Pracownicy

Streszczenie:
Concrete shielding structures in nuclear facilities must maintain both radiation attenuation capacity and transport barrier performance throughout their service life. Although gas permeability and radiation shielding properties have been widely investigated, their coupled evolution under load-induced damage remains insufficiently understood, particularly for concretes with low-clinker cements. This study evaluates the combined effects of low-clinker cement type, aggregate type, and mechanical preloading on the gas permeability and gamma-ray shielding performance of concretes intended for nuclear applications. Six mixtures were produced using CEM II/C-M (V–F–LL) and CEM V/A (S–V) cements combined with magnetite, basalt or limestone aggregates. Gas permeability was measured using the Cembureau method on specimens subjected to progressive preloading up to 90% of the splitting tensile strength. Gamma-ray attenuation parameters were determined using a 137Cs source (0.662 MeV), and microstructural observations were performed by SEM. Aggregate type was the dominant factor governing shielding performance. Magnetite concretes exhibited the highest compressive strength, the lowest gas permeability, and the highest attenuation coefficients, reaching μ = 0.258 cm⁻¹ and HVL = 2.68 cm. CEM V concretes generally showed lower permeability than the corresponding CEM II concretes. Mechanical preloading increased gas permeability, particularly above approximately 80% of the splitting tensile strength, indicating the formation of connected microcrack networks. Simultaneously, a reduction in attenuation factor was observed, demonstrating that load-induced damage adversely affected shielding effectiveness. A relationship between the increase in permeability and the reduction in attenuation factor was identified, suggesting a transition from pore-controlled to crack-controlled behaviour. The results demonstrate the suitability of concretes with low-clinker cements for shielding applications and provide new insight into the coupling between damage development, transport properties, and radiation shielding performance.

Słowa kluczowe:
Permeability, Shielding concreto, Load, Microstructure, Low-clinker cement, Gamma-ray attenuation, Microcracking

Streszczenie:
Rubber derived from end-of-life tires offers a sustainable solution for reducing the environmental impact of cement-based materials. In this study, recycled rubber aggregate (RRA) was used as a partial volumetric replacement (15% and 30%) of natural fine sand in cement-based mortars to evaluate its effectiveness in mitigating alkali–silica reaction (ASR). The experimental program included mechanical testing, ASR expansion measurements, and microstructural analyses. The results showed that increasing RRA content led to a reduction in compressive strength by up to 24.1% and flexural strength by up to 19.8% after 28 days of curing. Despite this reduction, a significant improvement in ASR resistance was observed. For mortars containing highly reactive aggregates, ASR expansion decreased from approximately 0.73% in the reference mixture to 0.47% with 30% RRA, corresponding to a reduction of up to 33%. Microstructural observations confirmed that RRA acts as a stress-relieving inclusion, limiting crack propagation and reducing ASR gel formation. Physicochemical analyses (XRD, TGA, and FTIR) indicated that alkaline treatment induces surface oxidation of RRA without affecting the stability of mineral components. The findings demonstrate that ASR mitigation is not solely due to dilution of reactive aggregates, but also to the elastic and microstructural buffering effects of RRA. Furthermore, a simple predictive model is proposed to estimate the required rubber content for effective ASR mitigation.

Słowa kluczowe:
Keywords Recycled rubber aggregate, Reactive aggregate, Flexural test, Compression tests, Microstructural analyses

