Development of Self-Sensing Cement Composite using Nanomaterials for Structural Health Monitoring of Concrete Columns – A Comprehensive Review

. Due to age, structural deterioration, and other factors, concrete constructions such as beams and columns will inevitably deteriorate. The growth of nanomaterials and recent advances in multidisciplinary research has broadened cement composites' applicability in various fields. A self-sensing cement composite can detect its own deformation, strain, and stress by changing its electrical characteristics, which may be measured with electrical resistivity. Carbon-based nanomaterials, such as carbon fiber, carbon black, and carbon nanotube, have a strong potential to increase cement composite's mechanical (strength) and electrical (resistivity, sensitivity) potentials due to their remarkable strength and conductivity. Due to the artificial integration of conductive carbon-based components will generate piezoresistive properties in typical cement composites, transforming them into self-sensing cement composites. As a result, the review focuses primarily on the development of nanoparticle-based self-sensing cement composites and their use in the health monitoring of structural columns. This research critically examines the materials used, fabrication techniques, strength, and sensing methodologies used to develop the self-sensing cement composite. The difficulties of commercializing self-sensing cement composites, as well as potential solutions, are also highlighted. According to the review, the difference in Poisson ratio and youngs modulus between the self-sensing cement composite and columns leads the self-sensing cement composite to have different strength and conductivity before and after embedding in columns. According to the study, the addition of conductive material diminishes the composite's workability due to its large specific surface area. Because of the well-distributed conductive network, the composite's resistivity is significantly lowered. The study also shows that the inclusion of a self-sensing cement composite has no bearing capacity influence on the column. Finally, according to the review, the self-sensing cement composite has the ability to monitor the health of structural columns.


Introduction
Environmental risks and concrete aging cause catastrophic structural collapses in concrete structures.Many breakthroughs have been made in concrete construction, both structurally [1] and in terms of material [2][3][4], akin to those made in structural steel [5,6]; however, concrete deterioration is unavoidable.In the domains of bricks [7,8], soil [9][10][11], and concrete [12][13][14], material modification for property enhancement is also increasing.The building's safety must be thoroughly and continuously evaluated through frequent inspection and maintenance to avoid catastrophic structural failures.Structural health monitoring systems are applied in critical infrastructures and buildings to analyze the structure's performance and detect aberrant responses [15].To monitor structural performance, piezoceramic sensors [16], ultrasonic sensors [16], and other conventional sensors [17] are offered.

is unavoidabl
.In the domains of bricks [7,8], soil [9][10][11], and concrete [12][13][14], material modification for property enhancement is also increasing.The building's safety must be thoroughly and continuously evaluated through frequent inspection and maintenance to avoid catastrophic structural failures.Structural health monitoring systems are applied in critical infrastructures and buildings to analyze the structure's performance and detect aberrant responses [15].To monitor structural performance, piezoceramic sensors [16], ultrasonic sensors [16], and other conventional sensors [17] are offered.

On the other hand, structural material evolution has gone through several stages, from highstrength materials to materials with high strength and low weight, and most recently, materials with both strength and self-sensing [3,18].Self-sensing materials may detect their own stress, strain, and damage [19,20].Compare On the other hand, structural material evolution has gone through several stages, from highstrength materials to materials with high strength and low weight, and most recently, materials with both strength and self-sensing [3,18].Self-sensing materials may detect their own stress, strain, and damage [19,20].Compared to conventional sensors that are included or attached, selfsensing cement composites are a sort of smart material that is innately smart.Those self-sensing cement composites are extremely robust, more compatible, have a huge sensing volume, and have no mechanical properties loss [18,20].Damage detection is important for structural health monitoring and predicting service life.
to conventional sensors that are included or attached, selfsensing cement composites are a sort of smart material that is innately smart.Those self-sensing cement composites are extremely robust, more compatible, have a huge sensing volume, and have no mechanical properties loss [18,20].Damage detection is important for structural health monitoring and predicting service life.

