No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Synergistic effects of carbon nanotube and carbon fiber on heat generation and electrical characteristics of cementitious composites
Abstract
The heat generation and electrical characteristics of cementitious composites incorporating carbon nanotube (CNT) and carbon fiber under various heating conditions were investigated in this study. Specifically, the synergistic effects of carbon nanotube and carbon fiber on the heat generation and electrical characteristics of cementitious composites were experimentally investigated. The test results show that the addition of carbon fiber improved the heat generation capability and the electrical stability of the cementitious composites incorporating CNT during heating. The long-term durability of construction materials is an important issue, however, there is a practical limit to measuring a property of specimen for a very long time in a laboratory level experiment. In addition, a modified micromechanical model was proposed here to estimate the long-term effect of heating on the electrical characteristics of cementitious composites. The model parameters were derived from the experimental results, and a series of numerical simulations was conducted to explore the influence of model parameters on the resistance of the composites. Comparisons between experimental data and the present predictions were made to assess the potential of the proposed model.
... Furthermore, the paste samples displayed significantly lower electrical resistivity than the mortar samples, as depicted in Fig. 4. This discrepancy is likely due to the lower content of CNT and CF per unit volume in the mortar samples, resulting from the addition of fine aggregate [28]. ...
... The temperature increases of the M-C-2, M-C-5, M-B-8, and M-B-13 samples under input voltage of 20 V were 65.6, 37.9, 30.1, and 14.7 • C, respectively. Unlike the P-C-2 sample, the temperature increase of the M-C-2 sample continued to rise even at high voltages, suggesting that the incorporation of fine aggregates reduced the damage to the electrically conductive network caused by thermal expansion [28,29]. Based on the previous studies, it is understood that the thermal expansion coefficient of fine aggregate (10×10-6/ • C) is notably lower compared to that of a cement paste (15-20×10-6/ • C) [28]. ...
... Unlike the P-C-2 sample, the temperature increase of the M-C-2 sample continued to rise even at high voltages, suggesting that the incorporation of fine aggregates reduced the damage to the electrically conductive network caused by thermal expansion [28,29]. Based on the previous studies, it is understood that the thermal expansion coefficient of fine aggregate (10×10-6/ • C) is notably lower compared to that of a cement paste (15-20×10-6/ • C) [28]. Therefore, incorporating fine aggregate can effectively decrease the thermal expansion coefficient of cement composites. ...
... The heating performance and heating stability of conductive composites can be guaranteed through the formation of stable electrically conductive pathways composed of carbon-based materials [12][13][14]. Therefore, combinations of CNT and other carbon-based materials have been considered [15][16][17]. ...
... The mix proportion of the cement mortar reinforced by CNT and CF is shown in Table 1. The mix proportion of the mortar samples used in this study was referenced from the earlier works performed by Kim et al. [16,22], with a few modifications. The amounts of the silica fume and superplasticizer were fixed, respectively, at 10.0 wt.% and 1.6 wt.% by the mass of cement. ...
... The current density between electrically conductive fillers can be described by the Simmons's tunneling theory equation [38,39]. One of the main parameters affecting the tunneling effect is the potential barrier width, which represents the distance between the conductive fillers in the cement matrix [16,40]. That is, the tunneling effect in the cement matrix occurs more as the gap between the conductive fillers increases due to the damage of the electrically conductive pathways. ...
The present study investigates the impact of freeze–thaw deterioration on the electrical properties and electric-heating capabilities of cement mortar incorporating with carbon nanotubes (CNT) and carbon fibers (CF). Mortar samples, containing 0.5 wt.% CNT and 0.1 wt.% CF relative to the mass of cement, were prepared and subjected to freeze–thaw tests for up to 300 cycles. The electrical properties and electric-heating capability were evaluated every 30 freeze–thaw cycles, and the physicochemical characteristics of the samples were analyzed using X-ray diffraction and mercury intrusion porosimetry. The results indicate a decline in both electrical conductivity and heat-generation capability as the freeze–thaw cycles progress. Furthermore, changes in the pore structure of the mortar samples during the freeze–thaw cycles contributed to damage in the conductive network formed by CNT and CF, resulting in decreased electrical conductivity and heat-generation capabilities of the mortar samples.
... However, the improvement in the electrical conductivity of CF-incorporated composites is limited, and the incorporation of a large amount of CF in a polymer matrix can cause significant deterioration of the composites [9]. Therefore, considerable work has focused on nanocomposites that incorporate CF with carbon nanotube (CNT) [9][10][11][12]. CNT is one of the nanoscale conductive fillers consisting of CPCs. ...
... The major issue when applying CPCs as a self-heating element is the negative temperature coefficient (NTC) effect, referring to a decrease in their resistance levels with an increase in the temperature [6,13,17]. This NTC effect can cause the conductive fillers to overheat due to the reduction of electrical resistance, which leads to a thermal shock in the composites [11,18]. Accordingly, it is essential in heating applications of such composites for the self-heating characteristics to be predictable and for the severe NTC effect to be detected in advance. ...
... The normalized electrical resistance decreased with an increase in the surface temperature for all specimens. These phenomena are closely associated with the NTC effect, i.e., a decrease in the electrical resistance of CPCs with an increase in the temperature [11,13,18,40]. Xiang et al. [18] reported that the rearrangement of the CNT at an increased temperature exceeding the melting point of the matrix causes the NTC effect, generating more electrical contact points in the composites. ...
A machine learning-based prediction of the self-heating characteristics and the negative temperature coefficient (NTC) effect detection of nanocomposites incorporating carbon nanotube (CNT) and carbon fiber (CF) is proposed. The CNT content was fixed at 4.0 wt.%, and CFs having three different lengths (0.1, 3 and 6 mm) at dosage of 1.0 wt.% were added to fabricate the specimens. The self-heating properties of the specimens were evaluated via self-heating tests. Based on the experiment results, two types of artificial neural network (ANN) models were constructed to predict the surface temperature and electrical resistance, and to detect a severe NTC effect. The present predictions were compared with experimental values to verify the applicability of the proposed ANN models. The ANN model for data prediction was able to predict the surface temperature and electrical resistance closely, with corresponding R-squared value of 0.91 and 0.97, respectively. The ANN model for data detection could detect the severe NTC effect occurred in the nanocomposites under the self-heating condition, as evidenced by the accuracy and sensitivity values exceeding 0.7 in all criteria.
... Accordingly, the reduction in the electrical resistance of the fabricated cement-based sensors, regardless of the embedded MWCNT content, was noted, as shown in Fig. 2. It was also found that the degree of reduction in electrical resistance was different based on the embedded MWCNT content. A substantial tunneling effect was observed in sensors with low levels of MWCNT, which can be attributed to the fact that the tunneling effect is inversely proportional to the embedded MWCNT content [35,36]. In addition, the tunneling-induced electrical stability of the sensors decreased when they were exposed to temperatures of 100, 200, and 400°C. ...
... In addition, the tunneling-induced electrical stability of the sensors decreased when they were exposed to temperatures of 100, 200, and 400°C. This can be explained by the decomposition of components in the cementitious composites, which may disturb the movement of electron charges and reduce the tunneling-induced electrical stability [35]. The sensors subjected to freeze-thaw cycles specifically demonstrated the lowest tunneling-induced electrical stability; this can be confirmed by the appearance of microcracks in the cement-based sensors during the freeze-thaw cycles. ...
... It can be observed that the electrical resistance was inversely proportional to the temperature. As reported in previous studies, the activation energy for electrical conduction increased, possibly leading to a decrease in the electrical resistance of the cement-based sensors as they were heated, indicating a negative temperature coefficient [5,32,35,37]. Similarly, the electrical resistance of the cement-based sensors increased as the temperature was decreased owing to the activation energy of electrical conduc-D. ...
Cement-based sensors are vulnerable to weathering conditions, such as exposure temperatures and freeze-thaw cycles, which have detrimental effects on their piezoresistive sensing behaviors; however, to the best of our knowledge, these effects have been rarely investigated. In this study, the electrical and piezoresistive sensing characteristics of multi-walled carbon nanotube (MWCNT)-embedded cement-based sensors exposed to various temperatures were investigated. Cement-based sensors with varying MWCNT content were fabricated and exposed to five different temperatures. Subsequently, the effects of these temperatures on the compressive strength and electrical properties of the sensors were observed. In addition, the electrical stability of the tunneling-induced and temperature-dependent electrical properties were examined. The electrical and piezoresistive sensing behaviors were found to be mainly affected by the exposure temperature, and the effects varied with the embedded MWCNT content. Thermo-gravimetric and scanning electron microscopy analyses served to characterize the microstructures of the cement-based sensors and the results helped in explaining the electrical and piezoresistive sensing behaviors.
... According to the aforementioned law, the flowing current can generate heat and is proportional to the square of applied voltage. Kim et al. [95,96] experimented with heating materials containing CNTs. They have discovered that 0.6 wt.% of CNTs allowed for the stable generation of heat of up to 70 • C [95]. ...
... They have discovered that 0.6 wt.% of CNTs allowed for the stable generation of heat of up to 70 • C [95]. Further research consisting of both CNTs and carbon fibers has shown improved results while creating stable heat conducting paths along with the material [96]. Frąc et al. [97] used expanded graphite combined with paraffin and obtained promising results with 20 wt.% of graphite/paraffin cementitious composite, achieving heat generation of 25.7 kW/m 2 with an applied voltage of 10 V. ...
... Heating/heat storage material Kim et al. [96] Frąc et al. [97] Energy harvesting Ghosh et al. [100] Wei et al. [99] Electromagnetic shielding Shielding material Nam et al. [102] Cui et al. [103] Sun et al. [51] Self-healing Autogenous healing material Siad et al. [105] Öztürk et al. [106] Modeling Material morphology Park et al. [107] Mechanical properties Eftekhari et al. [108] ...
A rising demand for efficient functional materials brings forth research challenges regarding improvements in existing materials. Carbon infused cementitious composites, regardless of being an important research topic worldwide, still present many questions concerning their functionality and properties. The paper aims to highlight the most important materials used for cementitious composites, their properties, and their uses while also including the most relevant of the latest research in that area.
