Use of untreated phosphogypsum as a raw material for autoclaved aerated concrete preparation

Abstract

Phosphogypsum (PG) is a common industrial waste from the production of phosphoric acid by the wet process. Usually, it requires pretreatment before use due to the presence of impurities. Developing a method that can be directly used to reutilize untreated PG in building materials is thus of great significance. Autoclaved aerated concrete (AAC) has a load-bearing and filling structure, the use of solid wastes as substitutes for siliceous and calcareous materials in the production of AAC has been widely demonstrated. Herein, a new type of AAC was developed by using untreated PG, lime, Al powder, fly ash and cement. The influence of untreated PG content on the foaming process, mechanical properties and hydration products of the final AAC product was investigated through X-ray Diffraction (XRD), Thermogravimetric analysis (TG-DTA), Fourier Transform Infrared spectroscopy (FTIR), Mercury intrusion porosimetry (MIP) and Scanning Electron Microscope (SEM). The results show that the sample with 15% PG content (PG4) exhibited the best performance, with the values of the bulk density and compressive strength being 715 kg/m3 and 7.5 MPa, respectively. In addition, the density range meets the B07 level and the compressive strength exceeds the standard 2.5 MPa (GB/T11968-2020). This study described the effect of untreated PG on the performance of the AAC product, which provides a new approach to use of untreated PG and the production of AAC.