The application of small sized ferromagnetic fillers provides a combination of high bulk density, increased strength and ferromagnetic properties of composite materials. If such materials are produced on the cement basis, the total strength of the composite can be compromised by poor adhesion of metal particles with the cement matrix. Potentially, the use of versatile additives like microsilica and metakaolin is able to improve the structure and mechanical properties of heavy concretes with ferromagnetic properties. The paper considers results of a study using specimens of heavy concretes with small sized ferromagnetic fillers aiming to estimate the structure, porous spacing and strength. Ultrasonic measurements, optical microscopy and compressive strength tests were used in the study. Characteristic features of the coupling of ferromagnetic particles with the cement matrix and fracture surfaces were revealed. It was found that the contact of metal fillers with the cement is not perfect, since the porous spacing appeared between them and the cement matrix during the cement hydration process (exothermal reaction). Due to the border porosity, the specimens with the metal fillers have lower compressive strength, lower ultrasound velocity and increased frequency slope of attenuation. Microsilica and metakaolin additives facilitate better contact zone between the cement matrix and metal fillers.