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While nanoparticles were first discovered almost a century ago, it was not until the birth of modern nanotechnology in the 1980s with the invention of the scanning tunneling microscope that scientists were really able to start deepening their understanding of the unique properties of nanoparticles and to develop them into a wide range of applications. Over the past few decades, nanoparticles have made a significant impact in numerous fields, including chemical, clean energy, composites, electronics, and healthcare.
Here, we will discuss one area in which nanoparticles have been used successfully - in composite materials, specifically, in creating enhanced cement mortars. Recent research has provided evidence that the addition of nanoparticles to concrete can improve its strength by initiating the hydrogen reaction and filling in the micropores of the cement paste structure.
Other recent findings have also revealed that carbon nano-species, in particular, nanotubes and graphene, have a great potential to enhance cement in numerous ways other than just improving its strength. Data has shown that the addition of nanoparticles impacts various mechanical and electrical properties of the concrete.
Currently, we are still at the beginning of developing our knowledge of nanoparticles. In terms of improving cement, we know that its strength and certain properties can be improved, but there is a lack of data comparing the impact of different nano-species on strength and toughness.
Scientists across various institutions in Greece have helped develop this knowledge. In January 2021, the team published its paper in the journal Sensors, which details how the team assessed the performance of nanotechnology-enhanced mortars using non-destructive testing.
Increasing Cement’s Strength with Nanoparticles
The homogeneous distribution and density of cement mortar’s hydrated product, usually calcium silicate hydrate (C-S-H) gels obtained from the hydration of dicalcium silicate (C2S) and tricalcium silicate (C3S), is related to its mechanical strength.
The addition of nanoparticles to the cement mortar increases this mechanical strength and augments its durability by decreasing its porosity. It does this by stimulating the hydration reaction as well as filling the micropores of the cement.
Acoustic Emission as a Non-Destructive Method for Assessing Concrete
The study investigated the impact of two types of nanoparticles on the properties of cement mortars using non-destructive testing. The impact of carbon nanotubes (CNTs) on the mortar’s compressive, electrical, flexural, and fracture mechanical properties were compared against graphene nanoplatelets (GNPs).
The scientists used acoustic emission (AE) as a non-destructive method to assess the structural integrity of the concrete. Materials release energy signals from various points in the form of elastic waves that travel through the material. They are released as sound energy, picked up by AE, and analyzed to gather data on the properties of the material.
Notably, the method is successful at discovering areas of damage to the structural integrity of a material and can gauge the extent of the damage. Studies have shown that AE can reliably detect structural damage such as cracks, fatigue, and corrosion in a range of materials including concrete and composites. The team leveraged this technique to compare the structural differences between concrete mortars enhanced with CNTs to those enhanced with GNPs.
The team found that GNPs were more effective than CNTs at enhancing the properties of the mortar (improvements for GNP-enhanced mortars were 21.52% higher than for CNT-enhanced mortars). Additionally, AE analysis found that mortars containing 0.4% weight of CNTs had a 479% improvement in fracture energy. GNT-enhanced mortars experienced an even greater improvement, with those enhanced with 1% weight exhibiting an 870% increase in fracture energy in comparison with controls.
Further assessments revealed that the electrical properties of CNT-enhanced mortars were improved; tests revealed a three-fold increase in electrical conductivity of the material in comparison with the control.
The research highlights the potential for GNT-enhanced mortars in developing new composites with significantly improved qualities. This helps the construction industry meet demands for materials with extreme fracture toughness.
The data also demonstrates the potential to develop CNT-enhanced mortars into materials with increased electrical properties. Additionally, the research shows that AE is a reliable technique for analyzing concrete materials and assessing the impact of incorporating nanoparticles. It opens the door to further research exploring the impact of other kinds of nanoparticles on multiple properties of concrete and other materials.
The combination of nanoparticle technology and non-destructive testing provides an opportunity to establish new materials that meet the changing needs of not only construction but electronics, biotechnology, chemistry, energy, and more.
References and Further Reading
Dalla, P., Tragazikis, I., Trakakis, G., Galiotis, C., Dassios, K. and Matikas, T., 2021. Multifunctional Cement Mortars Enhanced with Graphene Nanoplatelets and Carbon Nanotubes. Sensors, 21(3), p.933. https://www.mdpi.com/1424-8220/21/3/933
Du, S., Wu, J., AlShareedah, O. and Shi, X., 2019. Nanotechnology in Cement-Based Materials: A Review of Durability, Modeling, and Advanced Characterization. Nanomaterials, 9(9), p.1213. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6780866/
Ramakrishna, G., & Sundararajan, T. (2019) A novel approach to rheological and impact strength of fibre-reinforced cement/cementitious composites for durability evaluation. Durability and Life Prediction in Biocomposites, Fibre-Reinforced Composites and Hybrid Composites, 389-406. https://www.sciencedirect.com/science/article/pii/B9780081022900000179?via%3Dihub