... The resistivity of the specimens in Fig. 3 commonly decreased upon an increase in the input voltages. This phenomenon can be explained by the tunneling effect, which allows activated electrons to jump stochastically over an insulation gap, which may cause a decrease in the electrical resistivity as the input voltage is increased [33][34][35]. The tunneling-induced electrical current density of the composites with CNT can be expressed as Eq. ...
... The tunneling-induced electrical current density of the composites with CNT can be expressed as Eq. (1) as in Kim et al. [35]. As described in Eq. ...
... (1) by Kim et al., the tunneling-induced electrical resistivity is affected by the distances between the individual CNT particles [35]. As shown in Fig. 3, the electrical resistivity tended to decrease with the input voltage in all specimens regardless of the incorporated silica aerogel content, while the degree of the reduction in the electrical resistivity differed according to the silica aerogel content. ...
In the present study, CNT-embedded electric heating composites were fabricated and the effects of silica aerogel addition on the electric heating capabilities and heat-induced electrical stability were examined. Silica aerogel at levels of 0%, 0.5%, and 1.0% by mass of polymer were incorporated into the polymeric composites incorporating 4% CNT. The fabrication details, tunneling-induced electrical characteristics, and electric heating capabilities during cyclic and long-term heating conditions were reported. The electric heating test results were discussed in terms of the SEM observations, thermal images taken during the heating process, and schematic descriptions of the heating process. The test results showed that the incorporating silica aerogel could reduce the redistribution of the individual CNT particles, improving the electric heating capabilities including the heat generation stability and the heat-induced electrical stability during the heating process. Moreover, incorporating silica aerogel increased the cooling time, and improving the heat-storage capability related to the heating efficiency. Thus, it can be concluded that the silica aerogel addition has clear potential to improve the electric heating capability and heat-induced electrical stability of CNT-embedded electric heating composites.
... An alkali activator was obtained by blending sodium hydroxide pellets (Duksan Chemicals Co., Ansan, Korea), sodium silicate solution (Duksan Chemicals Co., Ansan, Korea; Na 2 O: 9.2%, SiO 2 : 33.3%, H 2 O: 57.5%), and water. Silicate modulus of 1.1 (Ms = ratio of SiO 2 /Na 2 O) was selected because the Ms of 1.1 is general value in terms of physical properties, such as mechanical, flowability, and setting time [7][8][9][21][22][23]. MWCNTs (Jeno Tube 8 ©, JEIO Co., Ltd., Ansan, Korea) with a purity level of 98.5% and PAN-based CFs (ACE &Tech, Ltd., Youngju, Korea) were used to prepare an electrically conductive specimen [24,25]. ...
... The contact phenomenon between MWCNTs and CFs filler is shown in Figure 5d. It is believed that the connection of two fillers causes a bridging effect in a AAS matrix, and it induces the formation of uniform conductive network [22]. The electrically conductive path of the AAS composites is susceptible to damage due to hydration and external impact, which in turn causes instability of electrical properties. ...
... The combination of MWCNTs and CFs filler implements nano-and micro-sized multiscale conductive pathways, and enables more stable and improved electrical properties. It is concluded that the small change in resistivity, over time, of the specimens containing CFs, is due to this bridging effect (shown in Figure 3) [22]. The TG and the derivative TG (DTG) results of the AAS composite are shown in Figure 6. ...
Herein, we investigated the synergistic effect of multi-walled carbon nanotube (MWCNT) and carbon fiber (CF) hybrid fillers on electrical and mechanical characteristics of alkali-activated slag (AAS) composites. Many studies on AAS composites have been conducted in the past; however, not much progress has been made regarding characteristics of AAS composites with hybrid conductive fillers. The specimens with different mix proportions were fabricated in the present study, and numerous material characteristics, including flowability, electrical resistivity, and compressive strength of AAS composites were measured. In addition, the synergistic effects were investigated through scanning electron microscopy and thermogravimetric analysis. It was found that the 0.5 wt.% of MWCNTs and CFs lead the effects of the bridging and reducing crack propagation, thereby improving its electrical and mechanical performances. The filler exceeding a percolation point improved the electrical performance of the AAS composites; however, it interfered with the hydration process during the curing period, and caused a decrease in compressive strength of AAS composites.
... In addition, the formation of expanded electrically conductive networks by micro-sized CF counteracts the decrease in electrical conductivity caused by the evaporation of the electrolytic pore solution (Kim et al., 2017). A study on the heat generation of cementitious composites with CNT and CF demonstrated that the addition of CF enhances both the heat generation capability and stability of the composite (Kim et al., 2018). This enhancement is attributed to the reduced damage to the electrically conductive pathways through the formation of overlapping conductive pathways consisting of CNT and CF (Kim et al., 2018). ...
... A study on the heat generation of cementitious composites with CNT and CF demonstrated that the addition of CF enhances both the heat generation capability and stability of the composite (Kim et al., 2018). This enhancement is attributed to the reduced damage to the electrically conductive pathways through the formation of overlapping conductive pathways consisting of CNT and CF (Kim et al., 2018). ...
The present study systematically investigated the influence of varied conductive filler contents on the negative/ positive temperature coefficient (NTC/PTC) effects in cement-based self-heating composites. Different composite formulations containing varying proportions of carbon nanotubes (CNT) and carbon fiber (CF) were prepared and subjected to self-heating tests at different input voltages. Analysis of temperature and electrical conductivity data obtained during the tests elucidated the NTC/PTC effects. Additionally, diverse analytical techniques were employed to characterize the physicochemical properties of the samples. Results indicated a correlation between NTC and PTC effects and thermal expansion as well as variations in electrical resistivity with increasing temperature. Moreover, a specific temperature and electrical resistivity range is identified where the NTC effect transitions to the PTC effect, a transition range influenced by the conductive filler content. Enhanced heat-generation accelerated the PTC effect by inducing structural alterations in the sample's physicochemical composition.
... In recent decades, numerous studies have been conducted to develop electrically conductive cement composites (ECCCs) [1,2] due to their potential for various applications, including self-heating [3,4], electric grounding [5,6], cathodic protection [7][8][9], and self-sensing [10][11][12][13]. Voltage-connected self-heating ECCCs are utilized in applications such as de-icing [14][15][16], accelerated electrical curing of concrete [17,18], and floor heating [19]. ...
... As shown in Fig. 11, the average surface temperature of all mixtures increased significantly during the first 2 h, followed by a continuous decrease up to 24 h. The tunneling electrical resistivity of all mixtures increased for 24 h, as shown in Fig. 12. Kim et al. [3,4] reported that internal thermal expansion and additional hydration products are responsible for the increase in electrical resistivity. ...
... Electrically conductive composites created with conductive additives added to cement-based mixtures offer an effective solution in construction and building materials engineering [1]. Cementitious composites have very low electrical conductivity. ...
... This is due to the fact that CFs form a continuous network in the mixture compared to other materials and facilitate electric current. The good electrical current bridging propertie of CF has also been confirmed in [1][2][3][4] studies. On the other hand, it was concluded that SWCNT did not have any positive effect on the resistivity and the values were close to the Ref sample. ...
... In the range of 0∼4% strain, the piezoresistive properties of the composites have excellent linearity and repeatability, which can well monitor the strain and cracks on the concrete surface. G. Kim et al. [128,129]discussed the thermoelectric properties of CNT/CF smart concrete. ey verified that adding CF to CNT concrete can reduce the damage of conductive path caused by thermal expansion, and its intelligence is shown in Figure 24. ...
... Schematic diagram of CB, PP fibers, and potential contact points in smart concrete.[13]. Schematics of the intelligent hybrid fiber concrete (CNT/CF).[128]. ...
Smart fiber reinforced concretes (FRC) are good in intelligent environmental response. With the smart FRC being used in buildings such as bridges and tunnels, the real-time online distributed monitoring of concrete state can be realized. It provides an excellent solution to reduce the emergencies caused by the accumulation of damages, resistance attenuation, etc. This paper analyzes smart FRC’s self-sensing and self-healing response characteristics under different environmental response fields. Furthermore, the intelligent response mechanism of smart carbon fiber reinforced concrete (CFRC), optical fiber reinforced concrete (OFRC), glass fiber reinforced concrete (GFRC), and nanofiber reinforced concrete (NFRC) would be summarized. The response fields include the stress field, temperature field, electromagnetic field, chemical field, and humidity field, among which the field response mechanism of smart NFRC is classified and summarized. Finally, the advantages and disadvantages, the intelligent response parameters, and the applications of smart FRC under different environmental fields are compared.
... Recently, many researchers have examined cementitious composites containing different types of electrically conductive fillers to improve their mechanical, electrical, and piezoresistive sensing behaviors (Al-Dahawi et al. 2016, Kim et al. 2018b, Han et al. 2015. Al-Dahawi et al. (2016) reported that mechanical and electrical properties of cementitious composites incorporating conductive fillers Synergistic effects of CNT and CB inclusion on the piezoresistive sensing behaviors of cementitious composites blended with fly ash with nano-sized (CNT and GNP) and micro-sized (CF) materials, indicating that the incorporation of different types of electrically conductive fillers can improve the mechanical and electrical properties of cementitious composites (Al-Dahawi et al. 2016). ...
... Kim et al. (2018) investigated the electrical characteristics of cementitious composites incorporating different replacement levels of CNT and CF. It was found that the well-formed conductive pathways composed of multiscale conductive fillers improved the effective electrical characteristics of the composites (Kim et al. 2018b). In addition, Han et al. (2015) investigated the synergistic effect of CNT and CB on the piezoresistive sensing. ...
The present study investigated the synergistic effects of carbon nanotube (CNT) and carbon black (CB) inclusions on the piezoresistive sensing behaviors of cementitious composites. Four different CNT and CB combinations were considered to form different conductive networks in the binder material composed of Portland cement and fly ash. The cement was substituted with fly ash at levels of 0 or 50% by the mass of binder. The specimens were cured up to 100 days to observe the variations of the electrical characteristics with hydration progress, and the piezoresistive sensing behaviors of the specimens were measured under cyclic loading tests. The fabricated specimens were additionally evaluated with flowability, resistivity and cyclic loading tests, and morphological analysis. The scanning electron microscopy and energy disperse X-ray spectroscopy test results indicated that CNT and CB inclusion induced synergistic formations of electrically conductive networks, which led to an improvement of piezoresistive sensing behaviors. Moreover, the incorporation of fly ash having Fe3+ components decreased the electrical resistivity, improving both the linearity of fractional changes in the electrical resistivity and reproducibility expressed as R2 under cyclic loading conditions.
