International Concrete Abstracts Portal

The report generalizes the results of wide range investigations of silica fume based superplasticized high- performance concrete. The rules of the strength and rheological behavior of cement silica fume - super-plasticizer systems are discussed. Usage of optimal superplasticizer to silica fume ratio (as 1: 10) allows to obtain ultra-dense packing for super fluid cement paste and provides high-performance properties of concrete. The mathematical models of fresh and hardened high-performance concrete based on processing and computerizing empirical results are created. The models provide a calculation of W/C required for the target compressive strength level up to 130 MPa as well as mixing water quantity for planning slump of 0 - 200 mm. For modelling purpose, concrete slump is considered as a function of aggregates proportioning, and volume and fluidity of cement paste. This approach became a basis of proposed high- performance concrete mixture proportioning method. Further, developing and integration of the mathematical models created a new computer program for high-performance concrete mixture proportioning. The program provides a solution for wide range design and optimization projects. The results of the computer program estimation can be easily transferred to any 3- dimensional plotting or data base program for consequent processing and performing.

The paper presents the results of an investigation about the behavior of reinforced concrete flat slabs made with high strength concrete, steel fibers and ordinary shear reinforcement, We tested twelve flat slabs made with different combinations of high strength concrete, ordinary strength concrete, shear reinforcement and steel fiber vohmre fraction (0%, 0.75% and 1.5%). The square-shaped slabs were designed to represent the slab-column connection in an interior column. A significant increase in the punching shear strength was observed, due to the use of high strength concrete and the addition of steel fibers. The combination of high strength concrete with 1.5% fiber volume fraction and shear reinforcement provided twice the punching shear resistance of an ordinary strength concrete slab without shear reinforcement and without fibers. Fiber addition is believed to be responsible for an increase of approximately 50% in the resistance and also for an increase in ductility. Comparisons with theoretical code previsions, including CEB/90, AC13 18/89 and Eurocode 2, are presented.

The Siberian State Academy of Mining and Metallurgy together with the joint-stock company of the West-Siberian Metallurgical Works and UralNIIStromproject have developed compositions and technology for fireproof concrete made from local materials and industrial by-products. The concrete is designated for the production of unburnt blocks and bricks to be used for lining heating facilities of metallurgical enterprises (there are four of them in Novokuznetsk). Concrete for producing blocks for soaking pits consists of the following components : quartzite’s of three grading fractions ( 0 to 8 mm - 36 %, 0 to 3 mm - 50 % , powder fraction - 14 % ) and a binder ( technical grade liquid glass ) with a density of 1.42 to 1.44 g/cm' (lo-14 % above 100 % aggregate). The technical grade liquid glass was made by solution of silica fume with the fineness of 60 to 90 m'/g and beyond 90 % free SiOz content in sodium hydroxide. The technical grade liquid glass developed increased the strength of concrete and its heat resistance by 35 to 45 % and 25 to 30 %, respectively, as compared with the commonly used liquid glass. The service life of the blocks manufactured at the pilot plant of the West-Siberian Metallurgical Works in walls of a soaking pit was 18 months while that of the blocks produced by the Pervouralsky plant ranges from 6 to 12 months. The construction of a department for producing blocks and bricks from the above concrete is in the stage of completion at the West-Siberian Steel Works.

In recent years, high strength concrete (HSC) has become an attractive alternative to traditional normal strength concrete (NSC). With the increased use of HSC, concern has developed regarding the behaviour of such concrete in fire. Studies are in progress at National Research Council of Canada for developing design guidelines for the use of HSC under fire conditions. The behaviour of HSC columns is illustrated by comparing the fire resistance performance of HSC columns with that of NSC columns. Results from experimental studies that were carried out to determine the thermal properties of HSC, with and without steel fibre-reinforcement, at elevated temperatures are also presented. The effect of temperature on thermal conductivity, thermal expansion, specific heat and mass loss of HSC is discussed. Test data indicate that the type of aggregate has significant influence on the thermal properties of HSC, while the presence of steel fibre-reinforcement has very little influence on the thermal properties of HSC.

This paper describes a basic study on the development of a new method to judge the saturated surface-dry condition of fine aggregates. The new method is based on the idea that the electric resistance of a sample depends on the moisture content of the sample. The relationship of the electric resistance with the moisture content of a sample is directly and radically changed by the existence of water on the surfaces of the particles. This becomes clearer when an electrolyte is added to the sample. The relationships between the electric resistance and the moisture content of a sample were investigated for various types of fine aggregates when an electrolyte was added. This relationship shows radical changes in the electric resistance near the saturated surface-dry condition. The chemical compositions of a sample do not influence the relationship of the electric resistance with the total moisture content of the sample. The applicability of the electric resistance test will be confirmed if the data of specimens with various physical properties will be investigated statistically.