ReviewEnvironmental impacts, life cycle assessment and potential improvement measures for cement production: a literature review
Introduction
Cement is a fine-powdered substance that, when mixed with water and aggregates, presents high adhesive (cementitious) properties. It is produced from limestone, clay, and sand; these raw materials provide lime, silica, alumina and iron, the key ingredients required. Cement production consists of three main stages: raw material preparation, clinker production, and cement preparation (International Energy Agency, 2009).
Limestone, clay, and other raw materials are quarried or mined and transferred to the manufacturing plant, where they are crushed and milled. They are mixed in the right proportions to reach the required composition. The composition depends on the quality and properties that each particular cement product demands.
The prepared composition is then fed into a kiln, usually after passing through a pre-heater, where it is exposed to temperatures up to 1450 °C. This process generates chemical and physical changes that transform the raw meal into clinker. This stage of the production is the most energy demanding.
The clinker is blended and ground with additives and other mineral components such as gypsum, slag, and fly ash that build up the required properties of the final product.
Depending on the moisture content of the material, cement production may be classified into four types: dry, semi-dry, semi-wet and wet. Dry and semi-dry processes are the most efficient and the most used nowadays (Benhelal et al., 2013, Galvez-Martos and Schoenberger, 2014, Wang et al., 2013). This literature review aims to (i) present the environmental impacts related to the cement industry worldwide, (ii) summarize previous Life Cycle Assessment (LCA) methodological approaches and results, and (iii) identify the environmental performance improvement measures in the reviewed studies.
In this study, previous studies regarding the environmental performance of cement products were reviewed. The review focused on those studies related to the environmental performance of cement production and those which applied LCA for the analysis.
Section snippets
Environmental impacts of cement production
On average, 1 ton of concrete is produced every year for every human being in the world (Lippiatt and Ahmad, 2004). Concrete is a composite material composed of cement, aggregates (sand, gravel, or crushed stone) and water. Cement manufacturing implies the use of large amounts of raw materials and energy (van Oss and Padovani, 2002), and its production accounts for 5% of global anthropogenic CO2 emissions (Hendriks, 2000). Due to vast urbanization, the use of cement has increased dramatically (
LCA of cement products manufacture
LCA is a tool for evaluating the environmental performance of a product (or service) during its life cycle. The life cycle of a product involves the processes that occur during resource extraction, production, logistics, use, and, end of life (EN ISO 14044:2006, 2006). The ISO14040-14044 series specify four steps for LCA execution: definition of goal and scope, inventory analysis, impact assessment, and interpretation (EN ISO 14044:2006, 2006):
Improvement measures
The International Energy Agency (IEA) focuses on four categories of improvement measures available for the cement industry regarding CO2 emissions reduction (International Energy Agency, 2009): energy efficiency, alternative fuels, clinker substitution, and carbon capture and storage (CCS). Among the reviewed literature, solutions regarding the first three categories are the most widely analyzed as they have been thoroughly developed through the years (Benhelal et al., 2013, Chen et al., 2014,
Discussion
Industrialization and urbanization greatly drive the growing demand for cement products. Current production levels result in important requirements of raw materials and energy resources by this sector. Also, this results in major environmental impacts. The environmental impacts caused by cement production are associated with mining and quarrying, waste disposal, materials storage, fuels and raw materials production, plant production capacity, clinker production, clinker content of the cement
Conclusions
Several case studies around the world assessed the environmental impacts of cement production. The reviewed literature identified hot spots and potential improvement measures in the cement industry. These measures are energy efficiency, alternative fuel use, material substitution, and CCS. Improvement measures focusing on the first three solutions are regarded as mature technologies, as they have been thoroughly studied and applied. These mature technologies are relatively low-cost and
Acknowledgments
This paper is based on work funded by Escuela Superior Politécnica del Litoral, ESPOL, Ecuador.
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