Interface Debonding Performance of Precast Segmental Nano-Materials Based Concrete (PSNBC) Beams

Materials Express

Interface debonding performance of precast segmental nano-materials based concrete (PSNBC) beams

Xinfeng Yin, Ming Zhang, Lei Wang, and Yang Liu∗ School of Civil Engineering, Changsha University of Science & Technology, Changsha 410114, Hunan, China

ABSTRACT The precast segmental concrete (PSC) structures and the nano-materials based concrete beams are widely

applied to civil engineering. On the other hand, it is well known that nano-materials have physical effects and Article can signiﬁcantly improve the concrete properties of cement-based materials. Therefore, the interface debonding performance of precast segmentalIP: 192.168.39.211 nano-materials On: based Sat, concrete25 Sep 2021 (PSNBC) 09:20:03 beams is investigated in this study. Two concrete specimens with nano-materialsCopyright: American and one concreteScientific specimen Publishers without nano-materials were prepared Delivered by Ingenta and bonded into PSC beams with a high strength epoxy adhesive. The smart aggregates (SAs) made of piezoceramic Lead Zirconate Titanate (PZT) and concrete are used as the intelligent transducer of monitoring test specimen. The PSC beam was loaded periodically by screw jack to simulate the random debonding damage of different degrees. The experimental results show that the interface debonding performance of the concrete specimens with nano-materials is signiﬁcantly enhanced and better than that of concrete specimens without nano-materials. Keywords: Precast Segmental Concrete (PSC), Nano-Materials, Smart Aggregates (SAs), Precast Segmental Nano-Materials Based Concrete (PSNBC), Interfacial Debonding Performance.

1. INTRODUCTION fields [4–6]. It is well known that nano-materials can pro- Precast segmental concrete (PSC) structures, which can vide significant enhancement in performance of concrete form long concrete beams through adhesive bonding, have using the concrete-based materials given their physical attracted considerable attention due to their convenient effect [7–8]. Therefore, the materials of nano-materials transportation [1–2], short construction period, easy to based concrete are introduced in the PSC structures, and coordinate with the surrounding environment, convenient thus, the interface debonding performance of precast seg- quality control, and saving construction and maintenance mental nano-materials based concrete (PSNBC) beams is costs [3]. Therefore, the prefabricated segment assembly investigated in this study. technology is the main development direction of future Prefabricated segment assembly technology is a con- construction. However, the interface filling material and struction method which has developed rapidly in recent concrete quality of the segment concrete beam play a decades. The principle of prefabricated segment assembly very important role in the bearing capacity and durabil- technology is to divide the beam into several segments, ity of the PSC. On the other hand, the superior prop- which are transported to the original fixed position after erties of nano-materials are widely applied in various prefabrication, and then installed in place, so that each segment becomes a whole and reaches the design strength. Prefabricated segment assembly technology represents ∗Author to whom correspondence should be addressed. standardized, rapid and factory manufacturing technol-

Mater. Express, Vol. 10, No. 8, 2020 1317 Materials Express Interface debonding performance of PSNBC beams Yin et al.

ogy, and is one of the development directions of modern the single or combined action of moving vehicles [9–10], prestressed concrete bridge construction. It has the follow- corrosion [11], or impact loads [12]. As the application ing technical characteristics: scope of concrete materials in engineering continues to (1) Economy expand, people’s requirements on the performance of con- PSC has the characteristics of uniform size, production crete materials are also gradually improving. Due to the standardization, and the template can be reused, which excellent performance of nano-materials, the combination has obvious economic advantages. The PSC construction of nano-materials and concrete materials can effectively method does not use temporary supports. promote the development and improvement of concrete (2) Quality and Durability applications. Nano-materials have the characteristics of PSC is usually produced in the prefabrication plant small size effect, quantum effect, surface effect and inter- with high degree of automation, which greatly reduces the face effect [4, 13], which can significantly improve the influence of various adverse factors on the segmental con- properties of cement-based materials. In cement-based crete beam, effectively ensures the quality of the segmen- materials, nano-materials mainly play the roles of fill- tal concrete beam, and reduces the construction error and ing, nucleation, optimization of interface transition struc- the probability of accidents. ture and chemical reaction with raw materials. At present, (3) Safety and Applicability advantages nano-materials doped into cement concrete matrix and