Steel fiber (SF) [21,22], carbon fiber (CF) [23,24], carbon nanofiber (CNF) [20,25,26], carbon black (CB) [27,28], and nickel powder (NP) [29,30] are some of the conductive elements that can be used to make self-sensing cement composites.As seen in Fig. 1, these materials in the composite create a conductive network [3 Steel fiber (SF) [21,22], carbon fiber (CF) [23,24], carbon nanofiber (CNF) [20,25,26], carbon black (CB) [27,28], and nickel powder (NP) [29,30] are some of the conductive elements that can be used to make self-sensing cement composites.As seen in Fig. 1, these materials in the composite create a conductive network [31].If the conductive particle concentration is high enough, a conductive network will form before applying the load, as shown in Fig. 1 (a).However, if only a low concentration of conductive materials is utilized, an external load is required to produce total continuous conduction, as shown in Fig. 1 (b).Furthermore, the generated hydration products will act as a barrier to the creation of the composite's conductive network.Because aggregates operate as a significant barrier to the continuous network channel in the composite, coarse aggregates are rarely used in self-sensing cement composites.Consequently, conductive and non-conductive phases exist in self-sensing cement composites [18,20,32].Conductive materials like CF and CB produce the conductive phase [20].Conventional materials like cement and hydration products like calcium-silicate hydrate (CSH) and portlandite, on the other hand, create the non-conductive phase.In some composites, a hybrid material combination improves the composite's self-sensing capacity [33,34].
].If the conductive particle concentration is high enough, a conductive network will form before applying the load, as shown in Fig. 1 (a).However, if only a low concentration of conductive materials is utilized, an external load is required to produce total continuous conduction, as shown in Fig. 1 (b).Furthermore, the generated hydration products will act as a barrier to the creation of the composite's conductive network.Because aggregates operate as a significant barrier to the continuous network channel in the composite, coarse aggregates are rarely used in self-sensing cement composites.Consequently, conductive and non-conductive phases exist in self-sensing cement composites [18,20,32].Conductive materials like CF and CB produce the conductive phase [20].Conventional materials like cement and hydration products like calcium-silicate hydrate (CSH) and portlandite, on the other hand, create the non-conductive phase.In some composites, a hybrid material combination improves the composite's self-sensing capacity [33,34].

Fig. 1 (a) Formation of the conductive pathway before loading and (b) formation of the conductive pathway under strain [31] Thus, the main objective of this paper is to investigate the creation of self-sensing cement composites utilizing an interdisciplinary approach and a range of conductive materials.The next phase focuses on using the self-sensing cement composites that have been produced to monitor the health of columns.


Materials and Methods

Cement, sand, and water are the most common raw materials used to make self-sensing cement composites [35][36][37].Fly-ash/silica fume has been employed as a binder material in fabricating se Fig. 1 (a) Formation of the conductive pathway before loading and (b) formation of the conductive pathway under strain [31] Thus, the main objective of this paper is to investigate the creation of self-sensing cement composites utilizing an interdisciplinary approach and a range of conductive materials.The next phase focuses on using the self-sensing cement composites that have been produced to monitor the health of columns.

Materials and Methods
Cement, sand, and water are the most common raw materials used to make self-sensing cement composites [35][36][37].Fly-ash/silica fume has been employed as a binder material in fabricating sensors on occasion [23,35].As a water lowering agent, a polycarboxylate superplasticizer was utilized, which can reduce water content by 30%.Conductive fillers such as CF, SF, and carbon nanotube (CNT) are often utilized [18].On the other hand, dispersion of conductive components in the composite is time-consuming.Hybrid CNT/NCB composite fillers are occasionally used because nano carbon black (NCB) self-assembles onto the surface of CNT by electrostatic adsorption, resulting in the formation of a grape-bunch structure as seen in Fig. 2. Mechanical stirring was also employed to achieve dispersion of CNTs and NCBs embedded in the cement matrix without using ultrasonic treatment.Finally, the use of fly ash and water reducers had evident effects on the dispersion of conductive materials in the cement matrix.Fig. 2 SEM image of cement composite with grape brunch shape of CNT and NCB [27] The self-sensing cement composite is typically made using two probe or four-probe technologies [18,20,[38][39][40].The cementitious composite, including conductive elements, was cast and cured according to the design calculations.Two stainless steel gauge electrodes separated by a distance of 10 mm were introduced into the specimens using the two-probe method, as illustrated in Fig. 3. Four copper or steel electrodes are utilized in the four-probe approach.In the two probe techniques, both current supply and voltage measurement are performed on the same electrodes [27].

