Silica Fume for Cement Replacement and its Influence on Strength and Permeability of Steam-Cured High-Strength Concrete

This paper describes how steam curing at atmospheric pressure is an important technique for obtaining high early strength values in precast concrete production. This paper explores the potential benefits of steam curing in concrete products made with different cements types and with supplementary cementitious materials. All concretes mixtures had the same workability and were produced with two cements both with and without silica fume replacement (10% by mass): high-early-strength portland cement and blast-furnace slag portland cement. For each mixture, specimens were subjected to three curing conditions. Immersion curing until the age of 7 days, curing in air and steam curing at temperatures of 60°C and 80°C maximum temperature over 4 h. Concretes were prepared and tested for initial surface absorption and air permeability. Compressive strength was also determined. The concretes were tested at different ages: 1, 3, 7, 28, 90, and 180 days. The results showed that the concretes with silica fume presented a lower air permeability and capillary absorption, mainly in later ages, when compared with concretes without silica fume for all curing procedures and both portland cements used. The inclusion of silica fume improved performance of concrete produced with blast-furnace slag portland cement at temperature of 80°C. High-early-strength portland cement had a good performance with silica fume replacement. The curing method adopted had significant effects on the near-surface properties of concrete incorporating silica fume.