Electron-conducting carbon concrete (ecˆ3) is a multifunctional cement-based composite material that combines mechanical robustness with electrochemical energy storage. To further expand our understanding of structure-function relationships in this complex multiphase material system and provide a roadmap for transitioning this technology from a simple proof-of-concept to a viable large-scale energy storage alternative, we report insights into the nanoscale connectivity of the electrode's conductive carbon network, explore different electrolyte compositions and material integration strategies, and highlight opportunities for device scaling. Through the use of FIB-SEM tomography, the electrode's percolating fractal-like nano-carbon black network has been visualized at the nanoscale, providing insights into the theoretical energy storage capacity of this material. To reduce the required times for the production of functional electrodes, we also present a cast-in electrolyte approach, where centimeter-thick electrodes could be produced without the need for postcuring steps. In these prototypes, device performance scales linearly with electrode thickness and cell count, and a simple analytical model was developed to explain these scaling phenomena. Furthermore, the exploration of alternative ionic and organic electrolytes further contribute to improved electrochemical behavior, with the fabricated designs ultimately achieving a 10-fold increase in supercapacitor energy density compared to previous designs. Finally, we were able to fabricate a 12 V, 50 F supercapacitor module and a 9 V arch prototype that integrate energy storage into load-bearing architectural elements. These functional prototypes highlight the potential for real-time structural health monitoring, while demonstrating the potential of our ecˆ3 technology for the production of a scalable, high-voltage concrete energy-storing infrastructure.

The large-scale implementation of renewable energy systems necessitates the development of energy storage solutions to effectively manage imbalances between energy supply and demand. Herein, we investigate such a scalable material solution for energy storage in supercapacitors constructed from readily available material precursors that can be locally sourced from virtually anywhere on the planet, namely cement, water, and carbon black. We characterize our carbon-cement electrodes by combining correlative EDS-Raman spectroscopy with capacitance measurements derived from cyclic voltammetry and galvanostatic charge-discharge experiments using integer and fractional derivatives to correct for rate and current intensity effects. Texture analysis reveals that the hydration reactions of cement in the presence of carbon generate a fractal-like electron-conducting carbon network that permeates the load-bearing cement-based matrix. The energy storage capacity of this space-filling carbon black network of the high specific surface area accessible to charge storage is shown to be an intensive quantity, whereas the high-rate capability of the carbon-cement electrodes exhibits self-similarity due to the hydration porosity available for charge transport. This intensive and self-similar nature of energy storage and rate capability represents an opportunity for mass scaling from electrode to structural scales. The availability, versatility, and scalability of these carbon-cement supercapacitors opens a horizon for the design of multifunctional structures that leverage high energy storage capacity, high-rate charge/discharge capabilities, and structural strength for sustainable residential and industrial applications ranging from energy autarkic shelters and self-charging roads for electric vehicles, to intermittent energy storage for wind turbines and tidal power stations.

From theory, calibration and application of the equipartition theorem of statistical physics to structural failure and instability analysis, we introduce the kinetic temperature of structures as an order parameter to ascertain equilibrium and out-of-equilibrium states in structural mechanics. Set within the framework of molecular dynamics-based structural mechanics, this is achieved by connecting the set of momentum balance equations to an outside bath reservoir maintained at a reference temperature history through the Nose-Hoover thermostat. The problem thus comes down to solving the momentum balance equation with a dissipative mass damping term, which evolves in function of the difference in temperature between the structure's kinetic temperature/energy and the bath temperature. Following the Zeroth Law of Thermodynamics, it is recognized that a structure is in (thermal) equilibrium as long as the structure's kinetic temperature attains the bath temperature; whereas it is out-of-equilibrium when the open system (structure plus bath) exhibits a sustained temperature difference. In this case, the structure has exhausted its fluctuation-dissipation capacity, which is indicative-for structures-of a progressive failure and instability. The implementation of the kinetic temperature as an order parameter in structural failure and instability analysis is illustrated for a prototype five-storey building subject to excessive wind and fire loads. It is suggested that the proposed order parameter becomes an integral part of the structural engineering toolbox for resilience studies of buildings and structures.

