STUDY ON COMPRESSIVE STRENGTH AND CHLORIDE ION PERMEABILITY OF HIGH FLY ASH CONTENT SELF-COMPACTING CONCRETE

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.