Search Results (8)

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. Full article

Analyses were conducted on extracts from the fruits of P. pyraster and P. ×myloslavensis. Extraction with 80% methanol was performed at room temperature. The total phenolic content was determined by spectrophotometry using the Folin–Ciocalteu reagent, with gallic acid as the reference standard. Phenolic compounds and organic acids were identified on a liquid chromatograph. The antioxidative activity of the extracts was tested in relation to linoleic acid incubation of the emulsions for 19 h based on the neutralization of the DPPH radical (2,2-diphenyl-1-picrylhydrazyl) and the ABTS cation radical (2,2′-azino-bis[3-ethylbenzothiazoline-6-sulfonic acid]) as well as by the ferric reducing antioxidant power (FRAP) assay. The analyses showed that the extract from P. pyraster fruits is characterized by a higher content of phenolic compounds and a higher antioxidative potential compared with that from P. ×myloslavensis. In extracts of both pear species, seven phenolic compounds and four organic acids were identified. The total fiber content in pears of P. pyraster and P. ×myloslavensis was determined at 36.45 g and 24.74 g/100 g d.m. of the pear fruits, of which most comprised the insoluble fraction (32.49 g and 20.86/100 g, respectively). The results of the conducted research are highly significant, as they confirm that pears contain many valuable nutrients and biologically active compounds, including antioxidants and dietary fiber. Adding pear extracts to food products may offer a way to boost their health benefits while also broadening the variety of items that have appealing sensory characteristics. Moreover, research has shown that fruit extracts can help to prolong the shelf life of food products by safeguarding them against lipid oxidation and the decline in their nutritional value. Full article

An alkali–silica reaction (ASR) is a chemical process that leads to the formation of an expansive gel, potentially causing durability issues in concrete structures. This article investigates the properties and behaviour of ASR products in mortar with the addition of low-purity calcined clay as an additional material. This study includes an evaluation of the expansion and microstructural characteristics of the mortar, as well as an analysis of the formation and behaviour of ASR products with different contents of calcined clay. Expansion tests of the mortar beam specimens were conducted according to ASTM C1567, and a detailed microscopic analysis of the reaction products was performed. Additionally, their mechanical properties were determined using nanoindentation. This study reveals that with an increasing calcined clay content, the amount of the crystalline form of the ASR gel decreases, while the nanohardness increases. The Young’s modulus of the amorphous ASR products ranged from 5 to 12 GPa, while the nanohardness ranged from 0.41 to 0.67 GPa. The obtained results contribute to a better understanding of how the incorporation of low-purity calcined clay influences the ASR in mortar, providing valuable insights into developing sustainable and durable building materials for the construction industry. Full article

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. Full article

This article examines the problem of the service life of reinforced concrete structures intended for nuclear power plants and radiation waste storage bunkers when exposed to radiation. This research focused on assessing the corrosion resistance of steel bars under conditions of simultaneous exposure to gamma radiation and various environmental conditions affecting the rate of carbonation. Electrochemical measurements of steel bars were carried out on samples in three environmental conditions: in a laboratory–dry; enclosed in a can at RH = 50%; and enclosed in a can at RH = 100%. The durability of the passivation layer of steel on non-irradiated and irradiated specimens after 8 months of exposure to gamma radiation was compared. A lower degradation effect of gamma radiation was visible in fully water-saturated specimens. Full article

This article presents the results of an experimental investigation into the mitigation of the alkali–silica reaction (ASR) resulting from using low-grade clay calcined at 850 °C. The clay used in the experiment was domestic clay with an Al₂O₃ content equal to 26% and a SiO₂ content of 58%. The performance of calcined clay in ASR mitigation was evaluated according to ASTM C1567 using reactive aggregates. The control mortar mixture consisted of 100% Portland cement (Na₂O_eq = 1.12%) binder and reactive aggregate. The test mixtures used the same reactive aggregate and binders, in which part of the cement was replaced with either 10%, 20% or 30% calcined clay. The microstructure of specimens was examined on the polished sections using a scanning electron microscope (SEM) operated in the backscattered mode (BSE). The results of expansion obtained from the mortar bars made with the reactive aggregate showed that replacing cement by calcined clay reduced their expansion, with the level of expansion decreasing with the increase in the level of cement replacement. Full article

During the wintertime, concrete pavements experience harsh exposure conditions due to the presence of both the freezing–thawing and wetting–drying cycles. Airport concrete pavements are commonly de-iced using chloride-free organic salts such as potassium formate or potassium acetate. However, these materials contain alkali ions which can have harmful effects on both the cement matrix and the aggregate. Specifically, there is an increased risk of occurrence of the alkali–silica reaction (ASR). The goal of this research was to estimate the influence of potassium formate on the potential of causing alkali–silica reaction in aggregates with different categories of reactivity (R0, R1, R2). The accelerated mortar bar test and its modification (which involves replacing sodium hydroxide solution with a potassium formate solution) were used. Detailed SEM-EDS examinations were performed to confirm the presence of alkali–silica reaction and to analyze the influence of potassium formate on the microstructure of mortar. Full article

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. Full article