The factory prefabrication of segmental concrete beam widely used mainly include nano-SiO2 [14–15], nano- can provide sufﬁcient construction working space. The Al2O3 [16], nano-TiO2 [17], nano-CuO, nano-CaCO3 [18], automation degree of bridge erection machine operation is nano-Fe2O3 [19], and nanotubes [20]. At the nanoscale high, less operation personnel are needed, and the qual- of nano-CaCO3 due to its inertia, the basic will not react ity of operation personnel is high. Therefore, the safety of with the concrete system, but can greatly improve con-

section prefabrication construction method can be better crete mixed with nano-CaCO3 such as cohesiveness, water guaranteed. For urban areas, such as rivers, canyons and retention, workability and so on [21]. In addition, nano-

other harsh terrain areas or important environmental areas, CaCO3 is widely available and the price is low [22–24]. the segmental prefabrication method can minimize the Therefore, nano-CaCO3 has the potential to be nano- interference of construction operations on the surround- materials which have a large number of applications in the ing environment and environmentallyIP: 192.168.39.211 sensitive areas, On: and Sat, 25concrete Sep 2021 construction, 09:20:03 and nano-concrete based on nano- Copyright: American Scientific Publishers eliminate the need for traffic dredging on traffic arteries, Delivered by IngentaCaCO3 has also been effectively promoted. Nano-TiO2 is thus reducing the impact on existing traffic. an n-type semiconductor material with good stability, high (4) Construction period advantages catalytic performance and no harm to human body [25].

Article The prefabrication of segmental concrete beams does When it is applied to concrete, it can absorb NOx from not take up the construction period, so the overall con- automobile exhaust, purify air, sterilize and deodorize, and struction period of the project can be greatly reduced. clean the surface. Therefore, the interface damage of PSC (5) The shrinkage and creep of concrete is relatively small structures can provide significant enhancement by using Due to the particularity of technology, the segment the cement-based material [26]. concrete beam has obtained sufficient curing time during It is urgent to find an effective method to identify the assembly. The strength and elastic modulus of the seg- interface debonding damage of PSNBC. Traditional detec- mental beam have reached the design requirements. The tion methods have some defects that do not meet the needs deformation caused by creep and shrinkage are relatively of current development. In addition, the damage of the small, so the concrete beam linetype can be effectively structure cannot be judged directly by the collected data. controlled. Therefore, the prospect of real-time and in-service mon- Joint is a special structure of PSC, and also the weak itoring is limited. The emergence of intelligent materials link of structure stress. The joint plays the role of force provides an effective way for engineering structural health transfer and displacement limitation in the structure. The monitoring technology [27–28]. Based on the piezoelectric mechanical properties and working conditions of the PSC effect of piezoceramics, it can be made into a piezoceramic are closely related to the strength of the joint material and transducer. Because of the positive and negative piezoelec- the reliability of the joint material connection. The con- tric effect, these piezoelectric ceramic sensors can be used crete and regular reinforcement at the joints of the PSC as bidirectional sensing elements, that is to say, they can be are discontinuous, and the bonding layer between epoxy used not only as actuators for exciting signal transmission resin and concrete at the joints is a weak point, which but also as sensors for signal reception. The application of affects its bonding performance. As there is a layer of intelligent piezoceramic materials in structural health mon- cement mortar matrix in the concrete at the interface, it itoring provides a new idea for the development of a new is not as dense as the integrally poured concrete, and it sensor with sensitive sensing, safe and reliable and wide is easy to become the access of external harmful sub- measurement range. However, due to the complexity of stances into the concrete. During complex environments civil engineering structure, construction difficulties, envi- or extreme events, brittle failure can easily occur due to ronmental impact and other factors, the wide application of

