Protecting concrete:

additives and coatings for greater durability in construction

“The compressive strength test is usually the most used parameter as an indicator of concrete quality; however, its value does not determine its durability by itself, that is, in addition to mechanical resistance, permeability and chemical resistance also influence its useful life”

The permeability of concrete is understood as the passage of water and aggressive ions through the capillaries between the aggregates and the cement paste; this is a complex phenomenon and depends above all on the atomic structure of the penetrating ions. One of the most harmful substances for concrete are chloride ions, these can be present from the beginning in the fresh mix, that is, dissolved in the aggregates, additives or in the water, or permeate from the outside, this being the case that exposes the greatest risk of corrosion. Although in general it can be said that the durability of concrete against atmospheric agents depends fundamentally on its permeability to water, while the durability with respect to aggressive salts, both for concrete and for reinforcement, depends on its resistance to the entry of chlorides. by different ways.

“The penetrability of the chlorides is manifested mainly by the diffusion of the ions in the concrete, rather than by the penetration of the entire solution into the samples. That is, the penetration of chlorides does not depend solely on the permeability of the water”

To protect concrete against corrosion, there are two main types of products: on the one hand, there are additives for fresh concrete mixes whose function is to act on the metal surface, canceling the anodic or cathodic reaction or both, and on the other, there are coatings. for the protection of hardened concrete. However, whatever the product used, anticorrosion protection is usually temporary, especially when the structures are subject to movements, loads or temperatures that could affect the performance of the protection or barrier placed.

In the previous article entitled Towards sustainable construction, we discussed the importance of the key nanometric component in the resistance of cement, known as hydrated calcium silicates (C-S-H) or tobermorite gel, and it’s interesting interaction with graphene oxide (GO) nanoparticles, a nanometric structure derived from graphite and of recent interest for the development of more resistant, durable and environmentally friendly structures.

GO is formed by nanometric sheets of carbon atoms linked in a hexagonal pattern and by a series of oxygenated groups anchored to its surface that facilitates its dispersion in water and combining with other materials, for example, with the nanoparticles present in cement (C-S-H).

In this regard, international studies show that the shape and surface chemistry of GO allow it to act as a platform to accelerate the hydration of cement and promote the creation of large amounts of C-S-H particles, from the formation of a new GO/ bond. C-S-H. This strong interaction gives rise to a denser network of interlocking cement crystals which, in addition to favoring the mechanical properties of the structures, also acts as a barrier against the infiltration of water through the capillary pores, but with an effect that last longer than currently available additives. This property is extremely important for the durability of concrete and for the prevention of alkali-silica reaction (ASR), an expansion reaction that occurs in the presence of moisture between alkaline cement paste and reactive amorphous silica causing cracks.

Electrical resistivity and corrosion rate Another important test for concrete is electrical resistivity and is defined as the resistance of a material to the passage of electrical charges; its measurement in concrete is a common test to identify the presence of moisture, as well as to predict the initiation period of corrosion in reinforced concrete based on the inverse relationship between electrical resistivity and ion diffusivity. That is, the higher the resistivity, the less movement of electrical charges caused by a lower porosity. The participation of graphene oxide nanoparticles in this property has also been evaluated in different studies that confirm that the GO/C-S-H interaction produces a more compact or less porous concrete that, in addition to reducing water and ion permeability, also limits the movement of electrical charges providing greater anticorrosive protection of metallic concrete structures.

Energeia Fusion (Graphenemex®), the leading Mexican company in Latin America in the research and production of graphene materials, for more than 10 years has been given the task of materializing the benefits of graphene on a scientific basis to turn it into real applications. Thus, after a long journey of research and with results comparable to those reported by various international studies regarding the use of graphene oxide in different products, including concrete, in 2018 it managed to launch Graphenergy Construcción®, the first additive on the market. for concrete with graphene oxide in the world; a multifunctional water-based additive that contributes to improve different properties of cement-based structures with a single application, such as:

1. Remodeling of the microstructure of the cement paste with better interfacial bond GO/C-S-H,
2. Better compactness of the cement,
3. Less movement of electric charges,
4. Decrease in the crack extension process,
5. Significant reductions in the rate of calcium hydroxide handling,
6. Greater mechanical resistance by improving its microstructure,
7. Greater durability of the structures due to improvements in impermeability, resistance to chloride penetration and reduction of penetration depth.

