Life Cycle Assessment of Conventional and High Performance Concrete with Partial Cement Replacement by Agroindustrial Ashes: A Strategy for Achieving Sustainable Development Goals
Posted: 18 Jun 2019
Date Written: June 16, 2019
Concrete and urbanization are almost described as synonymous due to intensive use of this material to build cities. Although "concrete cities" is a negative term to describe environmental deterioration of green areas replacement by impermeabilized ones, it is essential to recognize the role of this material in urban development. Portland cement, the main material of concrete, is a binder that applies cheap raw materials and has versatile uses due its strength and durability performance. On the other hand, decarbonation of limestone for clinker production is carbon intensive, representing about 50% of CO2 emissions from cement production. In this sense, even disruptive technologies must be investigated, there is a range of well-studied technologies that could be short-time implemented in order to reduce environmental impacts, especially global warming potential and depletion of natural resources of Brazilian building sector.
This article aims to evaluate the environmental performance of a traditional structural concrete compared with new concretes with partial cement replacement by ultrafine sugarcane bagasse ash and ultrafine rice husk ash applied in two classes of concrete, conventional (25MPa) and high performance (60 MPa). A cradle to gate life cycle assessment (LCA) was performed according to the ISO 14040:2006 using the CML-IA method and the SimaPro software. Based on functionality principle of the LCA, this study has incorporated a performance functional unit, including strength and durability aspects, defined as “the amount of concrete (m³) to delivery one MPa of compressive strength and one year of service life”. Results showed that partial cement replacement by agroindustrial ashes can provide longer service life while maintaining or enhancing mechanical performance. Because of that, its application enhances the environmental benefits achieved by 20% or 40% reduction of cement consumption. Besides, high performance concrete, even with more cement consumption, allows reducing volumetric dimensions and enhancing durability of the structure, which results in a better environmental performance in comparison with conventional concrete. Although rice husk ash has better pozzolanic properties, resulting in a reduction of more than 65% for all environmental impact categories, this study has also pointed out technical and environmental viability of sugarcane bagasse ash as supplementary cementitious materials, reducing approximately 25% of abiotic resources depletion and more than 30% of global warming potential impacts in both concrete classes. Moreover, ternary blended cement with 20% of each kind of ash decreases at least 40% of potential environmental impacts.
Recognizing the principles of circular economy and the sustainable development goals, including those intended to promote more sustainable industries with increased resource-use efficiency and greater adoption of clean and environmental technologies and to act to combat climate change, this technological route figures as an important strategy for cement industry in Brazil. Considering that cement solutions must be designed in regional scale, millions of tons of sugarcane bagasse ashes are already available as waste of biomass thermal power plant in Southeast region and an expressive amount of rice husk is produced in South region.
Keywords: sustainable concrete, CO2, global warming, cement, sugarcane, rice husk, life cycle assessment, lca, ash, pozzolan
JEL Classification: L61, O14, Q54, Q56
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