González Solá, Luis

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    Mechanical, durability and financial analysis of concrete mixtures with nanosilica, silica fume and fly ash
    (2020-05-14) González Solá, Luis; Molina-Bas, Omar I.; College of Engineering; Cáceres, Arsenio; Acosta-Costa, Felipe J.; Portela-Gauthier, Genock; Vidot-Vega, Aidcer L.; Department of Civil Engineering; Jiménez-Cabán, Esbal
    This study encompasses the analysis of mechanical properties, durability and cost-effectiveness of concrete mixtures with nanosilica particles, silica fume and fly ash utilized as admixtures. The cost of materials for the all mixture designs will be considered along with the data from the mechanical and durability tests in order to determine the most cost-effective admixture proportions. Previous studies have proven the increased performance of concrete, especially in compressive strength, when nanosilica is utilized as an admixture in concrete, however, due to the high cost of manufacturing the use of nanosilica is in some cases prohibitive. To reduce costs, nanosilica is often combined with less expensive admixtures such as silica fume and fly ash. Twelve different concrete mixture designs were considered. These mixtures were divided into four groups: mixtures with nanosilica as the only admixture, mixtures combining nanosilica and fly ash, mixtures combining nanosilica and silica fume, and mixtures that utilized all three. For the first three groups the values of the percentage of cementitious material consisting of nanosilica were 0%, 1.5% and 3%. For the second and third groups, the dosage of nanosilica remains unchanged and the percentages consisting of silica fume and fly ash were constant at 20% respectively. For the last group, which combined the three admixtures, the values of nanosilica were fixed at 1.5% and the dosage combinations of fly ash and silica fume were varied, but always totaled 20% of cementitious material in the mixture. The mechanical properties being studied are the compressive strength and tensile strength by means of the split log test. The durability properties analyzed are permeability measured in the rapid chloride ion penetration test, pore structure and composition utilizing mercury intrusion porosimetry analysis and chemical composition by means of differential thermal analysis and x-ray fluorescence analysis. The cost-benefit analysis will be performed in order to determine if the increase in mechanical properties and an improvement in durability properties can justify the increased costs of a mixture design containing high cost additives such as nanosilica particles. For each of the mixture sub-groups the best performing mixture will be determined taking into consideration all of the studied parameters: mechanical performance, durability properties and material costs. These results could serve as a guide for the construction industry. For example, it was shown that at an age of 180 days a concrete mixture design using silica fume and fly ash improves compressive strength and reduce permeability in a cost effective manner. For this mixture the compressive strength is 1.39 times higher than the control mixture and cost is 1.46 times that of the control. The increase of cost was directly proportional with the increase in compressive strength with the added benefit that permeability is reduced by a factor of 0.11 relative to the control mixture.