Frost resistance of concrete with and without silica fume, and the effects of external loads

Yixia Zhou, Purdue University

Abstract

A study of frost resistance of non-air-entrained concrete was carried out to explore the possibilities of making concrete with both high strength and high frost resistance. The relationship between frost durability and air spacing factor of the mixtures was also studied. The influence of curing duration before freezing-and-thawing exposure and the effects of silica fume incorporation were investigated, and an innovative test was designed to investigate the concurrent acts of freezing-and-thawing and external loading. A study of failure modes and its relation with cracking density was conducted to establish a relationship between preloading level and freezing-and-thawing damage. The results of this study indicated that increasing curing duration before freezing-and-thawing exposure is beneficial to portland-cement concrete, however, after a certain period of curing, any further curing only results in marginal gain in frost resistance. An undesirable curing period exists for silica-fume concrete of 14-21 days. This study concludes that silica-fume concrete has no advantage over portland-cement concrete in freezing-and-thawing durability, if the mixtures do not have air entrainment. On the other hand, air-entrained silica-fume concrete can achieve a high strength level similar to non-air-entrained portland-cement concrete, and in addition achieve much higher frost resistance. The results of this study indicate that silica-fume concrete has a lower value of critical spacing factor in comparison with portland-cement concrete. This study reveals that external loading plays an important role in concrete failure under the influence of concurrent acts of freezing-and-thawing and external loading. Different modes of failure were observed, which were found to be closely related to the level of preloading and the water-to-cementitious materials ratio of a mortar mixture. Extensive matrix cracking was found to be associated with gradual freezing-and-thawing damage, and "brittle" fracture with heavy external loading. By examining the advantages and disadvantages of commonly used freezing-and-thawing monitoring methods, the studies found that the pulse velocity technique and the resonant frequency method are well correlated in monitoring the changes due to freezing-and-thawing exposure until disintegration point of a concrete mixture is reached, and they differ significantly beyond that point. The studies also found that the resonant frequency method is more sensitive to the real changes in concrete, especially when severe freezing-and-thawing damage occurs.

Degree

Ph.D.

Advisors

Cohen, Purdue University.

Subject Area

Civil engineering|Materials science

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