1318 Mater. Express, Vol. 10, 2020 Interface debonding performance of PSNBC beams Materials Express Yin et al. piezoceramic transducers is hindered. This is because the material of piezoceramic is brittle and it is easy to be dam- aged if directly embedded into the main structure. In addition, the service life of civil engineering structures is long, which generally have decades or even hundreds of years. Moreover, piezoceramic transducers are susceptible to the influence of ambient temperature. Therefore, in order to satisfy the long-term monitoring of the structure, the piezoceramic transducer needs to have good durability. To solve this difficulty, Song et al. proposed the concept of smart aggregates (SAs), which combines concrete with piezoceramic Lead Zirconate Titanate (PZT) [29]. The presence of higher porosity in the interior of the concrete structure consumes the energy of propagation. The advantages based on the filling and nucleation effects of nano-materials and Fig. 1. Nano-CaCO material. the characteristics of piezoceramic materials are combined 3 to reduce energy dissipation and increase sensitivity. In this paper, the PZT sensor systems are used to detect the Nano-CaCO3 can improve bending strength and flexu- interface damage of debonding performance for PSNBC ral modulus of the materials. Figure 1 shows the nano- beams. CaCO3 material. Nano-TiO2 has the ability to improve At present, nanomaterials and PSC structures are rel- the hardness, density and anti-aging properties of materi- atively new research findings in the field of civil engi- als. Figure 2 shows the nano-TiO2 material. Commercial neering. It can even be determined that the PSC structures grade nano-TiO2 and nano-CaCO3 materials are purchased and nanomaterials will be widely used in future practical and used with the size range of 50–100 nm. Nanoparti- projects. However, there are few studies on both at the cles have a tendency to agglomerate in concrete with high Article same time in all the current studies. This paper uses piezo- concentration of nano-CaCO3 or nano-TiO2, resulting in ceramics as a new material to effectivelyIP: 192.168.39.211 evaluate the On: per- Sat, 25higher Sep particle 2021 09:20:03 sizes [30–32]. The tendency of nanoparti- formance of PSNBC structures. By comparingCopyright: the American wavelet Scientific Publishers Delivered by Ingentacles agglomeration reduces the ability to act as effective packet energy of different materials, it is found that the filler in concrete [33–35]. Therefore, the concentration of nucleation and filling effect of nano-materials reduce the nanomaterials should not be taken too high. In this exper- porosity of concrete, effectively improve the loading char- iment, nano-CaCO3 and nano-TiO2 with 2% concentration acteristics, and the interface debonding performance of were used to exhibit nucleation and filling effects and more nano-CaCO3 beam is better than that of Nano-TiO2 beam. homogeneous structure. In this paper, an active sensing approach based on stress wave propagation using embedded SAs is developed 2.2. Smart Aggregates to monitor the interface debonding performance of the In the practical application, the bonding mode and embed- PSNBC beams. The tests were conducted on three types of ded mode are the two common ways to combine the piezo- concrete specimens with and without nano-materials des- ceramic with the main structure. In this paper, embedded ignated as concrete with 2 wt% nano-CaCO and concrete 3 mode is mainly used for monitoring test. Appropriate pro- with 2 wt% nano-TiO . SAs transducers embedded in spa- 2 tective measures must be taken in the process of applica- tial positions of three different cross-sections in concrete tion to ensure the monitoring effect and monitoring life specimens are used as actuators and sensors, respectively. The debonding-induced cracks are monitored throughout the applied load process. The cracks attenuated the prop- agating stress wave energy which can be reflected by the received signal in the time domain and wavelet packet energy. The wavelet packet-based damage index quanti- fied the change of the signal energy. The experimental research validates the feasibility of monitoring the debonding cracks in PSNBC beam using SAs transducer based on active sensing approach.

2. EXPERIMENTAL METHODS 2.1. Nano-Materials In order to improve the performance of concrete, nano- materials with toughening and reinforcing are selected. Fig. 2. Nano-TiO2 material.

Mater. Express, Vol. 10, 2020 1319 Materials Express Interface debonding performance of PSNBC beams Yin et al.

Fig. 5. PSNBC beam 3D model.

Fig. 3. Photo of a SA and PZT. of structures [40]. Therefore, it is of great significance to develop a practical, economical, effective and convenient interface damage detection method for PSNBC beams. In due to the brittle texture of the piezoelectric material. To this paper, a piezoelectric stress wave based method for solve this difficulty, Song et al. [39] of the University of monitoring the interface debonding damage of PSNBC Houston in the United States creatively proposed the con- beams under vertical loading is proposed. In this paper, cept of smart aggregate (SA). SA is to encapsulate PZT three sets of reinforced concrete beam specimens were patch in pre-made cement mortar or small test blocks of made, one of which did not contain nano-materials, one fine stone concrete, and then embed them into the structure containing nano-CaCO3 and one containing nano-TiO2. after curing. In this way, the cement mortar plays a pro- The vertical loading test was carried out by two-point load- tective role on PZT patches, and the test block can be well ing. SAs were embedded in the fixed position of PSNBC combined with the concrete structure, which not only has beams, and used as actuators and sensors respectively the function of smart, but also hasIP: the192.168.39.211 role of aggregate. On: As Sat, 25to Sep monitor 2021 the 09:20:03 development of beam’s cracks and inter- a low-cost multi-functional device, SAsCopyright: can be used American for the Scientificface debonding Publishers damage. The actuator generates a stress comprehensive monitoring of concrete components,Delivered such by Ingentawave that propagates from inside one concrete member as concrete crack detection, concrete hydration character- through the interface to another concrete member and is istics monitoring and concrete-filled steel tube structure received by the sensor. The detection principle is shown Article debonding detection [37–39]. The smart aggregate with a in Figure 4. Before the load is applied, the PSNBC beam diameter of 25 mm and a height of 20 mm was made, as is in a healthy state and there is no crack, and a strong shown in Figure 3. The size of PZT patch is 15 mm × stress signal can be sensed by the sensor, as shown in 10 mm × 0.3 mm. Figure 4(a). The PSNBC beam begins to crack with the load increasing. The stress wave is reflected in the con- 2.3. Principle crete propagation process, and the received signal will be In order to solve the practical problems of health mon- attenuated, as shown in Figure 4(b). As the load continues itoring of PSC in the field of production and life, an to increase and exceeds the structural capacity, the struc- experimental study on interface damage of PSNBC beams ture fails significantly. The received signal is inversely pro- was carried out. The bonding interface of PSNBC beams portional to the severity of the structural damage, that is, is relatively weak and it is prone to interface debonding the former decreases while the latter increases, as shown damage, which directly affects the safety and durability in Figure 4(c).

