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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.

This report gives results of laboratory investigations to determine the strength characteristics and the pore size distributions of mortar and concrete incorporating condensed silica fume from a Japanese sourse. This report also gives results of the shrinkage, permeability and freezing and thawing resistance of concrete incorporating silica fume. A series of mortar mixes was made with a water-to-cement plus silica fume ratio of 0.65, and the percentage of silica fume used as partial replacements for normal portland cement of 0, 5, 1O, 20 and 30 % by weight. A total of twenty three concrete mixes were made with the water-to-cement plus silica fume ratio(W/C+S) ranging from 0.25 to 0.55, and the percentage of silica fume used as partial replacement for cement of 0, 5, 10, 20 and 30 % by weight. All mixes were not air-entrained except mix with the W/C+S of 0.55 which was air-entrained. A superplasticizer was used for all the mixes incorporating condensed silica fume. Condensed silica fume improved the compressive strength of the mortar and the concrete at 28 and 91 days and the impermeability of the concrete. The drying shrinkage of the condensed silica fume concrete was comparable to that of the control concrete without silica fume. Non air-entrained silica fume concretes with the W/C+S of0.35, 0.45, and 0.55 showed low durability factors, although the air-entrained concrete with a W/C+S of 0.25 performed satisfactorily to the repeated cycles of freezing and thawing. The air-entrained concrete incorporating 20 and 30 % silica fume with a W/C+S of 0.55 showed very poor durability as compared with the control concrete.

The purpose of this work was to determine the chloride ion content distribution profile through l0-cm concrete cubes made from conventional portland cement concrete and concretes containing condensed silica fume. The conventional portland cement concrete and four concretes containing condensed silica fume were prepared and tested using a test procedure developed at Wiss, Janney, Elstner Associates, Inc. (WJE). The chloride ion penetration characteristics were studied on l0-cm concrete cubes, which were immersed in 15 percent NaCl solution for 21 days. Following the 21-day soaking period and a subsequent 21-day air-drying period, concrete powder samples were removed by drilling at depth intervals of 0 to 12 mm, 12 to 25 mm, 25 to 37 mm and 37 to 50 mm, and tested for acid-soluble chloride ion content using a potentiometric titration procedure. The test results showed that weight gain and chloride ion penetration are both reduced by concretes containing condensed silica fume. The best performance for both reductions, at all tested depths, was shown by concrete containing 10 percent of condensed silica fume. The chloride ion content at a depth of 12 to 25 mm reached the acid-soluble corrosion threshold level of about 0.03 percent by weight of concrete (as normally assumed for reinforced concrete) and was lower than this criterion below the depth of 25 mm.

To-day's advanced techniques in tunnelling and gallery engineering call for high-quality shotcrete, i.e. a material which develops accelerated set and high early strength to suit the safety requirements in the heading phase, and also final strength requirements for the perliminary concrete lining (New Austrian Tunnelling Method, NATM). High early strength can be obtained with the addition of an accelerator to the shotcrete mixture. Many materials are known for accelerating the setting time of shotcrete including strongly alka-line reacting materials such as alkali metal hydroxides, alkali metal carbonates, alkali metal aluminates and alkaline earth chlorides. The adverse effects of these admixtures are also known. With the development of an efficient alkali-free shotcrete accelerator it has become possible to produce high early strength without undesirable effects on the final strength. Attempts to positively influence the fracture characteristics of cement mortars or concrete with fibres have a long history, while organic fibres were soon discardes, great efforts are still being undertaken with glass and steel fibres. Problems in the processing of steel-fibres reinforced shot-crete motivated us to introduce a new type of fibre. The addition of condensed silica fume increased the strengths and reduced sharply the permability. The resistance to freezing and thawing was also greatly improved. No long-term strength loss was obtained due to the use of a new alkali-free setting accelerator.

This paper deals with a basic investigation of the process technology and properties of superhigh-strength concrete which is made by applying a polymer impregnation technique to silica fume concrete. The main purpose of this investigation is to find appropriate process conditions for developing the superhigh-strength concrete. Silica fume concrete is prepared using fine aggregates such as river sand and calcined bauxite and polyalkylaryl sulfonate-type water-reducing agent, and cured in an autoclave. The cured silica fume concrete is dried at various temperatures, and impregnated with polymethyl methacrylate by thermal polymerization in hot water. The strength properties and pore size distribution of the superhigh-strength concrete and the silica fume concrete are tested. The effects of drying temperature and pore size distribution of the silica fume concrete on the compressive strength of the superhigh-strength concrete are discussed. It is concluded from the test results that the superhigh-strength concrete having a compressive strength of 225 to 255 MPa is obtained by the above process.