Hitherto, this book has focused primarily on ordinary aggregates for use in the normal concretes that make up about 90 per cent of concrete production. However, with the advent of a new generation of concrete admixtures, combined with a much better understanding of the fundamental mechanisms governing concrete rheology, strength, cracking, and durability, we can now largely 'tailor-make' concretes to provide the precise properties required for a particular project. In this chapter, we will examine the aggregate requirements for some of the special concretes listed in Table 7.1, for which the aggregate properties are particularly important.