(a) (b) (c)

Fig. 4. The diagrams to illustrate the active sensing approach.

1320 Mater. Express, Vol. 10, 2020 Interface debonding performance of PSNBC beams Materials Express Yin et al.

Nano-material concrete Epoxy resin adhesive Distributed reinforcement Table II. The mechanical properties of the steel. Ultimate Yield tensile Elastic 3 Diameter strength strength modulus Elongation 7.5 Type (mm) (MPa) (MPa) (GPa) (%) 1 12 Steel stirrups 2 3 Longitudinal 14 378 556 200 54 30 13 distribution SA1-1 SA2 SA1-2 reinforcements 12 1 Steel stirrups 8 325 490 200 23 7.5 3 10 10 10 10 10 10 Where N is the number of original signal sampling points, 60 and xk is the data point in each band signal of the ﬁnal layer after S decomposition and reconstruction. Then, the Fig. 6. Sketch of PSNBC beam plane (unit: cm). sum of the energy vector obtained by wavelet packet decomposition and reconstruction of S is

2.4. Wavelet Packet-Based Active Sensing Method 2N Wavelet packet analysis is developed based on the orthog- E = ek (4) onal wavelet theory. This method can not only decompose k=1 low-frequency signals, but also deeply decompose high- Damage index determined by the following formula- frequency signals. As the number of decomposition lay- tion is employed to evaluate the damage extent of the ers increases, the resolution is higher, and there is neither specimen [38]. redundancy nor omission in the decomposition. The signal N containing a large number of medium and high frequencies 2 E − E 2

i=1 k,i 1,i Article can be independently selected for localized time-domain DIk = N (5) 2 E 2 analysis, so it has a wide range of applications in structural i=1 1,i damage detection. IP: 192.168.39.211 On: Sat, 25 Sep 2021 09:20:03 Copyright: American Scientific EPublishers The principle of wavelet packet can decompose the col- where 1,i represents the signal energy in the structural Delivered by Ingenta E lected original signal S into different wavelet subspaces, health state, and k,i represents the signal energy of the k which can be decomposed into several frequency bands of structural damage state ( loading phase). equal width and contain corresponding signal frequency components. In this paper, the original signal is decom- 2.5. Specimen Fabrication posed by three layers of wavelet packet. In order to study the sensitivity of smart aggregate rein- The signal S is decomposed into the N -layer wavelet forced by nano-materials in concrete and identify the packet to obtain the 2N sub-signal, and the reconstructed interface damage degree of PSNBC beam by monitor- S is equal to the collection of the 2N sub-signals, namely: ing means, three specimens were designed. The PSNBC beam consists of a single-tooth concrete specimens, S = s + s + s +···+s 1 2 3 2N (1) nano-materials, epoxy resin structural adhesive, SAs, The energy vectors of sub-signals in each frequency longitudinal distribution reinforcements, and steel stirrups. band of the final signal are defined after the signal is The single tooth concrete specimen is made of steel form- decomposed by a wavelet packet, as shown in Eq. (2): work and poured with concrete according to the design drawing. The interface of each single tooth concrete spec- E = e e e e I 1, 2, 3, , 2N (2) imen is bonded by epoxy resin structural adhesive and where ei is the energy of each frequency band sub-signal cured to design strength to form PSNBC beam. The size in the final layer, and Ref. [36]: and reinforcement of the three beams are the same. The × n size of the PSNBC beam is maintained at 600 mm 2 × ei = xk (3) 300 mm 100 mm. The 3D model of the PSNBC beam k=1 drawn by CAD software is shown in Figure 5. The specific

Table I. Mixture proportions of the concrete specimens.

Specimen Cement Water Sand Stone Admixture Nano-CaCO3 Nano-TiO2 designation (kg/m3) (kg/m3) (kg/m3) (kg/m3) (kg/m3) (kg/m3) (kg/m3)

Beam1 509 144 736 1011 12.2 – – Beam2 509 144 736 1011 12.2 – 10.18 Beam3 509 144 736 1011 12.2 10.18 –

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Table III. Parameters of swept sine wave signal.

