Effects of active mineral admixture on mechanical properties and durability of concrete

The purpose of this study is to figure out the effects of the active mineral admixture on the mechanical properties and the durability of the concrete. In this paper, the orthogonal test was adopted to study the effects of the metakaolin, the ultra-fine fly ash, and the silica fume on the compressive strength and the splitting tensile strength of the concrete at various curing ages, and to further determine the optimal mix ratio. After that, the ordinary concrete was taken as the control group, the Na _2 SO _4 solution and the MgSO _4 + NaCl solution were used as the corrosive medium, and the dry-wet alternation method was adopted to make comparison and micro-analysis on the durability degradation processes of both the admixture concrete with optimal mix ratio and the ordinary concrete in the two solutions as mentioned above. The results show that: as for the concrete mechanical properties, the metakaolin shows the most significant and positive effects on the concrete cured for 7d-14d, while the silica fume affects the concrete with 28 d curing age most. The mechanical properties of the concretes at various curing ages reach their optimal levels when it is added with 10% metakaolin, 15% ultra-fine fly ash, and 3% silica fume. For the concrete durability, the application of mineral admixture could greatly improve the concrete capability in resisting the SO _4 ^2− corrosion. However the complex ions have destructive effects on the mineral admixture concrete. Compared with the ordinary concrete, it shows the most significant growth of corrosion product M–S–H, faster reduction of mechanical properties, and loose and porous micro-structure.