... CNTCS must serve for a long time as the embedded sensor for SHM, so the fatigue and creep conditions of CNTCS must be considered [53]. Kim et al. [54] estimated the long-term resistivity of CNTCS by effective medium theory and verified by experiments, all of which found that the resistivity of the composite would gradually increase with serving time in a dynamic change process. As shown in Figure 6, the resistivities of different CNTCS specimens over dynamic times have non-negligible gaps between the theoretical estimation and experimental results. ...
... Comparison of test data with predicted resistance and time responses of CNTCS[54] (Ex.test value; Pred.predicted value; N5F1-50 = 5 g CNT + 1 g CF + 50 g fine aggregate, the rests are similar). ...
Structural health monitoring (SHM) technology based on the mechanical–electrical sensing effect of various intrinsic smart materials has a good application prospect. Carbon nanotube (CNT) has excellent electromechanical properties and hence can be doped into cement by appropriate dispersive means to produce CNT-modified cement-based smart material (CNTCS) with excellent electromechanical (piezoresistive/piezoelectric) capacity. CNTCS can be developed into a static/dynamic intrinsic sensor for SHM after effective packaging and calibration. Based on the characteristics of CNT, the dispersion methods and the dispersity characterization techniques of CNT in the water/cement matrix are summarized, and then the influence laws of various factors on piezoresistive and piezoelectric sensing behaviors of the corresponding CNTCS are also discussed. The full-frequency domain sensing mechanism of CNTCS is analyzed by combining its finite element model and electromechanical coupling theory, and the practicability of applying CNTCS as an SHM static/dynamic intrinsic sensor is further investigated.
... The incorporation of nano fillers helps to enhance concrete composite performance, manipulate and design composite performance from bottom to up and lower structure life cycle cost. Since the early 2000 s, great efforts have been made on the research of nanoengineered concrete composites and a variety of nanofillers has been utilized including nano SiO 2 [10], nano TiO 2 [11], nano ZrO 2 [12], nano carbon black [13], carbon nanotube (CNT) [14][15][16] and multi-layer graphene [17]. ...
... Five types of Ni-CNTs, fabricated by chemical electroplating method (as shown in Fig. 1), were selected as the nano fillers to modify the mechanical properties of RPC. The physical parameters of Ni-CNTs are listed in Table 1 and the TEM images of Ni-CNTs are demonstrated in Fig. 2. Generally, the specific surface area and tap density of CNTs used in previous researches are >100 m 2 /g and < 0.35 g/cm 3 , respectively [14]. Table 1 shows that due to the existence of nickel coating, the specific surface area of Ni-CNTs is decreased by 66.7% and the tap density is increased by 196.4%. ...
Owing to their small size, good wettability, uniform dispersion ability and high thermal properties, the nickel-plated carbon nanotubes (Ni-CNTs) with different aspect ratios are used to reinforce reactive powder concrete (RPC) through modifying the nano/micro- structural units of concrete. Incorporating only 0.075 vol% of Ni-CNTs (0.03 vol% of CNTs) can significantly increase mechanical properties of RPC. The enhancement effect on compressive strength caused by the incorporation of Ni-CNTs with aspect ratio of 1000 reaches 26.8%/23.0 MPa, mainly benefiting from the high polymerization C-S-H gels, low porosity, and refined pore structure. The 33.5%/1.92 MPa increases of flexural strength can be attributed to the decrease of large pore, original cracks, molar ratio of CaO to SiO2, and gel water content when Ni-CNTs with aspect ratio of 125 are added. Ni-CNTs with aspect ratio of 1500 have the largest utilization rate of being pulled-out, resulting from the improvement of dispersibility and the pining effect of nickel coating and then leading to the increased toughness. Therefore, incorporating Ni-CNTs can fundamentally modify the nano/micro- scale structural nature of RPC, providing a bottom-up approach for controlling the properties of RPC.
... When the contents of CFs and CNTs were 0.2 to the weight of cement (wt.%) and 0.4 wt.%, respectively, the mortar had the lowest resistivity. Kim et al. [29] found that composite with the addition of CNTs and CFs had higher conductive stability. Despite the integration of CNTs and CFs demonstrating excellent performance at a reduced cost, this method does not effectively resolve the underlying issue of poor dispersion of CNTs. ...
Smart cement-based materials have the potential to monitor the health of structures. The performances of composites with various kinds of conductive fillers have been found to be sensitive and stable. However, poor dispersion of conductive fillers limits their application. This study adopted the coupling agent method to attach carbon nanotubes (CNTs) onto the surface of carbon fibers (CFs). The CNT-grafted CFs (CNT-CFs) were adopted as conductive fillers to develop a CNT-CF-incorporated cementitious composite (CNT-CF/CC). The feasibility of this approach was demonstrated through Scanning Electron Microscopy (SEM) analysis and X-ray Photoelectron Spectroscopy (XPS) analysis. The CNT-CF/CC exhibited excellent conductivity because of the introduction of CNTs compared with the CF-incorporated cementitious composite (CF/CC). The CNT-CF/CC reflected huge responses under different temperatures and moisture contents. Even under conditions of high humidity or elevated temperatures, the CNT-CF/CC demonstrated stable performance and exhibited a broad measurement range. The introduction of CNT-CFs also enhanced the mechanical properties of the composite, displaying superior piezoresistivity. The failure load for the CNT-CF/CC reached 25 kN and the maximum FCR was 24.77%. In the cyclic loading, the maximum FCR reached 20.03% when subjected to peak cyclic load at 45% of the failure load. The additional conductive pathways introduced by CNTs enhanced the conductivity and sensitivity of the composite. And the anchoring connection between CNT-CFs and the cement matrix has been identified as a primary factor enhancing the stability in performance.
... This synergistic interaction can reduce the required amount of conductive filler while simultaneously improving both electrical conductivity and functional properties [14]. For example, previous studies have demonstrated that the combination of CNTs and CFs can create hierarchical conductive networks within composites, leading to improvements in both electrical conductivity and mechanical properties [16,17]. However, fewer studies have investigated the synergistic effects of these fillers on enhancing the EMI shielding performance of cement composites, particularly in relation to reflection and absorption properties. ...
The growing importance of electromagnetic interference (EMI) shielding composites in civil engineering has garnered increasing attention. Conductive cement-based composites, incorporating various conductive fillers, such as carbon nanotubes (CNTs), carbon fibers (CFs), and graphene nanoplatelets (GNPs), provide effective solutions due to their high electrical conductivity. While previous studies have primarily focused on improving the overall shielding effectiveness, this research emphasizes balancing the reflection and absorption properties. The experimental results demonstrate an EMI shielding performance exceeding 50 dB, revealing that filler size (nano, micro, or macro) and shape (platelet or fiber) significantly influence both reflection and absorption characteristics. Based on a comprehensive evaluation of the shielding properties, this study highlights the need to consider factors such as reflection versus absorption losses and filler shape or type when optimizing filler content to develop effective cement-based EMI shielding composites.
... In previous studies, conductive fibers including carbon fibers (CFs), carbon black, steel fibers, stainless wire, nano carbon fibers (NCFs), and graphene, etc. showed a good ability to reduce the electric resistance of concrete [31][32][33][34][35][36]. Among these materials, CFs with a larger volumetric size exhibited a much better effect in terms of enhancing the electrical conductivity of the samples because it was reported to be easier to construct the macroscopic connected network inside the sample [37][38][39]. Although CFs are promising for improving the electrical conductivity of concrete, it is still important to clarify the effects of different factors on the electrical conductivity of concrete to ensure the ongoing OH curing process. ...
The development of electric resistance is a key factor affecting the performance of conductive concrete, especially the electrical–thermal performance. In this work, the effects of different influencing factors (including the water-to-binder ratio, coarse aggregate content and carbon fiber (CF) content) on the electric resistance of conductive concrete were systematically investigated. At the same time, ohmic heating (OH) curing was applied to fabricate CF-reinforced conductive concrete (CFRCC) under a negative temperature environment at −20 °C. The effects of different factors on the electrothermal properties (curing temperature and conductive stability) of the samples were studied. The mechanical strengths of the CFRCC cured by different curing conditions were also tested, and the feasibility of OH curing for preparing CFRCC in a negative-temperature environment was verified at various electric powers. This work aims to give new insights into the effects of multiple factors on the performance of CFRCC for improved concrete construction in winter.
... Meanwhile, Kim et al. found that adding carbon fibers improved the heat generation capability and electrical stability of cementitious composites with CNTs during heating, suggesting enhanced capacitive behavior at low and middle frequencies. This was possibly attributed to the formation of an overlapped area by adding the CF to the cementitious composites with CNT, which reduced the damage to the electrically conductive pathways induced by thermal expansion, additional hydration reactions, and internal cracking during the heating process [59], which could be corroborated through the here proposed model, for describing the electrical impedance. Other parameters estimated from the circuit model described in Figure 5 are presented in Table 5. ...
Structural health monitoring applications have gained significant attention in recent research, particularly in the study of the mechanical–electrical properties of materials such as cement-based composites. While most researchers have focused on the piezoresistive properties of cement-based composites under compressive stress, exploring the electrical impedance of such materials can provide valuable insights into the relationship between their mechanical and electrical characteristics. In this study, we investigated the connection between the mechanical properties and electrical impedance of cement-based composites modified with Au nanoparticles. Cylindrical samples with dimensions of 3 cm in diameter and 6 cm in length were prepared with a ratio of w/c = 0.47. The Au nanoparticles (Au NPs) were synthesized using pulsed laser ablation in liquids, and their size distribution was analyzed through dynamical light scattering. Mechanical properties were evaluated by analyzing the Young modulus derived from strain–stress curves obtained at various force rates. Electrical properties were measured by means of electrical impedance spectroscopy. The experimental results revealed a notable reduction of 91% in the mechanical properties of Au NPs-cement compounds, while their electrical properties demonstrated a significant improvement of 65%. Interestingly, the decrease in mechanical properties resulting from the inclusion of gold nanoparticles in cementitious materials was found to be comparable to that resulting from variations in the water/cement ratios or the hydration reaction.