Number Start Stop Sampling of frequency frequency Amplitude Duration rate Conﬁguration steps (Hz) (kHz) (v) (s) (MHz)

Differential 5000 100 150 10 1 1

2.6. Instrumental Setup Figures 7 and 8 show in detail the experimental instru- ments of the damage monitoring system used in this paper. PSNBC beams embedded with SA are spliced with epoxy resin and installed on concrete piers through fixed bearing and sliding support. The design load value generated by Fig. 7. Experimental setup. the screw jack is applied to the PSNBC beam with epoxy resin interface. The loading value is measured by a load cell. The steel pad and load distribution beam with sup- dimensions of PSNBC beams and the location of the rein- port transmit the load value generated by the jack to the forcement and SAs are shown in Figure 6. Type 32.5 Port- PSNBC beam. The data acquisition system NI-USB 6366 land cement was used to pour the PSNBC beam. Each can be used for excitation and sampling simultaneously. In PSNBC beam with single tooth interface is equipped with order to ensure the accuracy of the data, the data acqui- longitudinal distribution reinforcements and steel stirrups. sition system NI-USB 6366 needs to be verified before The diameter of longitudinal distribution reinforcement is the test. The data acquisition module was written using NI 14 mm, the modulus of elasticity is 200 GPa, and the LABVIEW software to support the data acquisition system thickness of protective layer is 30 mm. The diameter of NI-USB 6366. In this paper, the designed swept sine wave steel stirrup is 8 mm, the elastic modulus of steel stirrup is signal is used for excitation. The parameters of the swept 200 GPa, and the thickness ofIP: protective 192.168.39.211 layer is 30 On: mm. Sat, 25sine Sep wave 2021 signal 09:20:03 are shown in Table III. NI LABVIEW The two types of SA1 and SA2 areCopyright: respectively American fixed at Scientificsoftware Publishers is written to achieve data acquisition, storage, and predetermined positions (the middle of each singleDelivered tooth by Ingentafiltering. The program supporting the acquisition system concrete specimen) with steel wires. Table II describes in (NI-USB 6366) is written by NI LabVIEW, and the param- detail the mechanical properties of the reinforcement used eters of the input signal are set by NI LabVIEW program. Article in the test. In this experimental process, three different Data analysis was performed using matlab software. In this types of concrete samples were made. Beam 1 is a com- experiment, the sampling rate of data acquisition system mon concrete specimen without adding any nanomateri- issetto1MHz.

als. Beam 2 is mixed with 2 wt% nano-TiO2 in concrete. 2.7. Experimental Procedures Beam 3 is mixed with 2 wt% nano-CaCO3 in concrete. The detailed mix design used in the casting of concrete Two-point loading is adopted in the test. The concentrated specimens is given in Table I. load F is transformed into two forces of equal size through

Fig. 8. Specimen loading system.

1322 Mater. Express, Vol. 10, 2020 Interface debonding performance of PSNBC beams Materials Express Yin et al.

PSNBC beam

SAs SAs ( actuators) (sensors)

Signal Signal generation acquisition NI-USB 6366 Fig. 10. Time-domain signal of SA1-1 sensor in the beam 1 without nano-materials. Signal analysis that the cracking load and ultimate load of concrete Computer beams with nano-materials are signiﬁcantly higher than analysis terminal that of concrete beam 1 without nano-materials. The cracking load and ultimate load of beam 3 with nano-CaCO3 are higher than those of the beam 2 with nano-TiO2. Fig. 9. Monitoring system for experiment. Compared with beam 1 without nano-materials, cracking

load and ultimate load of beam 2 with nano-TiO2 are the distribution beam, which are respectively acted on two increased by 50% and 16.7%, respectively. Compared with 1/3 points of the test beam. In the experiment, a screw beam 1 without nano-materials, cracking load and ultimate load of beam 3 with nano-CaCO are increased by jack was used to provide shear force to perform a dam- 3 Article age test on the concrete beam, and a load cell was used 100% and 33.3% respectively. The analysis shows that the to display the load for easy control.IP: 192.168.39.211 The physical map On: of Sat, 25load Sep characteristics 2021 09:20:03 of the specimens can be improved by the loading system is shown in FigureCopyright: 8. The test American loading Scientificadding Publishers nano-materials to the concrete. The nano-CaCO3 method is to place a distribution beam with supportDelivered on the by Ingentaimproves the load characteristics of specimens better than top surface of the PSNBC beam, and place a screw jack the nano-TiO2. on the distribution beam. The force transferred by adjust- ing the position of the screw jack is equal. The thickness 3.2. Time Domain Analysis of the epoxy resin interface is 2 mm. Figure 9 shows the In the specimen of this experiment, the middle sensor is damage monitoring system. Before the start of test loading, used as the receiver, and the sensors on both sides are that is, when the load level is 0 kN, the SA is excited by used as the actuator. In order to reduce the length of the the frequency sweep signal and the data under the healthy article, only the typical working state of the SA1-1 sensor state is collected. In the process of loading, the data acqui- is listed in the time domain signal analysis in this experi- sition system is used to collect the signal data of the test ment. The typical working state of the specimen is health beam under the excitation of sweep frequency signal for state, initial debonding and complete debonding failure. each load level (10 KN). The sensor with abnormal data is First, the specimen was in a healthy state before loading. remedied by using the mode of one sending one receiving. Then, the structure appears the initial debonding damage; Eventually, the specimen is loaded until it completely loses 3. EXPERIMENTAL AND NUMERICAL ANALYSIS 3.1. Load Characteristics of the Specimens The load characteristic values of the test specimens are shown in Table IV. It can be clearly found from Table IV

