Self-Sensing Cementitious Composites: Review and Perspective

Insights on the Bonding Mechanism, Electronic and Optical Properties of Diamond Nanothread-Polymer and Cement-Boron Nitride Nanotube Composites

The success of composite materials is attributed to the nature of bonding at the nanoscale and the resulting structure-related properties. This study reports on the interaction, electronic, and optical properties of diamond nanothread/polymers (cellulose and epoxy) and boron nitride nanotube/calcium silicate hydrate composites using density functional theory modeling. Our findings indicate that the interaction between the nanothread and polymer is due to van der Waals-type bonding. Minor modifications in the electronic structures and absorption spectra are noticed. Conversely, the boron nitride nanotube-calcium silicate hydrate composite displays an electron-shared type of interaction. The electronic structure and optical absorption spectra of the diamond nanothread and boron nitride nanotube in all configurations studied in the aforementioned composite systems are well maintained. Our findings offer an electronic-level perspective into the bonding characteristics and electronic-optical properties of diamond nanothread/polymer and boron nitride nanotube/calcium silicate hydrate composites for developing next-generation materials.

Concrete-based energy storage: exploring electrode and electrolyte enhancements

The exploration of concrete-based energy storage devices represents a demanding field of research that aligns with the emerging concept of creating multifunctional and intelligent building solutions. The increasing need to attain zero carbon emissions and harness renewable energy sources underscores the importance of advancing energy storage technologies. A recent focus has been on structural supercapacitors, which not only store electrochemical energy but also support mechanical loads, presenting a promising avenue for research. We comprehensively review concrete-based energy storage devices, focusing on their unique properties, such as durability, widespread availability, low environmental impact, and advantages. First, we elucidate how concrete and its composites revolutionize basic building blocks for the design and fabrication of intrinsically strong structural materials. Afterward, we categorized concrete into two major parts of a supercapacitor, i.e., electrode and electrolyte materials. We further describe the synthesis of concrete-based electrodes and electrolytes and highlight the main points to be addressed while synthesizing porous surface/electroactive matrices. The incorporation of carbon, polymers, metals, etc., enhances the energy density and durability of electrode materials. Furthermore, as an electrolyte, how concrete accommodates metal salts and the mode of diffusion/transport have been described. Although pure concrete electrolytes exhibit poor ionic conductivity, the addition of conducting polymers, metal/metal oxides, and carbon increases the overall performance of energy storage devices. At the end of the review, we discuss the challenges and perspectives on future research directions and provide overall conclusions.

Additive Manufacturing Provides Infinite Possibilities for Self-Sensing Technology

Integrating sensors and other functional parts in one device can enable a new generation of integrated intelligent devices that can perform self-sensing and monitoring autonomously. Applications include buildings that detect and repair damage, robots that monitor conditions and perform real-time correction and reconstruction, aircraft capable of real-time perception of the internal and external environment, and medical devices and prosthetics with a realistic sense of touch. Although integrating sensors and other functional parts into self-sensing intelligent devices has become increasingly common, additive manufacturing has only been marginally explored. This review focuses on additive manufacturing integrated design, printing equipment, and printable materials and stuctures. The importance of the material, structure, and function of integrated manufacturing are highlighted. The study summarizes current challenges to be addressed and provides suggestions for future development directions.

Crack Detection of Reinforced Concrete Structure Using Smart Skin

The availability of carbon nanotube (CNT)-based polymer composites allows the development of surface-attached self-sensing crack sensors for the structural health monitoring of reinforced concrete (RC) structures. These sensors are fabricated by integrating CNTs as conductive fillers into polymer matrices such as polyurethane (PU) and can be applied by coating on RC structures before the composite hardens. The principle of crack detection is based on the electrical change characteristics of the CNT-based polymer composites when subjected to a tensile load. In this study, the electrical conductivity and electro-mechanical/environmental characterization of smart skin fabricated with various CNT concentrations were investigated. This was performed to derive the tensile strain sensitivity of the smart skin according to different CNT contents and to verify their environmental impact. The optimal CNT concentration for the crack detection sensor was determined to be 5 wt% CNT. The smart skin was applied to an RC structure to validate its effectiveness as a crack detection sensor. It successfully detected and monitored crack formation and growth in the structure. During repeated cycles of crack width variations, the smart skin also demonstrated excellent reproducibility and electrical stability in response to the progressive occurrence of cracks, thereby reinforcing the reliability of the crack detection sensor. Overall, the presented results describe the crack detection characteristics of smart skin and demonstrate its potential as a structural health monitoring (SHM) sensor.