We present results of a hybrid analytical-simulation investigation of the fracture resistance of heterogeneous materials. We show that bond-energy fluctuations sampled by Monte Carlo simulations in the semigrand canonical ensemble provide a means to rationalize the complexity of heterogeneous fracture processes, encompassing probability and percolation theories of fracture. For a number of random and textured model materials, we derive upper and lower bounds of fracture resistance and link bond fracture fluctuations to statistical descriptors of heterogeneity, such as two-point correlation functions, to identify the origin of toughening mechanisms. This includes a shift from short- to long-range interactions of bond fracture processes in random systems to the transition from critical to subcritical bond fracture percolation in textured materials and the activation of toughness reserves at compliant interfaces. Induced by elastic mismatch, they connect to a number of disparate experimental observations, including toughening of brittle solids by deformable polymers or organics in, e.g., gas shale, nacre; stress-induced transformational toughening in ceramics; and toughening of sparse elastic networks in hydrogels, to name a few.

Significance Changes to concrete production as well as in building and pavements systems—the largest consumers of concrete—can lead to more than 50% reductions in associated GHG emissions by 2050. Over this period, the operational phase of newly constructed buildings and pavements still generates most GHG emissions unless the electrical grid, heating, and transportation are decarbonized aggressively. Meeting decarbonization targets will require lowering the GHG emissions of concrete production as well as innovative uses to lower building and vehicle fuel consumption. Owing to their low abatement costs, several concrete solutions should be prioritized in climate change policies. More than one-third of the embodied impacts of building and pavement construction can be offset by implementing concrete solutions.

We develop a framework to address the shortcomings of current smartphone-based approaches for road roughness sensing and monitoring through combining vehicle dynamics, random vibration theory and a two-layer inverse analysis. The proposed approach uses in-cabin recordings of the vehicle’s vertical acceleration measured by a smartphone positioned inside the car for the estimation of road roughness. The mechanistic road roughness–vehicle interaction model at the core of the proposed framework links the frequency spectrum of the vehicle’s vertical acceleration to the road roughness power spectral density and lends itself to the quantitative characterization of roughness-induced energy dissipation. We demonstrate that the measure of roughness provided by the stochastic model of car dynamics interacting with a rough road is fully compatible, in a statistical sense, with the spatial but deterministic definition of road roughness, and validate the identification strategy that originates from it against laser measurements of road roughness. The critical crowdsourcing features of the proposed framework, such as the marginal impact of phone position and transferability, are examined and its utility to meld with big data analytics to identify the class of vehicles travelling on a roadway network is demonstrated.

Material heterogeneity at small scales is a key driver of material’s effective macroscopic properties and fracture response. We present a hybrid energy-based approach based on a potential of mean force formulation of lattice element method for reliable and efficient modeling of fracture and crack propagation in heterogeneous materials. The proposed framework rests on direct application of the Griffith fracture criteria and removes material points to create fracture surfaces in energetically favorable directions. Computational efficiency is achieved through a probing of high energy bonds and quasi-static relaxation leading to near global imposition of the energy-based criteria for crack path resolution. We validate the proposed hybrid approach against results in literature and use it to examine fracture response of defective and layered materials. For layered materials with fracture energy heterogeneity, the effective toughness is shown to be the maximum of fracture energies of layers irrespective of their volume fraction and the direction of crack propagation. For layered materials with elastic modulus heterogeneity, the maximum energy release rate occurs when the crack approaches the compliant-stiff interface from within the compliant phase. We examine the scaling of fracture toughness with modulus contrast, the link to volume fraction of the layers and the relationship between toughness anisotropy and the gradient of elastic modulus heterogeneity, offering insights with potential to inform the design of materials for fracture.

Cement is the most produced material in the world. A major player in greenhouse gas emissions, it is the main binding agent in concrete, providing a cohesive strength that rapidly increases during setting. Understanding how such cohesion emerges is a major obstacle to advances in cement science and technology. Here, we combine computational statistical mechanics and theory to demonstrate how cement cohesion arises from the organization of interlocked ions and water, progressively confined in nanoslits between charged surfaces of calcium-silicate-hydrates. Because of the water/ions interlocking, dielectric screening is drastically reduced and ionic correlations are proven notably stronger than previously thought, dictating the evolution of nanoscale interactions during cement hydration. By developing a quantitative analytical prediction of cement cohesion based on Coulombic forces, we reconcile a fundamental understanding of cement hydration with the fully atomistic description of the solid cement paste and open new paths for scientific design of construction materials.

We present results of a hybrid experimental, theoretical, and simulation-based investigation of the postbuckling behavior of thin elastic rods axially impacted by a projectile. We find a new postbuckling mechanism: mode coarsening. Much akin to inverse energy cascade phenomena in other nonlinear dynamic systems, energy is transferred during mode coarsening from higher to lower wave numbers-unless the rod breaks, abruptly dissipating in the course of fracture the rod's strain energy. We derive a model that provides a predictive means to capture mode coarsening in the form of a nondissipative, purely geometric force relaxation mechanism, and validate the model by means of molecular dynamics (MD) based structural dynamics simulations for rods of wood and pasta considering different thermodynamic ensembles. The scalability of theory and simulation for engineering applications opens new venues toward safe design of engineering structures subject to impact-induced risks of buckling, ranging from skyscrapers, to aerospace structures, to the crashworthiness of vehicles, for example.

