Silica fume on the strength of high performance concrete

Although the application of pure cement can be made up to 100 MPa compressive strength of HPC, but will be much easier when using silica fume. For the preparation of the concrete strength exceeds 100 MPa, the use of silica fume is almost indispensable. Silica fume in concrete filler material and volcanic ash from the same material. Using silica fume, greatly reducing the hydration slurry pore size, pore size distribution improved, so that strength, permeability decreases.
For example, the study results show that (CEB2FIP1988), in order to obtain 70 MPa concrete strength, the application of pure cement needs water-cement ratio 0.35, and when plus 8% silica fume, the water-cement ratio can be 0.50. Since silica particles are very fine, they can occur within a few hours early pozzolanic reaction. According to Carette and Malhotra 1992) reports, the contribution of silica fume concrete strength mainly in the 28d before. So, the long-term strength of growth, generally considered as pure silica fume concrete cement concrete or fly ash concrete. Almad (1994) cited the development of silica fume on the NSC strength test results show that silica fume dosage increases the relative intensity of the early development of such reduction, Sandvik 1992 at 65 MPa concrete were also found in this phenomenon.
However, although the same water-cement ratio relative strength of silica fume concrete in the early development of slower than pure cement concrete, such as silica fume added strength greatly increased, the absolute strength of silica fume concrete is higher than that of pure cement concrete. On the other hand, experience has shown, HPC early strength development faster than the NSC, although HPC setting time may be slightly delayed hydration after its condensation due superplasticizer and silica fume greatly accelerated. The result is usually very fast strength development after condensation.
For some air drying or curing of low water-cement ratio of silicon carbide silica fume concrete specimens with compressive strength retraction reports (De Larrard and Aiticin 1993). This reduction in strength usually occurs after the age of 90 d, is generally considered by an internal self-drying and drying cracks caused. However, many other researchers in laboratory and field studies have shown that, HPC's late strength is not reduced. For example, from 6 different HPC obtained in three months to three years, all drill core samples of test results show that the intensity is growing. Of course, compared with the NSC, HPC's long-term growth potential of smaller intensity.