Stronger concrete inspired by mollusk shells

In a recent article published in the journal Advanced functional materials, researchers from the United States of America focused on improving the breaking strength and ductility of brittle materials, such as concrete, using natural mother-of-pearl as inspiration. Natural mother-of-pearl exhibits high resistance to breakage through targeted material architectural designs.

The study presents “separated mother-of-pearl” and “grooved mother-of-pearl” cementitious composites inspired by the brick-and-mortar arrangement of mollusk shells. These composites are designed by laser processing to create individual tablets and intentional defects, laminated with elastomeric interlayers.

Background

Nature provides various mechanisms to improve fracture toughness, with natural nacre exhibiting inelastic deformation and hierarchical hardening mechanisms. The study aims to reproduce these mechanisms in technical cementitious composites. By introducing intentional defects and elastomeric interlayers, composites exhibit interlayer deformation, tortuous crack propagation, and crack bridging as key quenching mechanisms, leading to increasing strength curves.

The current study

Cementitious composites were prepared by laser processing cement paste to create individual tablets and grooved patterns. The cement paste has been carefully formulated to achieve the desired properties for the composites. Elastomeric interlayers, particularly polyvinylsiloxane (PVS), have been introduced between tablets during rolling to improve curing mechanisms.

The manufacturing process involved precise laser processing of the cement paste to create the desired shelf and groove patterns. For the “split like mother-of-pearl” composite, painter’s tape was strategically used to maintain tablet separation during lamination, ensuring the desired architecture. The tablets and grooved patterns were then laminated with the elastomeric interlayers to form the final composite samples.

After the rolling process, the composite samples were allowed to cure under controlled conditions to ensure good bonding between the tablets and the interlayers. Special attention was paid to the curing process to avoid any defects or inconsistencies in the final samples. Once cured, the samples were prepared for mechanical testing to evaluate their toughness and ductility.

The mechanical properties of the cementitious composites were evaluated using standard testing procedures. Various tests, including tensile, flexural and impact tests, were carried out to evaluate the toughness and ductility of the composites. Testing protocols have been meticulously followed to ensure accurate and reliable results.

In addition to experimental tests, numerical methods were used to analyze the behavior of the composites under different loading conditions. Coupled phase field and cohesive zone modeling frameworks were used to simulate significant deformation in soft interlayers and fracture in the bulk and interface of layered materials. These numerical analyzes provided valuable information on the hardening mechanisms at play in technical composites.

The data obtained from experimental tests and numerical analyzes were carefully analyzed to understand the quenching mechanisms and mechanical properties of cementitious composites. Statistical methods and modeling techniques were used to interpret the results and draw meaningful conclusions regarding the effectiveness of the bio-inspired design approach in improving the toughness and ductility of materials.

Results and discussion

The fracture toughness of mother-of-pearl cementitious composites has been extensively characterized, revealing remarkable improvements over traditional cast cement paste. The layered composite exhibited a fracture toughness of 6.62 ± 2.53 MPa.mm^0.5statistically like poured cement paste.

On the other hand, the grooved mother-of-pearl composite had a fracture toughness of 23.65 ± 3.96 MPa.mm^0.5, which represents a 5.5-fold increase compared to poured cement paste. The most significant improvement was observed in the separated nacre-like composite, with a fracture toughness of 73.68 ± 8.02 MPa.mm.^0.5exceeding all previously reported values ​​for cementitious materials and fiber-reinforced composites.

Toughening mechanisms in nacre-like composites were investigated, revealing key factors contributing to improved toughness and ductility. Tortuous crack propagation, interlayer deformation and tablet sliding were identified as the main hardening mechanisms.

Interlayer deformation, particularly extending over large volumes of the sample, was identified as the initial mechanism of energy dissipation in all three types of composites. This interlayer deformation, coupled with crack bridging and tablet sliding, contributed to the increase in strength curves observed during mechanical tests.

The introduction of intentional defects via laser processing and the incorporation of elastomeric interlayers have played a crucial role in improving the reinforcement mechanisms of composites. Tablet slippage, facilitated by the elastomeric interlayers, prevented premature composite failure and delayed overall composite failure. The combination of tablet sliding, interlayer deformation, and crack bridging closely mimics the hardening mechanisms observed in natural nacre, leading to a significant increase in fracture toughness without compromising strength.

Conclusion

By integrating laser-induced defects in tabulated cementitious-elastomeric materials, the study introduces a class of strong and ductile cementitious composites with high toughness values ​​comparable to ultra-high performance concrete. The research highlights the potential applications of these composites in resistance to impact, explosion and extreme loading conditions, where high resistance to cracking and ductility are crucial. The study contributes to advancing the bio-inspired design of architected materials for improved mechanical properties.

Journal reference

S. Gupta, HS Esmaeeli et al. (2024). Mother-of-pearl type cementitious composites, robust and ductile. Advanced functional materials2313516. https://doi.org/10.1002/adfm.202313516, https://onlinelibrary.wiley.com/doi/full/10.1002/adfm.202313516