ors on occasion [23,35
.As a water lowering agent, a polycarboxylate superplasticizer was utilized, which can reduce water content by 30%.Conductive fillers such as CF, SF, and carbon nanotube (CNT) are often utilized [18].On the other hand, dispersion of conductive components in the composite is time-consuming.Hybrid CNT/NCB composite fillers are occasionally used because nano carbon black (NCB) self-assembles onto the surface of CNT by electrostatic adsorption, resulting in the formation of a grape-bunch structure as seen in Fig. 2. Mechanical stirring was also employed to achieve dispersion of CNTs and NCBs embedded in the cement matrix without using ultrasonic treatment.Finally, the use of fly ash and water reducers had evident effects on the dispersion of conductive materials in the cement matrix.Fig. 2 SEM image of cement composite with grape brunch shape of CNT and NCB [27] The self-sensing cement composite is typically made using two probe or four-probe technologies [18,20,[38][39][40].The cementitious composite,

ncluding conductive elements, was cast and cured according to the design calculat
ons.Two stainless steel gauge electrodes separated by a distance of 10 mm were introduced into the specimens using the two-probe method, as illustrated in Fig. 3. Four copper or steel electrodes are utilized in the four-probe approach.In the two probe techniques, both current supply and voltage measurement are performed on the same electrodes [27].


Fig. 3 Schematic diagram of cementitious composite with electrode position in the composite

(Two probe method) [27] Self-sensing cement composite columns were cast in bulk form according to the design calculations.The concrete column is subsequently subjected to mechanical and electrical testing simultaneously.Fig. 4 shows the experimental setup for compressive strength, elastic modulus, and resistivity measurements.In compliance with IS code requirements, the concrete columns were tested using hydraulic testing equipment with a capacity of 2000 kN.Through a PC interface, the measurements were automatically recorded [27].


Fig. 4 Setting up an experiment to determine the strength and elastic modulus of concrete columns [27]


Results

Fig. 3 Schematic diagram of cementitious composite with electrode position in the composite
(Two probe method) [27] Self-sensing cement composite columns were cast in bulk form according to the design calculations.The concrete column is subsequently subjected to mechanical and electrical testing simultaneously.Fig. 4 shows the experimental setup for compressive strength, elastic modulus, and resistivity measurements.In compliance with IS code requirements, the concrete columns were tested using hydraulic testing equipment with a capacity of 2000 kN.Through a PC interface, the measurements were automatically recorded [27].

Workability
The conductive materials can reduce the relative slump of the composite.The use of hybrid shape memory alloys (SMA) and SF in cement composites can reduce relative slump [2].Because of the interplay between CFs and the restriction in aggregate movement imposed by CFs, adding 0.1% CF resulted in a 43% reduction in slump diameter [41].Even though CF-based specimens may have a more controllable disruption of the electrically conductive network, uniform dispersibility, initial manufacturing costs, and mechanical property impacts must be considered when choosing a carbon-based material.
composite.The use of hybrid shape me

ry alloys (S
A) and SF in cement composites can reduce relative slump [2].Because of the interplay between CFs and the restriction in aggregate movement imposed by CFs, adding 0.1% CF resulted in a 43% reduction in slump diameter [41].Even though CF-based specimens may have a more controllable disruption of the electrically conductive network, uniform dispersibility, initial manufacturing costs, and mechanical property impacts must be considered when choosing a carbon-based material.


