ABSTRACT
This chapter examines the different types of ultrafine particle and their mixture. The manufacture of very high strength concrete (28-day compressive strength higher than 80 MPa) often involves the addition of ultrafine particles together with large proportions of organic admixtures. The chapter compares the effectiveness of different fillers and their mixture. Then, the case of silica fumes is studied in greater detail, considering the amounts to be used and their performance in relation to their chemical composition. Silica fumes are found to be the most effective addition, and they are looked into more particularly in terms of their effect on the properties of mortars according to their proportion (optimum proportion) and quality (chemical composition). Silica fume is a by-product of the manufacture of silicon and of its alloys. Depending on the composition of the alloys, on the secondary products added to the main constituents, on the manufacturing method, silica fume properties can vary considerably.
