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Mechanical properties and flexural behaviour of reinforced concrete beams containing recycled concrete aggregate

Dawood Malak H., Al-Asadi Ali K.

Przegląd Naukowy Inżynieria i Kształtowanie Środowiska

2022

Vol. 31, No. 4

259--269

Increasing waste recycling has become an essential process in the construction industry due to the environmental and economic advantages, such as minimizing waste in landfills, saving natural resources, and decreasing pollution. Crushing and sieving waste from standard compression test cubes is used to produce the recycled concrete aggregate (RCA). A set of standard concrete cylinders, cubes, and beam specimens were made by utilizing coarse aggregate replacement ratios of 0%, 30%, 50% and 70%. At the day 28 stage, the specimens were tested to determine compressive strength, stress–strain relationship, splitting tensile strength, and flexural strength. In addition, four reinforced concrete (RC) beams were cast and tested under a four-point load to evaluate the flexural behaviour of RC beams with partial replacement of the natural aggregate with RCA. One was a natural aggregate (NA) control beam, while the others had varying RCA ratios (30%, 50% and 70%). The results show that the compressive strength of RCA concrete with the replacement by 30%, 50% and 70% decreased by 9.10%, 18.88% and 22.57% respectively, in comparison to the compressive strength of normal concrete (NC). The RCA concrete showed a high strain capacity, which indicated high ductility. The maximum RCA type strains ranged from 0.0056 to 0.0072. Concrete flexural strength showed a slight decrease in comparison to NC (18.83% decrease), where the tensile strength showed a 10.61% decrease in comparison to NC. As for RC beams, the load-carrying capacity decreased by 10.5% with increases in the replacement ratio.

Nowe aspekty metodyki oznaczania N-nitrozoamin

Witkowska Anna B., Zezula Marta, Glice Magdalena, Stolarczyk Elżbieta U.

Przemysł Chemiczny

2021

T. 100, nr 3

230--239

Przedstawiono przegląd literaturowy dotyczący rozpoznania mechanizmów powstawania N-nitrozoamin w różnych matrycach, takich jak próbki biologiczne, wody powierzchniowe i pitne, kosmetyki, substancje czynne lub produkty farmaceutyczne oraz kryteria ich oznaczania na bardzo niskich poziomach stężeń. Zastosowanie detektora spektrometrii mas i tandemowego detektora mas w chromatografii cieczowej i gazowej pozwoliło na opracowanie czułych metod oznaczania nitrozoamin z wykorzystaniem odpowiednich technik wyodrębniania i wzbogacania analitów.

A review, with 63 refs., of recognition of the N-nitrosamines formation mechanisms in various matrices, such as biolog. samples, surface and drinking waters, cosmetics, active substances or pharmaceutical products, and the criteria for detg. them at very low concn. The use of the MS detector and tandem mass detector in HPLC and GC allowed for the development of sensitive methods for the detn. of nitrosamines at a very low level, using appropriate techniques of isolation and enrichment of analytes.