Compressive strength

The CNFs/epoxy composites' compressive strength, poisons ratio, and elastic modulus was meas

Compressive strength
The CNFs/epoxy composites' compressive strength, poisons ratio, and elastic modulus was measured using a uniaxial compression test.As illustrated in Fig. 5 (a), increasing the CNF volume content to 0.58% resulted in a considerable increase in compressive strength.However, as the volume content of the CNF increased by 1.16%, there was a steady decrease in compressive strength.Because of the inhomogeneous dispersion of conductive materials in the composite, particle agglomeration occurs, lowering the composite's compressive strength at greater concentrations [42,43].The composites filled with 0.58% CNF had a compressive strength of 77.6 MPa, which was determined to be 16% higher than the control specimen.This is due to an interfacial connection between the CNF and the epoxy matrix, which enables the load to be transmitted to the CNF via the interface.It was eventually observed that when the concentration of CNFs grew, so did the elastic modulus, as seen in Fig. 5 (b).When the elastic modulus of the specimen containing 1.16% CNFs was compared to the control specimen, the elastic modulus increased by 26%.This is because the CNF has a stronger strength and elastic modulus than the epoxy matrix [44].The CNF pullout limits the composite's transverse distortion, which improves the composite's mechanical properties.

ed using a uniaxial c
mpression test.As illustrated in Fig. 5 (a), increasing the CNF volume content to 0.58% resulted in a considerable increase in compressive strength.However, as the volume content of the CNF increased by 1.16%, there was a steady decrease in compressive strength.Because of the inhomogeneous dispersion of conductive materials in the composite, particle agglomeration occurs, lowering the composite's compressive strength at greater concentrations [42,43].The composites filled with 0.58% CNF had a compressive strength of 77.6 MPa, which was determined to be 16% higher than the control specimen.This is due to an interfacial connection between the CNF and the epoxy matrix, which enables the load to be transmitted to the CNF via the interface.It was eventually observed that when the concentration of CNFs grew, so did the elastic modulus, as seen in Fig. 5 (b).When the elastic modulus of the specimen containing 1.16% CNFs was compared to the control specimen, the elastic modulus increased by 26%.This is because the CNF has a stronger strength and elastic modulus than the epoxy matrix [44].The CNF pullout limits the composite's transverse distortion, which improves the composite's mechanical properties.


Fig. 5 Epoxy composite showing (a) variation of compressive strength and (b) variation of the elastic modulus with differen

vol% of CNF [44] (modified form)

When MWCNT was embedded, the composites' compressive and flexure strengths increased by 36.07%and 18.11%, respectively.This
When MWCNT was embedded, the composites' compressive and flexure strengths increased by 36.07%and 18.11%, respectively.This was most likely due to microfracture bridging, nanopore filling, and other processes caused by the distributed MWCNT.CFs are simpler to distribute in dense ECC systems uniformly and are reported to increase the mechanical characteristics of the mixtures.
as most likely due to microfracture bridging, nanopore filling, and other processes caused by the distributed MWCNT.CFs are simpler to distribute in dense ECC systems uniformly and are reported to increase the mechanical characteristics of the mixtures.


Flexural strength

Fig. 6 depicts the rise in flexural (and compressive) strength of cement mortars, including CNT/NCB composite fillers.As the CNT concentration in the composites was 0.77 vol.% and 1.52 vol.%, there was a significant improvement in flexural strength of 6.7% and 18.3%, respectively, when compared to ordinary cement mortar.The crack-bridging impact of CNT, the draw-out effect of CNT, and the capillary filling effect of NCB all contribute to the increase in flexural strength [45].Compared to normal cement mortar, when the CNT content in composites was increased by 2.40 vol.% and 3.12 vol.%, the flexural strength was lowered by 15% and 45%, respectively.The composite's flexural strength is reduced due to the inhomogeneous distribution of CNT in the composite and an excess water binder ratio.


