Institute of Fundamental Technological Research

The experimental investigation on the frost-salt scaling resistance of air-entrained concrete containing CEM II/B-S 42.5N and CEM III/A 42.5N-HSR/NA slag-blended cements was performed. The air void system in concrete was evaluated in fresh concrete using AVA and in hardened concrete using an automated image analysis procedure. The mass of scaled material was increased for an increased slag content, in spite of increased compressive strength and flexural strength, decreased water absorption and decreased depth of water penetration of concrete. Increasing slag content resulted in a decrease of the total volume of air in hardened concrete and in a corruption of the air void system exhibited by a decrease of micropores content. The increase of mass of scaled material was proportional to the increase of the spacing factor of air voids, except for CEM III/A cement concrete exhibiting accelerated scaling.

Air-entrained concrete, Air voids, Frost-salt scaling, Image analysis, Slag-blended cement

Under general loading conditions, there is no guarantee that the crack surfaces will be fully open. Complete or partial closure of the crack could occur if the surrounding material is compressed. Such a phenomenon is illustrated for the situation of a single crack engulfed by a remote but uniform compressive stress field while tensile forces are applied at isolated points so that the material can counteract against the compressive field. Examples are provided illustrating partial crack closure with or without symmetry about the mid-plane normal to the crack surface. Considered will be mechanical and thermal loadings.

In traditional Saint Venant's principle formulations the loads leading to similar stress distributions are assumed to be statically equivalent, i.e. to yield identical resultant forces and moments. It is shown that this requirement may be replaced with a more general one according to which the first N+1 moments of order 0,1, ..., N of both loading systems should be compared. In the case of an elastic half-plane loaded at the boundary it is shown that the resulting stress differences calculated at large distances from the loaded region are of the order of kr-N - 2 where N denotes the highest order of identical moments of two loading systems, and r - distance from the loaded region.

A method of approximate analysis is presented concerning the state of stress, and the stress intensity factors in particular, in elastic media subject to a plane state of strain and containing arbitrary arrays of cracks. In the case when ·the crack distribution is not too dense, the method proposed makes possible the determination of the required stress parameters in a manner resembling that used in solving the statically indeterminate systems of structural mechanics.