Concrete is made from a mixture of cement, aggregates (crushed stone), additives and admixtures. Cement itself is created using limestone, clay, iron ore, sand, fly ash and plaster stone. Limestone, clay and iron ore are combined and then passed through a rotary kiln at temperatures between 1400 °C and 1500 °C.
Throughout this process, CaCO3 is transformed into CaO – which involves the splitting of CO2. Furthermore, fossil fuels are typically used for heating the kiln; this accounts for around 40 % of the total CO2 emission of cement production.
Moreover, this means that 60 % of CO2 is part of the chemical reaction and cannot be avoided even in advanced production processes for cement.
Carbon dioxide (CO2) is one of the major contributors to global warming. Resultingly, many countries are imposing penalty systems for each ton of carbon dioxide released into the atmosphere from fossil sources to reduce the emission of carbon dioxide. This is a serious issue for the cement and concrete industry.
The cement industry has imposed a large number of measures to limit carbon dioxide emissions – chiefly through the optimization of rotary kiln processes. Additional steps are being investigated and tested, but the chemical reaction places some restraint on these efforts.
Enhancing the mechanical properties of the concrete systems with new, state-of-the-art reinforcing materials is a way of reducing the carbon footprint of the construction industry, which is dependent on the use of concrete and cement. Trials have been conducted using glass fiber and carbon fiber fabric to reinforce the concrete in building applications.
Both reinforcement concepts have produced successful prototypes, but upscaling for widespread use was not possible.
The primary reason for this is due to the complicated application of amalgamating these fabrics with the concrete - they must be precisely laid out, and the concrete pour should not impact the direction of the fibers. This requires a considerable amount of additional manual work.
It has been proposed that graphene-based products could contribute to the reduction of the carbon footprint of concrete and cement by significantly improving mechanical properties significantly.
In recent years, an increasing number of scientific articles have been published detailing the positive impact graphene and/or graphene oxide has had on the mechanical properties of cement and concrete.
In 2020, Youli Lin and Hongjian Du described the status of graphene in cement composite (Youli Lin, Hongjian Du, Graphene reinforced cement composites: A review, Construction and Building Materials, Volume 265,2020). They hypothesized that graphene demonstrates very high application potential when used in cement composites.
Also published in 2020, Lui et al.’s “Review on the research progress of cement-based and geopolymer materials modified by graphene and graphene oxide” in Nanotechnology Reviews demonstrated a significant increase in mechanical properties when using very low concentrations of graphene oxide in cement systems.
They comprehensively detailed the interaction of the chemical mechanism between cement particles and graphene oxide. Several other studies have been published, all demonstrating the positive impact that graphene and graphene oxide have on cement and concrete systems.
The Sixth Element was initiated back in 2015, which explored how graphene and graphene oxide could boost the mechanical properties of concrete systems.
Combining cement, crushed stone and a reinforcing agent, it was established that the addition of graphene oxide offers a significant improvement in mechanical properties. The greatest improvement could be seen when 0.025 % of graphene oxide – calculated on cement – was introduced (Table 1).
Table 1. Influence of different concentrations of graphene oxide (SE2430) on mechanical properties of concrete. Source: The Sixth Element (Changzhou) Materials Technology Co.,Ltd.
These results can offer motivation to companies around the world to initiate product developments to introduce graphene oxide in their products.
The most convincing route for large-scale industrial application of graphene oxide in cement/concrete is to produce a masterbatch that mixes graphene oxide with other additives already used in the cement and concrete industry.
This could ensure that the equal distribution of this low concentration of primary graphene oxide particles is consistent throughout the concrete/cement mixture without complex and expensive equipment and processes within the cement/concrete industry.
As graphene and graphene oxide are known for their superior barrier properties, The Sixth Element conducted a series of routine investigations into how chlorine diffusion within cement/concrete products is affected by graphene and graphene oxide.
Exposing marine cement mortar to a chlorine stream of 10 to 28 m³/second for 28 days, the cement mortar containing graphene/graphene oxide showed a significant reduction in chlorine permeation than the system without graphene/graphene oxide.
Introducing just 0.005 % of graphene oxide particles enhanced resistance to chlorine by 40% (Table 2). This is clearly displayed in Figure 1.
Table 2. Chlorine permeation into marine cement using different graphene/graphene oxide concentrations. Source: The Sixth Element (Changzhou) Materials Technology Co., Ltd.
Figure 1. Chlorine permeation using 0.005 % of graphene oxide. Image Credit: The Sixth Element (Changzhou) Materials Technology Co., Ltd.
Further developments and potential ideas concerning how graphene/graphene oxide can be applied in concrete protection systems are being discussed throughout the concrete and cement industry.
With the size of the global consumption of concrete in mind, and to mitigate environmental impact, it is crucial to explore other combinations of graphene and graphene oxide with innovative admixtures to further improve the mechanical properties of concrete.
The Sixth Element (Changzhou) Materials Technology, a leading manufacturer of graphene/graphene oxide and reduced graphene oxide with a capacity of currently 1000 t/a, is consistently driving innovation, exploring new graphene-based applications, and designing suitable products for such applications.
This information has been sourced, reviewed and adapted from materials provided by The Sixth Element (Changzhou) Materials Technology Co.,Ltd.
For more information on this source, please visit The Sixth Element (Changzhou) Materials Technology Co.,Ltd.