The compressive strength of silica fume concretes was investigated at low water-cementitious materials ratios with a naphthalene sulphonate superplasticizer. The results show that partial cement replacement up to 20% produce, higher compressive strengths than control concretes, nevertheless the strength gain is less than 15%. In this paper we propose a model to evaluate the compressive strength of silica fume concrete at any time. The model is related to the water-cementitious materials and silica-cement ratios. Taking into account the author's and other researchers’ experimental data, the accuracy of the proposed model is better than 5%. 1. Introduction The use of silica fume in combination with a superplasticizer is now a usual way to obtain high-strength concretes. The improvement of mechanical properties of concretes with silica fume accounts for the increasing consumption of this admixture in concrete. Furthermore, apart from mechanical properties, the durability of high-performance concretes concerning the most common harmful ions (sulfate, chloride, and seawater) is also improved; indeed the reduction of permeability which is due to the more compact microstructure of concrete slows down the diffusion of ions. Nevertheless various authors point out some drawbacks regarding the use of silica fume in concretes. Among these, the loss of plasticity during the production of concrete and the great sensitivity to plastic shrinkage during the initial curing are the most important. However, researchers seem to disagree about the interpretation of the exact role silica fume plays in the increase of mechanical strengths. Some authors claim that silica fume improves the strength of the bond between the aggregates and the cement matrix [1–5]. The partial replacement of cement by silica fume increases the strength of mortar and concrete; yet it does not seem to have an important impact on the strength of pure cement paste. To other researchers, however, the positive result due to the admixture of silica fume stems from the increase in strength of the cement matrix [6, 7]. Researchers also disagree about the definition of the optimal content of silica fume which enables to obtain the highest strengths. To some researchers [8, 9], the content is about 15% whereas to others [5, 10] the increase in compressive strength may be reached at 30% to 40% of replacement of cement by silica fume. In this study we aim at defining the influence of the content of silica fume on the compressive strength of concrete. Moreover, we introduce a prediction model of the compressive
H. Cheng-yi and R. F. Feldman, “Influence of silica fume on the microstructural development in cement mortars,” Cement and Concrete Research, vol. 15, no. 2, pp. 285–294, 1985.
S. L. Sarkar and P. C. A？tcin, “Dissolution rate of silica fume in very high strength concrete,” Cement and Concrete Research, vol. 17, no. 4, pp. 591–601, 1987.
H. A. Toutanji and T. El-Korchi, “The influence of silica fume on the compressive strength of cement paste and mortar,” Cement and Concrete Research, vol. 25, no. 7, pp. 1591–1602, 1995.
X. Cong, S. Cong, D. Darwin, and S. L. McCabe, “Role of silica fume in compressive strength of cement paste, mortar, and concrete,” ACI Materials Journal, vol. 89, no. 4, pp. 375–387, 1992.
V. Yogendran, B. W. Langan, M. N. Haque, and M. A. Ward, “Silica fume in high-strength concrete,” ACI Materials Journal, vol. 84, no. 2, pp. 124–129, 1987.
M. N. Sautsos and P. L. J. Domone, “Strength development of low water-binder ratio mixes incorporating mineral admixtures,” Utilization of High-Strength Concrete, vol. 2, pp. 945–952, 1993.
V. M. Malhotra and G. G. Carette, “Silica fume concrete—properties, applications, and limitations,” Concrete International, vol. 5, no. 5, pp. 40–46, 1983.
E. J. Sellevold and F. F. Radjy, “Condensed silica fume (Microsilica) in concrete: water demand and strength development,” Fly-Ash, Silica Fume, Slag and Other Mineral By-Products in Concrete ACI SP-79, 1983.
J. P. Ollivier, A. Carles-Gibergues, and B. Hanna, “Activite pouzzolanique et action de remplissage d'une fumee de silice dans les matrices de beton de haute resistance,” Cement and Concrete Research, vol. 18, no. 3, pp. 438–448, 1988.
P. C. A？tcin, J. Baron, and J. P. Bournazel, “Viser une résistance à la compression,” in Dans les Bétons, Bases et Données pour leur Formulation, p. 294, Paris, France, Eyrolles, 1996.
H. H. Bache, “Densified cement ultrafine particle-based materials,” in Proceedings of the 2nd International Conference on Super-Plasticizer in Concrete, pp. 185–213, Ottawa, Canada, June 1981.
C. Bedard, G. Ballivy, and P. C. A？tcin, “R？le des caractéristiques physico-mécaniques des granulats sur la résistance en compression des bétons à très hautes résistances,” Bulletin de l’Association Internationale de Géologie de l’Ingénieur 30, Paris, France, 1984.
G. G. Carette and V. M. Malhotra, “Long-term strength development of silica fume concrete,” in CANMET/ACI, Fly, Silica Fume, Slag and Natural Pozzolans in Concrete, vol. 2 of ACI SP132-55, pp. 1017–1044, 1992.
F. de Larrard, “Prévision des résistances en compression des bétons à hautes performances aux fumées de silice ou une nouvelle jeunesse pour la loi de Féret,” Annales de l’ITBTP, no. 483, 1990.
J. Djellouli, P. C. A？tcin, and O. Chaallal, “Use of ground slag in high-performance concrete,” in High-Strength Concrete, vol. 2 of ACI SP121-18, pp. 351–368, 1990.
R. Le Roy, Déformations instantanées et différées des bétons à hautes performances, Ph.D. thesis, L’ecole nationale des ponts et chaussées, Paris, France.
V. E. Sorensen, “Freezing and thawing resistance of condensed silica fume (Microsilica) concrete exposed to deicing chemicals,” in CANMET/ACI Fly, Silica Fume, Slag and Natural Pozzolans in Concrete, vol. 2 of SP79-37, pp. 709–718, 1983.
V. M. Malhotra, “Mechanical properties and freezing-and-thawing resistance of non-air-entrained and air-entrained condensed silica-fume concrete using ASTM test C 666 procedures A and B,” in CANMET/ACI, Fly, Silica Fume, Slag and Natural Pozzolans in Concrete, vol. 2 of SP91-53, pp. 1069–1094, 1986.
S. Seki and M. Morimoto, “Recherche expérimentale sur l’amélioration du béton par l’incorporation de sous-produits industriels,” Annales de l’ITBTP, no. 436, 1985.
E. H. Kadri, R. Duval, S. Aggoun, and S. Kenai, “Silica fume effect on hydration heat and compressive strength of high-performance concrete,” ACI Journal of Materials, pp. 107–113, 2009.
L. S. Marusin, “Chloride ion penetration in conventional and concrete containing condensed silica fume,” in Fly, Silica Fume, Slag and Natural Pozzolans in Concrete, vol. 2 of ACI SP 91-55, pp. 1119–1133, 1986.
O. Skjolsvold, “Carbonation depths of concrete with and without condensed silica fume,” in CANMET/ACI, Fly, Silica Fume, Slag and Natural Pozzolans in Concrete, vol. 2 of ACI SP 91-51, pp. 1031–1048, 1986.
J. Wolsiefer, “Ultra high-strength placeable concrete in the range 10.000 to 18.000 psi (69 to 124 MPa),” in Proceedings of the ACI Annual Convention, Atlanta, Ga, USA, January 1982.