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Abstract
The article presents the results of original and relevant tests from the point of view of using self-compacting concrete admixtures, especially their compatibility with the cement and mutual compatibility in the case of using several admixtures in one mixture. The research contributes to the recognition of the effect of an unintentionally air-entraining superplasticiser (SP), anti-foam (AFA), viscosity-modifying (VMA) and air-entraining (AEA) admixtures on the internal frost resistance and compressive strength of self-compacting concrete. Positive and undesirable effects of the combined use of several admixtures in this area have not been the subject of extensive analyses and publications so far. Superplasticiser, which unintentionally introduced a large amount of air to the concrete mixture, had a negative effect on the strength of the concrete and a positive effect on frost resistance. The addition of AFA to such concrete did not change the strength but worsened the values of the parameters estimating frost resistance. The AEA admixture resulted in a decrease in the strength of concrete but contributed to a change in the tendency to weaken the frost resistance observed in non-air-entrained concrete. The article also deals with the problem of compliance of the frost resistance criteria estimated upon various measures. It may be disturbing that finding frost resistance based on one criterion does not always mean frost resistance on another criterion. The discrepancies can be significant and misleading.
Highlights
Frost-resistant concrete, including self-compacting concrete (SCC), should have an appropriate porosity structure
Other admixtures besides air entrainment, the necessity to obtain the proper consistency of SCC concrete or anti-segregation such as viscosity-modifying admixtures (VMA) [1,2], are not indifferent due to the resulting air content
The following conclusions concern the tests of self-compacting concrete with the mean compressive strength no less than 55 N/mm2, carried out in the range described in the article
Summary
Frost-resistant concrete, including self-compacting concrete (SCC), should have an appropriate porosity structure. Intentional aeration is achieved by the use of air-entraining admixtures. Air-entraining agents have a foaming effect and, most of all, they stabilise the introduced air, providing the appropriate structure (distribution and size) to the air microbubbles. Water freezing in the capillaries can press into the empty bubbles, which prevents the concrete structure from bursting. The microbubbles interrupt the continuity of the capillaries in the concrete, which prevents capillary and osmotic transport of water. The mechanisms mentioned above make the concrete resistant to the damaging effects of frost. Publications [3,4,5,6,7] analysed the influence of admixtures, mainly air-entraining ones, on the frost resistance of concrete
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