It is important to remember that these effects may vary since, in addition to the type of graphene or graphene oxide used, the final properties of cement-based structures also depend on factors such as the water-cement ratio, degree of compaction of the mixture; the characteristics of cement, aggregates, additives, among others, but with proper management and monitoring of graphene additives, the results can be very interesting.

Drafting: EF/DHS

Sources

1. Ultrahigh Performance Nanoengineered Graphene- Concrete Composites for Multifunctional Applications. Adv. Funct. Mater. 2018; 28: 1705183;
2. The role of graphene/graphene oxide in cement hydration. Nanotechnology Reviews. 2021;10(1): 768;
3. Experimental study of the effects of graphene nanoplatelets on microstructure and compressive properties of concrete under chloride ion corrosión. Construction and Building Materials, 2022; 360, 129564;
4. Effect Of On Graphene Oxide the Concrete Resistance to Chloride Ion Permeability. IOP Conf. Ser. 2018: Mater. Sci. Eng. 394 032020;
5. Effects of graphene oxide on early-age hydration and electrical resistivity of Portland cement paste. Constr Build Mater. 2017; 136, 506;
6. Recent progress on graphene oxide for next-generation concrete: Characterizations, applications and challenges. “J. Build. Eng. 2023; 69, 106192;
7. Graphene nanoplatelet reinforced concrete for self-sensing structures – A lifecycle assessment perspective. J. Clean. Prod. 2019; 240, 118202;
8. Graphene opens pathways to a carbon-neutral cement industry. Science Bulletin. 2021; 67;
9. Reinforcing Effects of Graphene Oxide on Portland Cement Paste. J. Mater. Civ. Eng. 2014; A4014010-1;
10. A review on the properties, reinforcing effects, and commercialization of nanomaterials for cement-based materials. Nanotechnology Reviews 2020; 9: 303–322, 10;
11. Permeabilidad a los cloruros del hormigón armado situado en ambiente marino sumergido. Revista Ingeniería de Construcción. 2007; 22: 1, 15;
12. Penetrabilidad del hormigón al agua y a los iones agresivos como factor determinante de su durabilidad. Materiales de Construcción, 1973; 23: 150;
13. La resistividad eléctrica como parámetro de control del hormigón y de su durabilidad. Revista ALCONPAT, 2011; 1(2),90;
14. Portland cement blended with nanoparticles. Dyna, 2007; 74:152, 277;
15. Improvement in concrete resistance against water and chloride ingress by adding graphene nanoplatelet. Cem concr res, 2016; 83: 114

Towards a sustainable construction:

how graphene oxide increases the resistance of concrete and favors the reduction of CO₂ emissions

The investigation of new technologies for the cement and concrete industry is not only limited to improving its durability, but also to seeking strategies to control its influence on climate change, taking as a background that this industry is the third largest source of emissions of carbon dioxide (CO2) and that the global challenge for 2030 is to reduce these emissions by at least 16%.

Nanotechnology

Nanotechnology for the cement industry is not a new concept, in fact, cement is considered a nanostructured material because 50 to 60% of its composition consists of nanoparticles of approximately 10 nm known as hydrated calcium silicates (C-S-H). or tobermorite gel. This important nanometric component is the foundation for the development of new formulations applying other nanoparticles such as Nano Silica (n. SiO2), Nano Titanium Oxide (n. TiO2), Nano Ferric Oxide (n. Fe2O3), Nano Aluminum Oxide or alumina (n. Al2O3), Clay Nanoparticles and Carbon Nanoparticles, such as carbon nanotubes, graphene nanoparticles or graphene oxide.

“C-S-H fills the empty spaces in the cement, improves the density, cohesion, impermeability and resistance of the cement”

Graphene oxide (GO) is a carbon nanoparticle obtained from the oxidation and exfoliation of graphite. Its well-known mechanical and impermeability properties, combined with a nucleating and densifying effect on the microstructure of cement, captured the attention of scientists and industries when they discovered that the use of low concentrations of this nanomaterial allows the development of more resistant, durable, and friendly structures with the environment.

“GO promotes the formation of C-S-H to improve and accelerate cement hydration through a new chemical bond”

How does GO interact with cement?

