Periodic Reporting for period 1 - StARS (Sustainable Aluminium Reinforced Seawater Concrete)
Reporting period: 2022-09-01 to 2024-08-31
Summary of the context and overall objectives of the project
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.
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.
Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far
This study aims to prepare a sustainable concrete by reducing freshwater consumption and cement. Work performed in this study in following phases:
Phase 1. Assessment of Cement Paste Behavior Using Seawater: Early-Age Behavior, Mechanical and Microstructural Analysis
This phase investigates the use of seawater as a sustainable alternative in cement paste. Cement pastes were prepared with a water-to-cement ratio of 0.5 using seawater and tap water for comparison. Fresh properties were evaluated through heat of hydration and initial setting time tests, while mechanical performance was assessed via compressive and flexural strength measurements. Microstructural investigations were conducted using XRD, SEM-EDS, and CT scanning.
Phase 2. An Experimental Investigation on Using Seawater in Sustainable Mortar Mixtures
In the phase, seawater is used in place of tap water for mixing and curing of mortar. Different tests such as heat of hydration, compressive strength, flexural strength, electrical resistance and test for water absorption and permeable voids were conducted to evaluate the effectiveness of mortar made with seawater and tap water.
Phase 3. Performance Evaluation of Cement Mortars Incorporating Seawater and Calcined Marl as Sustainable Alternatives
This study explores the combined use of seawater and calcareous calcined marl as sustainable alternatives in mortar production. Mortar mixes were prepared with 0–40% marl replacing cement, using either tap water or seawater for mixing and curing. Notably, the calcined marl used in this study contains significant amounts of calcium carbonate and is rarely explored in construction research. Its unconventional composition introduces a new perspective to its potential as a pozzolanic material, addressing gaps in existing literature. Mortar properties were evaluated through calorimetry, strength, water absorption, permeable voids, electrical resistivity, XRD and SEM-EDS tests.
Phase 4. Assessment of the impact of seawater on reinforced concrete properties
In this phase, Aluminium plates with hooks used as reinforcement in concrete. The properties of aluminium bars such as ultimate tensile strength and elastic modulus were determined. Two mixes of aluminium reinforced concrete will be prepared. The first mix was prepared with Al 6082 and another mix was prepared with Al 5083 with seawater. The reinforced concrete beam specimens of size 150x150x600 mm will be cast and tested for 4-point bending test at the curing age of 28 days. The flexural strength results obtained from experiments results was compared to the design strengths predicted by Eurocode 4. After flexural strength test, beams were cut and splitted to check the corrosion of the reinforcement bars.
Phase 1. Assessment of Cement Paste Behavior Using Seawater: Early-Age Behavior, Mechanical and Microstructural Analysis
This phase investigates the use of seawater as a sustainable alternative in cement paste. Cement pastes were prepared with a water-to-cement ratio of 0.5 using seawater and tap water for comparison. Fresh properties were evaluated through heat of hydration and initial setting time tests, while mechanical performance was assessed via compressive and flexural strength measurements. Microstructural investigations were conducted using XRD, SEM-EDS, and CT scanning.
Phase 2. An Experimental Investigation on Using Seawater in Sustainable Mortar Mixtures
In the phase, seawater is used in place of tap water for mixing and curing of mortar. Different tests such as heat of hydration, compressive strength, flexural strength, electrical resistance and test for water absorption and permeable voids were conducted to evaluate the effectiveness of mortar made with seawater and tap water.
Phase 3. Performance Evaluation of Cement Mortars Incorporating Seawater and Calcined Marl as Sustainable Alternatives
This study explores the combined use of seawater and calcareous calcined marl as sustainable alternatives in mortar production. Mortar mixes were prepared with 0–40% marl replacing cement, using either tap water or seawater for mixing and curing. Notably, the calcined marl used in this study contains significant amounts of calcium carbonate and is rarely explored in construction research. Its unconventional composition introduces a new perspective to its potential as a pozzolanic material, addressing gaps in existing literature. Mortar properties were evaluated through calorimetry, strength, water absorption, permeable voids, electrical resistivity, XRD and SEM-EDS tests.
Phase 4. Assessment of the impact of seawater on reinforced concrete properties
In this phase, Aluminium plates with hooks used as reinforcement in concrete. The properties of aluminium bars such as ultimate tensile strength and elastic modulus were determined. Two mixes of aluminium reinforced concrete will be prepared. The first mix was prepared with Al 6082 and another mix was prepared with Al 5083 with seawater. The reinforced concrete beam specimens of size 150x150x600 mm will be cast and tested for 4-point bending test at the curing age of 28 days. The flexural strength results obtained from experiments results was compared to the design strengths predicted by Eurocode 4. After flexural strength test, beams were cut and splitted to check the corrosion of the reinforcement bars.
Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)
Results obtained from the all phases of study beyond the state of the art are described following:
Results from phase 1:
Phase 1 of the study yields the following key findings:
• Cement mixed with seawater generates more heat and exhibits an earlier peak compared to tap water.
• Seawater mortar shows higher strengths at 1, 3, and 28 days than tap water mortar. There is a slight reduction in 90 days compressive strength for seawater mortar compared to tap water mortar.
