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Pre- and post-heating mechanical properties of concrete containing recycled fine aggregate as partial replacement of natural sand and nano-silica as partial replacement of cement: experiments and predictions

Shirvani Mohammad Asghari, Khodaparast Afshin, Herozi Morteza Rezaeizadeh, Mousavi Reza, Fallah-Valukolaee Saber

Archives of Civil and Mechanical Engineering

2023

Vol. 23, no. 4

art. 219, s. 1--27

In this study, the effect of colloidal nano-silica replacing a fraction of cement and recycled concrete fine aggregate replacing natural sand on the post-fire mechanical features and durability of concrete was explored. To achieve this goal, 189 concrete samples were manufactured in total, with key variables being the volume of fine aggregate at 0,50, and 100% replacing natural fine aggregate, the volume of nano-silica at 1.5, 3, 4.5, and 6% replacing the cement weight, and the exposure temperature at 20, 300, and 600oC. Parameters selected for consideration in the concretes consisted of compressive capacity, splitting tensile capacity, elastic modulus, ultrasonic pulse velocity (UPV), and weight loss. Furthermore, using scanning electron microscopy (SEM) imaging, the microstructural condition of different sample groups was investigated. According to the findings, as the content of the recycled fine aggregate (RFA) replacing natural fine aggregate increased, the compressive capacity of the unheated and heated concretes declined, and the rate of this drop became greater as the replacement volume increased. On the other hand, the presence of the nano-silica and an increase in its content replacing the cement content in recycled aggregate concrete improved the compressive strength relative to the reference concrete for all the exposure temperatures, with the greatest improvement for the replacement percentage of 4.5%. In addition, the heat-induced compressive capacity drop was more pronounced at higher replacement levels of nano-silica. With a rise in the exposure temperature of the samples with only the recycled fine aggregate, fewer microcracks formed compared with the samples containing both recycled fine aggregate and nano-silica. The maximum weight loss occurred in the recycled sample containing the highest contents of nano-silica and recycled aggregate. Afterward, it was attempted to estimate the mechanical features of concrete by developing several empirical formulas as a function of temperature and volume fractions of recycled fine aggregate and nano-silica. These formulas were evaluated against the test data of this study and others, which showed an acceptable correlation. Finally, the findings of the tests were evaluated against the predictions of ACI 216, EN 1994-1-2, EN 1992-1-2, and ASCE.

Wpływ stosowania drobnego kruszywa z recyklingu na wybrane właściwości kompozytów cementowych

Pawluczuk E., Kozak K.

Budownictwo i Inżynieria Środowiska

2016

Vol. 7, no. 1

39--45

Praca dotyczy ustalenia wpływu stosowania drobnego kruszywa z recyklingu na wybrane właściwości kompozytów cementowych. Frakcję z recyklingu uzyskano w wyniku rozdrobnienia wcześniej przygotowanych do tego celu próbek laboratoryjnych z normowej zaprawy cementowej. Do zrealizowania badań zaplanowano pełny eksperyment obejmujący w sumie 11 serii, w którym zmiennymi były: zawartość drobnego kruszywa z recyklingu (0-60%) oraz temperatura jego prażenia (0-850°C). Na podstawie uzyskanych wyników badań stwierdzono, że drobne kruszywo z recyklingu generalnie negatywnie wpływa na badane właściwości kompozytów cementowych. Efekt ten może być jednak ograniczony poprzez zastosowanie obróbki termiczno-mechanicznej drobnej frakcji recyklingowej.

The paper concerns the determination of the influence of using the fine recycled aggregates on selected properties of cement composites. Fine recycled aggregate was achieved as a result of crushing laboratory samples made of standardised cement mortar. To perform the test complete experiment consisting of 11 series was planned. Two different variables were: X1 – content of fine recycled aggregate (0-60%) and X2 – the temperature of mortar rubble roast (0-850°C). Based on the obtained results it was found that the fine recycled aggregate generally deteriorates the tested properties of cement composites. On the other hand this effect may be significantly limited by the use of thermal-mechanical treatment of recycled rubble.