Heavyweight concretes are an attractive alternative when heavyweight elements need to fill reduced spaces, because they present high densities and are able to take different forms according to the container where they are casted. The intended application for the heavyweight concrete referred to in this work is a power converter, which is a floating system that generates power through the waves of the sea. The design of this converter considers the use of elements of high mass at both ends of a metallic oval structure. Therefore, a heavyweight concrete with density of 4,000 and 4,500 kg/m3 was developed. For heavyweight concrete production with densities as high as the ones needed, it is necessary to use artificial aggregates of steel grit or corundum. Natural heavyweight aggregates such as hematite, magnetite or barite allow achieving maximum densities around 3,800 kg/m3, being unsuitable for the required application. For this reason, grit coarse aggregate 6-8 mm was used and a portion of the sand was replaced by a corundum fine aggregate 0.5-1.5 mm, being these materials out of the standard applications. In addition to the density requirements, consistency of the fresh concrete is also important as the use of heavyweight aggregates, whose density differs from the density of the mortar or paste, may lead to segregation of the mix. Due to the particularities of the concrete, the mix-design process was oriented to the specific application and quantitative and qualitative requirements were evaluated such as concepts related to the availability of the component materials, accessibility to the production area and casting. Therefore, the aim of this work is to present the considerations made during the mix-design process as well as the characterization of the heavyweight concretes produced, which showed results in agreement with the pre-established requirements.