Despite the many advantages of fresh concrete compression technique for improving the performance of hardened concrete under compression, no study has so far addressed various behavioral aspects of this type of concrete in different conditions and scenarios such as fire, which may occur during the service life for a structure made up of this concrete type. Here, the compressive performance of compressed concrete with steel fibers was addressed before and after experiencing elevated temperatures considering key variables including the volume quantity of steel fibers, diameter-to-thickness ratio of steel tube (mold), capacity of the reference concrete, and exposure temperature. To reach this goal, 60 concrete cylinders were tested under axial compression, and the results including the compressive strength, elastic modulus, strain at peak stress, toughness, axial stress–strain graph, and weight loss were assessed together with the results of a visual inspection, failure mode, and microstructure of concrete. The results demonstrated that although the fresh concrete compression technique notably improved the mechanical features of concrete, especially the compressive strength by up to 100 % at the ambient temperature, adding steel fibers, lowering the water-to-cement ratio (w/c), and using a tube with a thinner wall as the mold lowered the efficiency of this technique in improving the compressive performance. In addition, the amount of increase in concrete strength due to compressing the fresh concrete had a linear relationship with the amount of excess water removed from it. The positive impact of the fresh concrete compression technique on the concrete strength at high temperatures was significant. In this regard, the compressive strength reduction of the compressed concrete was 20 % lower than that of the uncompressed concrete. However, the fresh concrete compression technique was not very effective against the deterioration of the modulus of elasticity caused by high temperatures. Ultimately, the response surface method (RSM) was used to reach an optimum solution for the design variables that could maximize the compressive capacity of fibrous compressed concrete per different target temperatures.