From soft polymeric gels to hardened cement paste, amorphous solids under constant load exhibit a pronounced time-dependent deformation called creep. The microscopic mechanism of such a phenomenon is poorly understood in amorphous materials and constitutes an even greater challenge in densely packed and chemically reactive granular systems. Both features are prominently present in hydrating cement pastes composed of calcium silicate hydrate (C-S-H) nanoparticles, whose packing density increases as a function of time, while cement hydration is taking place. Performing nanoindentation tests and porosity measurements on a large collection of samples at various stages of hydration, we show that the creep response of hydrating cement paste is mainly controlled by the interparticle distance and results from slippage between (C-S-H) nanoparticles. Our findings provide a unique insight into the microscopic mechanism underpinning the creep response in aging granular materials, thus paving the way for the design of concrete with improved creep resistance.

Concrete is one of the most used materials in the world, second only to water. One of the key advantages of this versatile material is its workability in the early stages before setting. Here, we use in situ underwater Raman microspectroscopy to investigate and visualize the early hydration kinetics of ordinary Portland cement (OPC) with submicron spatial and high temporal resolution. First, the spectral features of the C-S-H gel were analyzed in the hydroxyl stretching region to confirm the coexistence of Ca-OH and Si-OH bonds in a highly disordered C-S-H gel. Second, the disordered calcium hydroxide (Ca(OH)2) is experimentally identified for the first time in the mixture before setting, suggesting that Ca(OH)2 crystallization and growth are essential in the setting of cement paste. Finally, the phase transformations of clinker, C-S-H, and Ca(OH)2 are spatially and temporally resolved, and the hydration kinetics are studied by analyzing the spatial relationships of these phases using two-point correlation functions. The results quantitatively validate that the setting occurs as a percolation process, wherein the hydration products intersect and form an interconnected network. This time-space-resolved characterization method can map and quantitatively analyze the heterogeneous reaction of the cementitious colloidal system and thus provide potential application value in the field of cement chemistry and materials design more broadly.

We present a simulation method to assess the quasistatic fracture resistance of materials. Set within a semi-grand-canonical Monte Carlo (SGCMC) simulation environment, an auxiliary field-the bond rupture potential-is introduced to generate a sufficiently large number of possible microstates in the semi-grand-canonical ensemble, and associated energy and bond fluctuations. The SGCMC approach permits identifying the full phase diagram of brittle fracture for harmonic and nonharmonic bond potentials, analogous to the gas-liquid phase diagram, with the equivalent of a liquidus line ending in a critical point. The phase diagram delineates a solid phase, a fractured phase, and a gas phase, and provides clear evidence of a first-order phase transition intrinsic to fracture. Moreover, energy and bond fluctuations generated with the SGCMC approach permit determination of the maximum energy dissipation associated with bond rupture, and hence of the fracture resistance of a widespread range of materials that can be described by bond potentials.

Nacre’s structure-property relationships have been a source of inspiration for designing advanced functional materials with both high strength and toughness. These outstanding mechanical properties have been mostly attributed to the interplay between aragonite platelets and organic matrices in the typical brick-and-mortar structure. Here, we show that crystallographically co-oriented stacks of aragonite platelets, in both columnar and sheet nacre, define another hierarchical level that contributes to the toughening of nacre. By correlating piezo-Raman and micro-indentation results, we quantify the residual strain energy associated with strain hardening capacity. Our findings suggest that the aragonite stacks, with characteristic dimensions of around 20 µm, effectively store energy through cooperative plastic deformation. The existence of a larger length scale beyond the brick-and-mortar structure offers an opportunity for a more efficient implementation of biomimetic design.

