In the face of challenging downhole conditions, the fresh state behavior of cement grouts employed for well cementation is as crucial as their mechanical properties. If not properly formulated, their primary purpose of providing zonal isolation of the steel casing from the surrounding formation may not be fulfilled. This study presents a rheological analysis of innovative lightweight slurry formulations utilizing finely ground seashell waste powder as a complete substitute for metakaolin. Replacing metakaolin with seashell waste powder aims to mitigate the environmental impact of well cementation and improve the fresh state behavior. Investigations are conducted using powders derived from various seashell wastes(Crassostrea gigas, Pinctada maxima, Pecten maximus, and Crepidula fornicata) without the addition of chemical additives. The influence of elevated temperature on gelation, Yield Stress (YS), and Plastic Viscosity (PV) of the seashell slurries is compared with that of a conventional geothermal formulation containing metakaolin. The development of strength under elevated pressure and temperature conditions, similar to those found in downhole environments, is also examined using the ultrasonic cement analyzer (UCA) technique. All slurries demonstrated shear-thinning behavior, with apparent viscosity decreasing as shear rates increase. The findings further reveal a reduction in PV and YS of all seashell waste powder-based slurries relative to the traditional formulation. Moreover, gelation of the slurries formulated with seashell powder occurred more slowly at both ambient temperature and 55 °C. At 85 °C temperature and 18 MPa confining pressure, the compressive strengths obtained from UCA results meet the minimum industrial requirement of 24 h, and the ultimate UCA compressive strength of the seashell slurries surpasses that of the conventional formulation.

Natural materials (e.g. nacre, bone, and spider silk) exhibit unique and outstanding mechanical properties. This performance is due to highly evolved hierarchical designs. Building a comprehensive understanding of the multi-scale mechanisms that enable this performance represents a critical step toward realizing strong and tough bio-inspired materials. This paper details a multi-scale experimental investigation into the toughening mechanisms in natural nacre. By applying extended digital image correlation and other image processing techniques, quantitative information is extracted from otherwise prodominantly qualitative experiments. In situ three point bending fracture tests are performed to identify and quantify the toughening mechanisms involved during the fracture of natural nacre across multiple length scales. At the macro and micro scales, fracture tests performed in situ with a macro lens and optical microscope enable observation of spreading of damage outward from the crack tip. This spreading is quantified using an iso-contour technique to assess material toughness. At the nanoscale, fracture tests are performed in situ an atomic force microscope to link the larger-scale damage spreading to sliding within the tablet-based microstructure. To quantify the magnitude of sliding and its distribution, images from the in situ AFM fracture tests are analyzed using new algorithms based on digital image correlation techniques which allow for discontinuous displacement fields. Ultimately, this comprehensive methodology provides a framework for broad experimental investigations into the failure mechanisms of bio- and bio-inspired materials.

Nacre, the iridescent material in seashells, is one of many natural materials employing hierarchical structures to achieve high strength and toughness from relatively weak constituents. Incorporating these structures into composites is appealing as conventional engineering materials often sacrifice strength to improve toughness. Researchers hypothesize that nacre's toughness originates within its brick-and-mortar-like microstructure. Under loading, bricks slide relative to each other, propagating inelastic deformation over millimeter length scales. This leads to orders-of-magnitude increase in toughness. Here, we use in situ atomic force microscopy fracture experiments and digital image correlation to quantitatively prove that brick morphology (waviness) leads to transverse dilation and subsequent interfacial hardening during sliding, a previously hypothesized dominant toughening mechanism in nacre. By replicating this mechanism in a scaled-up model synthetic material, we find that it indeed leads to major improvements in energy dissipation. Ultimately, lessons from this investigation may be key to realizing the immense potential of widely pursued nanocomposites.

In contrast to man-made materials, nature can produce materials with remarkable mechanical properties from relatively weak constituents. Nacre from seashells is a compelling example: despite being comprised mostly of a fragile ceramic (polygonal calcium carbonate tablets), it exhibits surprisingly high levels of strength and toughness. This performance is the result of an elegant hierarchical microstructure containing a small volume fraction of biopolymers at interfaces. The product is a composite material that is stiff and hard yet surprisingly tough, an essential requirement to protect the seashell from predators. Building a comprehensive understanding of the multi-scale mechanisms that enable this performance represents a critical step toward realizing strong and tough bio-inspired materials. This paper details a nanoscale experimental investigation into the toughening mechanisms in natural nacre and presents a way to translate this understanding to the design of new bioinspired composites. In situ three point bending fracture tests are performed to identify and quantify the toughening mechanisms involved during the fracture of natural nacre at the nanoscale. At the macro and micro scales, previous fracture tests [1] and [2] performed in situ enabled observation of spreading of damage outward from the crack tip. In this study, fracture tests are performed in situ an atomic force microscope to link the larger-scale damage spreading to sliding within the tablet-based microstructure. To quantify the magnitude of sliding and its distribution, images from the in situ AFM fracture tests are analyzed using standard and new algorithms based on digital image correlation techniques which allow for discontinuous displacement fields. Ultimately, this comprehensive methodology provides a framework for broad experimental investigations into the failure mechanisms of bio- and bio-inspired materials.

The purpose of this paper is to propose a methodology to optimise the granular skeleton assembly of cementitious materials containing non-spherical aggregates. The method is general and can be applied to any granular skeleton whatever the aggregate shape, size, or composition because it is simply based on the direct minimisation of the inter- granular porosity to consequently increase the skeleton’s compactness. Based on an experimental design approach, this method was applied to and validated for bio-based oyster shell (OS) mortar with 100% aggregate replacement. First, the best combination of seven crushed oyster shell particle classes was determined and compared with a stan- dardised sand skeleton (0/4 mm) and three other non-optimised OS gradings in terms of intergranular porosity. In particular, it is shown that simply mimicking a reference grading curve initially designed for spherical particles with non-spherical particles led to poor performances. Then, different mortars were cast with the standardised sand skele- ton, the optimised OS grading, and the three other non-optimised OS gradings by keeping the water-to-cement ratio (0.5), the aggregate bulk volume, and the cement paste content constant. Mechanical tests in compression confirmed the higher performance of the optimised OS mortar, validating the global optimisation approach. However, the high elongation of the oyster shell aggregates led to high skeleton intergranular porosities -- even after optimisation -- and the cement paste content needed to be adapted. For a given granular skeleton and for a constant aggregate bulk vol- ume, the increase of the cement paste content led to an increase of both the filling ratio and the mechanical properties (compressive and flexural strengths). Finally, it is shown that the proposed skeleton optimisation and a cement paste content adjustment allowed recovering good mechanical properties for an oyster shell mortar with 100% aggregate replacement, especially in flexural tension.