Table IV. Characteristic values for loads.

Specimen Cracking Increased Ultimate Increased designation load (kN) range (%) load (kN) range (%)

Beam120–60– Beam 2 30 50 70 16.7 Fig. 11. Time-domain signal of SA1-1 sensor in the beam 2 with Beam 3 40 100 80 33.3 nano-TiO2.

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Fig. 12. Time-domain signal of SA1-1 sensor in the beam 3 with Fig. 14. Wavelet packet energy of SA1-1 sensor in the beam 2 with

nano-CaCO3 . nano-TiO2.

work. The time-domain signals of SA1-1 sensor in the than that in a beam containing Nano-CaCO3. Therefore, beam 1 without nano-materials are shown in Figure 10. the porosity inside the concrete containing different nano- The time-domain signals of SA1-1 sensor in the beam 2 materials will also be different, and the porosity of beams with nano-TiO2 are shown in Figure 11. The time-domain containing Nano-CaCO3 is lower than that of beams con- signals of SA1-1 sensor in the beam 3 with nano-CaCO3 taining Nano-TiO2. The above analysis shows that the are shown in Figure 12. The time domain signal diagram nucleation and filling effect of nano-materials reduces the describes the response of a period of the sensor signal porosity of the concrete interior and increases the strength under the excitation of the frequency sweep signal. As the of the structure, so that the stress wave propagation is load increases, cracks and debonding damage of the spec- enhanced and the signal amplitude increases. At the same imen will occur. Crack and debonding damage can attenu- concentration, the nucleation and filling effect of nano- ate the stress wave signal produced by SA. Therefore, each CaCO3 is better than that of nano-TiO2. time domain signal diagram canIP: reflect 192.168.39.211 the initial damage On: Sat, 25 Sep 2021 09:20:03 and structural failure of the specimen. It can be seen from Copyright: American Scientific3.3. Wavelet Publishers Packet Energy Analysis Figures 10–12 that the amplitude of concrete beamsDelivered with by Ingenta In order to quantify the energy of the signal detected dur- nano-materials is significantly larger than that of beam 1 ing the applied load process, the signal energy is com- without nano-materials. The amplitude of the beam 3 with

Article puted by using the wavelet packet energy analysis. The nano-CaCO is higher than that of the beam 2 with nano- 3 results are shown in Figures 13–15. Figure 13 shows the TiO2. It is proved that the strength of the beam with nano- materials is greatly improved compared with the strength energy levels of SA1-1 sensor in the beam 1 without nano- of the beam 1 without nano-materials. The strength of materials during the applied load process. Figure 14 shows the energy levels of SA1-1 sensor in the beam 2 with nano- the beam 3 with nano-CaCO3 is higher than that of the TiO2 during the applied load process. Figure 15 shows the beam 2 with nano-TiO2. It can be found from Figures 11 and 12 that the amplitude of the signal received by SA in a energy levels of SA1-1 sensor in the beam 3 with nano- beam containing Nano-TiO is smaller than that of a beam CaCO3 during the applied load process. It is found from 2 Figures 13–15 that wavelet packet energy of the beam containing Nano-CaCO3 under the 0 kN loading stage. It is shown that the energy consumption during stress wave with nano-materials is greatly improved compared with the strength of the beam 1 without nano-materials. Before propagation in a beam containing Nano-TiO2 is greater

Fig. 13. Wavelet packet energy of SA1-1 sensor in the beam 1 without Fig. 15. Wavelet packet energy of SA1-1 sensor in the beam 3 with

nano-materials. nano-CaCO3 .

