Investigation of the effects of different sulfate types found in seawater on concrete containing micro fiber and silica fume

Abstract

Sulfate salts which available in seawater with high concentrations cause the formation of ettringite in hydrated structures which formed as a result of the hydration of cement. On the other hand, ettringite causes excessive volume expansions and eventually leads to cracking of the concrete due to the internal stresses in concrete since it is a large volume mineral structure. In this study, ultra fine cement and silica fume as mineral additive were used together for binder design. In addition, micro fiber has been added to the binder systems produced in different proportions. The produced specimens were kept separately in water, in solutions containing 2% Na2SO4 and 2% MgSO4 by weight for 90 days. The compressive strength test was performed at 28th and 90th days on cured specimens. In addition to the compressive strength test, the solution samples were taken from the curing solutions every 10 days and the concentrations of sulfate ions were also examined in the solutions. According to the results, more strength loss was observed in the specimens cured in MgSO4 solution. In parallel to this result, both the concentrations of SO42-ions in the MgSO4 solution were lower than those in the NaSO4 solution and no significant decrease was observed in the compressive strength of the specimens cured in NaSO4 solution, because the fibers can compensate the internal stresses. This situation shows that especially the micro fiber additive can compensate the expansion that will occur as a result of ettringite formation, and thus it can help the mechanical stability of the concrete.

Keywords

• sulfate attack
• ultra fine cement
• micro fibers
• sulfate concentration
• concrete