... The observed decrease in resistance over time in the steel series is hypothesized to be influenced more by disruptions in the conductive network due to hydration reactions rather than moisture. In cases where CNT and CF are jointly incorporated, the conductive network of the cementitious composite may exhibit enhanced robustness due to internal structural changes and disturbances induced by hydration reactions [29,30]. When CF is mixed with CNT, thermal disturbances reduce overlapping regions, thereby enhancing the uniformity of the conductive network, and consequently reducing resistance. ...
In the present study, the effects of electrodes type (copper, steel or CFRP) and design (plate or mesh) on electrical stability of conductive cement as exposed to various weathering conditions were investigated. To fabricate these composites, multi-walled carbon nanotube and carbon fiber were added to the cement composites by 0.6 and 0.4% by cement mass. Seven different types of electrodes were embedded to the samples, and their electrical stability was examined during the curing period. In addition, the fabricated samples were exposed to water ingress and cyclic heating conditions. Then, the compressive strength of the samples was evaluated to observe the interfacial bonding between the cement paste and electrodes. Based on the experimental results, it was found that the samples showed different electrical stability even their mix proportion was same. Thus, it can be concluded that the type and design of the electrodes are important in measuring the electrical properties of the conductive cement composites. Specifically, an improved electrical stability of electrodes is required when they are exposed to various weathering conditions.
... The thermal expansion differences between carbon textile and cementitious matrix can initially contribute to the strengthening effect [52], improving the mechanical performance. However, if the exposure temperature is excessively high, the thermal stress generated along the carbon textile and cementitious material interface can surpass the rupture stress, resulting in interface deterioration and reduced mechanical performance [53,54]. ...
The exposure to elevated temperatures and alkaline concrete pore solution can deteriorate the polymer coating in textile-reinforced concrete (TRC) and degrade its mechanical performance. To address this concern, this study experimentally investigated the influence of surface treatments on elevated temperature resistance of carbon textile-reinforced concrete (CTRC) and basalt textile-reinforced concrete (BTRC) and durability performance in the marine environment. Three types of surface treatments, including epoxy impregnation, immersion in nano-silica suspension, and combined treatment with the silane coupling agent and nano-silica, were utilized to enhance the elevated temperature resistance and durability properties of CTRC and BTRC. The flexural strength results revealed that the modification effect of nano-silica immersion on the interfacial bonding of CTRC was greater than that of the BTRC, and the improvement can be further enhanced by using the silane coupling agent. In addition, the in-situ three-point flexural tests of CTRC and BTRC specimens were conducted under elevated temperature conditions to examine their elevated temperature resistance. It was found that exposure to elevated temperature decreases flexural performances such as first cracking strength, flexural strength, and flexural toughness of CTRC and BTRC. The elevated temperature resistance of nano-silica treated specimens is higher than those treated with epoxy impregnation. Furthermore, the treatment with nano-silica increases the aging resistance of both CTRC and BTRC specimens in the simulated marine environment. The research outcomes can serve as a solid base for applying TRC materials in the harsh marine environment.
... Similarly, the resistance of carbon composites varies with temperature. On the one hand, the increase in temperature leads to an increase in the probability of electron transition and an increase in electrical conductivity [28,29]. On the other hand, the increase in temperature causes the material to produce expansion strain, which increases the potential barrier of electron transition, and the expansion strain will increase the interface resistance between fiber and matrix and decrease the conductivity. ...
The effects of temperature and water content on the electrical conductivity of cement mortar with different sizes of carbon nanotubes were studied, and the effect of the size of carbon nanotubes on the electrical conductivity of cement mortar was revealed. The results show that the small diameter carbon nanotubes have the best enhancement effect on the electrical conductivity of cement mortar. The electrical conductivity of cement mortar with different diameters of carbon nanotubes is positively correlated with water content, and with the decrease of the diameter of carbon nanotubes in the sample, the effect of water content on the electrical conductivity of carbon nanotube cement mortar becomes smaller and smaller. With the increase of temperature, the electrical conductivity of cement mortar containing carbon nanotubes of different diameters increases in varying degrees, but the increase of samples with small diameter carbon nanotubes is the smallest, indicating that the electrical conductivity of cement mortars with small diameter carbon nanotubes is less affected by temperature.
... In particular, cementitious composites that incorporate nanofillers such as carbon nanotubes (CNTs) can provide higher electrical conductivity compared to existing cement, and are expected to have a high impact by applying them to future infrastructure [4][5][6]. However, the CNTs-incorporated cementitious composites have difficulty in accurately predicting and analyzing characteristics due to the inherent heterogeneity of cement and limitation in understanding the nanoscale mechanisms [7][8][9]. To scrutinize and overcome the issues, several studies have previously been conducted on multiscale material simulations consisting of nanomicro-macro-scale theories. ...
Conductive cementitious composites are innovated materials that have improved electrical conductivity compared to general types of cement, and are expected to be used in a variety of future infrastructures with unique functionalities such as self-heating, electromagnetic shielding, and piezoelectricity. In the present study, machine learning methods that have been recently applied in various fields were proposed for the prediction of piezoelectric characteristics of carbon nanotubes (CNTs)-incorporated cement composites. Data on the resistivity change of CNTs/cement composites according to various water/binder ratios, loading types, and CNT content were considered as training values. These data were applied to numerous machine learning techniques including linear regression, decision tree, support vector machine, deep belief network, Gaussian process regression, genetic algorithm, bagging ensemble, random forest ensemble, boosting ensemble, long short-term memory, and gated recurrent units to estimate the time-independent and -dependent electrical properties of conductive cementitious composites. By comparing and analyzing the computed results of the proposed methods, an optimal algorithm suitable for application to CNTs-embedded cementitious composites was derived.
... Meanwhile, the tunneling-induced electrical resistivity values of the cementitious paste were observed as different applied input voltages were applied. Input voltages ranging from 0 to 20 V were applied to the cementitious paste using a DC power supply (PL-3005S), and the electrical resistivity of each cementitious paste was measured within 1 s, as the electrical resistivity of the cementitious paste can be affected by the movement of activated electrons as current flows through the cementitious paste [17]. ...
The present study investigated the influences of water ingress on the electrical resistivity and electromechanical sensing responses of CNT/cement composites. The water absorption, mechanical, electrical, and electromechanical sensing characteristics of the composites were assessed in terms of water absorption rate, compressive strength, electrical resistivity, tunneling-induced electrical resistivity, fractional change in the resistivity (FCR), and R-squared value. The water absorption rate increased, and compressive strength decreased as the CNT content and water-to-cement ratios increased. These were ascribed to an addition of the dispersion agent and water which caused microstructures of the composites more porous. In addition, the tunneling-induced electrical resistivity test exhibited that the tunneling effects became more pronounced with increase of the CNT and water contents. In electromechanical sensing test, FCR value reached the highest level at CNT content 0.2%, and R-squared value enhanced as water ingress was reduced. In this regard, it can be concluded that the new types of materials with high hydrophobicity are necessary to improve the stability of the electrical electromechanical sensing capability of the CNT-based cementitious sensors as exposed to the water conditions.
... From the characteristics and mechanisms introduced earlier, it was able to exhibit various functional characteristics that were difficult to perform in existing cement materials. The accelerated curing [16], monitoring [5], electromagnetic shielding [17], and thermal generation [18] of conductive construction composites are the representative examples. The present study has novelty compared to existing researches in two aspects: (1) Considering both cement and alkali-activated binders, a comprehensive study was conducted on how nanofiller affect the physicochemical properties of each binder. ...
Herein, we introduce p-type thermoelectric materials composed of Portland cement (PC) and slag-based alkali-activated cement (AAC) composites containing multi-walled carbon nanotube (MWCNT). Numerous characteristics related to the thermoelectric properties, in this case the electrical conductivity, compressive strength, thermal conductivity, Seebeck coefficient, and power factor of composites composed of two types of binders, were investigated, and various physicochemical properties were analyzed to determine their enhancement mechanisms. Based on the initial test results, MWCNT-embedded AAC composites were found to be feasible as a thermoelectric material, and an AAC thermoelectric module containing 2.0 wt% MWCNT was therefore additionally fabricated. The AAC-based thermoelectric module was tested with regard to its energy-harvesting performance, with the result confirming that the module was capable of generating electrical power.
This study examines the effects of steel fibers (SF) and carbon nanotubes (CNTs) on the performance of cementitious composites. Three types of mixes were analyzed: a reference mix (REF), a steel fiber-reinforced concrete (SFRC), and a hybrid mix containing both CNTs and SFs. The investigation included physicomechanical property evaluations, microstructural analysis, and ultrasonic pulse velocity (UPV) tests. Results indicate significant improvements in performance across the mixes, with the hybrid mix achieving the highest flexural and compressive strengths, highlighting a synergistic interaction between CNTs and SF to enhance load-bearing capacity. Additionally, the mixtures displayed reduced porosity and water absorption, signifying improved density and lower permeability. SEM analysis further confirmed a denser microstructure with enhanced crack-bridging capabilities due to the presence of CNTs and SF. UPV measurements supported these findings, demonstrating superior internal integrity and stiffness in the hybrid mix. These experimental results underscore the potential of hybrid reinforcement strategies for producing high-performance fiber concrete with enhanced durability, making it suitable for demanding construction applications.
This study investigates the heat-generation stability of carbon nanotube (CNT)/cement composites after exposing to cyclic loading conditions. The specimens were fabricated with varying CNT contents and levels of fly ash replacement. Results showed that increasing CNT content reduced electrical resistivity, while the impact on the electrical characteristics was found to be insubstantial, even though a considerable portion of fly ash was replaced. In addition, the electrical resistivity of the specimens after exposed to cyclic loading increased. Electrical heating tests revealed both negative and positive temperature coefficient effects depending on the applied voltages. Higher CNT contents improved the heat-generation capability, but the heating capability decreased after exposed to the cyclic loadings which is deduced from the damage of CNT networks during cyclic loadings. In this regard, the authors concluded that the heat-generation stability can be significantly affected by the applied loadings. Thus, the future research will be conducted to improve the heat-generation stability of the cement-based electrical heating systems as exposed to artificial deteriorations.
