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Currently, in Vietnam, the natural sand resource is depleted; thus, it is unable to meet the growing demand for construction. In this context, recycled fine aggregate (RFA) from waste concrete emerges as an effective alternative for sand in the production of self-compacting concrete (SCC). In this paper, the author presents the experimental results on the properties of SCC with high fly ash content using RFA. The research utilizes RFA to replace natural sand at the rates of 0% and 100%, respectively while applying fly ash concurrently at a 50% volume ratio of cement. The evaluated properties of the SCC include its workability, compressive strength, flexural tensile strength, chloride ion permeability, and water absorption. The research results show that the use of RFA combined with high fly ash content can produce SCC that meets EFNARC requirements, with only a 1.48% reduction in compressive strength, 1.85% decrease in flexural tensile strength, 19.79% reduction in chloride ion permeability, and 5.12% increase in water absorption compared to the use of natural sand. These findings demonstrate the effectiveness of incorporating RFA and high fly ash to replace natural sand and cement in SCC production, opening up prospects in the construction industry with positive environmental impacts. [ABSTRACT FROM AUTHOR]

In Vietnam, the annual emission of fly ash from thermal power plants into the environment is substantial. Previous studies have demonstrated that using a high content of fly ash as a fine additive in the production of self-compacting concrete (SCC) can effectively reduce concrete production costs and contribute positively to environmental protection. This article presents the results of experimental research on the influence of high fly ash content on workability, compressive strength, and chloride ion permeability of SCC. The research involved substituting a portion of cement with fly ash at proportions of 50% and 60%, respectively, and the results were then compared with control samples without fly ash ("control samples"). The experimental findings indicate that using 50% and 60% high fly ash content can produce SCC mixtures with excellent workability, meeting the requirements outlined in the European guidelines, and significantly reducing the superplasticizer dosage compared to control samples. However, employing high fly ash content at 50% and 60% resulted in a reduction in compressive strength at the 28th day of age for SCC, ranging from 19.86% to 30.49% compared to the control sample. At the 90th day of age, the compressive strength increased by approximately 22.2% to 24.5% compared to the 28th day value. Furthermore, the use of high fly ash content also notably reduced the chloride ion permeability of SCC in later stages (i.e., after 28 days). The reduction ranged from 71.97% to 83.72% on the 28th day and from 92.76% to 94.07% on the 90th day, compared to the control sample. The chloride ion permeability of SCC containing 50% and 60% fly ash falls within the category of very low permeability. This research sheds light on the potential incorporation of high fly ash content in SCC production, providing insights into its workability and environmental benefits while considering the impact on compressive strength and chloride ion permeability. [ABSTRACT FROM AUTHOR]

The article presents the results of an experimental study on curing self-compacting concrete with a curing compound. The experiment was carried out under two natural weather conditions: hot and dry (summer) and hot and humid (autumn), in the Hanoi area. To evaluate the effectiveness of the curing method with a curing compound, three main aspects were studied: plastic shrinkage, water evaporation, and compressive strength of the samples. The experiment was conducted with three methods: (i) using a curing compound, (ii) using water spraying and (iii) no curing. The experiments showed that the sample cured with a curing compound has the smallest plastic shrinkage, corresponding to 0.67mm/m in hot dry conditions and 0.37mm/m in hot humid condition. In addition, the sample cured with a curing compound also has the smallest rate of water evaporation, corresponding to 12.7% and 5.12% in hot and dry, and hot and humid conditions respectively. At the same time, the self-compacting concrete sample cured with a curing compound has the best R28 sample compressive strength value, reaching 101.4% R28 tc in hot and dry conditions and 100.9% R28 tc in hot and humid conditions. These results, thereby, have proved the effectiveness of the curing method with a curing compound for self-compacting concrete under Vietnamese weather conditions. [ABSTRACT FROM AUTHOR]