Preparation and Characterization of a Novel Nonautoclaved Aerated Concrete Based on Magnesium Phosphate Cement

In this study, nonautoclaved aerated concrete (NAAC) was produced by a chemical foaming method to reduce energy consumption during the autoclaving of traditional autoclaved aerated concrete. Magnesium phosphate cement and sodium bicarbonate were used as the cementitious material and foaming agent, respectively, for NAAC fabrication at ambient temperature (20°C±2°C). The influence of water–binder ratio and different contents of borax, calcium stearate, and sodium bicarbonate on the mechanical properties of NAAC were investigated. Furthermore, the phase composition and microstructure of NAAC specimens were characterized via X-ray diffraction and scanning electron microscopy. Results show that the optimal mechanical properties were obtained when the water–binder ratio was 0.14, and the specific contents of borax, calcium stearate, and sodium bicarbonate were 6.0%, 0.20%, and 1.0%, respectively. The optimal dry density, compressive strength, and specific strength were 647 kg/m3, 3.70 MPa, and 5,720 N·m/kg, respectively. K-struvite was the main source of NAAC strength, and it attached to the surface of unreacted magnesium oxide particles to form the microstructure of NAAC. The dense structure formed by the overlapping of K-struvite was conducive to the improvement of the mechanical properties of NAAC. Thus, lightweight, high-strength, energy-saving, and ecofriendly NAAC has potential applications as a wall material.