The Internet of Things is set to bring value to a broad range of networked applications. However, its high heterogeneity, scale, and connectivity will also carry challenging security risks. The advent of blockchains encompassing promising function and security features has paved the way for the development of several tailored solutions. This paper presents a survey on IoT-focused blockchain technologies targeting multiple industrial applications. A critical discussion regarding their limitations is also explored. Complementarily, key blockchain concepts, and their technical mapping are examined for completeness.