There has been an increase in construction with three-dimensional (3D) printing technology but 3D printed (3DP) structures also require weight reduction similar to conventional reinforced concrete structures. In addition, the behaviour of this type of structure against fire needs to be investigated. The number of printed layers and the time gap between layers for the 3DP specimens were among the variables examined. The test results demonstrate that as the replacement percentage of natural sand (NS) with expanded perlite (EP) increased, at 25% volume of replacement, the interlayer bond strength increased on average by 18.6%, while at the highest replacement level, of 75%, the strength decreased on average by 5.8%. Additionally, by incorporating EP, the compressive and flexural strengths of 3DP specimens declined on average from 9% to 29.7%, and from 39.3% to 49.3%, respectively. As the replacement level of NS increased, residual compressive and flexural strengths increased after exposure to 800°C. Furthermore, it was demonstrated that exposure to high temperature had the least effect on interlayer bond strength, whereas it significantly reduced the compressive and flexural strength. The results show that increasing the time gap between layers reduced interlayer bond strength and flexural strength while negligibly affecting compressive strength.