We investigated the formation of the conductive network of carbon nanotubes (CNTs) in alkali-activated nanocomposites for sulfate-sensing applications. The matrix was a one-part blend of fly ash and ground granulated blast-furnace slag, activated by sodium silicate and water. Sodium dodecylbenzenesulfonate was used as the surfactant for dispersion of the CNTs in the aqueous media. The nanocomposites were investigated by a laboratory-developed setup to study the electrical and sensing properties of the alkali-activated material. The electrical properties (i.e., conductivity) were calculated and assessed to discover the percolation threshold of the nanocomposites. Furthermore, the sensing behavior of nanocomposites was studied upon sulfate ( SO 4 2 - ) exposure by introduction of sulfuric acid ( ( H 2 SO 4 ) ) and magnesium sulfate ( MgSO 4 ). The sensors were able to preliminarily exhibit a signal difference based on the introduced media ( H 2 SO 4 & Mg SO 4 ), CNT content and H 2 SO 4 volumetric quantity. The results of this research demonstrated a sensing potential of CNT alkali-activated nanocomposites and can be applied in the concrete structural health monitoring.
This study explored the efficiency of the phase-change materials (PCM) to improve the heat storage capacity of carbon nanotube (CNT) and carbon fiber (CF) based self-heating cementitious composites. Composites were prepared with 0.8 wt% CNT and 0.2 wt% CF as conductive fillers, and five different PCM contents (0, 5, 10, 20, and 30 wt%), and their electrical conductivities, thermal conductivities, and compressive strengths were measured. To determine the self-heating capability, the heat-generation and heat-storage capabilities of the composites were investigated using monotonic and cyclic heating/cooling tests. The results of these tests were analyzed through a differential scanning calorimetry and micro-computed tomography, which showed that the PCM particles with high latent heat were well dispersed in the composites, improving the heat storage capacity. Therefore, it can be said that the addition of PCM may improve heat storage capacity and enhance energy efficiency of the cement-based self-heating composites.
The changes in electrical properties of cement pastes incorporating CNT and CF exposed to various deterioration factors were examined in this study. The electrical resistivity changes of the paste samples were measured via the two-probe method. In addition, microstructure changes of the samples before and after exposure to deterioration factors were investigated using various analytical methods. In the samples exposed to the various deterioration conditions, the electrical resistivity increased with exposure time, and a rapid change in the electrical resistivity due to the polarization effect was also observed. However, it can be found that the incorporation of micro-sized CF can mitigate the increase in the electrical resistivity of the samples resulting from the deterioration, improving their electrical stability upon exposure to various environments. Exposure to the deterioration conditions of the samples caused changes in their physicochemical structures, which resulted in changes in their electrical resistivity.
The elastic properties of cementitious composites reinforced by nano-tailored hybrid fibers are analyzed using a micromechanical method. The microstructural feature of the hybrid fiber is that uniformly aligned carbon nanotubes (CNTs) are grown radially on the circumferential surface of carbon fibers (CFs). The CNT waviness and CNT/cement interfacial region are considered. The predictions are compared with experiments, which guarantee the validity of the model. The mechanical properties of cementitious composites, especially in transverse direction, are enhanced due to the radial growth of CNTs on the CFs. The CNT/cement interfacial zone may have a significant effect on the elastic behavior of the nano-tailored hybrid fiber-cement composites. As the mechanical properties of interphase are higher than those of the cement matrix, increasing the interphase thickness causes an improvement in the elastic and shear moduli. The CNT non-straight shape decreases the transverse elastic modulus.
A multi-level micromechanics-based homogenization is proposed here to investigate the damage behavior of composites with multiscale fibers such as carbon nanotube (CNT) and carbon fiber. First, a molecular unit cell is constructed considering the interfacial characteristics between the CNT and a polymer matrix, after which molecular dynamics simulation and micromechanics are utilized to obtain the elastic properties of CNT-reinforced composites. A micromechanics-based progressive damage model is then adopted to predict the damage behavior of the CNT and carbon fiber-reinforced composites. Tensile tests are also conducted to investigate the stress–strain behaviors of the composites. To verify the applicability of the proposed model, the present predictions are compared with those obtained from the tensile test results. The proposed multi-level homogenization has shown to provide a close match to the experimental results. The proposed modeling scheme may facilitate a thorough investigation of the damage behavior of multiscale fiber-reinforced composites, proving the importance of each constituent at a different level.
As a low-carbon ecological cement-based material, SAC (sulfoaluminate cement) has become a research hotspot. This study developed a SAC-based high-performance concrete material with good durability and high toughness. The mechanical properties of different scales of MSF (macro steel fiber) and mSF (micro steel fiber) reinforced sulfoaluminate cement-based composites were mainly studied, including their compressive strength, flexural strength, toughness index, and toughness ratio, and their resistance to sulfate erosion was characterized. The results show that adding MSF and HSF (hybrid steel fibers) can significantly improve concrete’s compressive and flexural strength compared with the Plain group. The compressive strength of SSF1 (1% MSF) and SSF2 (1.5% MSF) increased by 10.9%, 19.6%, and the compressive strength of HSF1 (0.1% mSF, 1.4% MSF), HSF2 (0.2% mSF, 1.3%MSF), HSF3 (0.3% mSF, 1.2% MSF), and HSF4 (0.5% mSF, 1.0% MSF) increased by 23.9%, 33.7%, 37.0%, 29.3%, respectively, while the flexural strength of HSF1, HSF2, HSF3, and HSF4 groups increased by 51.4%, 84.9%, 88.1%, and 64.2%. Compared with the single steel fiber (SSF) group, the HSF group has higher initial crack strength, equivalent flexural strength, toughness index, and toughness ratio. Hybrid fibers have a higher synergistic effect when mSF content is 0.2–0.3% and MSF content is 1.2–1.3%. The mechanism of multi-scale reinforcement of hybrid-steel-fiber-enhanced sulfoaluminate cement-based composites was researched. MSF bridges macro-cracks, mSF bridges micro-cracks, and these two different scales of steel fibers, through filling, bridging, anchoring, pulling off, and pulling out, improve the toughness of composite materials. The mechanism of sulfate corrosion resistance of sulfoaluminate cement-based composites was obtained. SO42− entered the matrix and reacted and formed AFt, filling the matrix’s pores. The whole process is similar to the self-healing process of concrete.
The present study proposed a combined experimental and micromechanical approach to investigating positive temperature coefficient (PTC) and negative temperature coefficient (NTC) effects in carbon nanotube (CNT)-polypropylene composites under a self-heating condition. The electrical and heating performance of the composites were investigated by electrical conductivity measurements and self-heating tests with various input voltages. The test results showed that composites with a CNT content of 5.0 wt.% exhibited excessive heat generation, showing a transition of the PTC effect to the NTC effect. Moreover, a micromechanical modeling was proposed to predict the occurrence of the PTC and NTC effects in the composites, considering various distances between CNTs and wavinesses of CNT. The change of the distance between CNTs under a heating condition was estimated, using the molecular dynamics software Material studio. Comparisons between the predictions and the experimental results were made to show the applicability of the proposed modeling scheme.
Water ingress into heating composites can be a serious issue, having a deleterious effect on their heating performance during their service life. Herein, we present the effect of silica aerogel incorporation on stabilizing the heating characteristics of carbon nanotube (CNT)-embedded cementitious composites when the composites are exposed to water-absorbed condition. The water absorption test indicates that the incorporated silica aerogel was effective to mitigate the water ingress into the composites. A less reduction is observed in the heat generation of the silica aerogel-incorporated specimens when the heating and water-cooling are repeatedly applied to the composites. The improved heating performances of the composites incorporating silica aerogels can be attributed to the hydrophobic property of the silica aerogels. It is therefore concluded that utilization of silica aerogels in fabricating CNT-embedded cementitious composites is a viable means of enhancing the heating performance of the composites during their service life.
This work proposes a design concept of nano/micro-scale carbon modified multifunctional cementitious composites based on the original fabrication method of combined graphene/PVA nanofluid additive, in which nano carbon material graphene was produced from low-cost graphite raw material and surface functionalized by PVA in water in a one-step preparation process, which can directly substitute water in the cement casting. Incorporating the complementary advantages of the bridging three-dimensional micron-scale carbon fiber and the pore-filling and lubricating two-dimensional nano-material graphene, the composite modification can not only improve the mechanical properties of cementitious composites but also gift them with high electrical conductivity, whose electrical resistivity dropped to 0.72 kΩ·cm compared to 13.12 kΩ·cm of the blank. In particular, under such low resistivity, the mechanical strengths were not reduced as with the addition of other single carbon materials but were improved compared with the blank. The results of this work provide a novel approach for designing and developing multifunctional cementitious composites, which would be a promising building material for structural health monitoring.
This research evaluated the feasibility of using iron ore tailings (IOTs) to produce functional conductive composite materials as cement-based sensors based on carbon fiber (CF) reinforced cement composite. In this study, recycled IOTs are used as an alternative material to natural fine aggregate (0%, 30%, and 60%). Nine mixtures were produced. The effects of CF and IOTs content on mechanical properties and electrical conductivity were investigated; Based on the digital image correlation (DIC) system, the stress sensing ability of the specimen was evaluated and the strain field distribution was extracted; According to the results of compressive stress sensing, a predictive compressive stress model was proposed, and the ratio of fractional changes of resistivity (FCR) with unit stress and CF content were fitted; The pore size distribution was studied using nuclear magnetic resonance (NMR) technology; Besides, scanning electron microscope (SEM) and X-ray diffraction (XRD) were used to analyze the microscopic morphology and crystal phase composition. The experimental results revealed that the appropriate IOTs content could improve the pore size distribution and the mechanical properties, which is a maximum increase of 28.12% compared with the plain cement (PC). The DIC strain field distribution shows that the excessive IOTs could increase the brittleness of the matrix, and XRD crystal phase analysis showed that the calcium silicate hydrate (CSH) gel is reduced and the bond with CF is weakened. The addition of CF significantly reduces the resistivity of the composites by an order of magnitude, and the self-sensing capability can be increased by 3 times. The compression stress sensitivity has a linear relationship with the amount of CF, which can be used to predict the compression stress sensing efficiency. It is expected to develop industrial waste IOTs as an effective conductive filler to promote the wider use of CF conductive composite materials.
