Abstract
This article approaches concrete mix designs where cement is replaced by high amounts of slag and fly ash, with the purpose of turning it into a more sustainable construction material, that is, an authentic green concrete. Mix proportions with fly ash, ground-blasted furnace slag, and Portland cement were studied in binary and ternary mixtures for compressive strength levels of 40 MPa and 55 MPa. The replacement of cement with mineral additions ranged from 50% to 90% in mass. Mean decreases of 55% in the energy consumption, 78% in the CO² emissions, and 5% in the cost of the concrete m³, plus an increase of 40% in the mean index of durability were obtained, all ofwhich compared to the 40-MPa reference concrete. This study attests the technical, economical and environmental potentialities for theuse of concrete mixtures with until 90% of fly ash.
Highlights
The civil construction consumes great part of the natural resources extracted from the planet and concrete is the greatest cause of this consumption, regarded as the second most consumed material by mankind, topped by water
Mean decreases of 55% in the energy consumption, 78% in the CO2 emissions, and 5% in the cost of the concrete m3, plus an increase of 40% in the mean index of durability were obtained, all of which compared to the 40-MPa reference concrete
The know-how and the mastering of both technology and utilization of these residues improved during that period, and they are widely used nowadays in several types of concrete structures. The advantages of this substitution are significant in the technical field, in the economic aspects and, mostly, in the environmental issues because of the reduction in CO2eq emission, in energy consumption and, many times, in the direct cost, is proportional to the quantity of mineral additions used in the mixture instead of cement
Summary
The civil construction consumes great part of the natural resources extracted from the planet and concrete is the greatest cause of this consumption, regarded as the second most consumed material by mankind, topped by water. The use of mineral additions such as fly ash and ground granulated blast-furnace slag - in the concrete is worthy because it brings economic advantage when cement, a material of high added value in terms of cost and energy, is replaced by one or more types of mineral additions, by-products which feature economic and energetic low value This action fits in the sustainability concept where everybody profits: the producer, for delivering a product at a lower cost (or almost always); the consumer, for acquiring a more durable material; and the society, for keeping the environment with lower levels of pollution and better preserving natural resources. Mehta [4] declares that superplasticized concrete mixtures containing 60 to 70% of fly ash or slag in the mass of the total cementitious material have shown high strength and durability at relatively early ages, and that large-scale cement replacement in concrete with these industrial by-products will be highly advantageous from the standpoint of cost economy, energy efficiency, durability and overall ecological profile of concrete. Hand, an increase in durability, highlighting a holistic advantage of replacing cement with high contents of mineral additions
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