Although HPC with compressive strength up to 100 MPa can be made with pure cement, it will be much easier when silica fume is used. For the preparation of concrete with strength more than 100 MPa, the use of silica fume is almost indispensable. Silica fume is used as filling material and pozzolanic material in concrete at the same time.

After using silica fume, the pore size in the hydrated slurry is greatly reduced and the pore size distribution is improved, so the strength is improved and the permeability is reduced. For example, the research results show that (ceb2fip1988) in order to obtain the concrete strength of 70 MPa, the water binder ratio of 0.35 is required for the application of pure cement, and when 8% silica fume is added, the water binder ratio can be 0.50.

Because silica fume particles are very fine, they can react with volcanic ash in very early hours. According to Carette and Malhotra (1992), the contribution of silica fume to concrete strength is mainly before 28d. Therefore, in terms of long-term strength growth, it is generally considered that silica fume concrete is not as good as pure cement concrete or fly ash concrete. The test results of silica fume on NSC strength development cited by almad (1994) show that the increase of silica fume content reduces the early relative strength development. Sandvik 1992 also found this phenomenon in 65 MPa concrete.

However, although the early relative strength development of silica fume concrete is slower than that of pure cement concrete under the same water binder ratio, the strength of silica fume concrete is higher than that of pure cement concrete because the addition of silica fume greatly improves the strength. On the other hand, experience shows that the early strength development of HPC is faster than that of NSC. Although the setting time of HPC may be slightly delayed, the hydration after setting will be greatly accelerated due to superplasticizer and silica fume. The result is usually that the strength develops very fast after condensation.

For some silica fume concrete specimens with very low water binder ratio dried or cured in air, there are reports of compressive strength shrinkage (de larrard and aiticin 1993). This strength reduction usually occurs after 90 days of age and is generally considered to be caused by internal self drying and drying cracks.

However, laboratory and field studies by many other researchers have shown that the late strength of HPC has not decreased. For example, the test results of all drill core samples aged from 3 months to 3 years from 6 different HPCS show that their strength is increasing. Of course, compared with NSC, HPC has less long-term strength growth potential.

Through the above introduction, I believe you have a relative understanding of Chengdu silica fume. If you have other questions, please consult our company for details.