Streszczenie:
Quality requirements for mineral aggregate for concrete used to construct pavement for busy highways are high because of the fatigue traffic loads and environmental exposure. The use of local aggregate for infrastructure projects could result in important sustainability improvements, provided that the concrete’s durability is assured. The objective of this study was to identify the potential alkaline reactivity of local greywacke aggregate and select appropriate mitigation measures against the alkali–silica reaction. Experimental tests on concrete specimens were performed using the miniature concrete prism test at 60 °C. Mixtures of coarse greywacke aggregate up to 12.5 mm with natural fine aggregate of different potential reactivity were evaluated in respect to the expansion, compressive strength, and elastic modulus of the concrete. Two preventive measures were studied—the use of metakaolin and slag-blended cement. A moderate reactivity potential of the greywacke aggregate was found, and the influence of reactive quartz sand on the expansion and instability of the mechanical properties of concrete was evaluated. Both crystalline and amorphous alkali–silica reaction products were detected in the cracks of the greywacke aggregate. Efficient expansion mitigation was obtained for the replacement of 15% of Portland cement by metakaolin or the use of CEM III/A cement with the slag content of 52%, even if greywacke aggregate was blended with moderately reactive quartz sand. It resulted in a relative reduction in expansion by 85–96%. The elastic modulus deterioration was less than 10%, confirming an increased stability of the elastic properties of concrete.

Słowa kluczowe:
alkali-silica reaction, aggregate, concreto, metakaolin, highway pavement

Streszczenie:
The paper presents the results of research on the effect of partially replacing the sand fraction in cement mortar mixes with granulated rubber (GR) from waste tires on the potential for alkali–silica reaction (ASR) occurrence. ASR is a significant durability issue in cement-based composites, which can lead to substantial expansion and cracking in these materials. The study also analyzed the influence of rubber aggregate on the mechanical properties of mortars, particularly compressive and flexural strength, as well as on the microstructure of the mortars. Additionally, the impact of NaOH on the properties of granulated rubber aggregate was evaluated. Reference mortars were prepared using moderately reactive sand (R1) and highly reactive sand (R3), while in the experimental mixes, rubber aggregate was used as a volumetric replacement for a specific sand fraction at levels of 15% and 30%. ASR-related expansion tests were conducted in accordance with the RILEM AAR-2 guidelines. The results showed that partially replacing sand with rubber aggregate effectively reduced ASR-induced expansion, likely due to the rubber’s ability to absorb stress and restrict moisture migration, thereby mitigating the reaction. However, the use of rubber aggregate also led to a decrease in both compressive and flexural strength, which is a typical effect when introducing elastic materials, such as rubber, into cementitious mixes. The findings highlight the potential of granulated rubber from waste tires recycled as a sustainable additive in cement-based materials to control ASR, especially in structures exposed to aggressive environmental conditions. Additionally, the use of this type of aggregate aligns with the principles of the circular economy by utilizing rubber waste and simultaneously delivering both environmental and performance benefits

Słowa kluczowe:
ASR, durability, internal structure, rubber aggregate, waste tire

Streszczenie:
Dobór kruszyw mineralnych pod kątem odporności na wystąpienie szkodliwej reakcji alkalia-kruszywo jest jednym ze znanych wymagań stawianych przy projektowaniu betonu trwałego w środowisku wilgotnym, ewentualnie narażonego na oddziaływanie soli odladzających. Znaczenie reaktywności alkalicznej kruszywa drobnego (piasku naturalnego) wzbudza niekiedy kontrowersje. Przeprowadzono badania doświadczalne reaktywności alkalicznej mieszaniny kruszyw o zróżnicowanym składzie mineralnym – grysów szarogłazowych i amfibolitowych z piaskiem naturalnym z różnych kopalń. Do oceny reaktywności kruszyw wykorzystano metodę „Miniature Concrete Prism Test” (MCPT) polegającą na oznaczaniu ekspansji próbek betonu w roztworze NaOH w temperaturze 60°C w okresie do 84 dni. Wyniki badań wykazały znaczny wpływ reaktywności piasku na ekspansję betonu oraz na resztkową wytrzymałość betonu na ściskanie. Wykazano korelację zmierzonej ekspansji próbek z obniżeniem dynamicznego modułu sprężystości betonu. Z uwagi na rozsądnie niedługi czas badania i brak konieczności rozdrabniania kruszywa metoda MCPT okazała się praktyczną alternatywą dla innych metod określania reaktywności alkalicznej kruszywa, oferując jednocześnie możliwość oceny praktycznego stosu okruchowego