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Fig. 16. Damage index of SA1-1 sensor in the beam 1 without nano- Fig. 18. Damage index of SA1-1 sensor in the beam 3 with nano- materials. CaCO3. loading, the wavelet packet energy of the beam 2 with energy has the ability to detect the strength change and interface damage degree of PSNBC beam. nano-TiO2 and beam 3 with nano-CaCO3 was increased by 90.75% and 229.05% compared to the beam 1 without the nano-material. It is demonstrated that the strength of the 3.4. Wavelet Packet-Based Damage Index beam with nano-materials is higher than that of the beam Similarly, in order to quantitatively analyze the inter- 1 without nano-materials. The strength of the beam 3 with face damage degree of beams, the wavelet packet damage index is calculated, as shown in Figures 16–18. The dam- nano-CaCO3 is higher than that of the beam 2 with nano- age index of SA1-1 sensor in the beam 1 without nano- TiO2. The initial debonding cracks at the interfaces of beam 1, beam 2 and beam 3 occur at the stages of 20 kN, materials is shown in Figure 16. The damage index of Article 30 kN and 40 kN respectively, resulting in great reduction SA1-1 sensor in the beam 2 with nano-TiO2 is shown in in the stress wave signal energy received by the sensor. Figure 17. The damage index of SA1-1 sensor in the beam IP: 192.168.39.211 On: Sat, 253 with Sep nano-CaCO 2021 09:20:03is shown in Figure 18. It can be seen In the initial debonding crack stage,Copyright: the wavelet American packet Scientific Publishers 3 energy gradient of the beam with nano-materialsDelivered is greatly by Ingentafrom Figures 16–18 that the value of the damage indices improved compared to the beam 1 without nano-materials. increase as the loading progressing. Two obvious increas- The wavelet packet energy gradient of the beam 2 with ing values of each beam can be found in these figures, indicating that initial debonding cracks occur at the inter- nano-TiO and beam 3 with nano-CaCO was increased 2 3 face. The cracks exceed the limit of 2 mm epoxy resin by 50.20% and 131.74% compared to the beam 1 without thickness with the increase of load. Therefore, the inter- the nano-material. It is demonstrated that the interfacial face is completely debonded and the damage index value bond strength of the beam with nano-materials is higher is maintained closed to 1. It can be seen from Figure 16 than that of the beam 1 without nano-materials. The inter- that the initial debonding crack occurs in the 20 kN stage, facial bond strength of the beam 3 with nano-CaCO is 3 and the crack development quickly reaches the destruc- higher than that of the beam 2 with nano-TiO . Similarly, 2 tion. It shows that the debonding damage mainly occurs the downward trend of the wavelet packet energy can also in the initial stage of the experiment. It can be seen from reflect that the beam with nano-materials has better ductile Figure 17 that the initial debonding crack occurs in the failure. The above analysis shows that the wavelet packet 30 kN stage, and the crack has a development stage, but it is not very obvious. It can be seen from Figure 18 that the initial debonding crack occurs in the 40 kN stage, and the crack has a development stage, showing a certain ductile failure. The above analysis shows that the damage index can well reflect the development trend of interface debonding damage, and the typical stage (initial and complete debonding stage) can be clearly found in the damage index, creating an obvious index boundary for the field of engineering health monitoring.

4. CONCLUSIONS In this paper, an experimental study on PSNBC beam inter- Fig. 17. Damage index of SA1-1 sensor in the beam 2 with nano- facial debonding performance was conducted based on TiO2. SAs induced stress wave via the active sensing approach.

Mater. Express, Vol. 10, 2020 1325 Materials Express Interface debonding performance of PSNBC beams Yin et al.