Although it is perfectly documented that C-S-H is responsible for 60 to 80% of the strength of cement, recent research has shown that GO further favors these results and that it is not exclusive to improve mechanical strength, but also contributes with other properties such as impermeability, anticorrosiveness and/or thermal insulation. The benefits that GO brings to cement itself or to cement-based materials are attributed to the interaction between the carboxyl groups (COOH) of GO with the C-S-H of the cement to form strong GO/C-S-H chemical bonds. This occurs in the following way, when the cement comes into contact with water, it dissolves and releases large amounts of ions; On the other hand, GO, by presenting a large surface area and good capacity to increase the mobility of Ca2+ ions in the cement paste, GO allows them to be adsorbed on it. In other words, GO acts as a platform to enhance the nucleation or promotion effect to form a large number of C-S-H particles (fig. 1), a phenomenon that ultimately facilitates the hydration process at an early age and which in turn leads to the formation of denser, more resistant and less permeable microstructures.

“Hydration is the process by which cement reacts chemically in the presence of water, develops binding properties and becomes a bonding agent.”

Mechanical resistance vs. lower CO₂ emissions

The compressive strength test is the most common measure to control the quality of concrete and, therefore, it is also the most widely used technique to evaluate the effect of GO on these structures. According to tests carried out in the laboratory, the presence of GO in the concrete can exceed 50% of the expected resistance, while field evaluations report improvement fluctuations in the range of 5% to 50%. This variation is due to the fact that, in addition to the type of GO and dosage studied, like any concrete structure, the resistance also depends on factors such as the water-cement ratio, the degree of compaction of the mix; the characteristics of the cement, aggregates and additives; the age of the concrete; the temperature and hygrometry of the curing environment. However, these values are attractive enough to be used not only in the design of more resistant structures, but also with lower cement content to contribute to the reduction of CO₂ emissions. In fact, in 2019 a study carried out by researchers from the University of Cambridge revealed that, if the addition of graphene nanoparticles managed to reduce just 5% of the cement in the concrete mix, its effect on global warming would be reduced by one 21%”.

Due to the foregoing and, from the 21st Conference of the Parties to the United Nations Framework Convention on Climate Change (COP 21) held in 2015, which concluded with the adoption of the Decision and the Paris Agreement that, from 2020 promotes low-carbon development to keep the global temperature rise below 2°C, companies from countries such as England, Spain, the United States, Vietnam and Mexico have accelerated their efforts to promote the benefits of graphene nanotechnology in favor of the environment.

Energeia Fusion, the leading Mexican company in Latin America in the production of graphene materials and the development of applications, in 2018 launched Graphenergy Construcción®, the first additive for concrete with graphene oxide in the world; a multifunctional water-based additive that contributes to improving different properties of cement-based structures with a single application. Likewise, in the short term it hopes to have a graphene-reinforced cement available and contribute to achieving environmental commitments.

Sources

1. Ultrahigh Performance Nanoengineered Graphene- Concrete Composites for Multifunctional Applications. Adv. Funct. Mater. 2018, 28, 1705183;
2. The role of graphene/graphene oxide in cement hydration. Nanotechnology Reviews. 2021;10(1): 768;
3. Experimental study Construction and Building Materials, 2022, 360, 129564;
4. Effect Of On Graphene Oxide the Concrete Resistance to Chloride Ion Permeability. IOP Conf. Ser. 2018: Mater. Sci. Eng. 394 032020;
5. Effects of graphene oxide on early-age hydration and electrical resistivity of Portland cement paste. Constr Build Mater. 2017, 136, 506;
6. Recent progress on graphene oxide for next-generation concrete: Characterizations, applications and challenges. “J. Build. Eng. 2023, 69, 106192;
7. Graphene nanoplatelet reinforced concrete for self-sensing structures – A lifecycle assessment perspective. J. Clean. Prod. 2019, 240, 118202;
8. Graphene opens pathways to a carbon-neutral cement industry. 2021, Science Bulletin 67;
9. Reinforcing Effects of Graphene Oxide on Portland Cement Paste. J. Mater. Civ. Eng. 2014. A4014010-1;
10. A review on the properties, reinforcing effects, and commercialization of nanomaterials for cement-based materials. Nanotechnology Reviews 2020; 9: 303–322, 10;
11. Permeabilidad a los cloruros del hormigón armado situado en ambiente marino sumergido. Revista Ingeniería de Construcción. 2007, 22, 1, 15;
12. Penetrabilidad del hormigón al agua y a los iones agresivos como factor determinante de su durabilidad. Materiales de Construcción, 1973, 23, 150;
13. La resistividad eléctrica como parámetro de control del hormigón y de su durabilidad. Revista ALCONPAT, 2011, 1(2),90;
14. Portland cement blended with nanoparticles. Dyna, 2007, 74, 152, 277

