StARS · Sustainable Aluminium Reinforced Seawater Concrete

Sustainable Aluminium Reinforced Seawater Concrete

Concrete is a material that is used extensively on earth after water. It is evaluated that, approximately 33 billion tonnes of concrete is produced worldwide every year and around 4.7 tons of concrete is consumed by each human being per year. Water is the chief ingredient for the concrete mix proportion and also the most important need for continuing life. According to the study of World Resources Institute (WRI), necessity of water is increased due to urbanisation, population growth and socio-economic development. However, Europe (EU) is not considered as an arid continent, but nearly half of the EU population is now facing problems in accessing freshwater. The EU consumes almost 668 km3 of water annually for production of all its goods and nearly 38% of this water is carried from the countries, outside of its border. It indicates that EU economy greatly relies on the accessibility of water from different regions of the world. Also, there is an uneven water distribution in EU due to its climate and geography and the activities of humans are making it worse. This problem is becoming more complex due to the development of infrastructure in EU which is demanding more quantity of water for mixing and curing of concrete and ultimately pressurising natural water resources. So, the use of alternative sources for natural water is turned out to be essential for concreting purposes. The surface of the earth is comprised of approximately 71% of water, out of which 96.54% of this water is seawater, 1.74% is permanent snow and Glaciers and remaining 1.72% is present as freshwater. Focusing on this issue, the use of seawater as a replacement of natural water for concreting is desired to achieve freshwater conservation and sustainability which is a need of an hour. However, according to most of the engineers, seawater is unsuitable for preparing reinforced concrete because it increases the threat of steel rebar corrosion and reduces the durability of concrete. The presence of chlorides in seawater combined with carbonation may cause depassivation of steel rebar and speed up corrosion process which leads to damage of the structure. Nowadays, aluminium (Al) is also used frequently after steel in civil engineering applications. Aluminium is available in abundant quantity and is the third most available material in the Earth’s crust after oxygen and silicon. Al or Al alloys are exposed to atmosphere, they create a dense invisible oxide layer of Al2O3 on their surfaces. This layer protects the Al surface from corrosion by inhibiting further oxidation. Although, it is considered that the Al bars should not be employed as reinforcement because the high pH of Concrete. Concrete will degrade the outer layer of Al2O3 present on the surface of the Al and corrode the metal. So, there is a need to keep the pH of concrete so low that it will not degrade the Al and also not produce the hydrogen gas. In this respect, use of Supplementary Cementitious Materials (SCMs) in concrete is found beneficial because they consume calcium hydroxide produced by the hydration of cement and maintain the pH of concrete sufficiently low, thereby preventing the corrosion of Al reinforcement bars. Thus, StARS finds the possibilities of using seawater in aluminium reinforced concrete and reducing the burden of utilising freshwater. To resist the corrosion of reinforcement due to seawater, the first time the aluminium bars will be used as reinforcement in concrete with seawater. The use of SCMs in concrete to replace cement partially, leads to minimising the CO2 emission in the environment and ultimately StARS moves towards a more sustainable concrete for the future. The concept of this proposal is shown in Figure 1. Objectives: There are following Objectives of the study: 1. Use of an alternative water source for concreting: Considering the issue of natural freshwater scarcity, many studies have been conducted to find alternative sources of freshwater for construction purposes. Moreover, seawater has also been used in numerous studies because it is available in tremendous quantity. The previous and current studies state that seawater does not affect the properties of plain concrete substantially. The problem in concrete prepared with seawater rises chiefly because of the rusting of steel reinforcement. Due to the presence of substantial amounts of chlorides in seawater, steel rebars come in contact with free chloride ions and the passivation layer on the steel begins to deteriorate which increases the threat of corrosion of steel rebar. 2. Use of non-corrosive reinforcement: To overcome the problem of corrosion of steel reinforcement due to seawater, the current study utilises Al reinforcement. Al is popular due to its non-corrosive nature. The modulus of elasticity of pure Al is 70 GPa whereas of steel is 210 GPa and the density of Al is 2.70 kg/m3 which is around 1/3 of iron (7.87 kg/m3). The lower E-modulus is a challenge, although part of this could be mitigated by designing the Al rebars differently. Further, ultimate tensile strength of Al is 110 MPa whereas in case of steel this value is 400 MPa. But, tensile strength of Al can be enhanced by alloying it with zinc, magnesium, silicon, manganese and copper. The Al shows around 274 and 395 MPa tensile strength when alloyed with 5% and 10% magnesium respectively. Due to possession of all these properties, aluminium reinforcement is a feasible alternative to other reinforcements even in seawater. However, there is a challenge in using Al reinforcement in concrete due to its degradation by high pH of concrete. 3. Producing low pH and sustainable concrete: Degradation of Al in high pH of concrete can be avoided by using SCMs in concrete which consume Ca(OH)2 from concrete matrix and resisted the corrosion of aluminium. Natural pozzolanic material such as clay is available in abundant quantity around the world and can also be used as SCM after calcination. The use of Calcined Clay (CC) helps in taking down the pH of concrete sufficiently low by consuming Ca(OH)2 and also reduces the evolution of H2 gas from aluminium at high pH. Further, the cement manufacturing process is responsible for 5 to 8% of the total worldwide CO2 emissions. The calcination of 1 ton of cement at 1400-1450°C temperature produces around 1 ton of CO2 whereas 0.3 ton of CO2 is produced by 1 ton of CC at 600-800°C temperature which is quite lower as compared to cement production. Therefore, CC leads to minimise the discharge of CO2 in the environment which improves the sustainability in construction and diminishing the environmental impacts. Hence, StARS covers the issue of utilisation of seawater in aluminium reinforced concrete and minimizes the exploitation of freshwater which will reduce the water footprint and also the partial replacement of cement with CC will reduce the carbon footprint. Thus, this research is a way towards sustainability.

Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз