Asia’s concrete revolution and the role of graphene in sustainable construction (Part 1/2)

1. The embodied carbon challenge in Asian construction

In Asia, where infrastructure expansion and urbanisation are happening at an unprecedented rate, the construction sector is a key driver of economic growth. But the environmental cost of this expansion is high. Construction materials, particularly concrete, contain embodied carbon, which is a significant contributor to this expense. From the extraction of raw materials to the disposal of materials at the end of their useful lives, the total amount of greenhouse gas emissions produced is known as embodied carbon. Therefore, one of the most important steps in reducing embodied carbon in building is to achieve sustainable development goals and mitigate climate change.

About 38% of all energy-related CO2 emissions worldwide are caused by the construction industry (including building operations and construction).

With more than 70% of the world's cement production, the Asia-Pacific area is the world's biggest cement consumer. According to the International Cement Review, USGS, more than half of the cement produced worldwide is consumed in China alone.)because of the region's high need for concrete, lowering its embodied carbon is of utmost importance.

2. A historical perspective: Concrete's 200-year-old foundation and the need for innovation

The most common building material in the world, concrete, has been remarkably unchanged in its fundamental formulation for almost two centuries. Although there have been minor advancements over the years, the core technology is surprisingly outdated. It is important to understand this historical background in order to fully appreciate the revolutionary potential of graphene and other advanced composite materials in modernising the construction industry and addressing the unprecedented challenges

2.1 The blacksmith's legacy: Joseph Aspdin and Portland Cement

In 1824, Joseph Aspdin, an English bricklayer who was neither a scientist nor an engineer, received a patent for Portland cement, marking the beginning of modern concrete. The reason the name Portland was given is because the concrete produced with his cement looked like a valuable building stone that was quarried on the island of this city. A finely ground mixture of clay and limestone was burned in Aspdin's method, a major invention at the time, leading to the development of hydraulic cement which does not dry up but instead hardens via a chemical interaction with water. The fundamental chemical ideas behind Aspdin's Portland cement, despite being a groundbreaking discovery, continue to serve as the basis for the great majority of concrete used today across the world.

2.2 A century of incremental improvement, not transformation

Since Aspdin's creation, improvements in concrete technology have mostly concentrated on streamlining the cement production process to increase consistency and efficiency. The invention of rotary kilns, which enabled continuous production at higher temperatures, and the application of different chemical admixtures, such as accelerators, plasticisers, and air-entraining agents, to alter the characteristics of both fresh and hardened concrete were among the advancements. A greater variety of concrete kinds resulted from the optimisation of mix designs for certain uses. Even if they were worthwhile, these advancements were mostly small-scale. Neither the material's intrinsic limits nor its underlying chemistry were changed.

2.3 The 21st century's unprecedented demands

The construction industry today faces a set of challenges that were unimaginable in Aspdin's time. These demands necessitate a radical departure from traditional concrete technology:

• Sustainability: It is imperative that greenhouse gas emissions be severely reduced, especially the embodied carbon linked to the manufacture of cement.

• Resilience: Due to climate change, structures need to be able to endure more frequent and severe extreme weather events, such as hurricanes, floods, droughts, and sharp temperature swings.

• Smart functionality: More and more people are expecting modern buildings to be more than passive shelters. To become "smart" and responsive settings, they must incorporate sensors, communication networks, and energy management systems.

• Durability and longevity: Given that infrastructure projects are anticipated to last longer—often more than 100 years—materials with remarkable durability and resistance to deterioration are needed. With the expected cost of future megastructures to be even more expensive, enhanced durability/longevity will make financing them more “bankable”. 

2.4 The imperative for advanced composites

Incremental improvements to a 200-year-old technology are no longer sufficient for the building sector to satisfy these enormous 21st-century expectations. A major change is necessary, embracing cutting-edge composite materials that provide noticeably improved sustainability, performance, and utility. This essential shift is exemplified by graphene-enhanced concrete, which transcends the limitations of conventional concrete and ushers in a new era of innovative building. Building materials must now be sustainable, robust, and flexible enough to meet the changing demands of a world that is changing quickly. Their strength and durability alone are no longer enough.

3. Graphene: A revolutionary additive for concrete

Discovered in 2004 and awarded the 2010 Nobel Prize in Physics, graphene is a substance that has the potential to completely transform a wide range of industries, including the construction sector. The exceptional two-dimensional substance has a special set of qualities that make it a perfect addition to concrete to improve its sustainability and performance.

3.1 What is graphene? The Atomic structure

At the atomic level, graphene is essentially a single layer of carbon atoms organised in a hexagonal lattice, which resembles a honeycomb. It can be pictured as a sheet of graphite, the substance that makes up pencil lead, one atom thick. The secret of graphene's remarkable qualities lies in this seemingly straightforward, two-dimensional structure.

3.2 The extraordinary properties of graphene

Graphene's unique atomic arrangement gives rise to a set of exceptional properties that are unmatched by other materials:

• Unparalleled strength: The extraordinary strength of graphene is well known. With a tensile strength of about 130 GPa (gigapascals), it is about 200 times stronger by weight than steel, which has a tensile strength of 0.4–2.0 GPa. It is therefore among the strongest materials that science has discovered.

• Vast surface area: Graphene has an exceptionally large surface area since it is two-dimensional. Graphene can cover an incredible 2,600 square meters with just one gramme. For it to interact with the cement particles in concrete, this large surface area is essential.

• Superb conductivity: Heat and electricity are both exceptionally well-conducted by graphene. It is a potential material for electronics and, as we shall see, smart building technologies since its electrical conductivity is higher than copper's.

