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Water footprint of widely used construction materials : steel, cement and glass

Bosman, R. (2016) Water footprint of widely used construction materials : steel, cement and glass.

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Abstract:Although water is an abundant and renewable substance on earth, the available amount of water to man is limited as the amount of precipitation, water flowing through a river or ground water aquifer is always limited in a certain time period. Furthermore, the water demand is expected to increase in the future. When water use is not properly managed this can result in unsustainable water use. After agriculture, the industrial sector is responsible for the largest amount of water withdrawal, and the water use by this sector is expected to increase. In contrast to agricultural products where quite some research has been done on the water footprint of several products, industrial products have not been researched as much. This research focusses on widely used construction materials. Five end products are chosen to be researched: unalloyed steel, chromium-nickel alloyed steel, ordinary Portland cement, Portland composite cement and sodalime float glass. These are the most produced types of steel, cement and flat glass. The water footprint concept introduced by Hoekstra takes indirect water consumption into account. This means that beside direct water consumption like cooling and cleaning water also water consumption for the input products is accounted for in the water footprint of the end product. In order to determine the water footprint of the end product the entire supply chain is considered in the research. For steel cement and glass, the supply chain begins with acquiring the raw materials. Transport of materials is left out of the scope of this research, because it is expected that the water footprint of transport is to be negligible unless biofuels are used for transportation. After acquiring the raw materials they are processed though different production processes. Some processes for the production of materials like steel, cement and glass require large amounts of energy. The supply of the fuels and generation of electricity also requires water and therefore the energy required for the production of these materials results in a water footprint which have to be allocated to the final product. Furthermore, production processes for these materials can lead to an effluent containing certain polluting substances leading to a grey water footprint. Major processes along the supply chain and their direct process water consumption are taken into account for this research leaving the water footprint tied to the energy consumption as the remaining indirect blue water footprint. The study uses existing knowledge about the blue water footprint of some energy sources. For other fuel sources, i.e. petroleum products and cokes, the blue water footprint is calculated. Depending on the fuel type used for production processes the water footprint tied to energy use can be a significant part of the total blue water footprint. Water and energy consumption data as well as pollution data is mainly obtained from the ecoinvent database version 3.2. It was found that the blue water footprint of chromium nickel alloyed steel with 77 L/kg is much larger than that of unalloyed steel with 11 L/kg. This is attributed to the energy demanding ferroalloy production which usually occurs in electric arc furnaces using electricity as energy source. For cement, clinker production by pyroprocessing is one of the most energy and water consuming processes. Reducing the ratio of clinker in cement by using supplementary materials can reduce the water footprint of cement. A blue water footprint of ordinary Portland cement was calculated between 2.0 – 2.6 L/kg, depending on the source of gypsum. For CEM II/B Portland composite cement with 21-35% supplementary materials a blue water footprint was calculated between 1.7 – 1.8 L/kg. Choosing a Portland composite cement over an ordinary Portland cement can be beneficial for minimising the water footprint of structures. For soda-lime float glass it was found that, beside the energy consuming glass melting, the Solvay process for soda ash production is a large contributing process to the water footprint of float glass. Large amounts of water is used for the Solvay process. Water uses are for brine and milk of lime production, process steam and cooling. Overall the water footprint tied to energy consumption is a significant part of the blue water footprint of the researched materials. This is attributed to the energy demanding processes and to the large water footprint of electricity. The grey water footprint of the end products is calculated per process and polluting substance by using ecoinvent version 3.2 data for effluent loads and the lowest value from maximum concentration guidelines from Canada (CCME), Europe (EU) and the United States (US-EPA) and maximum concentrations from the EEC (1975) guideline. For steel it was found that the largest grey water footprint is produced by concentrating iron ore. The grey water footprint for unalloyed steel is 2,300 L/kg steel for the polluting substance cadmium. For chromium-nickel alloyed steel the grey water footprint was found to be 1,500 L/kg steel for the polluting substance cadmium. For cement, the grey water footprint depends on whether gypsum through flue gas desulphurisation is used and whether the grey water footprint from this process is allocated to gypsum and ultimately to cement or not. If this is the case then the grey water footprint for ordinary Portland cement and Portland composite cement was found the be 210 L/kg. If the grey water footprint from flue gas desulphurisation is not applicable then the grey water footprint of ordinary Portland cement was found to be 0.63 L/kg cement for cadmium and for Portland composite 0.45 L/kg cement for cadmium. For float glass the grey water footprint is largely dependent on the Solvay process. The effluent contains heavy metals and suspended solids resulting in a grey water footprint of 1,300 L/kg glass where suspended solids are the determining material for the grey water footprint. Overall the grey water footprint is potentially much larger than the blue water footprint of the researched materials.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering and Management MSc (60026)
Link to this item:http://purl.utwente.nl/essays/69751
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