Slags of different sorts may be used in SMA mixtures, providing they meet suitable requirements. For example, in Europe these can be determined in the National
Application Documents for the EN 13043 standard; examples were presented in Table 5.2 (for more information, see Chapter 14). When considering the possibility of using slag in an asphalt mixture, one should remember the following specific properties for these aggregates:
• The density could sometimes be substantially different from that of crushed rock aggregates and can be variable; when designing an SMA mixture using the weight method, differences can manifest themselves in differing volume relations between mixture components.
• The binder content should be determined carefully; a higher density of an aggregate mix usually brings about the necessity for reducing the quantity of binder, but the high porosity of external surfaces of slag grains should also be taken into account.
• The complex chemical composition of slag means that adhesion promoters should be carefully selected and confirmed with testing.
• One of the basic requirements imposed on slag aggregates is an invariability of properties determined during testing called chemical disintegration.
In addition to these properties, some research (Airey et al., 2004) has proven that mixtures with slag aggregates demonstrate very good interlocking characteristics and a relatively high resilient modulus. Conversely, mixtures with slag showed an increased susceptibility to age hardening (in long-term laboratory aging).
Other tests of slag aggregate show very high PSV values, which could be used for designing skid-resistant asphalt mixes.