The graphene additive for concrete:

a revolutionary thermal insulator in construction

In recent years, the construction industry is looking formward to improve the properties of mortar and concrete, to increase their durability, especially in structures exposed to aggressive or extreme environments. Among the properties that are sought to improve, is the resistance to compression, the resistance to compression tension, as well as to reduce cracking. With the increase in the volume of concrete in civil engineering projects, more attention has been paid to the thermal cracks that occur. Experimentation has shown that during the hydration process of the mortar and/or concrete, heat is generated due to the exothermic reactions that occur. Poor heat dissipation causes a gradient between the interior of the mass and its surface, which generates internal stresses and can lead to cracking or thermal cracking in the concrete.

Nowadays, graphene oxide (GO), a graphene precursor material, has attracted a lot of attention because it is an insulating material, with low thermal property and has extraordinary mechanical properties. GO has a large surface area (2600 m2/g) and the presence of oxygenated groups gives it unique properties that make it easily dispersed in water, making it an ideal nanomaterial for the development of concrete additives.

Although the mechanical properties of cement-based compounds and structures are important in building infrastructure, the thermal insulation property is very important to reduce energy consumption for air conditioning and heating in buildings. Therefore, GO is a good candidate due to its low thermal conductivity properties. Thermal conductivity is defined as the ability of a material to transfer heat. It is the phenomenon by which heat spreads from high-temperature areas (warmer) to colder areas within the material. In the case of GO, the presence of holes and functional groups on the GO surface cause local stress or instability, resulting in a reduction in thermal conductivity of up to 2 to 3 orders of magnitude (<100 W/m-K). In the GO, the propagation of heat flux occurs in the vacant regions (voids) and in the oxygenated functional groups of the GO surface (Figure 1). When a heat flux attempts to traverse the GO through some defect or vacancy, the heat flux not only propagates out of plane, but also disturbs the heat flux around the basal plane gap.

Recent investigations have reported the improvement of the thermal insulation properties of cement-based composite materials by adding different concentrations of GO, as well as the effect of GO on increasing compressive strength and greater impermeability to chloride ions. and water in concrete. The incorporation of GO decreased microcracking, the porosity of the material (decreases the volume of pores) and improved compaction. GO sheets become a barrier to crack propagation, which improves mechanical properties. The compressive strength of the specimens of the compounds with GO concentrations of 0.05% by weight increased by up to 18.7% and 13.7% at a curing age of 7 and 28 days, respectively. In the case of the evaluations of the thermal properties of the compounds, the thermal conductivity was 0.578 W/m K for the specimen without GO (control) and 0.490 W/m K for the compound with 0.1 % by weight of GO, while that the thermal diffusivity values oscillate between 0.38× 10-6 and 0.33× 10-6 m2/s (Figure 2). Thermal conductivity decreases with increasing GO content due to low conductivity or excellent insulating effect of GO sheets and good interactions between mortar and GO sheets. Generally, material with thermal conductivity values of less than 0.250 W/m K is known as a thermal insulator. Therefore, the thermal insulation of the mortar is improved in the compounds with the incorporation of GO.

Energeia -Graphenemex® developed and sells an admixture for concrete with graphene oxide (Graphenergy Construction). A nanotechnological additive that improves mechanical resistance, impermeability and provides an antimicrobial effect to any cement-based material. The additive can also manage to reduce the final number of pores in the set product, which translates into a more compact product and greater impermeability to the passage of water, improving the protection against corrosion of steel cores in concrete.

The thermal insulation property of the additive can achieve a reduction in the temperature of concrete-based structures, infrastructure, or buildings to a more comfortable temperature inside (up to 3 °C), reducing energy consumption for air conditioning and/or or heating in buildings.

References

1. Janjaroen, Khammahong. The Mechanical and Thermal Properties of Cement CAST Mortar/Graphene Oxide Composites MaterialsInt J Concr Struct Mater (2022).
2. Yi Yang, Jing Cao y col.Thermal Conductivity of Defective Graphene Oxide: A Molecular Dynamic Study. Molecules 2019, 24, 1103.
3. Guojian Jing, Zhengmao Ye y col. Introducing reduced graphene oxide to enhance the thermal properties of cement composites. Cement and Concrete Composites 109 (2020) 103559.