Fig. 6 Flexural and compressive strength of cement composite with CNT/NCB composite fillers [45]

The use of C

Flexural strength
Fig. 6 depicts the rise in flexural (and compressive) strength of cement mortars, including CNT/NCB composite fillers.As the CNT concentration in the composites was 0.77 vol.% and 1.52 vol.%, there was a significant improvement in flexural strength of 6.7% and 18.3%, respectively, when compared to ordinary cement mortar.The crack-bridging impact of CNT, the draw-out effect of CNT, and the capillary filling effect of NCB all contribute to the increase in flexural strength [45].Compared to normal cement mortar, when the CNT content in composites was increased by 2.40 vol.% and 3.12 vol.%, the flexural strength was lowered by 15% and 45%, respectively.The composite's flexural strength is reduced due to the inhomogeneous distribution of CNT in the composite and an excess water binder ratio.

Fig. 6 Flexural and compressive strength of cement composite with CNT/NCB composite fillers [45]
The use of CB and SF in a diphasic pattern may be an optimization option for improving concrete's crack formation self-sensing capabilities.The specimens showed fewer fractures, and larger cracks as the CF level rose.CNT composites demonstrated a substantially more significant fractional change at a lower moisture condition and superior self-sensing to pre-cracking than CF and control specimens.The macro-SFs are principally responsible for the high endurance and variety of fracture features of conductive concrete.

pattern may be an optimization option for improving concrete's crack formation self-sensing capa
ilities.The specimens showed fewer fractures, and larger cracks as the CF level rose.CNT composites demonstrated a substantially more significant fractional change at a lower moisture condition and superior self-sensing to pre-cracking than CF and control specimens.The macro-SFs are principally responsible for the high endurance and variety of fracture features of conductive concrete.


Conductivity

The electrical resistivity of smart concrete containing MWCNT and SF changes when the compressive load is raised from 2

Conductivity
The electrical resistivity of smart concrete containing MWCNT and SF changes when the compressive load is raised from 20 to 100 MPa, as shown in Fig. 7 [31].When the compressive strength was increased to 20 MPa, no changes in electrical resistivity were found.Electrical resistivity fell by 3.04%, 5.09%, 7.88%, and 9.30% as compressive strength was increased by 40 MPa, 60 MPa, 80 MPa, and 100 MPa, respectively.When the compressive stress and compressive strain increase proportionately, as shown in Fig. 1 (a) and Fig. 1 (b), the distance between the conductive fillers decreases, increasing the connection between the conductive fillers.

to 100 MPa, a
shown in Fig. 7 [31].When the compressive strength was increased to 20 MPa, no changes in electrical resistivity were found.Electrical resistivity fell by 3.04%, 5.09%, 7.88%, and 9.30% as compressive strength was increased by 40 MPa, 60 MPa, 80 MPa, and 100 MPa, respectively.When the compressive stress and compressive strain increase proportionately, as shown in Fig. 1 (a) and Fig. 1 (b), the distance between the conductive fillers decreases, increasing the connection between the conductive fillers.

The addition of SF to the composite improves the connection between the conductive components, resulting in a significant reduction in th The addition of SF to the composite improves the connection between the conductive components, resulting in a significant reduction in the composite's resistivity.Similarly, the quantum tunneling effect improves the piezoelectric response when fine steel slag aggregates (FSSA) are used.The composite will exhibit combination conductivity and piezoresistivity behavior if hybrid SF and FSSA are utilized [29].A lower piezoelectric response shows that the composite's piezoelectric response has been reduced due to the production of a few microfractures, which could potentially harm the conducting network.The composite's conductivity is enhanced by a consistent distribution of conductive components, fewer defects, and fewer cracks.
composite's resistivity.Similarly, the quantum tunneling effect improves the piezoelectric response when fine steel slag aggregates (FSSA) are used.The composite will exhibit combination conductivity and piezoresistivity behavior if hybrid SF and FSSA are utilized [29].A lower piezoelectric response shows that the composite's piezoelectric response has been reduced due to the production of a few microfractures, which could potentially harm the conducting network.The composite's conductivity is enhanced by a consistent distribution of conductive components, fewer defects, and fewer cracks.


