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The expansion of mortars containing up to at least 10% silica fume by weight of cement were about three times as great as that of the additive-free mortar. Concentrations of calcium and alkalies within opal grains in the silica fume mortars were determined by energy dispersive x-ray analysis(EDXA). The intrusion of smaller amounts of calcium into opal grains in the mortars at early ages seems to show that the conversion of alkali-silica gels into sols was delayed by the presence of silica fume. The delay of this conversion was also confirmed by microhardness measurements.

Although CSF is mostly strength, it also confers other durability-related properties. In pipes, CSF-addition is shown to bearing capacity of the pipes by used for increasing concrete advantages such as improved the manufacture of concrete increase the external load 40%. The resistance of the pipes against chemical attack is also increased considerably . Concrete pipes containing only about 5% CSF have 2-3 times longer service life than ordinary pipes when exposed to sulphates. Concrete containing CSF is known to have improved resistance to freezing-thawing attack, chloride penetration and deicer scaling, making it useful for road construction. CSF addition also increases the abrasion resistance of concrete, especially at higher dosages. A 20% dosage of Corrocem, a proprietory admixture based on CSF as a key component, shows 3O-35% higher abrasion resistance, compared to a good quality concrete. Due to the reduced permeability and lower free lime content in the cement paste, the CSF concrete is considered to have a high resistance against chemicals. For Corrocem-concrete a considerably increased service life is obtained in aggressive environments. Such concrete exposed to saturated ammonium nitrate-solution shows a weight loss of about 0,5% after 150 weeks exposure compared to a loss of 15% after 100 weeks for a plain concrete. The strength of the admixtured-concrete is about 70-75 MPa after 163 weeks and about 30 MPa after 21 weeks for the plain concrete after exposure to nitrate solutions. Similar trend was obtained for specimens exposed to saturated calcium nitrate.

Cores were drilled from 16 structures with silica fume concrete (SC-concrete) and 11 without it (OPC-concrete). The nominal strength of the concretes was 25 MPa. Testing was done at different periods. Carbonation depths were corrected to 60 months and 33 MPa. The mean corrected carbonation depth for all structures with SC-concrete was 11.6mm. The corresponding value was 8.8mm, for OPC-concrete. However, the dispersion in the results was to high to make conclusions. The standard deviati-ons were 5.9mm and 2.4mm respectively for SC- and OPC-concrete. Considering statistical variation in carbonation depths and concrete cover over the reinforcement, the observed carbonation depths indicate an initiation period for corrosion as short as 2 - 3 years for both types of concrete at the stated strength level. This initiation period is very short. Carbonation depths were also measured on beams and slabs that were cured under different curing conditions. Curing conditions had significant effect. The rate of carbonation was proportional to the water/cement-ratio. Therefore the compressive strength is an unreliable parameter to judge the quality of concrete containing condensed silica fume.

The objective of this study was to investigate the behavior of air flow through concrete and to make clear the effects of use of fly ash and condensed silica fume on the air permeability of concrete. The air permeability of concrete was estimated by means of the coefficient of air permeability, and the difference of the coefficient of air permeability between concretes with and without fly ash and condensed silica fume was investigated. Furthermore the improvement of the airtightness of concretes with fly ash and condensed silica fume was discussed from the view point of the internal structure of concrete such as porosity. As the results of this study, it was confirmed that the flow of air through concrete obeyed Darcy's law. It is possible to apply the coefficient of air permeability as the index of air permeability of concrete. In the case of use of fly ash, the coefficient of air permeability of concrete cured in water for the period of 28 days hadalmost the same value as concrete without fly ash when compared at the same level of compressive strength. However, the concrete with fly ash cured in water for the period of 91 days is more airtight than concrete without fly ash. In case of use of condensed silica fume, the coefficient of air permeability decreased with the increase of replacement ratio of condensed silica fume, and did not depend on the period of the curing in water. These results can be quantitatively understood by means of the internal structure of concrete.

This report presents the results of a study dealing with the resistance to repeated cycles of freezing and thawing of non air-entrained and air-entrained condensed silica-fume concrete when tested in accordance with ASTM C 666, Procedures A and B. A total of twenty-two air-entrained and non air-entrained concrete mixtures, 0.06 m3 in size, were made. The water-to-(cement + silica fume) ratio (W/C+S) of the mixtures ranged from 0.40 to 0.60, and the percentages of cement replacement by condensed silica fume were 0, 5, 10, 15, and 30 per cent on a weight basis. Any loss in slump due to the use of condensed silica fume was compensated for by the use of a superplasticizer. A number of test cylinders were made for testing in compression at various ages, and test prisms were cast for determining their resistance to repeated cycles of freezing and thawing in accordance with ASTM C 666, Procedures A and B. Sawn sections of the test prisms were used for determining the air-void parameters of the hardened concrete. Based upon the analysis of the test data it is concluded that the use of non air-entrained condensed silica-fume concrete is not recommended when it is to be subjected to repeated cycles of freezing and thawing. Furthermore, the users of condensed silica fume are cautioned against using high percentages of the material as replacement for portland cement in concretes with W/C+S of the order 0.40 if these concretes are to be exposed to repeated cycles of freezing and thawing.