Andrzej Ajdukiewicz

INFLUENCE OF RECYCLED AGGREGATES ON MECHANICAL PROPERTIES OF HS/HPC

Abstract Recently, aggregates derived from demolished concrete structures were of relatively low strength, and applications were of secondary importance. Since a short time, the necessity of demolition of structures with strong concrete, like building frames or bridge beams, has appeared and created the source of recycled aggregate of quite new generation. Besides of obvious environmental aims recycling of concrete has gained new economical aspects. Concrete in responsible structures, with strength of 40–70 MPa for instance, was originally mixed from aggregate of good quality, e.g. granite or basalt, and with large amount of cement. The aggregate obtained from crushing of such structures retained some binding abilities as may be activated by means of silica fume or fly ash admixtures. Generally, such aggregates are different from natural and, consequently, concrete made with use of them has specific properties. The results of research on mechanical properties of structural recycled high performance concrete (RHPC) are presented.

Differences in instantaneous deformability of HS/HPC according to the kind of coarse aggregate

In the analysis of concrete structures the knowledge of real values of modulus of elasticity is of great importance, particularly at displacements or losses of prestressing consideration. For two-dimensional problems the Poissons ratio is important too. Recommendations from the Standards can inform us roughly about these values but usually in the range of classes of ordinary concrete only. In general, greater the strength of concrete greater the differences in modules of elasticity for similar classes of concrete are. In the first row material factors have to be taken into consideration. To explain the range of variations the results of tests for high-strength/high-performance concrete manufactured with different components, particularly various kinds of coarse aggregates are presented. These results are compared with some other tests and with basic recommendations.

Rehabilitation of the highest wooden tower in Poland

Of about a dozen wooden telecommunication towers over 100 m high that were erected in Europe before the Second World War, the tower in Gliwice, Poland, is the only one still surviving. The tower was built as a spatial truss from larch wood of very high quality. Because of the size and importance of the structure, a wide range or measurements was required, particularly concerning the shape and dimensions of the structure. As a result of observations and calculations, it was decided to strengthen some bars and to apply a modern protective coating to the entire structure. This is the reason why transverse strengthening of split wooden bars by means of carbon fibre strips was used.

Trends in the Polish research on high-performance concrete

This paper is of general nature. The main trends in the research on high- performance concrete (HPC) in Poland are presented and discussed. Some examples of the relevant investigations are given. The fundamental engineering and economical problems concerning the structural applications of HPC in Poland are presented as well as the needs justifying the increased use of this material are briefly described.

Testing and Repair of Concrete Silos

Damages to concrete silos require exact appraisal and careful selection of repair methods. Repairs should be preceded and controlled by tests because, due to the large surfaces of these structures, errors in repair methods can be costly. Som testing methods are presented that are specifically for structures like silos and tanks, while others are similar to methods for concrete shell structures. General descriptions are illustrated by examples of effective rehabilitations of large concrete silos.