Fig. 7 Electrical Resistivity variation of the steel fibers (MF), fine steel slag aggregates (MS), steel fibers and fine steel slag aggregat

(MSF), carbon nanotube and steel fibers (MFMW)

embedded composite concerning the change in stress [31] The ECC system's flexural strength and conductivity have been proven to be improved by SFs or CB particles.Because of the bridging phenomena
embedded composite concerning the change in stress [31] The ECC system's flexural strength and conductivity have been proven to be improved by SFs or CB particles.Because of the bridging phenomena generated by the long bar shape, SFs may provide superior mechanical and electrical performance.On the other hand, the total conductive admixture had the opposite effect; higher gauge factors were seen for the lowest CF additions tested, demonstrating that CFRCC self-sensing capabilities are affected by percolation conditions.Increase the length of the fiber, and the conductivity will increase if the CF concentration remains constant.Percolation has been achieved for all PAN CF.Percolation was seen at lower CF values as the aspect ratio of the fibers increased.As the size and duration of the loading increased, the fractional change in resistivity (FCR) likewise increased.
enerated by the long bar shape, SFs may provide superior mechanical and electrical performance.On the other hand, the total conductive admixture had the opposite effect; higher gauge factors were seen for the lowest CF additions tested, demonstrating that CFRCC self-sensing capabilities are affected by percolation conditions.Increase the length of the fiber, and the conductivity will increase if the CF concentration remains constant.Percolation has been achieved for all PAN CF.Percolation was seen at lower CF values as the aspect ratio of the fibers increased.As the size and duration of the loading increased, the fractional change in resistivity (FCR) likewise increased.


Piezoresistivity

Piezoresistivity refers to the change in electrical characteristics of a composite as a result of a change in electrical propert

Piezoresistivity
Piezoresistivity refers to the change in electrical characteristics of a composite as a result of a change in electrical properties.Fig. 8 (a) depicts the change in FCR concerning stress, while Fig. 8 (b) depicts the change in FCR concerning strain (b).The change in FCR shows good agreement with the change in stress and strain of the composite, as shown in Fig. 8 (a) and 8 (b).It has been noticed that as the composite's stress/strain increases, the FCR value decreases [27,46].This is because as stress/strain increases, the conductive components in the composite converge and form a continuous conductive channel, increasing conductivity and lowering the composite's FCR.When compressive stress/strain reaches its maximum value, the accompanying FCR value reaches the polyline's bottom.vs. Strain (µε) concerning time [27] Fig. 9 (a) shows the experimental setup for measuring piezoresistivity and conductivity in the self-sensing column.Fig. 9 (b) and 9 (c) depict a concrete column's real and schematic failure.When the strain is 0.002, the cement composite exhibits peak stress of 9.1 MPa, as shown in Fig. 9 (d).It has been discovered that when concrete deforms, the space between conductive components shortens, lowering the composite's resistance [47].However, when the load on the composite increases, additional fractures occur, increasing the composite's resistance at greater stress levels.The specimen in Fig. 9 (c) has a crack between the two inner probes of the structure, and the purpose of providing mesh in this study is to prevent the crack from propagating through the structure indefinitely, as seen in Fig. 9 (b).The specimen had low electrical conductivity under no loading conditions because there were only a few CNFs installed and no contacts developed between them.In contrast, the epoxy matrix showed a much more significant deformation under loading conditions, causing the distance between the CNFs to decrease, as shown in Fig. 10.(a).Consequently, as shown in Fig. 10 (c), the electrical conductivity of the composites rises as the CNFs get much more extensive.As a consequence, the electrically conductive pathways generated by a few CNFs touching each other (blue lines in Fig. 10 (a) and 10 (c)) were assumed to be a significant cause of the reduction in electrical resistivity of composites containing a large number of CNFs.