Piezoresistive cementitious composite materials are promising for developing damage self-sensing structural components. This paper aims to develop a kind of giant piezoresistive Cementitious Carbon Fiber Composite (CCFC) for enabling a fatigue damage self-sensing bridge deck. In particular, 0.4 % and 0.8 %Vol. of short cut Carbon Fibers (CFs) in cementitious composite were respectively adopted. The fiber diameter and length were 7 μm and 3 mm. Based on a series of conducted material piezoresistivity tests, the material effective conductivity variation showed a linear response with a slight time delay to an external load induced compressive strain. The gauge factors of CFCC with 0.4 % and 0.8 %Vol. CFs were respectively above 6000 and 2000. Moreover, the effects of ambient temperature, humidity and polarization were investigated, and a linear relationship between the ambient temperature and the effective conductivity was regressed. Accordingly, CFCC blocks were cast and built into two full-scale segmental bridge deck specimens for a fatigue wheel loading test. The correlation between the CFCC effective conductivity and the fatigue damages, such as concrete cracks, deflections and strain, was discussed. The results confirmed a feasibility of using the giant piezoresistive CCFC to develop a bridge deck with damage self-sensing capability.
The present study proposes a micromechanical model composed of a two-level homogenization process for predicting the electrical conductivity of polymeric composites incorporating carbon nanotube (CNT) and carbon fiber (CF). The curviness of the CNT and the interfacial resistivity between the polymer matrix and the CNT are considered in the micromechanical model. A series of numerical studies with model parameters are carried out, after which a genetic algorithm is applied to determine the optimized model parameters. The electrical and morphological properties of the composites are experimentally evaluated according to the content of CNT and CF. To verify the predictive capability of the proposed model, the present prediction is compared with that obtained from experiments. The proposed model combined with the genetic algorithm is found to closely simulate the effective electrical conductivity of the composites, as evidenced by the credible accuracy to the experimentally measured values.
p>In recent years, many researchers have worked on the development of cementitious composites as self-heating components. To meet the requirements of self-heating composites, carbon-based nanomaterials have been considered as an electrically conductive filler in the cementitious matrix because of their excellent electrical and thermal characteristics. Most researches have focused on the heating performances of the CNT-incorporated hybrid cementitious composites, while fewer efforts were given to observe heat-dependent electrical characteristics of the modified cementitious composites under self-heating condition. In this regard, this paper summarizes recent studies in literature conducted to investigate heat-dependent electrical characteristics of cementitious composites with carbon-based nanomaterials.</p
Recently, various studies have been conducted in an effort to apply the outstanding properties of nanomaterials to construction fields. The present study aims to investigate the repetitive heating characteristics of magnesium oxide (MgO)-activated slag composites containing multi-walled carbon nanotubes (MWCNTs). MgO-activated slag composites with various mix proportions were fabricated through facile mechanical mixing method and cured at various temperatures. The electrical resistivity and compressive strength of the specimens were measured, and the cyclical heating performance was also analyzed under a constant ampere condition. Microstructural and thermal analyses of the MgO-activated slag composites were carried out by means of a scanning electron microscope and a thermogravimetry analysis, respectively. The content of MWCNTs and the curing conditions affected the overall electrical resistivity, compressive strength, and heat-generation properties of the composites. Here, related mechanisms are addressed in connection with the hydration process of the binder material. © 2021 The Korean Society for Composite Materials and IOP Publishing Limited
Continuous fiber-reinforced composites are important materials that have the highest commercialized potential in the upcoming future among existing advanced materials. Despite their wide use and value, their theoretical mechanisms have not been fully established due to the complexity of the compositions and their unrevealed failure mechanisms. This study proposes an effective three-dimensional damage modeling of a fibrous composite by combining analytical micromechanics and evolutionary computation. The interface characteristics, debonding damage, and micro-cracks are considered to be the most influential factors on the toughness and failure behaviors of composites, and a constitutive equation considering these factors was explicitly derived in accordance with the micromechanics-based ensemble volume averaged method. The optimal set of various model parameters in the analytical model were found using modified evolutionary computation that considers human-induced error. The effectiveness of the proposed formulation was validated by comparing a series of numerical simulations with experimental data from available studies.
This paper investigates a scouring sensor using electrical properties of carbon nanotubes(CNTs)-filled cement-based composite. First, for specimens filled with different amount of CNTs, the electrical behavior and the principle which it followed were studied. The effect of the different magnetic field intensity on the arrangement of CNTs in the base was presented. Furthermore, the environment effects (temperature and humidity) on sensors and its causes were revealed. Also, the design of the temperature and humidity self-compensation sensor based on separated electrode was proposed. Finally, by comparison of the sensitivity of the scouring electrode and the stability of the reference electrode, the optimal scheme of the electrode was determined.
Traditional concrete is effectively an insulator in the dry state. However, conductive concrete can attain relatively high conductivity by adding a certain amount of electronically conductive components in the regular concrete matrix. The main purpose of this study is to investigate the electrical and thermal properties of conductive concrete with various graphite contents, specimen dimensions and applied voltages. For this purpose, six different mixtures (the control mixtures and five conductive mixtures with steel fibers of 2% by weight of coarse aggregate and graphite as fine aggregate replacement at the levels of 0%, 5%, 10%, 15% and 20% by weight) were prepared and concrete blocks with two types of dimensions were fabricated. Four test voltage levels, 48 V, 60 V, 110 V, and 220 V, were applied for the electrical and thermal tests. Test results show that the compressive strength of specimens decreases as the amount of graphite increases in concrete. The rising applied voltage decreases electrical resistivity and increases heat of concrete. Meanwhile, higher electrical current and temperature have been obtained in small size specimens than the comparable large size specimens. From the results, it can be concluded that the graphite contents, applied voltage levels, and the specimen dimensions play important roles in electrical and thermal properties of concrete. In addition, the superior electrical and thermal properties have been obtained in the mixture adding 2% steel fibers and 10% graphite.
A viscoplastic damage model based on molecular dynamics (MD) and micromechanics is proposed to predict the rate-dependent inelastic behavior of nanoparticle-reinforced polymer composites. The constitutive equation is developed by combining the solution of the elastic problem and Laplace-transformed superposition principle. The MD simulation is then conducted to derive the interfacial adhesive energy of nanocomposites (silica/nylon-6), and the MD results are applied to the viscoplastic damage model. Influences of the strain rate sensitivity and the interfacial debonding damage on nanocomposites are discussed, and predictions from the proposed approach are compared with experimental measurements to elucidate the potential of the formulation.
In this paper, a self-sensing carbon nanotube (CNT)/cement composite is investigated for traffic monitoring. The cement composite is filled with multi-walled carbon nanotubes whose piezoresistive properties enable the detection of mechanical stresses induced by traffic flow. The sensing capability of the self-sensing CNT/cement composite is explored in laboratory tests and road tests. Experimental results show that the fabricated self-sensing CNT/cement composite presents sensitive and stable responses to repeated compressive loadings and impulsive loadings, and has remarkable responses to vehicular loadings. These findings indicate that the self-sensing CNT/cement composite has great potential for traffic monitoring use, such as in traffic flow detection, weigh-in-motion measurement and vehicle speed detection.
Electrophoresis can be an effective approach for depositing carbon nanotubes (CNTs) on the surface of carbon fiber (CF). Nevertheless, it has been rarely reported on polyphenylene sulfide (PPS) composites filled with CFs surface-modified by CNTs based on electrophoresis. In this study, we investigated the electrophoresis process conditions that can completely coat CF with multi-walled CNTs (MWCNTs) using self-manufactured electrophoresis equipment, and the enhancement of interfacial, electrical and flexural properties of PPS composites by introducing CFs coated with MWCNTs based on electrophoresis. In particular, interfacial shear strength (IFSS) of the PPS composites was measured by microbond tests and improved by about 41.7% due to the MWCNTs introduced on the surface of CFs. These enhancements were theoretically explained by an interface-modified CF-based micromechanical model. Introducing MWCNTs on the CF surface based on electrophoresis was demonstrated to be an effective method for improving the interfacial, electrical and flexural properties of PPS composites.
The importance of the thermal conductivity of engineering plastics reinforced with nanofillers is increasing in various industries, and the need for a model with which to make reliable predictions continues. We propose a micromechanics-based multiscale model that considers multi-shaped nanofillers to predict the thermal conductivity of composites. The distribution of each phase is assumed to be probabilistically distributed, and the Kapitza resistance at the interface between the filler and matrix was calculated by means of a molecular dynamics simulation. A polybutylene terephthalate (PBT) composite system embedded with multi-walled carbon nanotubes (MWCNTs) was used in a specific simulation. Composites containing MWCNTs of different lengths were also fabricated to obtain appropriate experimental results for the verification of the proposed model. Fourier-transform infrared (FT-IR) spectroscopy, Raman spectroscopy, and field-emission scanning microscopy (FE-SEM) were carried out to confirm that the selected materials could suitably be compared. Finally, the proposed model was applied to the finite element method to examine the heat flux of the composites according to the constitutive properties, and their results were compared to the experimental results.
Cementitious composites incorporating CNT and carbon fiber were produced in the present study, and the effect of the incorporation of carbon fiber on the electrical characteristics of the composites was investigated. Polycarboxylic acid based superplasticizer and silica fume were used to ensure the dispersion of the CNT and carbon fiber. Independent variables were the water to cement ratio, the amount of carbon fiber added to the composites. The test results showed that the cementitious composites incorporating CNT and carbon fiber had more stable electrical resistivity compared to those without carbon fiber. A microstructural analysis was conducted and the mechanism of the improved electrical characteristics of the cementitious composites incorporating CNT and carbon fiber was discussed.
