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1

Effect of concrete class, maximum aggregate size and specimen size on the compressive strength of cores and cast specimens

Merabti Salem

Advances in Materials Science

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2022

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Vol. 22, nr 4(74)

21--31

EN

Core sampling is the most accurate method of evaluating the compressive strength of concrete structures. However, it is preferable to take only small cores to avoid damaging the structures. It turns out that various elements influence the strength of compressed cores. This study examines the influence of specimen size, aggregate size, concrete class, and curing method on compressive strength. Three aggregates measuring 3/8, 8/15, and 15/25 mm are used to make six sets of concrete compositions with strengths of 25 MPa and 30 MPa. Nine specimens are made, one for each variety of aggregate and concrete. Cores of 100 mm, 75 mm, and 50 mm sizes are made. These cores are extracted from concrete blocks curing in the outside air to simulate the real concrete curing environment. Cast specimens cured in water and air with diameters of 50 mm, 100 mm, and 150 mm are also made. The objective is to compare the average compressive strength of all cast or extracted specimens with that of cylindrical standard specimens of diameter 150/300 mm and the cores and cast specimens. The obtained findings showed that the compressive strength is overestimated when we compare fp100 cores and standard air-cured specimens (fc), with a conversion factor varying from 0.69 to 0.96. However, a decrease is observed in comparison with water-cured specimens. The use of fp75 cores reduced the conversion factors, which are between 0.83 and 0.87 for B25 concrete. The highest fp/fc ratios are obtained for fc50 cores, which can reach 1.24. It turns out that the size of the core and the class of concrete have a much greater influence on the fp/fc ratios.

2

Comparative analysis of the effect of vernonia amygdaline on subsea transmission pipeline

Samson N., Nwaoha T. C., Emmanuel U. O.

Journal of Mechanical and Energy Engineering

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2018

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Vol. 2, No 4

269--276

EN

Subsea transmission pipelines (STP) are designed to transport liquids, gases or solid/liquid mixtures over some distances. STP are buried underground or submerged in water for transportation of natural oil and gas (O&G) products. A Vernonia amygdalina (VA) solution is prepared to act as an inhibitor. The specimens are kept in a workable state. Steps are taken to prepare each specimen. All cuts and sheared edges were ground out to prevent them from becoming sites for preferential attack. The finishing of the specimen surface with grit abrasive paper (sand paper) and rinsing of the specimens in distilled water are carried out. Then, degreasing of specimen in acetone and air-dried are carried out. Upon drying, the specimens are immediately weighed to obtain their initial weights. Twelve specimens are used for the test as follows: 6 Aluminum (Al); and 6 mild steel (MS) samples. With a 2M concentration of VA solution, the MS and Al samples are immersed in different plastic containers containing 400ml of seawater with pH value of 7.25 with no (0%) inhibitor added to it. A 5% (400ml) of the VA solution is poured into the measuring cylinder for each sample-Al and MS. The specimens are suspended by the strings and completely immersed in the different percentage test media. The same procedure is carried out for each of the different percentages (i.e. 10%, 15%, 20%, and 25%) and a total of 12 solutions are set up. The seawater used has 7.25 pH. At the end of every week (168 hours), the specimens are removed from the corrosive media. Observation and recording of appearance of the specimen, noting sites are done to analyze the effect of the VA solution on the AL and MS used for the STP. Values are obtained and graphs plotted on weight loss (WL) and corrosion rate (CR) versus the time. It is observed that the VA solution has different effect on the STP at different time and percentage of the VA solution introduced into the environment of the pipe. It was also observed that optimum inhibition of coupons is obtained between 15-25% of VA solution during the first four weeks of testing. At the fifth week, the inhibitor was gradually losing its effectiveness. This means that more inhibitor needs to be added at regular intervals in order to sustain the effectiveness of the inhibitor.

3

Wykorzystanie związków powierzchniowo czynnych na etapie przygotowania próbek do analizy jako zielona alternatywa dla konwencjonalnych technik ekstrakcji

Melnyk A., Wolska L., Namieśnik J.

Analityka : nauka i praktyka

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2014

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nr 4

16--23

PL

Związki powierzchniowo czynne stanowią doskonałą alternatywę dla rutynowo stosowanych, zazwyczaj żmudnych i czasochłonnych, technik przygotowania próbek, do przeprowadzenia których nierzadko wykorzystuje się duże ilości odczynników chemicznych.

4

New Method for the Objective Evaluation of Textile Hand

Strazdienė E., Gutauskas M.

Fibres & Textiles in Eastern Europe

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2005

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Vol. 13, no. 2 (50)

35--38

EN

The investigations presented show that pulling a disc-shaped specimen through the rounded hole can be considered as a perspective test method for textile hand evaluation. It was determined that the process of pulling a comparatively big specimen (∅ 113 mm) through a relatively small hole (∅ 20-40 mm) ends in the formation of a shell which has a complicated time-dependant shape. Under the stand of the test unit, the shell becomes cone-shaped, but above the stand it obtains the shape of a waved disc, the roughness of which increases with the decrease in its diameter. The aim of this research was therefore to reveal the application possibilities of pulling the material disc through the round hole for the objective evaluation of textiles hand, and to investigate the effect of fabric type, its anisotropy level, and the proper selection of testing regimes upon the character of the pulling process.

PL

Przeprowadzone badania pokazują, że przepychanie próbki materiału o kształcie krążka przez okrągły otwór w płytce, może być uważane za obiecującą metodę testowania dla oceny chwytu. Stwierdzono, że proces przeciągania stosunkowo dużej próbki (o średnicy 113 mm) przez stosunkowo mały otwór (o średnicy 20-40 mm) powoduje powstanie muszlo-kształtnego tworu o skomplikowanym kształcie, zmieniającym się podczas przeciągania. Pod płytką próbka przyjmuje kształt stożkowy a nad płytką kształt okrągłego wachlarza, przy czym jej szorstkość wzrasta z maleniem średnicy. Celem badań była ocena możliwości stosowania tego testu do obiektywnego określenia chwytu badanego materiału. Badano efekt rodzaju materiału i jego poziomu anizotropowości na wynik, jak również oceniano prawidłowy dobór warunków testowania na charakter procesu przepychania