s.Fig. 8 (a) depi
ts the change in FCR concerning stress, while Fig. 8 (b) depicts the change in FCR concerning strain (b).The change in FCR shows good agreement with the change in stress and strain of the composite, as shown in Fig. 8 (a) and 8 (b).It has been noticed that as the composite's stress/strain increases, the FCR value decreases [27,46].This is because as stress/strain increases, the conductive components in the composite converge and form a continuous conductive channel, increasing conductivity and lowering the composite's FCR.When compressive stress/strain reaches its maximum value, the accompanying FCR value reaches the polyline's bottom.vs. Strain (µε) concerning time [27] Fig. 9 (a) shows the experimental setup for measuring piezoresistivity and conductivity in the self-sensing column.Fig. 9 (b) and 9 (c) depict a concrete column's real and schematic failure.When the strain is 0.002, the cement composite exhibits peak stress of 9.1 MPa, as shown in Fig. 9 (d).It has been discovered that when concrete deforms, the space between conductive components shortens, lowering the composite's resistance [47].However, when the load on the composite increases, additional fractures occur, increasing the composite's resistance at greater stress levels.The specimen in Fig. 9 (c) has a crack between the two inner probes of the structure, and the purpose of providing mesh in this study is to prevent the crack from propagating through the structure indefinitely, as seen in Fig. 9 (b).The specimen had low electrical conductivity under no loading conditions because there were only a few CNFs installed and no contacts developed between them.In contrast, the epoxy matrix showed a much more significant deformation under loading conditions, causing the distance between the CNFs to decrease, as shown in Fig. 10.(a).Consequently, as shown in Fig. 10 (c), the electrical conductivity of the composites rises as the CNFs get much more extensive.As a consequence, the electrically conductive pathways generated by a few CNFs touching each other (blue lines in Fig. 10 (a) and 10 (c)) were assumed to be a significant cause of the reduction in electrical resistivity of composites containing a large number of CNFs.

(a) Schematic depiction of CNF orientation change before and during loading (b) Time history association between FCR and cyclic (a) Schematic depiction of CNF orientation change before and during loading (b) Time history association between FCR and cyclic compressive stress/strain with 0.29 vol.% CNF (c) Schematic of CNF orientation between electrodes during loading and unloading (modified form - [44]) ompressive stress/strain with 0.29 vol.% CNF (c) Schematic of CNF orientation between electrodes during loading and unloading (modified form - [44])


Scanning Electron Microscopy (SEM) Analysis

The SEM images of nanocomposites filled with varying amounts of CNFs (0 vol.%, 0.29

Scanning Electron Microscopy (SEM) Analysis
The SEM images of nanocomposites filled with varying amounts of CNFs (0 vol.%, 0.29 vol.%, 0.58 vol.%, and 1.16 vol.%) employed in their investigation are shown in Fig. 11 (a) -(i).It was discovered in their investigation that specimens containing the same amount of CNFs had microscopic features on the fracture surface [44].According to fig.11 (b) -(e), the conductive materials were equally disseminated in the composite at 0.29% and 0.58% CNFs, respectively.Fewer CNFs scrambled together at higher CNF concentrations (=1.16%), resulting in CNF agglomeration, as illustrated in Fig. 11.(f) -(i).The dispersion of CNFs was impressive, increasing the nanocomposites' characteristics.As a result, the SEM picture proved to be a suitable tool for demonstrating material dispersion and composite property enhancement.SEM micrographs of the surface layer of repaired cracks revealed that CF and CNT composites had better physical self-healing than control composites, resulting in more nucleation zones.SEM investigation of the core layer revealed bridged CFs across the healed microcracks, which is most likely the cause of low pre-cracking sensitivities with CF content [48].Thus SEM investigation proves to be the better solution to identify the modified conductive network inside the composite.

