## 1 Introduction
Low replacement levels of silica fume (5-10%) exhibited hydroxyl concentration drop in the pore solution during the first 28 days. Nevertheless, it increases after three months [27]. This long-term release of alkalis was not recorded for blended cements with blast-furnace slag or coal fly ash. It could be attributed to the presence of alumina in these two additions, i.e., alumina incorporation in the C-S-H gel forms C-A-S-H gel with a high alkali-binding capacity [29]. Nevertheless, the effect of the alumina on the alkali-binding capacity is still unclear [25]. There is an aspect in relation to which we can say that the pozzolanic reaction is similar to ASR. Reactive silica in the pozzolanic addition reacts with alkali hydroxides producing alkali-silica gel. Later on, calcium exchanges for sodium and potassium in mentioned gel leading to the formation of C-S-H gel with a low Ca/Si ratio compared to that of the Portland cement pastes. Thus, a shorter turnaround time and the absence of expansion in the pozzolanic reaction is the main difference with the ASR. Absence of expansion is due to the high fineness. This fact allows the alkali-silica gel formed in the pozzolanic reaction to be distributed throughout the blended cement. By contrast, larger aggregates form some local deposits of alkali-silica gel that turn into areas of expansion [14]. Summing up, the use of some Portland cement constituents, such as silica fume, metakaolin and siliceous fly ash, was found effective in mitigating ASR deleterious effects [24; 25]. The reasons for mentioned positive performance can be summarized as follows:  
* Reducing the clinker content in the blended cement, the concentration of alkali metals is lowered in the pore solution (dilution effect). * The additional pozzolanic calcium silicate hydrates formed (for short C-S-H gel), with lower Ca/Si ratio, provides a larger amount of nucleation sites for alkali's absorption, i.e., higher alkali binding capacity is achieved, then limiting the ASR gel production [26]. This C-S-H gel partially fill the capillary pores densifying the cement paste and the interfacial transition zone (ITZ) [27]. * The reduction of permeability and diffusivity of the mortars and concretes by densification the cement paste and ITZ enhanced by the pozzolanic reaction, lowers the external alkalis and water ingress through the capillary pores. * Mentioned pozzolanic materials also have a great influence on the of ASR gel properties. For instance, [PERSON] et al. [28] reported that gels with high CaO/Na\({}_{2}\)O\({}_{\text{eq}}\) ratio exhibited lower swelling capacity than gels with low CaO/Na\({}_{2}\)O\({}_{\text{eq}}\) ratio. Accordingly, silica fume and coal fly ash shrink the swelling capacity. * Finally, [PERSON] and [PERSON] reported that the presence of Al in C-S-H gel improves the alkali binding capacity [29]. Therefore, the alumina from the coal fly ash can be dissolved into the mortar or concrete pore solution and further incorporated into the C-S-H gel during the hydration of the cement and the pozzolanic reactions involved in the C-A-S-H gel formation. Nevertheless, high levels of aluminum which may be present in the pore solution could deplete the silica dissolution rate [30], due to the aluminum absorption on the silica surfaces leading to an aluminosilicate layer generation [31]. Consequently, the main objective of this work is to assess the effect of natural pozzolan, P, siliceous coal fly ash, V, silica fume, D, and blast-furnace slag, S on the suppression of ASR-induced expansion in mortar specimens made using one alkali-bearing reactive aggregate, one moderate reactive aggregate and one alkali-free non-reactive aggregate.