• Impermeability: Sheets of graphene create an almost impenetrable barrier against gases and liquids, including the tiniest atom, helium. This impermeability is essential for increasing concrete's durability.

3.3 Graphene's mechanism of action in concrete: A multi-faceted approach

When added to concrete in extremely small amounts (usually between 0.01% and 0.1% by weight of cement), graphene enhances the material's qualities through a number of complementary mechanisms:

• Enhanced hydration: For the hydration products of cement, mainly calcium silicate hydrates (C-S-H), graphene's enormous surface area offers an infinite number of nucleation sites. The inclusion of graphene encourages the creation of a denser, more uniform, and more robust C-S-H gel structure, which serves as the "glue" holding concrete together. As a result, the microstructure becomes better overall and the compressive strength increases.

• Crack arresting and bridging: Concrete will inevitably develop microcracks as a result of a number of variables, including loading, environmental stressors, and shrinkage. In order to stop these microcracks from spreading and getting wider, graphene sheets serve as tiny bridges over them. The concrete's tensile and flexural strength are greatly increased by this crack-arresting process, increasing its resistance to failure and cracking.

• Reduced permeability: Ingress of water, chlorides, sulphates, and other aggressive chemicals is made extremely difficult by the network of graphene sheets that form within the concrete matrix. This drastically lowers the concrete's permeability, preventing materials that can lead to deterioration—like sulphate attack and reinforcing steel corrosion—from penetrating. The longevity of concrete structures, particularly in abrasive conditions, is greatly increased by this improved impermeability.

Through a combination of physical and chemical processes, graphene serves as a multipurpose additive in concrete, improving strength, durability, and impermeability all at once. Because of this, it is a material that is genuinely ground-breaking for the construction sector.

4. Performance data and use cases: Demonstrating the graphene advantage

Significant performance improvements are currently being shown by numerous studies and practical applications that use graphene-enhanced concrete. Reduced material use, longer lifespans, cheaper maintenance, and a smaller environmental impact are all results of these advantages.

• Data Table (Compilation of Research Findings):

5. Carbon sequestration potential of graphene-enhanced concrete: Beyond embodied carbon reduction

Beyond merely lowering embodied carbon emissions by using less cement, graphene-enhanced concrete has several benefits. Concrete constructions can become long-term carbon sinks thanks to the fascinating and creative potential it offers for direct carbon sequestration. This potential has significant ramifications for attaining carbon neutrality objectives and reducing climate change, especially in quickly developing areas like Asia.

5.1 Accelerated mineralization: Trapping CO2 within the concrete matrix

The remarkably high surface area and reactivity of graphene are essential for quickening the mineralisation process in concrete. In order to permanently capture CO2 within the concrete matrix, stable carbonate minerals—most notably calcium carbonate (CaCO3)—are formed. Graphene makes this possible in a number of ways:

• Enhanced nucleation sites: Graphene provides a vast number of nucleation sites for the precipitation of calcium carbonate crystals. This accelerates the reaction between CO2 and calcium hydroxide (Ca(OH)2), a by-product of cement hydration, leading to increased CO2 uptake

• Improved CO2 diffusion: Graphene is impermeable in and of itself, but when it is present in the concrete matrix, it makes the diffusion of CO2 more difficult and lengthens the period that CO2 is in contact with the reactive cement paste ingredients. Studies have shown that graphene enhanced concrete can potentially help concrete absorb 10-30% more carbon than normal concrete 

5.2 CO2 introduction methods

The CO2 used for mineralization can be introduced into the concrete through various methods:

• During mixing: During the mixing process, CO2 gas can be directly introduced into the concrete mixer. This enables a quick reaction with calcium hydroxide to produce calcium carbonate, which efficiently traps CO2 in the newly mixed concrete. The amount of CO2 supplied can be highly controlled using this procedure

• Enhanced natural carbonation: Over the course of its life, concrete naturally absorbs CO2 from the atmosphere through a process known as carbonation. By enhancing CO2 diffusion within the concrete matrix and expanding the surface area available for reaction, graphene can greatly speed up this natural process

• Direct air capture (DAC) integration (future potential): In the future, graphene-enhanced concrete production may be combined with direct air capture (DAC) technology. In order to create a closed-loop system that actively removes CO2 from the atmosphere and permanently stores it in the building material, DAC systems directly take CO2 from the surrounding air. This CO2 can then be employed in the concrete mixing process

5.3 Biochar-graphene composites: A synergistic approach

When graphene is combined with biochar, a stable substance that resembles charcoal and is made from the pyrolysis (heat breakdown of biomass without oxygen), a composite material with even more potential for sequestering carbon is generated. Because the pyrolysis process transforms biomass carbon into a form that is resistant to degradation, biochar itself is a very effective carbon sink.

• Synergistic effects: Graphene increases the stability and reactivity of biochar, which increases its capability to sequester carbon and improves the concrete's overall performance. By encasing the biochar particles, the graphene network can slow down the deterioration and leaching of the particles over time

• Increased porosity: The porosity may be increased by adding biochar, which could aid in improved curing

5.4 Visualising the impact 

In conclusion, graphene-enhanced concrete may actively store carbon dioxide in a variety of ways, turning infrastructure and buildings from emission sources into useful carbon sinks. This feature makes it an effective tool for developing a more sustainable built environment, especially when paired with its other performance advantages.

illuminem Voices is a democratic space presenting the thoughts and opinions of leading Sustainability & Energy writers, their opinions do not necessarily represent those of illuminem.