• Seawater increases flexural strength by approximately 42.9% at 1 day, but it decreases at 3, 28, and 90 days.
• The use of seawater tends to reduce the electrical resistance and resistivity of mortar at both 28 and 90 days. This reduction diminishes as the mortar ages.
• The incorporation of seawater in mortar results in a reduction in water absorption and permeable voids, indicating a denser microstructure.
Results from phase 2: Results showed that seawater accelerated cement hydration, reduced setting time, and enhanced early-age strength. However, a slight reduction in compressive strength was observed at 28 days. XRD confirmed the presence of Friedel’s salt in seawater cement paste, while SEM-EDS revealed changes in elemental composition and showed higher presence of chloride-bound phases in seawater specimens. CT scan analysis provided unique 3D insights into internal voids and void distribution, revealing increased air voids in seawater cement paste due to rapid setting. These findings support the feasibility of seawater in cementitious systems and emphasize the value of advanced imaging tools like CT scanning for future durability assessments.
Results from phase 3: Results demonstrated that seawater accelerates early hydration and strength gain. While increasing marl content generally reduced strength, seawater-mixed mortars consistently outperformed their tap water counterparts, particularly in long-term durability. Marl incorporation increased porosity, but seawater mixes had consistently lower water absorption and fewer permeable voids than tap water mixes. Electrical resistivity improved with marl addition, especially in seawater mixes. XRD and SEM-EDS confirmed the formation of additional hydration products such as C-(A)-S-H, ettringite, and Friedel’s salt, contributing to matrix densification. These results highlight the potential of seawater and calcined marl to produce durable, low-carbon mortars while reducing freshwater demand.
Results from phase 4: The experimental results from Phase 4 demonstrated that aluminium-reinforced concrete, even when mixed with seawater, exhibited promising performance in terms of flexural strength and corrosion resistance. Both Al 6082 and Al 5083 reinforced mixes successfully met and, in some cases, exceeded the design strength predictions based on Eurocode 4, particularly in the case of Al 5083, which showed higher flexural capacity and durability. After 28 days of curing, the 4-point bending tests confirmed that the aluminium reinforcements contributed effectively to load-bearing capacity, with minimal visible corrosion observed upon splitting the specimens. These findings indicate that aluminium alloys, especially Al 5083, can serve as viable reinforcement materials in marine or saline environments, offering a durable alternative to traditional steel reinforcement.
Results from phase 1:
Phase 1 of the study yields the following key findings:
• Cement mixed with seawater generates more heat and exhibits an earlier peak compared to tap water.
• Seawater mortar shows higher strengths at 1, 3, and 28 days than tap water mortar. There is a slight reduction in 90 days compressive strength for seawater mortar compared to tap water mortar.
• Seawater increases flexural strength by approximately 42.9% at 1 day, but it decreases at 3, 28, and 90 days.
• The use of seawater tends to reduce the electrical resistance and resistivity of mortar at both 28 and 90 days. This reduction diminishes as the mortar ages.
• The incorporation of seawater in mortar results in a reduction in water absorption and permeable voids, indicating a denser microstructure.
Results from phase 2: Results showed that seawater accelerated cement hydration, reduced setting time, and enhanced early-age strength. However, a slight reduction in compressive strength was observed at 28 days. XRD confirmed the presence of Friedel’s salt in seawater cement paste, while SEM-EDS revealed changes in elemental composition and showed higher presence of chloride-bound phases in seawater specimens. CT scan analysis provided unique 3D insights into internal voids and void distribution, revealing increased air voids in seawater cement paste due to rapid setting. These findings support the feasibility of seawater in cementitious systems and emphasize the value of advanced imaging tools like CT scanning for future durability assessments.
Results from phase 3: Results demonstrated that seawater accelerates early hydration and strength gain. While increasing marl content generally reduced strength, seawater-mixed mortars consistently outperformed their tap water counterparts, particularly in long-term durability. Marl incorporation increased porosity, but seawater mixes had consistently lower water absorption and fewer permeable voids than tap water mixes. Electrical resistivity improved with marl addition, especially in seawater mixes. XRD and SEM-EDS confirmed the formation of additional hydration products such as C-(A)-S-H, ettringite, and Friedel’s salt, contributing to matrix densification. These results highlight the potential of seawater and calcined marl to produce durable, low-carbon mortars while reducing freshwater demand.
Results from phase 4: The experimental results from Phase 4 demonstrated that aluminium-reinforced concrete, even when mixed with seawater, exhibited promising performance in terms of flexural strength and corrosion resistance. Both Al 6082 and Al 5083 reinforced mixes successfully met and, in some cases, exceeded the design strength predictions based on Eurocode 4, particularly in the case of Al 5083, which showed higher flexural capacity and durability. After 28 days of curing, the 4-point bending tests confirmed that the aluminium reinforcements contributed effectively to load-bearing capacity, with minimal visible corrosion observed upon splitting the specimens. These findings indicate that aluminium alloys, especially Al 5083, can serve as viable reinforcement materials in marine or saline environments, offering a durable alternative to traditional steel reinforcement.