Effect of Amorphous Silica–Forming Additive on Porosity and Mechanical Strength in Autoclaved Aerated Concrete Thermal Insulation Board

Autoclaved aerated concrete (AAC) thermal insulation board has a density of 130–155 kg/m³, a compressive strength above 0.4 MPa and a thermal conductivity value of 0.045 W/m.K. It is a Class A non-combustible, mineral-based and non-toxic material and used for thermal insulation from the outside, inside, in the middle, underground, on floors, and roof surfaces. The porous structure of the material decisively affects its mechanical and thermal conductivity properties. In this study, the potential for pore size reduction was evaluated by adding ratios of 0%, 0.1%, 0.25%, 0.5%, 0.75% and 1% amorphous silica-forming additive to the AAC thermal insulation board by mass. Furthermore, the mechanical performance was compared with the corresponding pore size characteristics. In determining the pore distribution, the air pores in the structure were examined by image analysis technique based on the Monte Carlo approach. When the density and compressive strength of the samples obtained after hydrothermal curing were compared with the A value, it was observed that the highest increase was 29.94% with a 1% additive rate. Scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses showed that the amount of tobermorite increased continuously up to a dosage of 0.5%. The fact that the addition of the admixture by mass reduces the pore diameter, reduces density and increases compressive strength reveals that the amorphous silica-forming additive is usable in AAC thermal insulation board. Achieving the same compressive strength with less material during the production phase and reducing per-unit energy consumption during service due to improved thermal insulation associated with smaller pore sizes are critical for lowering the carbon footprint.