Self-Sensing Concrete in Smart Structures

Introduction:-

Concrete is one of the most widely used structural material used extensively in building various types of infrastructures. However, physical effects, including surface erosion, ageing, cracking, etc. and chemical products such as carbonation, sulphate attack leads to cement degeneration. Hence, to assess the health of the cement and avoid sudden accidents, Self-sensing Concrete is introduced. Self-sensing concrete (SSC) refers to a structural material that can monitor itself without the need of embedded, attached or remote sensors. By measuring the electrical resistance of the SSC, the stress, strain, crack, and damage can be monitored. Compared with conventional structural materials which require additional sensors for monitoring or detection, the SSC is advantageous in its high sensitivity, suitable mechanical property, biological compatibility, identical lifespan with concrete and easy installation and maintenance.

Structure and Composition:-

Self-sensing concrete has a highly complex structure and has both multiphase and multi-scale composition. Self-sensing concrete may be considered a two-phase material consisting of functional fillers dispersed in a concrete matrix at the macroscopic level. There is a third phase in self-sensing concrete at the microscopic level: the interfaces between functional fillers and concrete matrix and those between available fillers. The composition of self-sensing concrete determines its structure and sensing properties. Self-sensing concrete consists of the matrix material, functional filler, and material to aid filler dispersion. Generally, all types of concrete can be used as the matrix of self-sensing concrete. The selection of composition materials and their mixing proportions is critical in fabricating self-sensing concrete.

Processing of Self-Sensing Concrete:-

Self-sensing concrete is a multi-component system with complex thermodynamic and dynamic characteristics. Thus, the processing technology aims to incorporate each component into the composite to obtain self-sensing concrete with the desirable properties. The processing technology of self-sensing concrete includes three steps: mixing/dispersing, moulding, and curing. Mixing/ dispersing is the most important one as this decides the distribution of functional filler, hydration products, pore characteristics, and water content inside a concrete matrix. These varieties in structure induced by the processing technology will have substantial effects on the sensing property of self-sensing concrete.

Sensing Property:-

The sensing behaviour of the self-sensing concrete means the corresponding relationship between its electrical and mechanical properties. Such parameters can characterize the sensing properties of the self-sensing concrete as sensitivity, input/output range, linearity, repeatability, hysteresis, signal to noise ratio, and zero shifts. The sensing properties not only depend on the compositions and structures of the self-sensing concrete but also depend on the loading states and external environments. The electrical property of self-sensing concrete has a direct response to mechanical property under different temporal and spatial conditions. Strain, stress, crack, and damage inside the self-sensing concrete can therefore be detected through measurement of the electrical signal of the self-sensing concrete. Understanding the sensing mechanisms is the foundation of designing and optimizing self-sensing concrete—the sensing property results from the change of conductive network inside the composite under external force or deformation.

Application:-

With high sensitivity, excellent mechanical property, natural compatibility, lifespan identical to concrete structures, easy installation, and little maintenance needed, self-sensing concrete has been used to develop new facilities for structural health monitoring and traffic detection applications. Self-sensing concrete can be used for structural health monitoring in bulk, coating, sandwich, bonded, and embedded forms. In pavements of bridges, the ISSC (Intrinsic Self- sensing Concrete) can detect many traffic data, such as traffic flow rates, vehicular speed and traffic density. Structural parameters such as stress (or force), strain (or deformation), damage, and cracking can be monitored through changes in the electrical resistance of self-sensing concrete. Therefore, self-sensing concrete can provide useful input to ensure the safety, durability, serviceability, and sustainability of infrastructures.

WRITTEN BY: Ayusha and Shailesh