the economical press-forming pressure was just 10 MPa (1.45 ksi). Furthermore, the 7-day compressive strength of the as-prepared non-fired brick was up to 34 MPa (4.93 ksi), which was far beyond the property requirements of the highest grade (MU25) of non-fired rubbish gangue bricks stated in the Chinese standard (JC/T422-2007). The excellent characteristics resulted from the dense macrostructure of brick body formed by press-forming and the interlocking microstructure of dihydrate gypsum crystals attained by water-spraying and naturally curing.