CONTRADICTORY EFFECTS OF SILICA FUME CONCRETES IN SULFURIC ACID ENVIRONMENTS

In certain industrial activities sulfuric acid is used during the production process, which may cause degradation of concrete structures. Another important phenomenon where sulfuric acid is responsible for concrete corrosion is biogenic sulfuric acid corrosion, which occurs often in sewer systems. Therefore, researchers used sulfuric acid solutions to simulate of such aggressive environments. Also, they used suitable cement replacement materials such as silica fume to improve acid resistance of concretes. But some researchers reported lowest susceptibility of concrete containing silica fume to corrosion at such environments while the other groups reported unsuitable performance of silica fume. In this paper, control specimens and specimens containing 8% silica fume as cement replacement materials were immersed in sulfuric acid solutions with pH of 1.0 and 2.0. The dense packing of siliceous aggregates and cementitious materials were used to achieve low porosity concretes. They were periodically examined for appearance and measured for mass change up to 315 days. Total porosity of samples at the age of 90 days was measured. Results show that the porosity plays an important and twofold role in the mass loss of mortar specimens immersed in sulfuric acid solutions. In low pHs such as 1.0 corrosion rate of low porosity concretes is more than that of high porosity concretes. But, in the high pHs such as 2.0 corrosion rate of low porosity concretes is less than that of the high porosity concretes. In the low and high pHs of sulfuric acid solutions internal and external or surface degradations were observed respectively. Contradictory results were obtained for the concretes containing silica fume because of its effect on the porosity and the production of silica gel at ITZ by reacting of portlandite. Investigations by optical microscopy on thin section samples indicate that the use of silica fume makes mixtures more homogeneous and hence lowers the corrosion rate in sulfuric acid environments.

کلیدواژه ها:

silica fume ، sulfuric acid attack ، dense concretes ، porosity