No abstract

No abstract

In contrast to foreign practice, in Poland, for many years, there has been a belief, that in prestressed constructions, more expensive concretes on basalt aggregates should be applied. This habit is due to the low quality of national river and fossil aggregates. They allow to obtain low concrete strength and modulus of elasticity. In the paper, basing on two examples of post-tensioned slabs, it has been shown, that it is possible to use concretes with a low value of modulus of elasticity for large-span slabs. These results may be significant in popularizing the use of post-tensioned slabs in buildings in poorer countries, making them cheaper in execution.

The paper presents the experimental results of shrinkage, creep, and prestress loss in concrete with lightweight aggregate obtained by sintering of fly ash. Two concrete mixtures with different proportions of components were tested. Concrete with a density of 1810 and 1820 kg/m3, and a 28-day strength of 56.9 and 58.4 MPa was obtained. Shrinkage and creep were tested on 150 × 250 × 1000 mm3 beams. Creep was tested under prestressing load for 539 days and concrete shrinkage for 900 days. The measurement results were compared with the calculations carried out according to the Eurocode 2 as well as with the results of other research. A very low creep coefficient and lower shrinkage in relation to the calculation results and the results of other research were found. It was also revealed that there is a clear correlation between shrinkage and creep, and the amount of water in the concrete. The value of the creep coefficient during the load holding period was 0.610 and 0.537, which is 56.0 and 49.3% of the value determined from the standard. The prestressing losses in the analyzed period amounted to an average of 13.0%. Based on the obtained test results, it was found that the tested lightweight aggregate concrete is well suited for prestressed concrete structures. Shrinkage was not greater than that calculated for normal weight concrete of a similar strength class, which will not result in increased loss of prestress. Low creep guarantees low deflection increments over time.

No abstract