Polypropylene fibers were added (1.8 kg/m(3)) to a grit-free cement grout setted then for 30 days at 20 degrees C, heat treated at 100-600 degrees C and studied for tensile strength after cooling down to the room temp. The addn. of fibers resulted in decreasing the strength of the concrete after setting. After heat-treatment, the fibers-contg. concrete samples showed higher tensile strength than the fiber-free ones.