Title: Durability of High-Strength Concrete with Silica Fume: Temperature Attack and Freezing-and-Thawing Cycles
Author(s): I. Janotka
Publication: Symposium Paper
Appears on pages(s): 175-186
Keywords: concrete; freezing and thawing; hydration; porosity; strength; temperature elevation
This paper reports high-strength concrete behavior subjected to temperatures up to 200 °C and 100 freezing and thawing cycles in regime of 8 hours in water at + 20 °C and 16 hours at - 20 °C (weekends in frost). The concrete is composed of 425 kg/m3 of portland cement of CEM I 42.5 type, 32 kg/m3 of silica fume, 5.6 L/m3 of super plasticizer Melment and has a W/C of 0.32. Compressive strength is 78.5 MPa at 28-day curing on cubes for temperature resistance tests and 63.1 MPa on prisms for freezing and thawing tests, both after 28-basic curing in 20 °C/100 % R. H. - air. Evident C-S-H dewaterization of the cement paste is observed between 100 °C and 200 °C. Initial shrinkage within 24-hour period due to rapid cooling is more detrimental on the cement paste strength than shrinkage due to C-S-H dewatering at temperature elevation from 100 °C to 200 °C. The strength, elastic modulus and volume deformation of concrete are irreversibly influenced either by temperature elevation or rapid cooling to 20 °C. Differences in strength, elastic modulus and shrinkage or expansion after 100 freezing and thawing cycles relative to those in water are negligible. The compressive strength of prisms subjected to 118-day freezing and thawing was 62.9 MPa, compared to 65.2 MPa for those kept in water.