ol.%, 0.58 vol.%, and 1.16 vol.%) employed i
their investigation are shown in Fig. 11 (a) -(i).It was discovered in their investigation that specimens containing the same amount of CNFs had microscopic features on the fracture surface [44].According to fig.11 (b) -(e), the conductive materials were equally disseminated in the composite at 0.29% and 0.58% CNFs, respectively.Fewer CNFs scrambled together at higher CNF concentrations (=1.16%), resulting in CNF agglomeration, as illustrated in Fig. 11.(f) -(i).The dispersion of CNFs was impressive, increasing the nanocomposites' characteristics.As a result, the SEM picture proved to be a suitable tool for demonstrating material dispersion and composite property enhancement.SEM micrographs of the surface layer of repaired cracks revealed that CF and CNT composites had better physical self-healing than control composites, resulting in more nucleation zones.SEM investigation of the core layer revealed bridged CFs across the healed microcracks, which is most likely the cause of low pre-cracking sensitivities with CF content [48].Thus SEM investigation proves to be the better solution to identify the modified conductive network inside the composite.


Conclusions

The review concentrates on developing nanoparticle-based self-sensing cement composites for use in column health monitoring.Th

Conclusions
The review concentrates on developing nanoparticle-based self-sensing cement composites for use in column health monitoring.The self-sensing cement composite components, production techniques, strength, and sensing approach are all investigated.The challenges of commercializing self-sensing cement composites, as well as potential solutions, are also highlighted.From the review, the following conclusions are summarized: 1. Due to the high specific surface area of the composite, the addition of conductive material reduces its workability.2. Due to crack bridging and pore filling, the composite's compressive strength rises to a certain level (depending on the composite's specific potential).Compressive strength decreases beyond a certain point due to poor dispersion of conductive components and the production of air bubbles in the composite.3. Due to the addition of conductive material, the composite's flexural strength tends to rise because the conductive substance improves crack resistance, which positively impacts fatigue life and energy absorption capacity. 4. The composite's resistivity is significantly reduced due to the well-distributed conductive network. 5.The conductivity of the composite tends to improve as the length of the conductive material increases.The creation of a conductive network and the formation of hydration products in the composite are clearly visible in SEM analysis.As a result, the review paper investigates the numerous potentials required by the self-sensing cement composite and the potential of particular fillers in improving the composite's strength and conductive properties.

self-sensing
cement composite components, production techniques, strength, and sensing approach are all investigated.The challenges of commercializing self-sensing cement composites, as well as potential solutions, are also highlighted.From the review, the following conclusions are summarized: 1. Due to the high specific surface area of the composite, the addition of conductive material reduces its workability.2. Due to crack bridging and pore filling, the composite's compressive strength rises to a certain level (depending on the composite's specific potential).Compressive strength decreases beyond a certain point due to poor dispersion of conductive components and the production of air bubbles in the composite.3. Due to the addition of conductive material, the composite's flexural strength tends to rise because the conductive substance improves crack resistance, which positively impacts fatigue life and energy absorption capacity. 4. The composite's resistivity is significantly reduced due to the well-distributed conductive network. 5.The conductivity of the composite tends to improve as the length of the conductive material increases.The creation of a conductive network and the formation of hydration products in the composite are clearly visible in SEM analysis.As a result, the review paper investigates the numerous potentials required by the self-sensing cement composite and the potential of particular fillers in improving the composite's strength and conductive properties.

Fig. 8
8
Fig. 8 Concrete column self-sensing signals under cyclic loading with a stress amplitude of 10 MPA with the representation of (a) FCR (%) vs

Fig. 9 (
Fig. 9 (a) Experimental setup of concrete columns (b) failure of concrete columns -actual (c) failure of concrete columns -schematic and (d) Stress-strain and resistivity curve of concretecolumns (modified form)[47]