**3.4 Blast furnace slag**

Blast furnace slag is produced by grinding the glassy granular by-product of the steel industry. The fine ground blast furnace by-product is highly cementitious and contains calcium silicate hydrate (C-S-H), which enhances the strength of the hardened concrete, and improves its durability and appearance. Coarse and ground slag particles are shown in **Figure 5.**


#### **Table 3.**

*Typical composition of Ductal [11].*

**Figure 5.** *(A) Granular slag particles and (B) ground slag particles.*
