International Concrete Abstracts Portal

SP91 This contains 78 symposium papers, bringing together the expertise of representatives from industry, government and universities. These volumes present the latest advances in the use of fly ash, silica fume, slag and natural pozzolans in concrete. New technologies are explored to provide ways in which these valuable mineral by-products can best be used to conserve both resources and energy. Case studies include: the effect of fly ash on physical properties of concrete; evaluation of kiln dust in concrete; effect of condensed silica fume on the strength development of concrete, and the influence of slag cement on the water sorptivity of 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.

Three kinds of inorganic mineral admixtures (silica fume, alumina-type mineral and fly ash) were mixed with cement and aggregates and having water-to(cement + condensed admixture) ratio using high-range water reducing agent. This study clarified both the properties of fresh concrete and adequate concrete mix proportions. This test was made by dividing eight factors and three levels among the orthogonal array of L27, based on test plan method. (1) Flowability using fly ash concrete and alumina-type mineral concrete is increased with increase in dosage of admixture, but that of silica fume concrete is decreased. (2) In order that concrete slump with various admixtures have the same flowability at a slump of 18cm (for concrete without admixture), at a certain dosage of admixture (X1.6), the slump value is about 21cm with silica fume concrete, about 6cm with fly ash concrete and about 16cm with alumina-type mineral concrete. (3) Fly ash concrete and alumina-type mineral concrete show more segregation of aggregate. Silica fume concrete shows less with the passage of time. (4) Unit water content for all cements and aggregates can be determined by ordinary mix proportion. (5) Air-entraining-agent content required to get the same air content increases with increase in the amount of mineral admixture and superplasticizer.