Executive Summary
Nanotechnology enables self-healing pavements and improved binders which could revolutionise the longevity of roads. Nanosilica and nanocellulose fibres are highly effective in promoting self-healing of microcracks in cement-based materials. Renolith admixture provides a commercially available and well-proven method to efficiently disperse non-agglomerating nanosilica and nanocellulose fibres through the material, facilitating self-healing.
Nanomaterials in roads
In 2016-17, The Western Australian Road Research Innovation Program (WARRIP) investigated the use of nanotechnology in road pavement applications. The WARRIP Review of Future Pavement Technologies found:
To date, various studies have assessed self-healing using a number of nanomaterials. Findings indicate that these materials have the potential to seal micro-cracks, thus preventing macro-crack propagation.
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Nanotechnology has the potential to improve the material characteristics, durability and performance of pavements.
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Nanotechnology opens up the door to self-healing pavements and improved binders which could be significant game changers in longevity of our WA roads. These certainly warrant research on large scale applications to see if the nano-scale results can be achieved in large scale applications.
Nanomaterials and Self-healing
In A Scientometric Review Summarizing the Impact of Nanomaterials on the Fresh, Hardened, and Durability Properties of Cement-Based Materials, Shayan Ali Khan et al summarised a substantial body of evidence regarding the self-healing effects of nanomaterials; excerpts below:
4.6. Nanomaterials-Based Self-Healing Cementitious Composites
The self-healing capability in [cement based materials] CBMs is vital for ensuring the longevity of civil engineering structures, as it effectively prevents the formation of microcracks due to factors like drying shrinkage and external stresses [147]. When exposed to moisture, CBMs undergo chemical reactions that culminate in the creation of [calcium silicate hydrate] C─S─H gel, effectively sealing any fractures within the material. In the case of autogenous healing, the inclusion of nanomaterials, such as nanoSiO2, instigates the self-healing process by serving as nucleation sites for the formation of C─S─H gels.
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Wengui et al. [149] reported that the incorporation of nano-SiO2 enhances the self-healing efficiency of the material through two key mechanisms: the precipitation of calcium carbonate (CaCO3) and the formation of C─S─H.
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The introduction of nanofibers into cement and concrete acts as an effective self-healing method, resulting in the width of fractures reduction, by allowing hydration products and calcium carbonate (CaCO3) to settle on their surfaces. This deposition technique helps to close and seal fissures inside the material, improving structural integrity and longevity [152].
Renolith and self-healing
Renolith has been used in over 70 million square metres of cement-stabilised pavement base layers. No cracking has been reported. This ‘crack-free’ behaviour can largely be explained by the improved properties imparted to the material; notably reduced drying shrinkage, improved flexural strength, improved elastic modulus and increased strain limit. The improved material properties of cement-based materials (CBMs) achieved with Renolith admixture has been the subject of dozens of studies. However, the self-healing aspects of the product have not yet been characterised in the technical literature.
In chemical terms, Renolith 2.0 admixture is a colloidal suspension comprising a latex emulsion and stable colloidal dispersion of non-agglomerating nanosilica particles and nanocellulose fibres. Noting the self-healing attributes of nanosilica and nanofibres reported in the general technical literature, it is logical that Renolith promotes both autogenous and autonomous self-healing of CBMs.
Nanocellulose and nanosilica – role in self-healing
We posed this question to Perplexity AI: What role do nanosilica and nanocellulose have in self-healing of cemented materials? The response was as follows:
Nanosilica and nanocellulose play significant roles in enhancing the self-healing properties of cementitious materials:
Nanosilica
Nanosilica contributes to self-healing in concrete by:
- Improving the microstructure of concrete by refining the pore structure in hydrated phases[1].
- Enhancing the overall properties of the concrete, including its self-healing capabilities[1].
- Acting as a primary self-healing agent when encapsulated with other materials like nanocellulose[2].
Nanocellulose
Nanocellulose enhances self-healing in cementitious materials through:
- Increasing the density and strength of concrete while reducing shrinkage strain[3].
- Improving cement hydration due to its hydrophilic surface properties[4].
- Forming hydrogen bonds between nanocellulose and the cement matrix, facilitating better adhesion[4].
- Creating channels between unreacted cement particles and pore solutions, increasing the degree of hydration[4].
- Acting as a nucleus for cement hydration products, filling pores to create a compact microstructure[1].
- Controlling the progression of microcracks due to the shape of its particles[1].
When combined, nanosilica and nanocellulose can work synergistically to enhance the self-healing properties of concrete. For example, durian nanocellulose (DNC) and urea-formaldehyde (UF) were used to encapsulate silica, creating a composite (DNC-UF@SiO2) that showed better mechanical performance and lower water absorption than UF-encapsulated SiO2 alone[2]. This encapsulated self-healing material embedded in concrete demonstrated significant healing potential, surpassing control specimens[2].
The addition of these nanomaterials can lead to improved mechanical properties, better crack-sealing capabilities, and enhanced long-term durability of cementitious materials.
Conclusion
Nanotechnology enables self-healing pavements and improved binders which could revolutionise the longevity of roads. Nanosilica and nanocellulose fibres are highly effective in promoting self-healing of microcracks in cement-based materials. Renolith 2.0 is commercially available and offers a well-proven method to efficiently disperse non-agglomerating nanocellulose fibres and nanosilica throughout the material via conventional construction methods such as insitu stabilisation. This provides a practical approach to facilitating autogenous and autonomous self-healing of pavements. Further research is required to better characterise the self-healing mechanism of the Renolith 2.0 admixture in combination with different cementitious binders and pavement materials.