Faculty of Engineering, University of Shahrekord, P.O.Box 115, Shahrekord, I. R. IRAN
Micro silica (MS) is an extremely fine, spherical powder that is used as an additive for improving concrete performance. It is obtained as a by product of silicon metal and ferrosilicon alloy production. Due to its pozzolanic nature, micro silica can be used to enhance the qualities of both fresh and hardened concrete. Addition of micro silica into the concrete as a cement replacement, decreases its permeability. As a result, it forms very dense and chemically durable concrete to withstand the harsh and corrosive chemical environments.The results of detailed investigations on concrete made from type V cement with addition of micro silica as substituent and its curing by tap water shows dramatic increase is compressive strength (CS) of concrete after 7 days of hydration onwards. By repeating experiment in sodium sulfate solutions (50 gr/lit) prepared under ASTM C1012 requirements, the results were same as tap water but the extend of increase of compressive strength is lower. It is also confirmed that, micro silica modies pore size distribution and permeability of type V cement concreats in same way as reported for ordinary Portlant cement in various literature. By replacing micro silica as a substituent in type V cement composition, a concreat with high chemical durability and strength are formed, which easily can be used as suitable material for harsh environments such as marine and offshore structures or the places where the concentration of sulfate ions are high, such as concrete sewage pipe line networks.
 Aitcin, P. C. ,” Condensed silica fume”, University of sherbrooke, Quebec, Canada, (1983).
 Seishi G. et al., Diffusion of ions through hardened cement pastes, Cem. Concr. Res., 11, p. 751 (1981).
 Midgley, H. G. and Illston, J. M., The penetration of chlorides into hardened cement, Cem. Concr. Res., 14, p. 546 (1984).
 Ozyildirim, C., and Halstead, W., Resistance to chloride Ion Penetration of Concrete Containing Fly Ash, Micro silica, or slag, Permeability of concrete, ACI special Publication SP-100, PP. 35-62, (1998).
 Torij, K. and Kawamura, M., Pore structure and chloride permeability of concrete containing Fly Ash, Blast-Furnace slag and Micro silica, Proceed-ing of the fourth international conference on the use of Fly Ash, Micro silica. Slag and natural pozzolans in concrete, Istanbul. Turkey. V. M. Malhotra, Editor, Vol/ 1. ACi Special publication SP-132, pp. 135-150, (1992).
 Al-Amoudi, O. S. B., Rasheedzzufar, Maslehuddin, M. and Abduljawad S. N., Influence of sulfate ions on chloride induced reinforcement corrosion in Portland and blended cement concretes, Cement, Concrete and Aggregate, 16 (1), p. 3 (1994).
 Taylor, H. F. W., "Cement chemistry" Academic press (1990).
 Bernhardt, C. J, “Silica dust as cement additive”, Betongen Idag, N. 2, pp. 29-53, (1952).
 Markestad, A., “Addition of silica fume to concrete”, Proc. 6th Nordic Concrete Research Congress, Aug. (1969).
 Loland, K. E. and Gjorv, O, E., “Silica fume in concrete” Trondheim, Norway, 8 report June (1981).
 Markestad, A. “An investigation of concrete in regard to permeability problems and factors influencing the results of permeability test”, Ref. 4 Report No. 65A77027, pp. 238-242 (1977).
 Traettberg. A, “Frost action in mortar of blended cement with silica dust” Conf. On durability of building materials and components, ASTM STP 691, 536-548, (1980).
 Sellevold, E. J., Bager, D. H., Klitgaard, J., Jensen, E. and Knudsen, T., “Silica fume cement pastes: hydration and pore structure” Nordisk mini-seminar on silica in concrete, Norwegian Inst. Of Technology, Trondheim, Norway, 1-32 Dec. (1981).
 Bache, H. H. “Densified cement ultra fine particle based materials” Second Int. Conf. on Super-plasticizers in Concrete, Ottawa, 1-35, June (1981).
 Aitcin, P. C. “The use of union carbide slag and fume in concrete” University of Sherbrooke, Quebec, pudding report 11-71, (1971).
 Aitcin, P. C., Pinsonneault, P. and Rau, G., “The use of condensed silica fume in concrete” , Proc. Symp. on Fly Ash, Materials Research Society, Boston, 316-325, Nov. (1981).
 Swamy, R. N., Cement Replacement Materials, Surrey University Press, (1986).