Experiments show that the PSNBC beam becomes a good reduced graphene oxide nanocomposite modified glassy carbon elec- conduit for wave propagation due to the nucleation and trode for sensitive dopamine determination. Nanomaterials, 8(4), filling effect of nanomaterials. Therefore, the embedded p.194. 5. Yan, L., Yu, J., Zhong, Y., Gu, Y., Ma, Y., Li, W., Yan, J., Ge, Y., SA-induced stress wave is sensitive to the debonding con- Yin, J., Luo, Y., Mirzasadeghi, A. and Yuan, Y., 2020. Influence ditions of the interface. The experimental results demon- of scanning on nano crystalline -Ti alloys fabricated by selective strate that: laser melting and their applications in biomedical science. Journal (1) The interface debonding performance of the beams of Nanoscience and Nanotechnology, 20(3), pp.1605–1612. 6. Xie, S.W., Gong, G., Song, Y., Tan, H.H., Zhang, C.F., Li, N., with nano-materials is significantly enhanced and better Zhang, Y.X., Xu, L.J., Xu, J.X. and Zheng, J., 2019. Design of novel than that of beam without nano-materials. At the same lanthanide-doped core–shell nanocrystals with dual up-conversion concentration, the interface debonding performance of the and down-conversion luminescence for anti-counterfeiting printing. Dalton Transactions, 48, pp.6971–6983. beam with nano-CaCO3 is better than that of the beam with nano-TiO . 7. Zhou, H., Zhou, J., Wang, T., Zeng, J., Liu, L., Jian, J. and Liu, G., 2 2018. In-situ preparation of silver salts/collagen fiber hybrid com- (2) The signal amplitude (wavelet packet energy) of the posites and their photocatalytic and antibacterial activities. Journal beam without nano-material decreases faster than that of of Hazardous Materials, 359, pp.274–280. the beam with nano-material. At the same concentration, 8. Sanchez, F. and Sobolev, K., 2010. Nanotechnology in concrete— the signal amplitude (wavelet packet energy) of the beam Areview.Construction and building materials, 24(11), pp.2060– with nano-TiO decreases faster than that of the beam with 2071. 2 9. Wang, L., Dai, L., Bian, H., Ma, Y. and Zhang, J., 2019. Concrete nano-CaCO3. cracking prediction under combined prestress and strand corrosion. (3) The analysis shows that the nucleation and filling Structure and Infrastructure Engineering, 15(3), pp.285–295. effect of nano-materials reduces the porosity of the con- 10. Golewski, G.L., 2018. An assessment of microcracks in the inter- crete interior and effectively improves the load character- facial transition zone of durable concrete composites with fly ash istics, so that the stress wave propagation is enhanced and additives. Composite Structures, 200, pp.515–520. the energy consumption is reduced during propagation. At 11. Yin, X., Song, G. and Liu, Y., 2019. Vibration suppression of wind/traffic/bridge coupled system using multiple pounding tuned the same concentration, the nucleation and filling effect of mass dampers (MPTMD). Sensors, 19(5), p.1133. nano-CaCO3 is better than that of nano-TiO2. 12. Yin, X., Liu, Y., Song, G. and Mo, Y.L., 2018. Suppression of bridge (4) The wavelet packet theoryIP: was 192.168.39.211 successfully used On: for Sat, 25 Sepvibration 2021 induced 09:20:03 by moving vehicles using pounding tuned mass the realtime monitoring of the interfacialCopyright: debonding American pro- Scientificdampers. PublishersJournal of Bridge Engineering, 23(7), p.04018047. cess of PSNBC beams. The energy analysis andDelivered damage by Ingenta13. Song, Y., Zhang, Z., Yan, L., Zhang, L., Liu, S., Xie, S., Xu L. and Du, J., 2019. Electrodeposition of Ti-doped hierarchically meso- index based on wavelet packets are effective in explain- porous silica microspheres/tungsten oxide nanocrystallines hybrid ing the process of the PSNBC beam interface debonding films and their electrochromic performance. Nanomaterials, 9(12), Article progress. p.1795. 14. Tan, H., Gong, G., Xie, S., Song, Y., Zhang, C., Li, N., Zhang, In addition, this paper also verified the function of nano- D., Xu, L., Xu, J. and Zheng, J., 2019. Upconversion nanoparti-

materials in concrete by using the active sensing technol- cles@carbon dots@meso-SiO2 sandwiched core–shell nanohybrids ogy of SA. Meantime, the method is of significance for with tunable dual-mode luminescence for 3D anti-counterfeiting bar- checking the safety of PSNBC beams. codes. Langmuir, 35(35), pp.11503–11511. 15. Du, G., Song, Y., Li, N., Xu, L., Tong, C., Feng, Y., Chen, T. and Xu, J., 2019. Cage-like hierarchically mesoporous hollow silica Acknowledgments: The authors gratefully acknowl- microspheres templated by mesomorphous polyelectrolyte-surfactant edge the financial support provided by the Natural Science complexes for noble metal nanoparticles immobilization, Colloids Foundation China (Project Nos. 51108045, 51229801, and Surfaces A: Physicochemical and Engineering Aspects, 575, 51378081), the Natural Science Foundation of Hunan pp.129–139. 16. Li, Z., Wang, H., He, S., Lu, Y. and Wang, M., 2006. Investigations Province (Grant No. 2019JJ40313), the Hunan Provin- on the preparation and mechanical properties of the nano-alumina cial Innovation Foundation for Postgraduates (Project No. reinforced cement composite. Materials Letters, 60(3), pp.356–359. CX20190651). 17. Li, H., Zhang, M.H. and Ou, J.P., 2007. Flexural fatigue performance of concrete containing nano-particles for pavement. International Journal of Fatigue, 29(7), pp.1292–1301. References and Notes 18. Shaikh, F.U. and Supit, S.W., 2014. Mechanical and durability prop- 1. Yuan, A., Yang, C., Wang, J., Chen, L. and Lu, R., 2019. Shear erties of high volume fly ash (HVFA) concrete containing calcium

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Received: 1 January 2020. Accepted: 7 March 2020.

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