Herein, we report a theoretical study of polymeric nanocomposites to provide physical insight into complex material systems in elastic regions. A self-consistent scheme is adopted to predict piezoresistive characteristics, and the effects of the interface and of tunneling on the effective piezoresistive and electrical properties of the nanocomposites are simulated. The overall piezoresistive sensitivity is predicted to be reduced when the lower interfacial resistivity of multi-walled carbon nanotubes (MWCNTs) and the higher effective stiffness of nanocomposites are considered. In addition, thin film nanocomposites with various MWCNT weight percentages are manufactured and their electrical performance capabilities are measured to verify the predictive capability of the present simulation. From experimental tests, the nanocomposites show clear piezoresistive behaviors, exhibiting a percolation threshold at less than 0.5 wt% of the MWCNTs. Three sets of comparisons between the experimental data and the present predictions are conducted within an elastic range, and the resulting good correlations between them demonstrate the predictive capability of the present model.
In the present study, cementitious composite incorporating a carbon nanotube (CNT) with highly improved electrical conductivity comparable to that of a semiconductor is developed and investigated. The CNT and pore characteristics within a cementitious matrix are considered as the most influential factors which determine the overall performance of the material, and these factors are artificially controlled by incorporating silica fume and a superplasticizer. Additionally, a micromechanics-based model is proposed to predict the electrical performance and percolation threshold of the composites. A parametric study based on the developed model is conducted, and the influences of the constituent properties on the overall electrical characteristics of composites are discussed. The effectiveness of the proposed hypothesis is demonstrated by comparing it to the experimental results in the present study and from the previous work.
The nanoscopic characteristics of the multi-walled carbon nanotubes (MWCNTs) used in composites are crucial for attempting to understand and design nanocomposites of a novel class. We investigate the correlations between the nanofiller properties and effective electrical properties of MWCNT-embedded polycarbonate composites by theoretical and experimental approaches. A probabilistic computational model is proposed to predict the influence of MWCNT morphology on the electrical behaviors of MWCNTs-embedded polymer composites. A parameter optimization method in accordance with a genetic algorithm is then applied to the model, resulting that the ideal sets of model constant for the simulation are computationally estimated. For the experimental validation purpose, a comparison between the present theoretical and experimental results is made to assess the capability of the proposed methods. In overall, good agreement between the predictions and experimental results can be observed and the electrical performance of the composites can be improved as the MWCNT length increases.
Many experiments have shown that electrical conductivity and dielectric permittivity of graphene-polymer nanocomposites are strongly dependent on the loading frequency, but at present no theory seems to be able to address the continuous influence of frequency. In this work we present a new effective-medium theory that is derived from the underlying physical processes including the effects of filler loading, aspect ratio, percolation threshold, interfacial tunneling, Maxwell-Wagner-Sillars polarization, and the extra frequency-affected electron hopping and Debye dielectric relaxation, to determine the loading-frequency dependence of these two fundamental properties. The theory is formulated in the context of complex conductivity under harmonic loading. We highlight this new theory with an application to PVDF/xGnP nanocomposites, and demonstrate that the calculated conductivity and permittivity are in close agreement with the reported experimental data over the frequency range from 10² to 10⁷ Hz. We also show that the electrical conductivity tends to increase with frequency but the dielectric permittivity tends to decrease. We find that, at low frequency, the properties are dominated by filler loading but at high frequency the loading frequency is the dominant factor. The theory also reveals that the percolation phenomenon is clearly defined at low frequency but becomes blurred at high frequency.
A functional cementitious composite for smart structures has attracted much attention due to their potential possibilities of application. In this paper, the accelerated curing and thermal cracking reduction with carbon nanotube (CNT)/cement composites are studied experimentally and theoretically. The heating element was fabricated by incorporation CNT into cement, and the cementitious composite block was placed in the middle of mortar samples. In order to generate and evaluate the heating performance, copper wires connected to the composite block were extended to a DC power supply. The variations of material characteristics including curing, thermal, electrical and mechanical properties of both the composite block and the sample were investigated. The experimental test results showed that the proposed curing was capable of improving the compressive strength by 40% at 24 hrs. In addition, based on the experimentally obtained material constants, a series of thermal analysis of mitigation level of thermal crack in larger scale were carried out. The electrically conductive CNT/cement composite block was found to be applicable to the cement mortar curing and reduction of thermal cracking of massive concretes structures.
The thermal deformation behavior of hardened cement paste and coarse aggregate were conducted by the Workhorse-1 dilatometer made in Anter Corporation (USA). The results showed that thermal expansion coefficient of hardened cement paste was over two times than that of coarse aggregate with great diversity. After more thermal cycles, the micro-cracking induced by the thermal stress appeared and propagated along the interfacial zone between hardened cement paste and aggregate. When to experience 120 thermal cycles, the reduction percentage of compressive strength for cement-based was over-30%, which aggravated the structure damage under load. All of above results approved that the existence of thermal deformation difference between components influence the thermal stability and mechanical performance under the thermal fatigue.
Using electrically conductive concrete for deicing is an emerging material technology. Due to its electrical resistance, a thin layer of conductive concrete can generate enough heat to prevent ice formation on concrete pavement when energized by a power source. Under research sponsored by the Nebraska Department of Roads, a concrete mixture containing steel fibers and steel shavings was developed specifically for concrete bridge deck deicing. The mixture has a compressive strength of 31 MPa (4500 psi) and provides average thermal power density of 590 W/m 2 (55 W/ft 2) with a heating rate of 0.14°C/min (0.25°F/min) in a winter environment. The average energy cost was about 0.074/ft 2) per snowstorm. During development of the conductive concrete, several drawbacks about using steel shavings in the mixture were noticed. As a follow-up effort, carbon and graphite products were used to replace steel shavings in the conductive concrete design. The electrical conductivity and the associated heating rate were improved with the carbon products. A conductive concrete deck has been implemented for deicing on a highway bridge at Roca, located approximately 24 km (15 mi) south of Lincoln, Nebr. The Roca Spur Bridge has a 36 m (117 ft) long and 8.5 m (28 ft) wide conductive concrete inlay, which has been instrumented with temperature and current sensors for heating performance monitoring during winter storms. Experimental data and operating costs are presented in this paper.
Cementitious composites incorporated with CNT were developed in the present study as a self-heating element, and heating and heat-dependent mechanical characteristics of the composites were investigated. Silica fume and poly-carboxylic acid based superplasticizer were used as dispersion agents for the CNT particles to ensure a certain electrical resistivity value that is required to induce heat generation capability in the composites. The amount of CNT added to the composites and the input voltages were varied from 0.1 wt% to 2.0. wt% and from 3 V to 20 V, respectively. A cyclic self-heating test was conducted to investigate the stability in the heat generation capability and electrical resistivity of the composites. Moreover, compressive strength and TG/DTA tests were conducted to investigate the heat-dependent mechanical properties and the amount of hydration products of the cyclically heated composites. The test results showed that the heat generation capability of the CNT-embedded cementitious composites was improved with an increase in the amount of CNT and the composites having CNT less than 0.6. wt% is appropriate as a heating element.
In previous studies by the authors, it was found that a lower water-binder ratio led to enhanced dispersion of carbon nanotube (CNT) in the cement matrix. The objective of this study was to investigate the piezoresistive sensitivity and stability of CNT/cement mortar composites with low water-binder ratio. The effect of absorbed water on the piezoresistivity of the composites was also investigated, since it strongly affects the electrical properties of the composites. The changes in the electrical resistance of composite specimens induced by external cyclic loading were measured to investigate their piezoresistive sensitivity and stability. The experimental results indicates that the stability of piezoresistivity under cyclic loading and their time-based sensitivity can be improved by decreasing the water-binder ratio of the cement composites. Moreover, the variation of piezoresistivity induced by the moisture content can be decreased by low water-binder ratio.
In this work, carbon nanotubes (CNTs) were added into a carbon fiber cement system to produce carbon nanotube-carbon fiber/ cement nanocomposites in the form of pastes. The compressive strength, morphology, pressure-sensitive properties, and temperature-sensitive properties were tested. The results show strengthening of the mechanical properties and pressure sensitivity as the CNT content increases from 0.2 % to 1.0 % by mass of cement. The addition of CNTs into cement paste also leads to enhancement of the temperature sensitivity. Additionally, microscopic observation shows that CNTs act as fillers, which results in a dense microstructure of cement paste. Test results indicate that the carbon nanotube-carbon fiber/cement composites show potential either as stress sensors for vehicle detection, weigh-in-motion measurement, and vehicle speed detection or as thermistors for temperature monitoring in concrete structures.
The use of electrically conductive concrete for pavement deicing is an emerging material technology. Three kinds of electrically conductive concrete composites, namely, steel fiber, carbon fiber, and steel fiber-graphite, are measured, and the factors that affect conductivity are analyzed. A three-phase composite conductive concrete containing steel fiber, carbon fiber, and graphite is developed for pavement deicing. The conductive property test and the compressive strength of this concrete in the laboratory show that the dispersion uniformity of the carbon fiber, as well as the concrete voids, significantly affects conductivity. The composition ratio, preparation techniques and electrode layout mode of the three-phase composite conductive concrete are introduced and studied. A specimen consisting of a three-phase composite conductive concrete with an electrical resistivity of 322 Ω cm is used in the heating experiment and is proven to render satisfactory heat effects that meet the requirements of pavement deicing.
Electrically conductive cementitious composites carrying carbon fibers and carbon nanotubes were developed and their ability to sense an applied compressive load through a measureable change in resistivity was investigated. Two types of cement-based sensors, one with carbon fibers alone and the other carrying a hybrid of both fibers and nanotubes, were considered. Direct comparisons were also made with traditional strain gauges mounted on the sensor specimens.Sensing experiments indicate that under cyclic loading, the changes in resistivity mimic both the changes in the applied load and the measured material strain with high fidelity for both sensor types. The response, however, is nonlinear and rate dependent. At an arbitrary loading rate, the hybrid sensor, containing a combination carbon fibers and nanotubes, produced the best results with better repeatability.