Behavioral assessment of intrinsically formed smart concrete using steel fibre and carbon black composite

In recent years, health monitoring consists of the periodic observation and analysis of existing systems to predict and avoid structural breakdown, thereby saving lives and significantly lowering the cost of structural maintenance and repair. Normally, non-destructive testing techniques and sensor technology are used to detect damage in concrete structures are expensive in nature. Self-diagnosing or smart concrete has emerged a new paradigm in concrete research for damage detection. Smart concrete was cast by blending functional fillers such as carbon black, and steel fibers with concrete to improve the performance. Under various load conditions, the mechanical properties of the proposed smart concrete were examined. The electrical resistance of smart concrete was measured using the Four Probe Method and the Arduino UNO software. SEM and XRD were used to investigate the microstructures of intrinsically smart concrete. Thermogravimetric analysis was employed as a Non-Destructive Testing method to observe the hydration process. Furthermore, the obtained data were linked with the electrical resistivity of the smart concrete to assess corrosion damage. The electrical resistivity method is also an economical method and effective method to monitor the rate of corrosion.

Research on the Electrosensitivity and Electrothermal Properties of Intelligent High-Performance Concrete Materials

In order to enhance traditional building materials, High-performance concrete (HPC) is being modified by adding carbon and basalt fibers with volume contents of 0.75-1.25% and 0.15-0.35%, respectively. The original mechanical properties are maintained while developing the material's intelligent self-sensing and self-heating functions, which are tested for pressure sensitivity and bending sensitivity, and with electrothermal tests. The results demonstrate that carbon fiber can significantly reduce the matrix resistivity of high-performance concrete, reaching the percolation threshold at a content of 1%. The inclusion of basalt fibers in the material results in a decrease in resistivity. However, the addition of mixed fibers leads to improved mechanical-electrical sensitivity under compression and bending, with a positive hybrid effect. The optimal contents for carbon fiber and basalt are 0.75% and 0.3%, respectively. In electrothermal tests, the specimen can reach a temperature of 104.5 °C with a heating rate of 25.86 °C/h, indicating the potential for self-monitoring and the electric melting of ice and snow. These findings provide support for the intelligent improvement of building structures in the new era.

Pressure-Sensitive Capability of AgNPs Self-Sensing Cementitious Sensors

Intelligent monitoring approaches for long-term, real-time digitalization in structural health monitoring (SHM) are currently attracting significant interest. Among these, self-sensing cementitious composites stand out due to their easy preparation, cost-effectiveness, and excellent compatibility with concrete structures. However, the current research faces challenges, such as excessive conductive filler, difficulties in filler dispersion, and insufficient stress sensitivity and instability. This study presents a novel approach to these challenges by fabricating self-sensing cementitious sensors using silver nanoparticles (AgNPs), a new type of conductive filler. The percolation threshold of AgNPs in these materials was determined to be 0.0066 wt%, marking a reduction of approximately 90% compared to traditional conductive fillers. Moreover, the absorbance test with a UV spectrophotometer showed that AgNPs were well dispersed in an aqueous solution, which is beneficial for the construction of conductive pathways. Through various cyclic loading tests, it was observed that the self-sensing cementitious sensors with AgNPs exhibited robust pressure-sensitive stability. Additionally, their stress sensitivity reached 11.736, a value significantly surpassing that of conventional fillers. Regarding the conductive mechanism, when encountering the intricate environment within the cementitious material, AgNPs can establish numerous conductive pathways, ensuring a stable response to stress due to their ample quantity. This study provides a significant contribution to addressing the existing challenges in self-sensing cementitious materials and offers a novel reference for further research in this domain.

Nanomodification of Lightweight Fiber Reinforced Concrete with Micro Silica and Its Influence on the Constructive Quality Coefficient

A hypothesis was put forward that a nano-modifying additive of micro silica, which had a beneficial effect on achieving a perfect structure of heavy concrete, can also be effectively used in lightweight fiber-reinforced concrete. The nano-modifying additives of micro silica application in manufacturing lightweight fiber reinforced concrete products and structures can significantly enchain their strength characteristics without increasing their mass and consequently improve their design characteristics. The purpose of the work was to increase the structural quality coefficients for all types of strengths of lightweight fiber-reinforced concrete due to its modification with micro silica. The effect of nano-modifying additives of micro silica on the strength characteristics of lightweight fiber reinforced concrete was studied. The optimal amount of micro silica addition was experimentally confirmed and established of 10% of the cement mass. The coefficients of constructive quality for all experimentally determined strength characteristics of lightweight fiber-reinforced concrete modified with micro silica additives were calculated. The coefficient of constructive quality for tensile strength in bending of lightweight fiber reinforced concrete with additives was two and a half times higher than that of heavy concrete without additives and up to 37% higher than that of lightweight fiber-reinforced concrete without additives.