Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 5 de 5
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
Materials (Basel) ; 16(23)2023 Nov 23.
Artigo em Inglês | MEDLINE | ID: mdl-38068032

RESUMO

The rapid expansion of construction, fueled by industry and economic and population growth, has exacerbated the challenge of managing construction waste, especially concrete waste. One promising solution lies in the utilization of recycled fine aggregate (RFA), especially in combination with the emerging geopolymer technology, an innovative alternative to traditional cement. This study systematically explores the effects of incorporating varying qualities and quantities of RFA into geopolymer mortars. By using GGBS and FA as raw materials and replacing natural aggregates (NA) with RFA at different rates (25%, 50%, 75%, and 100%), the research investigates the fresh properties, mechanical characteristics, and drying shrinkage of geopolymer mortar. Key findings reveal that RFA significantly influences the flowability of geopolymer mortar: when RFA content is above 75%, preprocessed RFA (with particles below 0.15 mm removed) has substantially improved flowability, increasing it more than 20%. The critical impact of RFA preprocessing on enhancing mechanical properties and the higher the inclusion level (above 75%), the more pronounced is the advantage in enhancing the compressive strength compared to unprocessed RFA. Additionally, RFA was found to contribute to a denser interfacial transition zone (ITZ) than natural aggregate, which helps maintain the compressive strength at increased RFA dosages. Contrary to findings in cement mortar, a positive correlation exists between pore volume and compressive strength in geopolymer mortar incorporating RFA. This study underscores the potential of refined RFA preprocessing methods in advancing sustainable construction, highlighting avenues for the broader application of RFA in geopolymer mortar.

2.
ACS Omega ; 8(30): 27794-27801, 2023 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-37546604

RESUMO

Coal fly ash (CFA) is one of the industrial byproducts of burning coal for energy production and has unburned carbon, which negatively affects its full potential use. The flotation technology can be effective in separating unburned carbon from CFA, and the prestirring time is crucial for the ideal initial conditions during the flotation process. To find the suitable prestirring time, eight prestirring times, including 0, 1, 2, 3, 4, 5, 6, and 7 min, were selected in this paper, followed by flotation of CFA after prestirring. Parameters such as loss on ignition (LOI), the removal rate of unburned carbon (RUC), contact angle, and particle size volume fraction were used to assess the effect of prestirring time on flotation results. The results showed that the prestirring time significantly affects the CFA flotation performance. As the prestirring time increased, the LOI of CFA first decreased and then increased, and the contact angle showed the opposite trend. Besides, the prestirring time of over 2 min positively affected the fineness of the tailings. Overall, the prestirring time of 3 min had the most significant carbon removal effect, obtaining an LOI of tailings of 0.96%, a yield of 74.56%, an RUC of 72.70%, and a volume fraction less than 45 µm of 36.65%. This study provides theoretical support for improving stirring efficiency and saving flotation costs in industrial applications and is conducive to the recycling of CFA resources.

3.
Materials (Basel) ; 16(7)2023 Mar 27.
Artigo em Inglês | MEDLINE | ID: mdl-37048939

RESUMO

Curing temperature affects the compressive strength of cement paste systems via the pozzolanic reaction. However, different processes, climates, and weather conditions often result in different initial curing temperatures. The relationship between curing temperature and compressive strength is still an underexplored domain. To explore the effect of curing temperature on calcium hydroxide (CH)-based fly ash composites, fly ashes from different carbon sources were used to make CH-based composites, and the compressive strength, reaction rate, CH content, and C-S-H generation were analyzed. The correlation between the reaction rate and C-S-H content was analyzed. High-temperature curing improved the compressive strength of the cement paste system by affecting the CH-based reaction rate in the initial stage, with the highest initial reaction rate reaching 28.29%. However, after cooling to constant temperature, high-temperature curing leads to a decrease in CH and C-S-H content. The average decrease rate of calcium hydroxide content under high temperature curing is 38%, which is about 2.38 times that of room-temperature curing conditions. This led to a decrease in the compressive strength of the cement paste. Therefore, the performance of CH-based fly ash composites produced by low-temperature curing was superior to that of composites produced by high-temperature curing.

4.
Materials (Basel) ; 16(1)2022 Dec 28.
Artigo em Inglês | MEDLINE | ID: mdl-36614644

RESUMO

With the rapid development of urbanization, the construction industry consumes a lot of cement and produces a large amount of construction waste. To overcome this situation, the rational use of recycled aggregate produced from waste concrete is one of solutions. In some countries, the building industry has approved the use of recycled coarse aggregates in concrete, with some limits. However, practically all existing standards and regulations prohibit the use of recycled fine aggregate (RFA) in concrete. Therefore, study on improving the performance of RFA concrete is vital. In this study, the effects of fly ash and GGBS on concrete with RFA were investigated. Compressive strength, pore structure, drying shrinkage and accelerated carbonation were tested. The correlation between the pore structure and properties of concrete was analyzed. The results show that adding fly ash and GGBS to RFA concrete increased its compressive strength, modified pore structure, reduced drying shrinkage, and even achieved higher compressive strength and lower drying shrinkage than normal concrete. The compressive strength was mainly affected by the capillary pores, and the carbonation was mainly affected by the gel pores.

5.
Materials (Basel) ; 14(21)2021 Oct 29.
Artigo em Inglês | MEDLINE | ID: mdl-34772054

RESUMO

The unburned carbon in fly ash inhibits the performance of concrete. A device using the flotation method to remove unburned carbon in fly ash was developed, and the operating condition of the device was experimentally examined. According to the results, the device was able to remove unburnt carbon from fly ash by using the installed micro bubble nozzles and a whirl-type pump. The removal efficiency of unburnt carbon improved when prior forced stirring was carried out by a concrete mixer for 3 min, and a scavenger was added into the fly ash slurry at a density of about 60 wt%. It has also been confirmed that the method of circulating water is more effective than the method of not circulating water. The elements of the modified fly ash slurry (MFAS) have also been experimentally confirmed as not being too different from untreated fly ash, except for the fact that the content of unburned carbon is reduced. The compressive strength and drying shrinkage characteristics of concrete made with MFAS were investigated. The use of MFAS will reduce the performance of concrete compared to that of ordinary concrete. This shows that in a certain range (15-30%), the influence of MFAS on drying shrinkage is constant. The static elastic modulus and dynamic elastic modulus were also investigated. The above results show that the application of MFAS prepared by the flotation method to concrete is feasible.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...