A novel self-deicing road system with utilization of solar energy was proposed in this paper, this system is consisted of a carbon nano-fiber polymer (CNFP) thermal source, an AlN-ceramic insulated encapsulation layer, a multiwall carbon nanotube (MWCNT)/cement-based thermal conduction layer and a thermally insulated substrate. The electric and thermo-electric properties of a CNFP, which is composed of individual carbon nano-fibers (10–200 nm), were tested. The property of high thermo-electric efficiency was verified, and the resistivity of the CNFP exhibited piecewise linear temperature-dependent characteristics within a certain temperature range (0–280 °C). The MWCNT/cement-based composite, which was filled with 3% by weight MWCNT, was proposed as the thermal conduction layer because its thermal conduction properties are superior to those of cement with other fillers and to those of common cement-based composites. To ensure the efficient operation of the CNFP, an AlN-ceramic wafer (0.5 mm) was employed as the electro-insulated layer because of its favorable insulating and thermo-conductive properties. The constructed system was applied in deicing and field snow-melting studies, in which the effects of ambient temperature, heat flux density and ice thickness on the deicing and snow-melting performance of the self-deicing system were investigated. The efficiency, repeatability, cost and feasibility of the self-deicing road system in both deicing and snow-melting applications were analyzed. Indices for evaluating the deicing or snow-melting performance of the self-deicing road system were proposed and the optimal values for each parameter are presented.
It is particularly difficult to prepare a foam CPC material because its porous structure makes it hard to form a conductive network. We utilized acetone‐assisted dispersion to disperse CNTs into PU foam and successfully prepared a lightweight conductive CNT/assembled PU foam composite. The NTC effect, which exclusively exists in the melt state CPC materials, has unexpectedly been observed in the solid‐state lightweight conductive CNT/sPU composite. Higher gas fraction and lower matrix modulus could result in stronger NTC effect. The mechanism that thermal expansion of gas wrapped in the cellular structure induces more perfect conductive paths has been proposed to satisfactorily elucidate the NTC effect and its gas fraction and matrix modulus dependence.
magnified image
Knowledge of the coefficient of thermal expansion (CTE) is of paramount importance for the determination of the cracking risk of concrete structures at early ages. This paper presents a novel technique which is suitable to measure the CTE of hardening materials with high accuracy starting from casting time.The technique consists of casting a small amount of cement paste or mortar into flexible membranes. The specimens are immersed in an oil bath, whose temperature is rapidly changed and then kept constant in repeating cycles. By suspending the sample from a high-precision balance and reading the change of mass after each temperature step, the CTE is calculated with high accuracy from the measured temperature and strain.Results on cement pastes and mortars (water/cement 0.3) showed a good repeatability. In particular, a sudden decrease in the CTE at setting time, followed by a gradual increase as the cement paste self-desiccates, was measured.
The structural and chemical stability of multiwall carbon nanotubes (MWNTs) in ceramic nanocomposites prepared by spark plasma sintering was studied. High resolution electron microscopy, X-ray diffraction and Raman spectroscopy were used to evaluate any degradation of the MWNTs. They were found to be well preserved in alumina after sintering up to 1900 degrees C/100 MPa/3 min. In boron carbide, structural degradation of MWNTs started from similar to 1600 degrees C when sintered for 20 min. Multiwall carbon nanotubes maintained their high aspect ratio and fibrous nature even after being sintered in boron carbide at 2000 degrees C for 20 min. However, no Raman vibrations of MWNTs were observed for nanocomposites processed at temperatures >= 2000 degrees C, which indicates that they were severely degraded. Structural preservation of MWNTs in ceramic nanocomposites depends on the ceramic matrix, sintering temperature and dwell time. Multiwall carbon nanotubes were not preserved for matrices that require high sintering temperatures (>1600 degrees C) and longer processing times (>13 min).
Self-heating structural materials, being useful for deicing and space heating, are reviewed. They include cement–matrix and polymer–matrix composites that are rendered self-heating through enhancing their effectiveness for resistance heating. The enhancement is attained by the use of electrically conductive fibers (continuous or discontinuous) and interlayers. The interlaminar interface between continuous carbon fiber laminae provides a two-dimensional array of heating elements. Power up to 6.5 W, maximum temperature up to 134 °C and time to reach half of the maximum temperature rise down to 14 s have been attained.
Because of their high mechanical strength, carbon nanotubes (CNTs) are being considered as nanoscale fibres to enhance the
performance of polymer composite materials. Novel CNT-based composites have been fabricated using different methods, expecting
that the resulting composites would possess enhanced or completely new set of physical properties due to the addition of CNTs.
However, the physics of interactions between CNT and its surrounding matrix material in such nano-composites has yet to be
elucidated and methods for determining the parameters controlling interfacial characteristics such as interfacial shear stress,
is still challenging. An improvement of the physical properties of polymer nanocomposites, based on carbon nanotubes (CNTs),
is addicted to a good dispersion and strong interactions between the matrix and the filler.
A variety of outstanding experimental results on the elucidation of the elastic properties of carbon nanotubes are fast appearing. These are based mainly on the techniques of high-resolution transmission electron microscopy (HRTEM) and atomic force microscopy (AFM) to determine the Young's moduli of single-wall nanotube bundles and multi-walled nanotubes, prepared by a number of methods. These results are confirming the theoretical predictions that carbon nanotubes have high strength plus extraordinary flexibility and resilience. As well as summarising the most notable achievements of theory and experiment in the last few years, this paper explains the properties of nanotubes in the wider context of materials science and highlights the contribution of our research group in this rapidly expanding field. A deeper understanding of the relationship between the structural order of the nanotubes and their mechanical properties will be necessary for the development of carbon-nanotube-based composites. Our research to date illustrates a qualitative relationship between the Young's modulus of a nanotube and the amount of disorder in the atomic structure of the walls. Other exciting results indicate that composites will benefit from the exceptional mechanical properties of carbon nanotubes, but that the major outstanding problem of load transfer efficiency must be overcome before suitable engineering materials can be produced.
In this paper, the electrical conductivity and mechanical properties such as elastic modulus of multiwalled carbon nanotubes
(MWCNTs) reinforced polypropylene (PP) nanocomposites were investigated both experimentally and theoretically. MWCNT-PP nanocomposites
samples were produced using injection mold at different injection velocities. The range of the CNT fillers is from 0 up to
12wt%. The influence of the injection velocity and the volume fraction of CNTs on both electrical conductivity and mechanical
properties of the nanocomposites were studied. The injection speed showed some effect on the electrical conductivity, but
no significant influence on the mechanical properties such as elastic modulus and stress-strain relations of the composites
under tensile loading. Parallel to the experimental investigation, for electrical conductivity, a percolation theory was applied
to study the electrical conductivity of the nanocomposite system in terms of content of nanotubes. Both Kirkpatrick (Rev Mod
Phys 45:574–588, 1973) and McLachlan etal. (J Polym Sci B 43:3273–3287, 2005) models were used to determine the transition from low conductivity to high conductivity in which designates as percolation
threshold. It was found that the percolation threshold of CNT/PP composites is close to 3.8wt%. For mechanical properties
of the system, several micromechanical models were applied to elucidate the elastic properties of the nanocomposites. The
results indicate that the interphase between the CNT and the polymers plays an important role in determining the elastic modulus
of the system.
Multiwalled carbon nanotube (MWNT)-filled high-density polyethylene (HDPE) composites were prepared by a solution-precipitation process, and the temperature dependence of electrical conductivity of the MWNT/HDPE composites was studied. An obvious positive temperature coefficient (PTC) effect was found in the MWNT/HDPE composites with a relatively low MWNT concentration. Compared with that of carbon black (CB)/HDPE composite, the negative temperature coefficient (NTC) effect of the MWNT/HDPE composite at temperature above the melting temperature of HDPE was much less obvious and could be further eliminated after 80 kGy γ -ray irradiation. The mechanism of the PTC and NTC effects in MWNT/HDPE composites was discussed.
The porosity and microstructure of a Portland cement–multi-walled carbon nanotube composite were investigated. Multi-walled carbon nanotubes (CNTs), up to 1 wt.% of cement, synthesized by infusion chemical vapor deposition, and Portland cement type I (PC) were used to produce pastes with a water to cement ratio of 0.5. Mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) were used to characterize Portland cement–CNTs systems. MIP analysis of the results indicates that total porosity of the mixes with CNTs was found to decrease with increasing CNTs content. Moreover, an important effect of additional CNTs was a reduction in the number of mesopores, while SEM technique showed dispersion of CNTs between the hydration phases of Portland cement pastes.
In this research, an electrically conductive porous asphalt concrete, used for induction heating, was prepared by adding electrically conductive filler (steel fibers and steel wool) to the mixture. The main purpose of this paper is to examine the electrical conductivity and the indirect tensile strength of this conductive porous asphalt concrete and prove that it can be heated via induction heating. It was found that, to make porous asphalt concrete electrically conductive, long steel wool with small diameter is better than short steel fibers with bigger diameter. However, steel fibers with short length and big diameter have better strength reinforcement capability than steel wool with long length and small diameter. It was also proved that conductive porous asphalt concrete containing steel wool can be easily heated via induction heating. Finally, 10% (by volume of bitumen) of steel wool type 000 was proposed as an optimal content in porous asphalt concrete to obtain an optimal conductivity, a good induction heating rate and an acceptable indirect tensile strength. It is expected that the autogenous healing capacity of asphalt concrete will be enhanced with the increase of temperature during induction heating.
Cement matrix composites have been prepared by adding 0.5% in weight of multi wall carbon nanotubes (MWCNTs) to plain cement paste. In order to study how the chemical–physical properties of the nanotubes can affect the mechanical behavior of the composite, we compared the specimen obtained by mixing the same cement paste with three different kinds of MWCNTs. In particular, as-grown, annealed and carboxyl functionalized MWCNTs have been used. In fact, while high temperature annealing treatments remove lattice defects from the walls of CNTs, hence improving their mechanical strength, acid oxidative treatments increase chemical reactivity of pristine material, consequently chemical bonds between the reinforcement and the cement matrix are supposed to enhance the mechanical strength.Flexural and compressive tests showed a worsening in mechanical properties with functionalized MWCNTs, while a significant improvement is obtained with both as-grown and annealed MWCNTs.The phase composition of the composites was characterized by means of thermo gravimetric analysis coupled with mass spectroscopy, while the mineralogy and microstructure were analyzed by means of an X-ray diffractometer and scanning electron microscope. The results are interpreted and discussed taking into account the chemical and physical properties of the MWCNTs by means of EDX, TGA, SEM and Raman analysis.
Resistance heating using electrically conductive cements
- Wang
Development of graphite electrically conductive concrete and application in grounding engineering
- Qin
Conductive concrete overlay for bridge deck deicing
- Ye