The emergence of multifunctional cement-based materials in the construction industry has the potential to shift the paradigm from strength-only performance to new functionalities enabled by electron conducting capabilities in one of the most materialand energy-intensive industry sectors worldwide. To enable such developments, we present results of a hybrid experimental-theoretical investigation of the electrical conductivity and resistive (Joule) heating of highly heterogeneous nanocarbon (nCB)-cement-based composites (pastes and mortars). By analogy with diffusivity, we find that electrical conductivity is determined by the electric tortuosity of a "volumetric wiring" permeating a highly heterogeneous matrix from percolation to saturation. From a combination of electrical conductivity and Joule heat rate measurements, we show that the electric energy dissipation at the origin of the Joule heating originates from spatial electric-field fluctuations, reminiscent of the fluctuation-dissipation theorem. We report that these fluctuations-in first order-are well captured by functional relations of the electric tortuosity of the composite material, and synthesize these observations into a first-order dissipation-tortuosity model. We suggest that harvesting the benefits of electron conducting cement-based materials, such as resistive heating, electromagnetic shielding, and energy storage, will ultimately focus on settling the competition between conductor concentration and electric tortuosity. Given the global environmental footprint of concrete, the results open venues for the sustainable development of concrete for existing and emerging green technology applications.

Urban heat island (UHI) is a climate effect that magnifies air temperature in cities. In the US it affects over 80% of the population and in general is considered an adverse phenomenon with externalities ranging from increased air pollution to higher energy demand and deteriorated human comfort. Therefore, UHI and its mitigation strategies have been studied extensively to focus on hot summer months and demand for cooling energy. However, current approaches fail to recognize that for regions in cold climates UHI may be a positive phenomenon with benefits from decreased heating energy demand exceeding downsides of higher cooling energy demand. Here, for the period of 12 years we analyze for 48 US states the cost that UHI imposes on the $120B residential market with CO2 emissions that exceed 550 M tons each year. While for states situated in warm climates UHI significantly increases the energy bill, due to varying heating and cooling costs and emissions associated with generation of energy, for some regions located in cold climates, UHI significantly reduces energy demand and carbon emissions. This information will help legislators and policy makers understand better energy demand of buildings and subsequently reduce their carbon footprint at city and state levels.

A nanoporous carbon-loaded cement composite that conducts electricity. The nanoporous carbon-loaded cement composite can be used in a variety of different fields of use, including, for example, a structural super-capacitor as an energy solution for autonomous housing and other buildings, a heated cement for pavement deicing or house basement insulation against capillary rise, a protection of concrete against freeze-thaw (FT) or alkali silica reaction (ASR) or other crystallization degradation processes, and as a conductive cable, wire or concrete trace.

While shale gas has become a major source of energy, a more sustainable recovery requires a better understanding of the gas/kerogen matrix interactions. Here, we use replica exchange molecular dynamics to investigate the geological conversion of two important classes of gas-forming constituents of the terrestrial organic matter: lignin and cellulose. In agreement with results from pyrolysis experiments, we show that lignin produces twice as much kerogen and 5 times more methane than cellulose. In addition, while ex-cellulose kerogen is relatively stiff and almost nonporous, ex-lignin kerogen, despite having a very similar composition and bonding, is an order of magnitude more compliant due to the presence of large micropores. The obtained results can potentially improve the nanoscale brick of bottom-up models of shale gas recovery.

Using a 3D mean-field lattice-gas model, we analyze the effect of confinement on the nature of capillary phase transition in granular aggregates with varying disorder and their inverse porous structures obtained by interchanging particles and pores. Surprisingly, the confinement effects are found to be much less pronounced in granular aggregates as opposed to porous structures. We show that this discrepancy can be understood in terms of the surface-surface correlation length with a connected path through the fluid domain, suggesting that this length captures the true degree of confinement. We also find that the liquid-gas phase transition in these porous materials is of second order nature near capillary critical temperature, which is shown to represent a true critical temperature, i.e., independent of the degree of disorder and the nature of the solid matrix, discrete or continuous. The critical exponents estimated here from finite-size scaling analysis suggest that this transition belongs to the 3D random field Ising model universality class as hypothesized by F. Brochard and P.G. de Gennes, with the underlying random fields induced by local disorder in fluid-solid interactions.

Abstract We propose, calibrate, and validate a crowdsourced approach for estimating power spectral density (PSD) of road roughness based on an inverse analysis of vertical acceleration measured by a smartphone mounted in an unknown position in a vehicle. Built upon random vibration analysis of a half-car mechanistic model of roughness-induced pavement–vehicle interaction, the inverse analysis employs an L2 norm regularization to estimate ride quality metrics, such as the widely used International Roughness Index, from the acceleration PSD. Evoking the fluctuation–dissipation theorem of statistical physics, the inverse framework estimates the half-car dynamic vehicle properties and related excess fuel consumption. The method is validated against (a) laser-measured road roughness data for both inner city and highway road conditions and (b) road roughness data for the state of California. We also show that the phone position in the vehicle only marginally affects road roughness predictions, an important condition for crowdsourced capabilities of the proposed approach.