Results of experimental investigation on the mitigation of alkali–silica reaction (ASR) by low-grade calcined clay are presented. Domestic clay with an Al₂O₃ content equal to 26% and SiO₂—58% was used. The calcination temperatures were as follows: 650 °C, 750 °C, 850 °C and 950 °C, which were chosen much more widely than presented in previous studies. Pozzolanity of the raw and calcined clay was determined with the Fratini test. The performance of calcined clay to mitigate ASR was evaluated according to ASTM C1567 using reactive aggregates. A control mortar mixture was prepared with 100% Portland cement (Na₂O_eq = 1.12%) as a binder with reactive aggregate, and test mixtures were made with 10% and 20% of calcined clay as a cement replacement. The microstructure of the specimens was observed on the polished sections using scanning electron microscope (SEM) operated in backscattered mode (BSE). The results of expansion of mortar bars with reactive aggregate showed that replacing cement with calcined clay reduced the expansion of the mortar bars. The greater the cement replacement, the better results in terms of ASR mitigation. However, the influence of the calcination temperature was not as clear. The opposite trend was found with the use of 10% or 20% calcined clay.

The design of concrete for radiation shielding structures is principally based on the selection of materials of adequate elemental composition and mix proportioning to achieve the long-term durability in nuclear environment. Concrete elements may become radioactive through exposure to neutron radiation from the nuclear reactor. A selection of constituent materials of greatly reduced content of long-lived residual radioisotopes would reduce the volume of low-level waste during plant decommissioning. The objective of this investigation is an assessment of trace elements with a large activation cross section in concrete constituents and simultaneous evaluation of susceptibility of concrete to detrimental alkali-silica reaction. Two isotopes ⁶⁰Co and ¹⁵²Eu were chosen as the dominant long-lived residual radioisotopes and evaluated using neutron activation analysis. The influence of selected mineral aggregates on the expansion due to alkali-silica reaction was tested. The content of ⁶⁰Co and ¹⁵²Eu activated by neutron radiation in fine and coarse aggregates, as well as in four types of Portland cement, is presented and discussed in respect to the chemical composition and rock origin. Conflicting results were obtained for quartzite coarse aggregate and siliceous river sand that, despite a low content, ⁶⁰Co and ¹⁵²Eu exhibited a high susceptibility to alkali-silica reaction in Portland cement concrete. The obtained results facilitate a multicriteria selection of constituents for radiation-shielding concrete.

Piasek stosowany jako kruszywo drobne w betonie w niekorzystnych warunkach środowiska może spowodować reakcję alkaliczno-krzemionkową, a w konsekwencji – pogorszenie właściwości użytkowych i trwałości betonu. Celem pracy jest porównanie reaktywności alkaliczno-krzemionkowej 18 piasków naturalnych o różnym pochodzeniu. Wykonano badania potencjalnej reaktywności piasku zgodnie z procedurami PB/1/18 i PB/3/18 przedstawionymi w Wytycznych Technicznych GDDKiA. Prze- prowadzono analizę składu mineralnego kruszywa pod kątem zawartości reaktywnych minerałów, badanie wydłużenia próbek zapraw oraz analizę mikroskopową produktów reakcji alkalia-krzemionka. W toku badań dowiedziono, że 6 kruszyw (33%) spośród 18 przebadanych należy zaklasyfikować do kategorii „umiarkowanie reaktywne”, natomiast 12 kruszyw (67%) należy przypisać do kategorii „niereaktywne”. Wykazano wpływ pochodzenia piasku na jego podatność na wystąpienie reakcji alkalicznej.

The purpose of introducing air into the concrete mix is to increase the freeze-thaw and scaling resistance of hardened concrete. The utility of the sequential pressure method (Super Air Meter - SAM) for assessment of the air entrainment quality was verified by comparing the results obtained with this method with the results of the air-void analysis of hardened concrete. The results of the tests carried out on mixes designed and produced at a laboratory and the mixes produced on an industrial scale during expressway construction are considered. Furthermore, the relationships between the SAM number and the micro air-void content A300 in hardened concrete and the freeze-thaw and de-icing salt resistance are analysed as part of this research. A clear co-relation between the SAM number, a parameter that characterises the air-entrainment of the concrete mix, and the microvoid content has been demonstrated.